28.080 Stormwater Management Plans.

(1) Plan Requirements. The stormwater management plan required under MMC 28.070 shall contain any information the Director of Public Works may need to evaluate the environmental characteristics of: (a) an area affected by land development activity; (b) the potential impacts of the proposed development upon the quality and quantity of stormwater discharges; (c) the potential impacts upon the area’s water resources and drainage utilities; and (d) the effectiveness and acceptability of proposed stormwater management measures in meeting the performance standards set forth in this chapter. Stormwater management plans shall contain the following:

(a) Name, address, and telephone number for the following or their designees: landowner; developer; project engineer for design and certification of structural measures and nonstructural measures; person(s) responsible for installation of structural measures and nonstructural measures; and person(s) temporarily and permanently responsible for maintenance of structural measures and nonstructural measures.

(b) A legal description of the property where the land development activity will take place, referenced to the U.S. Public Land Survey system or to block and lot numbers within a recorded land subdivision plat.

(c) Existing site conditions, including:

1. One or more site maps at a scale of not less than one inch equals 100 feet. The site maps shall show the following: site location and legal property description; predominant soil types and hydrologic soil groups; existing cover type and condition; topographic contours of the site at a scale not to exceed two feet; topography and drainage network including enough of the contiguous properties to show runoff patterns onto, through, and from the site; watercourses that may affect or be affected by runoff from the site; flow path and direction for all stormwater conveyance sections, including time of travel and time of concentration applicable to each; watershed boundaries used in determinations of peak flow rates and discharge volumes from the site; lakes, streams, wetlands, channels, ditches, and other watercourses on and within 500 feet of the site boundary; limits of the 100-year floodplain; location of all public and private wells which are within 1,200 feet of the site; and the distance from any well head protection overlay zoning district.

2. Computations of peak flow rates and discharge volumes for the two-year/24-hour, 10-year/24-hour, and 100-year/24-hour storm events. All major assumptions used in developing input parameters for these computations shall be clearly stated. The computations shall be made for each stormwater discharge point on the site development, and the geographic areas used in making the computations shall be clearly cross-referenced to the required map(s).

(d) Proposed post-development conditions, including:

1. Explanation of the provisions which will be implemented to preserve and use natural topography and land cover features to minimize changes in the peak flow rates and discharge volumes to surface waters and wetlands.

2. Explanation of any restrictions on structural measures and nonstructural measures on the site imposed by a well head protection plan or well head protection overlay zoning district.

3. One or more site maps at a scale of not less than one inch equals 100 feet showing: changes in land use including vegetative cover type and condition; proposed impervious surfaces including all buildings, structures, and pavement; changes to the topographic contours of the site at a scale not to exceed two feet; changes to the drainage network including enough of the contiguous properties to show runoff patterns onto, through, and from the site; locations and dimensions of drainage easements; locations of maintenance easements specified in the maintenance agreement; flow path and direction for all stormwater conveyance sections, including time of travel and time of concentration applicable to each; location and type of all stormwater management conveyance and treatment practices including the on-site and off-site tributary drainage area; location and type of conveyance system that will carry runoff from the drainage and treatment practices to the nearest adequate outlet such as a curbed street, storm drain, or natural drainage way; watershed boundaries used in determinations of peak flow rates and discharge volumes; any changes to lakes, streams, wetlands, channels, ditches, and other watercourses on and immediately adjacent to the site.

4. Computation of the runoff volume resulting from the one-and-one-half-inch rainfall over a four-hour period and computations of peak flow rates and discharge volumes for the two-year/24-hour, 10-year/24-hour, and 100-year/24-hour storm events. All major assumptions used in developing input parameters shall be clearly stated. The computations shall be made for each discharge point in the development, and the geographic areas used in making the calculations shall be clearly cross-referenced to the required map(s).

5. Results of investigations of soils and groundwater required for the placement and design of structural measures.

6. Results of impact assessments on wetland functional values.

7. Design computations and all applicable assumptions for the stormwater conveyance (open channel, closed pipe) system.

8. Design computations and all applicable assumptions for stormwater quality practices (sedimentation-type, filtration-type, infiltration-type) as needed to show that practices are appropriately sized.

9. Detailed drawings including cross-sections and profiles of all permanent stormwater conveyance and treatment measures.

(e) A schedule for completing all structural measures and nonstructural measures.

(f) A maintenance program which covers the life of each structural measure and nonstructural measure including the required maintenance activities and maintenance activity schedule.

(g) Cost estimates for the construction, operation, and maintenance of each structural measure and nonstructural measure.

(h) Other information as required by the Director of Public Works to determine whether implementation of the proposed stormwater management plan will further the purpose of this chapter.

(i) All site investigations, plans, designs, computations, and drawings shall be certified by a professional engineer, registered with the State of Wisconsin, that they have been prepared in accordance with accepted engineering practices and in accordance with WDNR Technical Standards.

(j) Any other information as specified by the Director of Public Works.

(2) Exceptions. The Director of Public Works may prescribe alternative submittal requirements for applicants seeking an exemption to on-site stormwater management performance standards under MMC 28.060(3).

[Ord. 08-522 § 22, 2008. Prior code § 28.08]