Trapping efficiency of non-buoyant microplastics by river groynes

Effect of design factors for groynes on diversification of topography and restoration of ecosystems in straight and meandering streams

This study reports the resultus of velocity measurements among groynes in River Chikuma.Two large vortices contribute to flowing in, settling and heaping of suspended particles. The uppside vortex of the impermeable groyne has a characteristic life cycle. It has a negative correlation with fluctuation of a water level.In time of flood, streamwise vortices released from lowerside of the impermeable groyne rise and flush humus mud on a river bed.

River bank protection is a vital component of sustainable development. This study investigates and compares the scour and flow features around two different types of groynes, an unsubmerged I-head groyne (IHG) and T-head groyne (THG), to provide insights into their performance and efficiency in river reaches. Experiments were conducted to examine the scouring pattern, mean and turbulent flow characteristics including 3D mean flow velocity distribution, Reynolds stresses, turbulent kinetic energy, and bed shear stress near the bed region around the groynes under similar flow conditions. The results indicated that THG had a maximum equilibrium scour depth over three-fold greater than IHG. For both the IHG and THG cases, it was observed that there is a direct correlation between the location of maximum negative vertical velocity and its magnitude to the region of maximum local scour and its depth. All the stresses of high magnitude are found along the propagation of the detached shear layer profile, which turns back sharply downstream towards the bank containing the IHG while remaining mostly away from the bank in the case of THG. The effective bank protection length was estimated to be two-fold the groyne length in the case of IHG and three-fold the groyne transverse length in the case of THG. Cost–benefit analysis of the two groyne types shows IHG as the more cost-efficient groyne with respect to bank protection lengths. This study provides valuable insights for developing design methodologies aimed at promoting the wider utilization of different head-shape groynes in river reaches and aids in selecting appropriate groyne head configurations that align with specific field requirements.

The need for river bank protection in an ecologically appropriate manner has led to the investigation of shallow groynes as a nature-oriented countermeasure against bank erosion. Shallow groynes are in-stream structures which have a horizontal crest and are submerged even during low flow conditions in order to minimize the effect on the flood level. Rather than enhancing the resisting forces like traditional bank protection measures, e.g. riprap, shallow groynes are used to redirect the attacking flow away from the river bank. In this way, the bank itself becomes available as habitat and the water-land interface is rehabilitated or preserved. Moreover, the shallow groynes increase the heterogeneity of the flow field, bed topography, and bed material, which is one of the key elements requested by the EU Water Framework Directive to improve the ecological condition of rivers. However, guidelines are necessary for a successful and sustainable design of shallow groynes. The objective of the study was to develop design guidelines for shallow groynes in river bends by experimentally investigating the design parameters, namely groyne inclination, length, width, location and spacing in a river bend. The experiments were carried out in a curved flume in the laboratory of Leichtweis-Institut fur Wasserbau (LWI). The three-dimensional flow field was measured with an Acoustic Doppler Velocimeter. The hydraulic boundary conditions were kept constant throughout the experiments. A reference run was carried out without a groyne providing the basis for quantification of the hydraulic effects due to the shallow groynes. The optimum groyne parameters were defined based on the highest reduction of stream-wise velocity close to the outer bank. The manipulation of the flow field throughout the bend was investigated with a single groyne as well as with a group of groynes varying the number of groynes as well as the spacing. Further experiments with a fixed bed and a mobile outer bank confirmed the effectiveness of shallow groynes for bank protection. The results of the different sets of experiments were combined to develop a design method for bank protection with shallow groynes throughout a river bend. The method incorporates geometric parameters of the bend as well as the hydraulic boundary conditions.

River scale model of a training dam using lightweight granulates

Shear stress enhancement to account for increased turbulence in mixing layers along river groynes

Across a 1000‐km stretch of the River Nile, from the 1st Cataract in southern Egypt to the 4th Cataract in Sudan, many hundreds of drystone walls are located within active channels, on seasonally inundated floodplains or in now‐dry Holocene palaeochannel belts. These walls (or river groynes) functioned as flood and flow control structures and are of a type now commonly in use worldwide. In the Nile Valley, the structures have been subject only to localised investigations, and none have been radiometrically dated. Some were built within living memory to trap nutrient‐rich Nile silts for agriculture, a practice already recorded in the early 19th century C.E. However, others situated within ancient palaeochannel belts indicate construction over much longer time frames. In this paper, we map the distribution of these river groynes using remote sensing and drone survey. We then establish their probable functions and a provisional chronology using ethnoarchaeological investigation and the ground survey, excavation and radiometric dating of the structures in northern Sudan, focusing on the Holocene riverine landscape surrounding the pharaonic settlement of Amara West (c. 1300–1000 B.C.E.). Finally, we consider the historical and economic implications of this form of hydraulic engineering in the Nile Valley over the past three millennia.

