Sediment loading and controls in the grasslands of the Great Plains

Authors: Garbrecht, Jurgen; Starks, Patrick

Submitted to: Soil and Water Conservation Society Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/15/2009
Publication Date: 9/14/2009
Citation: Garbrecht, J.D., Starks, P.J. 2009. Sediment loading and controls in the grasslands of the Great Plains [abstract]. Soil and Water Conservation Society Proceedings, From Dust Bowl to Mud Bowl, Conservation measures and the Future of Reservoirs, September 14-16, 2009, Kansas City, MO. p. 31. Available on-line: http://www.swcs.org/documents/filelibrary/sedimentation/Sediment_Program_FINAL_web_A40C2200C17B7.pdf

Interpretive Summary: Abstract only.

Technical Abstract: In this study, the effects of upstream conservation measures on sediment delivery to and half-life of the Fort Cobb Reservoir in West-Central Oklahoma are investigated. Few conservation practices were implemented on the Fort Cobb Reservoir watershed before the 1950s. In the second half of the 20th century, extensive soil conservation measures were implemented to protect agriculturally fertile but erosion-prone soils. Fortuitously, the U.S. Geological Survey (USGS) collected discharge and suspended sediment measurements during the 1943-1950 time span, and again in 2004-2008. These two time periods are called pre- and post-conservation periods, respectively. These discharge and suspended sediment measurements offered the opportunity to compare sediment yield to the reservoir before and after implementation of conservation practices. A separate suspended sediment-discharge rating curve was developed for each the pre- and post-conservation period, and average annual sediment delivery to the reservoir was estimated based on these rating curves and the reservoir inflow record. The reduction in watershed sediment yield as a result of conservation practices was by about a factor of 2, less than anticipated by initial projections. Calculated sediment inflow was compared to a 1993 survey of reservoir sedimentation, and reservoir half-life was projected by extrapolation of (1) surveyed sedimentation rates, (2) sedimentation rates under the assumption of pre-conservation land use and management conditions, and (3) sedimentation rates under the assumption of post-conservation land use and management conditions. The calculated increase in the half-life of the reservoir under current post-conservation conditions was attributed to the wide range of conservation practices implemented in the second half of the 20th century. However, a climatic shift in the mid 1980s resulted in an increased soil erosion and transport activity that offset to a large extent the downstream beneficial impacts of upstream conservation efforts.