https://rosap.ntl.bts.gov/view/dot/25666/dot_25666_DS1.pdf

Stream stability at highway structures.

Scour is one of the main causes of bridge failures. It accounts for about 60% of bridge failures in the United States. Scour failures tend to occur suddenly without prior warning and are very difficult to monitor during flood events. This paper presents a comprehensive review of the up-to-date work on scour at bridge piers and abutments. First, a general introduction of bridge scour including the current situation of bridge scour problems and different types of bridge scour is given. Then, different approaches developed for predicting bridge scour are reviewed. Numerical and laboratory models established for bridge scour studies are also presented. Moreover, laboratory experiments and field tests conducted for bridge scour are reviewed. Different techniques and instruments developed for bridge scour monitoring are also presented with their advantages, disadvantages, and relative cost summarized in a table. Finally, various mitigation countermeasures developed for bridge scour are discussed.

Bridge Scour: Prediction, Modeling, Monitoring, and Countermeasures—Review

A three-dimensional (3D) numerical model for predicting steady, in the mean, turbulent flows through lateral intakes with rough walls is developed, validated, and employed in a parametric study. The method solves the Reynolds-averaged Navier-Stokes equations closed with the isotropic k-ω turbulence model of Wilcox, which resolves the near-wall flow and accounts for roughness effects in a straightforward manner. Calculations are carried out for flows through rectangular closed-duct and open-channel T-junctions. Comparisons of the predicted mean velocity field with laboratory measurements indicate that the model captures most experimental trends with reasonable accuracy. For the parametric study, flows are predicted for a range of discharge ratios, aspect ratios, and main channel-bed-roughness distributions. The numerical solutions are examined to elucidate the complex 3D flow patterns of lateral-intake flows, including zones of flow division, separation and reversal, vortices, and singular points within th...

Three-dimensional numerical model of lateral-intake inflows

Recent research results with the submerged‐vane technique for sediment control in rivers are described. Submerged vanes are small flow‐training structures (foils), designed to modify the near‐bed flow pattern and redistribute flow and sediment transport within the channel cross section. The structures are installed at an angle of attack of 15–25° with the flow, and their initial height is 0.2–0.4 times local water depth at design stage. The vanes function by generating secondary circulation in the flow. The circulation alters magnitude and direction of the bed shear stresses and causes a change in the distributions of velocity, depth, and sediment transport in the area affected by the vanes. As a result, the river bed aggrades in one portion of the channel cross section and degrades in another. The vanes can be laid out to develop and maintain any desired bed topography. Vanes have been used successfully for protection of stream banks against erosion and for amelioration of shoaling problems at water inta...

Sediment Management with Submerged Vanes. I: Theory

The present study examines the use of independent and continuous pier collars in combination with riprap for reducing local scour around bridge pier groups. The efficiency of collars was studied through experiments. The data from the experiments were compared with data from earlier studies on single piers with collars and bridge pier groups without collars. The data showed that in the case of two piers in line, combination of continuous collars and riprap results in the most significant scour reduction of about 50 and 60% for the front and rear piers, respectively. In other cases for two piers in line, independent collars showed better efficiency than a continuous collar around both piers. It was also shown that efficiency of collars is more on a rectangular pier aligned with the flow than two piers in line. Experiments however, indicated that collars are not so effective in reduction of scouring around two transverse piers.

Reduction of Local Scour in the Vicinity of Bridge Pier Groups Using Collars and Riprap

The theory of submerged vanes described in the companion paper is tested with laboratory and field data. The laboratory data are from experiments in curved, and straight, recirculating sediment flumes. The field data are from river bends in which, prior to installation of vanes, the banks were eroding, and from a straightened bridge waterway in which sediment deposits were causing a change of channel alignment, bank erosion, and undermining of the bridge abutment. All data support the theory, and they suggest that the vane technique is a viable alternative to traditional techniques. The design procedure is described and illustrated with numerical examples, and vane material and typical vane layouts are discussed. Layouts are presented for protection of stream banks against erosion and for amelioration of shoaling problems in navigation channels, at water intakes, in bridge crossings, at river confluences, and at diversions.

Sediment management with submerged vanes. II: Applications

Submerged vanes are small river training structures used for protection of streambanks against erosion and for amelioration of shoaling problems in navigation channels, at water intakes, in bridge crossings, and at diversions. The structures function by modifying the near-bed flow pattern and redistributing flow and sediment transport within the channel cross section. The theory of the structures is developed elsewhere. The paper describes the design guidelines and typical applications.

Sediment Management with Submerged Vanes

Submerged vanes are shown to be effective in preventing bed load transport from entering water intakes. By generating a secondary circulation in the flow, the vanes change the magnitude and direction of the bed-shear stresses and cause a redistribution of the flow and sediment transport in the area affected by the vanes. As a result, the riverbed aggrades in one portion of the channel and degrades in another. The performance of two vane installations, designed according to guidelines developed earlier, are evaluated by comparing the bed topography before and after vanes were installed. The design guidelines, which utilize a numerical model developed earlier, are shown to be appropriate. The guidelines apply only when the intake flow is small enough that the withdrawal causes little change in the river flow velocity in front of the intake.

Sediment control at water intakes

The purpose of this paper is to show how small, submerged vortex generators can be used for adjusting the flow pattern in open-channel flows. The vortex generators are vanes or foils installed on the channel bottom in certain configurations. Their height is typically 0.2 to 0.5 times flow depth, their length is about 2 to 3 times their height, and their angle with the flow between 15° and 30°. Described are the adjustments of the flow field effected by a single vane, a vane pair, and several vanes arranged in arrays along one side of the channel. Experimental data are used to develop formulas for calculating the flow adjustments across a channel having vane arrays along one side.

Flow control with vorticity

Laboratory experiments are described in which attempts are made to eliminate local scour at bridge piers using submerged vanes and pier collar. The submerged vanes direct bed load toward, and reduce flow depth around, the pier; the collar breaks the pier induced horse-shoe vortex which is believed to contribute to the generation of scour.

Yalin Wang

Papers

Sediment management with submerged vanes. II: Applications

Sediment Management with Submerged Vanes

Sediment control at water intakes

Flow control with vorticity

Scour Prevention at Bridge Piers