Public Works Design Guide 1-1-2016PUBLIC WORKS
DESIGN GUIDE
12/15/2014ENGINEERING AND PUBLIC WORKS
community service opportunity
SCHERTZ
CITY OF SCHERTZ DESIGN SPECIFICATIONS
i
Public Works Design Specifications
SECTION 1 – SUBDIVISION COMPLIANCE.................................................................................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...................................................................................................................3
2.3 PLAN SHEETS....................................................................................................................................4
2.4 PLAN AND PROFILE SHEETS..............................................................................................................4
2.5 SECTION SHEETS...............................................................................................................................5
SECTION 3 – STREET REQUIREMENTS.....................................................................................6
3.1 GENERAL..........................................................................................................................................6
3.2 PAVEMENT DESIGN..........................................................................................................................6
3.3 STREETS LAYOUT..............................................................................................................................7
3.4 MINIMUM TESTING REQUIREMENTS.............................................................................................21
SECTION 4 – STORM DRAINAGE REQUIREMENTS................................................................25
4.1 GENERAL........................................................................................................................................25
4.2 FLOOD HAZARDS............................................................................................................................26
4.3 STORM WATER MANAGEMENT PLAN............................................................................................27
4.4 WATER QUALITY.............................................................................................................................29
4.5 STORM DRAINAGE DESIGN CRITERIA.............................................................................................30
4.6 STORM WATER CHECKLIST........................................................................................................49
SECTION 5 – SANITARY SEWER REQUIREMENTS.................................................................53
5.1 GENERAL........................................................................................................................................53
5.2 MINIMUM STANDARDS..................................................................................................................53
5.3 MINIMUM SANITARY SEWER TESTING REQUIREMENTS...............................................................56
SECTION 6 – WATER REQUIREMENTS....................................................................................58
6.1 GENERAL........................................................................................................................................58
6.2 MINIMUM WATER STANDARDS.....................................................................................................58
6.3 DESIGN CRITERIA............................................................................................................................60
6.4 MINIMUM WATER TESTING REQUIREMENTS................................................................................63
SECTION 7 – INSPECTIONS, TESTING, AND CHARGES........................................................65
7.1 LABORATORY TESTING:..................................................................................................................65
CITY OF SCHERTZ DESIGN SPECIFICATIONS
1 April 2013
SECTION 1 – SUBDIVISION COMPLIANCE
1.1 PURPOSE AND SCOPE
A.) Every subdivision or development which requires the installation of 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 UDC or any other codes of the City pertaining to the
construction and installation of the improvements. This includes but is not
limited to the Illicit Discharge and Connection Storm Water Ordinance, the
Ordinance for the Control of Storm Water Run-off, the Construction Storm
Water Management Ordinance, and the Flood Damage Prevention
Ordinance. All public infrastructure improvement construction plans shall
be submitted and approved prior to an application for a final plat. (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 public
infrastructure.
Ultimate responsibility for the actual design remains with the design
engineer.
1.2 APPEAL
A.) Any deviation from this manual must be approved by the Director of Public
Works or City Engineer, provided:
it is not detrimental to the public welfare
it meets the requirements of the UDC or has an approved variance
it is based upon an engineering study performed by a Professional
Engineer
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SECTION 2 – REQUIRED SUBMISSIONS OF PLANS
2.1 PLAN REQUIREMENTS
A.) Three (3) full sized copies, one (1) half size and one CD or DVD with 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 registered professional engineer, registered in the State of Texas.
Construction plans shall be submitted to the Director of Public Works prior
to or concurrently with a development application as indicated in the UDC.
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”).
Plans should 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 and cover sheet, and Index and
quantity sheets.
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 centerline and exposure; the proposed
sidewalk dimensions and location in relation to curbs and property
lines; 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. HGL will be indicated on profile. Drainage
plans shall address interim (i.e. “during construction”) and final
drainage plan.
If detention ponds or water quality ponds are part of the
development or project, then a plan indicating dimensions, grading,
CITY OF SCHERTZ DESIGN SPECIFICATIONS
3 April 2013
outlet design, downstream protection, and stage-storage-discharge
tables should be included.
4.) 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 Director of Public Works. 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.
5.) 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. 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.
Retaining walls over 4-ft will require plans signed and sealed by a
registered professional engineer.
6.) Utility plans for water mains less than 16-inches in size will require
plan sheets with associated details. Utility plans for water mains 16-
inches and greater will require plan and profile sheets. Section
details only required at critical crossings of infrastructure.
7.) Utility plans for sanitary sewer will require plan and profile sheets,
and associated details.
2.2 ENGINEERING REPORTS
A.) In addition to the plans, the following reports are to be submitted for
review by the City Engineer. Except for the pavement design, these items
should be submitted at the time of 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.
Engineering Report for pavement design
TIA as indicated in the current UDC
Storm Water Management Plan Report
Storm Water Pollution Prevention Plan
Engineering Design Report for the water system
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4 April 2013
Engineering Design Report for the waste water 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. Format of submittal is two
(2) hard copies with copies of submittal on a CD or DVD.
2.3 PLAN SHEETS
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.
A.) 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’.
Variance to the preferred scale may occur with the approval of the City
Engineer or his/her designee.
B.) Two Bench Marks, at a minimum, shall be established on and set to NAD
83 and NAVD 88 coordinates and datum.
C) Plans sheets should include all pertinent property and right-of-way
information, easements, topographical features, notes and callout
necessary for design.
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.
Variance to the preferred scale may occur with the approval of the City
Engineer or his/her designee.
B.) Two Bench Marks, at a minimum, shall be established on and set to NAD
83 and NAVD 88 coordinates and datum.
Indicate the location, description and elevation of Bench Marks; 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.
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5 April 2013
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 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.
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6 April 2013
SECTION 3 – STREET REQUIREMENTS
3.1 GENERAL
A.) Plans for streets, alley, sidewalks and crosswalk ways shall be prepared in
accordance with the standards in this document.
B.) Any street design element not specifically addressed in this document
shall be designed in accordance with:
Latest edition of Policy on Geometric Design of Highways and Streets,
American Association of State Highway and Transportation Officials
(AASHTO);
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)
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 an 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 design for a 30-year service
life.
C.) Design Traffic Levels. Traffic load for the pavement design will be based
upon the expected cummulative18-Kip 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.
Because heavy vehicles cause a majority of pavement structural damage,
if the street is to serve as a main source of construction traffic during the
phases of subdivision development, then the pavement designer shall use
a higher ESAL as determined by the City Engineer or his/her designee.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
7 December 2014
Table 3.2A
Flexible Pavement Design Parameters
18-kip ESAL Reliability
Factor, %
Std Dev Serviceability
Po/Pt
Primary and
Secondary Arterials
1,500,000 90 0.40-
0.50
4.2/2.5
Collector 1,000,000 90 0.40-
0.50
4.2/2.5
Local Type street
with bus traffic
500,000 70 0.40-
0.50
4.2/2.0
Local Type
street/Fire Lane
100,000 70 0.40-
0.50
4.2/2.0
D.) Resilient modulus (Mr) is to be determined by the geotechnical engineer.
E.) There are areas within the city limits and surrounding region with
expansive soils, 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 geogrid, or
cement soil treatment, or drains/barriers, or combination as determined by
a pavement design. Treatment with lime is discouraged and must be
approved by the City. Treated subgrade may be used as a structural layer
in the pavement design.
F.) Minimum thickness for hot mix asphalt concrete surface layer is 3-inches
compacted depth. Minimum thickness for treated subgrade layer is 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 3.2B
Minimum Structural Number
Level Roadway Conditions
Street Classification SN
Secondary Arterial 3.25
Collector Street 2.9
Local/Residential 2.5
3.3 STREETS LAYOUT
A.) Adequate streets shall be provided by the Sub-divider and the
arrangement, character, extent, width, grade and location of each shall
conform to the Comprehensive Plan of the City and shall be considered in
their relation to existing and planned streets, to topographical conditions,
CITY OF SCHERTZ DESIGN SPECIFICATIONS
8 April 2013
to be served by such streets. The street layout shall be devised for the
most advantageous development of the entire neighborhood. The location
and type of traffic control device to be installed by the subdivision
developer shall be indicated on at least one (1) sheet of plans. This shall
include the proposal of all Stop, Yield, Speed, Parking and Movement
Series devices. 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 are 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 licensed in the State of Texas. Flexible and rigid
pavements shall be designed for a twenty-year and thirty-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.
