Impacts of backwater flow on river morphology change

Abstract

Backwater flow is mainly caused by downstream water level increments. The objectives of the study were to assess backwater extension length and its effect on study reach morphology changes for about 20 km length. HEC-RAS model and the direct step numerical method were used to predict erosion-deposition rate and estimate backwater extension length, respectively. The field measured data (river bank, bed material, and river cross-sections) was collected using standard surveying equipment. The secondary (stream flow, sediment, lake level, rainfall and climate) data was collected by Ministry of Water resources and irrigation engineering office. For sediment transport analysis study, the England-Hansen function was selected because, it showed good agreement with the field data. The river bed changes were studied from the period 2000–2005, and the average vertical adjustment was equal to 0.34 and 0.22 m, for upper and lower reach, respectively. The overall study reach has been exhibiting 0.12 m cumulative depositions. For backwater flow study, it is propagate 1.5 km in length. The steady flow simulation results confirmed the conveyance capacity of the considered reach is not enough to carry a 100-year return period discharge. Hence, Lake Regulation should be fixed without the disturbance of its tributaries.