Scour Volume Research Articles

Baffle-Enhanced Scour Mitigation in Rectangular and Trapezoidal Piano Key Weirs: An Experimental and Machine Learning Investigation

The assessment of scour depth downstream of weirs holds paramount importance in ensuring the structural stability of these hydraulic structures. This study presents groundbreaking experimental investigations highlighting the innovative use of baffles to enhance energy dissipation and mitigate scour in the downstream beds of rectangular piano key weirs (RPKWs) and trapezoidal piano key weirs (TPKWs). By leveraging three state-of-the-art supervised machine learning algorithms—multi-layer perceptron (MLP), extreme gradient boosting (XGBoost), and support vector regression (SVR)—to estimate scour hole parameters, this research showcases significant advancements in predictive modeling for scour analysis. Experimental results reveal that the incorporation of baffles leads to a remarkable 18–22% increase in energy dissipation and an 11–14% reduction in scour depth for both RPKWs and TPKWs. Specifically, introducing baffles in RPKWs resulted in a noteworthy 26.7% reduction in scour hole area and a 30.3% decrease in scour volume compared to RPKWs without baffles. Moreover, novel empirical equations were developed to estimate scour parameters, achieving impressive performance metrics with an average R2 = 0.951, RMSE = 0.145, and MRPE = 4.429%. The MLP models demonstrate superior performance in predicting maximum scour depth across all scenarios with an average R2 = 0.988, RMSE = 0.035, and MRPE = 1.036%. However, the predictive capabilities varied when estimating weir toe scour depth under diverse circumstances, with the XGBoost model proving more accurate in scenarios involving baffled TPKWs with R2 = 0.965, RMSE = 0.048, and MRPE = 2.798% than the MLP and SVR models. This research underscores the significant role of baffles in minimizing scouring effects in TPKWs compared to RPKWs, showcasing the potential for improved design and efficiency in water-management systems.

Numerical Simulation of Local Scour Around a Square Artificial Reef

Abstract Artificial reefs (ARs) are one of the key anthropogenic constructs used to restore offshore fishery resources and recover the ecological environment. However, many ARs lose their stability and function due to scour. To ensure the functional effect of ARs, it is of great significance to study the factors causing AR instability, such as burying caused by scour under different flow conditions. In present study, a three-dimensional numerical model is established in FLOW-3D to study the local scour characteristics around an AR in steady currents. Reynolds-averaged Navier–Stokes (RANS) equations, closed with the renormalization group (RNG) k–ɛ turbulence model, are established to simulate a stable flow field around one AR. The simulation results are compared with previous experimental results, exhibiting good agreement. The effects of the opening number and the incident angles of ARs on the scour characteristics, equilibrium scour depth, and maximum scour volume were also investigated. The results indicate that the scour depth and scour volume decreased as the opening number increased. Furthermore, empirical equations are proposed herein based on the numerical results derived for the effects of the AR opening number on the equilibrium scour depth and maximum scour volume. A change in the incident angle affected the bed shear stress at the most-upstream corner of the AR. The greater the bed shear stress was, the more intense the scour was. In this study, we provide theoretical support and practical guidance for the optimized engineering design and construction of ARs.

Numerical simulation of offshore wind power pile foundation scour with different arrangements of artificial reefs

The industrial integration of offshore wind power and marine ranches has been actively explored and developed in many countries. This emerging industrial synergy can significantly improve the ecological friendliness of offshore wind power and contribute to the development of the marine economy in the region. This industrial synergy is an important development direction for future offshore engineering. Artificial reefs (ARs) are critical components of marine ranches and are widely placed around offshore wind foundations (OWFs). The ARs can block the water flow and form a complex wake region behind it, which changes the original turbulence structure and reduces scour around the OWF. Therefore, determining the arrangement of ARs for scour protection around an OWF is of great engineering significance. In this study, a three-dimensional numerical model is established using a prototype of the first offshore wind power-marine ranch demonstration project in China. The turbulent change and sediment movement between the OWF and ARs are solved using the Reynolds-averaged Navier-Stokes (RANS) and sediment transport equations. Moreover, the variations in the maximum scour depth and scour volume around the OWF at different arrangements of ARs are explored. The results demonstrate that the arrangement of ARs weakens the horseshoe vortices in front of the OWF and destroys the vortex shedding behind the OWF, thereby producing a beneficial scour protection effect. Various arrangements of ARs have different effects on scour results around the OWF. Increasing the height of the AR could significantly reduce the scour results around the OWF and play an effective role in scour protection, followed by the tandem arrangement of ARs, whereas the parallel arrangement of ARs will produce negative scour effects. This study will serve a vital guiding role in the arrangement of ARs and practical significance for scouring protection around the OWF.

