SCOUR HOLE development, its time variation and evaluation of its equilibrium state are of great importance in designing and implementing of abutments. Variation of SCOUR HOLE dimensions and their development have a substantial effect on the SCOUR mechanism. In this research, time variation of SCOUR HOLE at short wing wall abutments was investigated. The results obtained showed that SCOURing 'starts from the upstream comer of the abutment and upstream slope of the SCOUR HOLE, termed the dynamic angle of repose was found to be 18% greater than the angle of repose of bed sediments. Time variation of SCOUR HOLE dimensions, namely dimensionless length of SCOUR at upstream, downstream, width of SCOUR with time found to be logarithmic. The relationship between SCOUR depth and time was also logarithmic and 60% of the maximum SCOUR depth took place at the first hour of the experiment. The results obtained also showed a good agreement with other works.

In order to investigate the effect of different parameters on dimensions of SCOUR HOLE Downstream of a flip bucket, extensive experiments were conducted. Effect of parameters like: radius of bucket, drop height, tail water depth and unit discharge have been investigated. It was observed that dimensions of SCOUR HOLE is a function of radius of bucket, drop height, tail water depth and unit discharge. Dimensionless equations for prediction of SCOUR HOLE dimensions are introduced.

In this paper, the geometrical similarity of SCOUR HOLEs downstream of a sluice gate is studied experimentally. Although, nowadays a comprehensive understanding on SCOUR of noncohesive sediments is attained, because of the complex nature of clay minerals, the SCOUR of cohesive sediments has received less attention. 36 experiments with 12 hours run time, was carried out in a rectangular flume of 9 m length, 0.6 m height and 0.5 m width. Six mixtures of cohesive and noncohesive sediments with different fractions of clay minerals ranging from 10 to 40 percent were tested. The results show that the SCOUR profiles are nonuniform across the flume width. Despite the noncohesive sediments, the SCOUR HOLE in cohesive beds could not be introduced as a unique equation. Therefore, three different types of SCOUR HOLEs are distinguished and in each case, graphs and equations are presented to determine the shape of the HOLE. Also, a novel equation is proposed to calculate Bw parameter which is used to nondimensionalize the SCOUR HOLE. Finally, the effect of tailwater depth is investigated.

SCOURing is a two phase flow and has been experimentally studied. Culverts are used to transfer the flow from one side of roads or banks to the other side. This experimental work is conducted to study the SCOURing down stream of a pipe culvert. The SCOUR HOLE properties is a function of various parameters like: discharge, height of drop, tail water depth, diameter of the pipe and sediment size. In this study, variations of SCOUR HOLE dimensions, and changes of the ridge caused by SCOURing were correlated to: pipe diameter, drop height, dens metric Froude number and tail water depth. It was observed that depth and width of the SCOUR HOLE and the height of the ridge increase with the increasing the pipe diameter, but the length of SCOUR HOLE decrease. Moreover, it was observed that increasing the tail water depth, width and depth of the SCOUR HOLE decrease, but the length of SCOUR HOLE and height of the ridge increases. In addition, with increasing the drop height, depth and width of SCOUR HOLE and height of the ridge increase, but length of SCOURing HOLE decrease. The ratio of the SCOUR HOLE dimensions and the height of the ridge to the drop height was related to Tw/D (tail water to pipe diameter ratio), SN (dens metric ّFroude number) and Hc/D (drop height to pipe diameter ratio).

Many experimental studies have been conducted on development of the SCOUR HOLE as a result of vertical jet impaction. Research has shown that aeration of the nappe flow in the model is much weaker than that in the prototype. Therefore, the influence of aeration on SCOUR HOLEs needs further study. Experimental investigation of the effects of air entrainment and tail water depth on the SCOUR HOLE developed by a vertical submerged jet impaction is carried out in this study. The SCOUR HOLEs with and without air entraining conditions were investigated while hydraulic parameters like jet velocity and tail-water depth were kept constant. The results showed that air entrainment effectively reduces the SCOUR depth and dimension. Variation of maximum relative depth and length of SCOURing i.e. ds/htw and Ls/htw versus tail- water Froude number parameter, i.e. Frtw were analyzed. By increasing the air concentration, maximum relative depth and length of SCOUR HOLE reduced. The changes in SCOUR HOLE dimension has a threshold. Results indicated that for Frtw more than 8.78, no meaningful effect on maximum SCOUR HOLE depth (ds/htw) and length (Ls/htw) was seen for air concentration of less than 3.25 percent.