Table 3.3A
Primary Arterial Streets
(Design Speed – 45 mph)~
Minimum right-of-way width 120 feet
Minimum pavement width 48 feet
Minimum horizontal curve radius 1200 feet
Minimum tangent between reverse curve 200 feet
Grades 0.5%-5%
Daily Traffic Volume Limit, (vehicles per day) >34,000
CITY OF SCHERTZ DESIGN SPECIFICATIONS
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Table 3.3B
Secondary Arterial Streets
(Design Speed – 45 mph)~
Minimum right-of-way width 86 feet
Minimum pavement width 48 feet
Minimum horizontal curve radius 750 feet
Minimum tangent between reverse curve 200 feet
Grades 0.5% -5%
Daily Traffic Volume Limit, (vehicles per day) 34,000
Table 3.3C
Major Collector Streets
(Design Speed – 30 mph)~
Minimum right-of-way width 60 feet
Minimum pavement width 42 feet
Minimum horizontal curve radius 400 feet
Minimum tangent between reverse curve 100 feet
Grades 0.5% -7%
Daily Traffic Volume Limit, (vehicles per day) 10,000
Table 3.3D
Minor Collector Streets
(Design Speed – 30 mph)~
Minimum right-of-way width 60 feet
Minimum pavement width 36 feet
Minimum horizontal curve radius 400 feet
Minimum tangent between reverse curve 100 feet
Grades 0.5% -7%
Daily Traffic Volume Limit, (vehicles per day) 5,000
Table 3.3E
Residential Streets
(Design Speed – 30 mph)~
Minimum right-of-way width 50 feet
Minimum pavement width 30 feet
Minimum horizontal curve radius 100 feet
Minimum tangent between reverse curve 50 feet
Minimum Grade 0.5%-10%
Daily Traffic Volume Limits, (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
CITY OF SCHERTZ DESIGN SPECIFICATIONS
10 April 2013
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.
3.) Pavement Crown shall have a cross slope of 2% percent.
4.) The developer shall be responsible for construction of pavement
width and rights-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. 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:
Current condition of the roadway.
Current daily traffic on roadway.
Estimated additional daily traffic resulting from proposed
subdivision;
Total cost for widening roadway;
Ability of City to finance road widening in the next several
years
5.) “Broken-Back” or compound curves shall not be permitted unless
approved by the Director of Public Works. 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 Curves: Combination of horizontal and vertical
curves shall be permitted provided sufficient sight distance is
CITY OF SCHERTZ DESIGN SPECIFICATIONS
11 April 2013
available for safe operation. Generally, the horizontal curvature
should be introduced on the upgrade of the vertical curve.
8.) No street or alley grade shall be less than half of one (0.5%)
percent unless otherwise specified by the Director of Public Works.
9.) Superelevation of road is permissible when minimum horizontal
curves are unattainable and when approved by City Engineer.
Design of superelevation will follow standard engineering practices
and the TXDOT Roadway Design Manual.
10.) 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 in
Degrees
Two Local
Local and
Collector Two
Collector
Local/Collector
With Arterial Two Arterial
CR PLR CR PLR CRPLR 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 50 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 35 150 140
E.) INTERSECTIONS
1.) The preferred angle of intersection is 90 degrees. Allowance for
non-perpendicular intersecting angles between 80 degrees and 100
degrees will be made on a case by case basis.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
12 April 2013
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
Primary Arterial 300 ft.
Secondary Arterial 300 ft.
Collector Street 250 ft.
Local/Residential 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 3.5 feet above pavement,
and the object is considered to be 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 Director of Public Works. 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.
5.) At “T-intersections”, the minimum intersection offsets is 125 feet
between center lines of local streets. In the case of collector-street
intersections, this offset shall not be less than 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)
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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 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 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
L = (V/30) x 2 x S
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.
Table 3.3H
Minimum Deceleration and Storage for Left Turn Lanes
Speed
(mph)
Deceleration
Length (ft)
Taper
Length
(ft)
Storage Length (ft)
30 160 50 100 100
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
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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.
L = KA
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 3.3I
Design Value for Constant “K”, Vertical Curvature
“K”“K”Street
Classification Crest
Curves
Sag Curves
Primary Arterial 70 60
Secondary Arterial 70 60
Collector Street 55 55
Local/Residential30 40
G.) CURB AND SIDEWALK REQUIREMENTS
1.) CURB
a.) Curb or curb and gutter shall be installed on all existing or
proposed streets forming the boundary of the subdivision
and internally on streets. A parallel five (5’) foot wide
sidewalk 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.
b.) Curb or curb and gutter shall be non-reinforced unless
otherwise stated. Cold joints shall be steel reinforced.
2.) SIDEWALK
a.) Sidewalks: Concrete sidewalks having a width of not less
than five (5’) feet and thickness of not less than four (4”)
inches shall be constructed on each side of each street
within the subdivision. Said sidewalks shall allow for a three
(3’) foot greenbelt behind face of curb, shall be one (1’) foot
inside of the right of way and shall extend along all street
frontage including the side of corner lots and block ends;
provided however, that where it is impractical for the Sub-
divider to provide such sidewalks on the side lot lines
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15 April 2013
abutting major thoroughfares or drainage ditches, then in
those instances, sidewalks may not be required.
b.) Where a new section of sidewalk is to connect with a walk
previously constructed, or abuts on the curbing, an
expansion joint must be made and filled as above provided.
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 and three eights (3 3/8”) inch 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
3000 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.
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.
e.) The completed walks and drive approaches shall be cured in
accordance with good engineering practices as approved by
the Engineer.
3.) MEDIANS
a.) The minimum width of a raised median is a function of
purpose.
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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 20 23 – 30
* 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 20 feet wider than
the width of driveway which they are serving, with a
minimum width of 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 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.
H.) ALLEYS
1.) Alley right-of-way minimum shall be twenty-four (24’) feet wide and
paved, see Section 21.14.4 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 – 3000 psi in commercial alleys and a minimum
of five (5”) inches in depth – 3000 psi in residential alleys. Alleys
shall be designed on the basis of a twenty-five (25) year frequency
to carry storm water from only the lots within the block abutting the
alley.
2.) Intersecting Alleys: Where two 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: Dead-end alleys are not permitted.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
17 April 2013
4.) Overhang Easements: In all alleys, overhang easements for
electric and telephone lines shall be provided if requested by the
appropriate electric utility company.
5.) Alleys Which Do Not connect on A Straight Course: If alleys are
not themselves straight within each of adjoining blocks, or if the
same do not connect on a straight course with the alleys of
adjoining blocks, then an easement may be provided for the placing
of guy wires on lot division lines in order to support poles set on
curving or deviating right-of-way of alleys as determined necessary
per the appropriate electric utility company.
I.) 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 10 ft to 12 feet in width for single, and not
more than 24 feet for double driveway apron. One curb cut per
residential property. Two curb cuts may be allowed for circular if
frontage is greater than 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 then 1
acre, frontage is greater than 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 24 and
40 feet measured at the right of way.
4.) Non-residential lots are permitted to have one (1) point of access
per lot or one (1) point of access per 200 feet of frontage of a
collector street. Separation of access points to be a minimum of 50
feet of frontage measured along the curb, or as shown in a traffic
Impact analysis to maintain safe traffic flow on the collector and
site. Total aggregate width of multiple access points not to exceed
50% of frontage.
5.) Non-residential lots are permitted to have one (1) point of access
per 400 feet of frontage of an arterial; if 400 feet is not available,
then the use of a common access easement would be required.
