Estimation of maximum possible scour depth around spur dike is an important step in the design of spur dike foundations To determine the maximum scour depth in the design of spur dike foundations, the equilibrium scour depth, which is commonly estimated using peak-flow conditions for engineering design of spur dike foundations, are used.. In fluvial rivers, significant transport of bed materials often takes place during peak-flow discharge in a flood event. For large rivers, the duration of a flood event may last for a few months, but for others the unsteadiness of a flood can be pronounced. The general practice of employing peak-flow discharge to evaluate the maximum scour depth for design may be questioned because the maximum scour depth occurring under a flood hydrograph can be much smaller than the calculated value using peak-flow discharge. In other words, using the peak-flow discharge for design can greatly overestimate the maximum scour depth in comparison to the actual conditions under the flood hydrograph. Therefore, when the flow unsteadiness is pronounced, investigation of temporal variation of clear water scour at spur dike is important to estimate the possible extension of the scour hole. This would provide useful information for safe design of footing and the selection of scour counter-measure to be implemented. The degree of severity of the problem is dictated by the magnitude of this scour hole. In this experimental study, the scour around the single spur dike was investigated under unsteady flow. These tests have been done in terms of clear water and non cohesive sediments. In order to investigating the scour around the spur dike, experiments have been done by changing the properties of normal hydrograph such as peak discharge and durability time. In order to producing the hydrograph, we used a device for adjusting the speed of pump motor and generating the variable discharge according to actual discharge time series. In the inlet pipe of pump, a magnetic flow meter is located that Measures the discharge in per one tenth of a second. Thus, the system verifies of requested discharge at any time. The results show that one of the influential parameters that affect the scour around the spur dike is the durability time of hydrograph. We concluded that when the durability time increases 6-times, scour depth will increase 40 percent, because with increasing durability time, the time that spur dike exposes tensions increases. Also, the depth of scour has increased 35 percent, by increasing 25 percent of peak discharge of hydrograph that is caused by increasing stresses imposed on the bed. Finally, the resulted scour under unsteady flow was compared with the resulted scour under steady flow (With flood peak discharge), with a significant difference between the scour under steady and unsteady flow. Then, an imperial equation was proposed for calculating the scour depth under hydrograph. This equation was obtained by adding the unsteady coefficient of flow in the equation of equilibrium scour depth under steady flow. This unsteady coefficient of flow includes effective parameters of hydrograph such as peak flow of hydrograph, peak time, durability time of hydrograph and equilibrium time of scour.

An important factor in increasing the scour around bridge piers is the accumulation of debris and trees. The effect of discharge¡ water depth¡ location of the debris¡ thickness¡ diameter and shape of the debris on pier scour been studied experimentally. 45 samples in the laboratory hydraulic and hydraulic structures¡ water engineering shahid Bahonar University of Kerman. The results showed that the maximum scour depth increases with increasing water depth less discharge occurs. The thickness and diameter debris on pier scour effective and maximum scour depth increases. The location of debris on the scouring effect. If the water level up to the debris hsub ¡ Water depth is ¡ In the range 00.3 scour reduced by increasing the submergence. The shape of the debris can affect scour¡ debris rectangular¡ cylindrical and triangular respectively scour more. Accumulation of debris such as branches and trunks of trees around the pier of the bridge scour increases about 90%.

One of the regular methods for stabilizing and protecting the riverbanks is use of groyne structure. Groynes alter flow direction to the main axis of the river resulting sediment deposition and stabilization of river sides. Therefore, scour around the groyne and the effect of nose on scour are important parameters in river engineering. It should be noted that change of flow pattern in river side is an affective factor on the rate of scouring around the groyne nose. In this study, the effects of the hockey groyne length (L) on scour in straight channel has been investigated through experimental tests. The results showed that there was a direct relation between scour hole dimensions (including the maximum scour depth (ds), the length of scour hole in up and downstream and the maximum scour width) and hockey groyne length. Also, scour hole distance the from channel wall was longer in hockey groyne comparing to that in straight groyne which prevent from scour in river bank and stabilizing the groyne structure. Thus, maximum scour around the hockey groyne was less than that straight groyne around due to suitable flow direction to the downstream.

Spur dikes are one of the protective and stabilizing tools of river banks by deviating the flow from the banks toward the central axis of the flow. This can however cause scouring at the head of the spur dike. If the depth of the scour extends to the foundation of the structure, the spur dike may be destructed. In this experimental study, the effect of the length of a spur dike and the grain size is investigated on the scouring around a Tshaped spur dike at 90 degree bend. Results showed that the dimensions of the scour hole is directly related to the length of the spur dike while the maximum depth of the scouring and the length of the scour hole in the upstream showed an indirect relation to the grain size.

