City of Overton, TX Design Criteria and Construction Standards

Ramp to be constructed with minimum three thousand (3,000) psi twenty-eight-day strength concrete.

Ramp concrete thickness shall be the same as the street (six-inch normal residential).

No. 3 bars shall be used for reinforcement (twenty-four-inch on centers).

Curb return shall match existing curb height of the street and taper to the connecting walk with a one-foot radius.

Street shall be blocked out (maximum twelve (12) inches) and dowels installed.

vii)

Saw joints shall be made one and one-half inch minimum depth and sealed with silicone joint sealant material.

viii)

Subgrade shall be prepared to a minimum depth of six (6) inches.

ix)

At no time shall the walk running parallel to the street be altered.

Surface of walk may be coarse and ribbed to provide extra traction.

(Ordinance 2018.04.19B adopted 4/19/18)

§ 107 (RESERVED)

§ 108 (RESERVED)

§ 109 (RESERVED)

§ 110 MISCELLANEOUS.

110.1

Private streets.

All streets, including streets in Planned Developments as defined by the Zoning Ordinance, not dedicated to the public shall be paved in accordance with these Design Standards and shall be maintained by means of a Homeowners’ Association, the property owner or other means as approved by the Commission.

Any request to dedicate a private street as a public street shall be approved only if arrangements are made to bring the street into conformity with all city standards and regulations in effect at the time of dedication at the cost of affected property owners.

All private streets that intersect with public streets shall be constructed with standard drive approaches. In such cases where an unusual condition exists, the City Engineer may approve standard intersection approaches if the approval is requested prior to the preparation of the plans. Private streets will be named and shown on the plat. Street signs for said private streets shall be erected and maintained by the Homeowners’ Association or property owner.

110.2

Trench safety.

In conformance with House Bills 662 and 665 as passed by the Seventieth Legislature Regular Session of the State of Texas, all construction projects within the City of Overton or its extraterritorial jurisdiction as provided by the Municipal Annexation Act (Article 970a, Vernon’s Texas Civil Statutes) shall contain provisions for trench safety.

On construction projects in which trench excavation will exceed a depth of five (5) feet, the uniform set of general conditions must require that the bid documents and the contract include detailed plans and specifications for adequate safety systems that meet Occupational Safety and Health Administration standards and that these plans and specifications include a pay item for these same safety systems.

110.3

Underground utilities.

All distribution lines, cables, etc. for utilities shall be installed below ground within the subdivision. Transmission lines or major cables to provide utilities such as electric, telephone and cable television to the area as a whole may be located above ground on the perimeter of the subdivision being served. The installation of these utilities shall conform to commonly accepted construction standards and be subject to review by the City Engineer.

110.4

Off-street parking.

All parking shall be off-street, meaning that all vehicle maneuvering is done on the subject parcel and not on the street or right-of-way. The following minimum dimensions apply for off-street parking:

Parking Angle	Stall Width	Stall Length	Maneuvering Space
90 Degrees	9 feet	18 feet	24 feet
60 Degrees	9 feet	18 feet	20 feet
45 Degrees	9 feet	18 feet	18 feet

(Ordinance 2018.04.19B adopted 4/19/18)

§ 111 PARKING.

111.1

Off-street parking.

All parking shall be off-street, meaning that all vehicle maneuvering is done on the subject parcel and not on the street or right-of-way.

Three thousand six hundred (3,600) psi reinforced concrete with a minimum thickness of six (6) inches or eight (8) inches of Type A, Grade 2, Limestone Flexible Base and two (2) inches of Type “D” HMAC.

Subgrade thickness and content shall be determined from a geotechnical report sealed by a licensed professional engineer registered in Texas provided by the developer.

Standard curb and gutter as shown on P-4 of the Construction Standards shall be placed around all landscaping areas and the external boundary of the parking area.

All off-street parking areas shall be striped in accordance with the latest addition of the Manual on Uniform Traffic Control Devices (MUTCD) published by the Texas Department of Transportation.

The following minimum dimensions apply for off-street parking (See Appendix A):

Parking Angle	Stall Width	Stall Length	Maneuvering Space
90 Degrees	9 feet	18 feet	24 feet
60 Degrees	9 feet	20 feet	20 feet
45 Degrees	9 feet	19 feet	18 feet

(Ordinance 2018.04.19B adopted 4/19/18)

§ 112 DRIVEWAYS.

112.1

Driveway approaches.

All driveway approaches connecting to city streets shall be composed of concrete and shall meet the construction requirements as specified in Sheet P-5 of the city’s Construction Standards. (See Tables as referenced F and G [G and H] in section 201.8 for driveway spacing and width details).

The normal driveway grade within the street right-of-way is set at one-quarter (1/4) inch per foot rise above the top of curb at the property line. The minimum elevation of a driveway at the right-of-way is two (2) inches above the top of curb. Barrier-free sidewalk construction requires a maximum driveway grade as measured from the gutter of eight (8) percent.

Where driveway construction or reconstruction must occur off the street right-of-way, the usual maximum grade is fourteen (14) percent. The maximum change in grade without vertical curve is twelve (12) percent for any ten (10) feet in distance. Driveways should be profiled for a distance of at least twenty-five (25) feet outside the right-of-way to ensure adequate replacement design.

Due to state laws requiring barrier-free construction of sidewalks, steps or other abrupt changes in sidewalk grades are prohibited at driveways.

(Ordinance 2018.04.19B adopted 4/19/18)

CHAPTER 2 IMPROVEMENTS

§ 201 STREET IMPROVEMENTS.

201.1

Street classification definitions.

Streets shall be classified according to the following:

Thoroughfare (principal, major, minor):

The main function of a thoroughfare is to carry traffic from one (1) urban area to another. The thoroughfare system serves the major activity centers of urbanized areas. A thoroughfare is used for longer urban trips and carries a high portion of the total traffic with a minimum of mileage.

Collector:

Carries traffic from local streets to thoroughfare. Also may serve local facilities such as schools, churches. Uses served would include medium and high density residential, limited commercial facilities, schools, some small offices and as direct access within industrial parks. Collector streets also carry heavy traffic to major commercial and industrial facilities from thoroughfare. Uses would include office parks, industrial parks, and community level commercial facilities.

Local:

Carries traffic from residential and commercial areas to collector streets and interconnects individual sites. Local streets carry light traffic volumes and trips are of a short duration.

201.2

General requirements.

The following general requirements apply to street improvements:

Adequate streets shall be provided by the subdivider. The arrangement, character, extent, pavement width, right-of-way width, grade and location of each street shall conform to the Master Plan. Each street shall be considered in its relation to existing and planned streets, topographical conditions, significant natural features such as mature trees or watercourses, public safety and convenience, and its relationship to the proposed uses of land to be served by such street.