Large-scale experimental study on scour around offshore monopile under combined wave and current condition

This work conducts large scale (1:13) experiments to study local scour around a monopile under combined irregular wave and current condition. The Keulegan–Carpenter (KC) numbers range from 1.1 to 6.73, and the relative current strength parameter Ucw numbers range from 0.17 to 0.77. The large-scale experiment indicates the 3D shape of scour holes is always an inverted cone under wave-current condition which has nothing to do with wave irregularity and Ucw. The changes of maximum scour location are associated with KC and Ucw numbers. The location of maximum scour depth is shifted from upstream to downstream of the monopile with large KC number under current-dominated condition. The characteristic scour timescale is closely related to KC, Ucw and Shields parameter θw when Ucw<0.3 and may be only related to θw when Ucw>0.7. The equilibrium scour depth is a function of vortex scale parameter referring to KC and Ucw numbers. A change in the definition of KC can improve the accuracy of existing formula under large-scale experimental condition, and scour volume formulae are further proposed from the relation with maximum scour depth. Finally, a scour volume formula of KC and Ucw numbers is suggested to estimate the protection material amount around monopile.

Experimental Study of the Effect of Morphological Changes due to the Permeable Type Groyne Structuren

The shape of a narrow river with a steep slope and high intensity of rainfall can affect the speed of the flow so that it has an impact on changes in flow dynamics that have the potential to cause erosion of the riverbed. This condition affects morphological changes with the emergence of degradation and agradation phenomena in certain areas. To determine the effect of morphological changes, laboratory tests were carried out using a permeable type groyne structure as an obstacle to reduce the flow velocity. The purpose of this study was to determine the effect of changes in basic morphology by changing the ratio of the groyne distance, which is 60 cm and 90 cm on variations in discharge and channel slope. The data required include flow velocity, flow depth, temperature and scour volume. In addition, the scour contours are drawn using Surfer software. The results showed that there was an effect of turbulent flow patterns on the use of groynes, causing local scour around the groynes and it was revealed that the use of groynes with a distance ratio of 90 cm was quite efficient in reducing scour.

Characteristics of Channel Incision Induced by Human Activity in a Wandering Reach in 20 Years

The wandering reach of the lower Yellow River has undergone significant channel degradation since the Xiaolangdi Reservoir operation, with a cumulative channel scour volume of 14.1 × 108 m3 in 1999–2018, and severe channel scour has resulted in rapid channel incision in this reach. The annual and cumulative river bed downcutting depths at section- and reach-scales and water stages at low and high flows were calculated to investigate the characteristics of channel incision quantitatively. The results show that the cumulative river bed downcutting depths at sedimentation sections varied significantly, with the magnitude varying between 1.1 m and 4.2 m. The cumulative reach-scale river bed downcutting depth reached up to 2.9 m and water stages at low flows decreased by more than 3.3 m at hydrometric stations. The previous 6-year average fluvial erosion intensity is the major influencing factor controlling channel incision, and empirical functions were established between cumulative river bed downcutting depths and the previous 6-year average fluvial erosion intensity in the wandering reach and three sub-reaches. The data calculated using the proposed equations agreed well with the observed downcutting depths, so these equations can be used to calculate the processes of channel incision in the recent 20 years in the wandering reach.

