Critical Investigation of the Bed Load Evaluation Models for the Mountainous Stream

For the computation of the bed load transport rate at a particular section of stream, the selection of any approach depends upon the ambient hydraulic condition as well as the nature of the sediment and the bed of the stream. The present study evaluates bed load transport rate in the upper reaches of a mountainous stream, which consists of large non-uniformity in the bed load. The best-suited instrument for bed load collection should have features to take care of the non-uniformity of the bed load and the bed material. In the present study, the USGS Sampler (a modified version of the Helley-Smith bed load Sampler) has been used. The sampling time is an important criterion as far as the direct measurement of the bed load from the natural stream is concerned. The natural channels are non-prismatic in nature, so the velocity distribution will vary in both directions of the stream. The non-uniformity of the velocity interacts in a complex fashion with the non-uniform bed material, which later on is converted into the bed load of the stream. In the present study, the comparison of the measured bed load transport rate and the computed bed load transport rate has been carried out using several approaches for the gravelly bedded stream. In the present study, thirteen equations have been selected for the bed load prediction at the selected sites. The best-suited approach for the bed load prediction is A. Recking’s approach, which scores 0.663 and 0.843 on the scale, subject to a maximum score of 1.