06-09-2004 Council Agenda - Laserfiche WebLink

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cannot be elevated to provide additional freeboard from West Vadnais Lake due to height restrictions of the railroad bridge. Because West Vadnais Lake is located within the Vadnais Lake Area Water Management Organization, Ramsey County requested this organization to convene a meeting of involved parties to discuss technical and administrative issues related to the potential project. The initial meeting was held in July 2003 with a total of four interagency meetings to date Agency staff participating in the interagency meetings and receiving periodic project updates are listed in Attachment 1 (below). St. Paul Regional Water Services has participated in these meetings and has identified flooding of their Vadnais Lake Pumping Station due to high water level in West Vadnais Lake as an important operational concern. Ramsey County and St. Paul Regional Water Services have committed to paying preliminary engineering design costs for the proposed West Vadnais outlet project. An elevation of 881.9 (1988 datum) is proposed for the West Vadnais outlet, which would provide approximately 2.5 feet of protection relative to the Rice St. surface elevation. The DNR conducted an Ordinary High Water (OHW) survey of West Vadnais Lake in 2003 and concluded that the proposed control elevation 881.9 is reasonably consistent with the observed OHW of 882.7 (1988 datum). A consultant to MnDOT has completed the preliminary engineering design. This information includes a proposed alignment and profile (grade or slope) of the 15 -inch diameter pipe from West Vadnais Lake, under I -694, and ending at Jiggs Pond, located between Levitz Furniture and the former Knox Lumber building along Country Drive in Little Canada. Jiggs Pond will be modified as part of the `Unweave' project, to a configuration with surface area of about 1.25 acres and depth at normal water level of 3 feet. The consultant also completed hydrologic modeling of the existing condition at Jiggs Pond as well as the proposed condition after the `Unweave' project. For the "after" condition, the effect of the West Vadnais outlet flow is estimated conservatively as 4 cubic feet per second, which corresponds to the outlet pipe flowing full. This condition is extremely unlikely to occur in practice, once the West Vadnais Lake level is set at the control elevation of 881.9. Modeling results for the Type II, 24 -hour, 100 -year storm event of 5.90 inches, for existing and proposed (i.e. with `Unweave' project and full pipe flow in the West Vadnais outlet pipe) conditions at Jiggs Pond are summarized in the Attachment 2 (below). A brief summation of these results is the proposed combined `Unweave' and outlet projects do not increase storm event peak outflow and high water elevation at Jiggs Pond, but each project will individually add some water volume to Gervais Lalce in the total amount flowing through the outlet pipe over time. For long periods of time, there will be no flow out of the West Vadnais outlet pipe. Once the outlet is in place and the control water elevation is reached, when outflow does occur, it will usually consist of a very low flow or trickle due to the limited inflow to West Vadnais Lake and the large lake surface area. The purpose of the proposed outlet is to provide an upper limit to West Vadnais Lake elevation during long -term periods of above - normal precipitation, such has occurred in the last several years. - 1 3 -