Agenda - Public Works Committee - 03/20/2012

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Location 100 -year HWL Depression 1 --- Existing 864.7 Depression 1 -- Proposed 863.8 Depression 2 — Existing 866.0 Depression 2 — Proposed 865.3 Location 100 -year HWL Depression 1 -- Existing 864.7 Depression 1 -- Proposed 863.8 Depression 2 -- Existing 866.0 Depression 2 — Proposed 859.9 Location 100 -year HWL Depression 1 -- Existing 864.7 Depression 1 -- Proposed 862.7 Depression 2 --- Existing 866.0 Depression 2 — Proposed 859.8 The following table summarizes the 100 -year HWL's for Depression 1, assuming the pond construction shown on Exhibit 15, and Depression 2: As shown, adding this additional outlet pipe has very little effect on the high water levels of the two depressions. After adding the pipe, stormwater actually flows from Depression 2 back to Depression 1 prior to flowing downstream, lowering the HWL in Depression 2. The estimated cost to construct this additional outlet pipe is $37,697. Table 25 includes the individual costs for this alternative. Alternative 5 Alternative 5 includes constructing a 36" outlet pipe from Depression 2. As shown on Exhibit 16, the new outlet pipe would run east from Depression 2 to the Rum River. The new outlet would be constructed at an elevation of 857.8. As part of this alternative, the existing outlet pipe from Depression 2 will be eliminated. This alternative also assumes that the new outlet from Depression 1, as discussed in Alternative 4, would also be constructed. The following table summarizes the 100 -year HWL's for Depression 1, assuming the pond construction shown on Exhibit 14, and Depression 2: The following table summarizes the 100 -year HWL's for Depression 1, assuming the pond construction shown on Exhibit 15, and Depression 2: As shown, adding this outlet pipe has a significant effect on the high water levels of the two depressions. This alternative would have to be approved by the Minnesota Department of Natural Resources.