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Project 10 of 10



Bringing an Aging Watershed Dam into Compliance

Gwinnett County, Georgia, USA

Client Gwinnett County Department of Water Resources
Industries Water, Resources
Services Construction Materials Testing/Engineering, Surface Water/Sediments

The Natural Resources Conservation Service (NRCS) Dam No. Y-14 is a flood protection dam in the Yellow River Watershed. Since its original construction in 1967, the area near the dam experienced significant residential development and was re-classified as a high hazard dam and required rehabilitation to comply with current NRCS and Georgia Safe Dams regulations. Golder was retained by Gwinnett County to prepare and evaluate emergency spillway remedial designs for the Y-14 dam, such that the PMP flood event could be safely routed through the structure.

Our Role
Our services included:

  • Hydrologic analyses of the drainage basins to derive flood inflow hydrographs for present and future watershed development. HEC-1 analyses were carried out for reservoir routing calculations and to simulate reservoir behavior and spillway discharges during design PMP floods
  • Extensive computer modeling of the PMP design storm event impacts on the watershed basins and downstream reaches. DAMBRK modelling was used to delineate the dam breach floodwave throughout the storm
  • Comprehensive analyses of a number of emergency spillway modifications utilizing HEC-1.  Golder evaluated reservoir behavior and spillway discharges for five spillway modifications during the design PMP flood. Hydraulic evaluations were conducted for both a roller compacted concrete (RCC) spillway and a labyrinth weir spillway. 
  • Geotechnical Investigation and laboratory testing. The results of the laboratory testing were used to carry out analyses to assess the stability of the existing earthfill embankment.
  • The final engineering design consisted of abandoning the original earthen auxiliary spillway and constructing an arc-shaped RCC overtopping protection on the existing dam with an Ogee shaped weir which will function as the new auxiliary spillway.
  • Technical input throughout the permitting phase of the project with Gwinnett County, the NRCS and Georgia Safe Dams Program.
  • Construction monitoring and quality assurance services during construction of the RCC upgrade to the existing embankment.

Associated Services

Surface Water & Hydrology Services
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