03-28-1988 - Agenda Packet City Council - regular meeting

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Zoning File #1223 March 8, 1988 Page 3 of 8 A) In general, a 2:1 slope (50% slope or l' vertical drop for every 2' of horizontal distance) is considered as adequate for stabilizing the slope in the clayey soil types present. B) If site factors make it unfeasible to create a continuous 2:1 slope, then artificial structural methods must be employed to provide adequate stability. These would appear to fall into two catagories: 1. Providing the bank with interior stability so that steeper s lopes can be created that wi 11 have less of a tendency to fai 1. OR 2. Providing exterior vertical support, such as retaining walls, that will allow the removal of excess overburden soil so that shorter lengths of flatter slopes can be employed. In either case the goal is to decrease the ability of the soil to move sideways as a result of forces from above it. A brief description of the nine options considered by staff is as follows: A. Backfill and grade the existing bank to a uniform slope with no stabilization measures. This would result in about a 1.4:1 slope which would have stability characteristics no better than what originally existed, if not worse because there would be disturbed soil in place of what was natural soil originally. This method would likely have little visual impact from the lake, but would be relatively troublesome for the re-establishment of vegetation. The short term potential impacts on lake water quality would be relatively low compared to other methods, presuming that the prime short term concern is the area of vegetated surface that will be laid bare for a period of time and subject to surface erosion. Note that use of proper erosion control methods (silt fence, hay bales, seed mesh, etc.) with each of the nine options will make the actual short-term impact relatively equal for all the options.