US Army Corps of Engineers
Hydrologic Engineering Center

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Sustainable Rivers

Water Management

Decisions that involve water are of interest to diverse stakeholders that share an appreciation of the many services that rivers, reservoirs, and other aquatic systems provide. Influences change with time reflecting new knowledge, social dynamics, and the balance of purposes and allocations.

By many measures (e.g., number of reservoirs, total storage, geographic distribution), the Corps is the largest water management organization in the nation. The Corps operates a varied suite of water infrastructure (e.g., storage reservoirs, diversions, pump stations, reregulation facilities, and navigation locks) and is increasingly asked to assess how that infrastructure might be operated to provide additional and increasingly diverse benefits to society, including more effective ecological stewardship, reduced environmental impact, and greater recreation opportunities.

The role of water managers is to manage water and conflict in the short-term and to help steer system operations to a sustainable optimized state of management in the long-term.


The Corps began building dams and reservoirs on a large scale starting in the 1930s in response to a string of devastating floods and the economic hardship of the Great Depression. The country’s rapid post-war growth in the 1940s and 1950s required not only flood control but also reliable water supplies and increased electrical output for prospering communities. The Corps was thus called upon to construct reservoirs around the country to serve a variety of purposes.

Environmental effects of dams, reservoirs and other water control structures were poorly understood when many of these projects were built. By the 1960s and 1970s, government agencies, conservation groups and citizens nationwide began to evaluate the ecological impacts of development. The Corps has since worked to understand the effects of human influences on water resources and, when possible, mitigate impacts and improve the environment.

One of the many ways reservoirs can be operated to benefit ecosystems is the release of environmental flows. For water managers, environmental flows guide operational decisions that manipulate water and land-water interactions to achieve ecological or environmental goals. Importantly, environmental flow targets are inherently seasonal, catering to the flow needs of natural communities associated with aquatic systems.

Reservoir operating policies are gradually evolving to incorporate scientific knowledge related to environmental flows, but there is still much work to be done. As of 2009, only 16% of reservoirs with federally authorized flood storage had environmental flow management strategies that were variable as a function of season, condition, or both.


At reservoirs, environmental considerations are most often associated with operations for fish and wildlife and water quality purposes. The Sustainable Rivers Program has developed methods and resources to help water managers, infrastructure operators, scientists, planners, and stakeholders to modernize strategies for operating purposes related to the environment. Software initiated by the Program is available to facilitate formulation of alternative management strategies for rivers and ecosystems. Capacity building is done through recurring professional training courses and as needed for new teams working to deliver more environmental benefits from built infrastructure. And importantly, past and ongoing site work demonstrates how environmental strategies can be advanced, implemented, and incorporated into the operations of water projects.