05-26-2004 Council Agenda - Laserfiche WebLink

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May 13, 2004 File: 823510J -0325 R. Green Company Honorable Chair and Planning Commission City of Little Canada 515 Little Canada Road Little Canada, MN 55116 RE: HIDDEN ACRES SUBDIVISION Dear Planning Commission Members: As requested we have reviewed the existing pond within the Yorkton Ridge Development to determine the possibility of utilizing the pond to treat the storm water discharge from the proposed Hidden Acres Development. The purpose of the review was to determine if the existing pond could be utilized to maintain the discharge rate and treat the storm water from the new Hidden Acres development rather than constructing a new pond within the development. We modeled the system in HydroCAD and reviewed the existing conditions versus the proposed improvements. With the additional drainage area from the Hidden Acres Development and the increase in discharge rates due to the improvements, the existing 100 -year high water elevation in the pond increases by approximately three feet. This increase would exceed the flood elevation in the pond, resulting in flooding over the berm to the creek to the west. In addition to insufficient live storage, the dead storage capacity of the pond would also need to be increased to provide a large enough pool of permanent water to provide adequate treatment. The attached exhibit shows the existing contours of the pond that vary between 1:2 and 1:3 in slope. The pond is bordered by a residential fence to the south, a building /parking lot to the north, and the creek to the west. Assuming that the residential fence is placed on the drainage and utility easement line and the building meets the 20 -foot rear yard setback, there does not appear to be sufficient area to expand the pond by a significant amount without additional easement acquisition. No property corners were found to verify the property lines or drainage and utility easements in the field. The second item to note is that the existing storm sewer pipe sizes within Yorkton Ridge Development would be undersized to accommodate the additional flow from the new development. The attached exhibit indicates the pipes that would need to be replaced with larger pipes to handle the increased water. All but one of these pipe runs would require the removal of curb and pavement from Yorkton Ridge. O: \PROJ \823510J \0240 \Ltr - 051304 -Ping. Comm..doc