Prediction of SCOUR due to outflows from hydraulic structures is an important field in hydraulic engineering. There have been many studies concerning this subject which have invocated field analyses or laboratory experiments. As SCOURing is a complex process and many parameters affect it, there is not any equation that contain all parameters and limited for predicting SCOUR HOLE dimensions. One of an important parameter that affect the SCOUR HOLE dimensions is sediment gradation. In the previous researches ,the sediment non-uniformity effects on the SCOUR HOLE dimensions due to free falling jets ,did not study completely. In this paper the effect of this parameter is studied. The experiments were performed in the hydraulic laboratory of Tarbiat Modares University. The results show that by using d90 instead of d50 in the densimetric Froude number as a sediment size characteristic better correlation between the densimetric Froude number and SCOUR HOLE dimensions can be obtained. The previous research data along the data that was obtained in this research were used for checking the accuracy of the previous equations and presenting new equations for predicting the SCOUR HOLE dimensions. By using the Frd90 and omitting the (d50/Hc) and sediment non-uniformity coefficient, the accuracy of the equations do not changed significantly. The results show that the new equation predict the SCOUR HOLE dimensions in the field more accurately in compare to the previous equations.

Submarine pipeline is one of the most popular research filed that many researchers focus on solving the issue of buckling of pipeline. The snaked laying is an effective method to control the lateral buckling. The SCOUR below offshore pipeline may affect the efficiency and performance of the snake lay pipeline. The objective of this study was to investigate the effect of SCOUR HOLE on the buckling of seawater pipelines. A three-dimensional numerical model developed to investigate the effect of SCOUR below offshore pipeline subjected to wave and current by using Abaqus software and Aqua Module. The results indicated that vertical deformation of straight pipeline increased by increasing SCOUR HOLE depth. This value changed 4.85 cm to 32.87 for HOLEs 11 to 200 cm respectively, but these parameters of the snake lay pipelines were not affected by the presence of SCOUR HOLE. Moreover, the effective axial force of snacked lay pipelines reduced 5 times in comparison to straight pipeline by applying wave and current. The results indicated that the value of stress of snaked-lay pipeline was independent on SCOUR HOLE depth. Therefore, this pipeline was effective method to limit and control buckling even in the presence of SCOUR below it

SCOUR HOLEs formed downstream from a stepped spillway may affect the safety and stability of a structure. The development of such SCOUR HOLE can cause failure of the structure by undermining the riverbed, thus it is important to develop criteria that result in understanding how such a SCOUR HOLE can develop. The literature contains many studies dealing with energy dissipation, aeration and oxygen transfer in stepped spillways. However, their downstream SCOUR HOLE depth and geometry is not well documented. In this study, a physical model is employed to study the impact of offtake channel base angle of stepped spillways on the SCOUR HOLE. The area of the longitudinal profile of the SCOUR HOLE is used to evaluate the amount of SCOUR at downstream from the stepped spillways. Experimental results showed that the takeoff angle of 30o is the optimum angle which gives minimum longitudinal area and maximum depth of the SCOUR HOLE.

In this research work, besides analyzing the SCOUR HOLE at the downstream of the siphon spillway physical model, some equations have been presented to predict SCOUR HOLE developing. A physical model of siphon spillway along with three flip buckets of angle 30°, , 45°,and 60°,for three types of sedimentary materials of mean size 1. 8, 3. 5 and 1. 4 (mm) were used to study SCOUR HOLE formation process. Geometric characteristics of the SCOUR HOLE were collected for four flow discharges of 39. 2, 42. 12, 42. 12, 49. 76 (lit/s) and five tail-water depths of 15, 20, 25, 30 and 35 (cm) using a mesh grid size of 10 (cm) ×10 (cm). Three dimensionless parameters were extracted for analyzing experimental results using dimensional analysis. Of all SCOUR HOLE dimensions, SCOUR depth (ds), SCOUR length (Ls) and distance of downstream hill up to bucket lip (L6) were adjusted for numerical modeling. Results showed that increasing flow rate causes growth and developing of SCOUR HOLE geometric properties simultaneously. Increasing the particle size showed an inverse relationship with three dimensions of the SCOUR HOLE. Also, the reduction of the bucket's angle led to a reduction in ds, Ls and L6. The maximum correlation coefficient obtained between ds, Ls and L6 with particle size, flip bucket angle and discharge/tailwater, respectively. Finally, predictors were presented to describe above-mentioned dimensions of SCOUR HOLE dimensions.

One of the economical energy dissipater structures applying in high spillways is flip-bucket which falling flow causes SCOURing in plunge-pool at downstream. In this research, the bed variation as a SCOUR HOLE at the downstream of a siphon spillway has been investigated. Dimensions and position of the SCOUR HOLE were analyzed both experimentally and theoretically. The experimental results showed that the maximum SCOUR HOLE depth was a function of discharge rate and downstream tail water depth. Also, flip-bucket angle had the most significant effect on distances of upstream hill and SCOUR HOLE bottom from the spillway. It was found that the SCOUR HOLE length, distances of downstream hill end point and maximum SCOUR from the spillway were affected by the hydraulic conditions but they were less effected by the flip bucket angle and bed particle size. Also, it was seen that the flip bucket angle had a significant effect on upstream hill height. The height of downstream hill height was a function of flow discharge and tail water. Applying Buckingham π theory, three variable linear equations were extracted to predict the dimension and situation of the SCOUR HOLE and hills. The comparison between the measured versus the predicted values showed a good agreement between them.