Whenever a tract to be subdivided abuts any part of any street so designated on the Master Plan, or where a street designated on the Master Plan crosses any part of the tract to be subdivided, such part of the proposed public street shall be platted. The right-of-way shall be dedicated, and the street shall be constructed by the subdivider, generally consistent with the location as indicated on the Master Plan, and to a width consistent with the Master Plan and the requirements of the Subdivision Ordinance.

Whenever a subdivision, development or new construction occurs adjacent to an existing street, the street shall be curbed and guttered according to the specifications given herein.

All streets shall be designed to coordinate with existing streets in adjoining subdivisions. When conditions permit, centerline offsets shall be at least one hundred thirty-five (135) feet. Greater centerline offsets may be required by the City Engineer and shall be planned where necessary for traffic safety.

Streets shall be named to provide continuity with existing streets. Names of new streets shall not duplicate or cause confusion with the names of existing streets. All street names are subject to approval by the Planning and Zoning Commission upon recommendation of the City Staff.

Where adjoining areas are not subdivided, the arrangement of streets in the subdivision shall make provision for the proper projection of streets into such un-subdivided area.

Streets should be platted to allow two (2) tiers of lots between streets when possible.

The reservation in private ownership of strips of land at the end of proposed or existing streets and intended solely or primarily for the purpose of controlling access to property not included in the subdivision shall be prohibited.

Half streets shall be prohibited, except divided thoroughfare streets where essential to the reasonable development of the subdivision in conformity with the other requirements of these regulations, and where the Commission finds it will be reasonable to require the dedication of the other half when the adjoining land is subdivided. The other half of the street shall be platted within the adjacent tract at the time it is platted.

10.

A median opening with an offset of less than one hundred twenty-five (125) feet from the centerline of an intersecting street or alley shall be prohibited.

11.

Eyebrows or partial cul-de-sacs are not permitted on thoroughfare or collector streets.

201.3

Cul-de-sac.

The following shall apply to cul-de-sacs:

Streets designated to be dead-ended permanently shall be platted and constructed with a paved cul-de-sac. Any dead-end street of a temporary nature, if longer than two hundred (200) feet, shall have a surfaced turning area eighty (80) feet in diameter for a cul-de-sac. Temporary dead-end streets shall have provisions for future extension of the street and utilities and, if the temporary cul-de-sac is utilized, a reversionary right to the land abutting the turnaround for excess right-of-way shall be provided.

A Street ending permanently in a cul-de-sac should not be longer than six hundred (600) feet and shall be provided at the closed end with a turnaround having an outside roadway diameter of at least eighty (80) feet, and a street property line diameter of at least one hundred (100) feet.

201.4

Street class requirements.

The following street class requirements shall apply:

Street layout shall provide for continuation of collector streets in areas between thoroughfares.

Those local streets designated by the Planning and Zoning Commission shall be extended through the tract to the tract boundary to provide future connection with adjoining unplatted lands. In general, these extensions should be at such intervals as necessary to facilitate internal vehicular circulation with adjoining unplatted lands.

Where single-family or duplex uses abut an existing or proposed thoroughfare or collector street, the plat or dedication instrument will provide:

Lots to side onto the arterial with a non-access restriction on the thoroughfare or collector side, or

Reverse frontage with screening and containing a non-access restriction along the rear property line, or

Other treatment as may be necessary or required for adequate protection of adjoining properties, and as approved by the City Council after taking into consideration the proposed method of off-street parking and maneuvering which will prevent the necessity of backing into the thoroughfare or collector street.

201.5

Street design general provisions.

The following general provisions shall apply:

All dedicated streets shall conform to the criteria set forth in the Master Plan. Additional right-of-way will be required at most intersections and may be required at high-volume driveways to provide for left and right turn lanes to maintain traffic volume capacities through the intersections. Additional utility easements may also be required beyond the right-of-way in some locations.

The dedicated streets shall conform to the minimal design parameters as detailed in the “Thoroughfare Planning and Design Guides, North Central Texas Council of Governments” and “Geometric Design of Highways and Streets by AASHTO.”

Streets shall be designed in accordance with The Texas Department of Transportation’s Highway Design Division Operations and Procedures Manual.

No street intersections of a thoroughfare (principal, major or minor) shall vary from a ninety-degree angle by more than five (5) degrees. Intersections of a collector or local streets shall not vary from ninety (90) degrees by more than fifteen (15) degrees.

All intersections shall have:

A tangent section at least fifty (50) feet long that meets the angle of intersection requirements, and

A centerline curve radius of at least four hundred (400) feet.

201.6

Pavement types.

The developer shall provide a geotechnical report, sealed by a licensed professional engineer, containing recommendations for subgrade thickness and content. The minimum pavement thicknesses are provided below.

For Local Streets serving primarily residential areas, the developer shall construct six (6) inches reinforced concrete or four (4) inches of Type “B” and two (2) inches of Type “D” asphalt on a minimum of eight (8) inches of stabilized subgrade.

For Collector Streets, the developer shall construct seven (7) inches of reinforced concrete on eight (8) inches of stabilized subgrade or as approved by the City Engineer.

For Thoroughfare Streets, the developer shall construct eight (8) inches of reinforced concrete on ten (10) inches of stabilized subgrade or as approved by the City Engineer.

201.7

Street signs.

The following requirements shall apply:

Street signs shall be furnished and installed by the Subdivider for all intersections within or abutting the subdivision.

Street signs shall be six (6) inches extruded, have white lettering on a green background, be engineer grade reflectorized, and include the block numbers along with the street name.

Stop signs shall be twenty-four-inch by twenty-four-inch in size and shall conform to the standards as set forth in the Texas Manual on Uniform Traffic Control Devices.

All signs shall be of engineer grade reflective material and be located in accordance with the Texas Manual on Uniform Traffic Control Devices.

The sign pole shall be buried to a minimum depth of two (2) feet and placed in twelve (12) inches diameter concrete filled posthole. The pole shall be tall enough to accommodate all applicable signs. The bottom of the stop sign shall be located seven (7) feet above the finished grade of the surrounding ground.

The developer shall submit a list of signs to be placed and a graphical representation of the signs for review by City Staff prior to installation.

201.8

Street Design Tables.

The following tables provide design information.

