علیرضا مسجدی

One of the erosion control options in the downstream of the overflows is to use crushed stone to reduce the excess output energy and to minimize the amount of erosion and scouring in the downstream of the overflow. In this research, experiments were conducted to check the stability of the rock in the downstream of the spillway by changing the threshold angle. For this purpose, a triangular cup overflow with four different threshold angles was made of fiberglass. Experiments were carried out using a piled stone density with four different diameters in clear water. In each experiment, the flow depth was measured under the movement threshold conditions and then the stability number was calculated using the obtained data. The results of this research showed that the highest stability number related to the overflow with a threshold of 45 degrees and the lowest stability number was observed in the overflow with a threshold of 15 degrees. Also, the relative diameter of the aggregates is also an effective factor in the stability of the aggregates, and the stability number at the threshold of movement in the four angles of the triangular overflow threshold decreases with the increase of the relative diameter of the aggregates. In order to provide a relationship to estimate the relative diameter of the checkered stone, the variables of the investigation and the correlation coefficient of the results obtained from this relationship with the laboratory results for the triangular overflow were obtained as 0.85.

The results of the dimensional analysis by Buckingham method showed that the discharge coefficient(Cd), function "Ht/P" (represents the total hydraulic head ratio (total hydraulic head to the height of the weir)), "Sf" (represents the form factor of the weir) and "Nnp".Physical and numerical modeling was done in a rectangular flume with the length of 8 meters, width of 0.6 meters and height of 0.6 meters.The results of the study showed that creating an additional cycle has a positive effect on the TRTPIO weir, and it causes the discharge coefficient as well as its hydraulic performance to increase compared to the placement of the nappe breaker.creating an additional cycle and placing the nappe breaker on the labyrinth weir at the same time makes the TPTPIO weir with 4 nappe breakers have a higher discharge coefficient than other models.Quantitative evaluation of the results of this study shows that, for example, in the hydraulic head ratio of 0.24, the discharge coefficient of TRTPIO weir compared to TPTPIO weir, TPTPIO with 4 nappe breakers, TRTPIO with 4 nappe breakers, is 21, 8.5 and 21% have higher discharge coefficient; On the other hand, the Mattos-Villarroel weir has a higher discharge coefficient than the TRTPIO weir by 7.8%.The results of numerical modeling showed that with the increase of hydraulic head, the discharge coefficient decreases.while the increase of hydraulic head in labyrinth weirs causes an increase in the interference of nappe flow, energy loss, local submergence, and finally, a decrease in the hydraulic efficiency of the weir.

The use of structures has economic and safety advantages compared to other energy-consuming structures. In this research, to investigate the effect of the length of the sill of the flip bucket spillway on the scour downstream, experiments were conducted in a rectangular laboratory flume made of Plexiglas. The scouring downstream of the flip bucket spillway was investigated using a flip bucket spillway with four relative sill lengths and four threshold angles at four current intensities in the channel in this research. The results of this research showed that by the increase in the length of the sill in the flip bucket spillway, the energy consumption in the spillway increased and the scour depth downstream decreased. Also, increasing the relative length of the sill by 70% at the sill angle of 45 degrees, the scouring depth is reduced by about 88%. Also, a relationship was presented to determine the maximum depth of relative scour, and the correlation coefficient of the results obtained from this equation with the laboratory results is about 0.92.

Today, abutments disrupt the normal flow of rivers and cause scouring and erosion of sedimentary materials around them, creating holes and resulting in much damage every year. Researchers have proposed various methods to reduce the power of water erosion. One of the essential methods in this regard is creating slots in abutments. Since the expansion of the scour hole endangers the stability of the bridge structure, this study examined the effect of slot dimensions in the support on the scour hole dimensions. The findings demonstrated that the presence of slots in abutments effectively reduces the dimensions of scour holes. With the slot, the volume of the scour hole can be reduced by up to 50%. Furthermore, as the relative speed of scouring increases by 75%, the depth of the scour hole also increased up to 140%. An increase in slot depth leads to a decrease in scour hole depth of up to 85%.