Physical Modeling of the Scour Volume Upstream of a Slit Weir Using Uniform and Non-Uniform Mobile Beds

This study presents new laboratory data on the time-varying scour upstream of a slit weir used for sediment release near hydropower intake. The governing parameters in temporal and spatial scour hole development under steady and unsteady flow conditions were experimentally investigated. This study includes 40 scenarios for steady flow at center and side slit weirs for uniform and non-uniform sediment with median sizes of d50 = 0.24, 0.55 mm and four scenarios of unsteady flow conditions at a center slit weir under different flow intensities. The steel slit weirs were built in a rectangular brick and concrete flume with dimensions of 1.25 m wide, 8.0 m long and 1.0 m deep. The dimensional analysis supports recent studies. This study demonstrates an increment in the resulted scour volume for fine and uniform sands at the center slit weir of about 2 times the value of coarse sand and 1.25 times the value measured with the side slit weir for uniform and non-uniform sands. However, the resulted scour volume for fine non-uniform sand at the center slit weir was recorded as 2.5 times that of coarse sand. There was a dramatic increase in the scour volume of about 4 times at the center slit weir and 3–3.5 at the side slit weir when the flow rate increased by 4 times.

Scour around underwater unexploded ordnances (UXOs): An experimental and computational investigation

Underwater unexploded ordnances (UXOs) pose a significant threat to human health and safety as well as the environment. The understanding of the scour around UXOs is essential for remediation actions. Many previous studies simplified UXOs as cylinders. We report an experimental and computational study on the hydrodynamics and morphodynamics around a real UXO and the comparison with a cylinder. With detailed flume data and simulation results, we show the UXO shape has a great impact on the hydrodynamics and the consequent scour and burial process. The shape effects also convolute with the flow’s angle of attack, making it even more important to consider the shape of UXOs. Hence, two angles of attack, 45° and 90° were investigated. The bulk behavior of scour around UXOs is akin to scour around any slender object placed on a sediment bed. However, the detailed scour process is significantly different. Our results show that flow contraction near the two ends of UXOs, recirculation behind the object, vortex shedding downstream, and jet-like flow under the object all play dominant roles during different stages of scour. In addition, we generalized the scour process around UXOs and other objects by applying a scaling analysis based on first principles of physics. A fitted saturation growth-rate equation relating scour volume and time collapses data reasonably well.

Engineering application of submerged water jets for sediment removal in a tidal riverbed

Sediment deposition problems have attracted the interest of engineers and researchers. Several experimental studies have been conducted on scour depth using turbulent jets. However, field observation and monitoring have rarely been reported. This study aimed to eliminate sediments on a tidal riverbed using a prototype device, which consisted of a set of submerged vertical water nozzles and submerged horizontal air nozzles. The effectiveness of the water jet in sediment removal during spring and neap tides was evaluated. The quantitative relationships of dimensionless parameters, such as (1) the relative sediment scour volume versus the number of flows from the jet exit, (2) the relative sediment scour volume versus the relative scour depth, and (3) the relative scour size versus the relative jet intensity, were analyzed. The results showed that the freshwater flowing to the sea affected the sediment scour volume during the falling cycle of spring tides. In contrast, the rising cycle of spring tides retarded the freshwater flow, resulting in a decrease in the sediment scour volume. A steep water surface slope accelerated the river flow and further influenced the cross-flow current around the study area. As a result, a highly diffusive turbulent flow was produced, causing suspended sediments to be rapidly removed from the scour hole center. An increase in the number of flows from the jets led to intensified diffusion of turbulent energy into the flow. The rapidly varying water depth caused jet energy to be dissipated before approaching the riverbed, and it significantly affected the scour process during the spring-tide period. The proposed equations can be used to estimate the scour volume, scour size, and re-suspended sediments in tidal rivers within defined ranges of parameters.

