PRESENTER: Presenter
Phillip Quast, Watershed Supervisor
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SUBJECT: Title
Approval of a resolution for the City Manager to execute the Comal River Watershed Supplemental Watershed Plan Agreement as a sponsor for the Rehabilitation of Floodwater Retarding Structure No. 4 of the Comal River Watershed, Comal County
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DEPARTMENT: Public Works
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COUNCIL DISTRICTS IMPACTED: All
BACKGROUND INFORMATION:
*The City of New Braunfels will not be responsible for the obligation of funds for cost-share, operation, and maintenance within the Comal River Watershed.
Historical floods in the past 57 years since FRS No. 4 was constructed have caused the auxiliary spillways to function on at least two occasions on FRS No. 4. This FRS was originally constructed as a low hazard potential dam. Residential development has occurred downstream of the dam and an increase in traffic has occurred downstream of FRS No. 4. These factors have caused concerns regarding the hydraulic capacity of the dam and human health and safety. As a result, FRS No. 4 has been reclassified as a high hazard potential dam. The dam does not comply with current high hazard potential dam safety and performance criteria and has been prioritized for Rehabilitation. The proposed rehabilitation of FRS No. 4 will allow the dam to comply with current performance and safety standards and maintain the present level of flood control benefits. The preferred rehabilitation of FRS No. 4 will include raising both auxiliary spillways 1.5 feet, widening the left auxiliary spillway channel to a 310-foot-wide earthen auxiliary spillway, constructing a 250-foot wide Roller Compacted Concrete (RCC)-step auxiliary spillway over the existing embankment which discharges into a concrete stilling basin, replacing the rock blanket on the 2.5:1 embankment slope, replacing the existing principal spillway inlet tower, and replacing the existing principal spillway conduit with a 54-inch-diameter pipe. Total project installation cost for FRS No. 4 is estimated to be $15,919,500, of which $11,245,500 will be paid from the Small Watershed Rehabilitation funds and $4,674,000 from local funds.
ISSUE:
Maintain dam safety compliance with TCEQ; Improve flood prevention capacity of dam structure.
FISCAL IMPACT:
No fiscal impact to the City New Braunfels.
Recommendation
RECOMMENDATION:
Staff recommends approval of a resolution for the City Manager to execute the Comal River Watershed Supplemental Watershed Plan Agreement as a sponsor for the Rehabilitation of Floodwater Retarding Structure No. 4 of the Comal River Watershed, Comal County