The U.S. Army Corps of Engineers operates and maintains approximately 740 dams and associated structures nationwide that provide significant, multiple benefits to the nation — its people, businesses, critical infrastructure and the environment. These benefits include flood risk management, navigation, water supply, hydropower, environmental stewardship, fish and wildlife conservation and recreation. The Corps of Engineers Dam Safety Program seeks to ensure these dams do not present unacceptable risks to people, property or the environment.
The St. Paul District Dam Safety Program is set up to manage the district’s 32 dams, including 13 navigation locks on the Mississippi River. It involves numerous staff from many different disciplines with tasks ranging from daily monitoring of most of these structures to completing engineering inspections or risk assessments scheduled periodically on 5- or 10-year intervals (depending on the dam’s hazard class). The inspections and risk assessments are used to justify repairs and prioritize rehabilitation needs across the Corps of Engineers’ portfolio of dams.
Cross Lake Dam
Many of the Corps dams have park rangers or lock staff at the site that maintain awareness of the dams and combine dam safety monitoring with other activities. Some dams have Automated Data Acquisition Systems that are used to capture frequent instrumentation data (mostly water pressures) and can be accessed in the office for real-time performance monitoring.
Inspections are often supplemented by the district’s dive team, but schedule site visits on different days. The divers monitor concrete damage, check for leakage, verify instrumentation results such as sounding data and scour protection, and provide underwater photographs and video. The same dive team routinely maintains the dams and locks by clearing debris or repairing broken parts such as bubblers for deicing, intake grating, concrete spalls, etc.
A ‘period inspection’ for a dam includes a thorough examination during a joint site inspection by all team members, with a goal to have hands-on access to all components. The inspection teams generally include structural, mechanical, electrical, hydraulic and geotechnical engineers in addition to the site staff. Risk assessments additionally include a geologist and economist. The Corps of Engineers uses a 90-day milestone for completion of periodic inspection and risk assessment reports and submittal to the division headquarters. This time includes reviews by a separate quality control team. Risk Assessment reports are also reviewed by the Corps of Engineers’ Risk Management Center and presented to a headquarters dam and levee oversight committee.
Orwell Dam
The Corps dam safety program has many other activities and management functions as described in Federal Guidelines for Dam Safety, first published in 1978. The most influential development in the last 20 years has evolved around risk assessments. Risk assessments can use many analytical tools and mathematics, but the global dam safety community has developed risk assessment protocols best adapted to understanding risks posed by dams. A summary of risk information for Corps of Engineers’ dams is now available in the National Inventory of Dams, or NID, under the “Summary” and “Risk” tab for each project. The NID also includes other useful data, such as the dams’ components, size and hazard potential.