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In this study, the effects of the grain size and gradation of riprap, the overtopping flow depth, and the downstream slope of the embankment on the scouring and deposition characteristics at the downstream toe of the embankment were investigated. For the experiment, three different downstream slopes (1:2, 1:3, and 1:4), three different overflow depths (1, 2, and 3 cm), and three different sizes of riprap particles (d50 of 16.41 mm, 8.48 mm, and 3.39 mm, herein referred to as coarse gravel, medium gravel, and granule, respectively) were used in the laboratory. The experimental results demonstrated that the scour depth and deposition height increased with increasing energy head for each downstream slope condition. Among the three particle sizes, coarse gravel shows the lowest scour depth and the highest deposition height. For the 1:2 slope, the coarse gravel particle size was 62% and 75% less resistant to scouring than the medium gravel and granule particles, respectively. For the 1:3 slope case, this was 31% and 46%, and for the 1:4 slope case, this was 39% and 49% less than the medium gravel and granule size particles, respectively. [ABSTRACT FROM AUTHOR]

Rivers and other freshwater ecosystems have been severely changed by humans. This resulted in a distinct decline in the abundance of many aquatic organisms, as well as those living in water‐dependent habitats. Our work aimed to study the habitat selection of breeding common sandpipers (Actitis hypoleucos) and the impact of river regulation on the occurrence of this species.Data were collected on a 100‐km stretch of the Vistula River, a semi‐natural, lowland and large European river. The distribution of birds was determined based on two censuses, while environmental variables were collected based on Sentinel‐2 satellite imagery classification, digital elevation model (DEM), digital surface model (DSM) and official data of river regulations.The length of the shoreline of either the river or vegetated islands had a positive effect on the number of breeding territories of the common sandpiper. This indicates the importance of the presence of a natural riverbed with a complex shoreline. Moreover, sandpipers preferred islands over the river shores as nesting habitat. River regulations, such as groynes and riprap, had a negative impact on the abundance of breeding common sandpipers even though the river regulation was not intensive. The negative effect has been persisting for many years after the regulation was implemented, despite the degradation of regulatory structures over this period. [ABSTRACT FROM AUTHOR]

In this study, the effects of the grain size and gradation of riprap, the overtopping flow depth, and the downstream slope of the embankment on the scouring and deposition characteristics at the downstream toe of the embankment were investigated. For the experiment, three different downstream slopes (1:2, 1:3, and 1:4), three different overflow depths (1, 2, and 3 cm), and three different sizes of riprap particles (d50 of 16.41 mm, 8.48 mm, and 3.39 mm, herein referred to as coarse gravel, medium gravel, and granule, respectively) were used in the laboratory. The experimental results demonstrated that the scour depth and deposition height increased with increasing energy head for each downstream slope condition. Among the three particle sizes, coarse gravel shows the lowest scour depth and the highest deposition height. For the 1:2 slope, the coarse gravel particle size was 62% and 75% less resistant to scouring than the medium gravel and granule particles, respectively. For the 1:3 slope case, this was 31% and 46%, and for the 1:4 slope case, this was 39% and 49% less than the medium gravel and granule size particles, respectively.

Organisms, such as fishes and invertebrates and including their larval stages, listen to underwater soundscapes to detect information about nearby habitats. Such soundscapes may be influenced by habitat degradation or enhancement, which can lead to acoustically mediated feedback loops affecting the overall ecosystem.Despite the importance of underwater sounds on ecological functioning, there have been limited studies documenting soundscapes of intertidal ecosystems and few, if any, of living shoreline soundscapes. Living shorelines would especially benefit from acoustically mediated effects for objectives like encouraging fish and invertebrate settlement.This case study used a Before‐After‐Control‐Impact design to sample soundscapes and nekton (i.e., fishes and mobile macroinvertebrates) at a living shoreline construction and a nearby hardened shoreline in Cedar Key, FL (USA). Diel soundscape patterns and acoustic attenuation at the two sites were also described a year following the living shoreline construction.In the acoustic sampling, the high frequency bands of both shorelines were dominated by invertebrate sounds that were influenced by season, site and time of day, while the low frequency band of the living shoreline was often dominated by a loud anthropogenic sound. About a year after the living shoreline installation—despite similar measured acoustic attenuation at both sites—the living shoreline featured louder sound pressure levels compared to the hardened shoreline, which may be particularly beneficial for promoting foundational species and other organism settlement.These results demonstrate that Gulf of Mexico intertidal habitats may have soundscape differences even within close proximity and that living shorelines may enhance acoustic characteristics in ways beneficial to continued shoreline development. This represents an important step in better understanding the relationships between habitat structures, nekton communities, and their associated soundscapes as well as the application of passive acoustic monitoring to improve coastal management and conservation. [ABSTRACT FROM AUTHOR]