Table A. Street Design Criteria
Reference Section 201 - Street Improvements of this Ordinance
Street Classification	Min. Design Speed (MPH)	Max.% Grade	Min.% Grade	Area Free from Storm Water, Using a 100-Year Frequency Storm
Thoroughfares
Principal	70	6	0.5	One lane in each direction
Major	70	6	0.5
Minor	60	6	0.5
Collector	50	8	0.5	One lane or center 12'
Local	30	10	0.5

Table B. Urban ROW Widths
Thoroughfare Planning and Design Guides, North Central Texas Council of Governments, June 1995
Functional Class	No. Lanes	Median	Min. (feet)	Recommended (feet)	Intersection (feet)
Principal	6	Yes	132	156	200
	4	Yes	108	132	150
Major	6	Yes	110	132	142
	4	Yes	86	102	112
	5	No	80	95	105
	3	No	58	70	75
Minor	4	Yes	80	100	110
	4	No	64	80	90
	3	No	56	68	80
	2	No	50	60	72
Collector	4	No	64	78	90
	3	No	56	68	66
	2	No	50	60	60

Table C. Lane Widths
Thoroughfare Planning and Design Guides, North Central Texas Council of Governments, June 1995
Location	Functional Classification	Min. (feet)	Recommended (feet)
Urban	Principal	12	12
	Major	12	12
	Minor	11	12
	Collector	10	12
Rural	Principal	12	12
	Major	12	12
	Minor	12	12
	Collector	12	15

Table D. Median Widths
Thoroughfare Planning and Design Guides, North Central Texas Council of Governments, June 1995
Design Speed	Minimum (feet)	Recommended (feet)
55+	40	54
45-54	22	30
40-44	18	22
< 40	14	18

Table E. Median Lane Widths for Two-Way Left Turn Lanes
Thoroughfare Planning and Design Guides, North Central Texas Council of Governments, June 1995
Speed Limit (mph)	Usual (feet)	Minimum (feet)
0-30	12-14	11
35-40	12-14	11
45-50	14	12
50+	16	14

Table F. Design Speeds
Thoroughfare Planning and Design Guides, North Central Texas Council of Governments, June 1995
Location	Functional Classification	Recommended Range (mph)
Urban	Principal	45-70
	Major	45-55
	Minor	40-50
	Collector	35-40
Rural	Principal	50-70
	Major	50-70
	Minor	40-60
	Collector	40-50

Table G. Access Management Minimum Spacing
Thoroughfare Planning and Design Guides, North Central Texas Council of Governments, June 1995
Functional Classification	Driveway Spacing	Median Openings
		Directional	Full
Principal	440	2,640	5,280
Principal (Svc. Rds.)	330	N/A	N/A
Major/Minor	220	440	880
Collector	100	N/A	330
Local	One Per Lot	N/A	N/A

Table H. Driveway Widths
Area	Minimum (feet)	Maximum (feet)
Residential	8	24
Commercial	10 - One Way	28
Industrial	10 - One Way	30

201.9

Horizontal curves and super elevation.

The alignment of the streets and thoroughfares is usually determined by the alignments of the existing right-of-way or structures which cannot be relocated. Changes in the direction of a street or thoroughfare are minimized by constructing a simple curve having a radius which is compatible with the speed of vehicular traffic. To increase the safety and reduce discomfort to drivers traversing a curved portion of a street or thoroughfare, the pavement may be super-elevated. Reference “Geometric Design of Highways by AASHTO” for design standards.

201.10

When two (2) longitudinal street grades intersect at a point of vertical intersection (PVI) and the algebraic difference in the grades is one (1) percent or greater, a vertical curve is required. Vertical curves are utilized in roadway design to affect a gradual change between tangent grades and should result in a design, which is safe, comfortable in operation, pleasing in appearance and adequate for drainage. The vertical curve will be formed by a simple parabola and may be a crest vertical curve or a sag vertical curve. Reference “Geometric Design of Highways by AASHTO” for design standards.

(Ordinance 2018.04.19B adopted 4/19/18)

§ 202 WATER SYSTEM IMPROVEMENTS.

202.1

General.

This section pertains to general design requirements for water distribution system construction in the City of Overton.

All water lines shall be sized and designed in accordance with the City of Overton Water Distribution System Master Plan or as determined by the City Engineer. In the absence of specific standards, all water supply, distribution, pumping, and storage improvements shall be designed in accordance with the most current standards of the American Water Works Association, the Standard Specifications for Public Works Construction of the North Central Texas Council of Governments, and criteria adopted by the Texas Administrative Code, Chapter 290, “Public Drinking Water.”

Water lines for multi-family, commercial and industrial fire protection lines shall be dedicated to the public, unless the system is isolated from the public system by a detector check.

The developer shall furnish, install, construct, or extend, at his own expense, water distribution facilities necessary for the proper development of the subdivision. The water system shall provide individual service to every lot in the subdivision. All water mains constructed within a proposed subdivision shall be extended to the perimeter of the proposed subdivision to allow for future extension of the water system into adjacent properties. The water system shall be designed and constructed in accordance with the specifications contained in these Standards. Where considered necessary by City Staff, the facilities shall be sized in excess of that dictated by these Standards to provide for the future growth and expansion of the city’s water distribution system.

202.2

Water line sizing.

All water lines shall be a minimum of six-inch diameter. Standard water line sizes are six-inch, eight-inch, twelve-inch, and sixteen-inch diameter. Other sizes must be approved by the City Engineer.

All water lines shall be looped except in cul-de-sacs. Dead-end lines shall not exceed fifty (50) feet on multi-family, commercial, or industrial sites.

202.3

Water line location.

Water lines shall be located in the parkway. Along State Highways, water lines are required to be constructed on both sides of roadway. New water lines crossing existing streets shall be placed by boring. A casing shall be required under major and minor collector roadways. Open cut excavation will not be allowed to cross existing streets, unless approved by the City Engineer.

All public water lines located on private property shall be centered in an easement. Water lines shall not be located under paved surfaces where possible. Easements for water line construction shall meet the following requirements:

The easement width shall be a minimum of fifteen (15) feet.

If the water line is less than twelve (12) feet deep, the outside diameter of the water line shall be located a minimum distance of six (6) feet from the edge of the easement, and if other utilities are located in the same easement, the outside diameter of the water line shall be located a minimum distance of three (3) feet from the outside diameter of the other utilities.

If the water line is greater than twelve (12) feet deep, the outside diameter of the water line shall be located a minimum distance of nine (9) feet from the edge of the easement, and if other utilities are located in the same easement, the outside diameter of the water line shall be located a minimum distance of six (6) feet from the outside diameter of the other utilities.

All piping with mechanical couplings, push-on, or similar joints subject to internal pressure shall be designed with blocking, anchors, and restraining harnesses to preclude separation of joints.

202.4

Water line materials.

All new water line installation shall be AWWA C-900 Polyvinyl Chloride (PVC) Pipe, blue in color, unless approved otherwise by City Engineer.

All materials shall be in accordance with section “500 Underground Construction & Appurtenances” as detailed in the “North Central Texas Council of Governments Public Works Construction Standards.”

