(A) Applicability. Applications for subdivision plat or site plan approval shall provide an analysis of low-impact development design practices to accommodate the storm water level of service established in § 153.1037 of this chapter. These practices shall be included as a condition of subdivision and site plan approval.
(B) Generally. At least 20% of the storm water design event established in §§ 153.1035 through 153.1053 of this chapter shall be treated through low-impact, storm-water management, integrated management practices (IMPs) and design features that are consistent with the practices described in Low-Impact Development Design Strategies: An Integrated Design Approach and Low-Impact Development Hydrologic Analysis, which are incorporated by reference and are referred to as the “LID Manuals” (Figure 153.1045(A) below) and this section.
(C) Integrated management practices. IMPs shall comply with the design standards described in Table 153.1045(A) below.
Sources: Low-Impact Development Design Strategies: An Integrated Design Approach
(Washington, DC: United States Environmental Protection Agency, January 2000); Low-Impact Development Hydrologic Analysis (Washington, DC: United States Environmental Protection Agency, January 2000)
Design Factor | Bioretention | Dry Well | Filter/Buffer Strip | Grass Swales and Level Spreaders | Infiltration Trench |
Design Factor | Bioretention | Dry Well | Filter/Buffer Strip | Grass Swales and Level Spreaders | Infiltration Trench |
Maintenance | Low requirement, property owner can include in normal site landscape maintenance | Low requirement | Low requirement, routine landscape maintenance | Low requirement, routine landscape maintenance | Moderate to high |
Maximum depth | 2- to 4-foot depth depending on soil type | 6- to 10-foot depth depending on soil type | Not applicable | Not applicable | 6- to 10-foot depth depending on soil type |
Proximity to build foundations | Minimum distance of 10 feet down gradient from buildings and foundations recommended | Minimum distance of 10 feet down gradient from buildings and foundations recommended | Minimum distance of 10 feet down gradient from buildings and foundations recommended | Minimum distance of 10 feet down gradient from buildings and foundations recommended | Minimum distance of 10 feet down gradient from buildings and foundations recommended |
Slopes | Not a limitation, but a design consideration | Not a limitation, but a design consideration. Must locate down gradient of building and foundations | Not a limitation, but a design consideration | Swale side slopes: 3:1 or flatter Longitudinal slope: 1.0% minimum; maximum based on permissible velocities | Not a limitation, but a design consideration. Must locate down gradient of buildings and foundations |
Soils | Permeable soils with infiltration rates > 0.27 inches/hour shall be used. Soil limitations can be overcome with use of underdrains | Permeable soils with infiltration rates > 0.27 inches/hour shall be used | Permeable soils perform better, but soils not a limitation | Permeable soils provide better hydrologic performance, but soils not a limitation. Selection of type of swale— grassed, infiltration, or wet—is influenced by soils | Permeable soils with infiltration rates 0.52 inches/hour shall be used |
Space required | Minimum surface area range: 50 - 200 feet Minimum width: 5 - 10 feet Minimum length: 10 - 20 feet Minimum depth: 2 - 4 feet | Minimum surface area range: 8 - 20 feet Minimum width: 2 - 4 feet Minimum length: 4 - 8 feet Minimum depth: 4 - 8 feet | Minimum length: 15 - 20 feet | Bottom width: 2 feet minimum, 6 feet maximum Minimum width: 2 - 4 feet Minimum length: 4 - 8 feet | Minimum surface area range: 8 - 20 feet |
Water table/ bedrock | 2- to 4-foot clearance above water table/bedrock recommended | 2- to 4-foot clearance above water table/bedrock recommended | Generally not a constraint | Generally not a constraint | 2- to 4-foot clearance |
(D) Bioretention.
(1) The major components of a bioretention system shall include the following:
(a) Pretreatment area (optional);
(b) Ponding area;
(c) Ground cover layer;
(d) Planting soil;
(e) In situ soil;
(f) Plant material;
(g) Inlet and outlet controls; and
(h) Maintenance.
(2) Design of bioretention areas shall comply with Table 153.1046(A) of this chapter. (See Figure 153.1046(A) of this chapter.)
(Ord. 3020, passed 9-10-2013, § 5.22.10)