A comparative study on equilibrium scour volume around circular cylinders in clay–sand mixed cohesive beds, at near threshold velocity of sand – an experimental approach

Abstract Local scour around a bridge pier is a complex phenomenon resulting from the interaction of the three-dimensional turbulent flow field around hydraulic structures. An accurate estimation of scour depth below the stream-bed is important during design since it determines the foundation levels and the expansion of the bridge foundation structures. The present study reveals the results of flume experiments on equilibrium scour depth and scour volumes around circular bridge pier models in clay–sand sediment mixtures. The scouring process in a cohesive sediment mixture is a complex interaction between clay–sand network structure and bed shear stresses. The bed shear stress reduces inside the scour hole as scour depth increases, and this is related to the different modes of scouring in clay–sand mixtures. An exponential equation for the non-dimensional scour volume is proposed considering all the experimental runs to get a specific understanding of the surrounding volume of scour hole from maximum equilibrium scour depth in a clay–sand mixed cohesive bed, when the approach flow velocity is near to the critical velocity for mixed sand. The proposed equations are validated using the pre-existing data from the literature dealing with experimental investigations on bridge scour using clay–sand mixed cohesive sediment and show good agreement with observed data.

Experimental Study on Aspect Ratio and Velocity Intensity of Scour Around Submerged Pile Groups

Submerged pile groups are important components of complex piers in hydraulic engineering and are analogs for a range of subsea structures. These may sustain severe damages from local scour. The velocity intensity (U / Uc, the ratio of critical velocity to mean velocity) and aspect ratio (H / Dp, the ratio of pile height to pile diameter) are critical variables in this scour process. However, previous studies on scour around submerged pile groups were conducted in clear-water conditions (U / Uc &amp;lt; 1). In addition, many research studies are being conducted in shallow water flow conditions, which cannot eliminate the effect of the water depth on the scour process. Thus, these research studies cannot directly be applied to live-bed scour around submerged structures. To expand the velocity intensity and aspect ratio of scour around submerged pile groups, flume experiments were conducted with uniform quartz sand in both clear-water and live-bed conditions. Pile groups with different heights are adopted as experimental models. An improved time factor for both clear-water and live-bed scour around submerged structures is determined with the present experiments to extrapolate the scour depth of the present work to the equilibrium scour depth. This new time factor is then tested with experimental data from the literature. The tests demonstrate that this new time factor can reliably predict the scour process and equilibrium scour depth for submerged structures. Empirical relationships to demonstrate the effects of the studied variables including the equilibrium scour depth, scour area, and scour volume are presented. Different methods to predict the effects of the velocity intensity and aspect ratio on the scour depth are compared based on the present work. Furthermore, a correction coefficient is proposed to illustrate the effect of aspect ratio on scour depth. Then, equations of scour area and volume are derived according to the present experiments.

Study On Scouring and Protection of USBR-III Type Downstream of Spillway

Abstract. In the downstream part of the spillway building, especially in the flood way, occurs phenomenon of changing flow conditions from super critical to sub critical which causes a hydraulic jump and used by energy absorbers to reduce flow energy. The hydraulic jump in the floodway causes scouring of the bottom, particularly in the unprotected downstream spillway. Using 3 different dimensional baffle block models provides three different discharge variations in four flow simulations. Based on the results of the analysis and planning of the baffle block, it is found that the effectiveness in protecting the downstream scour of the spillway, namely baffle block dimensions of 1:1, 1:3 and 1:5. The three models of baffle blocks are used to determine the change in channel cross-section, scour pattern, scour volume and flow parameters that occur in downstream of spillway. The results showed that without baffle block was 32.80%, 1:1 baffle block was 43, 24%, 1:3 baffle block was 10.01% and 1:5 baffle block was 47.77%. The results of the drainage simulation showed that the higher the water level and the velocity of the flow at the bottom of the channel, the less the flow will be and will not be able to lift the bottom material of the channel

