SEDIMENTATION OF RESERVOIRS - SOME CASE HISTORIES

Authors: McGregor, Keith; Cooper, Charles; Cullum, Robert

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 8/17/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Although the functions and physical characteristics of reservoirs may vary widely, all of them have one thing in common. All of them are collecting basins for sediment. This study summarized case histories to show the magnitude of sedimentation in reservoirs. Sedimentation records of Elephant Butte Reservoir on the Rio Grande River, the three largest reservoirs on the Missouri River, some of the other large reservoirs in the western United States, and from smaller reservoirs, natural lakes, and backwater impoundments along the main stem of the Mississippi River were reviewed. Elephant Butte Reservoir lost 18 percent of its storage capacity during 1915 to 1969, and lost 21.6 percent in 73 years from 1915 to 1988. Fort Peck Reservoir lost 4.4 percent from 1938 to 1987 in about 49 years. Garrison Reservoir lost about 3.7 percent in 35 years. A prevalent effect of water storage in the Missouri River Reaches has been the degradation of channels below the dams, while in the Rio Grande channels have aggraded both above and below Elephant Butte. Sediment accumulation rates, although slowing, continue to fill small reservoirs, backwater impoundments, and natural lakes along the main valley floor of the Mississippi River. All the reservoirs surveyed in this study will eventually fill with sediment. The final effect of sedimentation on Congressionally mandated uses of the stored water in reservoirs will be the ultimate loss in storage. This study summarizes the sedimentation records of many of the nations reservoirs, and will be of benefit to the public and to action agencies.

Technical Abstract: Storage losses of Elephant Butte Reservoir on the Rio Grande River, the main stem reservoirs on the Missouri River, and some of the large reservoirs in the western United States were estimated. Also, sediment accumulation rates for several small reservoirs, backwater impoundments, and natural lakes along the main valley floor of the Mississippi River were examined. Elephant Butte Reservoir lost 569,800 acre-ft of storage capacity from 1915 to 1988 for an annual average of 0.30 percent. Garrison Reservoir's average annual storage loss was 0.10 percent from 1953 to 1988. Oahe Reservoir's average annual storage loss was 0.08 percent from 1958 to 1989. Sediment accumulation rates for several small reservoirs, backwater impoundments, and natural lakes along the main valley floor of the Mississippi River declined by 30 percent during 1964- 1984 as compared to 1954-1964. Continuation of measured storage capacity losses means that 100 years after closure of the dams, potential storage in Keystone Lake, Lake Texoma, Lake of Ozarks, Elephant Butte, and Lake Mead will be reduced to about 1.0, 3.5, 1.4, 1.7, and 23.3 million acre- ft, respectively. The capacity of these reservoirs will be reduced about 45, 40, 31, 30, and 28 percent, respectively. The reduction in capacity of reservoirs in the United States will be reflected by changes in priorities of beneficial uses before the reservoirs eventually become filled