Minimum distance from corner/flare of intersection is the smaller of
90% of frontage, or 125 feet, or as shown in a traffic impact
analysis (TIA) to maintain safe traffic flow on the collector and site.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
18 April 2013
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 to be reinforced concrete per
City standard details, unless otherwise approved by Public Works
Director
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.) Fire lanes will only be allowed within the City, under special
circumstances as approved by the Planning and Zoning
Commission. A fire lane is interpreted as a hard-surfaced, all-
weather material, driving surface constructed specifically for the
use of emergency vehicles. Fire lanes shall be designed on the
basis of a twenty-five (25) year frequency to carry storm water from
only the lots abutting the fire lane.
2.) Fire lanes shall have a minimum pavement width of twenty-four
(24’) feet and shall connect on a straight course.
3.) Where two (2) fire lanes intersect or turn at right angles, a cut-off of
not less than then (10’) feet must be provided along each property
or easement line.
4.) Dead-end fire lanes are not permitted.
K.) CUL-DE-SAC TURNAROUND
1.) Cul-de-sac turnarounds shall meet the criteria set forth in the UDC
Section 21.14.1.E and at minimum shall not exceed five hundred
(500’) feet in length and have a turnaround of 120 feet in diameter
of ROW (100 feet pavement) in single-family residential areas and
all other uses not less than 150 feet in diameter of ROW (130 feet
pavement).
2.) “Knuckle” or elbow intersections with bulbs will meet the
requirements of intersection angles and curb return radii, and meet
the UDC requirements for cul-de-sac radius.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
19 April 2013
L.) STREET LIGHTS
Street lights in new subdivisions within the City Limits and the annexed
areas of the City shall be installed from time to time pursuant to
agreement between the City of Schertz and the appropriate electric utility
company in accordance with the Schertz UDC (Article 14.1.S). Street
Lights may be spaced a maximum of five hundred (500’) feet apart.
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 a Public Works
Department of the City of Schertz.
b) 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 required
within the subdivision shall be installed in accordance with the
latest revision of the Texas Manual on Uniform Traffic Control
Devices for Streets and Highways.
2.) All pavement markings shall be thermo plastic 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.
b) Collectors: centerline striping, lane lines, edge lines for non curbed
streets.
N.) REMOVING AND REPLACING PAVEMENTS, CURBS, AND GUTTERS,
DRIVEWAYS, AND SIDEWALKS
1.) Scope: The Specifications shall govern for all work necessary to
complete the removing and replacing of all types of pavements,
CITY OF SCHERTZ DESIGN SPECIFICATIONS
20 April 2013
curbs and gutters, driveways, and sidewalks as required to
complete the project.
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.) Concrete Pavement: Replace with eight (8”) inch thick 3000 psi
concrete slab, reinforced with No. 3 bars at twelve (12”) inch center,
cut No. 3 dowels into existing concrete at eighteen (18”) inch
minimum spacing. Repair to be five (5’) feet on each side wider
than ditch excavation. Concrete slab reinforcement to rest on at
least twelve (12”) inches of undisturbed soil on each side of ditch.
4.) Asphaltic Black Base Pavement: Replacement with eight (8”)
inches thick HMAC Type B. Tack coat of RC-2, cut back asphalt
shall be applied at a rate of ten one hundredths (0.10) gallons per
square yard. Apply hot mix-hot laid asphalt concrete applied at the
rate of 220 lb./sy compacted to two (2”) inch thickness. Hot mix
shall conform to Texas Highway Department Standard Specification
Item 340 Type D. Repair to be five (5’) feet on each side wider
than ditch excavation. Black base shall rest on at least twelve (12”)
inches of undisturbed soil on each side of the ditch.
5.) Replacing Concrete Driveway: Replace with 3000 psi concrete, six
(6”) inches thick, reinforced with 6” x 6” W/D4.7xW/D4.7 welded
wire mesh when no detail is shown on the drawings. Finish on
replaced section same as appearing on old driveway. Use an
epoxy-bonding agent, in conformance with the manufacture’s
recommendations, when bonding new concrete to old concrete.
6.) Replacing Concrete Sidewalks: Replace with 3000 psi concrete
four (4”) inches thick, reinforced with 6” x 6” W2.9xW2.9 welded
wire mesh when no detail is shown on the drawings. Finish on
replaced section same as appearing on the old sidewalk. Use an
epoxy-bonding agent, in conformance with the manufacture’s
recommendations, when bonding new concrete to old concrete.
Replacing Curbs and Gutters: Replace with 3000-psi concrete
section conforming in all details to original section. All cold joints
must be steel reinforced.
All street improvements shall meet the current requirements of the Master
Thoroughfare Plan, the City of Schertz Unified Development Code and
Section 3 of this document, but in no case shall be less than the following:
CITY OF SCHERTZ DESIGN SPECIFICATIONS
21 April 2013
Table 3.3K
Street Improvement Standards
Classification ROW Pavement Drainage
Width
Sidewalk
Width
Hike/Bike
Trail
Principal Arterial 120 ft 48 ft (with 16
ft median)
Curb and
Gutter
5 ft one
side
8 feet other
side *
Secondary Arterial 86 ft 48 ft Curb and
Gutter
5 ft one
side
8 feet other
side
Major Collector 60 ft 42 ft Curb and
Gutter
5 ft both
sides
-
Minor Collector 60 ft 36 ft Curb and
Gutter
5 ft one
side
8 feet other
side
Local Street - Residential 50 ft 30 ft Curb and
Gutter
5 ft both
sides
-
Local Street -
Commercial/Industrial
60 ft 42 ft Curb and
Gutter
5 ft both
side
-
Paved Alley 24 ft 24 ft Curb or Curb
and Gutter
None -
* For State Highway 8 foot trail on both sides
O.) Any retaining wall with 4 feet measured from foundation, to be designed
per accepted geotechnical engineering standards. Refer to TXDOT
Geotechnical Manual. Retaining wall plans should be signed and sealed
by an engineer registered in the State of Texas and submitted to the City
for permitting. Check walls to ensure minimum factors of safety are met
for all potential modes of failure including sliding, overturning, bearing
pressure, and stability. Retaining walls shall be designed to ensure
stability against overturning, sliding, excessive foundation pressure and
water uplift. Retaining walls shall be designed for a safety factor of 1.5
against lateral sliding and overturning. Any retaining wall located on
private property is the responsibility of the property owner or developer to
inspect and maintain.
3.4 MINIMUM TESTING REQUIREMENTS
A.) GENERAL
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 street construction and a series of
laboratory tests normally associated with road and street construction will
be required in subdivisions, 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.
The sub-divider shall notify the City at least one (1) week prior to the
contractor beginning construction. Contractor shall be required to notify
CITY OF SCHERTZ DESIGN SPECIFICATIONS
22 April 2013
the City a minimum of at least forty-eight (48) hours in advance of all
testing being performed. It is assumed that the preponderance of testing
required in the subdivision is that testing related directly to street
construction. For this reason, the following ration of testing is established:
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. Test for
density will be made within twenty-four (24) hours after compaction
operations are completed. 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 depth where pneumatic tire rolling is
to be used and shall not exceed eight (8”) inches in depth for rolling with
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 (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 20 or more) shall be treated by
removal and replacement, or geogrid, or cement soil treatment, or
drains/barriers, or combination as determined by a pavement design.
Developer 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.
Tests of density will be made within twenty-four (24) hours after
compaction operations are completed. 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.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
23 April 2013
Table 3.4A
Ratio of Testing
Densities
Sub-grade Minimum 1 per 300 ft. of street
Under Curb/Gutter Minimum 1 per 300 ft. of curb
Base Minimum 1 per 300 ft. of street
Backfill Density Control
Proctors (Moisture-Density Relationship)
Sub-grade (raw) -1 per subdivision unless material
changes
-1 per lift per 10,000 sq. ft. or Embankment (Street, Berm, Structural) -1 per lift per 100 ft. berm
Table 3.4B
Atterberg Limits & Gradation
Hot-Mix Control
Surface Course Design 1 per subdivision
Base Course Design 1 per subdivision
Extraction 2 per day/run minimum –
1 per 500 ton
Densities (in place) 1 per 1,000 ft. of street
G.) CONCRETE CYLINDER
1.) GENERAL:
Plant Certification Required
The above schedule is a minimum schedule for testing, failures not
included. 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 engineer shall notify the testing lab when tests are to be taken.