Experimental Investigations on Scour Volume Upstream of a Slit Weir

The frequent removal of sediment accumulation from reservoirs by dredging requires interruption of power generation. Alternatively, this can be avoided by using a slit weir. In the present study, the impact of sediment nonuniformity, slit weir dimensions, weir slit position, and discharge on the effectiveness of sediment removal was experimentally investigated using a flume with a length of 12m, a width of 0.30m, and a depth of 0.30m. In the flume, a slit weir was tightly fixed at the end of a 2m working section filled with nonuniform sediments up to 110mm. Results showed that using coarser sediment (d50 = 0.70mm) reduces the scour volume by 22-folds compared to finer sediment (d50=0.30mm). This study tested five different slit weir dimensions using two weir slit positions (slit positioned in the center and slit positioned on the side). The maximum scour volume was recorded when the crest level, z of the slit weir, was 0 cm from the mobile bed. The study concluded that a 3-fold increase in discharge corresponds to a 10-fold increase in scour volume regardless of bed material nonuniformity. The existing model for estimating scour volume for uniform sediments was validated using the data of this study, and it was observed that the model predicts the scour volume in nonuniform sediments with sufficient accuracy. Thus, the model can determine the scour volume, and maximum scour depth occurring upstream of a slit weir near a hydropower intake in reservoirs.

Hydraulics of flow over full-cycle cosine and rectangular sharp-crested weirs

Laboratory experiments were carried out to investigate the hydraulic characteristics of full-cycle cosine and rectangular sharp-crested weirs in free flow condition. The head–discharge relationships of full-cycle cosine weirs were determined theoretically and the discharge coefficients were correlated with weir geometry for both rigid and erodible bed conditions. The proposed model showed higher discharge coefficients in full-cycle cosine weirs in comparison with rectangular sharp-crested weirs. The three-dimensional velocity profiles of full-cycle cosine and rectangular weirs were measured by an acoustic Doppler velocimeter probe. The effects of weir geometry on mean flow and local erosion upstream of the weirs were studied for two sediment sizes of 0.7 mm and 1.2 mm. The time-averaged velocity profiles exhibited strong three-dimensional flow in full-cycle cosine weirs. The strength of the upper eddy in the crest location of full-cycle cosine weirs decreased by increasing the weir gap opening and the jet stream deflected upward due to uneven eddy sizes. The maximum streamwise velocity of cosine weirs increased by four times the average velocity at the crest level of the weir and the transverse velocity profiles captured strong vortices in the vertical plane closest to the weir. The effect of weir gap opening of full-cycle cosine weirs on the total scour volume was studied for two sediment sizes. It was found that the scour volume in the upstream region of cosine weirs was higher than the scour volume formed upstream of a rectangular weir with the same opening.

Characterization of large tsunamigenic landslides and their effects using digital surface models: A case study from Taan Fiord, Alaska

On 17 October 2015, a large landslide entered the marine waters of Taan Fiord, Alaska, and generated a displacement wave with a 193 m runup. The wave scoured the surrounding hillslopes of soil and vegetation and deposited significant volumes of material into the fjord, onto hillslopes on the opposite side of the fjord, and on top of Tyndall Glacier. For this study, we generated six, 2-m posting Digital Surface Models (DSMs) using DigitalGlobe/Maxar satellite imagery acquired near-annually between 2012 and 2019, and the Surface Extraction with TIN-based Search-space Minimization (SETSM) high-performance computing algorithm. We aligned the DSMs to exposed bedrock in the 01 March 2014 DSM acquisition, and then used them to characterize topographic and volumetric changes from before and after the 2015 Taan Fiord rock avalanche. We find that the landslide mobilized roughly 77. 0 ± 0.9 Mm3 of material, of which approximately 56.3 Mm3 were deposited in the fjord waters. Furthermore, we quantified an additional 27.2 ± 3.8 Mm3 of material scoured from fjord-adjacent hillslopes and deposited in the fjord waters, providing new constraints on the subaqueous deposition. This is the first time that DSMs have been used to estimate the volume of scour caused by a tsunami and the subsequent changes in extent and volume with time. Our results for the landslide and runout are consistent with field measurements published previously. This study offers improved estimates of both subaerial and subaqueous deposition for the 2015 Taan Fiord landslide and describes additional regional environmental conditions. We identify precursory motion prior to the 2015 landslide, characterize several smaller-scale landslides in the larger Taan Fiord region, delineate terminus positions and associated ice dynamics of the Tyndall Glacier, and detail seasonal changes in vegetation growth and snow melt/accumulation. This work provides important new insights into the geomorphic features and dynamics of this landslide and subsequent tsunami. The interdisciplinary applications associated with DSMs and the accuracy of the measurements presented here demonstrate that these methods are an effective tool to improve our understanding of the pre- and post-landslide processes, for monitoring areas at risk for landslides and other natural hazards, and for rapid response to catastrophic events.

