Deposition of fine sediments in irrigation canals

Sediment control structures constructed at the heads of run-of-river irrigation schemes have little effect on the very fine sands and silts that settle in the smaller distribution canals. One means of minimising the effects of fine sediment deposition in small canals is to design canals so that deposition occurs at selected locations, rather than throughout the canal network. Standard sediment transport predictors cannot be used to predict the effects of changing canal slopes and cross sections when sediment sizes are very small, and thus cannot be used to determine dimensions and slopes of small canal settling basins.The paper presents a simple method for estimating the transport and deposition rates of fine sediment suspensions, for sediments in the cohesive size range. The method, which has been tested against a large data set, enables the effects of changing canal cross sections and slopes on fine sediment transport to be quantified.