Resiliency Planning: Emergency Action Plan Updates and Dam Break Modeling, TransCanada Corporation, Multiple New England Locations

TransCanada, owner and operator 17 FERC-regulated hydropower dams in New England, asked GZA to provide dam engineering and resiliency consulting services to protect these critical sites.

CHALLENGE
Emergency Action Plan (EAP) updates were required for each of TransCanada’s 17 hydropower dams to conform with 2015 updates in the FERC Engineering Guidelines for the Evaluation of Hydropower Projects. While some EAP updates were routine, others required more extensive analysis, including dam breaks and modeling.

SOLUTION
GZA conducted dam break analyses for six of the dams.  The dam breaks were used to develop updated inundation maps for the EAPs.  For four 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 new mapper feature in HEC-RAS to map the results within minutes after breach runs were simulated.  

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; for this reason, the analysis was performed two dimensionally.  The model was used to evaluate if tailwater in the discharge channel causes submergence at the spillway.

GZA was also contracted to develop an interactive web-based application, hosted by Esri, that presents the inundation maps for TransCanada’s High Hazard dams.  The interactive maps allow the user to turn layers on and off to easily view the various features of an inundation map.  

The remaining dam updates were clear-cut and primarily involved reformatting the EAPs to conform to the new guidelines.

BENEFITS
GZA’s dam safety engineers completed EAP updates for numerous hydropower dams employing a process that included dam breaks, inundation mapping, hazard classification, Inflow Design Flood, and interactive web-based mapping. Dam breach analysis was completed for a total of more than 270 miles of river.