Improving the knowledge of the failure mechanism of riprap exposed to overtopping is valuable to enhance the construction and reinforcement techniques of rockfill dam defense systems. In this research, four experimental overtopping tests were carried out on 1∶10 rockfill dam models with placed riprap protection layers supported at the toe. Axial reaction loads were measured and 3D models were built using the structure from motion technique to study the displacement of riprap stones exposed to overtopping. The importance of throughflow in the rockfill shoulder is brought to light by comparing these results with previous data from a placed riprap model built on a ramp without throughflow. The structure from motion technique demonstrates to be very effective and highlights the existence of a buckling phenomenon, along with the compaction of the riprap. The displacement data show that the compaction mechanism is more important (both horizontally and vertically) and appears at lower overtopping discharges for less packed placed riprap layer. Finally, similar trends for vertical and horizontal riprap displacements are demonstrated between the initial position and the last position before failure. Such information suggests that the critical discharge value is not as critical as the riprap displacement to predict dam failure under overtopping conditions. [ABSTRACT FROM AUTHOR]

Roost selection by insectivorous bats in temperate regions is presumably influenced by roost microclimates in relation to thermoregulatory strategies, but few studies have included temperature measurements in habitat selection models. Rocky landscape features are an important source of roosts that provide both shelter from predators and beneficial microclimates for bats. Most information about rock-roosting bats has been derived from western North America. We studied microhabitat selection by the Eastern Small-footed Myotis (Myotis leibii) on natural talus slopes and human-made stone structures in the Appalachian Mountains of Virginia and New Hampshire, relative to thermal and structural characteristics of rock crevices. Roosts were located with a combination of radiotelemetry and randomized visual surveys. Roost-switching behavior and structural characteristics of roosts did not appear to be influenced by the methods we used to locate roosts. Compared to random crevices, both sexes selected crevices with narrow openings, likely to provide protection from predators. Reproductive females also selected rocks that were larger and more thermally stable than random crevices, whereas males selected crevices that were structurally similar to random crevices but warmed more during the day. Rock size and other structural characteristics influenced temperatures of roosts and random crevices alike by inhibiting excessive daytime heating and nighttime cooling. Because large rocks were important for reproductive females, and talus slopes with large rocks could be limited, we recommend including rock size as a variable in landscape scale habitat assessments for Eastern Small-footed Myotis. Protecting or managing for habitat features with large rocks that receive high solar exposure could benefit Eastern Small-footed Myotis, and perhaps other rock-roosting species. [ABSTRACT FROM AUTHOR]

