The developer shall obtain a permit from the city before any grading activities within the city or excavating within a watercourse; constructing, altering, or relocating a watercourse; altering any embankment within a watercourse; depositing or removing any material within a watercourse; constructing, altering or removing any structure within a watercourse; or planting or removing any vegetation within a watercourse. An application for a permit shall be accompanied by the payment of a fee in accordance with the duly adopted schedule of fees.

(Ord. No. 00-11, § 3, 3-20-00; Ord. No. 2011-14, § 3(Exh. C), 3-21-11)

(a)

Public improvement permit required. A person commits an offense if he constructs, alters or removes any public storm water improvement without a permit for the work from the city.

(b)

Application procedures. The developer shall submit an application for the permit on standard forms provided by the city. The application shall be accompanied by three complete sets of proposed construction documents. Such plans and one set of construction cost estimates shall bear the seal of an engineer registered in the state and shall be prepared in accordance with the latest city standards.

(c)

Issuance and fees. A permit for construction, alteration or removal of public improvements can be issued upon approval of the engineered documents and cost estimates for the work and payment of a plan checking and inspection fee in accordance with the duly adopted schedule of fees.

(d)

Construction documents.

(1)

Storm drainage construction plans. The developer shall submit storm drainage plans as part of a complete construction document package showing the information specified as follows:

a.

A plan and profile of proposed storm sewers or channels, showing hydraulic data, pipe grades and sizes, manholes, inlets, pipe connections, outlet structures, etc., in conformance with the criteria established in this article. All plans shall show existing and proposed topography with a minimum of two contour lines with at least one-foot intervals and all existing public improvements (streets, sewer, water, etc.) and public easements. Existing and proposed private improvements shall be shown including but not limited to building foundations, patios, decks, swimming pools, drives, parking lots, walks, landscape areas, etc. Surveyed spot elevations within the property shall be provided in a grid pattern with a maximum distance of 25 feet between points and along the property line at intervals of 25 feet. No elevations changes shall occur around the perimeter of the property.

Each plan shall show the seal and signature of an engineer registered in the state who prepared the plans. Each sheet shall include north point, scale (minimum engineering scale one inch to 40 feet), date and benchmark description to sea level datum. All elevations must be referenced to the datum used for the effective Flood Insurance Rate Maps published by the Federal Emergency Management Agency.

b.

A general location map of the tract showing the entire watershed (a USGS quadrangle is satisfactory).

c.

Calculations showing the anticipated stormwater flow, including watershed area, runoff coefficient and time of concentrations shall be included on the plans and submitted showing basis for design of all improvements. Drainage areas shall be clearly delineated on a drainage map.

d.

Detailed plans for any bridges, culverts, catchbasins, any other drainage structures, or any other improvements to be made. Hydraulic grade lines shall be shown on profiles and computations shall be included on the plans.

e.

Upon completion of construction, the developer must submit an as-built plan set to the city to verify the construction was completed in accordance with the approved plans. The city will not issue a certificate of occupancy after the completion of construction until an as-built plan has been submitted and approved by the city.

(2)

Design summary. The developer shall submit a separate report entitled "Engineering Design Summary" with final plans and specifications for construction of public improvements, and shall summarize calculations and such other engineering information pertaining to the major items of design significance as may be necessary in the city's review of the plans and specifications to determine whether the facilities proposed for construction have been designed in accordance with the intent of the city's design criteria. Calculations shall include drainage facilities, water demand, sewage flows and any others considered necessary by the city.

(3)

Format.

a.

The developer shall submit all improvement plans to the city on sheets 24 inches by 36 inches. A binding margin shall be provided of not less than one and one-half inches on the left side of the sheet and margins not less than one-half inch on the three other sides. Other media may be accepted if approved by the city prior to submission.

b.

Upon approval by the city and by the county flood control district (if required), of the engineering plans and conditional approval of the final subdivision plat, the developer will be issued a permit to construct public improvements.

c.

Upon completion of the required public improvements, the developer's engineer registered in the state shall present to the city as-built plans for all paving, drainage structure, storm drains, water lines and sewer lines within 30 days of the completion of each contract. The engineer registered in the state shall confirm in writing that the as-built plans are in fact true representations of the actual construction.

d.

The city shall not accept ownership or maintenance of any public improvements until the developer submits all final plats, all as-built plans and a one-year maintenance bond relating to the project to the city.

(Ord. No. 00-11, § 3, 3-20-00; Ord. No. 2011-14, § 3(Exh. C), 3-21-11; Ord. No. 2020-30, § 2(Exh. A), 12-21-20)

The developer shall design and construct drainage facilities in accordance with this article. The following design criteria are the city's minimum methods and standards. Other hydrologic and hydraulic design methods may be used to satisfy drainage requirements with prior approval of the city:

(1)

Channel design. The developer shall design all channels in accordance with county flood control district criteria and shall have such designs approved by the Harris County Flood Control District (HCFCD) and by the city's public works department and floodplain administrator.

(2)

Discharge points. The developer shall terminate all drainage improvements at a discharge point approved by the HCFCD.

