No application for development will be accepted unless it includes a storm water management concept plan detailing in concept how runoff and associated water quality impacts resulting from the development will be controlled or managed. The storm water management concept plan shall meet the following requirements:
1. Be prepared by a licensed professional engineer or landscape architect or individual credentialed in a manner satisfactory to the City.
2. Indicate whether storm water will be managed on site or off site and, if on site, the general location and type of practices BMPs, with clear citations to the Iowa Storm Water Management Manual.
3. Include sufficient information (e.g., maps, hydrologic calculations, etc.) 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 storm water BMPs proposed for managing storm water generated at the project site, refer to Section 161.06(4). The intent of this conceptual planning process is to determine the type of storm water BMPs necessary for the proposed project, and ensure adequate planning for management of storm water runoff from future development. To accomplish this goal, the following information shall also be included in the storm water management concept plan:
A. A soil management plan as defined by the Iowa Stormwater Management Manual shall be provided and include a technical assessment of soils that identifies the soil series and the site limitations based on soils data provided in the Web County Soil Survey hosted by Natural Resources Conservation Service (NRCS). It may only be used if soils have not been highly disturbed. Soil borings shall be included when necessary to confirm suitable site conditions for placement of buildings with basements and related structures, especially in areas with hydric soils and shallow depth to groundwater. If a stormwater BMP depends on the hydraulic properties of soils, then the assessment shall include soil borings and measurements of percolation/infiltration rates. The number and location of required soil borings and/or soil test sites shall be determined based on what is needed to determine the suitability and distribution of soil types present at the location of the BMP. Borings may range from a minimum of 5’ to 20’ below subgrade depending on the size of the BMP. This information shall be used to provide a summary of the associated risks and potential for adequate drainage related to infiltration practices, groundwater mounding and basement flooding. Consultation with a Certified Professional Soil Scientist, Soil Classifier, or Geotechnical Engineer may be necessary or required.
B. A map (or maps) indicating the location of existing and proposed buildings, roads, parking areas, utilities, structural storm water management and sediment and erosion BMPs. The map(s) will also clearly show 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; and the limits of clearing and grading. A written description of the site plan and justification of proposed changes in natural conditions may also be required. A copy of the current SWPPP may satisfy this requirement.
C. Sufficient engineering analysis to show that the proposed BMPs are capable of achieving City storm water requirements for the site in compliance with this chapter.
D. A written or graphic inventory of the natural resources at the site and surrounding area as it exists prior to the commencement of the project and a description of the watershed and its relation to the project site. This description should include a discussion of soil conditions, forest cover, topography, wetlands, and other native vegetative areas on the site. Particular attention should be paid to environmentally sensitive BMPs that provide particular opportunities or constraints for development.
E. Landscaping and stabilization shall be accomplished to prevent stormwater violations or impairment of BMPs. In addition, a landscaping plan must be submitted with the final as-built drawings describing the vegetation stabilization and management techniques to be used at the site after construction is completed. This plan will include the entity responsible for vegetation at the site and practices that will be used to ensure adequate vegetative cover.
F. A written description of the required maintenance burden for any proposed BMPs.
G. The City may also require a concept plan to consider the maximum development potential of a site under existing zoning, regardless of whether the applicant presently intends to develop the site to its maximum potential.
H. For development occurring on a previously developed site, an applicant shall be required to include within the storm water management concept plan BMPs for controlling existing storm water runoff discharges from the site in accordance with this chapter to the maximum extent practicable. The storm water management concept plan shall be referred for comment to all other interested agencies, and any comments must be addressed in a storm water management final plan.