Analysis of the effect of short dikes on flow hydraulics and sedimentation in Karun River within urban boundaries of Ahwaz

Abstract

Identification, analysis and prediction of the erosion and sedimentation or the increase and decrease in river bed level are among the most complex and yet up-to-date topics of deposit hydraulics and river engineering. If cross structures in rivers and canals are also to be considered the complexity of flow pattern and deposit transfer increases. In this research using the one-dimensional mathematical model HEC-RAS 4.1 the effect of short dikes on flow hydraulic and the trend of sedimentation and erosion in the Karun River were simulated and analyzed within the boundaries of Ahwaz City. The area introduced into the model started from the Ghir dike to Khoramshahr. Moreover, the Mollathani, Farsiat and Ahwaz hydrometric stations were used as the upper limit, lower limit and calibration limit of the model, respectively. The flow was assumed to be quasi-unsteady and based on the existing knowledge of different methods and experiences with the methods in other studies the Toffaleti method was used to solve the deposit equations. The model was prepared and applied in the following four states: without dike and with dikes 0.7, 1.2 and 1.7 m above the average level in the desired areas. Finally, results of the model applied with and without short dikes revealed that the short dikes and dikes 1.2 m above the average floor level of modeled areas were significantly ineffective under hydraulic conditions and morphological changes. Moreover, the majority of changes in the river bed and all the morphological changes, in general, were the result of other factors. Dikes with heights of 1.7 m above the average floor level significantly caused sedimentation in the upstream and affected the hydraulics of flow.