Fittings ductile iron in accordance with AWWA C110 or AWWA and section “500 Underground Construction & Appurtenances” as detailed in the “North Central Texas Council of Governments Public Works Construction Standards.”

202.5

Installation.

General.

All installations shall conform to the latest North Central Texas Council of Governments Public Works Construction Standards.

All six-inch and eight-inch water pipes shall be installed with a minimum of forty-two (42) inches of cover over top of pipe; twelve-inch water pipes shall be installed with a minimum of forty-eight (48) inches cover. Pipes sixteen (16) inches and larger shall be installed with a minimum of sixty (60) inches of cover over top of pipe.

The amount of trench excavation shall not exceed two hundred (200) feet from the end of the pipe laying operations, and no more than three hundred (300) feet of total open trench will be allowed. At the end of each work day, all trench excavation shall be backfilled to the end of the pipe laying operation. Barricades and lights will be required around any open trench left overnight.

All connections to existing water mains shall be made under pressure unless dry connections will not cause any loss of service. Under special conditions connections that cause an interruption of service may be performed with approval of the City Engineer.

Coated tracer wire shall be installed in the embedment material above the PVC pipe with the tracer wire terminating in the in-line gate valve boxes accessible by City Staff. Blue underground water line tape of a minimum four-inch width shall be installed above the embedment material.

Density tests shall be taken as directed by the City Engineer.

202.6

Fire hydrants.

Fire hydrants in commercial and industrial areas shall generally be at street intersections and so located that there will be a fire hydrant every three hundred (300) feet. Fire hydrants in a residential area shall be generally located on street intersections and not over five hundred (500) feet apart. Fire hydrants in a multi-family complex shall be generally located on street intersections and not over three hundred (300) feet apart.

Materials.

Fire hydrants shall be Mueller (Super Centurion 200) or approved equal.

The fire hydrant body shall be painted a high gloss alkyd fire hydrant red.

202.7

Valves.

Resilient seated gate valves shall be used for six-inch through sixteen-inch water lines. Butterfly valves shall be allowed for sixteen (16) inches and larger water lines when approved by the City Engineer.

Valves of approved design shall be installed at the intersections of all water mains so as to provide for proper maintenance and operation of the system and to provide a means of shutting off the supply to portions of the system for repairs. Valves shall be spaced such that only one (1) fire hydrant is out of service at any one (1) time. Three (3) valves shall be used on a four-way water line intersection and a minimum of two (2) valves shall be used on a three-way intersection.

Materials.

All valves shall conform with the “North Central Texas Council of Governments Public Works Construction Standards.”

Installation.

Valves shall be furnished with extensions, such that the working nut is a maximum of forty-eight (48) inches below grade.

Adjustable valve boxes shall be furnished and set on each valve in accordance with these standards. Valves that are deeper than forty-eight (48) inches, AWWA C900 PVC pipe shall be used for stacks, as long as the adjustable valve box is used at the top.

After the final clean-up and alignment has been complete, the contractor shall cast in place a concrete block, twenty-four (24) inches by twenty-four (24) inches around all valve box tops at the finish grade. See Construction Standards.

Valves located within a right-of-way shall be indicated on the face of the curb, or where curbs do not exist, on a conspicuous location adjacent to the valve location. Markings are to be the stamping of a four-inch high letter “V” with the point of the “V” pointing towards the valve location.

Valve markers shall be provided in rural areas.

Manufacturers.

Resilient seated gate valves shall be Mueller or approved equal.

Butterfly valves shall be Clow or approved equal.

202.8

Air Release and Flushing Valves.

Adequate air relief and flushing valves shall be provided for flushing, disinfection, daily operation requirements and repairs when required by the City Engineer. Air release valves shall be required on twelve (12) inches and larger water lines. Water lines shall be designed so that each section of the water line can be flushed at its lowest and highest points.

All dead-end lines shall have a fire hydrant installed for flushing purposes. If installation of a fire hydrant is not possible, a flushing valve is required.

A fire hydrant shall be required at high points on water lines smaller than twelve (12) inches for air relief and flushing.

Air release valves and air/vacuum valves shall meet or exceed the latest revision of AWWA C5.

202.9

Tapping sleeve.

A tapping sleeve and valve shall be used when connecting a new water line to an existing line. A resilient seated gate valve shall be flanged to the tapping sleeve. The tapping sleeve shall be a Smith-Blair type 664-665 stainless steel tapping sleeve or approved equal.

202.10

Water service.

The water meter box shall be placed a minimum of six (6) inches behind the back of curb, and the water service shall be no more than twenty-four (24) inches deep, covered with a meter box in place at grade. If no curb is present, the water service shall be located at the property line, no more than twenty-four (24) inches deep, covered with a meter box in place at grade. Along roadways without a curb the water service line shall be constructed at a minimum of eighteen (18) inches below the ditch flow line. All water services crossing beneath streets must be encased in four-inch diameter PVC casing.

Meter and service sizes will be determined by the developer prior to requesting service from the city. The minimum water service size between the water main and the meter shall be three-fourths (3/4) inches and the minimum meter size shall be five-eighth (5/8) inches.

Water services on undeveloped lots shall be located at the property line and shall be a minimum of one (1) inch in diameter.

Materials.

Service saddle shall be double strap bronze with brass body or stainless steel double bolt wide straps with stainless steel body. Minimum size tap shall be three-fourths-inch diameter.

Service lines shall be three-fourths-inch minimum diameter, poly or type K copper.

Corporation and Curb Stops.

Corporation stop shall be two-inch ball type with compression outlet fitting, designed for a minimum working pressure of two hundred (200) psi.

Curb stop shall be set with compression inlet fitting and lock ring.

Meter box for meters two (2) inches and smaller.

Meter boxes shall be provided as shown in the Construction Standards.

Installation.

General.

All water service shall be installed in accordance with these standards.

Each individual service location shall be saw cut into the face of the curb with a four-inch high blue “W” painted by the Contractor. If no curb exists, a similar mark should be placed in the pavement near the edge of the roadway.

Residential Meters.

All residential meters shall be the current manufacturer’s brand as set by the City and shall be purchased through the City.

Commercial Meters (two (2) inches and larger).

The developer shall purchase from the manufacturer a master compound meter approved by the City Engineer. The meter shall be installed by a utility contractor or plumber. All meters in this size class are required to have a strainer prior to the meter.

Acceptable Manufacturers for Corporation Stops, Curb Stops, and Service Saddles are Ford, Mueller and Smith-Blair.

202.11

Flushing valves.

Materials

Corporation stop shall be two-inch ball type with compression outlet fitting, designed for a minimum working pressure of two hundred (200) psi.