If it is necessary to retest, such retesting shall be at the engineer’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 at the city’s expense.
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
CITY OF SCHERTZ DESIGN SPECIFICATIONS
24 April 2013
subdivision test reports to be certified by a Registered Professional
Engineer (Texas Registration) and will further require that the City
be furnished a minimum of two (2) copies of testing reports.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
25 April 2013
SECTION 4 – STORM DRAINAGE REQUIREMENTS
4.1 GENERAL
A.) Unless otherwise stated in this document, all storm water management
facilities, or combination of facilities, shall be designed for ultimate
development. Facilities with drainage areas less than one hundred (100)
acres shall be designed for a twenty-five-year storm. Facilities with
drainage areas over one hundred (100) acres or areas within a designated
floodplain shall be designed for a 100-year storm or a twenty-five-year
storm plus freeboard (see Table 4.5G) if that elevation is higher.
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.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
26 April 2013
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
Director of Public Works prior to the approval of construction
drawings.
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.) New 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 five-year, twenty-five-year and one-hundred-year (100-yr) design
storm events, except as provided in subsection A, above.
G.) Redevelopment
Peak storm water runoff rates from an area of redevelopment due to
zoning or replatting shall be less than or equal to the peak runoff rates
produced by existing development conditions for the five-year, twenty-five-
year and one hundred (100) year design storm events, except as provided
in subsection A, above.
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.
B.) New subdivisions having a portion of that subdivision subject to the
special flood hazards shall dedicate on the plat a drainage right-of-way for
that area located within the special flood hazard area. If not already
determined, the new subdivision shall determine the base flood elevations
of the 1% annual chance 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. All public utilities
and facilities such as sewer, gas, electrical and water systems are located,
CITY OF SCHERTZ DESIGN SPECIFICATIONS
27 April 2013
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. Under story growth which impedes flow may be
cleared within the bank of watercourses within the proposed development
with Public Works approval however, removal of large trees with
diameters greater than eight (8”) inches is discouraged and shall follow
the requirements for the tree removal in the UDC Article 21.9.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 major watercourses shall comply with the City
Master Drainage Plan.
F.) Upon acceptance by the City of Schertz for construction consisting 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 spoil onto any public right-of-way and/or adjacent
owners lots.
Failure to comply shall result in a stop order of all construction on lots
owned by the landowner or homebuilder.
4.3 STORM WATER MANAGEMENT PLAN
A.) To standardize the review process and minimize the time for approval by
the City during review of the plat and construction drawings for a
subdivision, a complete submittal regarding the analysis of existing
drainage conditions and the design of modifications or new drainage
facilities is necessary. The owner of the property to be developed is
required by the Director of Public Works to provide, at the owner’s
expense and as a condition of construction plan 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 through
the City Manager or his/her designee prior to approval of any construction
plans.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
28 April 2013
B.) Contents of the SWMP
The SWMP shall contain all of the necessary support data, methodologies
used in calculations, and conclusions. A checklist is below that will be
used by the City reviewer 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 the preliminary plat or the initial
submittal of a minor plat, site plan, or Grading and Clearing permit
application. 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”.
The final SWMP should be submitted at the prior to final plat, minor plat,
or building permit. In addition to the information from the preliminary or
concept plan, shall include all of the information required in the final
Storm Water Management Plan (SWMP) checklist at the end of this
section.
In general the Final Storm Water Management Plan should contain the
following (for details see the checklist at the end of this section):
The contact information for the owner of the property or properties
affected.
A vicinity map of the site and affected reach of the outfall channel;
A topographic base map a detailed map of the area and the outfall
channel with all pertinent physiographic information, with 2 foot
contours;
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/rights-of-way required, flow path
to nearest downstream 100-year structure;
All hydrologic and hydraulic calculations: discharge calculations
specifying methodology and key assumptions used including a
table of discharges at key locations; hydraulic calculations
specifying methodology used, assumptions and values of the
design parameters;
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;
CITY OF SCHERTZ DESIGN SPECIFICATIONS
29 April 2013
Detention basin design calculations, including those used for
design of the control structure;
Additional back-water analysis data as described in the checklist
below
Certification of a professional engineer that the resulting impact of
the proposed development will not produce an adverse impact to
downstream properties, structures, drainage facilities, and public
infrastructure
Soils map indicating the type of soil and hydrologic group.
Maintenance and repair plan for permanent BMPs and a
maintenance agreement for on-site storm water management
measures.
Erosion and sediment control plans or Storm Water Pollution
Prevention Plans (SWPPP) for construction
Other Environmental Permits
4.4 WATER QUALITY
A.) Post construction storm water quality will eventually be regulated for the
quality of the water discharged. Standards for post construction water
quality of discharge are not currently being enforced.
B.) In accordance with the City of Schertz Construction Storm Water
Management Ordinance and Section 01410 of the Public Works
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.
b.) A natural resources map identifying soils, forest cover, and
resources protected by the City’s 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
CITY OF SCHERTZ DESIGN SPECIFICATIONS
30 April 2013
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,
the drafting of intermediate plans may be required at the
close of each season;
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; and
f.) Provisions for maintenance of control facilities, including
easements and estimates of the cost of maintenance, dust
control and cleaning, stock pile protection, etc.
2.) Major amendments of the SWPPP must be submitted for approval
by Public Works and Engineering.
3.) In addition to the report, appropriate details and instructions to be
included with the construction plan set.
4.) Provide the Public Works Department copies of all submittals to the
Texas commission on Environmental Quality (TCEQ), including the
notice of intent (NOI) and notice of termination (NOT).
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 designee.
2.) For small urban drainage areas less than 200 acres where
hydrographs are not required, for storm sewer inlets, for road side
ditches, for driveway culverts, or for “peak flow only” calculations,
the basis for computing peak flow runoff may be the Rational
formula. The Rational method is not allowed for the design or
detention ponds nor channels within the FEMA designated special
flood hazard area
CITY OF SCHERTZ DESIGN SPECIFICATIONS
31 April 2013
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 designee.
5.) Watersheds may have hydrologic and hydraulic models that are
available contact the City of Schertz Public Works’ Department for
more information. Developments proposed within the limits of these
watersheds must have the models updated by the consultant to
reflect changes in flow, channel configuration (including alterations
to vegetation) and channel structures. The updated models shall be
submitted to the Director of Public Works for incorporation into the
master models.
B.) Time of Concentration
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.
1.) Sheet flow - flow over plane surfaces based on TR 55 method and
roughness coefficients for sheet flow: Minimum is five (5) minutes.
Maximum allowable time is twenty (20) minutes, or a maximum
distance of 300 feet.
2.) Shallow concentrated flow – Use Manning's equation to estimate
travel time for defined swales, bar ditches and street sections, etc.
Figure 3-1 from TR-55 "Urban Hydrology for Small Watersheds",
SCS 1986, may be used where a geometric section has not been
defined.