Spillway is among the most economical energy dissipating structures used in dams to dissipate flow at the end of the structure. Scouring is a phenomenon that occurs next to the hydraulic structures, leading to their deterioration and even collapse. One of the methods to control scouring downstream of a dam is using riprap. In this study, the stability of riprap based on relative particle diameter (RPD) downstream of spillways of two different categories of energy dissipators: simple and dentated flip bucket was investigated. The experiments were performed in a rectangular test flume. Ripraps of the same density and of four different diameters were investigated at five discharges at the movement threshold. Results suggested that the RPD was an important factor in stability of the riprap. Besides, in both of the examined spillways, the stability number at the movement threshold was found to decrease with increase in the RPD. For all of the RPDs studied, the stability number downstream of the dentated flip bucket was found to be 11 percent greater than that of the simple flip bucket, which may be ascribed to the presence of dentate in the former. Likewise, dentated flip bucket offered a higher level of energy dissipation.

Piano key overflows have a high discharge capacity. Proper design of these overflows requires sufficient accuracy in predicting the type of overflows. In this study, experiments were performed in a rectangular laboratory flume made of Plexiglas to investigate the effect of the relative length and width of the two-cycle piano switch overflow crest on the discharge coefficient. In present research, the flow intensity coefficient was investigated by installing a rectangular piano switch overflow with relative crest lengths of 0.8, 1, and 1.2 and relative crest widths of 0.2, 0.3, and 0.4 in 10 flow intensities in the channel. The results of this study showed that by increasing hydraulic load, the flow intensity coefficient first increases and then decreases. Also, by increasing the relative length of the crest by 50%, the current intensity coefficient increases by 43% in the overflow. Increasing the relative width of the overflow crest by 50% increases the current intensity coefficient by 25% in the overflows. Also, an equation was presented to determine the maximum relative scour depth, and the correlation coefficient of the results of this equation with the laboratory results is about 0.90.

In this study, experiments were performed to investigate the relative energy losses in two models of simple triangular and toothed overflow made of fiberglass in four different landings at three depths of 100%, 90%, and 80%. The effective variables in this study were the landing number and the bottom depth at the end of the hydraulic jump. The results of this study showed that at three downstream depths, energy losses decrease with increasing landing number. Also, energy losses in the free projectile mode are higher than in the other two modes due to the full development of the hydraulic jump. In the general comparison mode, the performance of a toothed triangular overflow is better in energy dissipation than in the toothed mode, due to the fracture and compression of the flow lines in contact with the teeth at the end of the overflow projectile. In general, the use of teeth at the end of the overflow projectile causes energy loss in the conditions of 100% of the bottom depth in the toothed triangular overflow compared to the simple triangular overflow by an average of 7%, and in the conditions of 90% and 80% of the bottom depth by about 8% and 10%, respectively.

The present study used Flow-3D to investigate the effect of installing netted collars with different shapes on bridge piers. The results showed that installing netted triangular, circular, square, and rectangular collars with a hole diameter of 0.1 (d/D) reduced scouring by 49.5, 52.2, 52.7, and 56.5 percent, respectively, compared to the case with no collars. A hole diameter of 0.15 (d/D) for the same shapes resulted in reductions of 46.1, 43.3, 44.2, and 49.3 percent compared to the case with no collars, respectively, and the reductions for a hole diameter of 0.2 (d/D) were 15.9, 24.8, 26.4, and 26.5%, respectively. Moreover, increasing the collar hole diameter (d/D) intensified scouring, such that an increase in diameter from 0.1 to 0.2 increased scouring by an average of 44.1 percent.

One of the new methods for controlling erosion on the outer bank of river curve is the use of plates connected to the riverbank. Coastal vanes are the environmental structures which are used to control bank erosion, divert flow from bank to river center, improve sediment transport status, develop river for sailing, restorate and develop river's aquatic habitat. Despite the many advantages of coastal vanes, there is no detailed information about erosion and sedimentation and flow patterns around them under different hydraulic and geometric conditions and fewer research have been done. In the present study, the effect of different installation scenarios of triangular permeable vanes on bed sediment longitudinal and transverse profile changes in a laboratory channel with a 180-degree bend is evaluated.