Two-inch curb stop shall be ball type with compression inlet fitting with fee [tee] head shut-off.

Pipe shall be two (2) inches diameter, Type K copper as specified in ASTM B88.

202.12

Water line bore.

Casings shall be required under collectors and thoroughfares, highway crossings, and railroad crossings. Casings may also be required were deemed necessary by the City Engineer. The construction bore pit shall be located at a minimum distance of four (4) feet behind the back of curb or edge of pavement where no curb is present.

Materials.

Steel Casing Pipe.

Steel casing pipe shall be new (or used if approved by the City Engineer), a minimum of 1/4" thickness and suitable for the purpose intended and shall have a minimum yield strength of thirty-five thousand (35,000) psi.

All required materials and installation shall be in accordance with the “North Central Texas Council of Governments Public Works Standards - Section 503,” “Texas Department of Transportation Standard Specifications for Construction and Maintenance of Highways, Streets, and Bridges,” and governing railroad entity when applicable.

(Ordinance 2018.04.19B adopted 4/19/18)

§ 203 WASTEWATER SYSTEM IMPROVEMENTS.

203.1

General.

This section pertains to general design requirements for wastewater collection system construction in the City of Overton. All sewer lines shall be sized and designed in accordance with the Master Plan or as determined by the City Engineer. In the absence of specific standards, all collection, treatment, and disposal systems shall be designed in accordance with the most current criteria adopted by the Texas Administrative Code (TAC), Chapter 217, Design Criteria for Sewerage Systems.

All sewers shall be designed with consideration for serving the full drainage area subject to collection by the sewer in question; the drainage area may be modified with the concurrence of the City Engineer because of the projected rate of development or the financial feasibility of the proposed extension.

Sewers should be designed with straight alignment whenever possible. When horizontal curvatures must be used, the maximum joint deflection should be in accordance with the pipe manufacturer’s recommendations.

The developer shall furnish, install, construct, or extend, at his own expense, wastewater collection facilities necessary for the proper development of the subdivision. The wastewater collection system shall provide individual service to every lot in the subdivision. All sewer mains constructed within a proposed subdivision shall be extended to the perimeter of the proposed subdivision to allow for future extension of the wastewater collection system into adjacent properties. The wastewater collection system shall be designed and constructed in accordance with the specifications contained in these Standards. Where considered necessary by City Staff, the facilities shall be sized in excess of that dictated by these Standards to provide for the future growth and expansion of the city’s wastewater collection system.

All sewers shall be designed with hydraulic slopes sufficient to give mean velocities, when flowing full or half full, of no less than two (2) feet per second on Kutter’s or Manning’s formulas using an “n” value of 0.013. Slopes shall also conform to TAC Chapter 217, Sewage Collection System.

When a one hundred fifty (150) psi rated sewer, line is required due to its proximity to a water line, the one hundred fifty (150) psi rated pipe shall terminate at a manhole on each end. The pipe shall be extended to the interior wall of the manhole. No external boot connection will be allowed.

203.2

Sanitary sewer line sizing.

Standard sewer line sizes are six (6) inches, eight (8) inches, twelve (12) inches, fifteen (15) inches, and eighteen (18) inches in diameter; other sizes must be approved by the City Engineer.

Sewer lines shall be a minimum of six (6) inches in diameter.

203.3

Location.

Sewer lines shall be constructed at a minimum depth of four (4) feet. They shall be located in the parkway and are required to be constructed on both sides of a state highway. No sewer lines will be allowed to cross a state highway.

Easements for sewer line construction shall meet the following requirements:

The easement width shall be a minimum of fifteen (15) feet.

If the sewer line is less than twelve (12) feet deep, the outside diameter of the sewer line shall be located a minimum distance of six (6) feet from the edge of the easement, and if other utilities are located in the same easement, the outside diameter of the sewer line shall be located a minimum distance of three (3) feet from the outside diameter of the other utilities.

If the sewer line is greater than twelve (12) feet deep, the outside diameter of the sewer line shall be located a minimum distance of nine (9) feet from the edge of the easement, and if other utilities are located in the same easement, the outside diameter of the sewer line shall be located a minimum distance of six (6) feet from the outside diameter of the other utilities.

203.4

Materials.

All new sanitary sewer line installation shall be ASTM D-3034 SDR-26 PVC for four (4) inches through fifteen (15) inches, green in color, unless approved otherwise by City Engineer. ASTM Designation F-679 shall be used for pipe sizes greater than fifteen (15) inches.

203.5

Installation.

General.

All installations shall conform to the “North Central Texas Council of Governments Public Works Construction Standards.”

Sewer lines shall not be installed within nine (9) feet horizontally of any water main or fire hydrant.

Construction shall begin at the downstream end of project and continue upstream with the bell facing upstream. No upstream piping shall be installed before downstream piping unless approved by the City Engineer.

Excavation and Backfill.

When PVC pipe is used, green marker tape with the wording “Buried Sanitary Sewer” shall be installed in the backfill material no more than twelve (12) inches above the top of the pipe.

The amount of trench excavation shall not exceed two hundred (200) feet from the end of the pipe laying operations, and no more than three hundred (300) feet of total open trench will be allowed. At the end of each workday, all trench excavation shall be backfilled to the end of the pipe laying operation. Barricades and lights will be required around any open trench left overnight.

Density tests shall be taken as directed by the City Engineer.

203.6

Inspection.

All sanitary sewer lines shall be inspected as detailed in the “North Central Texas Council of Governments Public Works Construction Standards - Section 507.5.”

Criteria for repair.

The Contractor shall make repairs if the inspection reveals any deficiency in the sewer line. If repairs are required, the segment of line to be repaired shall be re-tested at the Contractor’s expense.

Repairs shall be made to the satisfaction of the City Engineer and Public Works Director.

203.7

Manholes.

Manholes shall be located at all intersections of sewer lines and at intermediate spacing along the line. Generally, the maximum spacing should not exceed five hundred (500) feet. Manholes should be located at all changes in grade, direction, and at the ends of all sewer lines that will be extended.

A manhole is required at the junction of sewer lines with different inside pipe diameters.

A drop of at least 0.1 feet is required through the manhole when a change in flow direction occurs.

A drop manhole shall be installed in instances when the flowline into a manhole should [sic] greater than two (2) feet above the flowline out.

Minimum manhole inside diameter is four (4) feet.

Drop-connection manholes shall have a minimum inside diameter of five (5) feet, with an interior drop connection if line size is greater than eight (8) inches.

Minimum cast-in-place manhole wall thickness is eight (8) inches. For depths greater than twelve (12) feet add an extra four (4) inches of thickness for each additional six (6) feet of depth.