3.) Channel flow: Use existing computer models where available or
Manning's equation if data is not available. Non-floodplain channel
velocities for ultimate watershed development should not be less
than six (6) fps when estimating time of concentration. 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.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
32 April 2013
C.) 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) - Percentage
Slope
Character of Area Up To
1%
1% To
3%
3% To
5%
Over
5%
Business or Commercial Area (90% or More
Impervious), Existing Pavement/Buildings 95 96 97 97
Densely Developed Area (80% To 90%
Impervious) 85 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 50-75% of Area) 37 41 49 53
Forest or Range (Grass Cover >75% of Area) 35 39 47 52
1.) In all cases, wet antecedent conditions shall be assumed. Runoff
rates shall be computed on the basis of 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. Use Table 4.5B to determine rainfall intensity.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
33 April 2013
Table 4.5B
Rainfall Intensities (inches/hour)
Duration Frequency
Minutes 2-
Year
5-
Year 10-Year 25-Year 50-Year 100-Year 500-Year
1 6.94 8.00 8.84 9.99 11.09 11.92 13.55
2 6.69 7.72 8.53 9.67 10.69 11.53 13.24
3 6.45 7.46 8.24 9.36 10.31 11.15 12.93
4 6.22 7.21 7.95 9.05 9.95 10.79 12.62
5 6.00 6.96 7.68 8.76 9.60 10.44 12.30
6 5.79 6.73 7.42 8.48 9.27 10.10 11.98
7 5.59 6.50 7.17 8.20 8.95 9.78 11.66
8 5.40 6.28 6.93 7.94 8.65 9.47 11.34
9 5.21 6.08 6.70 7.69 8.37 9.17 11.01
10 5.04 5.88 6.48 7.44 8.10 8.88 10.68
11 4.88 5.69 6.27 7.21 7.85 8.61 10.35
12 4.72 5.52 6.08 6.98 7.61 8.35 10.02
13 4.58 5.35 5.89 6.76 7.39 8.10 9.68
14 4.45 5.19 5.72 6.56 7.19 7.86 9.34
15 4.32 5.04 5.56 6.36 7.00 7.64 9.00
16 4.22 4.94 5.46 6.26 6.89 7.53 8.89
17 4.12 4.84 5.36 6.16 6.79 7.42 8.78
18 4.03 4.75 5.27 6.06 6.68 7.31 8.68
19 3.94 4.66 5.17 5.96 6.58 7.20 8.57
20 3.85 4.56 5.08 5.86 6.48 7.09 8.47
21 3.76 4.48 4.99 5.77 6.38 6.99 8.36
22 3.67 4.39 4.90 5.68 6.28 6.88 8.26
23 3.59 4.30 4.82 5.59 6.18 5.78 8.16
24 3.51 4.22 4.73 5.50 6.09 6.68 8.06
25 3.43 4.14 4.65 5.41 6.00 6.58 7.96
26 3.35 4.06 4.57 5.33 5.91 6.49 7.86
27 3.27 3.98 4.49 5.24 5.82 6.39 7.76
28 3.20 3.91 4.41 5.16 5.73 6.30 7.67
29 3.13 3.83 4.33 5.08 5.64 6.21 7.57
30 3.06 3.76 4.26 5.00 5.56 6.12 7.48
31 2.99 3.69 4.19 4.92 5.48 6.03 7.39
32 2.93 3.62 4.12 4.85 5.40 5.95 7.30
33 2.87 3.56 4.05 4.77 5.32 5.86 7.21
34 2.81 3.49 3.98 4.70 5.24 5.78 7.12
35 2.75 3.43 3.92 4.63 5.17 5.70 7.03
CITY OF SCHERTZ DESIGN SPECIFICATIONS
34 April 2013
36 2.69 3.37 3.86 4.56 5.09 5.62 6.94
37 2.64 3.31 3.80 4.50 5.02 5.54 6.86
38 2.59 3.26 3.74 4.43 4.95 5.47 6.77
39 2.54 3.21 3.68 4.37 4.88 5.40 6.69
40 2.49 3.15 3.62 4.31 4.82 5.32 6.61
41 2.45 3.10 3.57 4.25 4.75 5.25 6.53
42 2.40 3.06 3.52 4.19 4.69 5.19 6.45
43 2.36 3.01 3.47 4.13 4.63 5.12 6.37
44 2.32 2.97 3.42 4.08 4.57 5.05 6.29
45 2.29 2.92 3.37 4.02 4.51 4.99 6.21
46 2.25 2.88 3.33 3.97 4.45 4.93 6.14
47 2.22 2.85 3.29 3.92 4.40 4.87 6.06
48 2.19 2.81 3.25 3.87 4.34 4.81 5.99
49 2.16 2.78 3.21 3.83 4.29 4.76 5.92
50 2.14 2.74 3.17 3.78 4.24 4.70 5.85
51 2.11 2.71 3.13 3.74 4.19 4.65 5.78
52 2.09 2.69 3.10 3.70 4.15 4.60 5.71
53 2.07 2.66 3.07 3.66 4.10 4.55 5.64
54 2.06 2.63 3.04 3.62 4.06 4.50 5.58
55 2.04 2.61 3.01 3.59 4.02 4.45 5.51
56 2.03 2.59 2.99 3.55 3.98 4.41 5.45
57 2.02 2.57 2.96 3.52 3.94 4.37 5.38
58 2.01 2.56 2.94 3.49 3.91 4.33 5.32
59 2.00 2.54 2.92 3.46 3.87 4.29 5.26
60 2.00 2.53 2.90 3.43 3.84 4.25 5.20
120 1.10 1.54 1.83 2.21 2.50 2.78 3.48
18 0.86 1.19 1.41 1.68 1.88 2.08 2.53
240 0.70 0.97 1.13 1.33 1.50 1.65 1.99
360 0.51 0.71 0.83 0.98 1.09 1.19 1.41
720 0.28 0.39 0.46 0.55 0.61 0.67 0.81
1440 0.165 0.227 0.273 0.32 0.366 0.413 0.513
E.) SCS Curve Numbers.
1.) 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
Table 4.5E shall be used for hydrograph calculations. The SCS
curve numbers adopted for use by the City of Schertz are shown in
Table 4.5C. 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 (TR 55), which document is hereby incorporated by
CITY OF SCHERTZ DESIGN SPECIFICATIONS
35 April 2013
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.
Table 4.5C
SCS Curve Numbers
Curve Number for hydrologic soil group Cover Type and Descritpion
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 89 92 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 grazed
49 69 79 84
Meadow–continuous grass, protected from grazing and
generally mowed for hay
30 58 71 78
Brush–brush-weeds-grass mixture with brush the major
element > 75% ground cover
30 48 65 73
Woods–grass combination (orchard or tree farm). CN’s shown
were computed for areas with 50% woods and 50%
grass(pasture) cover
32 58 72 79
Woods–protected from grazing, and litter and brush
adequately cover the soil
30 55 70 77
Farmsteads–buildings, lanes, driveways and surrounding lots 59 74 82 86
2.) Percent Impervious Cover. The percent impervious cover for typical
land use types in Schertz are presented in Table 4.5D.
Table 4.5D
SCS Curve Numbers by Impervious Cover and Cover type
Curve Number for hydrologic soil group Cover Type and Description Average %
Impervious Cover 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 (town
houses) 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
CITY OF SCHERTZ DESIGN SPECIFICATIONS
36 April 2013
3.) Design Rainfall. A twenty-four-hour rainfall distribution shall be
applied for runoff calculations. Design Rainfall Values as adopted
for the City of Schertz are given in Table 4.5E and should be used
for HEC-HMS input. 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 4.5G), unless otherwise stated below.
Table 4.5E
Design Rainfall Values (inches)
Bexar County
Frequency Duration
2-Year 5-Year 10-Year 25-Year 50-Year 100-Year 500-Year
5 minute 0.60 0.70 0.78 0.93 1.04 1.13 1.52
15 minute 1.15 1.37 1.60 1.80 2.10 2.50 3.30
60 minute 2.07 2.46 2.76 3.32 3.85 4.35 5.80
2 hour 2.57 3.11 3.55 4.35 5.10 5.80 8.10
3 hour 2.80 3.42 3.95 4.90 5.70 6.60 9.40
6 hour 3.31 4.01 4.60 5.70 6.50 7.50 10.60
12 hour 3.78 4.60 5.40 6.40 7.50 8.80 12.40
24 hour 4.44 5.36 6.00 7.50 9.00 10.00 13.70
Comal and Guadalupe County
Frequency Duration
2-Year 5-Year 10-Year 25-Year 50-Year 100-Year 500-Year
5 minute 0.51 0.66 0.80 0.96 1.11 1.28 1.77
15 minute 1.05 1.34 1.58 1.89 2.16 2.47 3.37
60 minute 1.86 2.40 2.78 3.34 3.83 4.39 5.39
2 hour 2.24 2.95 3.43 4.16 4.79 5.51 7.55
3 hour 2.45 3.27 3.84 4.67 5.40 6.23 8.58
6 hour 2.80 3.85 4.58 5.64 6.57 7.61 10.58
12 hour 3.15 4.47 5.43 6.76 7.92 9.24 12.98
24 hour 3.52 5.17 6.40 8.07 9.52 11.17 15.88
4.) 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.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
37 April 2013
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 Director
of Public Works.