Nowadays, although the studies on anti-scour of monopile foundations for offshore wind turbines have made some progress, numerous problems in engineering applications still need to be solved. Based on the anti-scour mechanism and the corresponding construction methods of the riprap, composite solution of concrete mattress and sand blankets, and the solidified soil solution, the characteristics and the applicable engineering environments of the three solutions are analyzed. In an offshore wind power project in the sea areas of Jiangsu, the three anti-scour technical solutions were applied to protect the monopile foundations for the wind turbines, and the effects of anti-scour were assessed with the scoured depths obtained by scanning around the monopiles and the surrounding sea area. For the technical schemes with poor anti-scour effect, the reasons for poor anti-scour protection and anti-scour failure were analyzed, and corresponding recommendations were made to improve the anti-scour methods for offshore wind turbine monopile foundations. Through calculating the cost of the three solutions applied to a single offshore wind turbine monopile foundation, the economic benefits were analyzed and compared. The results showed that the solidified soil solution had a better anti-scour effect and lower cost, which had a splendid application prospect. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ground Improvement is the property of Journal of Ground Improvement Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Riprap resistance is a widely used solution for protecting earth dams from erosion but riprap can be displaced on the dam surface. This study examines the stability of riprap in the Taleqan Dam, Iran using rock mechanical tests and InSAR technology. Uplift of dam stairs and erosion of the riprap material have been observed during field work at the study site, and samples have been gathered from three rock categories. The purpose of this study is to explore the factors influencing the deformation of the Taleqan Dam. The InSAR method has been employed for monitoring surface deformation and the Los Angeles ASTM C test was used to establish the cause of dam deformation. InSAR analysis was carried out using Sentinel-1A images from 2014 to 2019. The results revealed subsidence at an average rate of 4 mm/yr over that period. The results of Los Angeles ASTM C indicated that the Andesite riprap was more easily eroded, has a relatively low durability and specific weight, and low resistance erosion. Therefore it is unsuitable for use as a protection layer for the crest and lower sectors of the riprap. It can also be concluded that the inadequate durability of certain rock materials may potentially cause weathering, depression, reduced thickness and displacement of the riprap.

One of the most important factors of damage and failure of hydraulic structures is the occurrence of local scouring around them. Scour is a natural phenomenon that occurs due to the flow of water in rivers and streams. If a hydraulic structure such as a bridge pier or abutment is placed against the flow of water, the flow pattern near the structure changes and causes scouring phenomenon locally around these structures.To control scouring around the bridge abutments, various methods have been proposed, which are generally divided into two categories: flow pattern modification methods and bed protection methods. Among the substrate protection methods that have been examined in this research is the use of riprap and vegetation, because riprap and vegetation are both fully available and inexpensive tools for protecting The base and abutment of the bridge are known to be washed away.The experiments were carried out in the hydraulics and water structures research laboratory of the water engineering department of Shahid Bahonar University of Kerman. In this study, two 90-degree rectangular abutment and a rectangular abutment with circular walls were used, both of which are galvanized and 10 cm long, 45 cm high and 6 cm wide was used (the abutment which is perpendicular to the flow was chosen as the width of the abutment). By conducting a long-term test of 12 hours at a flow rate of 34 liters per second for each of the abuments, the equilibrium time was estimated to be 5 hours.

Meandering rivers are characterized by geomorphic units like cut banks, point bars, and thalwegs. These units arise from interactions between hydrological and geomorphological forces. However, the individual contributions of geomorphic units to whole-river metabolism or nutrient processing are unclear because these quantifications are often done at larger spatial scales. We used closed recirculating chambers to measure benthic gross primary production (GPP), respiration (R), N uptake or release, and P uptake or release at bimonthly intervals over 1 y at different geomorphic units in the Mulde River, Germany. We compared GPP, R, and nutrient processing among a cut bank, a point bar, and the thalweg at a natural meander. We also compared the cut bank of this natural meander with a cut bank fixed by riprap at a human-altered meander. In the natural meander, GPP, R, and nutrient processing rates were higher at the point bar than the cut bank or thalweg. These differences are likely related to larger sediment grain sizes that provide a more stable substrate for microbial communities. A strong interaction between geomorphic units and time for GPP and NH4+ fluxes suggested that differences in nutrient processing rates among geomorphic units were restricted to specific times during the year. Specifically, we found that the nutrient processing rates differed among geomorphic units during the summer, but not winter. Furthermore, in June and August 2017, R was 2 to 3× lower at the cut bank stabilized by riprap than at the natural cut bank. Our results demonstrate that rivers are composed of functionally distinct geomorphic units susceptible to human-induced hydromorphological degradation. However, strong interactions between space and time and large within-geomorphic unit variability propose that local drivers influence ecosystem function, suggesting that we need additional research to resolve these drivers at the scales of geomorphic units. [ABSTRACT FROM AUTHOR]

