24-S-163 Amending the Public Works Specifications Manual adopted in Part III UDCORDINANCE NO.24-S-163
AN ORDINANCE BY THE CITY COUNCIL OF THE CITY OF SCHERTZ,
TEXAS, AMENDING THE PUBLIC WORKS SPECIFICATIONS
MANUAL WHICH IS ADOPTED BY REFERENCE IN PART III
SCHERTZ CODE OF ORDINANCES, THE UNIFIED DEVELOPMENT
CODE
WHEREAS, pursuant to Ordinance No. 10-S-06, the City of Schertz (the "City") adopted
and Amended and Restated the Unified Development Code on April 13, 2010, as further amended
(the "UDC"); and
WHEREAS, the Public Works Specifications Manual is adopted by reference in the UDC
Section 21.1.11; and
WHEREAS, City Staff has reviewed the Current Public Works Specifications Manual and
have recommended certain revisions and updates to the manual; and
WHEREAS, on October 2, 2024, the Planning and Zoning Commission conducted a public
hearing and, after considering the Criteria, made a recommendation to City Council of approval;
and
WHEREAS, on October 23, 2024, a legal notice of a public hearing before City Council
was published in the San Antonio Express News; and
WHEREAS, November 12, 2024, the City Council conducted a public hearing and after
considering the Criteria and recommendation by the Planning and Zoning Commission, determined
that the proposed amendments are appropriate and are in the interest of the public safety, health,
and welfare.
NOW THEREFORE, BE IT RESOLVED BY THE CITY COUNCIL OF THE CITY OF
SCHERTZ, TEXAS THAT:
Section 1. The Public Works Design Guide portion of the Public Works Specifications
Manual is hereby amended as set forth on Exhibit A hereto.
Section 2. The recitals contained in the preamble hereof are hereby found to be true, and
such recitals are hereby made a part of this Ordinance for all purposes and are adopted as
a part of the judgment and findings of the Council.
Section 3. All ordinances and codes, or parts thereof, which are in conflict or inconsistent
with any provision of this Ordinance are hereby repealed to the extent of such conflict, and
the provisions of this Ordinance shall be and remain controlling as to the matters resolved
herein.
Section 4. This Ordinance shall be construed and enforced in accordance with the laws of
the State of Texas and the United States of America.
Section 5. If any provision of this Ordinance or the application thereof to any person or
circumstance shall be held to be invalid, the remainder of this Ordinance and the application
of such provision to other persons and circumstances shall nevertheless be valid, and the
City hereby declares that this Ordinance would have been enacted without such invalid
provision.
Section 6. It is officially found, determined, and declared that the meeting at which this
Ordinance is adopted was open to the public and public notice of the time, place, and
subject matter of the public business to be considered at such meeting, including this
Ordinance, was given, all as required by Chapter 551, as amended, Texas Government
Code.
Section 7. This Ordinance shall be effective upon the date of final adoption hereof and any
publication required by law.
PASSED ON FIRST READING, the 12th of November, 20II24
APPROVED and ADOPTED ON FINAL READING, the l of ,
2024
CITY OF S ERTZ, TEXAS
Ralp a errez ayor
AT
n:
Shei'li Edmondson, City Secretary
EXHIBIT A
AMENDED PUBLIC WORKS DESIGN GUIDE
PUBLIC WORKS
DESIGN GUIDE
November 2024
CITY OF SCHERTZ DESIGN SPECIFICATIONS
Public Works Design Specifications
SECTION1 -GENERAL.................................................................................................................1
1.1 PURPOSE AND SCOPE.......................................................................................................................1
1.2 APPEAL............................................................................................................................................. 1
SECTION 2 - REQUIRED SUBMISSIONS OF PLANS..................................................................2
2.1 PLAN REQUIREMENTS...................................................................................................................... 2
2.2 ENGINEERING REPORTS................................................................................................................... 4
2.3 PLAN SHEETS....................................................................................................................................4
2.4 PLAN AND PROFILE SHEETS.............................................................................................................. 5
2.5 SECTION SHEETS............................................................................................................................... 5
SECTION 3 - STREET REQUIREMENTS......................................................................................6
3.1 GENERAL.......................................................................................................................................... 6
3.2 PAVEMENT DESIGN.......................................................................................................................... 6
3.3 STREETS LAYOUT.............................................................................................................................. 8
3.4 MINIMUM TESTING REQUIREMENTS............................................................................................. 20
SECTION 4 - STORM DRAINAGE REQUIREMENTS................................................................ 22
4.1 GENERAL........................................................................................................................................ 22
4.2 FLOOD HAZARDS............................................................................................................................ 24
4.3 STORM WATER MANAGEMENT PLAN............................................................................................ 25
4.4 WATER QUALITY............................................................................................................................. 27
4.5 STORM DRAINAGE DESIGN CRITERIA............................................................................................. 28
4.6 STORM WATER CHECKLIST............................................................................................................. 46
SECTION 5 - SANITARY SEWER REQUIREMENTS................................................................. 49
5.1 GENERAL........................................................................................................................................ 49
5.2 MINIMUM STANDARDS.................................................................................................................. 52
5.3 MINIMUM SANITARY SEWER TESTING REQUIREMENTS............................................................... 52
SECTION 6 - WATER REQUIREMENTS.................................................................................... 54
6.1 GENERAL........................................................................................................................................ 54
6.2 MINIMUM WATER STANDARDS..................................................................................................... 55
6.3 DESIGN CRITERIA............................................................................................................................ 56
6.4 MINIMUM WATER TESTING REQUIREMENTS................................................................................ 61
SECTION 7 - INSPECTIONS AND TESTING.............................................................................. 61
Z1LABORATORY TESTING...................................................................................................................61
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
SECTION 1 — GENERAL
1.1 PURPOSE AND SCOPE
A) Every subdivision or development which requires the installation of private
or public infrastructure improvements to serve the proposed subdivision or
development is required to submit construction plans to ensure that the
required improvements are constructed in accordance with all applicable
standards of the City of Schertz Code of Ordinances, Unified Development
Code (UDC), Public Works Specifications Manual, or any other codes of or
manuals of the City pertaining to the construction and installation of the
improvements are met. All public infrastructure construction plans shall be
submitted and approved in accordance with the Unified Development Code
Sec 21.4.15.
B) The purpose of this design manual and specifications is to establish
standard principles, criteria, and practices for the design of infrastructure
and to protect and preserve the public welfare. The design factors,
coefficients, formulas, and procedures described in this document are
intended to serve as guidelines for the solution and design of infrastructure.
C) Ultimate responsibility for the actual design remains with the design
engineer. Applicability of the Design Guide Standards are subject to
determination by the City Engineer or his/her designee.
1.2 APPEAL
A) Any departure from this manual must be approved by the City Manager
or his/her designee, provided:
1) It is not detrimental to the public welfare.
2) It meets the requirements of the UDC or has an approved deviation.
3) It is based upon an engineering study performed by a
Professional Engineer registered in the State of Texas.
1
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
SECTION 2 — REQUIRED SUBMISSIONS OF PLANS
2.1 PLAN REQUIREMENTS
A) PDF copy of plans and profiles for streets, alleys, sidewalks, water, sewage,
and drainage shall be submitted, and bear the signature and seal of a
Professional Engineer, registered in the State of Texas.
1) Construction plans shall be submitted to the City Engineer prior to or
concurrently with a development application as indicated in the UDC.
2) Any set over 4 pages should include an index sheet. The preferred
size of construction plans is 22" x 34" or 24" x 36" sheets (half sized
plans will be 11" x 17").
3) Plans must use and reference City of Schertz standard details.
B) The following are typical plans to be submitted. Each set of plans and what
is contained in that set will be dependent upon the project scope.
1) Front end sheets should contain a cover sheet, index and quantity
sheets, and City of Schertz General notes, project layout, and an
Overall Utility Plan.
2) Streets and alleys will be shown in plan and profile sheets and cross-
section sheets. Provide a plan sheet showing typical existing and
proposed street sections detail with the proposed pavement width,
type, thickness, and crown; the proposed curb or gutter type, location
in relation to curbs and property lines, the proposed sidewalk
dimensions, and location in relation to curbs and property lines, and
the proposed parkway grading slopes. This information shall be
given for each of the different types of streets and alleys in the
subdivision.
3) Drainage channels, storm drain, and culverts will be shown in plan
and profile sheets. Large drainage channel projects will include cross
section sheets. Construction details of all drainage structures,
including dimension, reinforcing and components, such as grates
and manhole covers. Hydraulic grade line (HGL) will be indicated on
profile. Drainage plans shall address interim (i.e. "during
construction") and final drainage plan.
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
4) If detention ponds or water quality ponds are part of the development
or project, a plan indicating dimension, grading, outlet design,
downstream protection, and stage -storage -discharge tables should
be included.
5) Plans for erosion and sedimentation controls during construction
shall be included as part of the construction plans and be in
compliance with the Texas Pollutant Discharge Elimination System
(TPDES) permitting requirements and specifications established by
the City Manager or his/her designee. All land disturbing or land
filling activities or soil storage shall be undertaken in a manner
designed to minimize surface runoff, erosion, and sedimentation and
to safeguard life, limb, property, and the public welfare.
6) Grading plan will include slab elevations, existing and proposed
contours, retaining walls, spot elevations, and shall indicate drainage
for all lots in the subdivision. Grading plans must include specific
paths for the direction of drainage flow away from the building pads
or the lots, as well as all trees to be preserved within the limits of
construction. In addition, whenever drainage flow will impact existing
developed land (residential, retail, or industrial), grading plans must
show how the adjacent land will be impacted and how the adverse
impact will be mitigated.
7) Retaining walls over four (4') feet (measured from the bottom of the
foundation to top of the wall), or as required by other applicable City
adopted code, require plans signed and sealed by a registered
Professional Engineer registered in the State of Texas. Any retaining
walls located on slope or retaining supercharged soils may require
plans signed and sealed by a registered Professional Engineer
registered in the State of Texas at the discretion of the City Engineer
or his/her designee.
8) Utility plans for water mains less than twelve (12") inches in size will
require plan sheets with associated details. Utility plans for water
mains twelve (12") inches and greater will require plan and profile
sheets. Section details only required at critical crossings of
infrastructure. The City Engineer or his/her designee may waive this
requirement or may require plan and profile sheets for smaller
diameter lines in special circumstances.
9) Utility plans for sanitary sewers will require plan and profile sheets,
and associated details.
3
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
2.2 ENGINEERING REPORTS
A) In addition to the plans, the following reports are to be submitted for review
by the City Engineer or his/her designee. Except for the pavement design
and SWPPP, these items should be submitted at the time of appropriate
development application and updated for and prior to final plat, site plan,
and construction plans approval. Pavement design shall be completed prior
to final plat, site submittal, or construction plan submittal.
1) Geotechnical Engineering Report for pavement design.
2) Traffic Impact Analysis (TIA) as indicated in the current UDC.
3) Storm Water Management Plan Report (SWMP)
4) Storm Water Pollution Prevention Plan (SWPPP)
5) Engineering Design Report for the water system
6) Engineering Design Report for the wastewater system
B) The content and level of detail of the reports shall be as described in this
manual, or as determined by the City Engineer or his/her designee. Format
of submittal is a PDF file of each document.
2.3 PLAN SHEETS
A) In general, plan sheets should be oriented with north pointing up, left, or
right on the sheet, with proper consideration given to existing and
proposed conditions.
All plans shall require a scale, north arrow, and date. The preferred scale
for plan view sheets is 1" = 20' or 1" = 40' or 1" = 50'. Deviation to the
preferred scale may occur with the approval of the City Engineer or his/her
designee.
B) A minimum of two benchmarks shall be established on and set to NAD 1983
State Plane Texas South Central FIPS 4204 feet coordinates and NAVD
1988 datum.
C) Plans sheets should include all pertinent property and right-of-way
information, existing easements, proposed easements, topographical
features, notes, and callout necessary for design and construction.
4
CITY OF SCHERTZ DESIGN SPECIFICATIONS
2.4 PLAN AND PROFILE SHEETS
The plan and profile sheets should, at the minimum, include the following:
A) All plans shall require a scale, north arrow, and date. The preferred scale
for profile view sheets is 1" = 20' or 1" = 40' or 1" = 50' horizontal and 1" _
5' or 1" = 10' vertical. Deviation to the preferred scale may occur with the
approval of the City Engineer or his/her designee.
B) A minimum of two benchmarks shall be established on and set to NAD
1983 State Plan Texas South Central FIPS 4204 feet coordinates and
NAVD 1988 datum.
Indicate the location, description and elevation of benchmarks, the top of
curb grade at each curb return; the centerline grade at each end and at each
fifty (50') foot station of alleys and drainage ditches; the gradient of each
tangent grade and the location and length of each vertical curve; the
direction of storm drainage flow at each intersection; the flow line elevation
of each storm sewer at each point of grade and each end and the
intervening gradients.
C) The profiles of streets, alleys and drainage ditches shall show the natural
ground at adjacent property lines and the proposed centerline.
D) Alignment of each street, alley, crosswalk way and drainage easement
showing a beginning and ending station; each deflection angle of the
centerline and the station of the point of intersection; the station of the point
of curvature and the point of tangency of each curve; the station and angle
of intersection of each intersection with another street, alley or drainage
easement; the station and radius of each curb return; the location of
adjacent right-of-way lines; the location and limits of sidewalks and curbs of
each street; the location of each drainage structure; the location and size of
all storm sewers; and the location of monuments.
E) All pertinent property and right-of-way information, easements,
topographical features, notes, and callout necessary for design will be
shown in the plan view.
2.5 SECTION SHEETS
A) When required, cross -sections shall be at every fifty -foot (50') station
(minimum) drawn at a scale of 1" = 10' horizontal and vertical.
B) Section will include existing ground and existing utilities, and proposed
finish ground and proposed utilities, right of way and easement limits.
5
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
SECTION 3 — STREET REQUIREMENTS
3.1 GENERAL
A) Plans for streets, alleys, sidewalks, and crosswalk ways shall be prepared
in accordance with Public Works Specification Manual as well as the City's
Master Thoroughfare Plan.
B) Any street design element not specifically addressed in this document
shall be designed in accordance with:
1) Latest edition of Policy on Geometric Design of Highways and Streets,
American Association of State Highway and Transportation Officials
(AASHTO).
2) Latest edition of Highway Design Division Operations and Procedures
Manual and the Standard specifications for Construction of Highways,
Streets and Bridges, Texas Department of Transportation (TXDOT)
3) Latest edition of Texas Manual on Uniform Traffic Control Devices for
Streets and Highways (TMUTCD)
3.2 PAVEMENT DESIGN
A) The City allows both flexible and rigid structures, as defined by the American
Association of State Highway and Transportation Officials (AASHTO).
Pavement design shall be based upon a geotechnical analysis of the project
conditions, upon AASHTO design methods, and shall be designed by a
Professional Engineer registered in the State of Texas.
B) Performance. Service life has been defined as the anticipated number of
years that a pavement will be functionally and structurally acceptable with
only routine maintenance. Flexible Pavements shall be designed for a 20-
year service life; Rigid Pavements shall be designed for a 30-year service
life.
C) Design Traffic Levels. Traffic load for the pavement design will be based
upon the expected cumulative 18-Kip equivalent single axle load (ESAL) for
the pavement's service life. A table of minimum values is shown below, but
a pavement designer may increase the expected ESALS based on the
results of a traffic study, or other unique situations as determined by the City
Engineer or his/her designee.
A
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Table 3.2A
Flexible Pavement Design Parameters
18-kip ESAL
Reliability
Factor, %
I Std Dev
Serviceability
Po/Pt
Arterials
3,000,000
90
90
70
0.45
0.45
0.45
4.2/2.5
4.2/2.5
4.2/2.0
Collectors
2,000,000
Local Type 1,000,000
Alleys/Low volume 100,000
Private Streets/Fire Lane
70
0.45
4.2/2.0
Rigid Pavement
Design Parameters
18-kip ESAL
Reliability
Factor, %
Std Dev
Serviceability
Po/Pt
Arterials
4,500,000
90
0.35
4.5/2.5
Collectors
3,000,000
90
0.35
4.5/2.5
Local Type
1,500,000
70
0.35
4.5/2.0
Alleys/Low volume
Private Streets/Fire Lane
150,000
70
0.35
4.5/2.0
D) Resilient modulus (MR) is to be determined by the geotechnical engineer.
E) There are areas within the city limits and surrounding regions with
expansive soil, water lenses, and drainage issues. It is expected that the
pavement design will address those issues. Swelling soils (soils with a P.I.
of 20 or more), may be treated by removal and replacement, or cement soil
treatment, or drains/barriers, or combination as determined by a pavement
design. Treated subgrade may be used as a structural layer in the pavement
design.
F) Minimum thickness for hot mix asphalt concrete surface layer is three (Y)
inches compacted depth. Minimum thickness for treated subgrade layer is
six (6") inches.
G) Minimum structural numbers will be as follows. These values are minimums,
and actual values used in design will account for the design criteria above.
Table 3.213
Structural Number
Level Roadway conditions
Street Classification
Minimum
Maximum
Arterial
3.80
5.76
Collector Street
2.92
5.08
Local/Residential
2.58
4.20
7
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
3.3 STREETS LAYOUT
A) Adequate streets shall be provided by the Developer and the arrangement,
character, extent, width, grade, and location of each shall conform to the
City's Master Thoroughfare Plan and shall be considered in their relation to
existing and planned streets, to be served by such streets, and to the
topographical conditions. The location and type of traffic control device to
be installed by the Developer or the City of Schertz shall be indicated on the
plans. This shall include the proposal of all Stop, Yield, Speed, Parking and
Movement Series signs and other devices in accordance with TMUTCD.
The design of location of intersections shall take into account intersection
site distance per AASHTO requirements. This specifically shall be utilized
for location of intersections in relation to curves and cutbacks to prevent the
location of sight barriers including signs, fences, and landscaping. See
Tables 3.3G below.
B) The following specifications are required minimums. The analysis of
supporting subsurface soils is to be determined and thickness of pavements
to be designed by the Developer. Substitutes for street geometric or
pavement thickness design shall not be less than the minimum design
requirements. The minimum horizontal curve radii and vertical curves shall
be assigned considering the service of the facility and the conditions of the
location of the street in relation to existing and proposed features.
C) STREET GEOMETRICS
1) The following specifications are required minimums. They are not to
be substituted as street geometric or pavement thickness design.
The geotechnical borings and analysis of supporting subsurface soils
is to be completed by the Developer and the design of the pavement
structure shall be signed and sealed by a Professional Engineer
registered in the State of Texas. Flexible and rigid pavements shall
be designed for a twenty (20) year and thirty (30) year service life
respectively. The minimum horizontal curve radii shall be designed
considering the conditions of the location of the street in relation to
existing and proposed features.
