Depth-Averaged Velocity Distribution in Straight Trapezoidal Channels

In trapezoidal channels that are not “wide,” the banks exert form drag on the fluid and thereby control the depth-averaged velocity distribution. As such, commonly used equations for predicting depth-averaged velocities in wide channels are not well suited for predicting depth-averaged velocities in trapezoidal channels. Using data from three previous studies, we developed two models for predicting depth-averaged velocity distributions in straight trapezoidal channels. The data used to develop the models had a range of discharges (8.05–4,248?L/s), velocities (0.16–1.03?m/s), bottom widths (0.305–3.62?m), flow depths (0.0518–0.805?m), and bank slopes (1.0–3.0, horizontal/vertical). The first model requires measured velocity data for calibrating the model coefficients, whereas the second model uses prescribed coefficients. The first model yielded velocity distributions with coefficients of determination (r2) from 0.84 to 0.90 and we recommend its use when possible because it yields predictions that are more accurate. The second model also yielded good results (r2 = 0.86 and 94% of the predicted velocities were within 20% of the observed values).