Fiscal Note
N/A
Title
Report of the City Engineer - Determination of Whether to Repair or Replace the Lake Wingra Dam.
Body
Introduction
The Lake Wingra Dam is located at the outlet of Lake Wingra, at the east end of Vilas Park. The dam controls the Lake Wingra water surface elevation and the flow rate from the lake to Wingra Creek. In 2002, staff from the Wisconsin Department of Natural Resources (DNR) inspected the dam. The inspection report noted deterioration of the concrete dam and other violations of state code. Following the inspection, the DNR required that the City repair the dam to bring it up to code. In response to the findings of the DNR, the City hired Strand Associates, Inc. (Strand) to perform a study of the dam, which included investigation of the structural integrity of the dam, hydrologic and hydraulic evaluations of the dam, estimation of the required spillway capacity of the dam, and recommendation of whether to repair or to replace the dam. The Strand report, which was completed in late 2006, recommends replacement of the dam because aesthetic, structural, hydraulic and environmental benefits could be achieved; however, the report indicates that the existing dam could likely be brought into compliance with DNR requirements with relatively minimal repairs. The City Engineer requests direction as to whether to recommend repair or full replacement of the dam. Relevant data are summarized in the sections that follow.
Existing Dam Safety
· If the existing dam were to fail, lake drainage would be directed to a wetland area in the Arboretum, south of Wingra Creek. Wingra Drive and adjacent homes would not be affected.
· The inundated area resulting from dam failure is within the floodplain zone and is not subject to future development; therefore the dam has a "low" hazard rating.
· An underwater inspection was performed on the dam, which indicated that there is cosmetic concrete deterioration of the above-the-water portio...
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