The three-dimensional quasi-steady vortex flow field around circular piers in a quasi-equilibrium scour hole under a clear water regime has been investigated experimentally. The main characteristic features of the flow, to be modeled, are a relatively large secondary vortex flow within the scour hole and skewed velocity distributions along the circumference of the pier. The flow field has been divided into a number of parts according to the flow characteristics. The components of quasi-steady velocity for different parts have been theoretically expressed in the form of equations satisfying the continuity equation and the requirements of fitting an individual profile of the measured velocity components. Using the suitable functions, the equations of the velocity components derived for different parts have been combined and matched at the junctions of these parts to get a single equation for each velocity component. The measured data have been utilized to determine the coefficients and exponents used in the...

The outcome of an experimental study on the turbulent horseshoe vortex flow within the developing (intermediate stages and equilibrium) scour holes at cylindrical piers measured by an acoustic Doppler velocimeter (ADV) are presented. Since the primary objective was to analyze the evolution of the turbulent flow characteristics of a horseshoe vortex within a developing scour hole, the flow zone downstream of the pier was beyond the scope of the investigation. Experiments were conducted for the approaching flow having undisturbed flow depth (=0.25 m) greater than twice the pier diameter and the depth-averaged approaching flow velocity (=0.357 m∕s) about 95% of the critical velocity of the uniform bed sand that had a median diameter of 0.81 mm . The flow measurements by the ADV were taken within the intermediate (having depths of 0.25, 0.5, and 0.75 times the equilibrium scour depth) and equilibrium scour holes (frozen by spraying glue) at a circular pier of diameter 0.12 m . In order to have a comparative s...

The results of an experimental investigation on scour of noncohesive sediment beds (uniform and nonuniform sediments) downstream of an apron due to a submerged horizontal jet issuing from a sluice opening are presented. Attempts are made to explain the similarity existing in the scour process and profiles (including dune in the downstream of the scour hole). The scour profiles at different times follow a particular geometrical similarity and can be expressed by the combination of two polynomials. Using experimental scour depth at different times, the time variation of scour depth is scaled by an exponential law, where time scale increases linearly with densimetric Froude number. The equilibrium scour depth, related to the sediment size relative to the sluice opening, decreases with increase in sediment size and sluice opening. On the other hand, the equilibrium scour depth increases with increase in densimetric Froude number. The variation of equilibrium scour depth with tailwater depth indicates a critic...

During the past decades, several investigations were conducted to assess the adequacy of countermeasures against local scour at bridge piers. The countermeasures can be broadly classified into two categories: (1) flow-altering and (2) bed-armouring countermeasures. Flow-altering countermeasures, as treated herein, can be classified into four main groups based on their shapes and performances. A comprehensive review of the up-to-date studies on various types of flow-altering countermeasures is presented, placing special emphasis on recently proposed methods while also revisiting studies of former methods. Experimental conditions of different studies under which the tests were performed are critically examined. A preliminary evaluation of the previously conducted experiments indicates that the results of several tests were influenced by side-wall, sediment size, flow shallowness and temporal effects. Experimental results on the combinations of different countermeasures, including their limitations and difficulties in field applications, are also discussed. Finally, suggestions are presented for further research on selected countermeasures.