02-17-1987 Planning Packet - Laserfiche WebLink

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J . • 2.Rates of runoff from an area will be dependent on the vol ume of storage available in lakes, ponds, or other natural depressions. Reduction of this available volume will generally cause an increase in water elevations in the stor age areas and in runoff rates. The hydrologic analysis considered the effect on marsh water level fluctuations and runoff rates when the proposed landfill is constructed. The 100 year storm event was considered as the design case. Two marsh areas would be influenced by the proposed demolition landfill. The east marsh is located to the east of the present landfill and includes the area to be filled by the proposed demolition landfill. This 29 acre marsh receives runoff from a drainage area of approximately 90 acres. The limits of the drainage area are generally Highway 12 on the north, the Burlington Northern Railroad tracks on the south, and Old Crystal Bay Road on the east. The marsh outlet is an open ditch along the south limits of the Eisinger property leading to Lake Classen Creek. With the fill constructed, the marsh will be reduced in area to 18 acres. Ultimate development of the drainage area was assumed as R-lC residential (minimum lot size of one acre). Our analysis indicated that the landfill construction would increase the east marsh levels by less than 0.3 feet for the 100 year storm event. Also, discharges through the open ditch would increase on the order of 1 cubic foot per second (cfs). The second drainage area is that included in the total area incident to the railroad culvert for Lake Classen Creek (shown in Figure 1 as Area A). This area includes 462 total acres of which 156 acres are lake or marsh. The drainage area includes residentially zoned (R-lC) areas and. also Orono High School. Our analysis predicted that the filling proposed at the landfill will cause an increase in lake and marsh levels during a 100 year storm event of less than 0.05 feet. The discharge at the railroad culvert should be increased less than 1 cubic foot per second. The proposed landfill will have an almost negligible hydrologic effect on the remaining marshes and on the ’.00 year flood flows in Lake Classen Creek. This is because of the large area of marsh in the drain age area in comparison to total area. The actual percentage of marsh 4 - 5 -