Department of Civil & Infrastructure Engineering

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IIT Jodhpur

This study presents a simplified approach to determine the end depth of a free overfall in horizontal U-shaped channels. The flow over the free overfall is simulated by that over a sharp-crested weir to calculate the end-depth ratio (EDR). The theoretical model is calibrated by the experimental data by considering the coefficient of velocity a free parameter. The EDR is 0.745 up to nondimensional critical depth 0.50; and then it decreases gradually as the nondimensional critical depth increases. A method to estimate discharge from the end depth is presented. The results obtained using the model agree satisfactorily with the experimental data and results obtained from the previous model of the author. Journal of Hydraulic Engineering © ASCE.

Journal of Hydraulic Engineering

End depth in u-shaped channels: A simplified approach

This paper presents a comparative study between the results obtained from the mathematical model and the experimental data of free overfall in circular channels (with and without flat base), following statistical and error analyses of data to ascertain the adequacy of the mathematical model. For the discharge predictions, the mathematical model tuned by an adjustable parameter is found to be accurate one, while the regression (empirical) formula fails to estimate discharge precisely. © 2005 International Association of Hydraulic Engineering and Research.

Journal of Hydraulic Research

Free overfall from circular channels with flat base

The three-dimensional turbulent flow field in a scour hole at a semicircular abutment under a clear water regime was experimentally measured in a laboratory flume using an acoustic Doppler velocimeter. The distributions of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy, and Reynolds stresses at different azimuthal planes are presented. Upstream, presentation of flow field through vector plots at azimuthal and horizontal planes shows the existence of a large primary vortex associated with the downflow inside the scour hole. On the other hand, downstream, the flow field is irregular. The bed shear stresses are determined from the Reynolds stresses and velocity gradients. The data presented in this paper would be useful for the development and validation of flow field models, which can be used to determine the strength of the primary vortex that is used to estimate scour depth at bridge abutments. © 2005 NRC Canada.

World University root node

Canadian Journal of Civil Engineering

Turbulent flow field in a scour hole at a semicircular abutment

Measurement of three-dimensional turbulent flow field at a vertical semicircular cylinder, attached to the sidewall of a rectangular channel, was taken in the laboratory using an Acoustic Doppler Velocimeter (ADV). The distributions of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy and Reynolds stresses at different azimuthal planes are presented. The vector plots of flow field at azimuthal and horizontal planes show the presence of a primary vortex upstream of the cylinder. The bed shear stresses in the vicinity of the cylinder are determined from the Reynolds stresses and velocity gradients. © 2003 Elsevier Ltd. All rights reserved.

Flow Measurement and Instrumentation

Measurement of turbulent flow field at a vertical semicircular cylinder attached to the sidewall of a rectangular channel

Experiments on local scour at short abutments (ratio of abutment length to approaching flow depth less than unity), namely vertical-wall, 45° wing-wall, and semicircular, embedded in a bed of relatively fine noncohesive sediment overlain by a thin armor-layer of coarser sediment, were conducted for different flow conditions, thickness of armor-layers, armor-layer, and bed sediments. The abutments were aligned with the approaching flow in a rectangular channel. The armor-layer and the bed underneath it were composed of different combinations of uniform sediments. In the experiments, the approaching flow velocities were restricted to the clear-water scour condition with respect to the armor-layer particles. Depending on the approaching flow conditions, three cases of scour at abutments in armored beds were identified. Effects of different parameters pertaining to scour at abutments are examined. The comparison of the experimental data shows that the scour depth at an abutment with an armor-layer in clear-water scour condition under limiting stability of the surface particles (approaching flow velocity nearly equaling critical velocity for the threshold motion of surface particles) is always greater than that without armor-layer for the same bed sediments. The characteristic parameters affecting the maximum equilibrium nondimensional scour depth (scour depth-abutment length ratio), identified based on the physical reasoning and dimensional analysis, are excess abutment Froude number, flow depth-abutment length ratio, armor-layer thickness-armor particle diameter ratio, and armor particle-bed sediment diameter ratio. The experimental data of clear-water scour condition in thinly armored beds under limiting stability of surface particles were used to determine the equation of maximum equilibrium scour depth through regression analysis. The estimated scour depths were in agreement with the experimental scour depths. Also, an equation of maximum equilibrium scour depth in uniform sediments was obtained. © ASCE.