One of the most significant problems faced by hydraulic engineers is the local scouring of in-stream structures. The optimal design of scour protection methods requires time consuming, laborious and costly studies. Fractional factorial methods have been provided to formulate experimental designs which can optimize designs with fewer experiments and high accuracy. Therefore, this study aimed at using Taguchi and grey relational analysis (GRA) methods to investigate the effect of three factors: (1) spur dike angle, (2) size of riprap stones, and (3) riprap extent on the local scouring. An additional goal was to achieve an economical pattern for the riprap apron so that it delivers the best performance in protecting spur dikes with different angles. The results show that the riprap apron decreases the scouring depth and moves the scouring hole away from around the structure. However, increasing the spur dike angle decreases its performance in scouring reduction. Increasing the area of the riprap apron protected the downstream walls better and reduced the edge failure of the riprap; however, the erosion in the opposite wall increased. In addition, analysis of variance showed that the riprap extent and the spur dike angle, respectively, have the highest effects on the riprap performance, respectively. The comparison of the predictions of the Taguchi and GRA methods with observed values showed that these two methods have high capabilities to predict the results of scouring studies. [ABSTRACT FROM AUTHOR]

Scour is one of the main causes of hydraulic structural failures. The present experimental study examines the use of riprap, submerged vanes, and a combination of these for scour reduction around vertical walls and spill-through abutments under clear-water conditions. Specifically, the influence of placing riprap stones with different apron shapes (geometry) and/or a group of submerged vanes of constant height and length on abutment scour was examined. The main aim is to propose the optimum apron geometry and placement of submerged vanes to (1) reduce edge failure at vertical walls and spill-through abutments; and (2) prevent shear failure at the spill-through abutment (no shear failure is observed around the vertical wall abutment). The results show that using ripraps for scour protection is more effective than submerged vanes. However, the highest reduction in scour depth was achieved when a combination of riprap and submerged vanes was used together. This arrangement can reduce the maximum clear-water scour depth by up to 54% and 39% with vertical walls and spill-through abutments, respectively. Furthermore, selecting appropriate apron scale ratios reduces the required riprap volume by up to 46% and 31% for the vertical wall and spill-through abutment, respectively. In addition, the installation of vanes increased the riprap stability and reduced edge failure in both abutments tested. Finally, using riprap aprons with proper scales ratios at the downstream side of the spill-through abutment also prevents shear failure in this zone. [ABSTRACT FROM AUTHOR]

The study of mechanisms and the accurate simulation of riprap movement caused by complex hydrodynamics are significant for harbor, channel and coastal engineering. Field measurement of current and riprap drift distance was conducted for a dike project in the port of Lianyungang, Jiangsu Province, China. Meanwhile, a well-validated three-dimensional hydrodynamic model was developed to study and analyze the riprap movement process and the influence of project position combined with the theoretical movement equation of riprap. At the moment of maximum flood, the riprap drift distance is greater than at the moment of maximum ebb. The riprap drift distance increase as the tidal inlet width decreases, which follows a second-order exponential distribution. The riprap mass reduces the riprap drift distance, and the magnitude of the reduction diminishes gradually as the riprap mass increases. Therefore, heavy riprap can reduce the horizontal drift distance in a construction. [ABSTRACT FROM AUTHOR]

Placing riprap is considered as a permanent layer and common countermeasure against local scour around the bridge pier. However, the typical design of the riprap layer by using empirical equations fails to consider the uncertainties, which are involved in effective parameters on its characteristics such as the size, thickness, and extent. Therefore, there is no information about the probability of failure for the designed riprap layer. Accordingly, this study presented a method for the reliability assessment of the riprap layer considering the uncertainties which are involved in effective parameters. All three different characteristics of the riprap layer were included in the analysis by using the Monte Carlo Simulation Technique. In addition, Fault Tree Analysis was employed for combining the interactions of different parameters and calculating the probability of the failure of a riprap layer system. Further, a case study was provided to demonstrate the capability of the present method, followed by evaluating the effect of each effective parameter on the probability of failure using sensitivity analysis. The results revealed that relative riprap stone density and flow depth have the highest and the least effect on the probability of failure of riprap layer, respectively. [ABSTRACT FROM AUTHOR]

