Flow Analysis of Large Triangular Weir

Accurate streamflow records are difficult to get on unstable alluvial channels. V-notch weirs have often been used to stabilize the ratings of streamflow stations in such areas. The first three parts of the article show the theoretical development and interaction of weir flow, submergence, and unsteady flow. Two different equations are derived. One equation assumes that a continuous record of the average velocity of approach is available. The other equation uses the rate of change of stage to approximate the effects of unsteady flow situations on weir flow and does not require a velocity. The fitting is described of the equation derived by theoretical analysis to a set of field measurements. The theoretical equations are then simplified as much as possible. The equations thus derived are more accurate than conventional weir flow equations. Results of the experiment show: (1) that if the weir rating is based upon both the static and velocity heads, the effect of submergence is one of a superposition of flows; and (2) that the rate of change of stage does not fully define unsteady flow.