In this study, a cyber-physical system (CPS) for river flow path control is proposed using reinforcement learning. Recently, there has been a frequent occurrence of river flooding due to heavy rains, resulting in serious economic losses and victims. One cause of river flooding is the meandering due to the river bed growing and flow path change. As a mean of avoiding the meandering, river groynes can be used to regularize the flow. However, the mechanism of the flow path growing, and its optimal control is unclear. Therefore, in this study, a dynamic flow path control system is proposed using a data-driven approach to solve the problem at once. As a data-driven approach, reinforcement learning is adopted. The proposed system is designed to control meandering by adaptively deforming and moving the groynes with the reward of the flow path health. The effectiveness of the proposed flow path control system is verified through a simulation of the river model.

Quantifying the loss of filtration services following mass mortality of invasive dreissenid mussels

Longitudinal training dams (LTDs) are a promising alternative for river groynes. Here we summarize findings of a recent study focused on the along river transition from a series of river groynes to an LTD, where the flow divides between the fairway and the side channel between the LTD and the river bank. A scale model is setup using lightweight granulates made of polystyrene to create conditions that are dynamically similar to a prototype situation in the River Waal. The key advantage of using lightweight granulates is that both the Shields number and the Froude number are similar in the model and the prototype. A high flow and a low flow experiment were carried out. The bedforms in the physical model have dimensions that correspond to theoretical dune height predictions, and also the channel incision due to width reduction is in accordance with expectations. The scour holes that develop near the tip of the groynes, however, are too deep, which may relate to improper scaling of the local turbulent vortices, initiated at the groynes. The morphodynamic developments in the flow divergence zone are subtle, and are overwhelmed by the mobile bed response to the presence of groynes. Considering that the physical model over-predicts the erosion caused by groynes, this suggests that the LTD configuration subject to study results in a comparatively stable bed morphology.

Shear stress enhancement to account for increased turbulence in mixing layers along river groynes

Experiments have been carried out in a fixed-bed flume for a schematized straight river reach with groynes on one side to study the dynamics of the flow near groynes. The flume had a geometrical scale of 1:40, based on typical dimensions of the Dutch River Waal. Both emergent and submerged groynes were studied. The measurements demonstrate the differences in the nature of the turbulence between submerged and emerged groynes stages; and provide insight into the flow pattern in the vicinity of groynes, the shape and the extent of the mixing layer at different flow stages, and the dynamic behavior of the velocity along the mixing layer between the main channel and the groyne fields. A parameterization of the turbulence characteristics of the flow near groynes is presented. Large-scale velocity fluctuations are found in all test cases, with timescales that vary with the flow stage. The large-scale u and v velocity fluctuations are in phase in the center of the mixing layer and out of phase for the points on the boundaries of the mixing layer.

River morphology is a condition that is constantly changing due to erosion and sedimentation in certain parts of the river. However, erosion and sedimentation that occur in undesirable parts of the river can cause significant losses to humans. One of the villages that has the potential to experience damage due to river erosion is Kalibuntu Village where there has been a shift in the river channel that has approached the residential area and increased the risk of landslides. Based on this, the construction of river groynes is planned to prevent further erosion. The use of river groynes must be in accordance with the characteristics of the river and its surroundings. Selecting appropriate designs and materials is very important to achieve effective results in preventing river erosion. To obtain the effect of groynes on changes in the magnitude and direction of flow velocity at the Kalibuntu bend, numerical modeling was carried out using MIKE 21 - Curvilinear software which is a hydrodynamic model. This method was chosen because the software can describe the morphological response of the river with relatively good accuracy. The numerical model was carried out with 2 series of models, the first simulating the existing conditions of the river, while the second simulated the normalization of the river with installed groynes as per the planned design. When compared to previous studies, this study only focuses on the effect of groynes on flow velocity as depicted from the results of 2D modeling and validated using field observation data based on several approaches, while a further novelty is that similar research has not yet been conducted at the selected study location. Based on modeling of 4 river segments, the installation of groynes showed a reduction in average flow velocity by 0.04 m/s at the starting point segment just before the river bend, by 0.111 m/s at the outer bend of the river, by 0.124 m/s at the outer bend segment of the river downstream, and an increase in average flow velocity by 0.157 m/s at the inner bend segment of the river.

Multifunctional river Groynes