(3)

Public streets as drainage facilities. The maximum depth of water to be allowed in local streets at a two-year design flow shall be at the top of the crown, or the top of the curb, whichever is least. The maximum spread of water in collector streets at ten-year design flow shall allow for one clear lane of traffic (12 feet wide). The maximum spread of water in arterial streets at ten-year design flow shall allow for two clear lanes of traffic (24 feet wide).

(4)

Storm drainage systems. The developer shall install an underground storm drain on curb and gutter streets beginning at the point where the calculated stormwater runoff is of such a quantity that it exceeds the height specified above. The developer shall construct the storm drain system from this point to an approved outlet. The developer shall design and construct storm drainage facilities to terminate at an outlet approved by HCFCD.

(5)

Habitable structures. The developer shall provide adequate means for stormwater runoff in excess of the streets' designed storm capacity (i.e., two, ten-year storm) to flow around habitable structures. New habitable structures and additions shall meet or exceed the minimum flood protection elevations as shown in table 14-5.

a.

If adjacent topography rises away from the street, the developer shall provide a grading/drainage plan which shows that all building sites can provide a finished floor elevation:

1.

At least one foot above the top of the curb using the highest point along the portion of such curb fronting the building site; or

2.

At least 18-inches above the top of ditch elevation, using the highest point along the portion of such ditch fronting the building site.

3.

The lowest finished floor elevation shall, at a minimum, meet or exceed the criteria of table 14-5 as determined by the effective flood insurance rate maps and flood insurance studies published by the Federal Emergency Management Agency. Areas outside of the FEMA regulatory floodplain limits shall, at a minimum, meet or exceed the criteria of table 14-5. An engineer or surveyor registered with the State of Texas shall provide documentation that this requirement is met. An elevation certificate shall be filed upon completion of the construction and prior to the issuance of a certificate of occupancy.

4.

All residential lots shall be sloped from back-to-front at a minimum grade of one percent.

b.

If adjacent topography falls away from the street, the developer shall provide a grading/drainage plan which shows that all building sites can provide a finished floor elevation at least one foot above the ground elevation along all sides of the building site and, at a minimum, meet or exceed the criteria of table 14-5.

c.

The developer shall design and construct all streets to minimize any fill required to bring building pads into compliance with this chapter.

d.

The lowest finished floor elevations shall meet or exceed the criteria of table 14-5.

e.

Alternate methods of building protection of those above may be accepted by the city upon submittal of detailed, engineered plans.

TABLE 14-5
MINIMUM FLOOD PROTECTION ELEVATION REGULATIONS

See minimum flood elevation protection graphics at Section 14-334.

(6)

Drainage system criteria. Storm drainage shall be by curb and gutter and underground pipe network. Flow velocities shall be between three and eight feet per second in the pipe.

(7)

Bridges and box culverts. The developer shall design and construct bridges and box culverts on all street crossings over all drainageways and floodways in accordance with HCFCD criteria.

(8)

Valley gutters. The developer shall provide concrete valley gutters if the gutter flow must be carried across intersections of curbed streets.

(9)

Public easements required. All public drainage facilities shall be placed in public easements as described in article VI of this chapter.

(Ord. No. 00-11, § 3, 3-20-00; Ord. No. 2011-14, § 3(Exh. C), 3-21-11; Ord. No. 2020-30, § 2(Exh. A), 12-21-20)

(a)

Basis for discharge. The developer shall design drainage improvements for watersheds less than 640 acres based on flood discharges determined from the Rational Formula. The Rational Formula for calculating storm flows is shown in figure 14-10. All outfalls and channels shall be designed in accordance with HCFCD criteria. Drainage areas in excess of 640 acres shall be analyzed in accordance with the HCFCD criteria.

(b)

Determination of time of concentration. The time of concentration may be calculated based on the average runoff velocities shown in table 14-7.

(c)

Storm frequency. Design storm frequencies for storm drainage improvements are shown in table 14-9.

(d)

Underground drainage facility design. The developer shall calculate underground drainage facility (storm drain) capacity by Manning's Formula (table 14-8).

TABLE 14-7
VELOCITY OF RUNOFF

For street or gutter flow, the velocity shall be based on the grade of the street. In the absence of detailed calculation by Manning's Formula for the specific street section, the average velocities shown in table 14-8 may be used.

FIGURE 14-10
THE RATIONAL FORMULA

Q = CIA,

where:

For IDF curves, TxDOT ^[9] uses a formula for approximating the intensity-duration-frequency curve. The formula is

i = b/(t _c +d) ^e ;b0; where:

AEP - annual exceedance probability

TABLE 14-8
AVERAGE VELOCITIES OF RUNOFF

Using the average velocities in table 14-8, the developer shall calculate the time of concentration by the formula shown in figure 14-12 or by other recognized formulas such as the Texas Department of Transportation formulas unless more data is shown on the plans for calculating time of concentration.

