Abstract :
Riverbank erosion is a natural process, but its measurement and prediction is still not an easy task. Bank
assessment for non-point source consequences of sediment (BANCS) model is a popular one for
evaluating stream bank erosion hazard potential (SBEHP) which includes two procedures, bank erosion
hazard index (BEHI) and near bank stress (NBS). In this paper, BANCS model has been applied for
about 20km of river Mahananda at the foothills of the Darjeeling Himalayas where bank erosion is
prominent. The results show that out of 22 sample points, 14 have high BEHI rating and 4 have a very
high and medium rating. In the case of NBS, 7 sample points have low, 9 have moderate and 6 have high
NBS rating. Field studies estimated the rate of bank erosion at 2510m /year. Less vegetation cover,
absence of surface protection at the toe of a bank, higher velocity of water, loose bank material,
fluctuation of thalweg, formation of numerous bars in the channel bed are the some of the major causes
for bank erosion in this stretch. In order to verify the suitability of BEHI and NBS rating as a predictor of
bank erosion, linear regression has been fitted that show a positive relationship between these ratings
and observed erosion rate. Hence, this model can be used as a suitable measure for predicting the
occurrence of bank erosion of the particular portion of the river.
Keyword :
Bank Assessment Non-point Source Bank Erosion Hazard Index Bank Erosion Hazard Potential Near Bank Stress Thalweg