(A) Every land development or construction activity that results in the discharge of stormwater to the Town stormwater management facilities, including but not limited to, detention ponds, rain gardens, underground storage, and any other facility intended to manage stormwater quality or quantity shall furnish a stormwater management plan to the Town. The stormwater management plan (narrative and/or plan sheets) shall include sufficient information to allow the Town to evaluate the environmental characteristics of the project site, the potential impacts of all proposed development of the site, both present and future, on the water resources, and the effectiveness and acceptability of the measures proposed for managing stormwater generated at the project site.
(B) To accomplish this goal the stormwater management plan shall include the following:
(1) Topographic base map. Topographic base map of the site which extends a minimum of 100 feet beyond the limits of the proposed development and indicates:
(a) Existing surface water drainage including streams, ponds, culverts, ditches, sink holes, wetlands, and the type, size, elevation, and the like, of nearest upstream and downstream drainage structures;
(b) Current land use including all existing structures, roads, and easements, and locations of utilities;
(c) All other existing significant natural and artificial features;
(d) Proposed land use with tabulation of the percentage of surface area to be adapted to various uses, drainage patterns, locations of utilities, roads and easements, the limits of clearing and grading;
(2) Proposed structural and non-structural BMPs;
(3) A written description of the site plan and justification of proposed changes in natural conditions may also be required;
(4) Hydrologic and hydraulic design calculations for the pre-development and post-development conditions for the design storms specified in the Town's BMP manual or this chapter. These calculations must show that the proposed stormwater management measures are capable of controlling runoff from the site in compliance with this chapter and the guidelines of the Town's BMP manual. These calculations shall include:
(a) A description of the design storm frequency, duration, and intensity where applicable;
(b) Time of concentration;
(c) Soil curve numbers or runoff;
(d) Peak runoff rates and total runoff volumes for each watershed area;
(e) Infiltration rates, where applicable;
(f) Culvert, stormwater sewer, ditch and/or other stormwater conveyance capacities;
(g) Flow velocities;
(h) Data on the increase in rate and volume of runoff for the design storms referenced in the Town's BMP manual; and
(i) 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 on-site boring logs or soil pit profiles and soil survey reports. The number and location of required soil borings or soil pits shall be determined based on what is needed to determine the suitability and distribution of soil types present at the location of the control measure.
(Ord. 2012-18, passed 11-12-12)