Selective withdrawal through an intake fitted with a collar

Experiments are described for vertical intakes projecting above the bed and fitted with a horizontal cap and vertical collar. These show that the internal geometry of the intake has no effect on drawdown of a surface layer over the range of variables studied. Equations are presented for predictive purposes and the effect of the collar is determined by comparison with other raised intakes. This shows that intakes fitted with a collar have significant advantages for shallow water operation.