TABLE 14-9
DESIGN STORM FREQUENCY

^[10]

FIGURE 14-11
MANNING'S FORMULA

The volume flow in the channel can be calculated as

q= A v = (k_n/n) R_h ⅔ S ^½

Manning's equation can be used to calculate average velocity flow in open channel

v = (k_n/n) R_h⅔S ^½

where

v = cross-sectional mean velocity (ft/s, m/s)

k_n = 1.486 for English units and k_n = 1.0 for SI units

n = Manning coefficient of roughness

R_h= hydraulic radius (ft. m)

S = slope - or gradient - of pipe (ft/ft, m/m)

Hydraulic radius can be expressed as

R_h= A/P_w

where

A = Cross sectional area of flow (ft², m)

P_w= wetted perimeter (ft, m)

• Flow Section Channels- Geometric Relationships

The volume flow in the channel can be calculated as

q = A v = (k_n/n) R_h⅔S ^½

where

q = volume flow (ft³/s, m³/s)

The elevation of the hydraulic gradient of the storm sewer shall be below the elevation of the adjacent street gutter. The developer shall use stormwater pipe sized so that the average velocity in the pipe is between three and eight feet per second. Tail water conditions at the outfall of the system shall be no less than the proposed top of pipe of the receiving system.

FIGURE 14-12
TIME OF CONCENTRATION

Tc = D/(V x 60) Example: If D=100', V=1.2fps, then: Tc=100'/(1.2fps*60) = (100'/72fpm) = 1.39 min. 1.39 min. < 10 min., therefore Tc=10 min.

where:

(1)

All new construction or substantial improvements shall be designed (or modified) and adequately anchored to prevent flotation, collapse or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy; and

(2)

All new construction or substantial improvements shall be constructed by methods and practices that minimize flood damage.

(3)

Storm water flows shall be contained within the property and discharged to a public right-of-way. Acceptable methods to contain flows include use of adequately sized swales, curbs, area inlets, or methods that will contain flows on the development parcel and prevent spill over onto adjacent private property. Fence lines shall be designed to avoid impeding storm water flows within the side lot swales. All swales must be contained within the development parcel unless a recorded easement is provided.

(4)

Storm water flows up to the city's design storm shall not go onto an adjacent private property without a drainage easement recorded at the Harris County Clerk's office. No private agreements between property owners will be allowed unless recorded at the county clerk's office and approved by the city.

(5)

The use of French drains are not permissible as a drainage element to contain and convey flows to public rights-of-way.

(6)

Area drains shall have a minimum grate size of 12 inches by 12 inches and be designed to accommodate the full design storm. Cleanouts shall be provided at all junctions and at every bend.

(7)

For single family residential developments, roof drains may be tied into a storm sewer system. All tie in points shall be identified on the construction plans. A minimum pipe diameter of four inches shall be allowed for one roof drain. A minimum pipe diameter of six inches shall be allowed for up to four roof drains. For all other land uses, roof drains shall be properly sized by a registered engineer or architect. The minimum pipe sizes listed for single family developments shall also be used.

TABLE 14-10
COEFFICIENT OF ROUGHNESS ⁽¹⁾

⁽¹⁾ Coefficient of roughness in accordance with HCFCD criteria, if required.

⁽²⁾ Will vary with straightness of alignment, smoothness of bed and side slopes, and whether channel has light vegetation or is choked with weeds and brush.

(Ord. No. 00-11, § 3, 3-20-00; Ord. No. 2011-14, § 3(Exh. C), 3-21-11; Ord. No. 2020-30, § 2(Exh. A), 12-21-20)

(a)

Permit required.

(1)

No structure or land shall hereafter be located, altered, or have its use changed without full compliance with the terms of this chapter and other applicable regulations.

(2)

A floodplain development permit shall be required to ensure conformance with the provisions of this chapter. This chapter shall apply to all areas of special flood hazard within the jurisdiction of the City.

(3)

The developer shall obtain a floodplain development permit from the city prior to locating, altering, or changing the use of any structure or land within an area of special flood hazard.

(4)

An application for a permit shall be accompanied by the payment of a fee in accordance with the duly adopted schedule of fees.

(5)

This chapter is not intended to repeal, abrogate, or impair any existing easements, covenants or deed restrictions. However, where this chapter and another ordinance, easement, covenant, or deed restriction conflict or overlap, whichever imposes the more stringent restrictions shall prevail.

(b)

Designation of flood hazard zones. The areas of special flood hazard identified by the Federal Emergency Management Agency (FEMA) in the current scientific and engineering report entitled, The Flood Insurance Study (FIS) of Harris County, Texas and Incorporated Areas, dated November 15, 2019 with accompanying Flood Insurance Rate Maps (FIRM) dated November 15, 2019, and any revisions thereto are hereby adopted by reference and declared to be a part of this chapter.

(c)

Designation of the floodplain administrator. The director of public works, or the director's designated agent, is hereby appointed the floodplain administrator to administer and implement the provisions of this chapter and other appropriate sections of 44 CFR (Emergency Management and Assistance - National Flood Insurance Program Regulations) pertaining to floodplain management.

(d)

Duties and responsibilities of the floodplain administrator. Duties and responsibilities of the floodplain administrator shall include, but not be limited to, the following:

(1)

Maintain and hold open for public inspection all records pertaining to the provisions of this chapter.

(2)

Review permit applications to determine whether proposed building sites and projects, including the placement of manufactured homes, will be reasonably safe from flooding.

(3)

Review, approve or deny all applications for [floodplain] development permits required by adoption of this chapter.

(4)

Review permits for proposed development to ensure that all necessary permits have been obtained from those federal, state or local governmental agencies (including but not limited to section 404 of the Federal Water Pollution Control Act Amendments of 1972, 33 USC 1334, and the Endangered Species Act of 1973) from which prior approval is required.

