(A) All developments requiring a stormwater plan shall be designed, constructed, and maintained to prevent flooding, minimize stream channel impacts, protect water quality, and achieve the purposes of this chapter, as stated above. The city has adopted performance standards to meet the objectives of managing the quantity and quality of stormwater runoff from a site as described below and in the current Wayne County Stormwater Control Program.
(B) Designers may select any combination of stormwater BMPs that meet the performance standards provided the selections:
(1) Comply with the requirements identified in this chapter and the current Wayne County Stormwater Control Program;
(2) Comply with all other local, county, state, or federal requirements; and
(3) Do not conflict with the existing, local stormwater management and watershed plans.
(C) The particular facilities and measures required onsite shall take into consideration the natural features, upland areas, wetlands, and watercourses on the site; the potential for onsite and offsite adverse stormwater impacts, water pollution, and erosion; and the size of the site.
(D) The following onsite stormwater management concepts must be followed.
(1) Natural topography and site drainage shall be preserved and site grading shall be minimized to the maximum extent reasonably achievable considering the nature of the development.
(2) The preferred conveyance strategy is to transport, wherever possible, untreated and treated runoff in conveyance facilities open to the atmosphere (e.g. swales, vegetated buffer strips, energy-dissipating structures, and the like), rather than through enclosed pipes, so as to decrease runoff velocity, allow for natural infiltration, allow suspended sediment particles to settle, and to remove pollutants.
(3) Watercourses shall not be deepened, widened, dredged, cleared of vegetation, straightened, stabilized, or otherwise altered without applicable permits or approvals from the City Engineer, relevant county agencies and the applicable state department(s).
(4) The stormwater plan and associated BMPs must demonstrate compliance with required volume and channel protection criteria by providing retention as necessary to meet volume and peak flow limits consistent with the requirements of the design manual. Specific details for achieving compliance with the volume and channel protection criteria are outlined in the design manual.
(5) The stormwater plan and associated BMPs must demonstrate compliance with required water quality criteria by providing treatment of total suspended solids (TSS) or by providing retention to achieve the same criteria for maximum TSS concentrations in the stormwater discharge from the site, with either approach being consistent with the requirements of the design manual. Specific details for achieving compliance with the water quality criteria are outlined in the design manual.
(6) The stormwater plan and associated BMPs must demonstrate compliance with required peak flow rate and flood control criteria by providing stormwater detention and/or retention consistent with the requirements of the design manual. Specific details for achieving compliance with the peak flow rate and flood control criteria are outlined in the design manual.
(7) Under certain conditions, the city, upon recommendation by the City Engineer, may impose the following additional restrictions on stormwater discharges.
(a) Peak discharge may be further restricted when it can be shown that a probable risk to downstream structures or unique natural areas exists, or that existing severe flooding problems could be further aggravated.
(b) Measures shall be imposed to protect against ground or surface water pollution where the nature of the soils or bedrock underlying a stormwater management structure constitutes a substantial risk of contamination, such as might be the case in limestone formations. Special provisions to be followed in these cases will be provided by the City Engineer.
(E) Stormwater offsets may be considered in accordance with the provisions provided in the current Wayne County Stormwater Control Program, where water quantity or water quality BMPs required by this chapter cannot be fully accommodated onsite.
(Ord. 22-002, passed 4-11-22) Penalty, see § 55.99