09-23-2002 Council Packet - Laserfiche WebLink

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Mr. Wyatt Pace 2 Rr. Camp TEKO Orono. MN _________Aufluat 7.2002 Improve the existing trail along the waters edge between the boating dock and the swimming beach. The applicants would like to work with the watershed to fix the existing erosion problems, widen the existing trail to promote a safer walking path, restore the lakeshore and reduce impacts to the lake. They are proposing increasing the width to 6 ’ and installing rip rap along the lakeshore and installing a retaining wall on the uphill side. Minor repairs to existing trails as shown on sheet C2.1, Including the addition of stairs between the Stone Lodge and the bathrooms to make the path less steep. Also, they would like to regrade at the swimming beach and along the trail between the changing tents aruj the beach to fix the existing erosion problems and make these areas safer for the kids. Hydrology We have done some Impervious computations and found that the Improvements stated above will increase the impervious area of the site by approximately 13,700 square feet. We performed rate control calculations to confirm that the change In Impervious area doesn’t Increase the runoff rate. According to Hennepin County Soil Survey the soils at this site are of the Erin Complex, in the hydrologic soil group B. The attached HydroCAD calculations show that the runoff rate hasn’t significantly increased for the 1- year, the 10>year or the 100-year storm event due to the approximate 1.7% increase In Impervious area, the summary table is below. Event Runoff, cfs Runoff, cfs Existing Proposed 1-year 1.4 1.4 10-year 15.1 15.1 100-year 33.4 33.4 The weighted curve number is the same since the increase in impervious is negligible in respect to the site area, see attached Hydrocad computation sheets. Water Quality In order to provide water quality treatment for the Increased Impervious area, we are pressing to construct a filter strip. The impervious area Increase is primarily due to the pavilion and the dining hall addition, approximately 0.16 acres. We have excluded the gravel trails from the impervious area calculation since the trails are less than 10 feet wide and have a 5’ pervious strip on either side. These Improvements are near the northwest comer of the site and the dining hall currently drains irrto the existing wetland in the northwest comer of the site. The attached Drainage Area Map shows the area we evaluated to treat the 0.16 acres of increased impervious. The drainage area is 1.6 eSOSUTUER NORTH BUILOWO 810 FIRST AVSNUEr»RTH ISNNEAROUS. MN OFFICE: tiamOOTO FAX 8124824077 mmi