(A) The applicant is responsible for submitting a stormwater management plan that meets the design requirements of this chapter. The plan shall be accompanied by a report that includes sufficient information to evaluate the environmental characteristics of affected areas, the potential impacts of the proposed development on water resources, and the effectiveness and acceptability of measures proposed for managing stormwater runoff. The developer or builder shall certify on the drawings that all clearing, grading, drainage, construction, and development shall be conducted in strict accordance with the plan.
(B) The stormwater management plan shall include the following information:
(1) Narrative description. A narrative description which includes the following information: a brief description of the proposed project; potential water quality and/or hydrologic impacts of the proposed project on surface and/or groundwater resources, existing infrastructure, and/or adjacent properties, and proposed measures or practices to mitigate potential impacts. All affected wetlands, surface water and groundwater resources, and any significant site constraints affecting the selection of stormwater management practices must be identified. The narrative shall include a discussion of protection of environmental resource functions and values, BMPs employed both during construction and post construction, and a description of construction and post construction maintenance of BMPs.
(2) Site plans. Site plans shall include existing and proposed contours, watershed patterns, wetlands, limits of clearing and grading, location of best management practices for erosion and sediment control and stormwater management, existing and proposed improvements, and easements and rights-of-way.
(3) Construction drawings. Construction drawings submitted for stormwater management plan approval shall include the following structural and construction details for all components of the proposed drainage system or systems, and stormwater management facilities, all necessary construction specifications, erosion and sediment control measures to be implemented in all construction phases along with final site stabilization plans, limits of clearing and overall site disturbance, data for total site area, disturbed area, new impervious area, and total impervious area, table of materials to be used for stormwater management facility planting, location and results of soil testholes, certification by the owner/developer that all stormwater management construction will be done according to this plan, and an as-built certification signature block to be executed after project completion.
(4) Calculations. Hydrologic and hydraulic design calculations for the pre-development and post-development conditions for the 2-, 10-, 25-, and 100-year frequency, 24-hour duration, type III distribution storm, storm events. These calculations shall use the methodology contained in the report entitled Urban Hydrology for Small Watersheds, Technical Release No. 55 (Second Edition) USDA, Soil Conservation Service, 1986, and any subsequent amendments thereto. Where the use of the above report is not practical for reasons based on accepted engineering practice, the use of alternate methodologies for calculating stormwater discharge may be permitted; provided, however, that such alternate methodologies shall not result in an increase in the rate of rain runoff during or after construction. Watershed maps must be provided depicting pre- and post-development sub-catchments; within each sub-catchment, the following information must be shown: areas, soil types, cover types and time of concentration flow. The calculations shall also include soil curve numbers or runoff coefficients, peak runoff rates for each watershed area, infiltration rates, where applicable, culvert capacities, flow velocities, documentation of sources for all computation methods and field test results.
(5) Soils information. If a stormwater management control measure depends on the hydrologic properties of soils (e.g., infiltration basins, then a soils report shall be submitted. The soils report shall be based on onsite boring logs or testhole data. The number and location of required soil borings or testholes should be determined based on what is needed to determine the suitability and distribution of soil types present at the location of the control measure.
(6) Maintenance plan. The design and planning of all stormwater management facilities shall include detailed maintenance and repair procedures to ensure their continued function. The maintenance plan shall comply with the requirements of § 153.24 of this chapter.
(Ord. passed 2-21-06)