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�� DEPARTMENT OF THE ARMY ` ST.PAUL DISTRICT,CORPS OF ENGINEERS / � Y 1421 U.S.POST OFFlCE 3 CUSTOM HOUSE �� C fS `'S�T.PAUI.MINNESOTA SS/01•9BOB v �� October 23, 1990 � n„�� _(��(�h ( -'�` REPIY TO �4` ATTENTION Of Construction-Operations I Regulatory (91-333N-92) -- SUBJECT: Pond Excavation, Fill (Sidecasting of Excavated Material) , and Grading in Unnamed Wetlands near but not adjacent to Lake Minnetonka, SW 1/4 SW 1/4 Sec. 16 and SE 1/4 SE 1/4 Sec. 17, T. 117 N. � R. 23 W. , City of Orono, Hennepin County, Minnesota Clair T. Rood 2215 Kenwood Way Wayzata, Minnesota 55391-9700 We have reviewed the information you provided about your project. The work is authorized by a nationwide Department of the Army permit, provided the enclosed conditions and management practices are followed. We also have provided some suggestions in this letter to improve the wildlife habitat value of the pond. In short, you can construct the pond as designed, but we suggest that you consider some modifications. . Although we have not made a site inspection of your property, the soil survey and wetland maps in our files suggest that the affected wetland is somewhat larger than the area outlined on your map. However, if your map shows all the excavation, grading, and fill, it appears that the total wetland that may be filled or graded would be 0.9 acre or less. Because this wetland appears to be part of a small drainage area separated from Lake Minnetonka except for a culvert drainage connection under the railroad right-of-way, the nationwide permit authorizes up to an acre of fill or grading. Zf you wish to enhance the wildlife value of the site, however, you should modify the design of the pond. A deeper pond, such as your proposed excavation, might support some fish over the winter, but the wildlife value of the excavation may be minimal with such steep side slopes. Enhanced wetlands or ponds designed to attract wildlife generally have very gentle slopes (at least 8:1 around a major part of the excavation, and ideally 10:1 or flatter) . They also incorporate irregular edges, rolling bottom contours, and organic soil to promote the growth of different types of wetland plants and to maximize use by waterfowl, other birds� and animals. For wildlife purposes, ponds are generally no deeper than 4 to 5 feet, with much of the pond less than 2 feet. To improve fish habitat, you need a deep pond, such as you propose, and different types of substrate materials, depending on the species you wish to support. The 12-foot depth you propose would keep some area at the bottom from freezing, and the aerator would help during both the colder and warmer. Unfortunately, even with aeration, the proposed pond might still be too small to support desireable fish during extreme temperatures. Side-slope sloughing may also be a problem that could decrease depths and alter the bottom material, rendering the pond less suitable for fish.