N.
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Table 3.3A
Principal Arterials
(Design Speed — 45 mph)
Minimum right-of-way width
120-130 feet
Minimum pavement width (not including curb and gutter)
48 feet
Minimum horizontal curve radius
1200 feet
Minimum tangent between reverse curve
200 feet
Grades
Flexible Pavement 1 % - 5%
Rigid Pavement 0.5% - 5%
Daily Traffic Volume Limit (vehicles per day)
>34,000
Table 3.313
Secondary Arterials (including Secondary Rural Arterials)
Design Speed - 45 mph)
Minimum right-of-way width
90 feet
Minimum pavement width (not including curb and gutter)
48feet
Minimum horizontal curve radius
750 feet
Minimum tangent between reverse curve
200 feet
Grades
Flexible Pavement 1 % - 5%
Rigid Pavement 0.5% - 5%
Daily Traffic Volume Limit (vehicles per day)
34,000
Table 3.3C
Collectors
(Design Speed — 30 mph)
Minimum right-of-way width
70 feet
Minimum pavement width (not including curb and gutter)
38 feet
Minimum horizontal curve radius
400 feet
Minimum tangent between reverse curve
100 feet
Grades
Flexible Pavement 1 % - 7%
Rigid Pavement 0.5% - 7%
Daily Traffic Volume Limit (vehicles per day)
10,000
Table 3.313
Local Type Commercial/Industrial
(Design Speed — 30 mph)
Minimum right-of-way width
60 feet
Minimum pavement width (not including curb and gutter)
39 feet
Minimum horizontal curve radius
400 feet
Minimum tangent between reverse curve
100 feet
Grades
Flexible Pavement 1 % - 7%
Rigid Pavement 0.5% -7%
Daily Traffic Volume Limit (vehicles per day) 1
5,000
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Table 3.3E
Local Type Residential Streets
(Design Speed — 30 mph)
Minimum right-of-way width
50 feet
Minimum pavement width (not including curb and gutter)
27 feet
Minimum horizontal curve radius
100 feet
Minimum tangent between reverse curve
50 feet
Minimum Grade
Flexible Pavement 1 % - 7%
Rigid Pavement 0.5% - 7%
Daily Traffic Volume Limit (vehicles per day)
1,000
2) Non-residential marginal access streets shall have a right-of-way
width of at least fifty (50') feet and a pavement width of at least
thirty (30') feet. Safety lanes shall have a right-of-way of at least thirty
(30') feet and a pavement width of at least twenty-four (24') feet. All
streets, alleys, non-residential driveways, and non-residential drive
aisles shall have a minimum pavement width of twenty-four (24') feet.
3) Pavement Crown shall have a cross slope of 2% percent.
4) As allowable by State Law, the Developer shall be responsible for
construction of pavement width and right-of-way dedication of streets
forming part of the boundary of the subdivision adjacent as follows:
a) New adjacent collector or residential access streets shall
conform to the specifications of this section.
b) Where the proposed subdivision abuts upon an existing minor
arterial street or half street that does not conform to the
specifications of this Section, the Developer shall be required
to make the necessary dedication and improvements in
conformance with the current UDC or any other applicable
code of the City as allowable by State Law. With regard to
paving the adjacent street, the City reserves the right to waive
all or a portion of this requirement. In considering such waiver,
the following factors shall be considered by the City:
1) Current condition of the roadway.
2) Current daily traffic on roadway.
3) Estimated additional daily traffic from proposed
subdivision.
4) Total cost for widening roadway
5) Ability of City to finance road widening in the next
several years
10
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
5) "Broken -Back" or compound curves shall not be permitted unless
approved by the City Engineer or his/her designee. Reverse curves
may be used provided due consideration for safe sight distance, has
been shown.
6) Transitional Curves may be used where comfort and safety of the
motorist will be enhanced.
7) Combination of horizontal and vertical curves shall be permitted
provided sufficient sight distance is available for safe operation.
Generally, horizontal curvature should be introduced on the upgrade
of the vertical curve.
8) Superelevation of road is permissible when minimum horizontal
curves are unattainable and when approved by City Engineer or
his/her designee. Design of superelevation will follow standard
engineering practices and the TXDOT Roadway Design Manual.
9) Before any pavement is laid to widen existing pavement, the existing
pavement shall be cut back two (2) feet on each side to assure an
adequate sub -base and pavement joint.
D) PROPERTY LINE AND CURB RETURNS
At each intersection the curb and the property line at each block corner shall
be rounded with a radius, R, varying with the interior angle as specified in
the following table:
Table 3.3F
Minimum Radii for Curb Returns (CR) and Property Line Returns (PLR)
Street Intersections
Interior Angles Two Local Local and Two Collector Local/Collector Two
in Degrees Collector with Arterial Arterial
CR PLR CR PLR CR PLR CR PLR CR PLR
150-45
15
5
15
6
20
10
25
15
25
15
145-40
15
5
15
6
20
10
25
15
25
15
140-135
15
5
15
6
20
10
25
15
30
20
135-125
15
5
15
6
20
10
25
15
35
25
125-85
15
5
15
6
20
10
25
15
30
25
85-75
20
10
20
11
25
15
30
20
56
40
75-65
25
15
25
16
30
20
35
25
80
70
65-55
30
20
30
21
35
25
40
30
90
80
55-45
35
25
35
26
40
30
45
35
110
100
45-00
35
25
35
26
40
30
45
35
150 1
140
11
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
E) INTERSECTIONS
1) The preferred angle of intersection is ninety (90) degrees. Allowance
for non -perpendicular intersecting angles between eighty (80)
degrees and one hundred (100) degrees will be made on a case -by -
case basis.
2) The following minimum sight distances shall be provided for a safe
stopping and intersection operations. Development design shall be
based upon actual conditions and speeds.
Table 3.3G
Minimum Stopping Sight Distance
Level Roadway Conditions
Street Classification
Sight Distance
Principal Arterial
300 ft.
Secondary Arterial and
Secondary Rural Arterial
300 ft.
Collector Street
250 ft.
Local
200 ft.
3) The "sight triangle" at an intersection is that portion of a property over
which motorists must see to safely judge and execute a driving
maneuver into the intersection and onto the street. The distance to the
approaching motorist is the "intersection sight distance", which is one
leg of the sight triangle.
The length of the required intersection sight distance shall be based
on AASHTO Policy on Geometric Design of Highways and Streets.
The driver's eyes are considered to be three and one-half (3.5') feet
above pavement, and the object is considered to be four and one-
half (4.5') feet above pavement.
This applies to intersections of two (2) or more streets as well as
junctions of driveways and streets.
4) Landscaping and Signing: No signs, walls or fences shall be placed
in the median area other than approved traffic control devices unless
approved by the City Engineer or his/her designee. No trees, shrubs
or other ground cover shall be placed in the median, which will
obstruct the driver's sight distance. The area enclosed by the sight
triangle must be free of visual obstructions.
12
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
5) At "T-intersections", the minimum intersection offsets are one
hundred twenty-five (125') feet between center lines of local streets.
In the case of collector -street intersections, this offset shall not be
less than two hundred (200') feet or the minimum distance required
to allow for left -turn storage between intersections, whichever is
greater. The distance between intersection offsets is measured from
the center line intersection of one intersecting roadway and the
centerline intersection of the next intersecting roadway, measured
along the centerline of the intersected roadway.
6) Right turn deceleration lanes shall be required when the daily
entering right -turn traffic volume a peak hour volume greater than
50 vehicles per hour (VPH) and the approaching design hourly
volume in the adjacent outside lane exceed five hundred (500)
vehicle trips; at street and driveway intersections in TxDOT right-of-
way at the option of TxDOT; or where unsafe conditions such as
limited sight distance, high travel speed, uneven grade, etc. may
exist, as determined in a TIA. Minimum turn lanes width is eleven
(11') feet.
7) Left turn lanes shall be required at all median openings on collector
and arterial streets; at all driveways or streets with an average daily
entering left -turn traffic volume of five hundred (500) vehicle trips; at
street and driveway intersections in TxDOT right-of-way at the option
of TxDOT; or where unsafe conditions such as limited sight distance,
high speed, uneven grade, etc. may exist, as determined in a TIA.
Minimum turn lanes width is eleven (11') feet.
8) Turn lanes should accommodate the anticipated deceleration length
and storage determined for the intersection. Lengths at signalized
intersections should be determined in a TIA. Lengths at non -
signalized intersections should be determined by the equation or
below.
L=(V/30)x2xS
Where: L is storage length (ft), V is turning vehicles per hour, S is
queue storage length in feet per vehicle (25).
The following table is a table of minimums values for storage and
declaration; taper length may be considered part of the deceleration
length. Preferred taper design is symmetrical reverse curve, per
AASHTO.
13
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Table 3.3F
Minimum Deceleration and Storage for Left Turn Lanes
Speed
(mph)
3(T
Deceleration
Length (ft)
Taper
Length
ft
50
Storage Length
(ft)
100 100
160
35
215
50
100
100
40
275
50
100
100
45
345
100
100
100
50
425
100
100
100
55
510
100
100
100
9) Site design shall take into account appropriate throat length for
driveways and intersections for safe and efficient traffic operations
for entry to and within the site.
F) VERTICAL CURVATURE
A gradual transition from one roadway grade to another shall be
accomplished by means of a vertical parallel curve connecting two (2)
intersecting tangents. The minimum length of vertical curve shall be
computed from the following formula and table.
ME1:n
Where: L = the length of vertical curve in feet, K = a constant related to
sight distance and geometry of a parabolic curve (See Table 3.3H),
A = the algebraic difference in grades in percent.
Table 3.3G
Design Value for Constant "K" Vertical Curvature
Street
Classification
"K" Crest
Curves
"K" Sag
Curves
Principal Arterial
70
60
Secondary Arterial
70
60
Collector Street
55
55
Local
30
40
G) CURB AND SIDEWALK REQUIREMENTS
1) PUBLIC CURB
a) With the exception of rural arterials, curb or curb and gutter
shall be installed on all existing or proposed streets forming
the boundary of the subdivision and internally on streets.
b) All curb or curb and gutter shall be non -reinforced unless
otherwise stated. Cold joints shall be steel reinforced.
14
CITY OF SCHERTZ DESIGN SPECIFICATIONS
2) PUBLIC SIDEWALK
a) Sidewalks: A sidewalk or multiuse path, in accordance with
the City's Master Thoroughfare Plan sections, meeting all
requirements of the American Disability Act shall be required.
All corner lots shall have such sidewalks on both the front and
sides thereof. Concrete sidewalks having a width of not less
than five (5) feet (or six (6) feet if abutting back of curb) and
thickness of not less than four (4") inches shall be constructed
on each side of each street within the subdivision. All curb
ramps shall have a minimum thickness of six (6") inches. Said
sidewalks shall allow for a minimum three (3') foot greenbelt
behind back of curb, shall be one (1') foot inside of the right-
of-way and shall extend along all street frontages, including
the side of corner lots and block ends. Modifications to this
standard are subject to approval by the City Engineer or
his/her designee.
b) Where a new section of sidewalk is to connect with a sidewalk
or concrete hike and bike trail previously constructed, or abuts
on the curbing, an expansion joint must be made and filled as
above. Reinforcing bars shall extend ten (10") inches beyond
the expansion joint and the ends shall be wrapped with
building paper so that the ten (10") inches shall not be bonded
to the concrete. Approved types of slip joints may be used in
place of wrapping ends of bars. When wire mesh reinforcing
is used, three - 3/8" round smooth dowel bars not less than
eighteen (18") inches in length, installed as specified above for
bar reinforcing, shall be provided at each expansion joint.
c) Concrete shall have a minimum compressive strength of four
thousand (4000) pounds per square inch at twenty-eight (28)
days. Concrete will conform to material and proportion
requirements for the concrete of Section 02751 of the Schertz
Construction Specifications. Concrete, which has partially set,
shall be disposed. All tests for ingredients and concrete shall
be made in accordance with the applicable methods of tests
of the American Society for Testing Materials (ASTM).
d) Sidewalks, curb ramps and crosswalks shall conform to all
ADA requirements mandated at the time of construction. They
shall have a monolithic finish and shall be floated and troweled
to a uniform smooth surface, then finished with a fine -haired
brush or wood float so as not to be left with a slick or glossy
finish.
15
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
e) The completed sidewalks and drive approaches shall be
cured in accordance with good engineering practices as
approved by the design Engineer.
3) MEDIANS
a) The minimum width of a raised median is a function of purpose.
Table 3.3J
RECOMMENDED MEDIAN WIDTHS (FOC TO FOC)
Function
Minimum
feet
Desirable
feet
Separation of Opposing Traffic
4*
6*
Pedestrian Refuge and Space for Traffic Control
6*
16
Left -Turn, Speed Change and Storage
14
16
Crossing/Entering Vehicle Protection
20
23
U-Turns, Speed change and Storage
20
23
Channelized: "T", Speed Change and Storage 25
23-30
f *Cannot accommodate left -turn lanes, hence, such turns must be made
from the through lanes.
Source: City of Austin, Department of Public Works and Transportation Based on ITE, Guidelines for
Urban Major Street Design
b) Raised median openings shall be at least twenty (20') feet
wider than the width of driveway which they are serving, with
a minimum width of sixty (60') feet.
c) Minimum separation distance between raised median
openings on local roads should be based on functionality and
proximity to street intersections; no closer than one hundred
twenty-five (125') feet. Minimum separation distance between
raised median openings for collector and arterial streets,
measured nose to nose, should provide sufficient storage and
deceleration length for the rate of speed on the through traffic
road.
16
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
H) ALLEYS
1) Alley right-of-way minimum shall be [twenty-four (24') feet wide and
paved, see Section 21.14.41 in the UDC. Eight (8%) percent is the
maximum sustained grade for an alley and shall not exceed three
hundred (300') feet. Concrete pavement shall be a minimum of six
(6") inches in depth — 4000 psi in commercial alleys and a minimum
of five (5") inches in depth — 3000 psi in residential alleys. Alleys shall
be designed based on a one hundred (100) year frequency to carry
storm water from only the lots within the block abutting the alley.
2) Intersecting Alleys: Where two (2) alleys intersect or turn at right
angle, a cutoff of not less than ten (10') feet shall be provided along
each property or easement line.
3) Dead-end Alleys are not permitted.
1) DRIVEWAYS AND APPROACHES
1) Driveways shall be designed as a "lay -down" curb or curb and gutter
or a straight driveway section. The driveway width at the property line
shall not be greater than the width approved by the City Engineer or
his/her designee.
2) Residential driveways ten (10') feet to twelve (12') feet in width for
single, and not more than twenty-four (24') feet for double driveway
apron. One (1) curb cut per residential property. Two (2) curb cuts
may be allowed for circular if frontage is greater than one hundred
(100') feet if approved by the City Engineer or his/her designee. No
new residential driveway curb cut on collector or arterial streets will
be allowed, unless lot size is greater than one (1) acre, frontage is
greater than one hundred (100') feet, traffic study indicates no
impact, and maneuvering is done off street for turn -around.
"Back out" driveway access to collector and arterial streets is not
allowed.
3) Non-residential driveway access width should be between twenty-
four (24') and forty (40') feet measured at the right-of-way.
4) Non-residential approaches shall have the minimum spacing
requirements identified in UDC Article 14.5 Spacing of approaches
shall be measured from the start of curve/taper to start of curve/taper
along the curb line. If the minimum spacing cannot be achieved, then
use of a common access easement will be required for adjacent
properties to share drive approaches and minimize the number of
drive approaches along collector and arterial streets.
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CITY OF SCHERTZ
DESIGN SPECIFICATIONS
5) Minimum distance of an approach from the corner/flare of an
intersection shall be one hundred twenty-five (125) feet or the length
of the turn lane for the intersection. The distance shall be measured
from the curb return or start of taper/curve of the pavement as it
widens next to the intersecting street to the edge of the driveway. A
lesser distance may be approved by the City Engineer, or his/her
designee provided a TIA demonstrates the lesser distance still
maintains safe traffic flow on the street and site. If the minimum
distance cannot be met, then use of a common access easement will
be required.
6) Frontage measured from property line to property line, or from
corner/flare of intersection to property line.
7) Drive approaches shall meet all criteria as minor intersection
concerning sight distance and stopping distances to ensure a safe
facility.
8) Driveway aprons within the City Limits shall be reinforced concrete
per City standard details, unless otherwise approved by the City
Engineer or his/her designee.
9) The site design shall take into account appropriate throat length for
driveways and intersections for safe and efficient traffic operations
for entry to and within the site.
J) FIRE LANES
1) A fire lane is interpreted as a private or public, hard -surfaced, all-
weather material (asphalt or concrete), driving surface constructed
specifically for the use of emergency vehicles.
2) Fire and safety lanes shall meet standards of the UDC Article
14.1.M.
3) Dead-end fire lanes are not permitted, unless approved by the Fire
Chief or his/her designee.
K) CUL-DE-SAC TURNAROUND
1) Cul-de-sac turnarounds shall meet the criteria set forth in the UDC
Section .14.1.E.
2) "Knuckle" or elbow intersections with bulbs herein and UDC
requirements of intersection angles and curb return radii.
In
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
L) STREET LIGHTS
Street lights in new subdivisions within the City Limits and the annexed
areas of the City shall be in accordance with the UDC Article 14.1.S.
M) STREET MARKERS
1) Two street name signs shall be erected at all street intersections in
subdivisions for street markers:
a) The material of the street name signs, the method of attaching the
sign to the post, the details of lettering, painting, and method of
installation, as well as the location of the sign at the intersection, shall
be in accordance with the specifications on file at the appropriate
entity (i.e., City of Schertz, TxDOT, etc.)
b) Construction plans shall include layout of all traffic control devices in
accordance with the TMUTCD.
c) All street signs in a new subdivision within the City limits, including
street name, speed limit, stop and yield signs, etc. shall be paid for
by the Developer and shall be provided by and installed by the City's
Public Works Department in accordance with the Public Works
Specifications Manual. Traffic Control Devices shall be installed in
accordance with the latest revision of the Texas Manual on Uniform
Traffic Control Devices for Streets and Highways. Street signs within
TxDOT right-of-way shall be installed according to the appropriate
standards by the Developer (as permitted by TxDOT).
2) All pavement markings shall be thermoplastic or preformed tape.
Follow TMUTCD and TxDOT standards and guidance for marking
standards. The following Pavement markings are required
a) Arterials: centerline striping, lane lines, turn bay islands, reflective
pavement markers, edge lines for non -curbed streets, and bike
lanes.
b) Collectors: centerline striping, lane stripping, edge lines for non -
curbed streets, and bike lanes.
