Hydraulic of Board Crested Weirs with Varying Side Slopes

The flow of water over a trapezoidal, broad-crested, or embankment weir with varying upstream and downstream slopes has been investigated. Data are presented comparing the effect of slopes of 2H:1V, 1H:1V and vertical in various combinations on the upstream and downstream faces of the weir. Pressure and surface profiles were self-similar for all cases tested. Increasing the upstream slope to the vertical decreased the height of the surface profile and, hence, the static pressure of the crest. It also reduced the discharge coefficient. The variation in downstream static pressures was negligible though. Varying the downstream slope had a negligible effect on the surface and pressure profiles over the weir. Changes in flow were constrained to the region downstream of the crest. Cavitation could occur at the downstream corner of the weir if the upstream head was sufficiently high and a sloped face was used. This paper presents data that will be of use in the design of hydraulic structures for flow control and measurement. © 2009 ASCE.