Abstract: A 3-D numerical model is used to simulate flows around submerged water intakes of mushroom-style and single-sided box-style. According to the simulations, the signs of horizontal velocity increment at the top-layer and intake-layer of the flows are observed to be the same or opposite under different conditions. On the basis of 3-D simulations and theory of open-channel flow, the mechanism of the above phenomena is studied. Theoretical analysis suggests that the operation of intakes disturbs the flow diffusion and dynamic water pressure, hence facilitating velocity variations of the top-layer flow in the opposite direction. Their combined effect is different when the water depth above the intake h′ varies. For the box-style intakes, when h′ is small, the viscous diffusion dominates the variation, and velocity increments of the same direction are produced at the intake-layer and the top-layer of the flows. When h′ is big, the pressure dominates the variation, and velocity variations of the opposite direction are produced at the intake-layer and the top-layer of the flows. Mushroom-style intakes absorb water from all horizontal directions, resulting in two areas of concentrated pressures above and below the intake. On the edge of these two areas, the water layers near the intake move towards the intake, and those at the bottom and the top are pushed away from the intake.

Key words: submerged water intake, 3-D numerical model, variation of vertical distribution of velocity