Abstract
An experimental investigation on the problem of local scour downstream Ogee spillway is presented here by using two types of noncohesive bed material. The paper briefly explains the effect of hydraulic conditions of flow and sediment characteristics on depth and the extent of scour. The obtained results show that the depth and extent of scour affect greatly by the rate of the discharge and the depth of tail water. The size and shape of bed material particles plays an important role in characteristics of the occurred scour. The experimental data was used to develop two empirical relations to predict the depth and the extent of the scour downstream the Ogee spillway. Keywords: Scour, Ogee type Spillway, Hydraulics
Highlights
The study of scour downstream of hydraulic structures such as large dams, stilling basins spillways, diversion works, underflow gate and culverts, constitutes an important field of research due to its frequent occurrence in engineering application, downstream of these structures, many types of local scour, each with its own particular geometry and local mechanism (Plunging jets and horizontal jets) can be distinguished
To illustrate the effect of bed material on scour, six experiments are done for the two types of bed material under same hydraulic conditions as seen in Figs. 13, 14. It clear from these Figs. that the depth and extent of scour are more in type A (D50 = 0.5 mm, σ = 10.8 γs = 26KN/m3, rounded particle shape) than type B, ( D50 = 4.5mm, σ = 2.77, γs= 17KN/m3, angular particle shape) and this due to fine size and rounded shape of type A than type B. These results show the great effect of size and shape of particles of bed material on characteristics of the occurred scour
It was found that increase in discharge by 10% led to an increase in scour depth of 20% for type A, 7% for type B and led to increase in extent of scour 7% for type A and 5% for type B
Summary
The study of scour downstream of hydraulic structures such as large dams, stilling basins spillways, diversion works, underflow gate and culverts, constitutes an important field of research due to its frequent occurrence in engineering application, downstream of these structures, many types of local scour, each with its own particular geometry and local mechanism (Plunging jets and horizontal jets) can be distinguished. Kell et al[20] investigated the influence of sediment gradation on the depth and area asymptotic scour profile that developed downstream of a short apron due to submerged jet issuing from a sluice opening. Dey and Sarkar[23] investigate experimentally the development of the scour hole in noncohesive sediments ( uniform and nonuniform ) downstream of an apron due to submerged horizontal jet issuing from a sluice opening. The aim of the present research is focused on evaluation of the depth and extent of local scour downstream from an Ogee spillway under different sediment and hydraulic conditions and to find out empirical equations to predict the depth and extent of this scour. A total of 28 Runs were carried out for the two types of bed materials under different hydraulic conditions. A total of 13 runs with different hydraulic conditions were carried out using bed material type A and 15 runs for type B
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