EROSION CONTROL PRACTICES INTEGRATED WITH POLYACRYLAMIDE TO REDUCE SEDIMENT LOSS IN FURROW IRRIGATION

In the Lower Yakima River Basin of Washington, surface irrigators need to reduce sediment loads exiting theirfields in order to comply with newly established water quality standards. The goal of this research was to assess methods forimproving the water quality of return flow from furrow irrigation by combining a patch application of polyacrylamide (PAM)with an additional erosion control practice in the tailwater ditch. A study was conducted in 2001 and 2002 that combinedPAM with: 1) surge irrigation, 2) grass filter strips, 3) check dams, and 4) surface drains. In order to test the treatments underdifferent cultural practices and slopes, the study was conducted at three site: two vineyards with silt loam soils at 1.2% slopein both the furrows and the tailwater ditch, and a cornfield with silt loam and sandy loam soil at 0.2% slope in both the furrowsand the tailwater ditch. During irrigation events, sediment samples were taken and outflow rates were recorded at periodicintervals to determine sediment concentration, run-off volume, and sediment load from each treatment. At all sites and at allmonitored irrigations, the control plot, which had only the patch application of PAM, produced sediment concentrationsgreater than the total maximum daily load standard of 56 mg.L-1 for the Lower Yakima River. All four erosion controlpractices in combination with PAM were more effective in reducing sediment load at the vineyards as compared to thecornfield. Only the grass treatment with PAM was consistent in reducing sediment concentrations below 56 mg.L-1 in boththe vineyards and the cornfield.