Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2004
Publication Date: 9/25/2005
Citation: Strelkoff, T., Clemmens, A.J. 2005. Transport capacity for eroded silts in irrigation furrows. Journal of Hydraulic Engineering. 13(10):921-926.
Interpretive Summary: Erosion and transport of soil from which furrows are formed can be a significant aspect of surface-irrigation performance. From western Nebraska to the Pacific Northwest, as well as in other parts of the world, loss of soil fertility and discharge of eroded sediments, sometimes with phosphorus adsorbed, into receiving streams are important problems. Like other measures of performance, sediment movement depends upon field hydraulic properties and system design and management. Simulation models applied to what-if scenarios can be a great help in arriving at proper design and management. Existing models based on a single representative soil-particle size are too sensitive to the selection of that size, and underestimate by far the total surface area of all sediments transported with the irrigation runoff. With phosphorus adsorption dependent primarily on surface area, it is essential that actual particle size distributions are incorporated into the model. The research reported is a work in progress, centering on the adaptation of empirical sediment transport models developed for rivers to the smaller scale of both cross-sectional dimensions and sediment sizes pertinent to furrow irrigation. When completed, the software is intended for use by federal agencies concerned with surface-irrigation management like the Natural Resources Conservation Service, consultants, and extension personnel.
Technical Abstract: An aspect of surface-irrigation performance is the erosion and transport of soil from which furrows are formed. From western Nebraska to the Pacific Northwest, as well as in other parts of the world, loss of soil fertility and discharge of eroded sediments, sometimes with phosphorus adsorbed, into receiving streams are significant problems. Like other measures of performance, sediment movement depends upon field hydraulic properties and system design and management. Simulation models applied to individual hypothetical events can be of great assistance in developing proper designs and management scenarios. Issues that arise when extending the single representative-particle-size approach in the erosion component of the simulation software, SRFR Version 4, to track individual size-fractions of the sediment mix through their entrainment, transport, and deposition, include the extension of existing empirical transport-capacity formulas to small silt particle sizes. A modification of Laursen's 1958 formula based on recognition of a laminar sublayer in the flow near the furrow boundary is proposed to eliminate computed negative transport of very small particles. The assumption that the formula basically is sufficiently well grounded theoretically to warrant some application to sediment sizes smaller than those in his empirical database leads to plausible results. Ultimate justification will be based on comparisons of simulated sediment-load hydrographs with field measurements.