Temporal and spatial distribution of bank retreat in the Jingjiang reach of the Yangtze River after the Three Gorges Project operation and its influence on channel adjustment

三峡工程运用后长江中游荆江河段河床持续冲刷，局部河段崩岸频发，影响河道内悬沙输移与河床形态调整.本研究采用实测长程河道地形及固定断面地形资料，确定了2002-2018年荆江河段的主要崩岸区域，估算了崩岸土体的泥沙总量，进而定量分析了河岸崩退对河床调整的影响.计算结果表明：荆江段累计河岸崩退体积约为2.0亿m³，约占该河段总冲刷量的17.5%；腊林洲及北门口河段累计崩岸体积与累计水流冲刷强度呈较好的幂函数关系（R²=0.95，0.97）；荆江段崩岸土体泥沙总量为2.7亿t，其中枝城-监利河段崩岸土体总量为1.67亿t，约占该河段沿程泥沙补给总量的30.7%，因此崩岸土体对悬沙沿程恢复有重要贡献；河岸持续崩退过程中，崩岸河段内的断面形态趋于宽浅，护岸工程修建后则明显趋于窄深，因此河道崩岸过程在一定程度上减缓了河床的冲深下切程度.;After the operation of the Three Gorges Project, the Jingjiang reach underwent remarkable channel degradation, and bank retreat occurred frequently in local sub-reaches, which affected the transport of suspended sediment and the adjustments of channel geometry. The measured fluvial topographic maps and cross-sectional profiles during the period of 2002-2018 were adopted to determine the main zones and volumes of bank erosion, and the effect of bank retreat was then analyzed quantitatively on the channel adjustments of the Jingjiang reach. Calculated results show that:the cumulative volume of bank erosion in the Jingjiang reach was about 2.0×10⁸ m³ during the period of 2002-2018, which accounted for 17.5% of the cumulative channel scour volume (11.4×10⁸ m³). Empirical relationships were developed between cumulative bank erosion volume and fluvial erosion intensity during flood seasons in the Lalinzhou and Beimenkou sub-reaches, with the determination coefficients of 0.95 and 0.97 respectively. In addition, the total sediment amount from bank erosion in the Jingjiang reach was around 2.7×10⁸ t, and the total amount in the reach between Zhicheng and Jianli was 1.67×10⁸ t, accounting for about 30.7% of the total amount of sediment supplied from the channel. Therefore, bank retreat played an important role in the suspended sediment transport, especially for the recovery of fine sand along the channel. Finally, cross-sectional profiles tended to be wide and shallow during the stage of continuous bank retreat, while they became narrow and deep after the construction of bank revetment engineering. Therefore, bank retreat can reduce the undercutting of the riverbed to a certain extent in the Jingjiang reach.

Large-scale experimental study on scour around offshore wind monopiles under irregular waves

The Keulegan-Carpenter (KC) number is the main dimensionless parameter that affects the local scour of offshore wind power monopile foundations. This study conducted large-scale (1:13) physical model tests to study the local scour shape, equilibrium scour depth, and local scour volume of offshore wind power monopiles under the action of irregular waves with different KC numbers. Systematic experiments were carried out with the KC number ranging from 1.0 to 13.0. With a small KC number (KC < 6), and especially when the KC number was less than 4, the scour mainly occurred on both cross-flow sides of the monopile with a low scour depth. When the KC number exceeded 4, the shape of the scour hole changed from a fan to an ellipse, and the maximum scour depth increased significantly with KC. With a large KC number (KC > 6), the proposed method better predicted the equilibrium scour depth when the wave broke. In addition, according to the results of three-dimensional terrain scanning, the relationship between the local equilibrium scour volume of a single offshore wind power monopile and the KC number was derived. This provided a rational method for estimation of the riprap redundancy for monopile protection against scour.