(5)

Determine the flood hazard boundary line, where interpretation is needed as to the exact location of the boundaries of the areas of special flood hazards (for example, where there appears to be a conflict between a mapped boundary and actual field conditions).

(6)

Notify, in riverine situations, adjacent communities and the state coordinating agency (the Texas Water Development Board and the Texas Commission on Environmental Quality), prior to any alteration or relocation of a watercourse, and submit evidence of such notification to the Federal Emergency Management Agency.

(7)

Ensure that the flood-carrying capacity within the altered or relocated portion of any watercourse is maintained.

(8)

Obtain, review and reasonably utilize any base flood elevation data and floodway data available from a federal, state or other source, in order to administer the provisions of the section when base flood elevation data has not been provided in accordance with subsection (b) of this section.

(9)

Require that no new construction, substantial improvements or other development (including fill) shall be permitted within flood hazard zones A1-30 and AE on the city's flood insurance rate maps [FIRM], when a regulatory floodway has not been designated, unless it is demonstrated that the cumulative effect of the proposed development, when combined with all other existing and anticipated development, will not increase the water surface elevations of the base flood by more than one foot at any point in the city, that the proposed development complies with all of the provisions of 44 CFR Chapter 1, Section 65.12, and that the proposed development shall meet the requirements of the Harris County Flood Control District.

(10)

In the interpretation and application of this chapter, all provisions shall be:

a.

Considered as minimum requirements;

b.

Liberally construed in favor of the city; and

c.

Deemed neither to limit nor repeal any other powers granted under State law.

(11)

The degree of flood protection required by this chapter is considered reasonable for regulatory purposes and is based on scientific and engineering considerations. On occasions greater floods can and will occur and flood heights may be increased by man-made or natural causes. This chapter does not imply that land outside the areas of special flood hazards or uses permitted within such areas will be free from flooding or flood damages. This chapter shall not create liability on the part of the city or any official or employee thereof that result from reliance on this chapter or any administrative decision made hereunder.

(e)

Permit procedures for flood hazard zone areas.

(1)

Application for a floodplain development permit shall be presented to the floodplain administrator on forms furnished by the city and may include, but not be limited to, site plans [as described in subsection 14-6(d)] and plans in duplicate drawn to scale showing the location, dimensions and elevation of proposed landscape alterations, existing and proposed structures, including the placement of manufactured homes, and the location of the foregoing in relation to areas of special flood hazard. Additionally, the following information is required:

a.

Elevation (in relation to sea level datum) of the lowest floor (including the basement) of all new and substantially improved structures;

b.

Elevation in relation to mean sea level to which any nonresidential structure shall be floodproofed;

c.

A certificate from an engineer or architect registered in the state that the nonresidential floodproofed structure shall meet the floodproofing criteria of subsection (h)(2) below;

d.

Description of the extent to which any watercourse or natural drainage will be altered or relocated as a result of proposed development; and

e.

Maintain a record of all such information in accordance with subsection (d)(1) above.

(2)

Approval or denial of a floodplain development permit by the city shall be based on all of the provisions of this section and emphasizing the following relevant factors:

a.

The danger to life and property due to flooding or erosion damage;

b.

The susceptibility of the proposed facility and its contents to flood damage and the effect of such damage on the individual owner;

c.

The danger that materials may be swept onto other lands to the injury of others;

d.

The compatibility of the proposed use with existing and anticipated development;

e.

The safety of access to the property in times of flood for ordinary and emergency vehicles;

f.

The costs of providing governmental services during and after flood conditions including maintenance and repair of streets and bridges, and public utilities and facilities such as sewer, gas, electrical and water systems;

g.

The expected heights, velocity, duration, rate of rise and sediment transport of the floodwaters and the effects of wave action, if applicable, expected at the site;

h.

The necessity to the facility of a waterfront location, where applicable;

i.

The availability of alternative locations, not subject to flooding or erosion damage, for the proposed use; and

j.

The relationship of the proposed use to the comprehensive plan for that area.

(f)

Appeal and variance procedures. A developer may appeal the decision of the [floodplain administrator] to the board of adjustment when it is alleged there has been an error in any requirement, decision or determination in the enforcement or administration of this chapter. The procedure for an appeal shall be according to the hardship relief procedures contained in section 14-9. The board of adjustment shall hear and render judgment on a developer's request for variance(s) from the requirements of this chapter. Prerequisites for granting variances are:

(1)

Variances shall only be issued upon a determination that the variance is the minimum necessary, considering the flood hazard, to afford relief.

(2)

Variances shall only be issued upon showing a good and sufficient cause, a determination that failure to grant the variance would result in exceptional hardship to the applicant and a determination that the granting of a variance will not result in increased flood heights, additional threats to public safety, extraordinary public expense, create nuisances, cause fraud on or victimization of the public, or conflict with existing local laws or ordinances.

(3)

Variances may be granted by the city for new construction and substantial improvements and for other development necessary for the conduct of a functionally dependent use, provided that the criteria outlined in subsection (e)(2) above, and this subsection are met, and the structure or other development is protected by methods that minimize flood damages during the base flood and 500-year storm and create no additional threats to public safety.