In this research, the main purpose is to investigate sedimentation and erosion patterns in the rivers’ bend using coastal triangular vanes; in this regard, the impact of distance between triangular vanes, their effective length, and Froud number on the erosion control of the outer bank of the 180 degree bend is focused. Experiments in a laboratory flume with a mild 180-degree bend with a  ratio and a rectangular cross section with a width of 0.6 meters is done. The angle of fixed triangular vanes is 60 degrees, the height of the permeable triangular vanes from the sediment surface is 10cm and the permeability of the triangular vanes is 12%. The experiments were carried out with limpid water mode. The effective lengths of the prepared vanes were 12, 15 and 20 cm with installation intervals of 60, 75 and 100 cm respectively and were run at two different inlet discharges.

Investigating the effect of the distance between permeable triangular vanes on bed topography shows that in each Froud number, with increasing the distance of vanes from each other, the maximum scour depth will be increased. The results demonstrate the use of permeable triangular vanes causes the flow deviation from the outer bank to the center and then the inner bank of the flume, which leads to control the erosion in the river outer bank. By increasing the inlet flow discharge and increasing the effective length of triangular vanes and the distance of triangular vanes from each other in a 180-degree bend, the maximum scour depth and volume are increased. The installation of triangular vanes with an effective length of  and a distance of 5L causes the flow deviation from the outer bank to the vanes cape and the middle of the flume, consequently results in a decrease in the shear stress in the middle of the flume and scour depth of the erosion channel and creates thalweg in the vanes cape.

The results illustrate that by installing the triangular vanes, the point-bars are created in the interval between them. Therefore, during the effective length of 12cm, the maximum height of the point-bar on the outer bank equals to 30 and 31% of water depth, between the 0 to 170 degrees and 68.7 to 115 degrees equal to 11 times and 3 times the distance between the vanes, for discharge values of 13.5 and 15.5 l/sec, respectively. Also, for the mentioned conditions the width of the point-bar on the outer bank reaches  85% and 75% of vanes’ effective length , respectively. Permeable triangular vanes with six pillars are recommended for meandering rivers like  Karun in 90 and 180-degree arcs. These rivers have high torsion and curvature as well as high flow depth and low flow velocity in them, which contain high suspended sediments and the slope of this type of rivers is 0.001 or less and due to the low slope, their sediment carrying potential. Sediment loads are mostly fine.

In this study, experiments are carried out to determine the deviation flow into the intake in a 90º convergent bend, aiming to investigate the effect of flow characteristics on deviation flow with and without submerged vanes. The effective variables include Froude number, convergence, and submerged vanes’ angle. For this research, a Rectangular channel with a 90º arc was used, which was studied using four different discharges, four different angles of submerged vanes and four degrees of convergence of the end of the channel. According to the results, the deviation flow to the intake increases by converging the laboratory flume. As the end of the flume is converged, the deviation flow is further increased. As the flume is converged (b/B) from 0 to 0.75, the deviation flow is increased from 64.9 to 81.4%, showing a 16.5% increase. Deviation flow is decreased by installing submerged vanes. A decrease in submerged vanes’ angle reduces the deviation flow. Compared to the model without a submerged vane, deviation flow is decreased by 14.9, 9.9, 6.8, and 2.3% by installing submerged vanes at angles of 25, 30, 45 and 60º, respectively. Deviation flow is also decreased by increasing the Froude number, such that it decreases by 5.3% with the increase of Froude number from 0.14 to 0.23.

