6.5. SR 11-17-1997 - Laserfiche WebLink

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Memo to Planning Commission/P 97-16 October 28, 1997 Page 4 Ail of the other lots in the plat meet the minimum lot size requirements; however, according to the drainage plan, some lots have storm water ponds in their rear yards. Ponds of this nature are typically provided in developments, however, staff has recommended a reasonable flat and usable area behind the homes be provided before sloping down into the pond. The pond between Lots 1 - 6, Block 4 appears to have about 30 feet of flat area prior to beginning the slope down into the pond. However, Lots 13, 14 and 15 has a distance of only about 20 feet from the high water level of 878.9. The plat should be adjusted to redesign the pond to allow a little more area behind the homes before getting to the ponding area. The proposed design raises a few questions since the river could backflow into the rear yards up to an elevation of 878 (100 year elevation). In some cases, this may put the edge of water within 10'-15' of the back of a house, or walk- out elevation. In addition, the water level could be about 3 feet higher than the lowest floor elevation. This may present a problem if the water level doesn't go down in a reasonable amount of time allowing lateral movement through the soil towards the home's basement. Floodway & Flood Fringe Both of these designations apply to the property. The surveyor should identify and include on the proposed plat edge of the floodway. This is the actual channel of the watercourse and is the area required to carry or store the regional flow (i.e., 100 year event). No activity can occur within the floodway. The plans appear to respect the floodway; however, the boundary should be noted. The flood fringe is the area outside the floodway. This area can be filled; however, the lowest floor elevation must be 879.1 and an elevation of 878.1 must extend for a minimum of 15' around all structures. This may not be a problem; however, the engineer should denote this boundary on the plans. The flood fringe on this plat is primarily on the northeast corner of the plat. Redesign Considerations Based on staffs concerns with back yard ponds and lowest floor elevations adjacent to the river back flowing into these areas, modifications will need to be made to the plat. There are several alternative designs that can be made. The developers may have a plan at Tuesday's meeting. fi\shrdoc\planning\pc\p97-16.doc