Laboratory study of sediment distribution at channel bifurcation

Abstract

Morphological behavior of bifurcations and confluences which are typical features of rivers and estuaries are still not properly understood phenomena. Recently a few researchers have done some work on bifurcation with the help of I-D model which are not developed particularly for this purpose. In these l-D models the bifurcation phenomena has been represented by the help of nodal point relations. The distribution of sediment at bifurcation is a three dimensional phenomena. It is very difficult to '~et a clear idea of three dimensional problems with the help of 1- D models. S0, to get some insight into phenomena and process, laboratory experiment was initiated at the laboratory of Department of Water Resources Engineering, BUET. As the bifurcation phenomena is a very complicated one, assumptions were made to make the problem as simple as possible.

After constructing the experimental set-up all the facilities were tested whether they were working according to simplification. All instruments were calibrated and the model produced results as .expected. After being satisfied that the experimental set-up was functioning properly, main experiments were carried out.

Experiments were carried out with two noses representing two different bifurcation conditions. The first nose gave results which fits well with the theory S2 = k(tJ2J "']. The only differences S3 q3 was that with the increase of discharges the value of m (nose geometry) did not remain constant rather it increased. In case of the second nose the value of m increased with discharge but at a lower rate. Here the calculated normal depths were far a way from the actual normal depths of the two downstream branches. This is because the shape of the nose created an additional influence in the model. So, the results of the two noses can not be compared since the conditions are not the same. But it can be interred trom the resuits that no gen~ral relation in the case of sediment distribution over the two downstream branches can be expected since it depends not only on the geometry of the nose but also on the condition of the downstream branches as compared to nose configuration. Further studies will help in better under standing the problem since this may be the beginning of such kind of study.