Permeable Groins Research Articles

The numerical investigation of turbulence and scour interaction around the permeable groynes at the channel bend

Turbulence, particularly Reynolds Stress, plays a significant role in the flow field surrounding groynes, causing local scour. A limited number of studies have comprehensively analyzed the flow and turbulence structures encompassing a series of groynes in channel bends. This study numerically investigated the interplay between turbulence, sediment deposition, and scouring in a sharp channel bend with permeable groynes. The results show that the inner bank maintained high velocity, while permeable groynes decreased longitudinal velocity near the outer bank. Implementing permeable groynes structures reduced bottom velocity and increased flow separation. Turbulent kinetic energy distribution across the bend, particularly streamwise, influenced scour development more than vertical motion.

Numerical Simulations of Effects of the Layout of Permeable Pile Groin Systems on Longshore Currents

Coastal permeable groins have been used to protect beaches from erosion for centuries. However, the hydraulic functioning of permeable groins has not been fully understood and their design heavily depends on engineering experiences. In this study, numerical experiments were executed to investigate the effects of layout configurations of a permeable groin system on longshore currents. The non-hydrostatic SWASH (Simulating WAve till SHore) model was employed to carry out the numerical simulations. Two data sets obtained from physical laboratory experiments with different permeable groin layouts on different slopes are used to validate the accuracy of the model. Then, the longshore current reduction by the permeable groin system with varying configuration parameters (e.g., groin spacing, groin length) was numerically investigated under different environmental conditions (e.g., a slight or a moderate wave climate). From the calculation results of numerical experiments, it is indicated that permeable groins function efficiently to reduce the maximal longshore current velocity under the condition that the groin length ranges from 84% and 109% of the wave breaker zone width. The longshore current reduction rate monotonously decreases with the increase in groin spacing; permeable pile groin functions best to reduce longshore current with the minimal groin spacing-groin length ratio 1:1 among the range between 1:1 and 2:1. When the groin spacing–groin length ratios are 1:1 and 1.5:1, the longshore current reduction is not sensitive to the investigated wave conditions in this study. When the spatial ratio is 2:1, the permeable pile groin system functions worse under a moderate wave climate than under a slight wave climate, from the view of longshore current reduction.

Laboratory investigation of flow and turbulent characteristics around permeable and impermeable groynes in a strongly curved meandering channel

ABSTRACT The study investigates the role of cocolog, an eco-friendly material, as groyne, in protecting the river banks in meandering channels. Laboratory experiments were conducted to compare the flow pattern and sediment dynamics in a mobile-bed meandering channel for cocolog (permeable) and impermeable groynes. It is observed that as the permeability increases, the vertical and transverse velocities are seen to be reduced in the groyne fields. The results also indicate that places of maximum scour depth display amplified velocity, turbulent intensity and turbulent kinetic energy. However, considerable reduction in these characteristics is being observed in the case of permeable groynes that have densities varying between 140 and 160 kg/m3. The eroded volume is seen to be reduced by 60% for permeable groynes of medium density compared to the tests done without groynes. Also impermeable groynes exhibit a wider distribution of the maximum values for scour depth, turbulence intensity and turbulent kinetic energy than that of permeable groynes. It is found that the cocolog groynes with suitable density (or permeability) can perform best in meandering channels by dampening the velocity and turbulence of the groyne fields.

Mean flow, secondary currents and bed shear stress at a 180-degree laboratory bend with and without enhanced permeable groins as an Eco-friendly river structure

River restoration aims to apply environmentally-friendly structures for bank protection in meandering rivers to restore their natural habitat. Enhanced Permeable Groin (EPG) is a novel river restoration technique that can improve the fish habitat environment in a river system by creating a series of eco-friendly scour pools. This study reports the results of two groups of 3D velocity measurements in a 180-degree channel bend in cases with and without an EPG for clear water conditions to characterize the mechanisms leading to the primary stages of the scouring phenomenon. The analysis revealed that the presence of an EPG amplified the velocity magnitude in the regions near the tip of the vane and increased its value in the middle of the channel 1.13 times the bend without the structure. In addition, the comparison showed that the EPG reduced the velocity magnitude in the recirculation zone by an average of 38%. Secondary currents including main and outer bank cells were observed in the case without the structure. The presence of the EPG in the flow field effectively increased the outer-bank cell strength by 11 times compared to that without the structure. The low-value contours of the bed shear stresses were observed in the zone downstream of the structure for a distance of 6 times the effective length of the structure. Based on the results of this study, the generation of a recirculation zone with low-velocity and shear stress values can provide suitable conditions for aquatic habitats, deep-bodied fish assemblages, aquatic vegetation, shrub roots, and tree roots along the outer bank.

