Changes in Turbidity Current Flow Velocity Due to the Obstacle Height and an Abrupt Decrease in a Reservoir Bed Slope

Subject Areas : Article frome a thesis

Shiva Keshtkar ¹ , Seyed Ali Ayyoubzadeh ² , Masoud Ghodsian ³

1 - دانش آموخته دکتری سازه های آبی دانشگاه تربیت مدرس.
2 - استاد، عضو هییت علمی گروه سازه های آبی دانشکده کشاورزی دانشگاه تربیت مدرس.
3 - استاد، عضو هییت علمی گروه مهندسی آب دانشکده عمران و محیط زیست دانشگاه تربیت مدرس

Received: 2016-01-13 Accepted : 2017-06-18 Published : 2017-05-22

Keywords: Turbidity Current, Obstacle, Reservoir of dam, Experimental study, Slope break, Vertical distribution profile of velocity,

Abstract :

Turbidity currents are the main process for the transport and deposit of sediments in reservoir, especially in the deepest part near the dam, where vital structures such as power intakes and bottom outlets are located. The existence of an obstacle in such current can cause a decrease in the velocity and thickness of the second turbidity current which, occurs after the obstacle. In this study that was carried out as a two-dimensional experimental study, the effect of a solid obstacle, its height on the vertical distribution profiles of the velocity, when there is an abrupt decreasing in the bottom slope, was investigated. Separate non-dimensional equations for the vertical distribution of velocity in different cases were developed. The coefficient of the non-dimensional equations were compared with each other. Results indicated that the existence of an obstacle can reduce the velocity of the turbidity current, which passes the obstacle, about 20%-50%, and also can reduce the discharge of the current by increasing the relative height of the obstacle from 0.0091 to 0.273 by about 20% -60%, respectively. This effect on turbidity current’s velocity and discharge would be increased by the increasing the height of the obstacle.  The results also indicate that the highest change in the current discharge occurred in the jet region of the velocity profile.   

References:

1)       اصغری پری، ا.، م. کاشفی پور. و م. قمشی. 1388. بررسی اثر غلظت جریان در کنترل جریان غلیظ با مانع در مخازن سدها، هشتمین سمینار بین­المللی مهندسی رودخانه، اهواز، دانشگاه شهید چمران. http://www.civilica.com/Paper-IREC08-IREC08_296.html.

2)       بهرامی، ح.، م. قمشی. و س. م. کاشفی­پور. 1388. بررسی آزمایشگاهی تغییر شکست شیب بستر بر خصوصیات جریان غلیظ. مجله­ی علوم و فنون دریایی. 8: 67-76.

3)       فیروزآبادی، ب. 1378. بررسی تجربی و تئوری جریان­های مطبق و تهیه­ی نمونه­ی ریاضی از جریان­های چگالی حاوی ذرات. رساله­ی دکتری. دانشکده­ی مهندسی مکانیک، دانشگاه صنعتی شریف.

4)       ماروسی، م .، م. قمشی. و ح. بشاورد. 1388. کنترل رسوبگذار توسط مانع در مخازن سدها، هشتمین سمینار بین­المللی مهندسی رودخانه، اهواز، دانشگاه شهید چمران.        http://www.civilica.com/Paper-IREC08-IREC08_223.html.

5)       کشتکار، ش.، س. ع. ایوب زاده. و ب. فیروزآبادی. 1389. بررسی آزمایشگاهی ضخامت و پروفیل­های سرعت جریان گل آلود. نشریه­ی آب و خاک. 24: 1073-1082

6)        ناجی ابهری، م. 1392. مطالعه­ی آزمایشگاهی اثر موانع بر جریان غلیظ. رساله­ی دکتری رشته عمران-هیدرولیک، دانشکده­ی عمران و محیط زیست دانشگاه تربیت مدرس.

7)        Alexander, J., and S. A. Morris. 1994. Observation on experimental non-channelized: high concentration turbidity currents and variation in deposits around obstacles. J. Sedim Petro. A64: 899-909.

8)       Altinaker, S., W. H. Graf and E. J. HopFinger. 1996. Weakly deposing tubidity current on a small slope,  J. Hydr. Res. 28: 55-80.

