Effect of Nonuniformity of Flow on Hydraulic Geometry Relations

The effect of nonuniformity of flow on hydraulic geometry relations is investigated. Using data from a historic channel in Isfahan, central Iran, which was constructed 400 years ago, it is found that the nonuniformity of flow significantly influences the prediction of depth and velocity. However, flow nonuniformity reveals less effect on the prediction of slope due to nonlinear shear stress distribution. It is considered that under the uniform flow assumption $\left(\tau =\gamma hS\right)$ , depth and slope acting as dependent and independent variables, respectively, result in spurious correlation. However, the depth equation reveals this is not a correct conclusion because $R^2$ is not large and the exponent of ${\tau }_{\ast }$ is quite small. Likewise, although the Shields parameter is among the controlling variables for the prediction slope, its application under the uniform flow assumption has a risk of spurious correlation.