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e-I <br />Hennepin Conservation District <br />12460 Way^ata Boulevard, Suite 205 • Minnetonka. Minnesota 55343 • Telephone (612) 544 8572 <br />April 3, 1985 <br />Ms. Jeanne Mabusth <br />Zoning Administrator <br />City of Orono <br />P.O. Box 66 <br />Crystal Bay, MN 55323 <br />rN' i <br />APR - 51985. I <br />^-------------------------------------• • . ; / <br />Dear Jeanne: <br />I have reviewed the grading and wetland alteratio'i plan <br />for the Gregory residence as you requested. I hope that the <br />following comments are helpful. <br />Cattail-sedge wetlands (Type 3) are the* most efficient <br />nutrient traps for treating surface water runoff. <br />Artificial ponds and open water wetlanjs (Type 5) are less <br />effective due to reduced nutrient uptake by rooted aquatic <br />plants. The efficacy of shrub swamps (Type 6) as nutrient <br />filters is not as well documented. Nutrient uptake in <br />Type G wetlands is believed to be less than in Type 3 <br />wetlands due to the slower growth of woody vegetation. The <br />conversion of part of the cattail-sedge-shrub v.etland into a <br />wildlife pond will reduce the nutrient retention capability <br />of this basin. The reduction however, will not <br />significantly impact the water quality of Brown's Bay. The <br />large off-site wetland that is upstream of the proposed <br />alteration will continue to treat the majority of the <br />runoff. The proposed wildlife pond should provide adequate <br />treatment for the localized runoff. The invert elevation of <br />the culvert under County Road 15 further ensures an adequate <br />retention (treatment) time in the wildlife pond during most <br />flow conditions. The following recommendations are intended <br />to minimize any potential impact of this wetland alteration <br />on the quality of water discharged to Brown's Bay. <br />1. The areas of the wildlife pond nearest the pond's <br />outlet and the inlet from the formal pond should <br />have a 7:1 slope (horizontal:vertical) rather than <br />the approximate 4:1 slope as shown in the plan. <br />This slope and the resulting increase in shallow <br />water area will provide a better habitat for re­ <br />establishing a fringe of emergent vegetation. <br />This fringe of emergent vegetation would provide a <br />buffer between the open water areas and the <br />outlet. This fringe would also serve as a filter <br />strip for runoff from the formal pond. <br />TON* I MVATKiN 14 VH<4 NT b* I » CV**VT MNVf Nl