In 2005, the U.S. Army Corps of Engineers began a Screening for Portfolio Risk Analysis (SPRA) of 671 dams and other structures in the Corps inventory in order to identify and classify the highest risk dams that require urgent and compelling action. This screening has yielded a clear but basic understanding of where the greatest risks and priorities are located. Completing the SPRA allowed the Corps to develop a Portfolio Investment Plan for more than 300 dams posing moderate to extremely high risks.
The analysis resulted in Dam Safety Action Classification (DSAC) ratings for each of the structures in order to prioritize them so they can be addressed on a “worst-first” basis. The DSAC rating is intended to provide consistent and systematic guidelines for appropriate actions to address the dam safety issues and deficiencies of Corps dams.
Corps dams are placed into a DSAC class based on their individual dam safety risk determined by a combination of two factors:
-- the probability of a dam’s failure and
-- the potential life safety, economic, environmental or other consequences.
The DSAC table shown below presents the levels and urgencies of actions that are commensurate with the different classes of the safety status of Corps dams. These actions range from immediate recognition of an urgent and compelling situation requiring extraordinary and immediate action for unsafe dams (DSAC I) through normal operations and dam safety activities for safe dams (DSAC V).
While the study, design and construction of long-term solutions are pursued, Interim Risk Reduction Measures (IRRM) are the most responsible way to manage the risk to public safety. Examples of nonstructural IRRMs include reservoir pool restrictions and operational changes, stockpiling materials, improving or increasing inspections and monitoring, awarding pre-placed emergency contracts, establishing pool levels for increased surveillance, updating Emergency Action Plans, conducting emergency exercises and coordination with stakeholders (includes communication), installing warning systems and conducting preventive maintenance. Examples of structural IRRMs include Improve seepage collection system installing shallow cut-off trenches, filling voids in embankments or foundations, grouting or sealing conduit joints, installing grout curtains, stabilizing downstream berms or installing inverted filters.