U.S. Department of Defense


Date of this Version



Published by Pacific Geoscience (1998) 1-22


Pacific GeoScience has completed a revised study of the erosion of Tribal lands (tracts) located along the Missouri River within the yankton Sioux Reservation. This riverbank erosion is related to the construction and operation of Fort Randall Dam. This study evaluated the erosion and accretion of Tribal tracts from 1941 through 1998 (the study period), and estimates the value of the net land eroded as a result of dam construction and operation. This report supersedes the ENVIRON report of 1992 and presents a more comprehensive evaluation of the monetary value of the lost acreage. This study utilizes the current tract identification numbers that are consistent with the Bureau of Indian Affairs' (BIA) database. The background and principal findings of this study are as follows:

• The Army Corp of Engineer's (COE) report entitled, Missouri River Review Report/or Water Resources Development completed in the late-1970s, shows that during the 1946-1952 construction period of the Fort Randall Dam, 945 acres were lost on the 36.3 mile reach of the Missouri River between Fort Randall Dam and Niobrara, Nebraska. During the following period, 1953-1975, an additional 1,058 acres were lost to erosion. This reach of river includes most of the western boundary of the yankton Sioux Reservation.

• In October 1981, the COB, at the request of the Tribe, provided a Section 55, Streambank Erosion Protection Technical Assistance Report. The COE report stated that during the 1953-1976 period the entire reach, which contains the study areas of our report, has "...experienced severe erosion; and it is not likely to cease in the forseeable future."

• The severe erosion that has occurred along 17 Tribal tracts of land, that is related to the construction and operation of Fort Randall Dam, has resulted in a loss of 450.3 acres, of which 427.1 acres is prime arable land.

• There are 18.7 acres of arable accreted land at tract T2016, resulting in a net loss of 408.4 acres of arable Tribal land (427.1 - 18.7 acres).

• The potential economic value of the lost Tribal land Was estimated based on returns from dryland alfalfa crop production uwested at 7 percent average annual yield for the period since the principal erosion occurred (either 1953 or 1976, as discussed in the text).

•The dryland alfalfa crop returns were estimated to be $122.37 per acre, assuming above average farm management practices and no land charges or management fees.

• The present day value of the lost Tribal landis estimated to be approximately $1,000 per acre. Given these figures, the estimated present day value of the net Tribal lands lost to erosion during the period from 1953, at the completion of the Fort Randall Dam,to 1998 is approximately $11,300,000.

• This evaluation does not take into consideration the future value of the eroded Tribal lands.