Studies of Bed Elevation Variations in Sand Bed Rivers Caused by Two Successive Knick Points

Document Type : Research Article




Knick points are generated, naturally or artificially, across the river beds in the form of sequential steps. In the present work, the experimental and numerical migration of two successive Knick points in a sandy bed of a rectangular channel is studied for different discharges. At the start of flow, the two Knick points became unstable in a short period of time. Erosion caused the migration of the first Knick point backward upstream and deposition, down the second Knick point, moved it forward to the downstream channel. At the same time a side bar was formed down the first Knick point and extended upward. Downstream of this bar and before the second Knick point the canal was meandered. Between the two Knick points, the channel developed a steep slope bed. Increase in discharge augmented the rate of movement of the two Knick points. Consequently, migration not only changed the channel elevation but also destabilized its alignment in plan. The flow and sediment transport equations were integrated by HEC-RAS (V4.1.0) for different sediment transport functions. In comparison with the available experimental data, Larsen and Ackers-White equations proved a better estimation for the prediction of bed level variations.


بوینگتن، ف. آر. (1366). تخلیص داده ها و تجزیه و تحلیل خطا برای علوم فیزیکى، ترجمه­ی عدالتی، ت. و بزرگ­نیا، ا.، چاپ اول، انتشارات آستان قدس رضوی، مشهد.
ژولین، پ. ی. (1387). مکانیک رودخانه، ترجمه‌ی جعفرزاده، م. ر.، چاپ دوم، انتشارات دانشگاه فردوسی مشهد، مشهد.
شفاعی بجستان، م. (1387). مبانی نظری و عملی هیدرولیک انتقال رسوب، چاپ اول، انتشارات دانشگاه شهید چمران اهواز، اهواز.
کوهستانی، ک. و جعفرزاده، م. ر. (1384). "بررسی تئوری و آزمایشگاهی تکامل نقطه‌شکست"، پنجمین کنفرانس هیدرولیک ایران، دانشگاه باهنر کرمان، ایران.
ASCE, (1982). “Relationships between morphology of small streams and sediment yields”, Journal of the Hydraulics Division, ASCE, vol. 108, no. HY 11, Proceeding Paper 17450, pp. 1328-1365.
Bhallamudi, S.M., and Chaudhry, M.H. (1991). “Numerical modeling of aggradation and degradation in alluvial channels”, J. Hydraulic Engineering, Amer. Soc. Civil Engrs., Vol. 117, No 9, pp. 1145-1164.
Bigi A., Hasbargen L. E., Montanari A. and Paola C. (2006). “Knickpoints and hillslope failures: Interactions in a steady-state experimental landscape”, Geological Society of America, Special paper 398, 295-307.
Brunner, G.W. (2010). “HEC-RAS river analysis system: hydraulic reference manual”, U.S. Army Corps of Engineers, Institute for Water Resources, Hydrologic Engineering Center (HEC), Davis, CA.
Brush, L.M. and Wolman, M.G. (1960). “Knickpoint behavior in non-cohesive material: A laboratory study”, Geological Society of America Bulletin, 71: 59-74.
Crosby, T.B. (2001). “Knickpoint migration in the waipaoa river and its tributaries”. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, First Generals Paper.
Cunge, J.A., Holly, F.M., and Verwey A. (1980). Practical aspects of computational river hydraulics. Pitman Advanced Publishing Program.
Cantelli, A. and Muto T. (2014). “Multiple knickpoints in an alluvial river generated by a single instantaneous drop in base level: experimental investigation”, Earth Surf. Dynam., 2: 271–278.
Grimaud, J.L., Paola1, C. and Voller, V. (2016). “Experimental migration of knickpoints: influence of style of base-level fall and bed lithology”, Earth Surf. Dynam., 4: 11–23.
Holland, W.N. and Pickup, G. (1976). “Flume study of knickpoint development in stratified sediment”, Geological Society of America Bulletin, 87: 76-82.
Loget, N. and Driessche, J.V.D. (2009). “Wave train model for knickpoint migration”, Geomorphology, 106: 376–382.
May, J.H. (1989). “Report 4: Geologic and hydrodynamic controls on the mechanics of knickpoint migration”, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.
Peakall, J., Warburton, J. (1996). “Surface tension in small hydraulic river models-the significance of the Weber number”, J. of Hydrology New Zealand. 35(2): 199-212.
Richardson, E.V., Simons, D.B. and Lagasse P.F. (2001). “River engineering for highway encroachments, Highways in the river
environment”, Hydraulic Design Series Number 6, U.S. Department of Transportation, Publication No. FHWA NHI 01-004.
Simon, A. and Darby, S.E. (2002). “Effectiveness of grade-control structures in reducing erosion along river channels: the case of Hotophia Creek, Mississippi”. Elsevier Scientific, Geomorphology. 42: 229-224
Thomas, J. and Papanicolaou, A. N. (2008). “Final report: the effects of headcut and knickpoint propagation on bridges in Iowa”, Proceedings of the 2007 Mid-continent Transportation Research Symposium, Ames, Iowa.
Vanoni, V.A., (1975). Sedimentation engineering. ASCE Manuals And Reports on Engineering-No. 54, ASCE Task Committee
  • Receive Date: 17 November 2015
  • Revise Date: 08 February 2017
  • Accept Date: 10 February 2017
  • First Publish Date: 10 February 2017