(4)

Variances may be issued for new construction and substantial improvements to be erected on a lot of one-half acre or less in size contiguous to and surrounded by lots with existing structures constructed below the base flood level, providing the relevant factors in subsection (e)(2) above, has been fully considered. As the lot size increase beyond the one-half acre, the technical justification required for issuing the variance increases.

(5)

Variances shall not be issued within any designated floodway.

(6)

Other variance provisions.

a.

The floodplain administrator shall maintain a record of all actions involving an appeal and shall report variances to the Federal Emergency Management Agency upon request.

b.

Variances may be issued for the reconstruction, rehabilitation or restoration of structures listed on the National Register of Historic Places or the State Inventory of Historic Places, without regard to the procedures set forth in the remainder of this chapter.

c.

Upon consideration of the factors noted above and the intent of this chapter, the appeal board may attach such conditions to the granting of variances as it deems necessary to further the purpose and objectives of this chapter.

d.

Variances may be issued for the repair or rehabilitation of historic structures upon a determination that the proposed repair or rehabilitation will not preclude the structure's continued designation as a historic structure and the variance is the minimum necessary to preserve the historic character and design of the structure.

(g)

General standards for flood hazard reduction. In all areas of special flood hazards the following provisions are required for all new construction and substantial improvements:

(1)

All new construction or substantial improvements shall be designed (or modified) and adequately anchored to prevent flotation, collapse or lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy;

(2)

All new construction or substantial improvements shall be constructed by methods and practices that minimize flood damage;

(3)

All new construction or substantial improvements shall be constructed with materials resistant to flood damage. FEMA Bulletins 1-93, 2-93, and 3-93 or subsequent revisions will serve as the guideline for this requirement;

(4)

All new construction or substantial improvements shall be constructed with electrical, heating, ventilation, plumbing and air conditioning equipment and other service facilities that are designed and/or located so as to prevent water from entering or accumulating within the components during conditions of flooding;

(5)

All new and replacement water supply systems shall be designed to minimize or eliminate infiltration of floodwaters into the system;

(6)

New and replacement sanitary sewage systems shall be designed to minimize or eliminate infiltration of floodwaters into the system and discharge from the systems into floodwaters; and

(7)

On-site waste disposal systems shall be located to avoid impairment to them or contamination from them during flooding.

(8)

All new construction or substantial improvements shall obtain approval of an elevation certificate verifying that the finish floor elevation meets or exceeds the criteria of table 14-5.

(9)

If any substantial improvement including the reconstruction, rehabilitation, addition or other improvement of a habitable structure where the cost of which equals or exceeds 50 percent of the marked value of the structure before "start of construction" occurs, then the entire existing nonconforming building must meet the requirements for new development.

(10)

If a structure is substantially damaged, where the damage of any origin sustained by a structure whereby the cost of restoring the structure to its before damaged conditions would equal or exceed 50 percent of the market value of the structure before the damage occurred, it shall not be reconstructed except in conformity with the provisions of this chapter.

(h)

Specific standards. In all areas of special flood hazards where base flood elevation data has been provided as set forth in subsections (b), (d)(8) and (l)(2) of this section, the following provisions are required:

(1)

Residential construction. New construction and substantial improvement of any residential structure shall have the lowest floor (including the basement), together with the attendant utility and sanitary facilities, and machinery and equipment, elevated so as to meet or exceed the criteria of table 14-5. A land surveyor registered in the state shall submit a certification to the city prior to receiving a development permit that the standard of this subsection is satisfied. No additional fill below the 100-year base flood elevation is permissible, however on-site soils may be used to construct a building pad area as long as there is no loss in the floodplain volume storage. Soil cut and fill quantities shall be provided on the construction plans to for earthwork quantities below the 100-year base flood elevation. Use of pier and beam construction, or stem walls with proper flood openings in the foundation as described in section 14-225(g) is permitted as long as the property shall have no net increase in volume of material on the lot below the base flood elevation, with the exceptions of the small amount of concrete used for construction. A dwelling unit's sanitary drains, such as where the flood level rim of the plumbing fixture is below the DFE, may be placed below the DFE where the building's sanitary sewer is protected with a backflow device.

(2)

Nonresidential construction. New construction and substantial improvements of any commercial, industrial or other nonresidential structure shall either have the lowest floor (including the basement) elevated so as to meet or exceed the criteria of table 14-5 or, together with attendant utility and sanitary facilities, and machinery and equipment, be designed so that below the base flood level the structure is watertight with walls substantially impermeable to the passage of water and with structural components having the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy. An engineer or architect registered in the state shall develop and/or review structural design, specifications and plans for the construction, and shall certify that the design and methods of construction are in accordance with accepted standards of practice as outlined in this subsection. A record of such certification which includes the specific elevation (in relation to mean sea level) to which such structures are floodproofed shall be maintained by the city as part of the permanent development permit file. A FEMA Floodproofing Certificate for Non-Residential Structures be used and approved. No additional fill below the 500-year floodplain elevation is permissible. Soil cut and fill quantities shall be provided on the construction plans to for earthwork quantities below the 500-year floodplain elevation. A building's sanitary drains, such as where the flood level rim of the plumbing fixture is below the DFE, may be placed below the DFE where the building's sanitary sewer is protected with a backflow device.