Minimum pre-cast wall thickness is five (5) inches.

A manhole is required where a sanitary sewer line enters and exits private property.

10.

All manholes shall be constructed of concrete.

11.

Installation.

Manholes shall be a minimum diameter of four (4) feet for lines 6"-18" in diameter, five (5) feet for lines 21"-27" in diameter, and six (6) for 30"-36" in diameter.

Cast-in-place.

Cast-in-place manholes will be constructed in accordance with the “North Central Texas Council of Governments Public Works Standards, Section 502.”

The manhole shall not be backfilled within twelve (12) hours after the concrete placement.

The face of curb shall be sawed with an “MH” to mark the location of all manholes. The location of the stamp shall be a line that intersects the center of the manhole cover and the curb perpendicular to the centerline of the street. For manholes located in intersections, the curb shall be stamped at the closest location to the manhole. If no curb exists, a similar mark should be placed in the pavement near the edge of the roadway.

Precast Manhole.

Precast manholes will be constructed in accordance with the “North Central Texas Council of Governments Public Works Standards, Section 502.”

Manhole base shall have a spread footing and be placed on a minimum of twelve (12) inches of crushed rock.

203.8

Manhole Frame and Cover.

Cover.

All manhole frames and covers shall conform to the “North Central Texas Council of Governments Public Works Standards - Section 502.”

All manhole[s] will have a minimum opening of thirty (30) inches in diameter.

All manhole covers shall have two (2) integrally cast pick bars.

Any manhole covers located below the 100-year water surface elevations, shall be bolted and gasketed.

Extension Ring.

All precast reinforced concrete extension rings shall conform to ASTM C-478.

The number of extension ring sections shall be kept to a minimum (i.e. use 1-12-inch extension ring instead of two- to six-inch extension rings).

A one inch by three and one-half inch bitumastic gasket shall be used to seal the extension ring at both joints.

Rain Pan.

Rain pans shall be high density polyethylene plastic.

Acceptable manufacturers include Knutson or approved equal.

203.9

Sewer Service.

No sewer service line (lateral) shall be less than four (4) inches in nominal diameter. Commercial sewer laterals shall be six (6) inches minimum diameter.

Sewer laterals shall be located at the center of the lot and extended to the property line and be a minimum of ten (10) feet downstream of the water service.

Sewer service laterals shall have no more than six (6) feet of cover at the property line unless otherwise approved by City Engineer.

A double cleanout shall be installed at the property line, and a cleanout shall be located on the service lateral at the time of connection to the building.

All lateral sewer service lines shall be PVC pipe type SDR-26.

[Reserved]

All service laterals shall be installed in accordance with the sanitary sewer embedment and backfill standards.

203.10

Cleanouts.

All cleanouts are to be constructed of PVC pipe type SDR-26, and shall be in accordance with the “North Central Texas Council of Governments Public Works Construction Standards - Section 502.2.”

203.11

Main Line Cleanouts.

Main line cleanouts shall be located on dead-end sewer mains at a distance no greater than two hundred fifty (250) feet from the preceding manhole. If the distance is greater than two hundred fifty (250) feet, a manhole shall be installed at the end of the line.

203.12

Aerial sewer.

Aerial sewer crossings shall be located in areas where the sewer line cannot be constructed with the appropriate minimum cover. All above-ground sewer installations shall be ductile iron, minimum Class 150, utilizing restrained joints and shall have a wall thickness required for the size and span as designed. The pipe shall have an internal polyurethane coating. The design engineer shall design the aerial crossing in accordance with these standards and submit a design for approval by the City Engineer.

The aerial pipe shall be connected to the sanitary sewer pipe by means of a manhole on each side of the aerial crossing.

The piers for the aerial crossing shall be designed in accordance with the guidelines of the Ductile Iron Pipe Research Association. Piers are to be constructed with a minimum of Class A three thousand five hundred (3,500) psi reinforced concrete. Pier placement and spacing shall be determined according to soils analysis performed by a geotechnical engineer. Piers shall be placed at a maximum span distance as indicated by the design engineer’s calculations. The design engineer shall submit a pier design for approval by the City Engineer.

203.13

Sewer line boring.

Materials.

Steel Casing Pipe.

All bores shall be installed at a grade no less than the minimum indicated by TAC, Chapter 217 for the desired pipe size.

203.14

Lift stations.

Lift stations must be designed in accordance with 30 TAC, Chapter 217.

Instrumentation and control.

The voltage supplied for pump operation shall be three-phase, four hundred eighty (480) volts. Converting single-phase power to three-phase power using additional mechanical equipment shall not be allowed.

Wet-well level control shall be achieved through the use of an ultrasonic level indicating transmitter.

Stations with a total pumping capacity rating less than one thousand (1,000) gpm shall be equipped with an automatic telephone dialing system.

Submersible pumps shall be provided with moisture and motor over-temperature sensors.

Site requirements.

A concrete pad will be required at the front of the control cabinet. The pad shall provide a three-foot working area away from the face of the cabinet and extend the width of the enclosure mounting structure. Pad depth shall be a typical four (4) inches.

A one-inch minimum potable water service is required. The water service may be set in a standard eighteen-inch galvanized water meter box with a one-inch brass angle stop.

The site shall be graded to drain away from the station to prevent storm water inflow or infiltration into the wet-well.

The site shall be located outside of the one-hundred-year floodplain.

The site shall not be located within one hundred (100) feet of an existing or proposed residence, if possible.

If applicable the lift station site driveway shall include driveway area for maintenance vehicles to park off public roadway while performing maintenance. The minimum driveway length shall be fifteen (15) feet. If the drive extends more than twenty (20) feet from main roads, a “t” shaped turning is [sic] with applicable turning radius will be required.

(Ordinance 2018.04.19B adopted 4/19/18)

§ 204 DRAINAGE AND STORM SEWER IMPROVEMENTS.

204.1

General.

Drainage facilities shall be provided and constructed by the developer in accordance with all city standards and the following basic requirements.

204.2

Runoff calculations.

The selection of which method to use for calculating runoff depends upon the size of the contributing drainage area at the most downstream point of the project. The “Rational Method” is acceptable for designing projects in which the drainage area is less than two hundred (200) acres. A unit hydrograph method is required for projects with larger drainage areas.

No matter which method is used to calculate runoff, a developer or builder of property greater than one (1) acre in size, or any property that was platted as a part of an overall tract which was greater than one (1) acre in size (including churches and schools), shall develop the property so that the rate of runoff created by the development as it leaves the property does not exceed the rate of runoff that would have been created if the property had developed as a single-family residential property.

