The bridge scour depths in cohesive soil have been predicted using the scour equations developed for cohesionless soils due to scarce of studies about cohesive soil. The scour depths predicted by the conventional methods will result in significant errors. For the cost effective design of bridge scour in cohesive soil, the Scour Rate In COhesvie Soil (SRICOS) for the singular circular pier in deep water condition was released in 1999, and has been developed for complex pier and contraction scour. The present study is the part of SRICOS-EFA method to predict the history of contraction scour, and local scours, such as abutment scour and pier scour. The main objective is to develop the prediction methods for the maximum and the uniform contraction scour depth, the maximum pier scour depth and the maximum abutment using flume test results. The equations are basically composed with the difference between the local Froude number and the critical Froude number. Because the scour happens when the shear stress is bigger than the critical shear stress, which is the maximum shear stress the channel bed material can resist from the erosion, and continues until the shear stress becomes equal to the critical shear stress. All results obtained from flume tests for pier scour have been conducted in Texas A&M University from 1997 to 2002 are collected and reanalyzed in this study. Since the original pier scour equation did not include soil properties. The effect of water depth effect, pier spacing, pier shape and flow attack angle for the rectangular pier are studied and correction factors with respect to the circular pier in deep water condition were newly developed in present study. For the abutment scour, a series of flume tests in large scale was performed in the present study. Two types of channel - rectangular channel, and compound channel - were used. The effect of abutment length, shape and alignment of abutment were studied and the correction factors were developed. The patterns of velocity and of scour were compared, and it was found that the maximum local scour occurred where the maximum turbulence was measured. For the contraction scour, the results obtained from a series of flume tests performed in 2002 and a series of flume tests for the abutment scour in the present study are analyzed. The methodologies to predict the maximum contraction scour and the uniform contraction scour in the compound channel was developed. Although all prediction methods developed in the present study are for the cohesive soils, those methods may be applicable to the cohesionless soils because the critical shear stress is included in the methods. All prediction methods were verified by the comparison with the databases obtained from flume test results and field data.

Computation of temporal variation of clear water scour is important for the design of bridge foundations. Previous studies conducted for determining equilibrium scour depth at bridge abutments indicated that very long flow duration was needed to achieve equilibrium scouring situations. However, the corresponding durations in the prototype conditions may yield considerably greater values than time to peak of the design flood. Therefore, there is a need to estimate the temporal variation of scour depth. An experimental study was carried out to observe temporal variation of scour depth and contours around vertical-wall and wing-wall abutments. The results of the experiments have been interpreted. A semi-empirical model has been developed for determining time-dependent variation of clear water scour depth at vertical-wall abutments. This approach is based on the application of sediment continuity equation to the scour hole around the vertical-wall abutment. To this end, time-dependent geometric features of the scour hole were investigated and a recent sediment pickup function was used to formulate the rate of sediment transport out of the scour hole. The results of the proposed model were compared with those of some empirical models. The findings of the model agree well with the experimental results.

Foundations of river bridges need to be protected with respect to excessive scouring. Degree of protection depends on the severity of scouring action around bridge piers and abutments. A case study is carried out to design appropriate protective measures for sequential viaducts located on Ankara-Pozant highway in Turkey. A number of analyses are conducted to obtain water surface profiles throughout the study reach. Local scour depths at piers and abutments of the viaducts are then obtained. The design process for countermeasures is performed concerning hydraulic, hydrologic, constructional, and economical requirements. To this end, riprap, partially grouted riprap, and articulated concrete blocks are studied in these view points. A criterion based on a selection index, which is defined by the National Cooperative Highway Research Program in the USA, is applied in this study. Implementation of partially grouted ripraps at infrastructural elements is found to be an appropriate solution.

Extreme rainfall events associated with global warming are likely to produce an increasing number of flooding scenarios. A large magnitude of hydrologic events can often result in submerged orifice flow (also called pressure flow) or embankment and bridge overtopping flow, in which the foundation of a bridge is subjected to severe scour at the sediment bed. This phenomenon can cause bridge failure during large floods. However, current laboratory studies have focused on only cases of free-surface flow conditions, and they do not take bridge submergence into account. In this study, abutment scour experiments were carried out in a compound channel to investigate the characteristics of abutment scour in free-surface flow, submerged orifice flow, and overtopping flow cases. Detailed bed contours and three components of velocities and turbulent intensities were measured by acoustic Doppler velocimeters. The results show that the contracted flow around an abutment because of lateral and/or vertical contraction and local turbulent structures at the downstream region of the bridge are the main features of the flow responsible for the maximum scour depth around an abutment. The effects of local turbulent structures on abutment scour are discussed in terms of turbulent kinetic energy (TKE) profiles measured in a wide range of flow contraction ratios. The experimental results showed that maximum abutment scour can be predicted by a suggested single relationship even in different flow types (i.e., free, submerged orifice, and overtopping flow) if the turbulent kinetic energy and discharge under the bridge can be accurately measured.