Analysis of Flow in River Cross Section Using Finite Elements Method

Alluvial rivers often have wide floodplains which play an important role in flood passage, enhancement of environmental habitat, soil fertility and extending recreational and agricultural activities. For calculation of flood discharges in main channel and floodplains and recognition of erodible sections of the river, simulation of lateral velocity and bed shear stress distribution are important. In the flooding situation, however, advanced and expensive pieces of equipment are required to measure lateral profile of velocity and specially bed shear stress. Therefore, application of quasi 2-D mathematical models based on solutions of continuity and momentum equations is important in river engineering projects. In this paper, at first, by application of Shiono and Knight model numerical solution and use of finite element method, lateral distribution of flow velocity in Minab river (at Berentin station) was calibrated based on field data. The maximum error was around 13 percent for flood discharge computation. Then, lateral distribution of bed shear stress for a flood event in the year 1374 (Iranian calendar) was simulated, based on which lateral variations of river cross section were analyzed. Results of this research showed that erosion and sedimentation situation in river width computed by mathematical model based on bed shear stress presented good agreement with the actual data.