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May 9, ..1978 <br />--, <br />TO: James F. Winkels, City Planner <br />.~ ~~~ <br />FROM: Leslie J. Proper, Director of Public Works ` <br />SUBJECT: Building Elevation Variance#184 <br />The. two small ponds which lie north and south of the home <br />the"variance is'being requested on are inter-connected <br />with Stony Lake on the east side of Silver Lake Road. <br />-;The area which drains to these ponds and Stony Lake is <br />shown on the attached map and contains about 43.3 acres <br />~total.•-Of this, 12.9 acres are water surface .and 30.4 `: <br />acres are land. The drainage area which drains to these <br />ponds and Stony Lake has no natural outlet which-makes <br />•high water elevations difficult to determine. For <br />example, a 100-year storm (a storm which has a probability <br />of one one-hundredth of occurring in any particular year} <br />would raise the elevation of the lake and ponds about one <br />..foot.. Since-the lake and ponds are all inter-connected, <br />they would equalize at the same .elevation. The problem is <br />in choosing the base surface elevation to add the 100-year <br />storm to. <br />As recent as 1975, the water surface elevation was testified <br />to be 928.14. The elevation was determined by our survey <br />crera from information from the residents that live on 26th <br />Avenue,-west of the two ponds. They indicated the location <br />on their lawn where the edge of the water had come in 1975. <br />Since the water's edge was very close to their home and some <br />sandbagging was necessary, we feel the location and, consequently, <br />the elevation of 928.14 is probably an accurate number. <br />As more homes are built in this 43.3 acre drainage area, the <br />area will become more impervious and the base surface elevation <br />will rise. There is a fairly large undeveloped area on the north <br />side of Stony Lake which will have a substantial impact on the <br />lake and pond levels when developed. When this development <br />occurs, I feel a lake overflow, maintaining a base elevation <br />of about 925 will be necessary. <br />At the present time the storm sewer at the intersection of 23rd <br />Avenue and 15th Street would back up and overflow the catch basins <br />