One of the measures to control the hydraulic jump at the downstream of hydraulic structures and to provide required sequent depth is to use a stilling basin with sudden contraction. Previous studies have shown that in this basin the jump length increases compare to the classical jump. On the other hand, it has been shown that roughening the bed is a measure that can be used to decrease the jump length. Therefore, it can bring a question that by roughening the bed of sudden contraction stilling basin how much can decrease the jump length? Therefore, in this study the effect of roughness on jump length at the mentioned stilling basin has been investigated. The tests have performed in a flume of 12-meter-long, 0.8-meter-wide and 0.7-meter height. The contraction ratio was 0.33 and the Froude number ranged between 2 to 10. The results have shown that the roughness can decrease the jump length up to 31% compare to the classic jump and can decrease up to 12% compare to the smooth bed of sudden contraction stilling basin. The jump length is equal to the USBR type II. It was found that the roughness can decrease the roller jump up to 20 percent compare to the sudden contraction of smooth bed.

Labyrinth weirs are structures designed for transferring large flows at low heads. In other words, labyrinth weirs are a particular type of nonlinear weirs used to control a flow as an economic and technical option. They are used when it is not possible to increase the capacity of a weir through increasing its width due to topographic conditions. These types of weirs enjoy a very high discharge capacity. As these types of weirs increase the effective length and following that the discharge efficiency, they can be used as dam weirs or water regulation structures. Considering the fact that there have been no comprehensive studies so far to investigate the weir discharge coefficient when the weir has a curved plan, in this research, some studies were conducted on trapezoidal arced labyrinth weirs with different arc radii and cycle lengths. Numerous experiments were performed using the physical modeling method to investigate the effect of the ratio of the inside apex width of the side weir cycles to the inside apex width of the middle weir cycle (w2/w1), the ratio of arc radius to the width of the middle weir cycle (R/w1), and the ratio of the length of a weir cycle to the width of the middle weir cycle (B/w1) on the weir discharge coefficient. The experiments revealed that by decreasing the inside apex width ratio of the weir cycles (w2/w1), the discharge coefficient shows an increasing trend up to 33%.

Scour is among the most critical topics in river engineering. A large number of bridges around the world are destructed mainly due to ignoring the hydraulic function in the design of bridges. The use of roughness, collars, submerged plates, and protective piles are among the methods for controlling and reducing local scouring. This study investigated the effect of protective piles in controlling and reducing scouring around spindle-shaped piers. According to the experimental results, by installing 5 piles at an angle of 30˚ with a relative distance (L/D) of 0.5, scouring decreased by 20% relative to the pile-less spindle-shaped pier. This scour reduction can be attributed to the transport of sediments around the pile toward the pier and accumulation of sediments in the middle of piles and in front of the spindle-shaped pier. The other factor reducing local scour is the change in the flow regime and reduced velocity and vortices in front of the spindle-shaped pier. Moreover, as the relative velocity (V/Vc, the ratio of the flow velocity to the critical velocity) increased from 0.54 to 0.95, scouring increased by 165.4% on average. The water flow colliding the spindle-shaped pier and the formation of a downward flow cause scouring. An increase in the flow velocity also increases the vertical velocity and vortices and thereby scouring. The mathematical model simulated by Flow-3D is consistent with the physical model showing an acceptable error rate of 4.3%.

The combination of a labyrinth weir with an orifice is a proper solution for floating material to pass over the weir and transfer sediment through the orifice. Additionally, creating a slot in the overflow wing leads to higher discharge. This study examined four discharges (5, 10, 15, and 20 liters per second) with channel width and height of 30 and 40 cm in trapezoidal-orifice, square-orifice, and triangular-orifice labyrinth weirs in the laboratory and using Flow3D with RNG k-epsilon (k-ε) turbulence model, the results were compared with one another. Comparing the discharge flow over weirs and measuring the discharge coefficient among the mentioned models showed that the triangular-orifice labyrinth weir had the highest discharge rate. Moreover, the increased Ht/P ratio (Ht represents total hydraulic head; P denotes weir height) for all models resulted in the increased discharge coefficient. Due to the efficiency of this type of weirs, the highest discharge coefficient was obtained at low Ht/P ratios. At lower ratios, since there was free flow, the coefficient of weir discharge increased, and as the ratio increased, the weir was partially submerged. Furthermore, for the weir design, the best Ht/P ratio was between 0.13 to 0.41, and the maximum discharge coefficient (Cd = 1.2) was within this range.