N) REMOVING AND REPLACING PAVEMENTS, CURBS, AND GUTTERS,
DRIVEWAYS, AND SIDEWALKS
1) Scope: The Technical Specifications and Standard Details shall
govern for all work necessary to complete the removing and
replacement of all types of pavements, curbs and gutters,
driveways, and sidewalks as required to complete the project.
iLi
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
2) Method of Cutting: The outline of the trench shall be marked on the
surface to be cut. The cut shall be made as nearly vertical as
possible. The excavated pavement or concrete shall be removed
from the site and disposed of by the contractor.
3) Ashpaltic Pavement: Repair to be five (5) feet on each side wider
than ditch excavation. Sawcut shall be vertical and perpendicular to
flow of traffic for trenching across street. Any asphalt repair needed
more than five (6) feet from the curb and gutter, or edge of payment
will require the asphalt repair limits to extend the entire width of the
roadway unless a smaller repair area is specifically permitted by the
City Engineer or his/her designee.
3.4 MINIMUM TESTING REQUIREMENTS
A) GENERAL
All materials to be used in subdivision construction shall be subject to
testing. The preponderance of testing to be performed in subdivisions is
directly related to street construction. A series of laboratory tests normally
associated with road and street construction will be required in subdivisions,
with said tests being performed by an independent testing laboratory using
qualified personnel. The design (or consulting) engineer or his designated
representative shall be present at all testing activities. The Developer or
his/her designee is responsible for scheduling and payment. The passing
test results shall be received prior to commencing additional construction
activities and after two (2) days of inactivity on the tested material, new
testing may be required.
The Developer shall notify the City at least one (1) week prior to the
contractor beginning construction. Contractor shall be required to notify the
City a minimum of at least forty-eight (48) hours in advance of all testing
being performed.
B) Sub -grade materials shall be compacted by approved mechanical tamping
equipment to an apparent dry density as determined by the ASTM 698 or
TEX-114-E compaction test made in accordance with the procedure
outlined in the Texas Highway Department Testing Manual. If the material
fails to meet the density specified, it shall be reworked as necessary to
obtain the density required.
C) When a fill or embankment is required to achieve the prescribed sub- grade,
or structural elevation, such fill shall be placed in uniform lifts covering the
entire width of the cross-section. Prior to compaction, the layers shall not
exceed a six (6") inch loose lift depth where pneumatic tire rolling is to be
used and shall not exceed eight (8") inches in loose lift depth for rolling with
20
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
other types of rollers. Each lift shall be compacted to the required density
before succeeding lifts are placed. Lifts shall be compacted to not less than
ninety-five (95%) percent of the maximum dry density as determined by the
ASTM 698 or TEX-114-E compaction test made in accordance with the
procedure outlined in the Texas Highway Department Testing Manual
D) Swelling soils (soils with plasticity index of twenty (20) or more) shall be
treated by removal and replacement, or cement or lime soil treatment, or
drains/barriers, or combination as determined by a pavement design or
other City requirements. Developers must provide the City with lab reports
on soil conditions.
E) Flexible base materials shall be compacted by approved mechanical
tamping equipment to an apparent dry density of the total material of not
less than ninety-five (95%) percent of the maximum dry density as
determined by the TEX-113-E compaction test made in accordance with the
procedure outlined in the Texas Highway Department Testing manual. If
the material fails to meet the density specified, it shall be reworked as
necessary to obtain the density required.
F) Each course of six (6") inches or less shall be compacted to full required
density before succeeding layers are placed.
Table 3.4A
Ratio of Testing
Subgrade
Minimum 1 per 100 ft. of street (each lift)
Under Curb/Gutter
Minimum 1 per 100 ft. of curb (each lift)
Base
Minimum 1 per 100 ft. of street (each lift)
Embankment (Street)
Minimum 1 per 100 ft. of street (each lift)
Embankment (Berm or Structural)
-1 per lift per 10,000 sq. ft.
-1 per lift per 100 ft. berm
Proctors (Moisture -Density Relationship)
Subgrade (raw) and Embankment -1 per material type per source, minimum 2
per subdivision (NOT VALID AFTER 1
YEAR)
Note: Testing frequencies double for pavement widths wider than 38'
Table 3.413
Atterberg Limits & Graduation
Hot Mix Control
5urrace Course Design 1 per subdivision
Extraction
Densities
subdivision
2 per day/run minimum — 1
per 500 ton
1 per 1,000 ft. of street
21
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
G) CONCRETE PAVING
1) GENERAL
Plant Certification Required
Testing shall be as required in City Technical Specification Section
02751. In the event of failures, additional tests will be taken. If
excessive rain occurs on a previously tested section, the City shall
have the right to order retests as necessary.
2) The Developer shall notify the testing lab when tests are to be taken.
If it is necessary to retest, such retesting shall be at the Developer's
expense. The scope of testing of materials incorporated in
subdivision construction is not necessarily limited to those tests
outline above. In the event of unusual conditions or factors which
may give the City reason to question the quality of the materials in
any portion of the subdivision, the City will have the right to order
such additional tests as are necessary.
3) All testing within these requirements will be performed in
accordance with the American Society of Testing Materials (ASTM)
latest revision, and/or as elsewhere provided in approved plans and
specifications for the subdivision. The City will require all subdivision
test reports to be certified by a professional engineer registered in the State
of Texas and will further require that the City be furnished with copies for
all testing reports.
SECTION 4 — STORM DRAINAGE REQUIREMENTS
4.1 GENERAL
A) All drainage facilities (including, but not limited to curb and gutter, inlets,
pipes, and channels), shall be designed to intercept and transport runoff
from a minimum twenty-five (25) year frequency storm. The drainage
system shall also be designed to intercept and convey flows greater than a
twenty-five (25) year frequency, up to and including a one hundred (100)
year frequency storm within defined rights -of -way of drainage easements.
All detention structures shall be designed to contain the one hundred (100)
year frequency storm. Peak discharge flows shall not be increased from the
pre -development flows for the 2-, 5-, 10-, 25-, and 100- year frequency
storm. Channels with drainage areas over one hundred (100) acres or
areas within a designated floodplain shall be designed for a one hundred
(100) -year storm or a twenty-five (25)-year storm plus freeboard (see Table
4.5E) if that elevation is higher.
22
CITY OF SCHERTZ DESIGN SPECIFICATIONS
B) Three (3) development conditions shall be analyzed for each
development.
1) Existing Conditions. This refers to current development conditions
in the watershed and on -site. Use as the baseline analysis for
determining the impact of development.
2) Proposed Conditions. This refers to existing conditions with the
proposed development added. Use to determine if the increased
runoff from the proposed development results in an adverse impact
to other properties.
3) Ultimate Conditions. This refers to ultimate development conditions
within the watershed used to design the drainage facilities. This
condition may be used in -lieu of subsection (2) above, to determine
if the increased runoff from the ultimate watershed development
results in an adverse impact to other properties.
C) RESPONSIBILITY TO ACCEPT STORM WATER
The owner or Developer of property to be developed shall be responsible
for the conveyance of all storm water flowing through the property. This
responsibility includes the storm water flowing onto the property by any
other developed property as well as the drainage naturally flowing through
the property by reason of topography. Future upstream development shall
be accounted for by assuming ultimate development when sizing drainage
systems as specified in this section.
D) POSITIVE OVERFLOW PATHWAYS
Storm water management facilities for local drainage systems will be
designed to ensure that a positive overflow pathway is provided to the
nearest one hundred (100) year conveyance facility. The overflow pathway
must be delineated on a plan that shows all existing structures in the vicinity
impacted by the overflow pathway.
E) MAINTENANCE
1) Maintenance of publicly owned facilities will be the responsibility of
the City. Maintenance of private facilities is the responsibility of the
property owner or the community association and must be specified
in the maintenance schedule submitted to the City. A maintenance
schedule for privately owned facilities must be approved by the City
Engineer or his/her designee. along with the approval of construction
drawings.
23
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
2) Authorized personnel from the City may conduct periodic inspections
of these facilities and structures. Any required repairs will be
consistent with current construction standards. Maintenance issues
identified by the City or State during inspections shall be the
responsibility of the current owner.
F) DEVELOPMENT
Peak storm water runoff rates from all new development shall be less than
or equal to the peak runoff rates from the site's predevelopment conditions
for the 2-year, 5-year, 10-year, 25-year, and 100- year design storm events,
except as provided in subsection A, above. Discharge from developed
property shall mimic other pre -developed discharge flow characteristics as
much as possible so as not to cause adverse impact to downstream
property.
4.2 FLOOD HAZARDS
A) New development within the FEMA designated special flood hazard areas
will follow the City's Flood Damage Prevention Ordinance, and the
requirements of CFR 44.60.3 whichever is more stringent.
B) New subdivisions having a portion of that subdivision subject to the special
flood hazards shall dedicate on the plat a drainage easement fully
containing the one hundred (100)- year one (1 %) percent annual chance)
special flood hazard area. If not already determined, the new subdivision
shall determine the base flood elevations of the 100-year event for that
portion of the special flood hazard area within the subdivision. This must be
based on a certified engineering study survey taking into consideration the
full development of the watershed.
C) Proposed subdivisions shall be reviewed to assure that all such proposals
are consistent with the need to minimize flood damage and that all public
utilities and facilities such as sewer, gas, electrical and water systems are
located, elevated, and constructed to minimize or eliminate flood damage
and adequate drainage is provided so as to reduce exposure to flood
hazards.
D) New or Replacement water supply systems and/or wastewater systems
shall be designed to minimize or eliminate infiltration of flood waters into the
system, discharges from the systems into flood water, and to require on -site
waste disposal systems to be located above the base flood elevation so as
to avoid impairment or contamination from them during flooding.
E) Preservation of the natural floodplain and native vegetation contained
therein is encouraged. Understory growth which impedes flow may be
24
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
cleared within the bank of watercourses within the proposed development
with City approval however, the alteration of natural vegetation or unique
features with diameters greater than eight (8") inches is discouraged and
shall follow the requirements for tree removal in the UDC Article 21.9.9.H.
Lower branches of large trees may be trimmed to provide a vertical
clearance of eight (8') feet. The alteration of natural vegetation or unique
features within the floodplain of watercourses is discouraged and must be
explicitly permitted.
F) Upon acceptance by the City of Schertz of Public Utilities, Streets and
Drainage, it shall be the responsibility of the homebuilder and/or lot owner
to maintain all erosion and sedimentation controls to prevent sedimentation
onto any public right-of-way and/or adjacent owner's lots. Failure to comply
shall result in a stop work order of all construction on lots owned by the
landowner or homebuilder.
4.3 STORM WATER MANAGEMENT PLAN
A) As part of the subdivision platting and construction plan review process, an
analysis of existing drainage conditions and the design of modifications or
new drainage facilities is required. The owner of the property to be
developed is required by the City Engineer or his/her designee to provide,
at the owner's expense and as a condition of approval, a Storm Water
Management Plan (SWMP) for the total development area to be ultimately
constructed. The SWMP shall be submitted to the City Engineer or his/her
designee prior to approval of any construction plans.
B) CONTENTS OF THE SWMP
The SWMP shall contain all necessary support data, methodologies used
in calculations and conclusions. A checklist (at the end of this section) will
be used by the City Engineer or his/her designee as a guide during the
evaluation of all SWMP reports submitted to the City. The purpose of the
checklist is to expedite the review process for both the engineer and the
City, and to aid the engineer in the preparation of reports for the City's
review.
A storm water management concept plan or preliminary drainage plan
should be submitted with master development plan or preliminary plat. The
concept plan should detail in concept how runoff and associated water
quality impacts resulting from the development will be controlled or
managed. It should address the pre, post and ultimate development
conditions of the watershed. The plan should be labeled "Concept" or
"Preliminary".
25
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
The final SWMP should be submitted with all other submittals including but
not necessarily limited to, a final plat, minor plat, site plan, grading and
clearing permit or building permit. In addition to the information from the
preliminary or concept plan, shall include all information required in the final
Storm Water Management Plan (SWMP) checklist (at the end of this
section), including construction details.
C) In general, the Final Storm Water Management Plan should contain the
following (for details see the checklist at the end of this section):
1) The contact information for the owner of the property or
properties affected.
2) A vicinity map of the site and affected reach of the outfall
channel.
3) On topographic base map, a detailed map of the area and the
outfall channel(s) with all pertinent physiographic information,
with two (2') foot contours.
4) A watershed map showing the existing and proposed
drainage area boundary along with all sub area delineations
and all areas of existing and proposed development; indicate
locations of all rights -of -way and additional easements/rig hts-
of-way required, flow path to nearest downstream 100-year
structure.
5) All hydrologic and hydraulic calculations: specifying
methodology and key assumptions used to include a table of
discharges at key locations; hydraulic calculations specifying
methodology used, assumptions and values of the design
parameters.
6) Profiles of the affected channels, including water surface
elevations for the specified design frequencies, all existing
and proposed bridge, culvert, and pipeline crossings, the
location of all tributary and drainage confluences, and the
location of all hydraulic structures.
7) Detention basin design calculations, including those used for
design of the control structure and construction details.
8) Additional back -water analysis data as described in the
checklist.
Ni
CITY OF SCHERTZ DESIGN SPECIFICATIONS
9) Certification by a Professional Engineer registered in the
State of Texas that the result of the proposed development
will not produce an adverse impact to downstream properties,
structures, drainage facilities, and public infrastructure.
10) Soils map indicating the type of soil and hydrologic group.
11) Maintenance and repair plan for permanent best management
practices (BMPs) and a maintenance agreement for on -site
storm water management measures.
12) Erosion and sediment control plans or A Storm Water
Pollution Prevention Plan (SWPPP) including erosion and
sediment control plans for construction.
13) Additional information as requested by the City Engineer or
his/her designee, including but not limited to, digital copies of
models and digital copies of detailed drawings (dxf or dwg
format).
14) Other Environmental Permits as required by local, state, orfederal
rules.
4.4 WATER QUALITY
A) Post construction storm water quality will eventually be regulated for the
quality of the water discharged. There are currently no quantitative limits for
post construction water quality of discharge, however post construction
BMPs are strongly encouraged, and consideration should be given to
provide suitable designs to not prohibit the retrofitting of facilities to meet
future water quality monitoring and discharge needs.
B) In accordance with the City of Schertz Construction Storm Water
Management Ordinance and Section 01410 of the Construction Technical
Specifications, no person shall be granted a Grading and Clearing Permit
or Construction Permit for land -disturbing activity without the approval of
a Storm Water Pollution Prevention Plan (SWPPP) report and plans.
1) The SWPPP follow the requirements of the Construction Storm
Water Management Ordinance and shall include:
a) Each application shall bear the name(s) and address(es) of
the owner or Developer of the site and of any consulting firm
retained by the applicant together with the name of the
applicant's principal contact at such firm, and the designated
operator as defined by TPDES General Permit.
27
CITY OF SCHERTZ DESIGN SPECIFICATIONS
b) A natural resources map identifying soils, forest cover, and
resources protected by the local, state, and federal
regulations.
c) A sequence of construction of the development site, including
stripping and clearing, rough grading, construction of utilities,
infrastructure, and buildings, and final grading and
landscaping. Sequencing shall identify the expected date on
which clearing will begin, the estimated duration of exposure
of cleared areas, areas of clearing, installation of temporary
erosion and sediment control measures, and establishment of
permanent vegetation.
d) All erosion and sediment control measures necessary to meet
the objectives of the City's regulations throughout all phases
of construction and after completion of development of the
site. Depending upon the complexity of the project,
intermediate plans may be required at the close of each
�D -16-1•r0
e) Seeding mixtures and rates, types of sod, method of seedbed
preparation, expected seeding dates, type and rate of lime
and fertilizer application, and kind and quantity of mulching for
both temporary and permanent vegetative control measure.
f) Provisions for maintenance of control facilities, including
easements and estimates of the cost of maintenance, dust
control and cleaning, stockpile protection, etc.
2) Major amendments of the SWPPP must be submitted for approval.
3) In addition to the report, appropriate details, and instructions to be
included with the construction plan set.
4) Copies of all submittals to the Texas commission on Environmental
Quality. (TCEQ), including the notice of intent (NOI) and notice of
termination (NOT) shall be submitted.
4.5 STORM DRAINAGE DESIGN CRITERIA
A) METHOD OF COMPUTING RUNOFF
1) The preferred method for computing storm water runoff shall be a
unit hydrograph method such as WinTR-20, WinTR-55, HEC HMS
models, or some other method provided it is acceptable to the City
Engineer or his/her designee. The Modified Rational Method is not
allowed.
ME
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
2) For small urban drainage areas less than fifty (50) acres where
hydrographs are not required, for storm sewer inlets, for roadside
ditches, for driveway culverts, or for "peak flow only" calculations, the
basis for computing peak flow runoff may be the Rational Method.
The Rational Method is not allowed for the design or detention ponds
nor channels within the FEMA designated special flood hazard area.
The Rational method may not be used if the time of concentration
exceeds twenty (20) minutes.
3) Normal depth channel calculations are permissible for constructed
open channels with a uniform geometric cross section where there is
no potential for the water surface elevations to be controlled by
backwater and the channel is not in a FEMA special flood hazard
area.
4) Hydraulic calculations for open channels with non -uniform geometric
cross sections shall be performed by using the HEC- RAS "River
Analysis System" computer models, or other method approved by
the City Engineer or his/her designee.
B) TIME OF CONCENTRATION
1) Sheet flow, shallow concentrated flow and channel flows are
components that need to be considered in the calculation of time of
concentration. The following methods are recommended for time of
concentration calculation. The total time of concentration (the sum of
the three (3) components described below) shall be a minimum of five
(5) minutes.
a) Sheet flow - flow over plane surfaces based on NRCS method and
roughness coefficients for sheet flow. Maximum allowable time is
twenty (20) minutes for sheet flow, or a maximum distance of one
hundred (100') feet.
b) Shallow concentrated flow — Use NRCS method to estimate travel
time for shallow concentrated flow.
c) Channel flow: Use existing computer models where available or
Manning's equation if data is not available. Open channels are
assumed to begin where surveyed cross section information has
been obtained, where channels are visible on aerial photographs, or
where blue lines (indicating streams) appear on USGS quadrangle
sheets.
m]
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
C) RUNOFF COEFFICIENTS
Runoff coefficients (C value) for use in the Rational formula shall not be
less than the values shown in Tables 4.5A as appropriate.
