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United States Department of Agriculture

Agricultural Research Service

Research Project: UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS

Location: Water Quality and Ecology Research

Title: Do We Know Enough about Controlling Sediment to Mitigate Damage to Stream Ecosystems?

Author
item Shields Jr, Fletcher

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 19, 2009
Publication Date: September 27, 2009
Citation: Shields Jr, F.D. 2009. Do We Know Enough About Controlling Sediment to Mitigate Damage to Stream Ecosystems? Ecological Engineering. 35(2009) 1727-1733. doi:10.1016/j.ecoleng.2009.07.004.

Interpretive Summary: Stream and river ecosystems in agricultural watersheds have been degraded by past management practices. Elevated sediment concentrations due to channel and gully erosion are often one of the major causes of ecological damage. To assess the effectiveness of orthodox control measures on channel erosion and thus the amount of sediment leaving a watershed, long-term records from six Mississippi watersheds that were part of a major federally-funded erosion control demonstration program were examined. No trends in flow-adjusted sediment concentration were found for five watersheds while a slight decline was observed in one watershed. These findings should impact future research priorities regarding development of channel erosion control measures.

Technical Abstract: Stream and river ecosystems have suffered extensive degradation and billions are expended annually on restoration efforts. However, few of these projects are monitored and restoration effectiveness is often unknown. Consequently, there is a poor scientific foundation for restoration designs. Since many stream restoration efforts are at least partially targeted at controlling erosion of channel banks and beds, the effects of a large-scale, long-term stream erosion control effort in 16 Mississippi watersheds was assessed using 10 to 16 years of suspended sediment and water discharge records from six of the watersheds. Seasonal Kendall tests were used to test for the presence of trends in the discharges, sediment concentrations, and flow-adjusted sediment concentration. Although sediment yields trended downward over the period of observation, water discharge was also in decline due to weather trends. Despite average expenditures for erosion control exceeding $400/ha of watershed area, flow-adjusted suspended sediment concentrations showed no project effects in five of the watersheds, and a slight reduction in one watershed. Results indicate the inability of orthodox channel erosion control structures (weirs and bank protection) to reduce watershed sediment yield and the need for a stronger scientific basis for stream restoration.

Last Modified: 8/27/2014
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