Experiments are described for vertical intakes projecting above the be
d and fitted with a horizontal cap and vertical collar. These show tha
t the internal geometry of the intake has no effect on drawdown of a s
urface layer over the range of variables studied. Equations are presen
ted for predictive purposes and the effect of the collar is determined
by comparison with other raised intakes. This shows that intakes fitt
ed with a collar have significant advantages for shallow water operati
on.