Experimental investigation of scouring around a single spur under clear water conditions

Abstract This study presents the effect of different parameters on the scouring process around spur dikes. Our research group's stated objective was to evaluate the effects of sediment gradation, flow depth, spur angle and spur length on the scouring process. Since most existing studies generally employed uniform sediment, in this study uniform and non-uniform sediment were selected. Experiments were made in a rectangular open channel in uniform flow conditions. Results showed that the effect of the spur dike length and the orientation angle on sediment scour varies with the type of sediment used. Scour volumes were 40% greater in uniform sediments than in non-uniform sediments. Measured scour depth was maximum at spurs perpendicular to the flow, whereas the scour volume was maximum at spurs directed upstream. The scour depth increased with an increase in the spur length; however, the effect of spur length on scouring varied at a contraction rate of 0.29 for uniform sediments and 0.36 for non-uniform sediments. A multiple regression analysis was also performed, and four equations were suggested to predict the scour depth and scour volume. Comparisons were made with the literature equations applicable for clear-water scouring to check the suggested equation. Because of the wide range of contraction ratios considered in this study, the equations which considered the contraction effect yielded better estimates.

Using nanomaterial to minimize the local scour downstream of sluice gate

Prediction of scour depths is an important aspect related to the overall stability of hydraulic structures. In this research, small-scale laboratory experiments were carried out to explore the effectiveness of mixing different percentages of Nanomaterial (Silica fume) to non-cohesive (alluvial) movable bed soil to develop mixture of bed material with significant characteristics to minimize the local scour caused by high-velocity jets downstream of a sluice gate. The experiments were executed employing 9 jet Froude numbers ranged from 1.88 to 2.81 associated with 3 heights for gate opening, and 3 tailwater depths. The bed material has 5 different percentages of Silica fume mixed by weight and 2 types of mixing with and without water were used. Ninety-nine experiments were conducted, out of which 9 experiments were done using fine sand as a bed material for the referenced cases. Graphical relationships were presented for maximum scouring and silting depths for different hydraulic conditions and bed materials. This research demonstrated that the type of mix (dry-mix or wet-mix) had a significant influence on the geometry of scouring and silting for the same flow conditions and the mixed percentage ratio of Silica fume. For dry-mix, the scouring and silting depths increased as the percentage ratio of Silica fume increased. While for wet-mix, the scouring and silting depths decreased as the percentage ratio of Silica fume increased. Also, the wet-mix effectively reduced the local scour volumes by 34.65% and 83.05% and decreased the silting volumes by 33.35% and 89.42% according to the percentage of Silica fume. Using a bed mixture of 8% Silica fume wet-mix showed 83.05% and 89.42% decrease in scouring and silting volumes, respectively, compared to pure fine sand bed material. From practical and financial aspects, the presented composition of bed material can effectively replace the smooth apron or at least decrease its length to reduce the construction cost. The obtained results present an untraditional technique for local scour protection downstream hydraulic structures.

Optimizing flow diversion structure as an effective pier-scour countermeasure

To reduce local scour around bridge piers, a mitigation measure requiring a submerged triangular flow diversion structure is proposed. Different dimensions, locations, and submergence ratios were examined experimentally. Using Taguchi’s method to minimize the number of alternative tests, 27 alternative tests were undertaken to ascertain the optimum size and location for the structure. Compared to the no flow diversion structure situation, it was found that the optimized structure resulted in a 40% reduction in the maximum scour depth and a 60% reduction in scour volume. Also, an experimental study of the flow field was conducted to investigate the influence of the structure on flows. Results showed that the structure influenced the down-flow and horseshoe vortex and consequently reduced the scour. Based on the investigation presented herein, a flow diversion structure is a simple and easy approach for mitigation of scour at existing and new bridges.