Runoff computations shall be based upon fully developed watershed conditions in accordance with the land use projections in the latest Master Plan. The design engineer shall size drainage facilities by disregarding the detention effects of upstream property and calculating the runoff as if the off-site property was developed without any detention. If an approved regional detention/retention facility is in operation, the design engineer may size downstream drainage facilities based on consideration of the detention effects of the regional facility.

Procedure for drainage areas less than two hundred (200) acres.

Computation of Storm Water Runoff for drainage areas less than two hundred (200) acres shall be by the “Rational Method,” which is based on the principle that the maximum rate of runoff from a given drainage area for an assumed rainfall intensity occurs when all parts of the area are contributing to the flow at the point of discharge. The formula for calculation of runoff by the “Rational Method” is:

Q = CIA
Where:
Q	=	the maximum rate of discharge, expressed in cubic feet per second.
C	=	Coefficient of Runoff.
I	=	Intensity of Runoff in inches per hour
(Use Appendix B - Intensity-Duration-Frequency Curve (IDF) Curve.)
A	=	Drainage Area in acres.

Park areas - No developed land	0.30
Developed Park sites	0.40
Single-family Residential	0.55
Duplex	0.60
Multiple-Family	0.70
Schools	0.70
Churches	0.70
Neighborhood Commercial	0.70
Office Commercial	0.70
Commercial	0.85
Industrial	0.85

Time of concentration is the longest time, without interruption of flow by detention devices, that a drop of water takes to flow from the farthest point of the drainage area to the point of concentration (i.e. the point of design). The time of concentration is composed of the inlet time and the flow time in a conduit or channel to the point of design.

When designing inlets and laterals, the time of concentration is equal to the inlet time. The design engineer will compare the above specified inlet times to the actual calculated inlet time by computing the flow time overland and along the gutter to the first inlet. Manning’s equation shall be used to determine flow time to the inlet. The design engineer may use the actual calculated or specified inlet time.

The inlet time shall be ten (10) minutes for property zoned multiple-family, churches, schools, local business, central business, commercial, or industrial.

An inlet time of fifteen (15) minutes shall be used for property zoned for parks, cemeteries, agricultural, and single-family residential.

Procedures for Drainage Areas greater than two hundred (200) acres:

For drainage areas in excess of two hundred (200) acres where the use of the “Rational Method” does not provide reliable results, the use of a unit hydrograph method shall be made. The use of a unit hydrograph calculation will be based upon standard and accepted engineering principles subject to the approval of the City Engineer. Acceptable methods include the Soil Conservation Service (SCS) Technical Release Number 55 or the Corps of Engineers HEC-1 models for drainage areas two hundred (200) acres or more.

The unit hydrograph method shall be based upon fully developed watershed conditions assuming no effects from the small on-site detention facilities for maintaining the rate of runoff as if the property was developed as single-family residential use. The detention effects of large regional detention facilities can be taken into account in unit hydrograph methods.

Circumstances that may require the use of a unit hydrograph method include sizing open channels, reclaiming floodplains, creating lakes, or building other types of drainage-related facilities on major drainage courses. Design engineers of these types of facilities should be aware that the requirement of designing for fully developed watershed conditions will mean that they will have to calculate these fully developed flows instead of using the flows calculated in the Federal Emergency Management Agency’s (FEMA) flood insurance studies for Overton or Rusk/Smith County.

204.3

Design storm frequencies.

The approved drainage system shall provide for positive overflow at all low points. The term “positive overflow” means that when the inlets do not function properly or when the design capacity of the conduit is exceeded, the excess flow can be conveyed overland along a grassed or paved course. Normally, this would mean along a street or alley, or shall require the dedications of special drainage easements on private property.

DRAINAGE FACILITY	DESIGN RECURRENCE INTERVAL
Closed Storm Sewer Systems	10-year with 100-year positive overflow in streets such that the depth of flow in the street does not exceed the top of curb.
Closed Storm Sewer Systems and Inlets at Street Low Point or Sag	100-year with positive overflow
Culverts and Bridges	100-year
Concrete-lined Channels	100-year
Earthen Channels	100-year

204.4

Street and alley capacity.

The depth of flow in the streets shall not exceed the top of curb for the one-hundred-year storm.

The flows created by the one-hundred-year storm shall be contained within the capacity of all paved alleys.

The first-floor elevations of all residential and other structures shall be set at a minimum elevation of one (1) foot above the top of the street curb elevation or the alley invert, and with positive drainage provided away from the structure. Positive overflow sections shall provide a minimum of one (1) foot of freeboard from the overflow invert adjacent to structures and the corresponding first floor elevation of all residential and other structures.

204.5

Inlet placement and capacity.

Storm sewer inlets shall be built along paved streets at such intervals that the depth of flow, based upon the one-hundred-year storm, does not exceed the top of curb. Inlets shall be located as necessary to remove the flow based on a ten-year storm. If in the opinion of the City Engineer the flow in the gutters would be excessive using the above design criteria, the storm sewers or inlet locations could be altered to relieve adverse conditions.

Inlets shall be placed upstream from an intersection whenever possible. At any intersection, only one (1) street shall be crossed with surface drainage and this street shall be the lower classified street. When an alley intersects a street, inlets shall be placed in the alley whenever flow down that alley would cause the capacity of the intersecting street to be exceeded.

The minimum inlet size shall be five (5) feet. No more than twenty (20) feet of inlet shall be placed along one (1) gutter at any given location. Minimum sizes of laterals shall be eighteen (18) inches for use with five-foot inlets, twenty-one-inch laterals with ten-foot, fourteen-foot, and drop inlets and twenty-four-inch laterals for twenty-foot inlets. Where laterals tie into trunk lines, place the laterals on a sixty-degree angle with the trunk line and connect them so that the longitudinal centers intersect.

204.6

Pipe design standards.

Storm sewer conduit shall be sized to flow full. Manning’s Equation shall be used to determine the conduit size.

Minimum and Maximum Velocities in Pipes.

The minimum velocities in conduit shall be two and one-half (2.5) feet per second.

Maximum velocity in the pipe shall not exceed twelve (12) feet per second.

The maximum discharge velocities in the pipe shall also not exceed the permitted velocity of the receiving channel or conduit at the outfall to prevent erosive conditions. The maximum outfall velocity of a conduit in partial flow shall be computed for partial depth and shall not exceed the maximum permissible velocity of the receiving channel unless controlled by an appropriate energy dissipater (e.g. stilling basins, impact basins, riprap protection).

In general, storm water shall be carried in concrete pipe conduit, but other types of conduit can be used to carry storm water. However, prior permission to use other conduit materials must be obtained from the City Engineer.

Hydraulic Gradient.

Conduits must be sized, and slopes must be set such that runoff flows smoothly down the drainage system. To insure this smooth passage, the hydraulic gradient must be at the proper elevations. The hydraulic grade line shall be established and shown on the plans for all storm sewer design.