Experimental investigation on scoring and determination of depth of scoring are among the most important issues in T-shape spur dike designation with model T-shape spur dike was measured in a laboratory flume with 180 degree bend under clear water. In this study, we conducted evaluate the effect of relative distance between two T-shape spur dikes in the bend on the occurred scour. For this purpose, two spur dikes were installed at four different relative distances and four different relative lengths in the first half of an180 degree bend. All experiments were performed in four Froude number and a constant flow depth. The results show that with increasing the relative distance of T-shape spur dikes, the relative maximum scour depth increase at the opening of the spur dikes. Measuring depth of scouring based on experimental observation, an empirical relation is developed with high regression coefficient 0.98.

Piano Key Weirs (PKWs) are amongst the newly developed long-crested weirs that offer a higher discharge capacity relying on their more extended crest compared to labyrinth weirs of the same width. However, the use of barriers at the outlet of PKWs to increase energy dissipation has received little attention so far. In the present work, stepped and baffled models (with a bench height of 30 mm and baffle dimensions of 30 * 30 mm) were adopted to conduct experiments, and the Flow3D software was used for 3D simulation. Experiments were performed using discharge rate of 10 to 50 lit/s. The results revealed by increasing the discharge rate, the energy dissipation reduces. The energy dissipation rate using the baffles was 8.75% higher than that of the stepped model, and 15.21% higher than that of the case with no barriers.

In this study, in order to examine the joint of the cable and the collar in control of scour around the bridge piles, experiments were carried out in a rectangular plexiglass flume as a direct path. The experiments were carried out using three different cable diameters, three different thread angles and three rounds of the cable threaded at a steady current in clear water. The results of this study showed that, installing a cable and collar around the base of the cylinder is an effective factor in reducing the depth of scouring around it. Also, in all conditions of use of cable and collar, compared with the without collar mode, it increases the percentage of reducing scour depth around the cylindrical base. The use of collar on average reduces scour depth by about 43 percent compared to without collar condition. Also, the maximum scour depth in cable and collar conditions at a thread angle of 15 degree, a diameter ratio of 0.1 percent and triple threaded was about 63 percent.

The effect of submerged pipe diameter on scour controlling a direct laboratory flume was experimentally studied. Experiments were carried out on a cylindrical pipe with or without a lower blade. For these experiments, four pipe diameters, four blade lengths, and five horizontal placement modes for the lower blade were considered using a constant discharge under clear-water conditions. At the end of each experiment, the length and depth of scour beneath the pipe were measured. According to the results, the location of the lower blade and increased pipe diameter affect the scour depth around the pipe. In all cases, the use of a longitudinal blade caused an increase in the percentage of scour depth reduction around the submerged pipe. For a pipe with a diameter of 3.1 cm, the use of a blade length of 2.5 cm downstream the center of the pipe reduced the scour length by 70% on average as compared to the pipe without a lower blade.

Permeable vanes are structures that move the erosion of the outer bank of the river by diverting the erosive flow from the outer arch of the river to its center. In this study, the pattern of erosion and sedimentation around the hydraulic structure in the installation conditions of different distances from each other has been studied. Six-pillar concrete elements are materials that form a permeable structure overlapping and are applicable without drying the riverbed. These blocks need to be examined for how the structure works. With this concept, in the present study, the performance of this structures were performed in a laboratory channel with a width of 60 cm and a 180 degree flume under different hydraulic conditions (Fr = 0.227, 0.244, 0.261, 0.278). The required data were measured at different distances (5L, 6L, 7L, 8L) with an effective length equal to 20% of the width of the flume (L=12cm). Control experiment was performed in similar conditions to other scenarios without groins construction. Comparison of the results of the control and main experiments showed that the construction of permeable rectangular groin with a distance of 5L had the best efficiency in reducing the maximum depth of scour at the outer bank compared to the control experiments equal to 70.1% and 57.9% in Froud numbers of 0.227 and 0.261, respectively.

