Document Type: Original Article

Authors

1 PHD student of hydraulic structure, Faculty of Water Sciences Engineering, Shahid Chamran Ahvaz University, Ahvaz, Iran

2 Professor of hydraulic structure, Faculty of Water Sciences Engineering, Shahid Chamran Ahvaz University, Ahvaz, Iran

10.33945/SAMI/IJABBR.2019.4.7

Abstract

Turbidity currents in the ocean and lakes are driven by suspended sediment. The vertical profiles of velocity and excess density are shaped by interaction between the current and bed as well as between the current and the ambient water. This paper presents 48 series of experiments in which saline gravity currents flow through a laboratory sinuous flume. flume contains three successive bends with three different relative curvature radiuses: R/B=2, 4 and 6, 8.5m length, 20cm width and 70cm height. Experiments performed by four discharges (0.7, 1, 1.5, 2 lit/s) and four concentrations (10, 15, 20, 25 gr/lit). ADV was used to record the local velocity. According to the results of experiments on the mobile bed, increasing the concentration of the incoming flow, the flow velocity of the fluid is also increased and, the maximum velocity occurs near the bed instead of the top of the current. The important point in the flow rate profiles is that the rate of increase in velocity depends on changes in the form of the bed due to the increase in concentration. By increasing concentrations of turbidity flow, the shear stress of the bed is also increased. Therefore, the rate of increase in velocity will occur by removing the bed forms and reducing the roughness and shear stress of the bed. Thus, increasing the concentration increases the power of the current, so at the beginning, the roughness and shear stress of the bed increased and then by removal of bed forms shear stress decreased.

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Main Subjects

Altinakar, MS, Graf, WH, Hopfinger, EJ. (1996). “Flow structure in turbidity currents.” J. Hydraul. Res., 34:713–718.

Buckee, C, Kneller, B, Peakall, J. ( 2001). “Turbulence structure in steady, solute-driven gravity currents.” Particulate gravity currents, Special Publication of the International Association of Sediemtologists 31, McCaffrey, WD, Kneller, BC, and Peakall, J. eds., Blackwell Science, Oxford, U.K., 31:173–187.

Chen, G, Shen, HS. (1984). River curvature-width ratio effect on shear stress. In: Elliott, C.M. (Ed.), Proceedings Conference on Rivers, New Orleans, LA., 687-699.

Dey, S, Barbhuiya, AK. (2005). Flow field at a vertical wall abutment. Technical Notes, J. Hydraul. Eng., 131(12):1126-1135.

Duan, JG. (2009). Mean flow and turbulence around a laboratory spur dike. J. Hydraul. Eng., 135(10):803-811.

Ellison, TH, Turner, JS. (1959). “Turbulent entrainment in stratified flows.” J. Fluid Mech., 6:423–448.

Richardson, E.V., Simons, D.B., Lagasse P.F. (2001). River Engineering for Highway Encroachments. Report No. FHWA NHI 01-004 HDS 6.

García, MH. (1993). “Hydraulic jumps in sediment-driven bottom currents.” J. Hydraul. Eng., 11910:1094–1117.

García, MH. (1994). “Depositional Turbidity currents laden with poorlysorted sediment.” J. Hydraul. Eng., 12011:1240 1263.

García, MH, Parker, G. (1993). “Experiments on the entrainment of sediment into suspension by a dense bottom current.” J. Geophys. Res., [Oceans], 98(C3):4793–4807.

Huthnance, JM, Humphery, JD, Knight, PJ, Chatwin, G, Thomsen, L, White, M. (2002). Near-bed turbulence measurements, stress estimates and sediment mobility at the continental shelf edge. Progres. Oceanog., 52:171- 194.

Ippen, AT, Drinker, PA, Jobin, WR, and Noutsopoulos, GK. (1962). “The Distribution of Boundary Shear Stresses in Curved Trapezoidal Channels."  J. Hydraulics Division, 88(5): 143-180.

Keller, EA. (1971). Areal sorting of bed load material: the hypothesis of velocity reversal. Bull. Geolog. Soc. Am., 82:753-756.

Kneller, BC, Bennett, SJ, and McCaffrey, WD. (1999). “Velocity structure, turbulence and fluid stresses in experimental gravity currents.” J. Geophys. Res., 104(C3):5381–5391.

Lofquist, K. (1960). “Flow and stress near an interface between stratified liquids.” Phys. Fluids, 32, 158–175.

Middleton, GV. (1966). “Experiments on density and turbidity currents, II. Uniform flow of density currents.” Can. J. Earth Sci., 3:627–637.

Parker, G, Fukushima, Y, Pantin, HM. (1986). “Self-accelerating turbidity currents.” J. Fluid Mech., 171, 145–181.

Parker, G, García, M, Fukushima, Y, Yu, W. (1987). “Experiments on turbidity currents over an erodible bed.” J. Hydraul. Res., 251:123–147.

Sear, DA. (1996). Sediment transport in pool-riffle sequences. Earth Surface Proces. Landform., 21:241-262.

Sequeiros, OE, Naruse, H, Endo, N, García, MH, Parker, G. (2009). “Experimental study on self-accelerating turbidity currents.” J. Geophys. Res., 114:C05025. doi.org/10.1029/2008JC005149.

Smith, R, Möller, N. (2003). Sedimentology and reservoir modelling of the Ormen Lange field, mid Norway. Marine  Petrol. Geology., 20:601–613.

Tilston, M. (2005). Three-dimensional Flow Structure, Turbulence and Bank Erosion in a 1800 Meander Loop. Thesis, University of Montreal, Quebec, Canada.

Xu, JP, Noble, MA, Rosenfeld, LK. (2004). “In-situ measurements of velocity structure within turbidity currents.” Geophys. Res. Lett., 31:L09311.

Watson, CC, Biedenharn, DS, Thorne, C.R. (2005). Stream Rehabilitation.  Version 1.0, 201 pp., Cottonwood Research, Fort Collins, Colorado.

Winn, RD, and Dott, RH, Jr. (1977). “Large-scale traction produced structures in deep-water fan channel conglomerates in southern Chile.” Geology, 5:41–44.