Various methods have been attempted to control scouring around bridge piers, such as using riprap, slots through the pier, a group of small piles in front of the pier, and collars. Following successful application of collars on circular piers for reduction of scouring, in this work the effectiveness of collars on rectangular piers was tested. Experiments were carried out in the threshold of sediment motion with piers aligned and skewed at 5° and 10° to the flow, and with collars of different widths and at various elevations. It was found that wider collars at lower levels are more effective and that effectiveness of collars reduces by increasing the skewness of the pier. Maximum reduction of scouring was 74, 56 and 35% for a collar with a width equal to the pier width at streambed elevation when pier was aligned, skewed at 5° and skewed at 10° to the flow respectively.

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.

Channel confluence is one of the important features of each river system and some hydraulic structures. The features that can dominantly control flow characteristics in a confluence are confluence angle, discharge, width ratios, and Froude number of flow. Several research studies have been conducted however a comprehensive three-dimensional (3-D) numerical study of flow characteristics in a confluence has not yet been reported. In the present study, SSIIM2.0, a 3-D numerical model, is validated and applied to investigate secondary currents, velocity distribution, flow separation, and water surface elevation in different conditions. The results of the present study illustrate that flow structure and water surface variations in a confluence are highly influenced by confluence angle, discharge, and width ratios as well as Froude number because of their effect on flow deflection, separation, and secondary currents. The graphs from the present study can be used to analyze water surface variation, velocity field, and flow separation dimensions in difference conditions for engineering designs.

The effect of the intake head wall slope and the installation of a trash rack on the type and strength of vortices are studied experimentally. The strength within each vortex was determined by measuring its tangential velocity utilizing an Acoustic Doppler Velocimeter (ADV). Experiments were carried out with a projected intake and an intake with various head wall slopes, discharges and submerged depths. The results from the projected intake tests indicated that Type 6 vortex was present. However, the vortex strength and type reduced as the intake head wall slope increased up to the vertical position. In addition, increasing the intake head wall slope increased the vortex instability. All tests were repeated with a trash rack. A relationship was developed for vortex strength and the intake critical submerged depth based on the intake Froude number and the head wall slope. Moreover, a relationship has been found between vortex strength and type.