SEDIMENT TRANSPORT IN RIGID BOUNDARY CHANNELS

Abstract

Over the years, unlined and lined channels have been used for various purposes. Lined channels have obvious advantages over unlined channels such as reduction in seepage losses, maintenance costs etc. Since in these channels, there is no problem of scour, design considerations require that the channel dimensions be adequate to carry the sediment load without any objectionable deposition on the bed. Many studies aimed at determining this upper limit of sediment concentration have been carried out. The available relationships fall into two broad categories, one for bed load and the other for suspended load. Oja (1980), Novak and Nalluri (1984), Mayerle et al. (1991), and Singh (1993) suggested relationships for the limiting concentration of sediment moving as bed load in channels of rectangular cross-section. On the other hand, Novak and Nalluri (1984), May (1982), Ackers (1984), Mayerle et al. (1991), and Ab. Ghani (1993) proposed relationships for limiting concentration of sediment moving as bed load in channels of non-rectangular cross-section, especially circular channels. Pullaiah (1978), Westrich and Juraschek (1985) and, Celik and Rodi (1985) have all developed relationships for limiting concentration of sediment moving as suspended load in rigid boundary channels of rectangular cross-section. Nalluri and Ab. Ghani (1994) proposed a method for predicting suspended load transport at the limit of deposition in circular pipes. Arora et al. (1984) proposed a relationship for limiting concentration of suspended load in channels of various shapes. Sinha (1994) proposed a single relationship for the limiting concentration moving as bed and suspended load in rigid boundary channels of rectangular cross-section. In the present study, available relationships for the limiting concentration of sediment moving as bed load and suspended load have been reviewed and checked for their adequacy. Checks made on these relationships revealed their inadequacies to predict the limiting concentrations accurately. Also some of these relationships are not applicable to channels of non-rectangular section.