Title: Simulation of unsteady flow and soil erosion in irrigation furrows Authors
Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 8, 2011
Publication Date: April 1, 2012
Citation: Zhang, S., Duan, J.G., Strelkoff, T., Bautista, E. 2012. Simulation of unsteady flow and soil erosion in irrigation furrows. Journal of Irrigation and Drainage Engineering. 138(4):294-303. Interpretive Summary: In many parts of the world, soil erosion induced by surface irrigation is a significant economic and environmental problem. With topsoil washing away in the furrow flow, the productivity of a field can be severely reduced, to the point of requiring periodic hauling of soil eroded from the upper reaches and deposited in the lower portions of a field back into the upper reaches to restore some degree of fertility. Soil that is discharged from the field, in the furrow tailwater, is cause for environmental concern for the receiving water bodies – the sediment itself can be harmful to aquatic life and, in addition, nutrients and other agricultural chemicals, adsorbed to the sediment particles can be harmful both to aquatic life, and a cause of eutrofication in the drainage itself. Reported magnitudes of the problem include 22 tons/acre in a 24-hour irrigation; 1/2 to 12 tons/acre per irrigation in Wyoming; 75% of Idaho furrow-irrigated fields losing the entire A horizon in the upper reaches together with a 2 to 4-fold increase in “topsoil” at the lower ends, reducing productivity by 25% over pre-erosion values, and reducing yields by 20 – 50% in areas with lost top soil. Modeling of what-if scenarios can lead to rational recommendations for design and management of surface irrigation. The proposed model should be of interest to hydraulic engineers and other researchers working in related surface-subsurface flow problems.
Technical Abstract: Soil erosion in irrigation furrows significantly impacts the efficiency of irrigation,infiltration and fertilization. This study developed a one-dimensional numerical model to simulate unsteady flow and the resultant soil erosion and sediment transport in irrigation furrows. The model solves a revised version of the Saint-Venant equations by considering the loss of mass and momentum due to infiltration and sediment transport. The transport rate of fine sediment was predicted by a modified Laursen’s equation in which the tractive shear stress was treated as a function of both Reynolds number and the particle size. The modified Laursen’s formula was verified using the measurements from experiments in furrows and a laboratory flume. The developed model was then used to simulate unsteady flows in irrigation furrows at Kimberly, Idaho. The simulated advancing time and flow hydrograph agreed well with the measurements, while the simulated sediment discharge showed some discrepancies from the measurements. These results suggested that sediment transport in irrigation flows is important for accurately predicting infiltration and irrigation efficiencies.