This paper presents, a set of experiments was conducted in a Plexiglas flume setup to investigate the simultaneous use of pipe and blade in the scour control around a submerged pipe. A vertical cylindrical pipe with and without a blade placed below it was selected for the experiments. The experiments were carried out in two different sates: with blade and without blade the pipe. Moreover, they were performed for four different pipe diameters, flow intensities, and blades where clear water was also used. The results showed for all states that simultaneous installation of pipe and blade below it caused a substantial decrease in the scour length. In other words, applying the blade produced a decrease in the scour length below the pipe by %21. Furthermore, in all states, simultaneous use of pipe and blade engendered a more increased scour depth than the absence of the blade, by %22. Besides, maximum scour depth for simultaneous use of pipe and blade was obtained equal to %55 when the blade width, pipe diameter, and Froude number were set to 1.24, 4.8 cm, and 0.42, respectively.

Labyrinth weirs are structures for transferring large flows at low heads, in which the effective length of crest for a given channel width is increased. In this study trapezoidal arced labyrinth weirs with different arc radius and cycle length were investigated. Several experiments were conducted using physical models to evaluate the effect of R/w1 (ratio of arc radius to middle cycle width) and B/w1 (ratio of weir length in flow direction to middle cycle width) on weir discharge coefficient. The experiments were carried out using a 6 m long test flume with cross section of 0.6 m width and 0.6 m height. Using Buckingham method of dimensional analysis, it was found that the discharge coefficient is a function of three variables; hydraulic head, arc radius of weir and weir length ratio. In general, the results of this study showed by increasing arc radius ratio, discharge coefficient of trapezoidal arced labyrinth weir increases up to 27.3%. Besides, by decreasing the weir length ratio from 1.5 to 1, discharge coefficient increased up to 29.7%.

Water supply at a desired rate at any time to meet the water requirements regardless of river discharge must be considered in the general design of intakes provided that the needs do not exceed the river flow. Due to the lack of necessary information in this field and the importance of sediment transport to the lateral intakes at river bends, this study aimed at understanding the mechanism of this phenomenon. To this end, the combined effect of convergence and divergence in lateral intakes on the sediment transport was investigated. According to the results, the diversion discharge to the intake was increased by converging the laboratory flume. By narrowing and converging the end of the flume, the diversion discharge was increased further, so that as the flume was converged to the size (b/B) of 0.75 and 0.5, the diversion discharge to the intake was increased by 13.6% and 75%, respectively. This could be connected to narrowing, flow obstruction and backflow to the intake. In contrast, different results were found by diverging the flume. In other words, the inflow to the intake was decreased by diverging the flume. As the flume end was diverged, the diversion discharge was decreased further. By diverging the flume to the size (b/B) of 0.75 and 0.5, the diversion discharge to the intake was decreased by 21.9 and 31.8%, respectively. The average diversion discharge to the intake at 30, 60 and 90º was 13.2, 15.2 and 11.5%, respectively. By converting the flume to the size (b/B) of 0.75 and 0.5, the diversion sediment to the intake was increased by 18.5 and 71.4%. In contrast, by diverging the flume to the size (b/B) of 0.75 and 0.5, the diversion sediment to the intake was decreased by 35.4 and 49.9%, respectively.

The discharge coefficient of labyrinth weirs increases with increasing the crest length within a certain width range. This study compares the discharge coefficient in two types of one-cycle triangular and trapezoidal labyrinth weirs. Experiments were conducted on a laboratory flume with length of 6, width of 0.6 and height of 0.6 m. The hydraulic performance of one-cycle triangular and trapezoidal labyrinth weirs with two, four and 6 guide vanes was compared. According to the results, the vanes with a placement angle of 60∘ in the trapezoidal weirs and a placement angle of 45∘ in the triangular weirs on the crests of weirs caused a further increase in the discharge coefficients of weirs. Consequently, at a constant hydraulic head (Hd/P) of 0.2, the discharge coefficient of a trapezoidal weir with two and six guide vanes increased by 38.8 and 10.3%, respectively, as compared to a trapezoidal weir without a guide vane. Furthermore, at a constant hydraulic head (Hd/P) of 0.2, the discharge coefficient of a triangular weir with two and six guide vanes increased 28.3% and 11.7%, respectively, as compared to a triangular weir without a guide vane.