Clear-water scour at abutments in thinly armored beds

Laboratory experimental results on local scour at short abutments (abutment length:flow depth ratio ≤ 1), namely vertical-wall, 45° wing-wall and semicircular, in uniform and non-uniform sediments under a clear water scour condition are presented. The equilibrium scour depth is related to the sediment size and approaching flow depth relative to the abutment length. The equilibrium scour depth increases with decrease in abutment length and increase in sediment size and flow depth. The scour depth is independent of flow depth at higher flow depths. The effect of sediment gradation on scour depth is pronounced for non-uniform sediments, which reduces scour depth significantly due to the formation of an armour layer in the scour hole. The time variation of scour depth for uniform sediments shows a family of parallel lines for different abutment lengths and sediment sizes. For non-uniform sediments, the time variation of scour depth reduces with increase in non-uniformity of the particle size distribution of sediments. The characteristic parameters affecting the maximum equilibrium non-dimensional scour depth (scour depth:abutment length ratio), identified based on the physical reasoning and dimensional analysis, are excess abutment Froude number, flow depth:abutment length ratio, and abutment length:sediment diameter ratio. The experimental data in clear water scour condition under limiting stability of upstream bed sediments are used to determine the equations of maximum equilibrium scour depth through regression analysis. The estimated scour depths are in agreement with the experimental data.

Proceedings of the Institution of Civil Engineers: Water Management

Clear water scour at abutments

An experimental study on critical bed shear-stress for initial movement of non-cohesive sediment particles under a steady-uniform stream flow on a combined lateral (across the flow direction) and longitudinal (streamwise direction) sloping bed is presented. The aim of this paper is to ascertain that the critical bed shear-stress on a combined lateral and longitudinal sloping bed is adequately represented by the product of critical bed shear-stress ratios for lateral and longitudinal sloping beds. Experiments were carried out with closed-conduit flow, in two ducts having a semicircular invert section, with three sizes of sediments. In laboratory flumes, the uniform flow is a difficult - if not impossible - proposition for a steeply sloping channel, and is impossible to obtain in an adversely sloping channel. To avoid this problem, the experiments were conducted with a closed-conduit flow. The critical bed shear-stresses for experimental runs were estimated from side-wall correction. The experimental data agree satisfactorily with the results obtained from the proposed formula. © IWA Publishing 2004.

Nordic Hydrology

Critical bed shear for initial movement of sediments on a combined lateral and longitudinal slope

Failure of bridges due to local scour has motivated many investigators to explore the causes of scouring and to predict the maximum scour depth at abutments. In this paper, a detailed review of the up-to-date work on scour at abutments is presented including all possible aspects, such as flow field, scouring process, parameters affecting scour depth, time-variation of scour and scour depth estimation formulae.

Fulltext

Sadhana - Academy Proceedings in Engineering Sciences

Local scour at abutments: A review

Experimental investigation of the 3D turbulent flow field around a 45° wing-wall abutment, resting on a rough rigid bed, is reported. The experiment was conducted in a laboratory flume using the Acoustic Doppler Velocimeter (ADV). Profiles of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy and Reynolds stresses at different azimuthal planes are presented. Vector plots of flow fields at azimuthal and horizontal planes show the presence of a primary vortex associated with the downflow in the upstream side of the abutment and a wake vortex on the downstream side. The shear stresses acting on the bed around the abutment are estimated from the Reynolds stresses and velocity gradients. The data presented in this study would be useful to researchers for future development and comparison of theoretical models of flow fields around bridge abutments.

Velocity and turbulence at a wing-wall abutment

An analytical model is presented to determine the threshold bed shear stress for noncohesive sediment motion subject to upward seepage on horizontal sedimentary bed under a stream flow. Hydrodynamic, seepage, and micromechanical forces acting on a solitary sediment particle, resting over a sedimentary bed under slip-spinning condition, are analyzed. The correlation coefficient between the results obtained using the present model and the experimental data of threshold bed shear stress with upward seepage on the horizontal bed is 0.767. It indicates that the model predicts satisfactorily the threshold bed shear stress with upward seepage. © ASCE/SEPTEMBER 2004.