يادداشت تحقيقاتي: بررسي آزمايشگاهي اثر شعاع انحناو موقعيت استقرار آبشكن هاي T در قوس 90 درجه بر ميزان آبشستگي اطراف آنها

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 center line (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 dso =1.28 mm was used with a thickness of 0.35 m and covered the whole length of channel. Experiments were conducted for 25 1/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.