Local Scour Downstream of Positive-Step Stilling Basins
Publication: Journal of Hydraulic Engineering
Volume 135, Issue 10
Abstract
This note focuses on the temporal and spatial evolution of local scour below low-head spillways. Steady-flow experiments were carried out in a 1-m wide and 20-m long rectangular straight channel. The jet was generated by an ogee-crest spillway followed by a positive-step stilling basin. Nearly uniform sandy beds were generally tested, but additional tests were also performed with a special bed of lead spheres. To circumvent the combination of local and general scour phenomena, tailwater depths were set such that tailwater flow intensities were below the threshold of sediment motion. As a consequence, for each run a submerged hydraulic jump formed. Tests were of long durations (of order of days) mainly to achieve conditions of quasi-equilibrium. Based on the data collected, literature approaches are discussed. Then, empirical models are proposed to estimate: (1) the maximum scour depth at the quasi-equilibrium stage and its horizontal distance from edge of stilling basin; (2) the time variation of scour depth; and (3) the axial scour profiles. The proposed equations agree well with experimental data. Findings also highlight that affinity rather than similarity may be the typical property of low-angle eroding jets.
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Published In
Journal of Hydraulic Engineering
Volume 135 • Issue 10 • October 2009
Pages: 846 - 851
Copyright
© 2009 ASCE.
History
Received: Jul 22, 2008
Accepted: Feb 23, 2009
Published online: Feb 25, 2009
Published in print: Oct 2009
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