Table 4.5A
Runoff Coefficients (C)
Slope
Character of Area Up to 1 % to 3 to 5% Over 5%
1 % 3%
Business or Commercial Area (90% or more
95
Impervious), Existing Pavement/Buildings
.96
.97
.97
Densely Developed Area (80% to 90%
85
Impervious)
.88
.91
.95
Closely Built Residential Area and School Sites
.75
.77
.80
.84
Large Lot Residential Area
.55
.57
.62
.64
Average Residential Area
.65
.67
.69
.72
Undeveloped Areas
Undeveloped and Ultimate Land Use is Unknown
.68
.70
.72
.75
Cultivated or Range (Grass Cover <50% of Area)
.44
.47
.49
.53
Range (Grass Cover <50% of Area)
.37
.41
.49
.53
Forest or Range (Grass Cover >75% of Area)
.35
.39
.47
5�
1) In all cases, wet antecedent conditions shall be assumed. Runoff
rates shall be computed based on the ultimate development of the
entire watershed to the proposed subdivision. For determination of
time for concentration, times shall be figured on the basis that there
shall be an improved drainage system upstream from the point under
consideration.
D) RAINFALL INTENSITY
National Oceanic and Atmospheric Administration (NOAA) Atlas 14
Precipitation frequency data should be used. Tables of rainfall intensity -
duration -frequency for the precipitation areas across Schertz are provided
in Appendix A of this document. If a site is located within more than one
precipitation area, it is acceptable to use the higher intensities for the entire
site.
30
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
E) NRCS/SCS CURVE NUMBERS
For the NRCS method, the rainfall distribution type III shall be used in
the runoff model and shall be in accordance with the San Antonio River
Basin standards for analysis. Design rainfalls values listed in Appendix
A shall be used for hydrograph calculations. The NRCS/SCS curve
numbers adopted for use by the City of Schertz are shown in Table
4.513. The hydrologic soil groups are listed in the latest version of the
United States Natural Resources Conservation Service, "Urban Hydrology
for Small Watersheds", Technical Release No. 55 JR 55), which
document is hereby incorporated by this reference. Soil types that relate to
the hydrologic soil group may be found in the latest version of the United
States.
Natural Resources Conservation Service Soil Surveys for Bexar,
Guadalupe and Comal Counties, Texas which documents are hereby
incorporated by this reference. Soil types may also be based on a
Geotechnical Engineering Report. Alternative curve numbers may be
approved by the City Engineer or his/her designee.
Table 4.5B
NRCS (SCS) Curve Numbers
Cover Type and Description
Curve Number for Hydrologic Soil Group
A
B
C
D
Open Space (lawn, parks, golf courses, cemeteries, etc.)
Poor condition (grass cover, < 50%)
68
79
86
89
Fair condition (grass cover 50% to 75%)
49
69
79
84
Good condition (grass cover > 75%)
39
61
74
80
Impervious areas
Paved parking lots, roofs, driveways, etc., (excluding ROW)
98
98
98
98
Streets and roads
Paved curbs and storm sewers (excluding ROW)
98
98
98
98
Paved open ditches (including ROW)
83
83
89
93
Gravel (including ROW)
76
85
89
91
Dirt (including ROW)
72
82
87
89
Pasture, grassland, or range — continuous forage for grazing,
50%-75% ground cover and not heavily razed
49
69
79
84
Meadow — continuous grass, protected from grazing and
generally mowed for ha
30
58
71
78
Brush — brush -weeds grass mixture with brush the major 30
element > 75% ground cover
Woods -- grass combination (orchard or tree farm). CN's shown 32
were computed for areas with 50% woods and 50% (grass/
pasture) cover
Woods — protected from grazing and forest litter and brush 30
-adequately cover the soil
48
65
73
58
72
79
55
70
77
Farmsteads -- Buildings, lanes, driveways, and surrounding lots
59
74
82
86
31
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
1) Percent Impervious Cover.
typical land use types (as
presented in Table 4.5C.
The percent impervious cover for
opposed to lots) in Schertz are
Table 4.5C
NRCS (SCS) Curve Numbers by Impervious Cover and Cover type
Cover Type and Description
Average %
Impervious Cover
Curve Number for Hydrologic Soil Group
A
B
C
D
Commercial and business
85
89
92
94
95
Industrial
72
81
88
91
93
Residential: 1/8-acre lot or less
townhouses. average lot size
65
77
85
90
92
Residential: 1/ 4-acre average lot size
38
61
75
83
87
Residential: 1/3-acre average lot size
30
57
72
81
86
Residential: 1/2-acre average lot size
25
54
70
80
85
Residential: 1-acre average lot size
20
51
68
79
84
Residential: 2-acre average lot size
12
46
65
77
82
F) DESIGN RAINFALL DISTRIBUTION
1) Design Rainfall. A twenty -four-hour rainfall distribution shall be
applied for runoff calculations. NOAA Atlas 14 Design Rainfall Values
for the precipitation areas across Schertz are provided in Appendix
A of this document and should be used for HEC-HMS input. If a site
is within more than one precipitation area, it is acceptable to use the
higher depth values for the entire site. The lag value for a subarea
shall be calculated as 0.6 times the time of concentration. Facilities
with watersheds greater than one hundred (100) acres must be
designed for the 100-year frequency storm or the 25-year event plus
freeboard (see Table 4.5E), unless otherwise stated below.
2) Routing of Runoff. Routing of the runoff hydrograph through the
channel from one subarea calculation point to the next in the HEC-
HMS shall be computed using one of the following methods:
a) Overbank/channel storage not significant: use normal depth
channel routing.
b) Overbank/channel storage is significant: use the Muskingum
method where a hydraulic model is not available. Use
Modified Puls Storage method where a hydraulic model is
available to develop storage/out flow relationship.
32
CITY OF SCHERTZ DESIGN SPECIFICATIONS
c) Kinematic wave method for channel reaches where inflow from
overbank runoff or multiple point sources (Example: storm sewer
outfalls) is significant and where hydrograph attenuation is
insignificant. Channel routing methodologies currently being
applied in the existing HEC-HMS model of the watershed shall
not be replaced with a different methodology without approval or
direction from the City Engineer or his/her designee.
G) STREETS
1) GENERALLY
a) Design of streets shall consider public safety and limit
potential conflicts between storm water conveyance, traffic,
parking, pedestrian access, ADA requirements, and bicycle
traffic.
b) Streets and associated drainage facilities, draining a
watershed greater than one hundred (100) acres must be
designed for the 100-year frequency storm.
c) Streets may be used for storm water drainage only if the
calculated storm water flow does not exceed the criteria
herein and/or the velocity does not exceed ten (10') feet per
second.
d) Where streets are not capable of carrying storm water, as
outlined above, inlets or curb openings discharging to
drainage channels or storm sewers shall be provided. Partial
flow past the inlet will be allowed when the capacity of all
downstream street systems can accommodate the flow.
e) Street width shall not be widened beyond the width as
determined by the street classification for drainage purposes.
f) Storm water conveyance on streets shall be designed to
account for the cumulative impact of peak flows and runoff
volumes on the system as the storm water progresses
downgrade.
g) Curb cuts for driveways on all streets shall be designed for
compatibility with the storm water conveyance function of
streets.
33
CITY OF SCHERTZ DESIGN SPECIFICATIONS
h) Potential flooding problems or conflicts at the connection
points where new or modified drainage systems (including
streets, storm sewers, etc.) and the existing portions of the
downstream street system and storm water conveyance
system shall be identified and resolved either in the design of
the new or modified drainage system or in modifications to the
existing system.
i) Structures located on the downhill side of a T- intersection
shall be sited to avoid obstruction of the drainage discharge
from the street (including the case of a blocked or otherwise
ineffective inlet) or channel flow patterns.
2) An arterial street is a street designated as such on the City's Master
Thoroughfare Plan. One (1) lane in each direction on arterial streets
shall remain clear during a twenty-five (25)-year storm event. The
maximum depth of water in the street section must not exceed seven
(7") inches (the height of a standard city curb).
3) A collector street is a street designated as such on the City's Master
Thoroughfare Plan. One (1) lane on collector streets shall remain
clear during a twenty-five (25)-year storm event. The maximum depth
of water in the street section must not exceed seven (7") inches (the
height of a standard city curb).
4) Local Streets. Local streets shall be designed on a basis of a twenty-
five (25) - year frequency. The maximum depth of water in the street
section must not exceed seven (7") inches (the height of a standard
city curb). A one hundred (100) -year frequency storm must be
contained within the street right-of-way.
5) CULVERTS AND BRIDGES
a) Where streets cross existing or proposed watercourses,
culverts or bridges shall be adequate to allow passage of
twenty-five (25)-year design storm. In the instance the
crossing conveys runoff from a watershed greater than one
hundred (100) acres, then culverts or bridges shall be
adequate to allow passage of the one hundred (100)-year
design storm.
b) All crossings, culverts and bridges shall be designed for an
HS-25 or equivalent loading.
34
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
H) CHANNELS
1) This section addresses proposed improvements or modifications to
drainage channels and watercourses required to convey storm water
runoff from or through the proposed development.
2) Except as authorized by a development plan approved by the City
Engineer or his/her designee, no person shall place or cause to be
placed any obstruction of any kind in any watercourse. The owner
of any property within the city, through which any watercourse may
pass, shall keep the watercourse free from any obstruction not
authorized by a development plan.
3) CHANNEL MODIFICATIONS
a) Modifications to existing watercourses or newly created open
channels may be designed as earth channels, sod channels
or as concrete lined, or otherwise hard armored channels.
Liners other than sod or concrete which enhance the
aesthetics or habitat value of the watercourse, and which
reduce future maintenance requirements are encouraged.
Preliminary planning for the applicability of other channel
liners shall be reviewed with the City Engineer or his/her
designee prior to the submittal of construction plans for
approval.
b) Runoff that results from upstream development and is
discharged to an unimproved waterway can cause flood
damage to properties adjacent to the waterway. Natural
undeveloped waterways do not receive regular maintenance.
Design of natural waterways shall take into consideration
fluvial geomorphologic principles and practices. Consulting
engineers and development review officials shall work to
resolve potential downstream impact issues.
4) Design of new channels or alterations to existing channels shall
consider future maintenance requirements. A maintenance schedule
for any private channel shall be submitted to and approved by the
City Engineer or his/her designee prior to approval of construction
plans. Maintenance requirements of concrete channels consist of de -
silting activities, prevention of vegetation establishment in
construction joints, and repair of concrete as necessary.
Maintenance of earthen channels includes regular observation and
repair, as necessary, of erosion, scouring, and removal of silt
deposits, as necessary to maintain design parameters. Developers
shall be responsible for maintaining newly planted channels until
35
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
coverage is established throughout eighty- five (85%) percent of the
area. This area shall include slopes, floor, and any attendant
maintenance easement. New earthen channels shall be planted
with drought resistant, low -growth, native species grasses, which will
allow unobstructed passage of floodwaters. Johnson grass, giant
ragweed and other invasive species shall not be allowed to
promulgate in channels. Suggested species shall include, but not be
limited to, common bermuda, buffalo grass, side oats grama, seep
muhly, little bluestem, and Indian grass. Mowing frequencies vary
with the vegetation growth rates but is required when the grass
exceeds the design roughness coefficient of the channel.
5) Planned multiple use of a watercourse is allowed (e.g. bike paths or
greenbelt). If multiple use of the watercourse is to be incorporated,
the applicant shall form a community association that shall assume
maintenance responsibility for private amenities. The appropriate
government agency will be responsible for maintenance of public
amenities. The applicant shall provide overlay easements for public
or private use.
6) Table 4.5D shall be used to determine maximum permissible
channel velocity.
Table 4.5D
Velocity Control
Hydraulic
Correction
Max.
Velocity
Type Drain Required
Radius
Factor
Permissible
Velocity
5 fps
0-1 ft
0.8
1 to 6 fps
1-3 ft
0.9
5.5 fps
(Maximum
Grass Lined Channel
3-5 ft
1.05
6.3 fps
Average Velocity
5-8 ft
1.15
6.9 fps
= 6 fps)
8-10 ft
1.225
7.35 fps
Over 10 ft
1.25
7.5 fps
6 to 8 fps
Concrete retards
N/A
N/A
N/A
re uired
8 fps and over
Concrete lining or Drop
N/A
N/A
N/A '
Structures Required
a) Where velocities are in the supercritical range, allowance shall
be made in the design for the proper handling of the water by
the design of energy dissipaters at the outfall, and the lining of
the channel, and the inclusion of freeboard.
36
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
b) Ensure that the channel will contain the hydraulic jump
(sequent depth) throughout the extent of the supercritical
profile. An exception to this criterion is where concrete lined
lateral channels discharge down the side slopes of channels.
These channels may be designed for normal depth plus
freeboard provided velocity controls are established at the
main channel flow line.
c) Ensure that the energy grade of the channel will not result in
upstream flooding at existing or proposed lateral facility
connections.
7) Retard spacing shall be computed as using the following equations
and subject to the Velocity Control standards in Table 4.5D:
L=1.0=(S1-S2)
Where: L = Distance required between retards in feet.
S1 = Actual slope of channel in ft./ft.
S2 = Slope of proposed channel for maximum permissible velocity
established from Table 4.5F. For example:
S2 = (V=(1.486*n*R23)]2
Where:
V = maximum permissible velocity established from Table 4.5F
n = .035, manning's roughness coefficient for grass lined channel
R = area/wetted perimeter
8) Concrete Lined Channels. The design of concrete lined channels
shall comply with the following general requirements:
a) Freeboard consistent with Table 4.5E will be applied to the
twenty-five-(25) -year design.
Table 4.5E
Drainage Freeboard for Concrete Lined and Earth Channels
for 25-Year Storm
Design Depth of Flow
Required Freeboard
0-5 ft
0.5 ft
Over 5ft
1.0ft
b) From the top of the concrete lining to the top of the ditch, a
side slope not steeper than four (4) horizontal to one (1)
vertical shall be required; nor shall the slope be less than
twelve to one (12:1).
37
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
c) For normal conditions, the concrete lining shall be a minimum
of five (Y) inches thick and reinforced with No. 3 round bars
at twelve (12") inches on center each way. Where surcharge,
nature of ground, height, and steepness of slope, etc.,
become critical, design shall be in accordance with latest
structural standards. All concrete lining shall develop a
minimum compressive strength of not less than three
thousand (3,000) pounds per square inch in twenty-eight (28)
days. The depth of all toe downs shall be thirty-six (36) inches
upstream, and eighteen (18) inches for side slopes. The City's
Engineering Inspector may permit an eighteen (18")-inch toe
down in rock sub grade in lieu of the above toe down
requirements. The horizontal dimensions of toe downs shall
not be less than six (6") inches.
d) Maximum concrete riprap side slopes shall be one and one-
half (1-1/2) horizontal to one (1) vertical, unless soil tests
made by a geotechnical engineer show that a greater slope,
or a special design, will be stable. Where vehicular traffic may
travel within a horizontal distance equal to one-half (1/2) the
vertical rise of the slope, a two (2')-foot surcharge load shall
be included in the design.
e) Fencing (or other approved safety barrier) will be required
adjacent to the channel where channel vertical wall heights
exceed two (2') feet. Fencing or barrier will also be required
adjacent to the channel where channel side slopes exceed
three to one (3:1) and the channel depth is greater than two
(2') feet. The barrier must not cause sight distance problems
for motorists.
f) Easements or rights -of -way for concrete lined channels shall
extend a minimum of two (2') feet on both sides of the extreme
limits of the channel. "Extreme limits" of the channel shall
mean the side slope intercept with the natural ground or
proposed finished ground elevation. This two (2') foot space
shall be constructed of concrete or some other maintenance
free material.
g) A minimum "N" value of roughness coefficient of 0.015 shall
be used in Manning's formula. Recommended "N" are
available in Table 4.5F below. For approval to alter, contact
the City Engineer or his/her designee.
KRI
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
h) Channel shall have a bottom width of eight (8') foot minimum with
a vehicular access point of seven (7) horizontal to one (1) vertical
slope at least every one thousand (1000') feet. For channels less
than eight (8') foot bottom width, a fifteen (15') foot wide
access road is required adjacent to the channel.
Table 4.5F
mannings Kougnness Looemcient _.N..
Channel Description
"N" Value
Concrete Lined Channel
0.015
Grass Lined Channel with Regular Maintenance
0.035
Grass Lined Channel without Recent Maintenance
0.050
Vegetated Channel with Trees, Little or No Underbrush
0.055
Natural Channel with Trees, Moderate Underbrush
0.075
Natural Channel with Trees, Dense Underbrush
0.090
Natural Channel with Dense Trees and Dense Underbrush
0.100
Reinforced Concrete Pipe
0.013
Concrete Box Culverts
0.013
Overbank Description
"N" Value
Pasture
0.035-0.055
Trees, Vegetation, Multiple Fences and Structures
0.060-0.075
Dense Vegetation, Multiple Fences and Structures
0.075-0.090
Pipe
"N" Value
Corrugated Metal Pipe - %Z" corrugations
0.024
Corrugated Metal Pipe - 1" corrugations
0.027
Concrete Pipe
0.013
9) Vegetated Earth Channels.
a) Freeboard consistent with Table 4.5E will be applied to the
twenty- five (25)-year design
b) No earthen channels will be permitted with less than an eight
(8') foot bottom width. All channels not meeting the minimum
width shall be concrete channels (see Section 8 above). The
side slope shall not be steeper than four (4) horizontal to one
(1) vertical.
c) Easements or rights -of -way for improved earth channels shall
conform to the requirements stated in subsection (d) of this
section and shall extend a minimum of two (2') feet on one (1)
side and fifteen (15') feet for an access road on the opposite
side of the extreme limits of the channels when such channels
do not parallel and adjoin an alley or roadway. When such
channels do parallel and adjoin an alley or roadway, the
easement or right-of-way shall extend a minimum of two (2')
feet on both sides of the extreme limits of the channel. Where
utilities are installed in the access road of the drainage right-
of-way, the right-of-way shall extend two (2') feet on one (1)
39
CITY OF SCHERTZ DESIGN SPECIFICATIONS
side and seventeen (17') feet on the opposite side of the
design limits of the channel. These seventeen (17') feet are
to provide an access way along the channel with a maximum
cross slope of one (1 ") inch per foot toward the channel. Where
designed channel bottoms exceed one hundred (100') feet in
width, fifteen (15')- foot extra width shall be provided on both
sides of the channel. Interceptor drainage easements shall
extend a minimum of two (2') feet on both sides of the extreme
limits of the channel.
d) Channel shall have a bottom width of eight (8') foot minimum
with a vehicular access point of seven (7) horizontal to one (1)
vertical slope at least every one thousand (1000') feet. For
easements crossing streets there shall be an access drive on
both sides of the street right-of-way. Improved earthen
channels will be vegetated by seeding or sodding. Eighty-five
(85%) percent of the channel surface area must have
established vegetation before the City of Schertz will accept
the channel.
