Embankment Failure Analysis of the Tampa Bay Region Reservoir

Abstract Only - Proposal of municipal reservoir near Tampa has raised several concerns with regard to dam safety. Public awareness of the potential for embankment failure has been augmented by a failure of a phosphate mining impoundment located within the same watershed as the proposed Tampa Bay Regional Reservoir. Through a partnership with Hillsborough County, an emergency action plan will be provided that incorporates dam failure inundation maps generated from a hydraulic modeling analysis. These estimate the amount of damage resulting from flooding and most importantly the anticipated flood wave arrival time. This is critical to providing notification to the population-at-risk in the unlikely event of a failure.

The Tampa Bay Regional Reservoir is a proposed off-stream, aboveground reservoir with a water surface area of approximately 1,200 acres. At the maximum operating level, the storage volume will be approximately 15 billion gallons (48,000 acre-feet). Earthen embankments that vary in height from approximately 35 feet to 65 feet surround the impoundment on all sides, thus there is no clear indication of where a breach may occur or what receiving water will convey the flow. This and the fact that there is an expansive floodplain adjacent to the reservoir site adds to the complexity of the modeling effort.

Flood Wave (FLDWAV), the latest model developed by the National Weather Service, was used to route the flood downstream to either the Old Hillsborough Bay or a point where the flood attenuated to below 100-year flood levels. Since FLDWAV solves the conservation of momentum in one-dimension, and the expected flow characteristics in the very mild sloping, wide terrain are two-dimensional, the description of the conveyance channel required additional considerations. This included a sensitivity analysis of the assumptions developed for effective and ineffective flow areas as well as roughness coefficients.