The paper briefly describes the mechanics of local scour process around bridge pier and gives an in-depth review of the various techniques employed for local scour control and protection. The most common armoring device is placing of riprap stones around the pier. Despite the effectiveness of riprap armoring countermeasure, it faces some limitations such as cost ineffectiveness and susceptible to channel bed degradation. The performance of various flow-altering devices is studied. The combination of slot and collar plate can be a suitable solution to prevent the local scour if well designed and constructed properly. The combination of permeable sheet piles with riprap can even reduce the scour depth effectively up to 91% in live bed scour conditions. The combination of vanes and collar plate around oblong bridge pier results into less extent of scour and produces a higher degree performance potential of 86.36% as compared with unprotected oblong pier. Although the composite device has higher scour reduction potential than individual device, there is no guarantee that there will be complete elimination of local scour. Therefore, more research is needed to analyze the stability of this device on the prototype and field application and enhance their efficacy furthermore. [ABSTRACT FROM AUTHOR]

The construction of Levee or river embankment is one method adopted for flood control in Palembang. The stability of the embankment is affected by water seepage inside the embankment due to several factors including rainfall as well as the repeated rise and fall of water surface in the sea due to gravity of moon and sun. Palembang is located 106 km from the east coast of Sumatra, thus the free water surface in Musi river and its tributaries is affected by the sea level. The stability of the levee is affected by the repeated change in the water level which induces changing seepage direction. This paper discusses the stability of levees constructed along Sungai Lacak, one of Musi river tributaries. In this case the stability of the existing levees was evaluated for different conditions of free water level i.e. normal, low tide and high tide. Analysis was also conducted for the case when the levee was constructed following the guidance in Standard Nasional Indonesia (SNI 1724-2015) and Guidelines of Public Work Department (2017). Improvement on the stability was obtained if the embankment was to be rebuilt according to the specification given in the standard. The presence of riprap protects the embankment from the effect of changing seepage direction due to the rise and fall of water level, thus increased the safety factor of the ideal levee during high tide from 1.270 to 2.325.

The effect of turbulence intensity on riprap stability was studied experimentally. Riprap stones were placed on a flat streambed and turbulence intensity was changed with a turbulence generator. An acoustic Doppler velocimeter (ADV) was used to measure turbulence intensity. Results showed that in a constant flow condition, by increasing the near-bed turbulence intensity from 10% to 25%, the stable riprap diameter increased about 2.5 times. Based on the results of the present work and using all existing data, an empirical equation was developed for calculating stable riprap stone size considering the time averaged near-bed velocity and near-bed turbulence intensity. [ABSTRACT FROM AUTHOR]

The value of biodiversity and of documented biodiversity surveys is well established. Extracting historical biodiversity data and synthesizing them with current data can provide a more comprehensive estimate of total diversity and guide future monitoring. We demonstrate the utility of compiling historical and recent biodiversity data to better characterize taxon richness and composition. Our focus is an otherwise unmonitored habitat in an unmonitored British Columbia provincial park, in a heavily impacted region of the Salish Sea that was designated a United Nation Biosphere Reserve in 2021. We conducted surveys and compiled historical records that together spanned three intertidal habitats and 43 years. From these combined data we report a total of 99 taxa, an order of magnitude increase over the number listed in the park's Master Plan. These include seven non-native species, of which four are newly reported here. Rarefaction, extrapolation, and multivariate dissimilarity analyses revealed the roles of methods and habitat types in contributing to differences in taxon richness and composition among surveys. This data compilation illustrates many of the challenges and opportunities in aligning and assembling independent space-time snapshots of alpha (i.e., local) diversity to better understand the gamma (i.e., regional) diversity of a marine protected area and provides the foundational data needed to design effective future monitoring at molecular to ecosystem scales. [ABSTRACT FROM AUTHOR]