10) Channel Bends. Allowance for extra freeboard shall be made when
the centerline radius of the channel is less than three (3) the bottom
width. Where sharp bends or high velocities are involved, the
applicant shall use the following formula for computing the extra
freeboard:
02 - d, = VA * (T + B) + (2*g*R)
Where: di = depth of flow at the inside of
the bend in feet. d2 = depth of flow at the
outside of the bend in feet.
B = bottom width of the channel in feet.
V = the average approach velocity in the channel in
feet per second.
T = width of flow at the water surface in feet.
g = 32.2 feettsecond squared.
R = the center line radius of the turn or bend in feet.
a) The quantity d2 - di divided by two (2) shall be added to the
normal depth of flow before adding the required freeboard in
calculating required right-of-way widths.
b) Where sharp turns are used without curved sections, the depth
required shall be large enough to provide for all head losses.
Allowance shall be made for any backwater head that may
result.
40
CITY OF SCHERTZ DESIGN SPECIFICATIONS
c) For normal design conditions no extra freeboard is required.
An accepted rule of thumb to follow is this: Centerline radius
of channel should be at least three (3) times the bottom width.
11) Trickle Channel. All channels and detention basins with a bottom
width of eight (8') feet or greater must have a trickle channel, a
minimum of five (6) feet wide, following the centerline to facilitate
positive drainage to the outfall or the entire length of the channel.
1) STORM SEWERS
1) For all ordinary conditions, storm sewers shall be designed on the
assumption that they will flow full under the design discharge;
however, whenever the system is placed under a pressure head, or
there are constrictions, turns, submerged or inadequate outfall, etc.,
the hydraulic and energy grade lines shall be computed and plotted
in profile. In all cases adequate outfalls shall be provided and the
system adequately designed. Show the HGL in the profile.
2) No public storm sewers shall be less than twenty-four (24") inches in
diameter, and all junctions shall have an access manhole a minimum
of five (5') foot in diameter meeting the access criteria in the latest
version of the Standard Construction Details and the Technical
Specifications. All structures shall conform to the HS-25 loading
standard within streets or along any potential vehicle route (including
drainage easements)
3) Minimum easement widths for storm sewers will be the greater of
fifteen (15') feet or six (6') feet on both sides of the extreme limits of
the storm sewer width (e.g. the easement width for a three (3) barrel
ten (10')-foot wide box culvert with six (6")-inch walls would be (3 x
10') + (4 x 0. 5') + (2 x 6') = 44').
J) INLETS AND OPENINGS
1) Drop Curb Openings - Where drop curb openings are used to take
storm water off the streets and into drains or swales, the length of
the curb opening can be calculated from the weir formula using the
coefficient of 3.087 in the following formula:
41
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
L = Q = (C,N * h3/2)
Where:
L = the length of drop curb opening required in feet
Q = amount of flow in cubic feet per second (cfs) based on twenty -five-year
design frequency
C = 3.087
h = head of weir in feet
Gutter line depressions will be permitted where such depressions will
not hinder the flow of traffic. For amount of curb exposure, conform
to Texas Department of Transportation San Antonio District Inlet
Type I or II.
2) Curb or Drop Inlets. Where drop inlets are used, the City standard
inlets with adequate reinforcing steel may be used. All other types
or designs shall be subject to the approval of the City Engineer or
his/her designee. The following formulas for inlet capacity are
based on drop inlets in sag points. Inlet capacities on grades will be
considered less, the amount of which depends on street grades,
deflections, cross slopes, depressions, etc.
3) Grate Inlets. The flow of water through grate openings may be
treated as the flow of water through a rectangular orifice. The
following formula may be used for determining grate capacity:
Q = Co *A * (2*g*h)112
Where:
Q = discharge in cubic feet per second
Co = orifice coefficient of discharge (taken as 0.70)
g = acceleration due to gravity (32.2 ft./sec2)
h = head on the grate in feet
A = net area of the openings in the grate in square feet
This formula gives the theoretical capacity of the grate inlet. Since
grate inlets are subject to considerable clogging, capacity of the grate
inlet will be taken as one-half (1/2) on the value given by this formula.
4) Curb Opening Inlets. The capacity of curb opening inlets will depend
on whether or not the opening is running partially full or submerged.
If the depth of flow at the curb opening inlet is such as to cause a
partially full opening, a weir effect will develop, and the following
formula will apply:
42
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Q=CK,*L *h-v2
Where:
Q = the discharge of capacity in cubic feet per second
CW= the weir coefficient of discharge (3.087)
L = the length of curb opening in feet
h = the head or depth of water at the opening in feet
If the depth of flow at the curb opening is such as to fully submerge
the opening, the orifice effect will develop, and the formula used shall
be identical to that given under grate inlets with the exception that
the head, h, on the curb opening orifice shall be taken as the depth
from the top of the water surface to the center of orifice or opening;
one hundred (100%) percent efficiency will be allowed for curb
opening inlets. In no case, shall a pedestrian facility be placed in an
area to be inundated by water during the design storm event.
5) The pedestrian facility should be elevated so as to avoid inundation and
adequate railing shall be provided as required per paragraph H.8.e
of this section.
K) DETENTION BASINS
For projects with an increased impervious area of greater than 0.1 acres,
for all new developments or redevelopment of individual parcels of property,
detention basins may be used to mitigate peak flow rates to predevelopment
or existing development conditions.
1) The maximum allowable outflow rate from the detention facility must
be restricted to the flow rate from the undeveloped or existing
development tract for the 2-year, 5-year, 10-year, 25-year and 100-
year frequencies. Best management practices shall be used in the
design of detention facilities in accordance with this section. The
timing of the hydrograph released from the detention facility must be
checked against the timing of the flow rate in the first open
watercourse to prevent any increase in the peak flow rate in the
receiving watercourse. For detention basins constructed in -line on an
existing watercourse, the creation of the basin shall not increase flood
elevations in the channel upstream of the new development
boundaries.
2) On -site detention facilities must be privately owned and shall be
maintained by the community or property owner association or
property owner. A maintenance schedule shall be submitted to the City
43
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Engineer or his/her designee prior to approval of construction plans.
The City will have the right to do periodic inspections of privately
owned and maintained detention facilities to ensure that the
maintenance schedule is being implemented.
3) Multi -use facilities are encouraged, but not required (multi -use facilities
allows for water quality, satisfy TPDES requirements, enhance around
water recharge, provide open space, provide recreation or other
amenities, and/or provide habitat) and may be utilized so long as the
facility meets the standards set forth in subsection (F.1) of this section
and does not increase the rate or volume of erosion above that which
would result from the use of a facility without multiple uses. The use of
multi -use detention facilities to alleviate existing flooding problems,
enhance and provide amenities for older neighborhoods, and support
the revitalization of economically depressed areas is encouraged in
public and private redevelopment initiatives.
4) Maximum water depths over six (6') feet will not be allowed without
prior approval of the City Engineer or his/her designee.
5) Fencing or other approved safety barrier is required when side slopes
and total depth meet the criteria specified for channels in paragraph
H.8.e. of this section.
6) Parking areas may be used as detention facilities provided the depth
does not exceed eight (8") inches, and the impounding of storm
water does not impact the adjacent buildings.
7) Stage- Storage- Discharge tables for basins and associated outlets
will be required upon plans and within the SWMP.
8) Pumped detention systems will not be an acceptable method of storm
water mitigation unless the facility will remain privately owned,
operated, and maintained. The City will approve the use of a pumped
facility for private use under the following conditions:
a) A gravity system is not feasible from an engineering and
reasonable economic standpoint.
b) At least two (2) pumps are provided, each of which is sized to
pump the design flow rate.
c) The selected design outflow rate must not aggravate
downstream flooding.
d) Controls and pumps shall be designed to prevent
unauthorized operation and vandalism.
e) Adequate assurance is provided that the system will be
operated and maintained appropriately on a continuous basis.
44
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
9) Storm water retention with permanent wet pool systems will not be
an acceptable method of storm water mitigation unless the facility
will remain privately owned, operated, and maintained. The City will
approve the use of a wet pool system for private use under the
following conditions:
f) A gravity system is not feasible from an engineering and
reasonable economic standpoint.
g) The volume below the discharge invert shall not be considered
for detention capacity.
h) Mitigation measures must be included in the design of the
facility to ensure water quality and prevent nuisances and
environmental hazards.
i) Facility shall not promote a bird hazard or any other hazard that
would negatively impact Joint Base San Antonio (JBSA) or its
mission.
j) Adequate assurance is provided that the system will be
operated and maintained appropriately on a continuous basis.
L) OUTFALLS/OUTLETS/TRANSITIONS
If the velocity at an outfall or outlet of a channel, storm drain, or detention
pond to an earthen/grass lined channel is greater than six (6') feet per
second (fps), provide energy dissipaters or other means to reduce velocity
and prevent erosion.
Provide retard spacing and concrete transition length calculations to
account for the effect of hydraulic jumps.
Adequate space shall be provided for the transition of flow from a
concentrated point to Sheet Flow (to mimic predevelopment
conditions) before the discharge leaves the developed Property.
45
CITY OF SCHERTZ
4.6 STORM WATER CHECKLIST
City of Schertz
Storm Water Management Plan (SWMP) Checklist
DESIGN SPECIFICATIONS
a
z
E
°
°
C>
c
A. GENERAL
1.
Signed, sealed & bound SWMP
Introduction & Project description
Narrative of existing and proposed hydrology
Summary of calculations (indicate methodology and key assumptions, time
Of concentration calculation, Curve Number and Runoff Coefficient
determination)
Table of runoff values
2.
Certification by Engineer that the resulting impact of the proposed
development will not produce a significant adverse impact to downstream
properties, structures, drainage facilities, and public infrastructure.
3.
Project Location Map
4.
Flood Insurance Rate Map (FIRM) with site superimposed
5.
Grading Plan (As required by City Engineer): Lots grading property according
to FHA Lot Grading Type (A, B, C) An upstream watershed no more than the
depth of 1 residential lot or 120 feet, whichever is greater. may drain to a
platted lot unless an interceptor drain is provided
6. Aerial map: Delineate site boundary, contributing watershed, downstream flow
path to 1 00-ear faciIi . ,flood plain and floodway location
B. HYDROLOGY
1.
Drainage Area Map (to scale) for Existing and Ultimate Conditions
Show site boundaries, overall drainage areas and sub- areas, acreage of
each of each drainage area, and discharge locations, downstream flow path
to 100-year facility
Provide Existing & Design time of concentration flow paths with length &
slope shown Table of runoff values at key locations
Existing and proposed topographic information with maximum two (2) foot
contour elevations
Flood plain and floodway location, with BFE indicated
2.
Detailed Q calculations include:
Time of Concentration (provide detailed calculations) (NRCS method):
Minimum 5 minutes total
Overland Sheet — Length, slopes, (max 20 minutes) max 100 feet
Shallow Concentrated Flow — Length, slopes
Concentrated Flow — Length, slopes, assumed v > 6 fps
Rational Method:
Rational Method for watersheds 0 to 50 Acres, Tc<20 minutes, peak flow
analysis only, no flow routing required, no floodplain analysis
Verify Rainfall Intensities (i) & Runoff Coefficient (C)
Unit H dro ra h Method TR 20 or HEC HMS etc.):
SCS or other Hydrograph Method for larger watershed or flow routing
Required (detention pond)
SCS curve number, CN value: provide detailed calculations & exhibit
Routing Values if used): Provide detailed calculations_
Routing Method: Modified Puls or Muskingum
Soil Survey Map of area (site delineated, soil type & acreage of each
soil groue)
M1
CITY OF SCHERTZ
r LJ%fr%M A l 11 1/101
DESIGN SPECIFICATIONS
1. General:
For all storm water facilities with drainage area > 100ac, design for Q100
All storm water facilities shall be designed for Ultimate development
2. Street Capacity:
Local: Q25 contained within curbs, Q100 contained within ROW
Collector: 025 contained within curbs AND one lane shall remain clear
Arterial: Q25 within curbs AND one lane in each direction shall remain clear
Streets draining a watershed greater than one hundred (100) acres must be
designed for the one hundred (100) year frequency storm
Velocity <10 fps
Street draining to unpaved surface runoff velocity < 6fps
Lateral curb opening sized as weir
3.
Channels: (provide detailed calculations)
If Drainage area < 100ac: Q25 plus freeboard
If Drainage area > 100ac: the greater of Q100 or Q25 plus freeboard
Slope Conveyance Method (Mannings) — for small channels (BW<20) not
floodplain, nor affected by backwater. Provide section of channel
Indicating normal depth, velocity, Froude number
Standard Step Back Water Model (HEC RAS or similar) — for large
channels (BW>20'), channels within floodplain, or channels controlled by
backwater. Provide plan and profile indicating HGL and EGL
Concrete channel:
Manning's "n" minimum of 0.015
Hydraulic jump calculations
Earthen channel:
Appropriate Manning's "n"
Velocity < 6 fps
Channel bend extra freeboard calculations
Turf Reinforcement Matting: 6 fps < Vel < 12 fps
If > 12 fps, engineer's report should certify that material is appropriate for
velocity. Include manufacturer spec's & installation instructions.
Engineer to certify at final inspection that material was installed correctly.
Interceptor Channel:
Easement width calculation
Floodplain Submittal is required if property is within or next to a FEMA
designed special flood hazard area
Storm Sewer
Inlet designed for 25-yr capacity
HGUEGL: provide detailed calcs (including junction losses). Show in
4.
profiles of pipe
EGL: below top of junction box or, if approved by City, specify bolted
manhole covers.
HGL: below gutter _
Downstream tail water depth calculation
Min storm sewer pipe diameter = 24 inches.
Pipe velocity between 2 fps and 12 fps
5.
Culverts
Culvert design for 25-year event unless upstream watershed is greater
than 100 acres, then it shall convey the 100-year runoff.
Designed according to FHWA HDS-5
Headwater does not overtop road
Box culvert, headwalls and wingwalls to conform to TxDOT design
standards
6.
Detention Basins
Indicate area to drain to detention basin
47
CITY OF SCHERTZ
DESIGN SPECIFICATION
Provide inflow and outflow hydrographs for 2-yr, 5-yr, 10-yr, 25-yr, and 100-
yr (proposed, ultimate)
Provide required storage for the 2-yr, 5-yr, 10-yr, 25-yr, and 100-yr
(proposed, ultimate) _
Check tailwater conditions on outlet structure
Include a stage/storage/discharge table
Provide details on outlet structure (invert, sizes, slopes, details on plan
sheet) indicate depth per rainfall event.
Verify pond height is 6' high or less from toe on downstream side of
embankment (existing grade) to the top of the structure. If not, overflow
spillway must have capacity for 100% of the ultimate development probable
maximum flood PMF and TCEQ approval may be required.
Modified rational is not accepted
Provide maintenance schedule
Provide results in tabular format with detailed calculations for
allowable/existing, proposed, and ultimate discharges from the structure.
Provide Electronic files of model
Outfalls/Outlets/Transitions
If velocity > 6fps at transition to earthen channel, provide energy
7
dissipaters or other means to reduce velocity. Provide retard spacing and
concrete transition length calculations (hydraulic 'um
Receiving facility (street, channel, culvert, etc.) capacity to accept runoff.
8.
Easements
Widths include freeboard and access
9.
Storm Water Pollution Prevention Plan
10.
Maintenance agreement/plan
D. ADDITIONAL
_
ITEMS IF FLOODPLAIN WORK IS PROPOSED
1.
Narrative
Table of Contents and abstract or executive summary
Introduction that includes project description and history, location, scope and
objective of analysis, previous and related studies that may affect this analysis.
Summary, conclusions, vicinity map and recommendations. Include the
Impact on the floodplain's Q, WSEL & velocity.
2. Provide detailed Hydrology calculations for changes in hydrology or for
unstudied stream reach, see SWMP above with electronic copy of model)
3. Provide detailed Hydrology calculations for changes in hydrology or for
unstudied RAS or standard step backwater analysis model:
25 year existing and ultimate development condition hydraulic analysis
100 year existing and ultimate development condition _hydraulic analysis
4. Provide plans and calculations for channel outfalls perpendicular to the
floodplain. Channel outfall must be taken to the invert of the receiving channel
or show the velocity to be less than 6 fps going down the side slope.
5.
Plotted water surface profiles for the 100-year flows (if applicable)
6.
Provide channel cross sections (existing superimposed on proposed) show the
drainage easement, Manning numbers, property lines, structures, etc.)
7.
Provide a summary table of the hydraulic model (HECRAS) of the floodplain
within the platted area
8.
Copy of all permits needed under the authority of USACE, TCEQ, or any other
applicable regulatory authority
9.
Current Effective dFIRM of project area
10.
Grading Plan (existing and finished contours)
11.
Provide Topographic Work Map: show plan view of project limits, cross
sections, existing/proposed contours, proposed development, current and
revised flood plain limits, property lines, drainage easement, engineers
signature and seal
48
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
12.
Provide U.S.G.S. Quadrangle maps showing overall drainage areas, runoff
coefficients, time of concentration, intensity.
13.
F000dplain Development Permit
14.
Elevation Certificated (if applicable)
15.
FEMA CLOMR / LOMR/LOMRa/LOMRf
Provide the applicable items listed above
MT-2 Form 1 Sec D: Provide Owners and Engineer's original signature
MT-2 Form 2 Sec A: Provide an attached explanation if sediment transport is
not considered
MT-2 Form 2 Sec B 4: Model names in this section must match the models
listed in the CD
For Map Revision Detail study includes 10, 50, 100, and 500-year Analysis
If applicable, provide As Built Grading Plan with engineer's seal and
signature
Recommend providing Check-RAS output
Provide existing and proposed FEMA FIRM Maps with the following:
Existing — Label Map "Current" and show the site boundaries.
Proposed — Label Map "Revised", show site boundaries, show only the
proposed floodplain limits, floodplain must be in the existing floodplain
upstream and downstream, show the proposed streets centerline only and
label, show the upstream and downstream limits of study.
SECTION 5 — SANITARY SEWER REQUIREMENTS
5.1 GENERAL
All subdivisions shall be provided with an approved sewage disposal system. An
Engineering Design Report for wastewater shall be submitted for review by the
City Engineer or his/her designee. The report should contain a map of the service
area, development LUE count, design flow rates and calculations (Average Dry
Weather, Peak Wet Weather flow), design capacity of the sewer, minimum and
maximum velocities, and a statement declaring that minimum velocities and pipe
capacities have been met. If the project is to require a lift station and force main,
the sizing of the wet well, pumps, controls, and force main shall be included in the
report. The sanitary sewer collection system shall be designed in accordance with
the standards and specifications set forth hereinafter.
A) The Developer shall dedicate, at their own cost, such right-of-way and
construct such sanitary sewer main and appurtenance of such size as to
adequately serve the area being subdivided as determined by the City or
the utility company under whose jurisdiction the subdivision falls.
