The Effect of April 2019 Flash Flood on the Morphology of the Meandering Confluence of the Dinver River to Gamasiab Using SRH-2D Numeric Model

Understanding the morphodynamics of river junctions is an important part of fluvial geomorphological studies that were provided suitable conditions to measure erosion and sediment changes at the junction of Dinver and Gamasiab rivers by the occurrence of floods in April 2019.  Due to the complexity, 3D numerical simulation is not cost-effective, and one-dimensional models, also, have some errors. For this reason, the use of two-dimensional models can be useful. Therefore, the SRH-2D model was used to investigate the effect of the flood on the morphology of the confluence of the Dinver River to Gamasiab. To study the morphological changes in the study area, elevation position and topography was mapped in two stages before and after the flood and also a granulometric experiment was performed. Due to the fact that the SRH_2D model does not have the ability to network, the required mesh was prepared using SMS software and the output file of the model was saved in TECPLOT format. The results showed that in a flood with a 35-year return period of the Dinver River to Gamasiab junction, with a meander- meander junction at a 40-degree angle, bed erosion in the downstream part of the junction begins to occur early in the onset of flooding and gradually expands to the upstream. However, sedimentation occurs shortly after the peak of the flood in the stagnation zone and then growing the spurs as the flood decreases, and developing the outer arch of the Gamasiab River as at the flood goes to end.