(3)

Enclosures. New construction and substantial improvements, with fully enclosed areas below the lowest floor that are usable solely for parking of vehicles including detached or attached garages, building access or storage in an area other than a basement and that are subject to flooding shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting this requirement must be certified by an engineer or architect registered in the state that meet or exceed the following minimum criteria:

a.

A minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding shall be provided or the requirements in the National Flood Insurance Program's NFIP Technical Bulletin 1, dated March 2020, or subsequent revisions shall serve as guidelines for this requirement.

b.

The bottom of all openings shall be no higher than one foot above grade.

c.

Openings may be equipped with screens, louvers, valves or other coverings or devices, provided that they permit the automatic entry and exit of floodwaters.

d.

Construction materials shall be resistant to flood damage.

e.

No additional net fill at each lot is permissible with the exception of fill for slab-on-grade foundation forms if located outside of the limits of the 100-year floodplain and minimal fill as determined by the city used to meet the International Residential Code or International Building Code requirements for drainage away from a structure if located outside of the limits of the 100-year floodplain. Soil cut and fill quantities shall be provided on the construction plans for all earthwork activities.

(4)

Manufactured homes.

a.

All manufactured homes to be placed within flood hazard zone A shall be installed using methods and practices which minimize flood damage. For the purpose of this requirement, manufactured homes must be elevated and anchored to resist flotation, collapse or lateral movement. Methods of anchoring may include, but are not limited to, use of over-the-top or frame ties to ground anchors. This requirement is in addition to applicable state and local anchoring requirements for resisting wind forces.

b.

All manufactured homes shall be in compliance with subsection (c)(1) of this section (first floor elevation must meet or exceed the criteria of table 14-5.

c.

All manufactured homes to be placed or substantially improved within flood hazard zones A, and AE on the city's FIRM shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is elevated so as to meet or exceed the criteria of table 14-5; and be securely anchored to an adequately anchored foundation system in accordance with the provisions of subsection (h)(4)a. of this section.

d.

A person commits an offense if he places any manufactured home in the regulatory floodway in other than an existing manufactured home park or manufactured home subdivision.

e.

No additional net fill at each lot is permissible with the exception of fill for slab-on-grade foundation forms if located outside of the limits of the 100-year floodplain and minimal fill as determined by the city used to meet the International Residential Code or International Building Code requirements for drainage away from a structure if located outside of the limits of the 100-year floodplain. Soil cut and fill quantities shall be provided on the construction plans for all earthwork activities.

(i)

Standards for subdivision proposals.

(1)

The developer of subdivisions, including manufactured home parks and subdivisions, shall obtain a development permit (see subsection (a) above) prior to final platting.

(2)

Base flood elevation data shall be generated for subdivision proposals and other proposed development including manufactured home parks and subdivisions which are greater than 50 lots or five acres, whichever is lesser, if not otherwise provided pursuant to subsection (b) of this section, subsection (d)(8) of this section or elsewhere in this article.

(3)

All subdivision proposals, including manufactured home parks and subdivisions, shall have adequate drainage provided to reduce exposure to flood hazards.

(4)

All subdivision proposals, including manufactured home parks and subdivisions, shall have public utilities and facilities (sewer, gas, electrical and water systems) located and constructed to minimize or eliminate flood damage.

(5)

No additional net fill at each lot is permissible with the exception of fill for slab-on-grade foundation forms if located outside of the limits of the 100-year floodplain and minimal fill as determined by the city used to meet the International Residential Code or International Building Code requirements for drainage away from a structure if located outside of the limits of the 100-year floodplain. Soil cut and fill quantities shall be provided on the construction plans for all earthwork activities.

(j)

(Reserved.)

(k)

Floodways. Floodways are located within areas of special flood hazard established in subsection (b) of this section. Since the floodway is an extremely hazardous area due to the velocity of floodwaters which carry debris, potential projectiles and erosion potential, the following provisions shall apply:

(1)

Encroachments are prohibited, including fill, new construction, substantial improvements and other development within the adopted regulatory floodway unless it has been demonstrated through hydrologic and hydraulic analyses performed in accordance with standard engineering practice that the proposed encroachment would not result in any increase in flood levels within the community during the occurrence of the base flood discharge.

(2)

Where subsection (1) of this subsection (k) is satisfied, all new construction and substantial improvements shall comply with all applicable flood hazard reduction provisions of subsections (b), and (g) through (k) of this section.

(Ord. No. 00-11, § 3, 3-20-00; Ord. No. 2007-24, § 1, 6-18-07; Ord. No. 2011-14, § 3(Exh. C), 3-21-11; Ord. No. 2013-46, § 4(Exh. A), 12-16-13; Ord. No. 2014-15, § 1, 5-19-14; Ord. No. 2019-05, § 2, 2-18-19; Ord. No. 2019-21, § 1, 6-17-19; Ord. No. 2019-32, § 1, 8-19-19; Ord. No. 2020-30, § 2(Exh. A), 12-21-20; Ord. No. 2022-41, § 2, 11-21-22)

(a)

Detention required. The developer shall provide stormwater detention according to the standards established in this section for all developments meeting the following criteria:

(1)

In any nonresidential development;

(2)

In any residential development greater than one acres, except a single-family residential structure and accessory buildings proposed on an existing lot.

(b)

Definitions.

