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Abstract:
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This paper deals with two dimensional local scour in anerodible bed below solid apron resulting from residual energy of stream flow leaving the hydraulic jump basin. A comprehensive discussion of the topic is given based on literature survey. Factors influencing local scour are mentioned. The stability of descrete particles under a stream flow is briefly explained. Different stages of the process of scour hole development and the effect of clear and sediment loaded water on the latter are presented and discussed. An assessment is made of scour hole profiles obtained from varying magnitudes of bed material type, stream flow, and apron length in order to observe the existence of similarity between them. The influence of bed material type, apron length, appurtenances of stilling basins, and of flow characteristics on the ultimate magnitudes of length and depth of scour hole are presented and discussed. Ways of predicting the depth of scour hole are pointed out. Similarity criteria required to reproduce the same type of flowin a scale model as in its prototype, the criteria of moderscale selection, and time scale between moder and prototype local scour are explained. Prevention of local scour by using energy dissipation devices and estimation of the region of erodible bed susceptible to local scour and the method of protection are also explained. Measuring techniques of the flow parameters related to local scour (bed topography, water level, flow velocities, discharge, and sediment transport), and measuring devices and instruments for the above are briefly presented. /Kir09 |