5.2 MINIMUM STANDARDS
A) Design Criteria: All gravity sewers shall be PVC gravity sewer pipe and
fittings meeting the requirements of ASTM Specifications D 3034 and shall
be SDR 26. All structures shall conform to the HS-25 loading standard
within streets or along any potential vehicle route (including sewer
easements).
49
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
B) Minimum size of sewer mains shall be eight (8") inches in diameter and all
house connections in streets or alleys must be six (6") inches in diameter
belonging to the owner of the lot. The minimum and maximum pipe slopes
and velocities shall be in accordance with TCEQ standards (30 TAC Ch
217.53(1)(2)(A) table C.2). All sanitary sewer collection mains shall be of
sufficient size to serve the peak dry weather flow from the service area plus
infiltration and inflow. Provide flow calculations including the details of the
average dry weather flow, the dry weather flow peaking factor, and the
infiltration and inflow. The flow calculations must include the flow expected
in the facility immediately upon completion of construction and at the end of
a fifty (50) year life. The line must conform to the City's current Sanitary
Sewer Master Plan.
C) The following criteria shall be used in formulas in the design of sewer
system:
1) Average Dry Weather Daily Flow is based on 245 gpd/LUE (living
unit equivalent).
2) Peak Dry Weather Daily Flow is based on a peaking factor of 3.0.
3) Peak Wet Weather Flow is Equal to Peak Dry Weather Flow plus
Inflow/Infiltration.
Table 5.2A
Flow From Contributing Population (245 gpd/LUE)
Residential
LUE/each
1
Apartments & Extended Living
LUE/unit
3/5
Hotel/Motel
LUE/unit
1 /3
Business
LUE/person
20/245
School
LUE/student
15/245
4
Unknown future development
LUE/acre
Rates for other non-residential development may be obtained from actual water usage, TCEQ,
Wastewater Usage Rates (30 TAC §285.91 Table III (use rates without water saving devices for
existing facilities and rates with water saving devices for future facilities) or other method approved
by City Engineer.
Table 5.2B
Infiltration
Source of Infiltration
Residential Area — Level to 7% slope
Amount of Infiltration In
Gallons Per Day Acre
700
Residential Area — 7% To 15% Slope
500
Totally Undeveloped Areas
360
High Water Table (Creek Beds, Lake Areas)
1450
Business and Industrial Areas
1000
50
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
D) The Developer shall furnish lift stations with Supervisory Control and Data
Acquisition (SCADA) equipment where necessary. These shall be
constructed only after approval by the City.
E) Sewage treatment plants and sewer systems must conform to the
requirements of Texas State Department of Health.
F) Manholes: All manholes shall be a minimum of five (6) foot in diameter for
all Base and riser sections (no cones less than five (6) in diameter) with
watertight manhole ring and cover meeting the Current Standard
Specification and Standard Detail criteria and minimum of thirty (30") inch
diameter opening.
1) Precast concrete manhole sections with steel reinforced concrete
base with confined O-ring joints in conformance with ASTM C-443.
2) Base shall be manufactured in accordance with ASTM C-478. The
precast base may have formed smooth invert channels cast at the
angles. The invert channel shall have W = 1' fall toward the outlet
and inverts shall be designed to prevent reverse flow.
3) Resilient joint connectors for a watertight seal between the manhole
base and specified line pipe shall be provided. This joint shall comply
with ASTM C-923.
G) Construction methods shall be in strict accordance with the
manufacturer's installation procedures and recommendations. The items
below are listed for emphasis:
1) The City shall be advised forty-eight (48) hours before any
construction is started for adequate scheduling inspection to be
provided.
2) Sewers shall be located in the centerline of streets and four (4') feet
from the north or east lines where in alleys or as otherwise approved.
Mains within earthen channels/drainage ways shall be protected
from scour; a scour analysis may be required.
3) All sewer lines shall be placed on line and grade as directed by the
Design Engineer.
4) Manholes shall be placed at all deflection, intercept and terminating
points on the public system and spaced not more than five hundred
(500') feet apart.
5) Manholes shall be provided at intersecting streets or alleys where
there is a possibility of future extensions.
51
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
6) Drop Manholes should be used sparingly and generally, only when it
is not economically feasible to steepen the incoming sewer, in no
case should a drop be used for a fall less than two (2') feet and all
shall be interior drop manholes.
7) Sewer laterals shall be terminated in a cleanout at the property line.
A sewer lateral may only serve a single customer. No cleanouts may
be used on any public sewer main.
8) All non-residential service customers shall provide a sample port
meeting the current City of Schertz specifications or approved by the
City Engineer or his/her designee on all service laterals within the
property. The sample port should be in an area readily accessible to
City and/or sewer service provider's representative and clear of
pedestrian and vehicular traffic.
9) Manholes located in the area to be paved shall be left covered below
sub -grade until the street contractor has completed the street and
then it shall be reset to finished grade.
10) Compaction of sewer trench and lateral backfill shall be according to
Section 02317 — Excavation and Backfill for Utilities of Schertz
Technical Specifications. Each lift of backfill shall be tested and pass
density requirements prior to the next lift of material being placed.
11) Construction over the Edwards Aquifer: For subdivisions constructed
over Edwards and associated limestone formation, all construction
shall meet the latest revision and requirement of the Texas
Commission on Environmental Quality.
12) All manhole section joints shall be wrapped with an external seal
wrap meeting Technical Specification 02082 and installed according
to manufacturer's recommendations.
13) Encapsulate manholes with flowable fill from bottom of base,
minimum of one (1') foot around walls, up to bottom of concrete
collar.
5.3 MINIMUM SANITARY SEWER TESTING REQUIREMENTS
A) PUBLIC SANITARY SEWER LINE AIR TESTING
1) Description: This item shall cover the testing of completed sections
of installed sewer pipe using low-pressure air tests on all completed
sections of sanitary sewer mains.
52
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
2) The air test will be used to evaluate materials and construction
methods on the pipeline sections and successful air tests shall be
mandatory for the acceptance of the lines.
B) MATERIALS FOR TESTING
1) Compressor Air Supply: Any source which will provide at least three
hundred (300) cubic feet per minute at one hundred (100 psi) pounds
per square inch.
2) Plugs, Valves, Pressure Gauges, Air Hoses, Connections, and
other equipment necessary to conduct the air test, shall be furnished
by the contractor. The test equipment for air testing will consist of
valves, plugs and pressure gauges used to control the rate at which
air flows to the test section and to monitor the air pressure inside the
plugs. Test equipment shall be assembled as follows:
a)
Hose connection
b)
Shut-off valve
c)
Throttle valve
d)
Pressure -reduction valve
e)
Gage cock
fl
Monitoring pressure gauge
3) Test Procedures:
a) Determine and isolate section of line to be tested
b) Apply air pressure until the pressure inside the pipe reaches 4 psig.
c) Maintain 4 psig for duration of test length and record.
If no decrease for the duration shown in the allowable table, the pipe
shall be presumed to be free from problems If any pressure decrease
is detected, or pipe breakage, joint leakage or leaking plugs are
indicated, an inspection must be made to determine the cause.
The contractor shall make such repairs as may be required to
accomplish a successful air test. If repairs are needed an additional
thirty (30) day waiting period for final backfill will be required before
follow-up deflection and pressure testing (see Section 4 below).
See Section 02533 — Acceptance Testing for Sanitary Sewers. City
of Schertz Technical Specifications for a table of time allowed for
pressure loss.
53
CITY OF SCHERTZ DESIGN SPECIFICATIONS
4) Deflection by testing
Flexible gravity sewer lines shall be tested for deflections by use of
a go -no-go testing mandrel calibrated for five (5%) percent maximum
deflection of the inside diameter to the pipe. No deflection testing can
occur until a minimum of thirty (30) days after final (density -tested)
backfill.
5) Additional Testing and Criteria
See Section 02533 — Acceptance Testing for Sanitary Sewers. City
of Schertz Technical Specifications for a table of mandrel sizes, as
well as vacuum testing of manhole procedures and requirements for
filming of sewer mains. No vacuum testing on manholes or sewer
mains shall be performed before final pavement is laid or final backfill
and grading is complete. If any additional work is done in the vicinity
of the manholes or sewer mains after testing is completed, an
additional round of testing may be required at the Developer's
expense.
SECTION 6 — WATER REQUIREMENTS
6.1 GENERAL
All subdivisions within the City and its ETJ shall be provided with water supply and
water distribution systems constructed in compliance with an approved water
system. An Engineering Design Report for the water system will be submitted for
review by the City Engineer or his/her designee. The report should contain a map
of the area to be served, development LUE count, design flow rates and
calculations, available local pressures, and a statement declaring that minimum
pressures and flow rates will be provided. If additional storage of pressure will be
needed the sizing and design of the pumps and storage facilities will be included
in the report.
A) Facilities Required: Every lot in a subdivision shall be provided with an
approved supply of water, either by the construction of a supply and
distribution system connected to an adequate approved public water system
or, if such public source is not available, by construction of a complete water
system, including a safe, adequate water source, proper treatment facilities,
pumps, storage facilities and distribution system, approved by the TCEQ.
B) The Developer shall dedicate, at his own cost, such right-of-way or
easement and construct such water main, water lines, fire hydrants and
appurtenance as such size as to adequately serve the area being
subdivided as determined by the City or the utility company under whose
jurisdiction the subdivision falls.
54
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
6.2 MINIMUM WATER STANDARDS
A) FIRE HYDRANTS
1) Hydrant location must follow both of two rules:
a) No structure should be further away than four hundred
(400') feet from a fire hydrant as a fire house would lay (or
as required by the Fire Marshal)
b) Hydrant spacing along a water main should not exceed five
hundred (500') feet in single-family residential areas or
three hundred (300') feet in any non-residential, multifamily
dwelling, or heavily congested residential area.
2) Fire Hydrants branch lines shall connect to an eight (8") -inch water
main and in no case be longer than one hundred (100') feet.
3) Any new fire hydrant along a roadway is required to have a hydrant
locator Type II blue reflector installed in the roadway or fire lane,
perpendicular to the hydrant two (2') feet off centerline.
4) No private fire lines shall exceed one thousand (1000') feet in length
without redundant connections to public main and shall meet all the
design criteria and construction specifications required within the
most current editions of the Technical Specifications Manual, NFPA
24, and the most current, adopted International Fire Code. See
additional criteria in Section 6.3.G below.
B) WATER MAINS
1) Design Specifications: The water distribution system design shall
include the minimum requirements of the Texas State Fire Insurance
commission for residential, mercantile, and industrial areas in
addition to the requirements for a peak hour customer demand a
determined by the City Engineer or his/her designee.
2) Supply Mains: Supply mains in the distribution system shall be
looped and have a minimum size of twelve (12") inches diameter.
Supply mains should be located generally where shown on the City
of Schertz Water Master Plan but should be sited so the length
between cross connecting supply mains does not exceed six
thousand (6000') feet.
55
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
3) Distribution Mains: Mains shall be looped between supply mains and
shall have a minimum of eight (8") inches in diameter. The maximum
length between distribution main cross connections shall be the
shorter of the two following lengths: three thousand (3,000') feet, or
a length that would by fluid friction render the line incapable of
producing the flows and pressure set out herein for the type of area
to be served considering pressure and flows that exist at the supply
main's connections as determined by the City Engineer or his/her
designee.
a) Mercantile and Industrial Mains: Mains in all mercantile
areas shall be located in rights -of -way or water easements
and shall be sized to provide minimum fire flow from any
single hydrant of not be less than one thousand five
hundred (1,500 gpm) gallons per minute with twenty (20
psi) pounds per square inch residual pressure.
b) Residential Mains: Domestic mains shall be installed in
dedicated street right-of-way or water easements and sized
so that the minimum fire flow at any single fire hydrant shall
not be less than seven hundred fifty (750 gpm) gallons plus
two (2 gpm) per minute for every lot in the subdivision with
thirty (30 psi) pounds per square inch residual pressure.
4) One LUE (Living Unit Equivalent) produces a water demand of:
1. 2 gpm peak hour flow demand
2. 1 gpm peak day flow demand
3. 300 gpd (0.208 gpm) average daily flow
4. Peak Flow Factor formula:
PFF = (18+ (0.0144*F) 0-5) / (18+ (0.0144*F) 0-5)
Where, F = avg flow (gpm) = 70*gpcd*population/1440
5) Connections for combination domestic and fire service lines are not
permitted. Separate connections to the main are required for
domestic and private fire lines.
6.3 DESIGN CRITERIA
A) Water Mains within the City's Jurisdiction shall be ANSI/AWWA C900 or
C905 PVC DR 14 or as allowed in Sections 02511, 02501, 02502, 02506 of
the Technical Specifications or other material as approved by the City
Engineer or his/her designee.
56
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
1) Minimum Working Pressure in any part of the system shall be twenty
(20psi) pounds per square inch during fire flow conditions and two
thirds (2/3) of the normal water use domestic or commercial. This
pressure pertains to the point of delivery of water to the consumer at
the house service line, and for residences not exceeding two stories.
A minimum working pressure of thirty-five (35) psi should be
provided wherever possible.
2) Normal Working Pressure under average conditions of flow should
range between thirty-five (35) psi and seventy (70) psi.
3) Maximum Pressures in excess of one hundred (100) psi should be
avoided. Anything over 80 psi shall be protected with pressure
release valve to be owned and maintained by the homeowner.
4) No Private Water Supply shall be installed in any subdivision in the
City limits or City of Schertz service area without City Council approval
and a water franchise agreement.
B) The depth of cover of the main shall be not less than forty-eight (48") inches
from the top of pipe. Any mains with less than forty-eight (48") inches of
cover from the top of pipe shall be lowered to meet the minimum depth of
cover. Mains within earthen channels shall be protected from scour (a
scour analysis may be required).
1) Any new water mains to be placed under a non-residential driveway
shall be cased in steel pipe. Exceptions to the requirement for casing
will be determined by the City Engineer and will be based on
conditions such as depth of planned or existing main, availability of
other site access, type of facility accessed by driveway, and other site
constraints.
2) Water mains crossing thoroughfare right-of-way (collector class and
larger) shall be encased in steel pipe.
3) Utility trench backfill shall be in accordance with Section 02317 —
Excavation and Backfill for Utilities of the Technical Specifications.
Each lift of backfill shall be tested and pass density requirements
prior to the next lift of material being placed.
4) The practices of water jetting or ponding backfill in roadways,
drainage right-of-way, driveways, concrete or paved easements
are NOT ACCEPTABLE
57
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
C) Water Service Lines shall be constructed using an approved double
strapped saddle copper service line with suitable brass CC threaded
compression gasket and compression stops. Developers will also be
required to install the angle stop and meter box before acceptance by the
City. Meter boxes are to be as shown in standard details and shall be
installed at the finish grade of the property to be served. A blue painted dot
on the curb over and 'Y' etching shall mark location of new meters.
D) AIR RELIEF AND BLOW -OFF VALVES AND DEAD-END MAINS
1) Air relief valves and blow -off valves should not be used except in
locations where fire hydrants are not practical or at true dead-end
mains. Air relief valves shall be located at high points on the line and
blow -off valves shall be placed at low points. Air release valves shall
be cast-iron stainless -steel screens and have a two (2") inch operating
nut and a PVC plug.
2) No new dead-end mains shall be installed except as temporary stub -
outs to future development or along ROWs to undeveloped properties
as approved by the City Engineer or his/her designee. No dead-end
water main providing domestic service shall be permitted. Looping is
required for redundancy and water quality. In no case shall a dead-
end main be longer than five hundred (500') feet. No new blow -offs
will be accepted except at the end of a temporary dead-end main to
be extended with further development. No blow -offs will be allowed at
the end of cul-de-sacs. Mains should be looped at the end of the cul-
de-sacs through water easements. A reduced main size (less than 8")
may be approved if line is only provided to connect the end of a cul-
de-sac within a subdivision. Water easements should not cross single
family residential lot lines unless approved by the City Engineer or
his/her designee.
E) GATE VALVES
1) Location of the valves shall be uniformly located in a standard area
such as street curb line extension to facilitate location. A valve box,
with its cover at the finish grade, shall always be placed over a buried
valve. A sufficient number of valves should be placed in the
distribution system so that a short section of main may be repaired
or serviced without interruption of service of more than one block. A
minimum of three (3) vales shall be used as crosses and two (2)
valves at tees. Generally, valves shall be placed along a main at
every other fire hydrant or at maximum one thousand (1000') foot
spacing. Valves shall also be installed on each side of thoroughfare
streets, railroad crossings and drainage channels.
58
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
2) Material for gate valve construction shall comply with the current
AWWA Standard C-509-80 Resilient Seat Gate Valves Per
Technical Specification Section 02521. All valves shall be left open
(counterclockwise).
3) A blue painted "V" shall be etched into curb face to mark valves.
4) Operation of Valves: No existing valves in the City's water distribution
system shall be operated by the contractor without prior permission
from the Public Works Department. The contractor shall notify the
Public Works Department, Engineering Inspector, all affected
customers a minimum of two (2) working days or forty-eight (48)
hours in advance of any outage. Contractors shall not operate a
valve outside the presence of the City's representative.
F) FIRE HYDRANTS: Five and one fourth (5 '/") inch steamer outlet (storz
connection), NST and two and a half (2 Y2) outlets, NST fire hydrants shall
be installed as part of the water distribution system per the City design
standards. Fire hydrants shall be installed with a separate gate valve and
valve box shall be per Technical Specification Section 02520. Public
hydrant bodies to be factory painted red with the bonnets and caps factory
painted white. Private hydrants shall be factory painted all red.
G) Private fire lines shall meet the City's specifications for pipe material and
trench backfill.
1) A Double Check Assembly (DCA) if metered, or a Double Check
Detector Assembly (DCDA) backflow device if not metered, shall be
provided within one hundred (100') feet of the City's water main on
private fire lines.
2) The DCA or DCDA may be installed in a vault if proper consideration
is given for drainage and clearance to vault walls for access and
repair in accordance with manufacturer's specifications.
H) PROTECTION OF WATER MAINS
1) Horizontal Separation: Whenever possible, water mains shall be
laid at least nine (9') feet, radially, from any existing or proposed
sewer. Should local conditions prevent a lateral separation of nine
(9') feet, a water main may be laid closer than nine (9') feet to a sewer
if it complies with 30 Texas Administrative Code JAC) (or TCEQ
rules) Chapter 217: Rule 217.53.d.
59
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
2) Vertical Separation: Whenever sewers cross under water mains,
the water main shall be laid at such an elevation that at the bottom
of the water main is a least nine (9') feet above the top of the sewer.
