Experimental Study of the Effect of Base-level fall at the Beginning of the Bend on Reduction of Scour around a Rectangular Bridge Pier Located in the 180 Degree Sharp Bend

Document Type: Research Paper


Department of Civil Engineering, Faculty of Engineering, Persian Gulf University, Bushehr, Iran.


Base-level fall in river beds occurs due to varying natural or unnatural causes. Base-level fall causes the change in the behavior of flow at the location of drop in base-level. In such situations, most of scour occur at the foot of the slope, and slope wall retreats in the upstream direction. This phenomenon widens the wall of the river bank, thus leading to its destruction. The amount of bed topography variations and scour around a rectangular bridge pier with an oblong nose located in the 90 degree angle of a 180 degree sharp bend was studied in this work by generating base-level fall at the beginning of the 180 degree sharp bend, and it was compared with a case without a base-level fall. The results indicated that in the case of base-level fall at the upstream side of the bridge pier, increase in flow depth, as well as reduction in velocity at the area around the pier, is observed, and the maximum depth of scour hole and the volume of scour hole around the pier respectively reduce by 73 and 97% in comparison with those in the case where no base-level fall occurs.


  1. Begin, Z. E. B., Schumm, S. A. and Meyer, D. F. (1980). "Knickpoint migration due to base level lowering." Journal of the Waterway, Port, Coastal and Ocean Division, 106(3), 369-388.
  2. 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.
  3. 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.
  4. Chiew, Y.M. and Melville, B.W. (1987). "Local scour around bridge piers." Journal of Hydraulic Research, 25 (1), 15–26.
  5. Garcia, M. H. and G. Parker. )1993(."Experimental on the entailment of sediment into suspention by a dense bottom current." J. Geophys.Res. (Oceans) 98:4793-4807.
  6. 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.
  7. Holland, W.N. and Pickup, G. (1976). "Flume study of knickpoint development in stratified sediment." Geological Society of America Bulletin, 87: 76-82.
  8. Julien, P. Y. (2002). "River mechanics." Cambridge University Press.
  9. Leschziner, M. A. and Rodi, W. (1979). "Calculation of strongly curved open channel flow." Journal of the Hydraulics Division, 105 (10), 1297–1314.
  10. 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.
  11. Melville, B.W. and Chiew, Y.M., (1999), "Time Scale for Local Scour Depth at Bridge Piers." Journal of Hydraulic Engineering, ASCE, Vol.125, No.1, 59-65.
  12. Melville B. W. and Sutherland A. J. (1988). "Design method for local scour at bridge piers." American Society of Civil Engineering. Journal of the Hydraulics Division, Vol. 114, No. 10, pp. 1210–1225.
  13. 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.
  14. Oliveto, G. and Hager, W.H., (2002). "Temporal evolution of clear-water pier and abutment scour." Journal of Hydraulic Engineering, 128 (9), 811–820.
  15. Raudkivi, A.J. and Ettema, R., (1983). "Clear-water scour at cylindrical piers." Journal of Hydraulic Engineering, 109 (3), 338–350.
  16. Turmel, D., Locat, J. and Parker, G. (2012). "Upstream migration of knickpoints: geotechnical considerations." In Submarine Mass Movements and Their Consequences (pp. 123-132).
  17. Vaghefi, M., Akbari, M. and Fiouz, A. R. (2016). "An experimental study of mean and turbulent flow in a 180 degree sharp open channel bend: Secondary flow and bed shear stress." KSCE Journal of Civil Engineering, 20(4), 1582-1593.