Longitudinal Dispersion Characteristics of Rivers and Natural Streams in Greece

An optimized parameterization of the non-dimensional longitudinal dispersion coefficients in Greek rivers, $K_{x_a } $ , is described in terms of parameters derived from cross-section river geometry and longitudinal velocity data. Optimization is accomplished, using various combinations of the selected parameters, either for subsets of $K_{x_a } $ values, according to the cross-section aspect ratio range, or for the entire $K_{x_a } $ population. The use of shape factors associated with the river cross-section transverse profiles of depth-mean longitudinal velocities and the normalized intensities of longitudinal velocity variations from the overall mean cross-sectional velocity improves the parameterization. The statistical behavior of $K_{x_a } $ in terms of skewness, flatness and other shape coefficients is also examined. $K_{x_a } $ histograms show that these coefficients have a log-normal distribution. An empirical expression for $K_{x_a } $ is also proposed that takes into account both contributions from the transverse velocity profile and from the vertical profile of longitudinal velocities, at each cross-section, in shaping the value of dispersion coefficients when the aspect ratio of the cross-section is of O(1) and/or when $K_{x_a } $ is of O(1).