Menager’s Dam Rehabilitation

Challenges

The original Menager’s Dam was constructed between 1913 and 1927 and consisted of a 30-foot-tall earthen embankment.  The embankment was constructed without a spillway and drains, filters, and other seepage management facilities.  The original outlet works had been non-functional since the 1960s.  The Bureau of Indian Affairs (BIA) had identified numerous potential failure modes that exceeded the BIA’s tolerable risk guidelines, including overtopping of the embankment and various modes of internal erosion of the embankment.

Solution

RJH was tasked with developing a comprehensive design for the repair or replacement of the dam to address these failure modes.  Eight alternatives were considered and an opinion of probable construction cost was developed for each alternative.  A feasibility workshop was conducted to evaluate alternatives based on cost, design risk, overall risk reduction, construction risk, operations and maintenance requirements, and user acceptance.

The preferred concept consisted of a rockfill dam with an earthfill core.  RJH and BIA implemented a value engineering workshop and a risk reduction workshop. Input from both workshops was used to finalize the design.  RJH led the work from initial evaluation and assessment of the existing dam through identification of dam safety issues, alternatives development, federal permitting, final design, and construction engineering.