F.) 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 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 exceed not the flows as
outlined below 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.
h.) Potential flooding problems or conflicts at the connection
points where new or modified drainage systems (including
CITY OF SCHERTZ DESIGN SPECIFICATIONS
38 April 2013
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.) Dwelling units located on the downhill side of a T-
intersection with a street or drainage channel discharging
onto the intersection shall be sited so as to avoid obstruction
of the drainage patterns.
2.) An arterial street is a street so designated on the current major
thoroughfare plan. One (1) lane in each direction on arterial streets
shall remain passable with a flow depth not to exceed 0.30 feet
during a twenty-five-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 maximum flow depth to the top of curb on a collector street
section will be allowed during a twenty-five-year storm event. A
collector street is a street with a width of forty-two (42) feet or more
and not shown as an arterial street on the current master
thoroughfare plan.
4.) Local Streets. Local streets shall be designed on a basis of a five-
year frequency. A twenty-five-year frequency storm must be
contained within the street right-of-way.
5.) Alleys shall be designed for five-year frequency within the limits of
the alley pavement/curbs and twenty-five-year frequency within the
right-of-way/easement to carry storm water.
6.) All-Weather Crossings.
a.) Where streets cross existing or proposed watercourses, all
weather crossings shall be required. Culverts or bridges
shall be adequate to allow passage of 25-year design storm.
In the instance the crossing conveys greater than 100 acres
of runoff the crossing then must be adequate for a 100-year
design storm.
b.) All crossings, culverts and bridges shall be designed for an
H-20-44 or HS-20 loading.
G.) CHANNELS
CITY OF SCHERTZ DESIGN SPECIFICATIONS
39 April 2013
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
director of public works or his designee, no person shall place or
cause to be placed any obstruction of any kind in any watercourse
within the city and its ETJ. 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 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 director of public works or his representative 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 principals 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 director of public works 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 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
CITY OF SCHERTZ DESIGN SPECIFICATIONS
40 April 2013
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, coastal
bermuda, buffalo grass, sideoats 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 property owners' 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 4.5F shall be used to determine maximum permissible
channel velocity.
Table 4.5F
Velocity Control
Velocity Type Drain Required Hydraulic
Radius
Correction
Factor
Max.
Permissible
Velocity
0-1 ft 0.8 5 fps
1-3 ft 0.9 5.5 fps
3-5 ft 1.05 6.3 fps
5-8 ft 1.15 6.9 fps
8-10 ft 1.225 7.35 fps
1 to 6 fps
(Maximum
Average Velocity
= 6 fps)
Grass Lined Channel
Over 10 ft 1.25 7.5 fps
6 to 8 fps Concrete retards
required NA NA NA
8 fps and over
Concrete Lining or
Drop Structures
Required
NA NA NA
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.
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.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
41 April 2013
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 4.5F:
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*R2/3 )]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 4.5G will be applied to the
twenty-five-year design.
Table 4.5G
Drainage Freeboard for Concrete Lined
and Earth Channels For 25 Year Storm
Design Depth of
Flow Required Freeboard
0-5 ft 0.5 ft
5-10 ft
10% of Design
Depth
Over 10 ft 1.0 ft
b.) From the top of the concrete lining to the top of the ditch, a
side slope not steeper than three (3) horizontal to one (1)
vertical shall be required; nor shall the slope be less than
twelve to one (12:1).
c.) For normal conditions, the concrete lining shall be a
minimum of five (5) 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
CITY OF SCHERTZ DESIGN SPECIFICATIONS
42 April 2013
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, twenty-four (24) inches downstream, and
eighteen (18) inches for side slopes. The city's construction
inspector may permit an eighteen-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-foot surcharge load shall
be included in the design.
e.) Fencing will be required adjacent to the channel where
channel vertical wall heights exceed two (2) feet. Fencing
will also be required adjacent to the channel where channel
side slopes exceed two to one (2:1) and the channel depth is
greater than two (2) feet. The fencing must not cause sight
distance problems for motorists.
f.) Vertical walls will not be permissible for depths greater than
two (2) feet unless properly fenced or enclosed. Walls will
have a minimum thickness of six (6) inches.
g.) 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.
h.) A minimum "N" value of roughness coefficient of 0.015 shall
be used for a wood float type surface finish. This "n" value is
as used in Manning's formula. Recommended “N” are
available in Table 4.5H below for approval to alter contact
the City Engineer.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
43 April 2013
Table 4.5H
Manning's Roughness Coefficient "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, Little or No Underbrush, Scattered Structures 0.060-
0.075
Dense Vegetation, Multiple Fences and Structures 0.075-
0.090
Corrugated metal pipe "N" Value
Unpaved ½” corrugated 0.024
Unpaved 1” corrugated 0.027
Asphalt 0.018
9.) Vegetated Earth Channels.
a.) Freeboard consistent with 4.5G will be applied to the twenty-
five-year design
b.) The side slope shall not be steeper than three (3) 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) 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
CITY OF SCHERTZ DESIGN SPECIFICATIONS
44 December 2014
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, the fifteen-
foot extra width shall be provided on both sides of the
channel.
d.) Interceptor drainage easements shall extend a minimum of
two (2’) feet on both sides of the extreme limits of the
channel. 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 for maintenance.
10.) Channel Bends. Allowance for extra freeboard shall be made when
the centerline radius of the channel is less than three (3) times the
bottom width. Where sharp bends or high velocities are involved,
the applicant shall use the following formula for computing the extra
freeboard:
d2 - d1 = V2 * (T + B) ÷ (2*g*R)
Where: d1 = 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 feet/second squared.
R = the center line radius of the turn or bend in feet.
a.) The quantity d2 - d1 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.
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 twelve (12’) feet or greater must have a trickle channel, a
CITY OF SCHERTZ DESIGN SPECIFICATIONS
45 June 2015
minimum of five (5’) feet wide, following the centerline to facilitate
positive drainage to the outfall or the entire length of the channel.
H.) 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 storm sewers shall be less than twenty-four (24) inches in
diameter
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-foot wide box culvert with six-inch walls would be (3 x
10')+(4 x 0.5')+(2 x 6') = 44').
I.) INLETS AND OPENINGS.
1.) Drop Curb Openings - Sidewalk Does Not Abut Opening. 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:
L = Q ÷ (Cw * 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 director of
CITY OF SCHERTZ DESIGN SPECIFICATIONS
46 June 2015
developments services in consultation with the director of public
works. 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)1/2
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:
Q = Cw * L * h3/2
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.
J.) 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
CITY OF SCHERTZ DESIGN SPECIFICATIONS
47 April 2013
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 five (5)-year, twenty-five (25)-year and
one-hundred (100)-year frequency. 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 association or property owner. A
maintenance schedule shall be submitted to the public works
department and approved by the Director of Public Works 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. When a regional detention facility accepts flow from
an area exceeding three hundred (300) acres, the facility shall be
considered serving a public purpose and shall be dedicated to the
City.
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 6 feet will not be allowed without prior
approval of the City Engineer.
5. Parking areas may be used as detention facilities provided the
depth does not exceed 8 inches, and the impounding of storm
water does not impact the adjacent buildings.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
48 April 2013
6. Storm water retention with permanent wet pool or pumped
detention systems will not be acceptable methods 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
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 on a continuous basis.
7. Stage- Storage- Discharge tables for basins and associated outlets
will be required upon plans and within the SWMP.
K.) 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 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.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
49 April 2013
4.6 STORM WATER CHECKLIST
City of Schertz
Storm Water Management Plan (SWMP) Checklist
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A. GENERAL dress this section for these revi
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)
1.
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 properly 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 100-year facility, flood plain and floodway location
B. HYDROLOGY
Drainage Area Map (to scale) for Existing and Ultimate Conditions.
Show site boundaries, overall drainage areas and sub-areas, acreage 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 minimum two (2)
foot contour elevations
1.
Flood plain and floodway location, with BFE indicated
Detailed Q calculations include:
Time of Concentration (provide detailed calculations) (TR 55 method
preferred):
Overland Sheet - Length, slopes, (5 min < to< 20 max), max 300 feet
Shallow Concentrated Flow - Length, slopes
Concentrated Flow - Length, slopes, assumed v ≥ 6fps
Rational Method
Rational Method for watersheds 0 to 200 Acres, peak flow analysis only,
no flow routing required, no floodplain analysis
Verify Rainfall Intensities ( I ) & Runoff Coefficient (C )
2.