Detention basin. A facility that provides for temporary storage of stormwater runoff and controlled release of this runoff during and after a flood or storm.

(c)

Detention facilities design. The developer shall design the maximum storage to be provided in a detention basin based on the runoff from the 100-year storm event with a 24-hour rainfall depth and reservoir routing methods. The developer shall calculate detention storage using the following hydrograph method:

(1)

Types of storage facilities. Detention ponds may be either on-stream or off-stream facilities. An on-stream pond is defined as one that is located on a Harris County Flood Control District ("HCFCD") or Texas Department of Transportation ("TxDOT") ditch and receives runoff from areas significantly larger than the development project under design. An off-stream pond generally receives runoff from a small drainage area consisting primarily of one development project. In the following regulations, the design methods presented are generally oriented to off-stream detention facilities. Specific reference will be made to methods for on-stream facilities.

(2)

Design consideration. The developer shall design a gravity detention pond according to the following steps:

a.

Determine a design inflow hydrograph for the proposed detention pond.

b.

Determine the maximum allowable outflow rate from the detention pond.

c.

Determine the design tailwater elevation at the downstream end of the outflow structure and the maximum water elevation in the pond.

d.

Determine the preliminary sizing of the pond storage capacity and the outflow structure.

e.

Determine that the maximum allowable outflow rate is not exceeded by routing a design inflow hydrograph through the pond with adjustment of storage and outflow structure, as required.

f.

Insure that these systems will operate properly under design water surface conditions in the pond. Analysis of the hydraulic gradients for storm sewers and inflow channels entering the pond.

g.

Analyze rainfall events in excess of the design frequency for structural and flood considerations, including provisions for an emergency spillway or overflow structure.

h.

Define any potential geotechnical and structural problems.

(3)

Geotechnical design. The developer shall submit to the city a detailed soils investigation by a geotechnical engineer registered in the State of Texas prior to initiating final design of a detention pond.

At a minimum, the soils investigation shall address:

a.

The ground water conditions at the proposed site.

b.

The type of material to be excavated from the pond site and its suitability for fill material.

c.

If a dam is to be constructed, adequate investigation of potential seepage problems through the dam and attendant control requirements, the availability of suitable embankment material and the stability requirements for the dam itself.

d.

Potential for structural movement on areas adjacent to the pond due to the induced loads from existing or proposed structures and methods of control that may be required.

e.

Stability of the pond side slopes.

(4)

Hydraulic design for drainage areas greater than one acre. For draining of areas greater than one acre, no detailed determination of the inflow hydrograph is required. The maximum allowable outflow rate shall be based on the 100-year, undeveloped runoff from the site and is determined as follows:

Q _MAX = 1.2 A

Where Q is the maximum outflow rate in cubic feet per second and A is the drainage area in acres. For ponds discharging into a roadside ditch or storm sewer, the maximum outflow rate should be restricted to the three-year frequency runoff from the undeveloped site. The allowable undeveloped outflow rate is:

Q _MAX = 0.5 A

The required storage volume, S, of a detention pond for either of the outfall conditions discussed above is a function of the drainage area and determined by:

S = 0.55A

Where A is the drainage area in acres, no further hydrologic design is required.

(5)

Hydrologic design for drainage areas greater than 50 acres. For drainage areas greater than 50 acres, the small watershed method procedure is recommended for use in accordance with the procedures described in Section 3 - Hydrology of the Policy Criteria and Procedure Manual, dated October 2004 and subsequent revisions for the Design of Flood Control and Drainage Facilities, Harris County Flood Control District. Please note areas updated for Atlas 14, per HCFCD.

In the small watershed method, the maximum inflow rate and the volume of runoff to the detention facility shall be determined. With the peak flow and volume of runoff determined, an inflow hydrograph may be developed.

The maximum allowable outflow rate shall be restricted to the flow rate from the undeveloped tract. Design inflow hydrographs and maximum allowable outflow rates shall be determined for both the 100-year and 10-year frequency, except in cases where the receiving stream has less than 100-year frequency capacity. In such cases, the maximum allowable outflow rate shall be limited to the flow from the undeveloped tract for the return period which produces bankfull capacity in the outflow channel. Otherwise, the detention facility could aggravate downstream flooding.

(6)

On-stream detention ponds. The developer shall complete a routing study for the design of an on-stream detention pond such as a TxDOT ditch or a HCFCD ditch to develop the design inflow hydrograph and the maximum allowable outflow rate. The specific procedures and assumptions to be used shall be approved by TxDOT, HCFCD and the city prior to initiating design.

(7)

Hydraulic design. The developer shall complete the hydraulic design of a detention pond according to the following:

a.

Determine the preliminary sizing of pond storage and outflow structure.

b.

Determine the design tailwater elevation at the downstream end of the outflow structure and maximum water deviation in the pond.

c.

Verify that the storage and outflow rate is not exceeded by routing of design inflow hydrograph through the pond with adjustments as necessary.

d.

Ensure that the systems operate properly under design water surface conditions in the pond by analyzing of the hydraulic gradients for any storm sewers and inflow channels entering the pond.

e.

Analyze rainfall events in excess of the design frequency for structural and flood considerations.