Bridge scour (contraction, pier and abutment scour) is one of the main factors of bridge failure. The bridge abutment scour has been reported to be one of the main causes of bridge failure around the world. Therefore, during the past decades, it has been trying to introduce new practical and economical methods for controlling abutment scour of the existing bridges. In this study, the effect of submerged vane on the scour abutment has been experimentally investigated. Different alternatives, including number of vanes, vane locations and different angle of vane have been studied under different flow conditions. The results were compared with tests without vane to find out the reduction of the scour depth. The results showed that the vane can decrease the score depth up to 89 percent. It was also found that a single submerged vane attached to the upstream corner of abutment with an angle of 40 degrees is the most effective alternative. The submerged vane was found to be highly effective in moving the scour away from around the abutment.

Prediction of local scouring at downstream of hydraulic structures is one of the subjects which has been paid attention by researchers in recent years. In this study, the effects of shape of broad- crested weir with side slopes at different Froude numbers on local scouring were investigated at different particle Froude numbers. Firstly, the main factors affecting the process of downstream scouring were detected and adjusted as dimensionless parameters using dimensional analysis. Then variation of the sizes of scour hole dimensions were investigated by changing the lengths of weir crest and the horizontal apron, downstream slope of the weir at different particle Froude numbers. The results showed that the effects of weir crest length and the angle of downstream slope on scour hole depended on particle Froude number, while the scouring was less affected by particle Froude number with changes of the length of horizontal apron. Meanwhile, it was confirmed that there was a similarity between the various profiles of the scour. The parameters of the scour hole were presented as the dimensionless graphs that could be used in structure design to protect the bed against scouring.

We studied downstream scour at the triangular labyrinth spillway. In this study, we used labyrinth spillway with 6 different angles (150, 300,450, 67.50, Linear) and seven ratios (H/P=0.1-0.7 ). In this experiments the effect of H/P, Froude number and cycle angle on scour depth and hole dimensions were investigated. The results indicated that H/P, Froude number and cycle angle had a significant effect on scour depth and hole dimensions. When H/P increased 7 times, scour depth increased 12 times and scour length 10 times. Furthermore, whit increasing cycle angle 6 times, scour depth decreased 70%. There is no reasonable relationship between hydraulically parameters and the maximum height of sediment mound. Finally, with analyzing data and the results of experiments, we presented some empirical formulas for estimating of scour-hole dimensions.

The scour around the bridge piers is one of the main causes of bridge failure and the extraction of aggregates may aggravate this phenomenon. The present study comprehensively investigated the scour around the groups of bridge piers in the presence of aggregate extraction pits, using different discharges. The bridge piers roughened by gravel had been compared with the simple bridge piers; so, the results showed that the roughening caused the reduction of the scour depth. Scour depth change rate led to an increase in the equilibrium time. The results also showed that the reduction of the scour depth at the downstream groups of piers was more than that in the upstream. For the lowest discharge, the aggregate extraction pits had a considerable effect on the scour depth difference for the groups of piers in the downstream and upstream. On the other hand, the effects were decreased when the rate of discharge was increased. The experimental results obtained by the rough surface models showed that as the discharge was increased, the local scour was increased too; at the same time, the bed profile was posed at the low level. Generally, the scour depth of the groups of piers in the downstream of the extraction pit was more than that in the upstream. The results of the current research, therefore, demonstrated that the surface of the bridge pier roughened by gravel reduced the scour depth.

Weirs are widely used in many different shapes to control a water level, facilitate flow diversion, and to regulate the flow of water. Given that the overflow zone is often laterally restricted, the overflow depths can become excessive. As a result, non-linear weirs e.g., Labyrinth with different forms have been developed to increase weir length and discharge capacity within a fixed overflow width. Accurate estimation of the maximum possible depth of scour at weirs is important in decision-making for the safe depth of burial of footings. The design of labyrinth weirs foundations based on equilibrium clear water scour depths may yield considerably greater values than if the flow is of short duration. For a known time-to-peak value of the design flood hydrograph, smaller scour depths may be obtained, which reduces the total cost of construction. Therefore, investigation of temporal variation of clear water scour at labyrinth weirs is important to estimate the possible extension of the scour hole. This would provide useful information for the safe design of footing and the selection of scouring counter-measure to be implemented. In the present study, temporal variation of scour and at labyrinth weirs was studied. In experiments, labyrinth weirs were used and seven head to weir height ratios ( H/p =0.1-0.7) for cycles with 6 different sidewall angles (150, 300,450, 67.50, Linear). In this study, the effect of Alfa and sidewall angles on temporal variation of scour depth and scour depth location were investigated. The results indicated that the mechanism and the value of scouring at weir varied for the different value head and sidewall angles. When head to height weir increased, the value of instantaneous scour depth significantly increased. The results also showed that in all experiments, the scour rate is more severe in the early stages and 80% of the development of scour depth occurs in the early 10% of equilibrium time. Furthermore, When H/P increased 5 times, the equilibrium time of scour depth increased to 6, while whit increasing the sidewall angles to 6 times, equilibrium time decreased 45%.