The vertical separation shall be maintained for that portion of the
water located within ten (10') feet horizontally of any sewer it crosses.
3) Special: When it is impossible to obtain proper horizontal and vertical
separation, both the water main and sewer shall be constructed in
accordance to 30 TAC Chapter 217: Rule 217.53.d.
4) Relation to Sewer Manholes: No water main shall pass through, or
come in contact with, any part of a sewer manhole. All sewer design
shall meet 30 TAC Chapter 217: Rule 217.53.d.
5) Cross Connections: There shall be no physical connection between
the distribution system and any pipe, pumps, hydrant, or tanks,
which are supplied, or may be supplied, with water that is, or maybe,
lesser standards or contaminated.
6) Water Mains Near or Crossing Obstructions: Water mains within
ten (10') feet of railroad tracks or crossing under railroad tracks shall
be Ductile Iron Pipe equipped with restrained clamps or other
acceptable provisions to minimize the effect of vibration. For mains
crossing under waterways, a valve shall be placed at both ends of
such crossing to permit isolation for repair and testing of the section.
7) Sampling taps shall be provided to facilitate sanitary control, typically
one (1) per subdivision. These taps shall not be subject to flooding.
1) Disinfection of Water Mains: The mains shall be disinfected in accordance
with AWWA Standard for Disinfecting Water Mains — C651, the
requirements of the TCEQ, and the City of Schertz Technical Specifications
Section 02514 — Disinfection of Water Lines. This applies to newly laid
mains or after main system repairs are made.
J) Asbestos Cement (AC) Mains: AC mains shall be replaced with currently
acceptable pipe materials a minimum of five (5') feet from the limits of any
new taps including fire line, domestic, and irrigation taps. Regardless of
where that five (6) foot distance falls, any AC main removal must be done
from collar to collar (whole pipe lengths only). AC mains shall also be
replaced where any grading work removes any depth of cover from the
water main.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
6.4 MINIMUM WATER TESTING REQUIREMENTS
Flushing, hydrostatic testing and chlorination of the City water main shall be in
accordance with the City of Schertz Technical Specifications Section 02515 —
Hydrostatic Testing of Pipelines, current AWWA standards as well as TCEQ rules
and regulations.
For all water lines, expel air and apply minimum test pressure of 200 psi for four
(4) hours. During the test, pressures shall not vary more than ±5 psi.
SECTION 7 — INSPECTIONS AND TESTING
7.1 LABORATORY TESTING:
A) The sub -divider shall notify the City at least one week prior to the contractor
beginning construction. Contractor shall be required to notify the City a
minimum of at least forty-eight (48) hours in advance of all testing being
performed.
B) All materials to be used in subdivision construction shall be subject to
testing if warranted. The preponderance of testing to be performed in
subdivisions is directly related to ensure quality of construction. Street
construction and a series of laboratory tests normally associated with road
and street construction will be required in subdivisions with said tests being
performed by an independent testing laboratory using qualified personnel.
The design (or consulting) engineer or his designated representative and
the City Inspector shall be present at all testing.
Whenever a Developer, contractor or engineer needs an inspection of any
street or utility improvement, the City Engineer or his/her designee shall be
contacted first a minimum of at least forty-eight (48) hours in advance of the
inspection. The design engineer or his designated representative shall be
present at all inspections.
Regarding testing of water and sewer lines, all testing will be done
according to American Water Works Association (AWWA), ASTM and
ASCE Standards.
In addition, the following procedures for testing of these lines will be as
follows:
1) No new water lines will be connected directly to an existing
City line. A backflow preventer with a hand valve (jumper)
shall be used between old and new lines for loading.
61
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
2) No new sewer lines will be installed in a manner that would
prevent testing of any part of the new line. All new sewer lines
will be tested. No connection to or work on the existing
system shall begin until testing has been completed
satisfactorily and notice has been given to the City.
3) Pre -testing of water and sewer lines will be conducted by
contractor prior to calling for an inspection to assure all lines
will hold required pressure.
C) With regard to street inspection: Streets shall be checked by contractor, to
ensure readiness; prior to calling for an inspection. No streets covered with
debris, vehicles or equipment will be inspected.
D) No piecemeal inspection of parts of lines or small sections of streets will be
made. However, with regard to subgrade or base inspections, sections of
the street can be inspected when needed to protect the subgrade from
bad weather or other conditions that may deteriorate the subgrade or
base.
E) The City staff, or an authorized inspector, may at the direction of the City,
inspect all subdivision site work at any time and any stage. The City shall
bear the cost of all inspections and the sub -divider shall bear the cost of all
re -inspections. The judgment of the City and/or the City Engineer as to the
need for any re -inspections of any part thereof, at any stage, shall be final.
F) Testing will be performed by an approved, independent testing laboratory.
The following test schedule will be adhered to:
1) Streets: subgrade moisture, density test at the rate of one per
one hundred (100') feet of street.
2) Flexible Base: P.L., L.L., P.I. and gradation of material used;
moisture, density test on same spacing as subgrade.
3) Concrete Structures: Concrete cylinders, one/100 cy placed or
for each pour is less than 100 cy shall be taken for curbs,
drainage structures and sidewalks.
4) All testing is the responsibility of the Developer. Copies of all test
results shall be furnished to the City as soon as possible. All
results are to be provided before final acceptance of the
subdivision by the City.
62
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
G) Before acceptance of a subdivision by the City for street or utility work, the
consulting engineer responsible for the design of said work shall issue a
letter to the City stating that he/she has inspected such improvements
and that said improvements were constructed in accordance with the
approved construction plans. Submitted along with the letter shall be "As
Built" drawings showing the work to be accepted for use by the City as
one (1) PDF and one (1) CAD format. These should include final
surveyed coordinates and elevations of valves, fire hydrants, storm and
sanitary manholes (including rim and inverts), drainage inlets (including
flow lines and inverts), junction boxes, stormwater discharge structures
and other surface utility features.
H) Guarantee of Material and Workmanship: The Developer shall be
responsible for guaranteeing that all materials required under this Code and
workmanship in connection with such improvements are free of defects for
a period of two (2) years after such acceptance of the improvements by
the City. The responsibility for all costs of the in -place improvements shall
be borne by the sub -divider, and all criteria of Section 21.4.15 of the
Schertz UDC shall be met before acceptance.
:c
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Appendix A
Rainfall Data
64
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
National Oceanic and Atmospheric Administration Atlas 14
City of Schertz Precipitation Areas
65
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Precipitation Area PA-1
CITY OF SCHERTZ DESIGN SPECIFICATIONS
Intensity -Duration -Frequency (IDF) Values for PA-1
Time
Atlas 14 Rainfall Intensity (inches/hour) by Storm Frequency PA-1
Minutes
Hours
1-
year
2-
year
5-
year
10-
year
25-
year
50-year
100-
year
200-
year
500-
year
1000-
year
5
0.083
5.34
6.34
7.96
9.31
11.22
12.72.
14.26
15.91
18.19
19.99
6
0.100
5.03
5.98
7.53
8.81 10.64
12.06
13.53
15.06
17.14
18.76
7
0.117
4.79
5.70
7.17
8.40 10.16
11.52
12.91
14.36
16.30
17.79
8
0.133
4.58 5.45
6.87
8.05
9.74
11.04
12.37
13.75
15.58
16.99
9
0.150
4.40
5.24
6.61
7.73
9.36
9.00
10.60
11.88
13.20
14.95
16.29
10
0.167
4.24
5.05
6.36
7.44
10.20 11.43
12.69
14.38
15.67
11
0.183
4.09 4.87 6.13
7.17
8.66
9.82
11.00
12.22
13.85
15.10
12
0.200
3.96 4.701
5.92
6.91
8.34
9.46
10.59
11.77
13.35
14.57
13 0.217
3.83
4.54
5.71
i
, 6.67 8.03
9.11
10.19
11.33
12.88
14.08
14
0.233
3.70
4.39
5.51
6.43 7.73
8.77
9.81
10.92
12.43
11.99
13.61
13.16
15
0.250
3.58
4.24 5.32
6.20
7.44
8.44
9.43
10.51
16 0.267
3.47
4.10 5.14
5.99
7.18
8.14
9.10
10.14
11.57
12.71
17
18
1 0.283
0.300
3.36 1 3.98 1 4.98 5.801
3.27 . 3.86 . 4.84 5.63
6.95
6.75
7.88
7.64
7.42
t 8.80
8.53
9.811
9.51
11.20
10.86
12.31 1
11.94
19 0.317
3.18
3.76
4.71 5.47 6.56
8.29
9.24
10.56
11.62
20 0.333
3.10
3.66
4.58 5.33
6.39
7.22
8.07
8.99
10.28 11.32
21 0.350
3.03
3.58 4.47
5.20
6.23
7.04
6.87
7.86
7.67
8.76
8.56
10.03
9.79
11.04
10.79
22 0.367 2.96
3.50
4.37
5.08
6.08
23 0.383 2.90
3.42
4.27
4.96
5.95
6.71
7.50
8.36
9.57
10.55
24 0.4001 2.84 3.35. 4.18
4.86
5.82
6.57
7.34 8.18 9.37
10.33
25 0.417 2.78
3.28
4.10
4.76
5.70
6.43
7.19
8.01 9.18
10.13
26 1 0.433
2.73
3.22
4.02
4.67
5.59
6.31
7.04
7.86
9.01
9.93
27 40 50
2.68
3.16
3.94
4.58
5.49
6.18
6.91
7.71
8.84
9.75
28 0.467 2.63
3.101
3.87
4.49
5.39
6.07 6.78 7.57 8.68
9.58
29
0.483
2.58
3.05
3.81
4.42
5.29
5.96 6.66 j 7.43 I
8.53
9.42
30
0.500
2.54
3.00
3.74
4.34
5.20
5.86 6.55 7.31
8.39
9.27
31
0.517
2.50
2.95
3.68
4.27
5.11
5.76 6.44 7.19
8.25
9.12
32
0.533
2.46
2.90
3.62
4.20 5.03
5.67 i 6.33 7.07
8.12
8.98
33
0.550
2.42
2.85 1
3.56
4.13 4.95
5.58 6.23
6.96
8.00
8.85
34
0.5671
2.381
2.81 1
3.51 4.07
4.88
5.49 6.14 6.86 7.88
8.72
35
0.583
2.34
2.77
3.45
4.01 j
4.80.
5.41 6.05 6.76
7.77
8.60
36
0.600
2.31
2.72
3.40
3.95
4.73 5.33
5.96
6.66
7.66
8.48
37
0.617
2.27
2.68 3.35
3.89 4.66 5.25
5.87
6.56
7.55
8.36
38
0.633 1
2.24 j
2.65 3.30
3.83
4.60
5.18
5.79
6.47
7.45
8.25
39
0.650
2.21
2.61
3.25
3.78
4.53
5.11
5.71
6.39
7.35
8.15
401
0.667 2.18 2.57 ,
3.21 1
3.73 4.47
5.04
5.63
6.30
7.26 1
8.04
41
0.683 2.15 2.53 3.16 3.68 4.41 4.17
5.56
6.22
7.17
7.94
42 1
0.7001 2.12 1 2.50 3.12
3.63
4.35 4.90
5.48
6.14
7.08
7.85
67
CITY OF SCHERTZ
Time
Minutes
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
120
180
240
360
Hours
0.717
0.733
0.750
0.767
0.783
0.800
0.817
0.833
0.850
0.867
0.883
0.900
0.917
0.933
0.950
0.967
0.983
1.000
2.000
3.000
4.000
6.000
1-
2.09
2.06
2.03
2.00
1.97
1.95
1.92
1.89
1.87
1.84
1.82
1.79
1.77
1.74
1.72
1.70
1.67
1.65
0.99
0.72
0.57
0.41
DESIGN
Atlas 14 Rainfall Intensity (inches/hour)
2-
5-
10-
25-
year
year
year
year
50-year
2.46
3.08
3.58
4.29
4.84
2.43
3.04
3.53
4.24
4.78
2.40
3.00
3.48
4.18
4.72
2.36
2.96
3.44
4.13
4.66
2.33
2.92
3.39
4.08
4.60
2.30
2.88
3.35
4.02
4.54
2.27
2.84
3.31
3.97
4.48
2.24
2.80
3.27
3.92
4.43
2.21
2.77
3.22
3.88
4.38
2.18
2.73
3.18
3.83
4.32
2.15
2.70
3.14
3.78
4.27
2.12
2.66
3.11
3.73
4.22
2.10
2.63
3.07
3.69
4.17
2.07
2.59
3.03
3.64
4.12
2.04
2.56
2.99
3.60
4.07
2. 1
2.53
2.95
3.56
4�.02
1.99
2.49
2.92
3.51
3.981
1.96
2.46
2.88
3.47
3.93
1.21
1.55
1.85
2.29
2.64
0.90
1.16
1.40
1.77
2.07
0.72
0.93
1.13
1.44
1.70
0.53
0.69 1
0.85
1.09
1.30
SPECIFICATI
by Storm Frequei
100- 200-
year year
5.41 6.06
5.34
5.98
5.28
5.91
5.21 5.84
5.15
5.77
5.08
5.70
5.02 5.63
4.96
5.56
4.90
5.50
4.84 5.43
4.79 5.37
4.73
5.31
4.68 5.25
4.62 5.19
4.57
5.13
4.51
5.07
4.46
5.02
4.41
4.96
3.03
3.48
2.41 2.80
2.00 1 2.33
1.54 T 1.81
am
cy PA-1
500- 1000-
year year
6.99 7.75
6.90 7.66
6.82 7.57
6.74
7.48
6.66
7.40
6.58
7.31
6.51
7.23
6.43
7.15
6.36
7.07
6.29
6.99
6.22
6.92
6.15
6.84
6.08
6.77
6.02
6.70
5.95
6.63
5.89
6.56
5.82
6.49
5.76 ' 6.42
4.13 4.67
3.37 3.84
2.82 3.23
2.21
2.55�
720 i 12.000 1 0.23 1 0.30 0.40 1 0.50 1 0.64 1 0.771 0.92 1.09 1.35 1.57
1440 24.000 0.13 , 0.17 0.23 0.29 0.37 0.45 0.54 0.64 0.80 0.93
C:i
CITY OF SCHERTZ DESIGN SPECIFICATIONS
Design Rainfall Values - PA-1
Depth -Duration -Frequency (DDF) Values for PA-1
Duration Atlas 14, Volume 11 Design Storm Depth (inches) by Storm Frequency
Period
hr
1-
year
2-
year
5-
year
10-year
25-year
50-year
100-year
200-year
500-year
1000-year
5-min:
0.0833
0.45
0.53
0.66
0.78
0.94
1.06
1.19
1.33
1.52
1.67
10-min:
0.1667
0.71
0.84
1.06
1.24
1.50
1.70
1.90
2.12
2.40
2.61
15-min:
0.2500
0.90
1.06
1.33
1.55
1.86
2.11
2.36
2.63
3.00
3.29
30-min:
0.5000
1.27
1.50
1.87
2.17
2.60
2.93
3.27
3.65
4.19
4.63
60-min:
1.0000
1.65
1.96
2.46
2.88
3.47
3.93
4.41
4.96
5.76
6.42
2-hr:
2
1.98
2.42
3.09
3.69
4.57
5.28
6.07
6.96
8.26
9.34
3-hr:
3
2.15
2.69
3.48
4.21
5.30
6.21
7.24
8.40
10.10
11.52
6-hr:
6
2.46
3.16
4.15
5.09
6.54
7.80
9.23
10.86
13.26
15.29
12-hr:
12
2.78
3.62
4.80
5.94
7.70
9.25
11.02
13.10
16.23
18.90
24-hr:
24
3.11
4.10
5.49
6.85
8.93
10.76
12.88
15.34
19.12
22.37
2-day:
48
3.58
4.72
6.36
7.94
10.41
12.37
14.88
17.78
21.92
25.62
3-day:
72
3.90
5.11
6.88
8.58
11.27
13.17
15.92
19.03
23.13
27.00
4-day:
96
4.18
5.44
7.32
9.13
12.02
13.75
16.72
20.04
23.99
28.03
7-day:
168
4.79
6.19
8.23
10.15
13.03
15.44
18.19
21.31
25.99
29.89
10-day:
240
5.24
6.70
8.85
10.84
13.80
16.25
19.02
22.12
26.78
30.61
20-day:
480
6.67
8.33
10.73
12.99
16.24
18.81
21.63
24.68
29.35
32.93
30-day:
720
7.99
9.84
12.39
14.91
18.45
21.14
24.00
27.01
31.79
35.14
45-day:
1080
9.76
11.89
14.44
17.36
21.33
24.20
27.14
30.07
35.25
38.24
60-day:
1440
11.26 1
13.68
15.27j
19.29
23.691
26.74 1
29.751
32.61
38.451
41.07
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Precipitation Area PA-2
70
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Intensity -Duration -Frequency JDF) Values for PA-2
Time
Atlas 14 Rainfall
Intensity (inches/hour) by Storm Frequency PA-2
Minutes
Hours
1-
year
2-
year
5-
year
10-
year
25-
year
50-
year
100- 200-
year year
500-
year
17.68
1 1000-
year
19.36
5
0.083
5.35
6.34
7.94
9.29
11.14
12.60 14.01 15.56
11.94 13.30 14.73
6
0.100
5.04
5.98
7.52
8.80
10.53
1 16.67
18.16
7
0.117
4.79
1 5.70
7.17
1 8.39
10.03
1 11.40
12.69
14.05
15.85
17.22 '
8
0.133
4.59
5.45
6.87
8.04
9.61
10.92
, 12.16 13.45
15.15
16.44 .
