SOME RECENT DEVELOPMENTS IN FLUVIAL HYDRAULICS

Abstract

Evaluation of the hydraulic conditions of incipient motion of sediment particles comprising the bed and sides of the stream, needs careful attention for safety against erosion and deposition of sediment. This troublesome process of erosion and deposition along stream beds poses threat to the hydraulic structures, e.g. inundation and raising of flood heights, reduction in storage capacity of reservoirs, scour around spurs, bridge piers etc. Changing bed forms in these rivers complicate the determination of the resistance to flow under varying conditions and hence stage-discharge curve. For evaluation of the extent of deposi-tion in the reservoirs, the sediment transportation capacity of the river should be known. Reliable estimates of the parameters such as maximum depth of scour, the magnitude and the length of degradation etc. can-not be made at present because of the complex nature of the phenomena involved in erosion, transportation and deposition of sediments. Vast amount of literature related to alluvial channel flow and allied problems is available and one is at a loss to know the correct application of these techniques to solve the field problems. An attempt has been made, herein, to summa-rise some of the existing methods or techniques which have gene- ral applicability to the field problems and can be readily em-ployed by practising engineers, Step^by-step computational pro-cedures have been given for preparation of stage-discharge curve and for estimation of sediment transport rates and mode and rate (v) of silting of reservoirs. A typical case of a bridge pier of various shapes has been considered for studying scour around hydraulic structures. Wherever possible, typical application of these techniques have been illustrated. It is not possible to discuss all the problems associated with alluvial channel flow in a dissertation of this type. There-fore, the topics selected for discussion include incipient-motion condition, resistance to flow, sediment transport and river bed variation only.