Unit Hydrograph 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
CITY OF SCHERTZ DESIGN SPECIFICATIONS
50 April 2013
Routing Method: Modified Puls or Muskingam
Soil Survey Map of area ( site delineated, soil type & acreage of each
soil group)
C. HYDRAULICS
1. General:
For all storm water facilities with drainage area > 100ac, design for Q100
All storm water facilities shall be designed for Ultimate development
Street Capacity:
Local ‘A’: Q5 contained within curbs, Q25 contained within ROW.
Collector/Local ‘B”: Q25 contained within curbs
Arterial: Q25 within curbs AND one lane in each direction shall remain
passable with a flow depth not to exceed 0.3 ft
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.
2.
Lateral curb opening sized as weir
Channels: (provide detailed calculations)
If Drainage area < 100ac : Q25 plus freeboard (see Public Works
Specifications)
If Drainage area > 100ac : Q100 and Q25 plus freeboard (see Public
Works Specifications)
Slope Conveyance Method (Mannings) – for small channels (BW≤20’),
not in 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 back water. 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
3.
Floodplain Submittal is required if property is within or next to a FEMA
designated special flood hazard area
Storm Sewer
Inlet designed for 25-yr capacity
HGL/EGL: provide detailed calcs (including junction losses). Show in
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
4.
Min storm sewer pipe diameter = 24 inches.
Pipe velocity between 2 fps and 12 fps
CITY OF SCHERTZ DESIGN SPECIFICATIONS
51 April 2013
Culverts
Culvert design for 25-year event unless upstream water shed is greater
than 100 acres, then it shall convey the 100-year runoff.
Designed according to FHWA HDS-5
Headwater does not overtop road
5.
Box culvert, headwalls and wingwalls to conform to TxDOT design
standards
Detention Basin
Indicate area to drain to detention basin
Provide inflow and outflow hydrographs for 5-yr, 25 yr 100 yr
(proposed, ultimate)
Provide required storage for the 5 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 unless approved by City Engineer.
Provide maintenance schedule
6.
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
dissipaters or other means to reduce velocity Provide retard spacing and
concrete transition length calculations (hydraulic jump)
7.
Receiving facility (street, channel, culvert, etc) capacity to accept runoff.
8. Easements
Widths include freeboard and access
9. Storm Water Pollution Prevention Plan
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0. Maintenance agreement/plan
CITY OF SCHERTZ DESIGN SPECIFICATIONS
52 April 2013
City of Schertz
Floodplain Submittal
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1. Narrative (Per section 35-B119(d) of UDC)
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 analysis of (with hard and electronic copy of) the following using HEC
RAS or standard step backwater analysis model:
25 year existing and ultimate development condition hydraulic analyses
100 year existing and ultimate development condition hydraulic analyses
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, Mannings 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
12. Provide U.S.G.S. Quadrangle maps showing overall drainage areas, runoff
coefficients, time of concentration, intensity.
13. Is this development over the Edwards Aquifer Recharge Zone?
14. Flood plain Development Permit Application (1 COPY ONLY).
15. Elevation Certificates (if applicable)
16. 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 tie in with the existing floodplain
upstream and downstream, show the proposed streets centerline only and
label, show the upstream and downstream limits of study.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
53 April 2013
SECTION 5 – SANITARY SEWER REQUIREMENTS
5.1 GENERAL
All subdivisions shall be provided with an approved sewage disposal system. An
Engineering Design Report for waste water shall be submitted for review by the
City Engineer. 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 Sub-divider shall dedicate, at his 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.
B.) The Sub-divider shall provide, prior to the beginning of such subdivision
improvements, a guarantee of performance. Upon completion of the
system and acceptance by the City and appropriate utility company, the
installation shall become the property of the City and the utility company to
operate and maintain.
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.
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.1). 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 its 50-year life. The line and must conform
to Sanitary Sewer Master Plan recommendations on file in the office of the
Director of Public Works.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
54 April 2013
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
Unknown future development LUE/acre 4
Rates for other non residential development may be obtained from actual water usage, TCEQ
Waste Water Usage Rates (30 TAC §285.91(figure 3), or other method approved by City Engineer.
Table 5.2B
Infiltration
Source of Infiltration Amount of Infiltration In
Gallons Per Day Per Acre
Residential Area - Level to 7% Slope 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
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: Five (5’) Feet Diameter Precast Manhole Base with watertight
manhole ring and cover and 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.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
55 April 2013
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 ¼” = 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 Public Works Department shall be advised forty-eight (48)
hours before any construction is started in order 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. (See Utility Layout Plat). 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.) Manhole 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.
6.) Drop Manholes should be used sparingly and generally, only when
it is not economically feasible to steeping 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.) Cleanouts may be used only where not more than one customer is
on the line.
8.) 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 finish grade.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
56 April 2013
9.) Compaction of sewer lines shall be according to Section 02317 –
Excavation and Backfill for Utilities of the City of Schertz Public
Works Standard Specifications.
10.) Construction over the Edwards Aquifer: For subdivisions
constructed over Edwards and associated limestone formations, all
construction shall meet the latest revision and requirement of the
Texas Commission on Environmental Quality.
11.) All manhole section joints shall be wrapped with an external seal
wrap meeting Specification 02082 and installed according to
manufacturer’s recommendations.
12.) Below paved areas, encapsulate manhole with cement stabilized
sand or flowable fill; minimum of 1-foot below base, minimum 1-
foot around walls, up to within 12-inch of pavement subgrade per
specification 02317.
5.3 MINIMUM SANITARY SEWER TESTING REQUIREMENTS
A.) 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.
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:
Hose connection
Shut-off valve
Throttle valve
Pressure-reduction valve
Gage cock
CITY OF SCHERTZ DESIGN SPECIFICATIONS
57 April 2013
Monitoring pressure gauge
3.) Test Procedures:
Determine Section of line to be tested
Apply air pressure until the pressure inside the pipe reaches 4 psig.
Allow the pressure inside the pipe to stabilize: then bleed back to 3.5
psig.
At 3.5 psig, the time, temperature and pressure will be observed and
recorded. A minimum of five (5) readings will be required for each test.
If the time in seconds for the air pressure to decrease from 3.5 psig
is greater than that shown in the following table, the pipe shall be
presumed to be free from defect. When these rates are exceeded,
pipe breakage, joint leakage or leaking plugs are indicated and 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.
See Section 02533 – Acceptance Testing for Sanitary Sewers. City
of Schertz Public Works Standard Specifications for a table of time
allowed for pressure loss.
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.
See Section 02533 – Acceptance Testing for Sanitary Sewers. City
of Schertz Public Works Standard Specifications for a table of
mandrel sizes, as well as vacuum testing of manhole procedures
and requirements for filming of sewer mains.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
58 April 2013
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. The report should contain a map of the service
area, 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 required, 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 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 Sub-divider shall dedicate, at his own cost, such right of way 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.
C.) The sub-divider shall provide, prior to the beginning of such subdivision
improvements, a guarantee of performance. Upon completion of the
system and acceptance by the City and appropriate utility company, the
installation shall become the property of the city and the utility company to
operate and maintain.
6.2 MINIMUM WATER STANDARDS
A.) FIRE HYDRANTS:
1.) Hydrant location must follow both of two rules:
No structure should be further away, in a direct fire hose line,
than five hundred (500’) feet from a fire hydrant
Hydrant spacing along a water main should not exceed five
hundred (500’) feet in single-family residential areas or three
hundred (300’) feet in mercantile, industrial and heavily
congested residential area.
CITY OF SCHERTZ DESIGN SPECIFICATIONS
59 April 2013
2.) Fire Hydrants branch lines shall connect to an 8-inch water main.
3.) Any new fire hydrant is required to have a hydrant locator reflector
(blue bump) installed in the roadway perpendicular to the hydrant.
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 Public Works Director.