The hydraulic grade line shall in no case be closer to the surface of the ground or street than one (1) foot.

Hydraulic gradient calculations shall account for all head losses that may occur in the storm sewer line. Friction head loss shall be determined by direct application of Manning’s Equation. Minor losses due to turbulence at structures shall be determined using Appendix C - Minor Head Losses of this section.

204.7

Culvert design.

One (1) foot of freeboard is required between the one-hundred-year water surface elevation and the top of curb elevation. Exceptions must be approved in writing by the City Engineer.

Culverts must be designed using standard methods and engineering judgment. Culverts shall be designed in accordance with the latest edition of the Texas Department of Transportation (TxDOT) Hydraulic Design Manual. Standards of the City of Overton will take precedence over TxDOT Manual in cases of conflict.

Culvert hydraulic grade line calculations shall consider both inlet and outlet control.

Culverts shall be skewed such that impacts due to the flood and normal flow angles of attack on the structure are minimized.

The maximum velocity through a culvert shall be fifteen (15) feet per second.

Stream stability shall be assessed when determining the number of barrels, height and width and culvert skew. Potential for scour shall be accounted for in the design.

204.8

Bridges.

Two (2) feet of freeboard is required between the one-hundred-year water surface elevation and the low chord of the bridge. Exceptions to this requirement must be approved by the City Engineer in writing.

The skew of the bridge piers and abutments shall be oriented as close to the normal or flood direction of flow resulting in an angle of attack as close to zero (0) degrees as possible.

Bridges shall be designed using standard methods.

Stream stability shall be assessed when designing the abutments and interior bents of the bridge. Scour shall be accounted for in the design.

204.9

Channels.

Open channels are discouraged in urban areas. Open channels may be used instead of an enclosed system when the pipe size, necessary to carry the design storm event, exceeds the capacity of two- to sixty-inch RCP. Open channels shall not be permitted when two- to sixty-inch RCP pipes will carry the design flow, unless approved by the City Engineer.

Open channel design criteria:

Channels may be left in their natural state provided that the channel velocities are six (6.0) feet per second or less and that one (1) foot of freeboard is available during the design storm event.

If the natural channel is to be replaced by an improved channel, the flow from the one-hundred-year design flood must be contained within the improved channel while allowing for one (1) foot of freeboard.

Improved channels shall be trapezoidal shaped and include a lined section if the design velocity is greater than six (6) feet per second. Lining types such as concrete, rock walls and gabions may be used upon approval of the City Engineer. The maximum velocity allowed in concrete-lined channels is fifteen (15) feet per second.

Unless shown to be feasible in a soils report sealed by a licensed professional engineer in the State of Texas and approved by the City Engineer, improved channels shall have minimum side slopes of:

Four (4) feet horizontal to one (1) foot vertical for earthen, grassed-lined side slopes.

One and one-half (1.5) feet horizontal to one (1) foot vertical for concrete-lined side slopes in rock.

Where practicable, all unpaved channels should have sufficient grade to avoid ponding during backwater flow conditions. A minimum slope of 0.40 percent is required for earthen channels and swales, except those used as part of a wetlands area.

The developer or owner shall use low maintenance vegetation for vegetative cover, as approved by the City Engineer prior to planting. The selection of materials shall comply with the current ground cover listing for North Central Texas furnished through the Texas Agricultural Extension Service.

Manning’s equation can be used to design channels and determine water surface elevations and velocities when backwater effects are negligible. Channels where backwater effects occur must be designed using models accepted by FEMA.

All channel sections must consider and account for channel stabilization in their design. This requirement pertains to all sections whether they are left in their natural condition or are modified in any manner. The design of all drainage channels and swales shall assure adequate capacity and minimum maintenance to overcome the result of erosion, silting, sloughing of bends or similar occurrences.

When performing hydraulic analyses for channel or drainageway design, the starting water surface shall be based on the following criteria:

When the ratio of the drainage area of the receiving creek (at the confluence location) to the drainage area of the channel or drainageway being designed is fifteen (15) or greater, the ten-year water surface of the receiving creek shall be used as the starting water surface for hydraulic design calculations. For creeks where the ten-year water surface is not available, the slope-area method will be used for starting design calculations.

When the ratio of the drainage area is less than fifteen (15), the one-hundred-year elevation on the receiving creek shall be used as the starting water surface for design calculations.

204.10

Detention design.

Detention/retention facilities shall be designed for the one-hundred-year design flood according to the following criteria:

Dedicated detention/retention basins shall also include an additional one (1) foot of freeboard and two (2) feet of sediment storage. The volume of runoff storage for drainage areas greater than two hundred (200) acres shall be computed using unit hydrograph procedures. Unit hydrograph calculations shall be signed and sealed by an Professional Engineer licensed in the State of Texas.

For drainage areas less than two hundred (200) acres, the above methods are recommended; however, an approximate routing method based on the rational formula is allowable.

All detention facilities designed shall consider the timing of the flood peak in the main channel into which the detention facility drains. Delaying the peak from a site in lower portions of a watershed may result in a higher peak on the main channel.

A detention facility shall have enough gradient to ensure positive drainage to the outlet structures so as to avoid nuisance conditions such as standing water, odors, insects, and weeds. A minimum slope of 0.40 percent towards the outlet structure is required for all detention facilities.

Detention areas in parking lots shall not be:

In required parking spaces but in extra spaces.

Behind speed bumps unless the speed bumps are made with reinforced concrete.

Deeper than six (6) inches unless otherwise approved by the City Engineer and warning signs shall be posted.

Drainage easements shall be provided for all regional detention/retention facilities and for other detention/retention facilities where two (2) or more owners are involved.

Detention facilities shall be designed to empty in less than twenty-four (24) hours, unless it is also serving as an erosion control facility.

Detention facilities used as a sediment control device shall meet the following requirements:

The sediment control facility shall be designed with minimal velocities such that sediment is dropped and not picked up by flows at any time during the storm event.

The basin shall be designed with adequate sediment storage area so that sediment removal is not required more than twice a year. Expected removal periods greater than twice a year must be specified in the maintenance plan and approved by the City Engineer.

Sediment control facilities cannot be used to meet detention requirements unless the volume of sediment is included in the calculations for the detention basin design.

The owner shall maintain detention/retention facilities unless the facilities are dedicated to the City of Overton. The following measures are required to ensure the facility functions properly.

Facilities should be mowed at least twice a year to control weeds and discourage woody growth.

Debris, litter and accumulated sediment should be removed from detention facilities at least twice a year. Particular attention should be given to removal of debris, litter and sediment around outlet structures.