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� <br /> � CONTINUED MEETING OF THE ORONO COUNCIL APRIL 27, 1977 Page 16 <br /> � Mr. Greg Frank, City Engineer, presented a report DREDGING & RIPRAPPING <br /> concerning the dredging and riprapping application North Star Marina <br /> �or the North Star Marina, 3324 North Shore Driveo <br /> . hich states: <br /> � At the �equest of the City Council, we have reviewed <br /> the subject dredging and riprapping application. <br /> � Based on a site inspection, it appears that the <br /> � drainage area flowing directly into the lake <br /> includes roughly a 75' strip abutting the shore- <br /> � line. Drainage from the remaining area of the <br /> � marina flows across the side property lines and <br /> into the adjacent properties before reaching the <br /> � lake. As such, erosion and siltation directly <br /> in front of the marina is not as significant as <br /> � it would be if the entire property drained <br /> directly to the lake. <br /> • <br /> • Several small erosion channels (several inches <br /> deep) were evident along the shoreline of the <br /> � marina. All of these were located between the <br /> end of the sod and the actual shoreline, a <br /> � distance of roughly ten feet. The primary reason <br /> for this is that a significant break in grade <br /> • occurs at the end of the sod, with a steeper <br /> unprotected slope extending into the water. If <br /> � '-he shoreline were riprapped, this problem could <br /> • ssentailly be eliminated. <br /> � Upland from the break in the grade, the ground <br /> slopes very gently and there is no evidence of <br /> � erosion. It would,therefore, appear that Orono`s <br /> setback ordinance is effective in controlling <br /> • erosion from storm water runoff by filtering <br /> runoff through pervious cover materials. <br /> • <br /> In conjuction with the applicant' s request to I <br /> � dredge the shoreline to the natural lake bottom, i <br /> � we have the following comments: <br /> � l. Hennepin County normally considers blue clay <br /> soil as representative of Lake Minnetonka' s <br /> • actual bottom. <br /> � 2. The soil types that were encountered in the <br /> � soil borings (included in the application) <br /> indicate that sedimentation and erosion has <br /> � occurred. However, the time frame over which <br /> this may have happened may include hundreds <br /> � of years. To determine the rate of sedmen- <br /> tation, extensive topographic data of the <br /> � lake ' s bottom would need to be determined <br /> � at different points in time. The volume <br /> changes divided by the time frame theoretcially <br /> � represent the rate of sedimentation. However, <br /> factors such as lake bottom disturbances caused <br /> � AY �ats can also be expected to impact th� results. (Continued) <br /> • <br />