There are increasing demands from dam safety regulations and guidelines to upgrade the rockfill dams, especially in Norway where over 180 large rockfill dams are present. To protect the hydraulic structure against overtopping events or leakages, it is important to use defence mechanisms such as a protective layer of riprap on the downstream slope. In this article, we display 9 experimental setups of riprap, conducted at the hydraulic laboratory of NTNU (Trondheim) and subjected to overtopping phenomena with increasing water discharge, until the complete failure of the model. These tests were performed on models with dumped and placed riprap, with or without toe support, with or without the downstream rockfill shoulder, and finally on models with a full dam profile. The models with downstream rockfill shoulder as well as with full dam profiles allowed for throughflow. The model behaviour during these experimental tests is described and discussed, according to their respective critical discharge values and associated failure mechanisms. Limitations are also discussed. The results bring to light the benefit of placed riprap compared to dumped riprap structures. As the results show a placed riprap can withstand a significantly higher overtopping discharge than a dumped riprap. Also, the use of toe support enables a significant increase of resistance against overtopping of placed riprap structures. However, toe supports have not proven any significant improvement in stability for dumped riprap structures. This research also puts forward that dumped riprap undergoes a surface erosion process with smaller slides. Placed riprap undergoes a sliding failure mechanism when unsupported at the toe, and a buckling deformation when supported. [ABSTRACT FROM AUTHOR]

The large pier of an emblematic bridge built in 2008 in the Ebro River (Zaragoza, Spain) obstructs the flow in high floods. Clear-water scour experiments in a scale model were conducted to anticipate maximum local scour depths and design riprap protections. These proved to be effective during a large flood event in 2015, but bed aggradation under the left bridge span and deep scour under the right one, not mirroring the bed deformation observed in the model, raised concerns about the bridge safety. The effects of the protected pier on the changes in the aftermath of the 2015 flood are discussed. It is shown that a large meander upstream generated an imbalance in the spanwise bedload distribution, leading to sedimentation on the left and contraction scour on the right. The paper argues for the need to take into account the effects of large piers on river morphology at the bridge planning phase. The case study shows that using a clear-water model to design the riprap protection is adequate, but more importantly, that the fluvial processes during a flood could only be studied with a live-bed model with geometrical detail of the full river reach, namely, the upstream meander. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian University of Technology / Dalian Ligong Daxue Xuebao is the property of Journal of Dalian University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study was conducted to assess scour problems at three selected bridge sites in the Tigray region, northern Ethiopia, namely the Ilala, upper Geba, and Tankwa bridges. Smart-GIS, ArcGIS, Hydrologic Engineering Centre Hydrologic Modeling System (HEC-HMS), and Hydrologic Engineering Centre River Analysis System (HEC-RAS) were used for the river morphology, hydrologic, and hydraulic analysis. The riverbanks were subjected to higher degradation and instability problems. The estimated 100-year flows were 272.5, 940.4, and 249.9 m3/s for Ilala, upper Geba, and Tankwa bridges, respectively. Flow depth calibration were resulted in model performance with Nash Sutcliffe Efficiencies of 0.90, 0.88, and 0.87 for Ilala, upper Geba, and Tankwa bridge sites, respectively. Scour depths were 1.3, 1.6, and 0.8 m at contracted sections; 3.2, 3.0, and 2.2 m at the piers; 2.6, 3.6, and 2.2 m at the left abutment; and 1.6, 3.0, and 2.1 m at the right abutment of Ilala, upper Geba, and Tankwa bridges, respectively. The use of riprap at the bridges resulted in the reduction of scour depths by 60–100%. Overall, the hydrologic and hydraulic models performed well. [ABSTRACT FROM AUTHOR]

Rockfill dams are hydraulic structures of major importance. They can be exposed to extreme flood events, in turn leading to overtopping. These phenomena erode and affect structural and geotechnical integrity, which in turn can cause dam breach. Ripraps are broadly used for rockfill dam protection against such erosion processes. For steep slopes, as the one considered in this study (S = 1:1.5, vertical: horizontal), understanding the riprap behavior during overtopping is an important issue to improve dam design and reinforcement techniques. In this work, datasets are obtained from five experimental models of placed riprap built on a rock filter layer in a flume, at the hydraulic laboratory of the Norwegian University of Science and Technology, Trondheim. The riprap stones were placed in an interlocking pattern with a metallic support at the toe. The models were subjected to successive and incremental overtopping discharges until their complete failure. A laser traverse system was used to measure the coordinates (3D) of individual marked riprap stones between each discharge increase. Six load cells located at the toe measured the imposed loads during the entire procedure. From the total load values, two different types of load contributions could be distinguished: the self-weight of the stones and the hydraulic load depending on the discharge level of the overflow. This article highlights the strong relation in each of the five tests between riprap stone displacements, axial reaction load values measured at the toe and overtopping discharges. Moreover, as demonstrated in previous works, a buckling deformation of the riprap layer was observed and described. The results demonstrate that as the hydraulic load induces 2D deformations of the riprap, a larger part of the riprap weight is supported at the toe. Thus, the measured axial load during overtopping arises both from the hydraulic load and from the load imparted due to the compaction of the riprap layer. This compaction effect induces an even greater load than the one imposed due to the hydraulic contribution. The results from this study are finally put into perspective with the Norwegian Water Resources and Energy Directorate recommendations for full scale dams and suggest the great resistance of supported riprap at the toe. [ABSTRACT FROM AUTHOR]

