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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #204723
Title: Relative magnitudes and sources of sediment in benchmark watersheds of the Conservation Effects Assessment Project

Author
item Simon, Andrew
item KLIMETZ, LAUREN - UNIVERSITY OF MISSISSIPPI

Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2007
Publication Date: 11/30/2008
Citation: Simon, A., Klimetz, L. 2008. Relative magnitudes and sources of sediment in benchmark watersheds of the Conservation Effects Assessment Project. Journal of Soil and Water Conservation Society. 63(6):504-522.

Interpretive Summary: The Conservation Effects Assessment Program (CEAP) is aimed at evaluating the effectiveness of erosion control measures in agricultural watersheds. These measures have traditionally focused on uplands and fields. There is, however, a growing body of evidence that the primary source of sediment erosion has shifted from fields and uplands to channels. This paper compares rates of sediment transport from CEAP-Benchmark watersheds with data from stable streams in the associated ecoregion to determine relative impacts due to sediment. Evaluations of channel stability are used to document the extent of sediment contributions from the channel boundary. All but one of the CEAP-benchmark watersheds investigated (Little River, GA) are shown to produce appreciably more suspended-sediment than stable systems within the same ecoregion. Rapid geomorphic assessments indicate that channel contributions are probably a significant source of sediment in the studied watersheds in Iowa, Mississippi, New York, and Oklahoma. Annual suspended-sediment yields for the CEAP-benchmark watersheds exceed the median value for stable streams by: 226% in Iowa, 290% in New York, 630% in Mississippi and between 2120% and 3090% in Oklahoma. Results indicate that erosion from channel sources, particularly streambanks is significant and will need to be controlled to improve downstream water quality.

Technical Abstract: Sediment is one of the principle pollutants of surface waters of the United States. Efforts by the USDA to quantify and control sediment erosion have historically focused on fields and upland areas. There is, however, a growing body of evidence in agricultural areas that the locus of sediment erosion has shifted from fields and uplands to channels. This is due in part to successful conservation efforts and the natural attenuation of erosion processes with time. This is a critical issue in the USDA's Conservation Effects Assessment Program (CEAP) as the agency evaluates the effectiveness of controls on sediment erosion. Methodologies developed for this study have proved successful in differentiating sediment production between stable and unstable channel systems. All but one (Little River, GA) of the CEAP-benchmark watersheds investigated have been shown to produce appreciably more suspended-sediment than stable systems within the same ecoregion. Rapid geomorphic assessments indicate that channel contributions are probably a significant source of sediment in the studied watersheds in Iowa, Mississippi, New York, and Oklahoma. The relative importance of channel processes can be obtained by comparing "reference" yields for the ecoregion and the respective watershed yields. Annual suspended-sediment yields for the CEAP-benchmark watersheds exceed the median value for stable streams by: 226% in Iowa, 290% in New York, 630% in Mississippi and between 2120% and 3090% in Oklahoma. If the CEAP-Benchmark watersheds are considered representative of agricultural systems in these five ecoregions, results indicate that erosion from channel sources, particularly streambanks, is a critically important process that must be addressed in management strategies aimed at controlling sediment production and delivery in these regions.