(A) A comprehensive plan, in preliminary form (or in combined preliminary and final form), designed to safely handle the stormwater runoff and detain the increased stormwater runoff.
(B) The plan shall provide or be accompanied by maps or other descriptive material indicating the feasibility of the drainage plan and showing the following:
(1) The extent and area of each upstream, offsite watershed tributary to the subject site. Required materials for preliminary review include:
(a) Exhibit showing each upstream, offsite drainage area tributary to the subject site on USGS Quandrangle Maps or other more detailed topographic maps; and
(b) Preliminary plan to convey upstream, offsite runoff through the subject property, shown on the preliminary drainage plan for the site.
(2) The capacity of the downstream, offsite receiving system (outlet). Information must be submitted to show that the downstream, offsite drainage system has the capacity to convey the expected runoff from the subject property and any upstream, offsite areas. The County Surveyor may also determine the capacity of the downstream drainage system;
(3) The general drainage plan for the subject property must include the following items:
(a) The extent and area of each watershed on the subject property in the existing condition. Calculations to determine the allowable release rate from the subject property should also be included;
(b) The extent and area of each watershed affecting the design of detention facilities as shown on USGS Quadrangle Maps or other more detailed topographic maps;
(c) Elevations in either National Geodetic Vertical Datum of 1929 (NGVD) or North American Vertical Datum of 1998 (NAVD);
(d) The estimated location and percentage of impervious surfaces expected to be constructed when the development is completed;
(e) Existing detention/retention facilities to be maintained, enlarged, or otherwise altered and new ponds or basins to be built and the basis of their design;
(f) The estimated depth and amount of storage required by design of the new facilities;
(g) The preliminary layout and design of street storm sewers, where proposed, and other storm drains to be built, the outfall and outlet locations and approximate elevations, the receiving stream or channel, and its 100-year return period water elevation;
(h) The preliminary layout of swales which collect runoff from onsite and/or offsite watersheds;
(i) Proposed culverts and bridges to be built, their material, elevations, waterway openings, and basis of their design; and
(j) Identification of overland flow routes to detention/retention facilities;
(4) Existing streams and floodplains to be maintained, and new channels to be constructed, their locations, cross-sections, and profiles;
(5) Any interim drainage plan which is to be incorporated into the development pending completion of the development and the final drainage plan;
(6) A copy of the effective FEMA map, annotated to show the project location and property boundaries in relation to the regulatory floodplain and floodway;
(7) The location of any regulatory wetlands on the subject property; and
(8) A report summarizing the hydraulic design parameters and detailing how this design satisfies this subchapter.
(Ord. 1997-16, passed 12-8-1997; Ord. 2005-01, passed 2-17-2005) Penalty, see § 153.999