Transport Capacity for Eroded Silts in Irrigation Furrows

An aspect of surface-irrigation performance is the erosion and transport of soil from which furrows are formed. The current single representative-particle-size approach in the erosion component of the U.S. Water Conservation Laboratory surface irrigation-simulation software, is being extended to track individual size fractions of the sediment mix. This requires the adaptation of existing empirical transport-capacity formulas to the small silt particle sizes in the mix. A modification of Laursenʹs 1958 formula based on recognition of a laminar sublayer in the turbulent flow near the furrow boundary is proposed to eliminate computed negative transport of very small particles. The assumption that the formula is sufficiently well grounded theoretically to warrant some application to sediment sizes smaller than those in its empirical database leads to plausible results. Ultimate justification will be based on comparisons of simulated sediment-load hydrographs with field measurements.