(A) The applicant shall install or construct, or pay the city fees for all storm water management facilities necessary to manage increased runoff, so that the two-year, ten-year, and 100-year storm peak discharge rates existing before the proposed development must not be increased. Also accelerated channel erosion must not occur as a result of the proposed land disturbing or development activity. An applicant may also make an in-kind or a monetary contribution to the development and maintenance of community storm water management facilities designed to serve multiple land disturbing and development activities undertaken by one or more persons, including the applicant.
(B) Infiltration of treated stormwater is required whenever new development results in an increase in the stormwater runoff volume and when redevelopment maintains or increases the stormwater runoff volume provided that past and existing land use practices do not have limitations and restrictions as described in the city’s Engineering Guidelines.
(C) The city will require new development to infiltrate storm water runoff in all areas except where either there are limitations or restrictions as described in the city’s Engineering Guidelines. For projects that use infiltration, the following policies apply:
(1) Pretreatment of storm water to NURP guidelines will be required prior to discharge to an infiltration basin.
(2) The infiltration basin will be sized to infiltrate the runoff from the impervious surface area as required in the city’s Engineering Guidelines.
(3) Infiltration rates of the soil shall adhere to the city’s Engineering Guidelines:
Hydrologic Soil Group | Infiltration Rate |
A | 0.50 in/hr |
B | 0.25 in/hr |
C | 0.10 in/hr |
D | 0.03 in/hr |
(D) The applicant shall consider reducing the need for storm water management facilities by incorporating the use of natural topography and land cover such as natural swales and depressions as they exist before development to the degree that they can accommodate the additional flow of water without compromising the integrity or quality of the wetland or pond.
Commentary:
The sensitivity of a wetland to degradation varies with the type of vegetation. Sedge meadows, open bogs and swamps, coniferous bogs, calcareous fens, low prairies, lowland hardwood swamps, and seasonally flooded basins are highly sensitive to degradation, while flood plain forests, reed canary grass meadows, shallow (reed canary grass, cattail, giant reed or purple loosestrife) marshes are only slightly sensitive to degradation. See the current version of the Minnesota Pollution Control Agency’s publication “Storm-Water and Wetlands: Planning and Evaluation Guidelines for Addressing Potential Impacts of Urban Storm-Water and Snow-Melt Runoff on Wetlands” for details.
(E) The following storm water management practices must be investigated in developing the storm water management part of the storm water pollution control plan in the following descending order of preference:
(1) Protect and preserve as much natural or vegetated area on the site as possible, minimizing impervious surfaces, and directing runoff to vegetated areas rather than to adjoining streets, storm sewers and ditches to promote the infiltration of water;
(2) Flow attenuation by use of open vegetated swales and natural depressions;
(3) Storm water wet detention facilities; and
(4) A combination of successive practices may be used to achieve the applicable minimum control requirements specified in division (A) above.
(5) The applicant shall provide justification for the method selected.
(Ord. 128, passed 2-8-00; Am. Ord. 0802, passed 3-11-08; Am. Ord. 1501, passed 1-27-15)