Experiments and Numerical Simulations of Water Flow over a Slit Weir for Measuring Very Small Discharges at River Intakes

The current research presents a procedure to calibrate rectangular contracted slit weirs for measuring flow rates less than 5 L/s at various diversion facilities of water intakes along small mountain rivers. The stage-discharge relationship obtained from CFD - 3D numerical simulations is validated with the corresponding curve obtained through experiments performed using a laboratory flume, on which the weir has been calibrated. Qualitative and quantitative comparison of the flow nappe over the weir and of the rating curve obtained from simulations and experiments prove a very good agreement. Increased sensitivity with head at low discharges proves the slit weir being a good measuring device for these flow ranges. Results show a new methodology of using CFD flow simulations over slit weirs to express small discharges at river intakes. This methodology is expected to be used even for more complex flow configurations.