Experimental Study on Effect of Bend Curvature and Location of the T Shaped Spur Dike on Scour in a 90° Channel Bend

Spur dikes are used for preventing river banks erosion. The flow and scouring pattern around the spur
dikes used in the outer bank are complicated especially when spur dikes are used in the bends. This is
mainly due to the interaction between the flow pattern associated with the spur dike and the helical
currents in the bend. In this paper result of experiments on scour around a T shaped spur dike and the
effect of spur dike location on the amount of scouring and the effect of curvature of bend on the
variation of bed topography are reported. Experiments were conducted in a re-circulating rectangular
channel having 0.6 m width, 0.7 m height with different values of radius of bend to centerline
(R/B=2,3,4). The main channel consisted of a 7.1 m long upstream and a 5.2 m long downstream
straight reaches. A 90 degree channel bend was located between the two straight reaches. The bed and
sides of channle were made of glass supported by metal frames. Natural uniform sediment with
median size d50 =1.28 mm was used with a thickness of 0.35 m and covered the whole length of
channel. Experiments were conducted for 25 l/s discharge. Results show that when spur dike installed
at section 75 degree, the amount of scour is maximum. Also, by increasing the curvature of bend the
amount of scour increases. But the lateral development of scour hole decreases.