Denver Water Semi-Quantitative Risk Analyses

Challenges

Denver Water owns and operates a portfolio of 20 dams throughout Colorado.  Many of their dams were designed and constructed decades before modern engineering and dam safety practices were developed.  As dams age, uncertainty regarding material properties, foundation conditions, and long-term performance increases, while deterioration, changing hydrologic and seismic criteria, and downstream development can affect the overall risk profile.

Solution

Denver Water utilizes a risk-based approach to manage their portfolio of dams.  RJH was retained by Denver Water to perform semi-quantitative risk analyses (SQRA) at four dams: Harriman, Antero, Marston, and Ralston Dams.  These dams were specifically selected by Denver Water because of RJH’s expertise in geotechnical and geological engineering.

For each dam, RJH reviewed existing data and reports, performed a site visit to observe dam conditions and features, and prepared initial descriptions of Potential Failure Modes (PFMs).  For PFMs that were categorized as having a moderate, high, or very high likelihood of occurrence, RJH prepared a risk event tree and identified adverse and positive factors related to PFM development.

RJH participated in a SQRA workshop for each dam with engineering staff from Denver Water and the Colorado Office of the State Engineer.  After the workshops, RJH prepared summary memorandums with recommendations for additional investigations or evaluations to further characterize and understand the likelihood of critical PFMs.