For a bridge pier in the flow path, a three-dimensional and complex flow pattern is formed around the pier leading to the formation of a scour hole around it. The development of the scour hole will cause the instability of the bridge pier and ultimately the destruction of the pier and the bridge. This problem becomes very important during the floods, when the flow in the river increases rapidly and has the highest potential of destruction. Most studies have investigated scouring in steady flow conditions. The maximum scour depth that occurs under a flood hydrograph can be much smaller than the equilibrium depth resulting from steady flow under peak discharge conditions (Kothyari et al., 1992; Lai et al., 2009). Therefore, the use of flood peak discharge for design can greatly overestimate the maximum scour depth compared to the actual flood conditions (Chang et al., 2004). Considering the importance of scouring investigation in the conditions of unsteady flow and the limited available studies in this regard, more research in this field is necessary. The purpose of this research is to investigate the effect of the time of the rising and falling limbs of the hydrograph, as well as the duration of the hydrograph on the temporal variations of scour depth and its maximum value around the cylindrical pier.

The experiments were carried out in a rectangular flume with glass walls and a straight length of 10 m, a width of 0.74 m and a depth of 0.6 m in the Physical and Hydraulic Modeling Laboratory of Shahid Chamran University, Ahvaz. The test section in the flume was covered with uniform sand with an average size of d50=0.7 mm and geometric standard deviation σ=1.3. In order to achieve the goals of this study, a total of 13 experiments were examined. In order to investigate the effect of the time of the rising and falling limbs of the hydrograph on the temporal variation and the maximum scour depth, a number of 6 hydrographs with a constant duration of 100 minutes and the ratio of the time to reach the peak (Tp) to the duration time (Td) of the hydrograph (skewness) equal to 0.1, 0.2, 0.4, 0.6, 0.8 and 0.9 were designed. Also, 7 hydrographs with Gaussian distribution and duration times (Td) of 10, 20, 45, 80, 100, 120 and 160 were simulated to investigate the effect of flood duration on scouring (Fig. 3 and Table 1). A hydrograph generation system was used to create unsteady flow in the flume. This system included a programmed inverter that was used to adjust the variable flow rate of the hydrograph. The inverter was connected to the pump on one side and to the electromagnetic flow meter on the other side and was run by a computer through a software.

The results of the temporal variations of scouring showed that scouring starts from the sides of the pier and reaches the nose of the pier over time, and finally, the maximum depth of scouring occurs in the nose of the pier. The results showed that the maximum scour depth in the hydrograph with a Gaussian distribution occurs after the peak time (about 10% of duration time) (Fig. 5). Investigating of the effect of the rising limb of the hydrograph showed that in hydrographs with similar duration, the time to reach the peak of the hydrograph has no effect on the maximum scour depth, but it has a significant effect on the temporal changes of shear stress and scour depth. By reducing the time of the rising limb of the hydrograph from 90 minutes to 10 minutes, the shear stress change rate increases 9 times and the scouring rate increases about 6 times. Investigating the effect of the falling limb of the hydrograph on the maximum scour depth showed that the effect of the falling limb on the maximum scour depth increases with the decrease of the time of the rising limb of the hydrograph. The results also showed that the maximum scour depth in hydrographs with skewness of 0.1, 0.2, 0.4, 0.6 and 0.8 is 51.35, 21.28, 12, 5.56 and 1.79 percent more than the scour depth at peak discharge, respectively (Fig. 6). It was also observed that in hydrographs with the same peak time but different duration time, the time of the falling limb is effective on the value of the maximum scour depth. With the increase of 9, 4, and 1.5 times the time of the falling limb of the hydrograph, the maximum scour depth increases by 30.23, 14, and 1.82 percent, respectively. Investigating the duration time of the hydrograph showed that the increase in the duration time increases the depth and dimensions of the scour hole around the pier. It was observed that the maximum scour depth for hydrographs with a duration of 20, 45, 80, 100, 120 and 160 minutes were 19.44, 38.89, 52.78, 58.33, 66.67 and 69.44% more than a hydrograph with a duration of 10 minutes, respectively (Fig. 7). In addition, the slope of the time variations of the scour depth decreases with the increase of the duration time due to the lengthening of the flow rate changes interval along the rising limb of the hydrograph (Fig. 8).

In this study, scouring around a cylindrical pier was investigated under unsteady flow conditions. The results showed that for hydrographs with similar peak discharge and duration time, the time of the rising limb of the hydrograph has a significant effect on the temporal variation of shear stress and scour depth, but it has almost no effect on the maximum scour depth. In addition, it was found that by reducing the time of the rising limb, the influence of the falling limb of the hydrograph on the maximum scour depth increases. Investigating the results of the effect of hydrograph duration time on local scour showed that with the increase of hydrograph duration time, the maximum scour depth increases and the slope of temporal variations of scour depth decreases.