Evaluation Of Local Scour Development Around Curved Non-Submerged Impermeable Groynes

Groynes are man-made hydraulic structures constructed for a variety of purposes. They extend outside the bank in the depth of streams. Local scour usually occurs around groynes resulting in problems of interest to hydraulic engineers. In this study laboratory experiments were conducted to evaluate the local scour around different number of groynes distributed on different spacing with different shapes. Physical models have been developed for groynes installed in a straight hydraulic channel grounded with uniform cohesionless soil as bed material with medium grain size d50 0.69 mm. The experiments were conducted under subcritical flow and Clear- water conditions. Three different numbers of groynes single double and triple were used to indicate the impact of the numbers on the local scour such impact have been observed to be as reverse relationship specially for the intermediate groynes. Different spacing between groynes as 1 1.5 and 2 times the length of groynes were used in this study. For the range tested it has been observed that for each spacing decrease by 0.5 Lg there was a decrease in scour depth about 20. Also several lengths of groynes 13 10 and 7 cm were used and it has been observed that scour depth is decreased about 20 - 53 by decreasing the ratio of groyne length to main flow width LgB by 7.5. Two different shapes of curved groynes namely as quadrant quarter of a cylinder and semi-parabolic shaped groynes were used to indicate the effect of groyne shape on the local scour. Generally scour is decreased about 75 in quadrant shape groynes as compared with that of semi-parabolic shape groynes.