Effect of sediment load from main canal on maximum scour depth at river confluence

Document Type : Original Article

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Abstract

River confluence is an important element of river system. At this place, because of complex three dimensional flow structure, scour and sedimentation is occur which can damage the surrounding area, change river morphology and can be harmful to navigation. Many variables can effect the sedimentation pattern at river confluence such as bed load coming from the main channel which has not been studied in the past. Therefore it is the main goal of this study to experimentally investigated the effect of bed load. To do so first a general non dimensional relation was developed, then a sediment feeder was designed and calibrated. Afterwards, series of experimental tests were conducted in various hydraulic conditions and sediment discharge. The results indicate that increasing the amount of bed load sediment, reducing the maximum scour depth from up to 35 percent. Also it was observed that bed scour and sedimentation patterns can change when the bed load is presented. Finally, an equation was developed to predict the scour depth in terms of sediment load. The accuracy of the new is within 95 percent. The sensitivity analysis of this equation shows that it is more sensitive to Densimetric Froude. The new relation was compare with Ghobadian and Shafai Bejestan (2007).

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References

1. برقعی س.م.، س.م. سخائی فر و ع. دائمی. 1381. بررسی آزمایشگاهی اتصال کانال ها. مجموعه مقالات ششمین سمینار بین اللملی مهندسی رودخانه. اهواز، صفحه 611-619.
2. برقعی س.م. و ا. نظری. 1382. بررسی آزمایشگاهی الگوی رسوب درتقاطع کانال‌ها. مجموع مقالات ششمین کنفرانس بین المللی مهندسی عمران. اصفهان، صفحه 247-255.
3. Best, J.L. 1988. Sediment transport and bed morphology at river channel confluences. Sedimentology, 35, 481-498.
4. Best, J.L. 1987. Flow dynamics at river channel confluences: Implications for sediment transport and bed morphology.  Recent Devel. In Fluvial Sedimentology, SEPM Spec. Publ. 39, F.G. Etheridge, R.M. Floers and M.D. Harvey, eds., 27-35.
5. Best, J.L. and I. Reid. 1984. Separation zone at open channel junctions. J. Hydr. Engrg.,  ASCE, 100(11):1588-1594.
6. Borghei, S.M. and A. Sahebari Jabbari . 2010.  Local scour at open channel junctions . Journal of Hydraulic Research, 48: 4:538-542.  
7. Bradbrook, K.F., S.N. Lane, K.S. Richards, P.M. Biron and A.G. Roy. 2001. Role of bed discordance at asymmetrical river confluences. J. Hydr. Engrg. 127:351-368.
8. Ghobadian, R. and M. Shafai Bejestan. 2007. Investigation of sediment patterns at river confluence. J. Applied Sci., 7(10):1372-1380.
9. Gurram, S.K., K.S. Karki and W.H. Hager. 1997. Subcritical junction folw. J. Hydr. Engrg., ASCE, 123(5):447-455.
10. Hager,  W.H. 1989. Transition flow in channel junctions. J. Hydr. Engrg., ASCE, 115(2):243-259.
11. Hsu, C.C., F.S. Wu and W.J. Lee. 1998 a.  Flow at 90 equal width open channel junction. J. Hydr. Engrg., ASCE, 124(2):186-191.
12. Hsu, C.C., Lee W.J. and C.H. Chang. 1998 b. Subcritical open channel junction flow. J. Hydr. Engrg., ASCE, 124(8):847-855.
13. Huang, J.L., L.J. Weber and G.L. Yong. 2002. Three Dimensional Numerical Study of Flows in Open Channel Junctions flow. J. Hydr.Engrg., ASCE, 128(3), 268-280.
14. Modi, P.N., P.D. Ariel and M.M. Dandekar. 1981. Conformal mapping for channel junction flow. J. Hydr. Engrg., 107(12), 1713-1733.
15. Mosley,  M.P. 1976. An experimental study of channel confluences. J. Geol., 84,535-562.
16. Melville, B.W. and Y.M. Chiew. 1999. Time scale for local scour at bridge piers. J. Hydr. Engrg., ASCE,125(1),59-65.
17. Ramamurthy, A.S., L.B. Carballada and D.M. Tran. 1988 . Combining open channel flow at right angled junctions. J. Hydr. Engrg., ASCE, 114(12), 1449-1460.
18. Roy, G.A. and R. Roy. 1988. Changes in channel Size at river Confluences with coarse bed material. Earth surface processes and Land forms, 13, 77 – 84.
19. Shafai Bejestan, M. and M. Hemmati. 2008. Scour depth at river confluence of unequel bed level. Journal of Applied Sciences 8(9): 1766-1770.
20. Webber, N.B. and C.A. Greated. 1966.  An investigation of flow behavior at the junction of rectangular channel. Proc., Instn. of Civ. Engres., Vol. 34. Thomas telford Lte., London. 321-334.
21. Weber, L.J., E.D. Schumate and N. Mawer. 2001. Experimentals on flow at a 900 open channel Junction. J. Hydr. Engrg. ASCE, 127, 340 – 350.
22. Weerakoon, S.B., Y. Kawahara and N. Tamia. 1991. Three dimensional flow structure in channel confluences of rectangular section. Proc., 24th IAHR., 373-380.
Irrigation and Water Engineering
Volume 2, Issue 1 - Serial Number 5
December 2011
Pages 1-14

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