This study introduced a new riprap placement design for the purpose of reducing bridge pier scour. The design consisted of embedding a layer of the riprap around the pier, flush with the surrounding bed, with a depression to help guide the horseshoe vortex. The new countermeasure design was tested among other conventional riprap placement designs in clear-water flow conditions and transition-flow conditions. The transition-flow condition is the evolution period from clear water to live bed where the bed has yet to reach an equilibrium state. The new countermeasure design was found to reduce greatly the depth and volume of scour in both flow conditions, up to 81.0% and 92.3%, respectively, which was more than any other riprap countermeasure tested. In addition, the new design used 18% less riprap material while also experiencing less shape deterioration when compared with a traditional flat riprap cover. Therefore, installing riprap in this specified shape yields an improved scour countermeasure that could help preserve infrastructure and increase public safety. [ABSTRACT FROM AUTHOR]

A comprehensive experimental study was conducted to evaluate the effects of soil properties and the rip-rap as well as cohesive and non-cohesive soil material and the riprap particle size on the breaching process and the failure mechanism of the levee. The results showed the crucial role of the riprap coverage and the soil properties in the breaching of the protective levees. In this regard, breaching was developed in both vertical and transverse directions. In the levee without riprap coverage, breach development was observed in the transverse direction while the levee was eroded in the streamwise direction. In contrast, in the levee with riprap coverage, breach development mainly occurred in the vertical direction. Furthermore, the flow rate across the breach was higher in the tests with no riprap compared to those with the riprap coverage. Comparisons suggested that the shorter the failure time, the longer the equilibrium time. The present research has some major implications for coastal and hydraulic engineering designs since the construction of levees is of great importance. Furthermore, the findings can be used to predict flooding and erosion induced by the embankment failure. [ABSTRACT FROM AUTHOR]

Scour is one of the main causes of hydraulic structural failures. The present experimental study examines the use of riprap, submerged vanes, and a combination of these for scour reduction around vertical walls and spill-through abutments under clear-water conditions. Specifically, the influence of placing riprap stones with different apron shapes (geometry) and/or a group of submerged vanes of constant height and length on abutment scour was examined. The main aim is to propose the optimum apron geometry and placement of submerged vanes to (1) reduce edge failure at vertical walls and spill-through abutments; and (2) prevent shear failure at the spill-through abutment (no shear failure is observed around the vertical wall abutment). The results show that using ripraps for scour protection is more effective than submerged vanes. However, the highest reduction in scour depth was achieved when a combination of riprap and submerged vanes was used together. This arrangement can reduce the maximum clear-water scour depth by up to 54% and 39% with vertical walls and spill-through abutments, respectively. Furthermore, selecting appropriate apron scale ratios reduces the required riprap volume by up to 46% and 31% for the vertical wall and spill-through abutment, respectively. In addition, the installation of vanes increased the riprap stability and reduced edge failure in both abutments tested. Finally, using riprap aprons with proper scales ratios at the downstream side of the spill-through abutment also prevents shear failure in this zone.

