Comparison of Preconstruction and 2003 Bathymetric and Topographic Surveys of Lake McConaughy, Nebraska

Authors

W. H. Kress
S. K. Sebree
G. R. Littin
M. A. Drain
M. E. Kling

Document Type

Article

Date of this Version

May 2005

Comments

Scientific Investigations Report 2005-5040.
Published by U.S. Department of the Interior and U.S. Geological Survey.

Abstract

The U.S. Geological Survey, in cooperation with The Central Nebraska Public Power and Irrigation District, conducted a study that used bathymetric and topographic surveying in conjunction with Geographical Information Systems techniques to determine the 2003 physical shape, current storage capacity, and the changes in storage capacity of Lake McConaughy that have occurred over the past 62 years. By combining the bathymetric and topographic survey data, the current surface area of Lake McConaughy was determined to be 30,413.0 acres, with a volume of 1,756,300 acre-feet at the lake conservation-pool elevation of 3,266.4 feet above North American Vertical Datum of 1988 (3,265.0 feet above Central datum). To determine the changes in storage of Lake McConaughy, the 2003 survey Digital Elevation Model (DEM) was compared to a preconstruction DEM compiled from historical contour maps. This comparison showed an increase in elevation at the dam site due to the installation of Kingsley Dam. Immediately to the west of the Kingsley Dam is an area of decline where a borrow pit for Kingsley Dam was excavated. The comparison of the preconstruction survey to the 2003 survey also was used to estimate the gross storage capacity reduction that occurred between 1941 and 2002. The results of this comparison indicate a gross storage capacity reduction of approximately 42,372 acre-feet, at the lake conservation-pool elevation of 3,266.4 feet in NAVD 88 (3,265.0 feet in Central datum). By comparing preconstruction and 2003 survey data and subtracting the Kingsley Dam and borrow pit, the total estimated net volume of sediment deposited over the past 62 years is 53,347,124 cubic yards, at an annual average rate of 860,437 cubic yards per year. The approximate decrease in the net storage capacity occurring over the past 62 years is 33,066 acre-feet, at an annual average decrease of approximately 533 acre-feet per year, which has resulted in a 1.8 percent decrease in storage capacity of Lake McConaughy. The lake has accumulated most of the sediment in the original river channel and in the west end of the delta area on the upstream end of the lake.