Scouring is one of the main reasons for the failure of bridges in the United States and the world. The flow characteristics, the base shape and the angle of its deposition relative to the flow and characteristics of the sediments are all factors that interfere with the complexity of the scouring problem of bridge bridges. It should be noted that the final scour depth created near the bridge base is equal to the total erosion depth due to local, general, and narrowing of the flow width. Determining the depth of erosion within the range of bases requires knowledge of the displacement of sedimentary materials in the river bed. The bases disrupt the normal flow of the river, and the turbulence and disturbances resulting from it erode sedimentary materials around the base. Since the propagation of the scour hole threatens the stability of bridge structure, a common engineering practice in the field of river engineering involves the prediction of scour depth to take necessary controlling measures. Accordingly, this study aimed at investigating the effect of air foil lattice collars on airfoil bridge piers. According to the results, scouring decreased further with increasing collar length. By installing lattice collars with a length (L/D) of 6, 8, and 10 at a relative depth (Z/D) of 0.1, scouring reduced by 16.6, 22.3 and 24.7%, respectively, compared with a collarless bridge pier. By installing lattice collars with a length (L/D) of 6, 8, and 10 at a relative depth (Z/D) of 0.5, scouring reduced by 35.2, 37.4 and 38.4%, respectively, compared with a collarless bridge pier. By installing lattice collars with a length (L/D) of 6, 8, and 10 at a relative depth (Z/D) of 1, scouring reduced by 27.7, 31.6 and 31.4%, respectively, compared with a collarless bridge pier. Scouring increased by 113.8% on average by increasing the relative velocity (V/Vc) from 0.54 to 0.95. By installing the collar at a relative depth (Z / D) of 0.1, 0.5 and 1, we see 16.6, 35.2 and 27.7 percent lower scouring than the collar less base. Also, by increasing the depth of the lattice aerodynamic collars (Z / D) from 0.1 to 0.5, the scour reduction decreased by 22.3% and also with increasing the depth of the lattice aerodynamic collars (Z / D) from 0.5 to 1, increasing the scour 11.6 percent. In this way, it can be seen that the best depth of the collar is about half the diameter of the base of the bridge. Also, simulation with the Flow-3D math model is close to the physical model, with an average of only 5.4% error, which is acceptable.

A ‘spillway’ is a structure used to provide the controlled release of flood water from upstream into downstream area of a dam. As an important component of every dam, a spillway should be constructed strongly, reliably and efficiently to be used at any moment. Labyrinth and stepped spillways are presented as appropriate modifications to those spillways hardly capable of managing the maximum potential discharge. Owing to their nonlinear crests for a given width, labyrinth and stepped spillways have a larger discharge rate than linear- crest spillways at an identical height. Compared to other energy dissipaters, the combination of stepped and labyrinth spillways is known as a very strong energy dissipater. In the following part, the combination of these two structures and their dimensional change for increasing the water- energy dissipation are addressed. To conduct this study, an experimental flume with a 90- degree bend in the Islamic Azad University of Ahwaz was used. In total, 90 experiments were conducted on three different labyrinth- shape stepped spillway models with two different lengths, three different widths, and five different discharges. Analysis of the results showed a greater energy loss reduction in triangular rather than rectangular or trapezoidal labyrinth- shape stepped spillways. In addition, energy loss was greater in labyrinth spillways with two cycles than those with one cycle. Energy loss was increased by raising the Froude number from 0.05 to 0.1; in contrast, energy loss was decreased with increasing the Froude number from 0.1 to 1.0, which was due to the submergence of steps, a decrease in the roughness of steps and an increase in the intensity of aeration.