(A) Applicability. This section applies to a proposed development that creates a net increase in impervious area of at least 4,000 square feet, and that elects not to participate or is not eligible to participate in the RSWMP.
(B) Level of service. Standard storm water detention shall mitigate peak flow rates to predevelopment or existing development conditions.
(C) Maximum outflow rate. The maximum allowable outflow rate from the detention facility must be restricted to the flow rate from the undeveloped or existing development tract for the five-, 25- and 100-year frequency. The timing of the hydrograph released from the detention facility must be checked against the timing of the flow rate in the first open watercourse to prevent any increase in the peak flow rate in the receiving watercourse. For detention basins constructed in line on an existing watercourse, the creation of the basin shall not increase flood elevations in the channel upstream of the new development boundaries.
Design Factor | Standard |
Ground cover area | 3 inches of mature mulch recommended |
Hydrologic design | Determined by state or local agency |
In situ soil | Infiltration rate = 0.5 inches/hour without underdrains Infiltration rate = 0.5 inches/hour underdrain required |
Inlet and outlet controls | Non-erosive flow velocities |
Maintenance | Routine landscape maintenance |
Plant materials | Native species, minimum three species |
Planting soil | Depth = 4 feet. Soil mixtures include sand, loamy sand and sandy loam. Clay content = 10% |
Ponding area | Typically limited to a depth of 6 inches |
Pretreatment area | Required where a significant volume of debris or suspended material is anticipated, such as parking lots and commercial areas. Grass buffer strip or vegetated swale are commonly used pretreatment devices |
(D) On-site detention. On-site detention facilities must be privately owned and shall be maintained as required by § 153.0980 of this chapter. A maintenance schedule shall be approved by the Code Enforcement Officer prior to approval of construction plans.
Source: Low-Impact Development Design Strategies: An Integrated Design Approach (Washington, DC: United States Environmental Protection Agency, January 2000).
(Ord. 3020, passed 9-10-2013, § 5.22.11)