(8)

Storage requirements. The developer shall determine preliminary sizing of the storage volume requirements by plotting the computed inflow hydrograph and a straight line from the origin to the maximum allowable outflow rate on the recession side of the inflow hydrograph, then plan metering the resulting area under the inflow hydrograph above the straight line.

The outflow structure may be sized as follows:

a.

Determine the maximum allowable water surface elevation in the pond for the 100-year frequency inflow hydrograph.

b.

Determine the maximum flow line elevation for the outflow structure.

c.

Estimate the size of the structure required to pass the allowable outflow rate based on the difference in elevation between the 100-year water level in the pond and the top of pipe.

d.

Estimate the size of overflow spillway required to pass the 100-year flow.

Once the preliminary storage and outflow structure have been determined, routing of the inflow hydrograph through the pond shall be performed.

As required input to the reservoir procedure, plots of stage (water surface elevation) versus storage and outflow must be determined. The maximum or 100-year water surface elevation in the pond shall be based on local topography or the 100-year water surface in the outfall channel. Also, of prime consideration in developing the stage-outflow curve is the downstream water surface elevation (tailwater) on the outflow structure. This tailwater elevation may affect the discharge capacity of the outflow structure and must be considered in determining the outflow versus stage relationship.

There are two tailwater conditions which may be applied to detention pond routing: a constant tailwater elevation or tailwater elevations varying with time. Routing a hydrograph through a detention pond should incorporate the effect of the variable tailwater on the outflow. In most cases development of a storm hydrograph in the outfall channel would require extensive watershed modeling.

For drainage areas greater than 50 acres, a constant tailwater elevation for determining the stage-versus-outflow relationship is acceptable. The developer shall use a tailwater elevation either two feet below the 100-year water surface in the detention pond or the 100-year water surface in the channel, whichever is lower.

Once the inflow hydrograph is routed through the pond, the resulting outflow rate shall be compared to the maximum allowable rate. Adjustments in the storage volume and the outflow structure size shall then be made as required to insure that the maximum outflow rate is not exceeded and that the resulting outflow rate is not significantly smaller than required. This process may require several iterations to determine the required storage volume and the outflow structure size. The minimum outflow pipe size shall be 12 inches.

Once the pond has been sized and the outflow structure determined for the 100-year frequency, the resulting maximum ten-year water surface elevation in the pond shall be determined by routing the ten-year inflow hydrograph through the pond. The developer shall use the ten-year water surface in the outfall channel as the constant tailwater elevation for determining the stage-versus-outflow relationship.

Storm events in excess of the 100-year event must be considered in the design of detention facilities from the standpoint of overtopping. For a detention facility which is an excavated pond and has no dam associated with it, the outflow structure shall be designed with an overflow structure or swale.

For ponds which require a dam, the possibility of dam failure due to overtopping of the dam embankment must be considered. Downstream flood damage and loss of life must be evaluated and, if a significant hazard exists, the dam must be adequately designed to prevent such hazards. Specific dam criteria for storm events with frequencies in excess of the 100-year frequency shall be established by the city on a case-by-case basis. These criteria should be established in the preliminary design phase.

The use of hydrograph timing as a substitution for detention on any project is prohibited.

(9)

Pump systems. Where it is determined that a pump system is necessary, approval by the city of the preliminary conceptual design shall be obtained before any detailed engineering is performed.

The city shall not approve the use of pump-type detention systems for private use except under the following conditions:

a.

A gravity system is not feasible from an engineering and economic standpoint;

b.

At least two pumps are provided, each of which is sized to pump the design flow rate, if a triplex system is used, any two of the three pumps must be capable of pumping the design flow rate;

c.

The selected design outflow rate must not aggravate downstream flooding (Example: A pump system designed to discharge at the existing 100-year flow rate each time the system comes on-line could aggravate flooding for more frequent storm events.);

d.

Fencing of the control panel is provided to prevent unauthorized operation and vandalism;

e.

Adequate assurance is provided that the system will be operated and maintained on a continuous basis;

f.

No public drainage can be tied to a permanent pumped detention facility;

g.

An emergency source of power is provided; or

h.

Detention facilities which utilize pumps shall be designed in such a way that should the pump fail, the detention pond will not overflow onto adjacent property. All overflow must be retained on site.

(10)

Erosion control. The developer shall provide adequate erosion control and re-vegetation during and following construction of the pond.

(11)

Safety, aesthetic consideration and multi-purpose use. Detention ponds may be utilized as private parks and recreational facilities on a case-by-case basis. Also, a parking area may be used for a portion of the storage as long as the 100-year water depth is six inches or less where cars are parked. The proposed use and the facilities to be constructed within the pond area must be specifically approved by the city.

(d)

Other standards. For additional details regarding design and construction of stormwater detention facilities refer to Sections 3, 4, and 5 of the Criteria Manual for the Design of Flood Control and Drainage Facilities in Harris County, published by the Harris County Flood Control District and adopted by Harris County Commissioners Court in October 2018. Other methods of design may be used upon prior written approval from the city engineer.

(Ord. No. 00-20, § 1, 6-19-00; Ord. No. 2010-44, § 1, 10-18-10; Ord. No. 2011-14, § 3(Exh. C), 3-21-11; Ord. No. 2019-05, § 2, 2-18-19; Ord. No. 2020-30, § 2(Exh. A), 12-21-20)