9
0.150
4.41
5.24
6.60
7.73
9.23
10.48
11.68 12.91
14.54
15.76
10
0.167
4.25
5.05
6.36
7.44
8.88
10.08
11.23
12.42
13.98
15.16
11
0.183
4.10
4.87
6.13
7.17
8.56
9.70
10.81
11.95
13.46
14.61
12
0.200
3.97
4.70
5.92
6.91
8.25
9.34
10.41
11.51f 12.98 14.10
13
0.217
3.84
4.54
5.71
6.67
7.96
8.99
10.02. 11.08 12.52 13.62
14
0.233
3.72
4.39
5.51
6.43
7.67
8.65
9.64
10.67 12.08
13.17
15
0.250
3.61
4.24
5.32
6.20
7.40
8.32
9.27
10.27 11.65
12.73
16
0.267
3.49
4.10
5.14
5.99
7.14
8.03
8.94 9.91 11.24
12.30
17
0.283
3.39
3.98
4.98
5.79
5.62
_ 6.91 7.77 8.64 9.58 10.88
6.71 7.53 8.38 9.29 10.55
11.91
18
0.300
3.29
3.86
4.83
11.55
19
0.317
3.21
3.76
4.69
5.46 6.52 7.32 1 8.141
9.03
1 10.26
11.23
20
0.333
3.13
3.66
4.57
5.32 6.35 7.12 1 7.92 8.78 9.99
10.94
21
0.350
3.05
3.58
4.46 5.19 6� 6.94 7.72
8.56 9.74
10.68
22
23
0.367
0.383
2.98 3.50
2.92 3.42
4.35
4.26
5.061 6.04 6.78 , 7.53 8.36 9.51
4.95 5.91 6.62 7.36 8.17. 9.30
10.43
10.20
24
0.400
2.86
3.35
, 17 4.84 5.78 6.48 7.20. 7.99 9.10 . 9.99
25
0.417
2.80 3.28
4.08 4.74
5.66 6.34 7.05 7.83. 8.92
9.79
26
0.433 2.75 r 3.22
0.450 2.70I 3.16
4.00
4.65
5.55 6.22
6.91
7.67
8.74
9.61
27
3.93
4.56 5.44: 6.10
6.78
7.53
8.58
9.43
28 0.467
2 65 3.10
3.85 4.48
5.34
5.99
6.65 7.39 8.43
9.26
29 0.483
2.60 3.05
3.79 ! 4.40
5.25
5.88
6.53
7.26
8.28
9.11
30 0.500 2.56 3.00
. 3.72 . 4.32
5.16
5.78
6.42
7.13
8.14
8.96
31. 0.517 2.52
2.95 3.66 4.25
5.07
5.68
6.31
7.02
8.01
8.82
32 0.533
2.48
2 90
3.60 4.18
4.99
5.59
6.21 6.90
7.89
8.68
33
0.550
2.44. 2.85
3.54
4.11
4.91
5.50 6.11
6.80
7.77
8.55
34
0.567 2.40
2.81
3.49
4.05
4.84
5.42 6.02
6.69
7.65
8.43
35 0.583
2.36
2.77 3.43
3.99
4.76
5.34 5.93
6.59
7.54
8.31
36, 0.600
2.33 _
2.72
3.38
3.93
4.69
5.26 5.84
5.18 5.76
6.50
7.43 8.20
37 0.617. 2.29
2.68
3.33
3.87
4.63
6.41
7.33I 8.09
38 0.633
2.26
2.64
3.28
3.81
4.56
5.11
5.68
6.32
7.23 7.98
39 . 0.650
2.22
2.61
3.24
3.76
4.50
5.04
5.601 6.23 7.141 7.88
40 1 0.667
2.19
2.57
3.19
3.71
4.43
4.97
5.52 6.15 7.04 7.78
41 0.683
2.16
2.53
3.14
3.65
4.37
4.90
5.45 1 6.071 6.95
7.68
42 0.700
2.13
2.50
3.10
3.60 1
4.311
4.83 1
5.38 5.99 6.87
L7.58
71
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Time
Atlas 14 Rainfall
Intensity (inches/hour) by Storm Frequency PA-2
Minutes
Hours
1-
year
2-
year
5-
year
10-
year
25-
year
50-
year
100-
year
200-
year
500-
year
1000-
year
43
0.717
2.10
2.46
3.06
3.56
4.26
4.77
5.31
5.91
6.78
7.49
44
0.733
2.07
2.43
3.02. 3.51
4.20
4.71
5.24
5.84.
6.70
7.40
45
0.750
2.04
2.40
2.98
3.46
4.15
4.65
5.17 5.77 6.62
7.32
46
0.767
2.01
2.36
2.94
3.42
4.09
4.59
5.11
5.70
6.54
7.23
47
0.783
1.98
2.33
2.90
3.37 4.04
4.53
5.04
5.63
6.46
7.15
48
0.800
1.95
2.30
2.86
3.33
3.99
1 4.48
4.98
5.56
6.39
7.07
49
0.817
1.93
2.27
2.82
3.29
3.94
4.42
4.92
5.49
6.31
6.99
50
0.833
1.90
2.24
2.79
3.24
3.89
4.37 4.86 . 5.43
6.24
6.91
51
0.850
1.87
2.21
2.75
3.20
3.84
4.31
4.80
5.36
6.17
6.83
52
0.867
1.85
2.18
2.72
3.16
3.79. 4.26
4.75
5.30
6.10
6.76
53
0.883
1.82
2.15
2.68
3.12
3.75
4.21.
4.69
5.24
6.03
6.69
54
0.900
1.80
2.12
2.65
3.08
3.70
4.16 4.64
5.18
5.97
6.61
55
0.917
1.77
2.09
2.61
3.05
3.66
4.11
4.58
5.12
5.90
6.54
56
0.933
1.75
2.06
2.58
3.01
3.61 4.06
4.53
5.06
5.84
6.47
57
0.950
1.72
2.04
2.55
2.97
3.57
4.01
4.48
5.01
5.77
6.41
58
0.967
1.70
2.01
2.51
2.93
3.53
3.96
4.42
4.95
5.71
6.34
59
0.983
1.67
1.98
2.48
2.90
3.48
3.92
4.37
4.90
5.65
6.27
60
1.000
1.65
1.96
2.45
2.86
3.441
3.87
4.32
4.84
5.59
6.21
120
2.000
0.99
1.21
1.54
1.84
2.26
2.60
2.98
3.40
4.02
4.53
180
3.000
0.71
0.89
1.15
1.39
1.75
2.04
2.37
2.74
3.28
3.73
2401
4.000
0.56
0.71
0.93
1.13
1.42
1.67
1.96
2.28
2.75
3.14
360
6.000
0.41
0.52
0.69
0.84
1.07
1.28
1.51
1.77
2.15
2.47
720
12.000
0.23
0.30
0.40
0.49
0.63
0.76
0.90
1.06
1.31
1.52
1440
24.000
0.13
0.17 1
0.23 1
0.28 1
0.361
0.441
0.52 1
0.62
0.771
0.90
72
CITY OF SCHERTZ DESIGN SPECIFICATIONS
Design Rainfall Values - PA-2
Depth -Duration -Frequency (DDF) Values for PA-2
Duration
Atlas 14, Volume 11 Design Storm Depth (inches)
by Storm Frequency
Period
hr
1-
year
2-
year
5-
year
10-year
25-year
50-year
100-year
200-year
500-year 1000-year
5-min:
0.0833
0.45
0.53
0.66
0.77
0.93
1.05
1.17
1.30
1.47
1.61
10-min:
0.1667
0.71
0.84
1.06
1.24
1.48
1.68
1.87
2.07
2.33
2.53
15-min:
0.2500
0.90
1.06
1.33
1.55
1.85
2.08
2.32
2.57
2.91
3.18
30-min:
0.5000
1.28
1.50
1.86
2.16
2.58
2.89
3.21
3.57
4.07
4.48
60-min:
1.0000
1.65
1.96
2.45
2.86
3.44
3.87
4.32
4.84
5.59
6.21
2-hr:
2
1.97
2.41
3.08
3.67
4.52
5.20
5.95
6.80
8.03
9.06
3-hr:
3
2.14
2.67
3.46
4.18
5.24
6.12
7.10
8.21
9.84
11.20
6-hr:
6
2.44
3.13
4.11
5.05
6.45
7.66
9.04
10.59
12.90
14.84
12-hr:
12
2.76
3.58
4.75
5.871
7.58
9.06
10.76
12.74
15.73
18.27
24-hr:
24
3.10
4.04
5.44
6.76
8.74
10.45
12.47
14.85
18.45
21.51
2-day:
48
3.53
4.65
6.23
7.73
10.06
12.13
14.27
17.00
21.09
24.55
3-day:
72
3.83
5.03
6.75
8.35
10.85
13.09
15.12
18.03
22.34
25.97
4-day:
96
4.10
5.37
7.20
8.87
11.52
13.93
15.73
18.83
23.37
27.16
7-day:
168
4.72
6.08
8.04
9.87
12.58
14.86
17.39
20.28
24.56
28.16
10-day:
240
5.17
6.58
8.64
10.55
13.34
15.68
18.21
21.11
25.35
28.93
20-day:
480
6.58
8.18 1
10.48
12.65
15.73
18.24
20.82
23.71
27.84
31.39
30-day:
720
7.88
9.67
12.09
14.52
17.89
20.56
23.20
26.09
30.09
33.74
45-day:
1080
9.61
11.69
14.07
16.90
20.70
23.62
26.33
29.22
33.04
37.06
60-day:
14401
11.07 1
13.44
15.53
18.75
22.99 1
26.16
28.94
31.83
35.48
40.11
73
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Precipitation Area PA-3
74
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Intensi -Duration-Fre uenc IDF Values for PA-3
Time
Atlas 14
Rainfall
Intensity (inches/hour) by Storm Frequency PA-3
Minutes
Hours
1-
year
2-
year
5-
year
10-
year
25-
year
50-
year
100-
year
200-
year
500-
year
1000-
year
5
0.083
5.34
6.30
7.88
9.20
11.00
12.36
13.79
15.24
17.20
18.71
6
0.100
5.03
5.95
7.45
8.73
10.43
11.75
13.08
14.43
16.21
17.56
7
0.117
4.78
5.66
7.11
8.33
9.95
11.24
12.49
13.76
15.41
16.65
8
0.133
4.58
5.42
6.81
7.98
9.54
10.78
11.97
13.17
14.74
15.90
9
0.150
4.40
5.21
6.54
7.67
9.17
10.35
11.49
12.65
14.14
15.24
10
0.167
4.24
1 5.02
6.30
7.38
8.82
9.96
11.05
12.16
13.60
14.66
11
0.183
4.10
4.85
6.08
7.11
8.50
9.58
10.64
11.70
13.10
14.13
12
0.200
3.97
4.68
5.86
6.85
8.19
9.22
10.24
11.27
12.62
13.63
13
0.217
3.84
4.53
5.66
1 6.60
7.89
8.87
9.85
10.85
12.17
13.17
14
0.233
3.73
4.38
5.47
6.36
7.60
8.53
9.48
10.45
11.74
12.73
15
0.250
3.62
4.24
5.28
6.12
7.32
8.20
9.12
10.06
11.33
12.31
16
0.267
3.50
4.10
5.10
5.91
7.07
7.91
8.79
9.70
10.93
11.88
17
0.283
3.39
3.97
4.94
5.72
6.84
7.66
8.50
9.38
10.58
11.50
18
0.300
3.30
3.86
4.80
5.55
6.63
7.42
8.24
9.10
10.26
11.16
19
0.317
3.21
3.75
4.66
5.40
6.45
7.21
8.00
8.84
9.97
10.85
20
0.333
3.13
3.66
4.54
5.26
6.28
7.02
7.79
8.60
9.71
10.57
21
0.350
3.06
3.57
4.43
5.13
6.12
6.84
7.59
8.38
9.46
10.31
22
0.367
2.99
3.49
4.33
5.01
5.98
6.68
7.41
8.18
9.24
10.07
23
0.383
2.92
3.41
4.23
4.90
5.84
6.53
7.24
8.00
9.04
9.85
24
0.400
2.86
3.34
4.14
4.79
5.72
6.39
7.08
7.82
8.84
9.65
25
0.417
2.81
3.27
4.06
4.70
5.60
6.26
6.93
7.66
8.66
9.45
26
0.433
2.75
3.21
3.98
4.60
5.49
6.13
6.80
7.51 j
8.50
9.27
27
0.450
2.70
3.15
3.90
4.52
5.38
6.02
6.66
7.37
8.34
9.10
28
0.467
2.65
3.09
3.83
4.43
5.28
5.91
6.54
7.23
8.19
8.94
29
0.483
2.60
3.04
3.76
4.35
5.19
5.80
6.42
7.10
8.04
8.79
30
0.500
2.56
2.98
3.70
4.28
5.10
5.70
6.31
6.98
7.91
8.65
31
0.517
2.52
2.93
3.64
4.21
5.01
5.60
6.21
6.87
7.78
8.51
32
0.533
2.48
2.89
3.58
4.14
4.93
5.51
6.11
6.76
7.66
8.38
33
0.550
2.44
2.84
3.52
4.07
4.85
5.43
6.01
6.65
7.54
8.25
34
0.567
2.40
2.79
3.47
4.01
4.78
5.34
5.92
6.55
7.43
8.13
35
0.583
2.36
2.75
3.41
3.95
4.71
5.26
5.83
6.45
7.32
8.02
36
0.600
2.32
2.71
3.36
3.89
4.64
5.18 1
5.74
6.36
7.221
7.91
37
0.617
2.29
2.67
3.31
3.83
4.57
5.11
5.66
6.27
7.12
7.80
38
0.633
2.25
2.63
3.26
3.78
4.50
5.04
5.58 1
6.18
7.02
7.70
39
0.650
2.22
2.59
3.22
3.72
4.44
4.97
5.50
6.10
6.93
7.60
40
0.667
2.19
2.55
3.17
3.67
4.38
4.90
5.43
6.01
6.84
7.50
41
0.683
2.16
2.52
3.13
3.62
4.32
4.83
5.35
5.93
6.75
7.41
421
0.700
2.12
2.48
3.08
3.57
4.26
4.77
5.28
5.861
6.66
7.31
75
CITY OF SCHERTZ
DESIGN SPECIFICATIONS
Time
Atlas 14 Rainfall Intensity (inches/hour) by Storm Frequency PA-3
Minutes Hours
43 0.717
1-
year
2-
year
5-
year
10-
year
25-
year
50-
year
100-
year
200- 500-
year year
- 5.78 6.58
1000-
year
2.09
2.45
3.04
3.52
4.20
4.70
5.21
7.23
44
0.733
2.06
2.41
3.00
3.48
4.15
4.64 5.15
5.71
6.50
7.14
45
0.750
2.03
2.38
2.96
3.43
4.09
4.58
5.08
5.64
6.42
7.06
46
0.767
2.00
2.35
2.92
3.39
4.04
4.52
5.02
5.57
6.35
6.97
47
0.783
1.98
2.32
2.88
3.34
3.99
4.47
4.96
5.50
6.27
6.89
48
0.800
1.95
2.28
2.84
3.30
3.94
4.41
4.89
5.43
6.20
6.81
49
0.817
1.92
2.25
2.81
3.26
3.89
4.36
4.83
5.37
6.13
6.74
50
0.833
1.89
2.22
2.77
3.21
3.84
4.30
4.78
5.31
6.06
6.66
51
0.850
1.87
2.19
2.73
3.17
3.79
4.25
4.72
5.24
5.99
6.59
52
0.867 1
1.84
2.16
2.70
3.13
3.74
4.20
4.66
5.18
5.92
6.52
53
0.883
1.81
2.13
2.66
3.09
3.70
4.15
4.61
5.12
5.85
6.44
54
0.900
1.79
2.11
2.63
3.05
3.65
4.10
4.55
5.06
5.79
6.37
55
0.917
1.76
2.08
2.59
3.02
3.61
4.05
4.50
5.00
5.72
6.31
56
0.933
1.74
2.05
2.56
2.98
3.56
4.00
4.45
4.95
5.66
6.24
57
0.950
1.71
2.02
2.53
2.94
3.52
3.95
4.39
4.89
5.60
6.17
58
0.967
1.69
1.99
2.49
2.90
3.47
3.90
4.34
4.84
5.54
6.11
59
0.983
1.66
1.97
2.46
2.87
3.43
3.86
4.29
4.78
5.48
6.04
60
1.000
1.64
1.94
2.43
2.83
3.39
3.81
4.24
4.73
5.42
5.98
120
2.000
0.98
1.19
1.52
1.81
2.22
2.55
2.90
3.30
3.88
4.35
180
3.000
0.71
0.88
1.14
1.37
1.71
1.99
2.30
2.65
3.15
3.57
240
4.000
0.56
0.70
0.91
1.11
1.39
1.63
1.90
2.20
2.64
3.00
360
6.000
0.40
0.51
0.67
0.82
1.05
1.24
1.46
1.70
2.06
2.36
720
12.000
0.23
0.29
0.39
0.48
0.61
0.73
0.86
1.02
1.25
1.45
1440
24.000
0.13
0.17
0.22
0.27
0.35 1
0.42 1
0.50
0.59
0.73
0.85
76
CITY OF SCHERTZ DESIGN SPECIFICATIONS
Design Rainfall Values - PA-3
Depth -Duration -Frequency (DDF) Values for PA-3
Duration
Atlas 14, Volume
11 Design Storm Depth (inches) by Storm Frequency
Period
hr
1-
year
2-
year
5-
year
10-year
25-year
50-year
100-year
200-year
500-year
1000-year
5-min:
0.0833
0.45
0.53
0.66
0.77
0.92
1.03
1.15
1.27
1.43
1.56
10-min:
0.1667
0.71
0.84
1.05
1.23
1.47
1.66
1.84
2.03
2.27
2.44
15-min:
0.2500
0.90
1.06
1.32
1.53
1.83
2.05
2.28
2.51
2.83
3.08
30-min:
0.5000
1.28
1.49
1.85
2.14
2.55
2.85
3.16
3.49
3.96
4.32
60-min:
1.0000
1.64
1.94
2.43
2.83
3.39
3.81
4.24
4.73
5.42
5.98
2-hr:
2
1.96
2.38
3.04
3.62
4.44
5.10
5.81
6.60
7.75
8.70
3-hr:
3
2.12
2.64
3.43
4.11
5.14
5.98
6.91
7.95
9.46
10.72
6-hr:
6
2.42
3.08
4.05
4.95
6.31
7.45
8.74
10.20
j 12.36
14.17
12-hr:
12
2.73
3.53
4.66
5.73
7.36
8.76
10.36
12.22
14.99
17.36
24-hr:
24
3.07
3.96
5.31
6.56
8.46
10.06
12.00
14.20
17.51
20.35
2-day:
48
3.49
4.55
6.06
7.49
9.69
11.62
13.60
16.15
19.95
23.18
3-day:
72
3.77
4.91
6.55
8.07
10.42
12.51
14.37
17.07
21.09
24.46
4-day:
96
4.02
5.23
6.97
8.55
11.03
13.29
14.90
17.77
21.99
25.52
7-day:
168
4.67
5.96
7.85
9.57
12.13
14.25
16.60
19.27
23.24
26.52
10-day:
240
5.12
6.46
8.44
10.23
12.88
15.04
17.42
20.08
24.05
27.29
20-day:
480
6.53
8.07
10.25
12.29
15.22
17.53
19.98
22.64
26.69
29.75
30-day:
720
7.83
9.55
11.84
14.11
17.33
19.78
22.30
24.97
29.21
32.10
45-day:
1080
9.56
11.57
13.78
16.42
20.07
22.73
25.36
28.03
32.77
35.42
60-day:
1440
11.02
13.33
15.21
18.20
r 22.29
25.17
27.90
30.57
36.08
38.47
77