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

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'oning File #1223 March 8, 1988 Page 4 of 8 B. This method proposes to excavate the bank slope area, build a cribbed interior stabilization structure and then refill the bank to the original (1.4:1) grade. The interior cribbing becomes invisible because it is covered with soil, hence allows the steeper slope to be maintained while making it much more stable. In order to construct the cribbing, a large amount of soil must be excavated and stock piled on the site, but this is merely a short-term concern. There would be slightly greater area of bare soil during the re -vegetation period as compared to Option A. This method is relatively expensive due to the materials and excavation involved, but would allow for a relatively stable restoration of the approximate original grade. C. Layered fabric stabilization system. This system results in a slope similar to Option B, but involves the use of parallel horizontal layers of soil backfill separated by a geotechnical fabric, which acts to greatly reduce the vertical mass movement of soil. The amount of excavation needed and both the short-term and long-term effects are very similar to those of the cribbing method, as are the greater expenses involved. D. This method make use of a total retaining wall system, with nearly vertical faces ar.3 nearly level beds for planting of landscape and screening materials. This system would have a major visual impact from the lake, and the trac,: record of similar installations on the lakeshore has shown that they are rarely screened so as to be unobtru::i.ve. Depending on the method of construction and design, this system would have fair to good long term stability. The potential short-term effects of erosion due to bare ground would be relatively minimal as compared to other methods. E. This system makes use of a single 3-4' height retaining wall at the edge of the flat lawn area, which al lows the slope from the base of the retaining wall to the lakeshore to be somewhat flatter than Options A through C. Another ver-ion of this option would be to construct a retaining wall of a greater height so that the slope from its base to the lake would meet the 2:1 standard desired. Obviously, the greater the height of such a wall, the greater the visual impact it will have from the lake. Stability also decreases as the height of such a wall becomes greater. The short-term and long-term effects on lake water quality are Simi li.r to those of Options Band C.