Emergency Action Plan Updates and Dam Break Modeling for Great River Hydropower Dams

Challenge

Great River Hydro is the owner and operator of 16 dams in New England (13 for hydropower, 3 for storage). TransCanada, the former owner, engaged GZA to perform dam break analyses, hazard classification assessments, spillway capacity analyses, and Emergency Action Plan (EAP) updates for their dams.

Solution

GZA conducted dam break analyses for 6 of the dams. The dam breaks were used to develop updated inundation maps for the EAPs. For 4 dams, the dam break analyses were also used to evaluate the hazard classification and Inflow Design Flood (IDF). GZA performed the dam break analyses with a 1-D unsteady flow model using HEC-RAS version 5.0.1. GZA used the mapper feature in HEC-RAS to map the results after breach runs were simulated.

Additionally, for one dam, GZA used a HEC-RAS 2-D unsteady flow model to evaluate the capacity of the dam’s spillway discharge channel. The downstream channel opens into an unconfined terrain with no channel path, and for this reason, the analysis was performed as two dimensional. The model was used to evaluate if tailwater in the discharge channel causes submergence at the spillway.

The majority of the EAP updates involved reformatting the EAPs to conform with updates in the FERC Engineering Guidelines for the Evaluation of Hydropower Projects. The FERC guidelines were revised in 2015 to conform with the FEMA Publication No. P-64 – Federal Guidelines for Emergency Action Planning for Dams.

Benefit

GZA was also contracted to develop an interactive web-based application that presents the inundation maps and data for Great River Hydro’s High Hazard dams. The web-based application, the GZA GeoTool ©, displays data, documents and imagery that is hosted on GZA’s Enterprise Portal and allow the user to easily and securely view the various features of an inundation map.