Inundation Mapping Updates for Emergency Action Plans
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The Tennessee Valley Authority (TVA) River Operations, which regulates a system of 49 reservoirs spanning seven states, maintains Emergency Action Plans (EAPs) for dams throughout the Tennessee River System.

TVA's current EAP floodplain maps are primarily based on older steady-state hydraulic models, estimated reach lengths and overbank elevations, and outdated floodplain mapping techniques.  Geosyntec was retained as part of a team to help TVA update their floodplain inundation maps for different dam-break scenarios for all of the major dams in their system.

Geosyntec's Scope of Services

Using pre-defined inflows for multiple scenarios, we used the U.S. Army Corps of Engineers (USACE) Hydrologic Engineering Center River Analysis System (HEC-RAS) to simulate the passage of flood waves through the system. We coordinated a strategic bathymetric surveying effort to fill in data gaps and compiled and assessed the existing HEC-RAS (and others such as HEC-2 and ADYN) models and channel geometry from TVA and USACE for use in the inundation modeling. We geo-referenced and extended the historical cross-section geometry data to encompass Probable Maximum Flood (PMF)-sized events, incorporating dam structure geometry and associated operation and theoretical dam breach information into the hydraulic model.

We also developed and updated the flood inundation models for the Hiwassee River System (Hiwassee River, Nottely River, and Ocoee River), the Great Falls Dam on the Caney Fork, and the Tims Ford Dam on the Elk River to Wheeler Lake. We used the updated HEC-RAS unsteady flow simulation models to examine three flooding scenarios: PMF without failure, PMF with failure, and sunny day failure.

Notable Accomplishments

Through a high level of coordination with TVA, the prime contractor, and other contractors working in the TVA's nuclear division, Geosyntec was able to share data and modeling experience and ensure the most accurate HEC-RAS models were developed. This project allowed TVA to update their EAP and continue to operate their facilities under optimum conditions throughout the year while also keeping up with the latest safety practices for their dams.

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Project Summary

  • Location: Knoxville, Tennessee
  • Client: Tennessee Valley Authority
  • Project Practice Areas: Geotechnical
  • Type of Facility: Hydropower dams
  • Services Provided: Bathymetric surveys, Hydraulic model development, Geo-referencing, Unsteady flow simulations, Floodplain inundation mapping
  • Type of Work: Hydraulic modeling
  • Governing Regulation: Federal