Flow unsteadiness in flood events has a significant effect on the structure of the flow field and motion of sediment particles, thereby affecting dispersion of pollutants and river ecology. The aim of the present article was to evaluate state-of-the-art research efforts concerning flow characteristics and sediment transport in unsteady flow condition. The paper is organized in four sections: The first section deals with the unsteady parameters which affect sediment transport. In the second section, the flow characteristics in unsteady open channel flow are presented. Different studies showed that the flow characteristics which affect sediment transport including velocity distribution or shear stress during passage of a hydrograph differ from steady flow condition. In addition, measurements during passage of a hydrograph show that turbulence intensity is generally larger in the rising limb of the hydrograph rather than in the falling limb. This causes the peak of sediment load and pollutants occur during the rising limb of the storm hydrograph. The third and forth sections deal with bed load and suspended load in unsteady flow condition, respectively. Studies show that the methods which are based on steady flow conditions generally underestimate the sediment transport rates in unsteady flows. The larger the unsteadiness, the bigger is the difference. Finally, with considering different findings from previous studies, suggestions are presented for further research.

Abstract-Spur dikes are structures that often be utilized for three main purposes, such as increasing water level, river bank protection, and sedimentation. This type of construction's use for a long time shows its usefulness and good features. Experimental investigation on flow pattern around 3 spur dikes in clear water with 2-D velocimeter has been achieved. These experiments have been accomplished in 3 different occasions of series of spur dikes (the first spur dike at 30 degrees, 45 degrees, and 90 degrees). In each experiment, flow pattern has been measured from 20 degrees before and 20 degrees after spur dike. Also bed topography has been determined in all cases and in obvious distance. In this paper bed shear stress, exist vortexes and flow pattern has been surveyed and analyzed, furthermore interaction between flow pattern and bed variations has been mentioned. Results showed that by increasing the position of spur dikes to the downstream the length of separation zone decreases, and also the width of separation zone remain almost constant.

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An experimental approach was carried out to study the time development and extension of scouring around a circular pier protected by collars. The experiments included the study of scouring around an unprotected pier as well as the pier protected with collars located at different levels. Width of collars was 3 times the pier diameter. It was found that with collars, though the scour depth and the rate of scouring decrease, extent of the scour hole increases. Number of collars and their levels are effective factors on the equilibrium depth and extension of scouring. Different collar arrangements were tested for an optimum result. Best results were found with one collar at the bed level and another one at one pier diameter below the bed level. In this arrangement, scouring did not penetrate below the lower collar even after 200 hours. Therefore, with the lower collar at 1D below the bed level scour depth reduced by more than 50% whereas, the area of scouring increased by 30% compared with an unprotected pier.