Agenda Packets - 2009/02/08 - Laserfiche WebLink

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February 9, 2009 Item No. 11B 1 Page 3 It must be noted that the predicted overtopping of the trail would occur only during very large storms, only for a limited length of the trail, and only for a relatively short duration. The overtopping of the trail would occur during the “50-year” storm and the “100-year” storm. There is a 2% chance that a “50-year” storm will occur during any given year. Similarly, there is a 1% chance that a “100-year” storm will occur during any given year. The trail is not predicted to be overtopped by storms of less than the “50-year” intensity. The following table summarizes the predicted overtopping of the trail: County Road 10 Trail: Segments 1-5 Summary of Predicted Overtopping Maximum Water Depth Across Trail Length of Trail Affected* Duration Trail Below Water Likelihood of Occurrence 3.5 inches < 250 feet 1 hour, 10 minutes 2% in any given year 9 inches < 250 feet 2 hour, 30 minutes 1% in any given year * total length of Trail Segments 1-5 is 8,960 feet. Note: The storm water model predicts that the pond would crest at its high water level while the rain is still falling. The model further predicts that by the time the rainfall has ended, the pond water level would have dropped to an elevation lower than the trail. The information above shows the model prediction that there is a very low probability that the trail will be overtopped with water during any given year. And even in the instance where it were, the portion of trail affected would be relatively small (less than 3% of the total trail length), and the condition would abate itself by the time the rainfall ended. Options The plans for Trail Segments 1-5 have been completed, and have been reviewed by both Ramsey County and the Minnesota Department of Transportation. All necessary approvals from RCWD and the Corps of Engineers have been obtained. However, the project has not yet been advertised for bids, so there is the opportunity to modify the plans if desired. Staff has identified two options for addressing this situation: x Option 1 – Deem the Situation Acceptable If the predicted overtopping of the trail is considered to be low enough in impact and frequency of occurrence, then Council could deem the situation acceptable, and simply proceed with the project as currently proposed. There would be no impact to project costs or schedule.