EROSION PROCESSES IN COMPOSITE RIVERBANKS: EXPERIMENTS AND MODELLING

Abstract

Erosion processes in a composite bank is a very complex phenomenon due to many factors involved such as: seepage, variability of the bank stratifications, river stage variations, fluvial processes, soil stabilities. This study was focused to understand the primary processes responsible for bank erosion, and methodology to predict the bank erosion. Finally, a stochastic bank erosion model is proposed to estimate the seasonal bank erosion in a composite river bank. In the first stage, the developed model was simulated with known stage hydrograph, bank soil erodibility, and the bank stratification of a river bend in a reach of the Brahmaputra River in India. The critical shear stresses of the bank soils were determined through submerged-jet tests and the seepage erosion parameters were determined through laboratory lysimeter experiments. The predicted seasonal bank erosion rates for four consecutive years were compared with the observed rates. The results showed a good agreement between the observed data and modelling results. In the second stage, the uncertainty in the stage hydrograph, soil erodibility and the bank stratifications were considered. The stochastic bank erosion predictions were compared with the observed distribution of the bank erosion in 45 bends of the Brahmaputra River over 700 km long reach. Since the model has predicted satisfactorily therefore, the developed model can be used to obtain morphological dynamics of a sand-bed river bend with composite banks.