Consulting Solutions that Work for People and the Environment

Salmon River Dambreak and EAP Mapping

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Gomez and Sullivan was retained by Brookfield Renewable Power to address recommendations made by the Independent Consultant during the Part 12D inspection for Bennett’s Bridge and Lighthouse Hill dams. These dams are FERC regulated dams located on the Salmon River in Oswego County, NY. The Independent Consultant’s recommendations included updating the spillway rating curve for Lighthouse Hill Dam to account for the current tainter gate opening height, and developing a HEC-RAS dambreak model to study the impact that a failure of the right and/or left abutments at Bennett’s Bridge and Lighthouse Hill dams would have at downstream locations. A total of 6 failure scenarios were examined, which included the failure of the earthen abutments, retaining walls and an RCC dike. The downstream cross sections required for routing the failure flows were prepared using ArcGIS and the HEC-GeoRAS extension. Site visits were carried out to collect data on the dams and downstream road crossings.

Gomez and Sullivan also performed Emergency Action Plan dam failure inundation mapping for both Bennetts Bridge and Lighthouse Hill dams. The HEC-RAS hydraulic model previously developed to address the Independent Consultant’s recommendations was utilized to determine the PMF, PMF plus breach, Fair Weather, and Fair Weather plus breach downstream water surface profiles needed to develop the EAP inundation mapping. The inundation extents were determined using ArcGIS and the HEC-GeoRAS extension. The hard copy and digital format inundation mapping and associated GIS files were developed in accordance with the FERC Engineering Guidelines.