The following is the Executive Summary from a white paper developed by the National Reservoir Sedimentation and Sustainability Team entitled: Reservoir Sedimentation Management: Building a Legacy of Sustainable Water Storage Reservoirs. This white paper has been written by the National Reservoir Sedimentation and Sustainability Team (NRSST). The NRSST is composed of engineers and scientists from federal agencies, consulting firms, industry, and universities who have expertise and experience with sedimentation. The purpose of this white paper is to inform dam owners and operators, government decision makers and regulators, and the interested public about reservoir sedimentation and the need for long-term sediment management strategies to preserve the benefits of the nation’s reservoirs for our own children and future generations.
The United States economy and welfare depends on a continuous and reliable system of water supply and infrastructure for municipal, industrial, agricultural, flood control, and hydropower uses. Water storage reservoirs are essential for regulating highly variable river flows, making water available whenever needed, creating a singularly important, but often unseen foundation for modern society. These water systems are also important for environmental management, recreation, and groundwater aquifer recharge. The estimated 90,000 dams and reservoirs in the U.S. (National Inventory on Dams, 2017) constitute a critical component of the nation’s water infrastructure. There are perhaps more than a million additional dams that are too small to be included in the national inventory.
The vast majority of the nation’s water storage reservoirs were constructed decades ago, and since construction, they have been trapping the sediment (clay, silt, sand, and gravel) eroded from the land surface of the upstream watershed, and carried downstream by river flow (Morris and Fan, 1998). The downstream transport of sediment by river flow is particularly evident during floods, when waters run turbid with eroded soil. In most reservoirs, the accumulating sediment consists of clay, silt, sand, and gravel particles (Morris and Fan, 1998; Randle and Greimann, 2006; and Morris et al., 2007).
Without active management, the continual accumulation of sediments gradually displaces the storage volume in a reservoir, which risks ultimately rendering the reservoir useless for capturing and storing water. In addition, long before the reservoir has lost its water storage capacity, numerous problematic sedimentation impacts can occur, including reduction in the reliability of water supply, burial of dam outlets and intakes for water supply and power production, damage to hydropower and pumping equipment, burial of boat ramps or marinas, impairment to navigation, reduction in the surface area for lake recreation, increased flood levels upstream, downstream channel degradation, and other environmental impacts.
The loss or degradation of legacy water infrastructure will impose significant financial and environmental burdens on future generations, compounded by the fact that replacement sites for most dams and reservoirs are not readily available. The most appropriate dam sites have already been utilized, and they are losing their storage capacity. Removal and storage of large volumes of sediment on land, while technically feasible, can be costly, and there typically isn’t room to sustainably store inflowing sediments. Fortunately, multiple measures are available to manage sediment, to help ensure the long-term viability of reservoirs while minimizing the difficulty and cost of maintaining the nation’s water resources.