9)       Barahmand, N., and A. Shamsai. 2010. Experimental and theoretical study of density jumps on smooth and rough beds. J. Lakes and Reserv: Res Manag, 15: 285-306. 

10)   Bradford, S. F., and N. D. Katopodes. 1999. Hydrodynamics of turbid underflows I: formulation and numerical analysis. J. Hydr. Eng. ASCE, 125: 1006-1015.

11)   Bursik, M. I., and A.W. Woods. 2000. The effects of topography on sedimentation from particle-laden turbulent density currents: J. Sedim. Res. 70: 53–63.

12)   Cabeza, C., J. Varela., I. Bove., D. Freire., A. C. Marti., L. G. Sarasua., G. Usera., R.   Montagne., and M. Araujo.  2009. Two-layer stratified flows over pronounced obstacles at low-to intermediate Froude numbers. J. Phys. Flu 21: 102-110.

13)   De Cesar, G., J. L. Boillat., and A.J. Schleiss. 2006. Circulation in stratified lakes due to flood-induced turbidity currents. J. Envron. Eng. 132: 1508-1517.

14)   Firoozabadi, B., b. Farhanieh., and M. Rad. 2003. Hydrodynamics of 2-D laminar tubidity current. J. Hydr. Res. 41: 623-630.

15)   Garcia, M. H., and G. Parker. 1993. Experimental on the entainment of sediment into suspention by a dense bottom current. J. Geophys. Res. (Oceans) 98:4793-4807.

16)   Graf, W. H., and M. S. Altinakar. 1998. Fluvial hydraulics-flow and transport processes in channels of simple geometry. Chap. 7. Wiley ,New-York.

17)   Hug, M. 1975. Mecanique des fluides appliqué eyrolles. Paris. F.

18)   Kneller, B., and C. Buckee. 2000. The structure and fluid mechanics of turbidity current; a review of some recent studies and their geological implications. J. Sediment. 47: 62-94.

19)   Komar, P. D. 1971. Hydraulic jumps in turbidity currents. Geol. Sec. Am. Bull. 82: 1477-1488.

20)   Kostic, S., and G. Parker. 2007. Conditions under which a supercritical turbidity current traverses an abrupt transition to vanishing bed slope without a hydraulic jump. J. Flu Mech. 586:119-145.

21)   Migeon, S., T. Mulder., B. Savoye., and F. Sage. 2011. Hydrodynamic processes, velocity structure and stratification in natural turbidity currents: results inferred from field data in the turbidite system. J. Sedimen Geo. 245:48-62.

22)   Morris, S. A., and J. Alexander. 2003. Changes in flow direction at a point caused by obstacles during passage of a density current. J. Sedimen. Res. 73: 621-629.

23)   Oehy, C., and A. J. Schleiss. 2001. Numerical

 

modeling of a turbidity current passing over an obstacle- practical application in lake Grimsel, Switzerland. Proc. Int. Symp. Env. Hydr., Tempe, AZ, (CD-Rom).

24)   Oehy, C., G. De Cesare., and A. J. Schleiss. 2010. Effect of inclined jet screen on turbidity current. J. Hydrau Res. 48: 81-90.

25)   Reger, A., S. Hassid.,  and M. Poreh. 2004. Density jumps in smoke flow along horizontal ceilings. Fire Saf. J. 39: 465-479.

26)   Reger, A., S. Hassid., and M. Poreh. 2006. Calculation of entrainment in density jumps. J. Environ. Fluid  Mech. 6: 407-424.

27)   Shleiss, A., and C. Oehy. 2002. Verlandung von stauseen und nachhaltigkeit. Wasser. Energie. Luft-Eau, Nergie, Air. 169: 227-234.

28)   Stephan, A., S. A. Morris., and J. Alexander. 2003. Changes in flow direction at a point caused by obstacles during passage of a density current. J. Sedimen Res. 73: 621-629.

29)   Turner, J. S. 1973. Buoyancy effects in fluids. Cambridge Univ. Press, Cambridge, GB.

30)   Varma, C. V. J., B. S. K. Naidu., and A. R. G. Rao. 2000. Silting problems in hydro power plants. A. A. Balkema, Rotterdam.