2.) Supply Mains: Supply mains in the distribution system shall be
looped and have a minimum size of twelve (12”) inches diameter
and shall not exceed six thousand (6,000’) feet in length between
cross connecting mains.
3.) Mercantile and Industrial Mains: Mains in all mercantile areas shall
be looped between supply mains and shall have a minimum size of
eight (8“) inches inside diameter and shall be the shortest of the
two following lengths: three thousand (3000’) feet of a length that
would by fluid friction render the line incapable of producing flows
and pressures set out herein for the type of area to be served and
with pressure and flows that exist at the supply mains connections
as determined by the Public Works Director. Mains in mercantile
areas shall be located in streets or fire lanes 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.
4.) Residential Mains: Mains in residential areas shall be looped, shall
have a minimum size of eight (8”) inches inside diameter, and shall
be the shortest of the two following length: three thousand (3,000’)
feet, or a length where fluid friction would render the line incapable
of producing the flows that exist at the supply mains connections
and as determined by the Public Works Director. Domestic mains
shall be installed in dedicated street right-of-way and sized so that
the minimum fire flow at any single fire hydrant shall not be less
than seven hundred fifty (750 gpm) gallons per minute with thirty
(30 psi) pounds per square inch residual pressure and a domestic
use of two (2 gpm) gallons per minute for every lot in the
subdivision.
5.) One LUE (Living Unit Equivalent) produces a water demand of:
2 gpm peak hour flow demand
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1 gpm peak day flow demand
300 gpd (0.208 gpm) average daily flow
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
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 Public Works Construction Specifications; other material as
approved by Public Works.
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 excesses 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) See section 6.4 for testing pressure
5.) No Private Water Supply shall be installed in any subdivision in the
Schertz ETJ or City limits without City Council approval and a water
franchise agreement.
B.) The depth of cover of the main shall be not less than the forty-eight (48”)
inches from the top of pipe, and shall be sufficient to safely sustain all
anticipated live and dead loads in conjunction with the pipe material
design. Mains within earthen channels shall be protected from scour; a
scour analysis may be required.
1.) The initial material in backfilling utility trenches to be in accordance
with Section 02317 – Excavation and Backfill for Utilities of the City
of Schertz Public Works Standard Specifications and applicable
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manufacturer’s instructions: The City requires water and sewer
utilities to be encased in six (6”) inches of sand.
2.) After the initial material has been properly compacted, the
remaining upper portion of the trench can be backfilled. Backfill
shall be of selected materials according to Section 02317 –
Excavation and Backfill for Utilities of the City of Schertz Public
Works Standard Specifications. Certified laboratory shall provide
City proctor density testing results. The use of flowable backfill in
streets and driveways may be required in areas subject to traffic.
The mix shall utilize cement, fly ash, fine aggregate (100 % passing
¾” sieve), and water with a shrinkage compensator as per City’s
specification.
3.) The practices of water jetting or ponding backfill in roadways,
drainage right-of-way, driveways, concrete or paved easements are
NOT ACCEPTABLE
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 2” blue painted
dot on the curb shall mark location of new meters.
D.) Air Relief And Blow-Off Valves:
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 screened with
Stainless Steel No. 16 Mesh. Blow-off valves shall be AWWA approved
cast iron with two (2”) inch operating nut.
E.) Gate Valves:
1.) Location of the valves shall be uniformly located in some standard
area such as street or curb line to facilitate their 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.
Valves should be located on all branches from feeder mains and
between distributors and fire hydrants. Three (3) vales shall be
used as crosses and two (2) valves at tees; the valves should be
places on the smaller lines at each cross or tee. On arterial mains
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and minor distributors, valves should be placed at least every six
hundred (600’) feet. Valves shall also be installed on each side of
major streets, railroad crossings and drainage channels.
2.) Material for gate valve construction shall comply with the current
AWWA Standard C-509-80 Resilient Seat Gate Valves from list of
approved manufactured parts located at the Public Works
Department for Ordinary Water Lines. All valves shall be left-
handed open valves.
3.) Valves will be accompanied by a “v” etched into curb face, painted
blue.
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 Director when a valve is to be
operated and shall only operate the valve in the presence of the
City’s representative.
F.) Fire Hydrants: Five and one fourth (5 ¼”) inch steamer outlet, NST and
two and a half (2 ½) 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 from
the list of approved manufactured parts located at the Public Works
Department. Bonnets and caps to be painted white.
G.) Private fire lines shall meet the City’s specifications for pipe material and
trench backfill.
1.) A Double Check Assembly (DCA) or a Double Check Detector
Assembly (DCDA) backflow device will be provided on private fire
lines within 100 feet of the City’s water main; DCA for fire line for
sprinklers (no chemicals), DCDA for fire line with fire hydrants.
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.
H.) PROTECTION OF WATER SUPPLIES
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 (TAC) (or
TCEQ rules) Chapter 217: Rule 217.53.d.
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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 with 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 may
be, 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 affect of vibration. 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. These
taps shall not be subject to flooding.
I.) Disinfection of Water Mains: For disinfecting newly laid mains or after
repairs to the system, 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 Public Works Standard
Specifications Section 02514 – Disinfection of Water Lines.
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 Public Works Standard Specifications
Section 02515 – Hydrostatic Testing of Pipelines, current AWWA standards as
well as TCEQ rules and regulations.
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For all water lines, expel air and apply minimum test pressure of 200 psi. During
the test, pressures shall not vary more than ±5 psi.
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SECTION 7 – INSPECTIONS, TESTING, AND CHARGES
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, 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.
Whenever a developer, contractor or engineer needs an inspection of any
street or utility improvement, the Public Works Director shall be contacted
first, a minimum of at least forty-eight (48) hours in advance of the
inspection. When the Public Works Director or his Department should be
contacted, messages should not be left on a proposed date and time for
inspection with anyone other than the Public Works Director or his
designated representative. The design engineer or his designated
representative shall be present at all inspections. With regard to 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:
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.
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.
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. If City representatives arrive and find
the lines have not been pre-tested, they have been instructed to
leave the inspection site immediately and the re-inspection will
have to be rescheduled.
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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.) Inspections of water and sewer lines and streets will be made at the same
time on all such lines and streets within that particular subdivision.
Minimum test spacing set out shall be not less than five hundred (500’)
feet. No piecemeal inspection of parts of lines or small sections of streets
will be made. However, with regard to sub-grade inspections, sections of
the street can be inspected when needed to protect the sub-grade from
bad weather or other conditions that may deteriorate the sub-grade. No
more than three (3) sub-grade inspections will be made in any one (1)
subdivision.
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. The sub-divider shall immediately reimburse the city for the full
actual cost and expense of all such re-inspections after the initial
inspection requested by the developer, except street sub-grade
inspections as noted above, upon being billed therefore.
F.) Testing will be performed by, an approved, independent testing laboratory.
The following test schedule will be adhered to:
Streets: sub-grade moisture, density test at the rate of one per
each block not to exceed five hundred (500’) fee spacing.
Flexible Base: P.L., L.L., P.I. and gradation of material used;
moisture, density test on same spacing as sub-grade.
Concrete Structures: Concrete cylinders, one/50 cy. Or for each
pour is less than 50 cy. Shall be taken for curbs, drainage
structures and sidewalks.
All testing is the responsibility of the developer. Copies of all test
results shall be furnished to the City before final approval of the
subdivision is given.
G.) Before initial final acceptance of a subdivision is given 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 made an
inspection of such improvements and that said improvements were
constructed in accordance with the approved construction plans. Attached
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67 April 2013
to the letter shall be one (1) set of reproducible “As Built” drawings
showing the work to be accepted for use by the City as well as one (1)
PDF and one (1) CAD drawing on CD. These should include location of
valves, fire hydrants, manholes, storm drain inlets and outlets (with
elevations), and blow-off valves.
H.) Guarantee of Material and Workmanship: The sub-divider or developer
shall require of his construction contractors with whom he contracts, and
shall himself 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 one (1) year after such acceptance of
the improvements by the City. The responsibility for all cost of the in-place
improvements shall be borne by the sub-divider, and all criteria of Section
4.15 of the Schertz UDC shall be met before acceptance