North Dakota Dams Portfolio Risk Assessment

Challenges

The North Dakota Department of Water Resources (NDDWR) Cost-Share Program is the state’s primary funding source for dam repairs, rehabilitation, and improvements.  Because annual funding is limited, NDDWR needed to establish a method to prioritize high-hazard dams for cost-share funding based on their risk.

Solution

NDDWR retained RJH to perform a Screening-Level Portfolio Risk Assessment (SLPRA) for 18 high-hazard dams across the state.  For each dam, RJH reviewed available data and performed engineering analyses to estimate the population at risk and the likelihood of dam failure.  Consistent with the screening-level scope and project budget, RJH focused on the primary potential failure modes of overtopping, internal erosion through the embankment or foundation, auxiliary spillway erosion, and embankment instability.

RJH prepared and facilitated two four-hour workshops to demonstrate the risk assessment process and train NDDWR Dam Safety Program staff to develop event trees and evaluate the likelihood of events progressing to dam failure.  Results for each dam were presented to NDDWR personnel, and overall risks were plotted on a simplified risk matrix modeled after those used in semi-quantitative risk assessments.  RJH also provided recommendations for risk reduction action or for future studies that could significantly increase the confidence of the risk estimates.