When depth of flow past a river bridge exceeds opening under the bridge, the flow under the bridge becomes pressurized. The water is directed downward and under the bridge deck, causing increase in velocity and shear stress on the bed thereby increasing bed Scour. This is termed as Pressure Flow Scour. The present study investigates the phenomenon of pressure flow Scour resulting from a submerged bridge deck over an unprotected erodible bed. Velocity of approaching flow, depth of flow, degree of submergence and width of bridge are some of the parameters that are likely to affect the Scour under a submerged bridge. The effect of fluctuations in the flow depth on the depth of Scour increases with decrease in constriction. The experimental data of Edward et al. (1) has been merged with the present study and a conceptual relation is developed between Scour depth and degree of submergence in the form of Scour fraction and constriction ratio. For incipient flow conditions on the upstream of a submerged bridge, the final clearance under the bridge is equal to the depth of approaching flow. The study has been extended to include effect of unsteady flow in the form of a hydrograph, Interference of two similar submerged bridges, Interference of a submerged bridge with an un-submerged pier and a submerged bridge in conjunction with a circular bridge pier.

Most previous laboratory studies of local Scour at bridge abutments were performed in rectangular channels in which the distributions of flow velocity and bed shear stress were considered uniform in the transverse direction. In reality however, bridge abutments are usually located in the floodplain zone of rivers where velocity and shear stress distributions are directly affected by the lateral momentum transfer. The influence of channel geometry and lateral momentum transfer in compound flow field on Scouring phenomenon, however, has not been fully investigated and understood as yet. This paper presents the results of an experimental study performed to investigate the impact of both sediment size and lateral momentum transfer on local Scour at abutments terminating in the floodplain of a compound channel. It is shown that, by accounting for lateral momentum transfer at small floodplain/main channel depth ratios (ya/H<0.3), estimates of maximum local Scour depth are increased by up to 30%. In relation to the sediment size, earlier studies of Scouring around circular bridge piers proposed a limit for the relative size of sediment (pier diameter/median size of bed material) beyond which the sediment size has no effect on the equilibrium sconr depth (Ettema, 1980; Chiew, 1984). The results of the current laboratory studies, however, indicated that the limit established for circular bridge piers might not be appropriate for the abutment case installed in the floodplain zones; further studies are required to draw a more general conclusion regarding the effects of relative grain size in the abutment case.

In this paper, Scour profiles downstream of adverse stilling basins, due to the submerged jet issuing from a sluice gate, were investigated. Experiments were conducted in a wide range of sediment sizes, incoming flow Froude numbers, tail water depths, length and slope of the stilling basin. The results showed that the Scour profiles at any bed slope are similar in shape. However, the longitude evolution of Scour profiles and the volume of eroded materials increased in accordance with the slope of the basin. It was observed that the maximum depth of the Scour hole occurs in the vicinity of the side walls and slightly decreases towards the centerline. A polynomial equation was derived to describe the nondimensional Scour profiles at different slopes. Based on experimental data, the Scour characteristics have been correlated with the time of equilibrium stage by developing some empirical relationships. Finally, a power-law equation was derived and fully defined to include the dimensions of the Scour hole time scale and the geometry of the sluice gate.

River confluence is a common feature of most irrigation and drainage channels and river systems, where tributary conflicts the main channel. In these section, rapid changes in velocity and discharge, sediment distribution and flow turbulent result in a deep confluence Scour, a bar point in the separation zone at downstream of junction corner and finally vortex flow. Thus, the main goal of this study is to conduct a series of experimental tests to investigate the required size of rocks to control the Scour hole. The results show that for a constant ratio discharge, Qr, the size of riprap in the incipient motion increases with decreasing in tailwarer depth. In other words, for any rock size the tailwater depth required for incipient motion increases with increasing the ratio of discharge, Qr. For each constant ratio discharge, or, the size of riprap in the incipient motion increases with increasing in tailwater velocity, Vt. Finally, some equations are presented for predicting the size of rocks and the proposed equations has been compared with existing ones.