The design of sluiced settling basins. A numerical modelling approach

Settling basins can be used to prevent excessively large sediment quantities from entering irrigation canals; they work by trapping sediment in slowly moving flow produced by an enlarged canal section. The report presents two numerical models which can be used in the design of these structures. One model predicts conditions as a basin fills with sediment: deposition patterns and, more importantly, the sediment quantities passing through the basin are predicted. A second model predicts the sluicing process; in particular it predicts the time required for a basin to be flushed empty using a low level outlet at its downstream end. The models and the assumptions which underlie them are described in detail, and model predictions are compared against field measurements from three sites. The models give accurate predictions and are a significant improvement on existing design methods, in both the scope and accuracy of predictions. Aspects of basin design for which the models do not give guidance include determining the optimum width for a basin, the design of the basin entry and outlet, and the escape channel design. Each aspect is discussed and design methods are presented