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For developments which are larger than 50 acres, Harris county Flood Control District and/or the City <br />Engineer shall approve the detention facility criteria, however, a minimum detention storage rate of 0.55 <br />acre-ft/acre will be required. <br /> <br />5.2.2 Outlet Sizing <br /> <br />1. The outlet structure shall be designed using the orifice equation as follows: <br /> <br />½ <br /> Q = CA x (2gh) <br /> Where, <br /> C = 0.8 <br /> A = cross sectional area <br /> g = 32.2 feet / sec^2 <br /> h = head differential <br /> <br />For head differential use 2’ or the 100-year water surface in pond minus the 25-year <br />water surface in receiving channel, if available. <br /> <br />2. Minimum restrictor shall be 6” diameter. <br /> <br />5.5.3 Additional Standards for Detention Basins <br /> <br />The detention facility shall be designed for easy maintenance. For smaller developments the designer is <br />encouraged to use parking lots, underground piping, swales, green spaces, etc. to achieve the volume <br />required. <br /> <br />For larger developments every consideration shall be given to designing of the facility for multipurpose <br />use, such as playgrounds, ballfields, miniparks, required green spaces, etc. to assure that maintenance will <br />be accomplished. The design shall include the following: <br /> <br />1. an earthen detention basin shall have minimum side slopes of 4:1 and a minimum bottom width <br />of ten feet; <br />2. the bottom of the detention basin shall have a minimum 0.50% cross slope to facilitate quick <br />drainage. <br />3. a v-shaped trickle channel a minimum of 5’ wide, six-inch thick, reinforced concrete shall be <br />constructed through the detention basin at a longitudinal slope of 0.20% to accommodate low flow <br />and facilitate rapid drainage. For developments less than 3 acres, the trickle channel may be 2 feet <br />wide and 4” thick. <br />4. a minimum 12-foot wide maintenance berm shall be provided around the perimeter of the <br />detention facility. <br />5. ingress and egress for maintenance including a dedicated right-of-way if required, shall be <br />provided to the detention basin and clearly shown on the construction drawings or site plan <br />subdivision plat. <br />6. the detention basins, slopes, bottom, maintenance berm, and other associated right-of-way shall <br />be final graded with a minimum of 6” top soil then hydro-mulch or drill-seeded and watered to <br />facilitate full grass coverage. <br />7. parties responsible for maintenance of the detention facility must be shown on the plat and or <br />plans. <br />8. Pumped detention systems may be allowed with specific approval from the City Engineer. <br /> <br />5.5.4 Ownership and Maintenance of Facilities <br /> <br />The City will not accept maintenance of on site facilities that serve only one tract or development, unless it <br />is determined to have other public benefits, is recommended by staff and approved by the Planning and <br />Zoning Commission. <br /> <br />Stormwater Criteria Page 5 of 10 <br /> <br />