There are increasing demands from dam safety regulations and guidelines to upgrade the rockfill dams, especially in Norway where over 180 large rockfill dams are present. To protect the hydraulic structure against overtopping events or leakages, it is important to use defence mechanisms such as a protective layer of riprap on the downstream slope. In this article, we display 9 experimental setups of riprap, conducted at the hydraulic laboratory of NTNU (Trondheim) and subjected to overtopping phenomena with increasing water discharge, until the complete failure of the model. These tests were performed on models with dumped and placed riprap, with or without toe support, with or without the downstream rockfill shoulder, and finally on models with a full dam profile. The models with downstream rockfill shoulder as well as with full dam profiles allowed for throughflow. The model behaviour during these experimental tests is described and discussed, according to their respective critical discharge values and associated failure mechanisms. Limitations are also discussed. The results bring to light the benefit of placed riprap compared to dumped riprap structures. As the results show a placed riprap can withstand a significantly higher overtopping discharge than a dumped riprap. Also, the use of toe support enables a significant increase of resistance against overtopping of placed riprap structures. However, toe supports have not proven any significant improvement in stability for dumped riprap structures. This research also puts forward that dumped riprap undergoes a surface erosion process with smaller slides. Placed riprap undergoes a sliding failure mechanism when unsupported at the toe, and a buckling deformation when supported.

Rockfill dams are hydraulic structures of major importance. They can be exposed to extreme flood events, in turn leading to overtopping. These phenomena erode and affect structural and geotechnical integrity, which in turn can cause dam breach. Ripraps are broadly used for rockfill dam protection against such erosion processes. For steep slopes, as the one considered in this study (S = 1:1.5, vertical: horizontal), understanding the riprap behavior during overtopping is an important issue to improve dam design and reinforcement techniques. In this work, datasets are obtained from five experimental models of placed riprap built on a rock filter layer in a flume, at the hydraulic laboratory of the Norwegian University of Science and Technology, Trondheim. The riprap stones were placed in an interlocking pattern with a metallic support at the toe. The models were subjected to successive and incremental overtopping discharges until their complete failure. A laser traverse system was used to measure the coordinates (3D) of individual marked riprap stones between each discharge increase. Six load cells located at the toe measured the imposed loads during the entire procedure. From the total load values, two different types of load contributions could be distinguished: the self-weight of the stones and the hydraulic load depending on the discharge level of the overflow. This article highlights the strong relation in each of the five tests between riprap stone displacements, axial reaction load values measured at the toe and overtopping discharges. Moreover, as demonstrated in previous works, a buckling deformation of the riprap layer was observed and described. The results demonstrate that as the hydraulic load induces 2D deformations of the riprap, a larger part of the riprap weight is supported at the toe. Thus, the measured axial load during overtopping arises both from the hydraulic load and from the load imparted due to the compaction of the riprap layer. This compaction effect induces an even greater load than the one imposed due to the hydraulic contribution. The results from this study are finally put into perspective with the Norwegian Water Resources and Energy Directorate recommendations for full scale dams and suggest the great resistance of supported riprap at the toe.

A novel gridded cemented riprap (GCRP) composed of loose riprap stones and cemented stone clusters is proposed, which combines high stability of large stones and excellent flexibility to follow ground deformation. A series of physical experiments were performed in a large-scale flume, and two extreme wave-current conditions of an offshore wind farm with a return period of 50 and 100 years, respectively, were selected. The anti-scouring performance of riprap and GCRP is studied in detail. It is found that the magnitude of wave leads to downstream movement of the maximum scour point. The armor stones around monopile cannot maintain their stability under the extreme wave-current condition, and riprap layer gradually disintegrates during scour process. The stability of riprap layer is significantly improved by fully or gridded grouting. Fully cemented riprap (FCRP) and GCRP remain intact even under the combined wave-current condition of return period of 100 years. For FCRP, scour occurs at the downstream edge and the erosion of underlying sand bed takes place. The anti-scouring performance of GCRP is better than riprap and FCRP, the maximum depth of scour hole around GCRP is reduced 80% than unprotected monopile. • A novel gridded cemented riprap composed of loose riprap stones and partially cemented aggregates is proposed. • The stability of riprap layer can be significantly improved by grouting cementitious materials in a grid pattern. • The anti-scouring performance of gridded cemented riprap is better than riprap and fully cemented riprap. [ABSTRACT FROM AUTHOR]