R-1999-31 - Laserfiche WebLink

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e e For developments, which are larger than 50 acres, Harris County Flood Control District and the City Engineer shall approve the detention facility criteria. 5.5.2 {}utlet Sizing 1. The outlet structure shall be designed using the orifice equation as follows: Q = CA X (2ghi12 Where, C=0.8 A = cross sectional area g = 32.2 feet / sec2 h = head differential For head differential use 2' or the 100-year water swface in pond minus the 25-year water surface in receiving channel, if available. 2. Minimum restrictor shall be 6" diameter. 5.5.3 Additional Standards For Detention Basins The detention facility shall be designed for easy maintenance. For smaller developments the designer is encouraged to use parking lots, underground piping, swales, greenspaces, etc. to achieve the volume required. For larger developments every consideration shall be given to designing of the facility for multipurpose use, such as playgrounds, ballfields, miniparks, required greenspace, etc., to assure that maintenance will be accomplished. The design shall include the following: I. an earthen detention basin shall have minimum side slopes of 4:1 and a minimum bottom width of ten feet; 2. the bottom of the detention basin shall have a minimum 0.50% cross slope to facilitate quick drainage. 3. a v-shaped trickle channel a minimum of 5' wide, six-inch thick, reinforced concrete shall be constructed through the detention basin at a longitudinal slope of 0.20% to accommodate low flow and facilitate rapid drainage. For developments less than 3 acres, the trickle channel may be 2 feet wide and 4" thick. 4. a minimum 12-foot wide maintenance berm shall be provided around the perimeter of the detention facility. 5. ingress and egress for maintenance including a dedicated right-of-way if required, shall be provided to the detention basin and clearly shown on the construction drawings or site plan and subdivision plat. Stonnwater Criteria 6 of 12