IMPACT OF GRASS HEDGES ON SEDIMENT YIELD FROM A HEL WATERSHED

Authors: Alberts, Edward; Ghidey, Fessehaie; Kramer, Larry

Submitted to: Interagency Conference on Research in the Watersheds
Publication Type: Proceedings
Publication Acceptance Date: 9/25/2003
Publication Date: 10/27/2003
Citation: ALBERTS, E.E., GHIDEY, F., KRAMER, L.A. 2003. IMPACT OF GRASS HEDGES ON SEDIMENT YIELD FROM A HEL WATERSHED. PROCEEDINGS FIRST INTERAGENCY CONFERENCE ON RESEARCH IN THE WATERSHEDS. UNITED STATES DEPARTMENT OF AGRICULTURE. AGRICULTURAL RESEARCH SERVICE. WASHINGTON, D.C. P. 428-433 CDROM.

Interpretive Summary: Since 1985, considerable progress has been made in reducing soil losses from lands designated by the USDA-Natural Resources Conservation Service (NRCS) as being highly erodible. Many of these lands have been terraced, plus farmers have increased adoption of conservation tillage and no-tillage practices that keep crop residues on the soil surface to reduce raindrop and runoff detachment of soil. In countries such as China, India, and Indonesia, earthen terraces are formed by the natural process of erosion rather than by the mechanical method where soil is excavated and moved. The approach generally taken is to plant narrow rows of native grass that act as "leaky" dams reducing runoff velocity and causing significant sediment deposition just upslope of the grass hedge. In the early 1990s, the USDA-Agricultural Research Service began to investigate the effectiveness of grass hedges in erosion control for U.S. conditions. In 1991 and 1992, rows of stiff-stemmed grass hedges were planted within a 6-ha watershed located in western IA. The watershed was instrumented with a weir, water-stage recorder, and automated sediment sampler in 1974. Continuous runoff and sediment yield data were collected from 1975 through 2002. The 28-year period was separated into a 17-year period without grass hedges (1975-1991) and an 11-year period with established grass hedges (1992-2002). Several approaches were used to quantify the impact of the grass hedges on sediment yield during the 11-year period, including comparing differences in surface runoff and sediment yields between the two periods and prediction approaches including using the WEPP Watershed model. Depending upon the approach used in the assessment, grass hedges reduced sediment yield from 39 to 64%. The results show that stiff-stemmed grass hedges are an inexpensive alternative to terracing as an erosion control practice, but the hedges are susceptible to wash out where they cross areas of concentrated flow, such as ephemeral gullies. These results will be useful to the USDA-NRCS to better design and plan for the use of stiff-stemmed grass hedges as an erosion-control practice. Results will also be useful to scientists, extension/education personnel, and to farmers that have erosion or other environmental contamination problems to solve.

Technical Abstract: Stiff-stemmed grass hedges offer many opportunities to control erosion and other environmental contaminates leaving a field. The objective of this research was to evaluate the erosion-control effectiveness of narrow rows of grass hedges planted on 15.5-m spacings within a 6-ha watershed located in the deep loess hills region of western Iowa. Because only one watershed was planted in grass hedges, three different approaches were used to evaluate the erosion control effectiveness of the grass hedges as measured by sediment yield at the watershed outlet. The first approach was to compare measured surface runoff and sediment yields from the 1975-1991 period without hedges to the 1992-2002 period with hedges. The second approach was to develop a linear regression between annual sediment yield and surface runoff from data collected during the 1975-1991 non-hedge period and then estimate sediment yield without hedges for the 1992-2002 period from measured runoff values. The third approach was to use the WEPP Watershed model. The model was calibrated with data from the 1975-1991 period and then used to predict runoff and sediment yields without hedges for the 1992-1999 period using measured climatic and cropping and management inputs. Predicted sediment yields without hedges for the second and third approaches were compared with measured values with hedges. Stiff-stemmed grass hedges planted within the 6-ha watershed reduced sediment yield from 39 to 64% depending upon the approach used. Grass hedges had little to no impact on surface runoff losses, thus grass hedges acted as leaky dams temporarily ponding runoff, reducing sediment concentrations, and reducing sediment yield at the watershed outlet.