Influence of permeable groins with radial arrangement on local scour around groins: an experimental study

ABSTRACT Local scour control around the groins is one of the most important designs and construction factors. In this study, a new radial arrangement style of permeable groins Permeable Groins with Radial Arrangement (PGRA) is introduced and the performance of the groins in this layout is compared to that of the traditional straight arrangement of groins in one and two rows. 90 experiments were performed using permeability of 40%, 60 and 80 per cent and two different discharges. The clear water condition with smooth and homogenous bed sediment materials was considered. The results show that groins arrangement permeability rate and flow discharge affect the sediment conditions around the groins. The most effective arrangement in reduction of scour depth is PGRA with 7 piles in which the scour depth is reduced by 75%, 80% and 66% in permeability rates of 40%, 60% and 80%, respectively.

Combining Landsat-8 and Sentinel-2 to investigate seasonal changes of suspended particulate matter off the abandoned distributary mouths of Yellow River Delta

Suspended particulate matter (SPM) is the primary component of coastal waters. The spatiotemporal dynamics of SPM has an important influence on water bio-optical properties, pollutant diffusion, landform evolution, and carbon, oxygen, and nutrient cycles. This study presents the spatial distribution of monthly average SPM concentrations from 2017 to 2020 in the abandoned Diaokouhe and Shenxiangou distributary mouths of the Yellow River Delta (YRD). The SPM concentrations were derived based on 161 Landsat-8 OLI and Sentinel-2A/B MSI satellite images. Accuracy assessment using the synchronous in-situ measurements (R2 = 0.91, root mean square error (RMSE) = 38.79 mg/L, and relative percentage difference (RPD) = 23.45%) and cross comparison between SPM concentrations derived from the two sensors (R2 = 0.97, RPD = 8.77%) showed convincing performances. Our results show that the monthly average SPM is characterized by significant seasonality, with a higher concentration and wider range in dry seasons compared to that in wet seasons. The spatial distributions of SPM are closely associated with coastal water depths. The SPM concentration in the Shenxiangou mouth is always lower than that of the shallower Diaokouhe mouth. The long-term seabed erosion provides a continuous supply of sediment. Wind-wave forces explain the seasonal variations of SPM by inducing the resuspension of bottom sediments. The residual currents control the transportation of SPM to the offshore and to the east. The artificial groins located between the two river mouths show obvious sediment trapping effects. Moreover, the interception capability of impermeable groins is considerably better than that of permeable groins.

Hybrid engineering on permeable groins to reduce the longshore current

This study aims to determine the effectiveness of hybrid engineering technology to be applied to the groin to reduce longshore currents. The application of hybrid engineering as a breakwater and sediment trap in coastal areas has given good results so that it can be developed in permeable groin structures. The research method used is laboratory experimental with physical modeling to make prototypes and conduct tests on the wave flume to determine changes in current velocity against the existence of a hybrid engineering structure with several model scenarios by changing the characteristics of brushwood groin such as length and distance between groin to surface height. water. The expected result of this study is an engineering model of the permeable groin that can function as an efficient and effective hybrid engineering in reducing longshore currents.

Keseimbangan Dasar Sungai Pada Belokan Sedang (Ii) Dengan Uji Model Fisik Krib Permeabel Ban Mobil Bekas

This research is aimed at analyzing the slope is average in a model of river bed, the slope of each section and the maximum depth of the degradation which result from the construction of permeable on the model for the river that is using moderate bends (II), of minimum discharge , average discharge and maximum discharge, in order to determine the proper course of water flow, so as to achieve balance in river beds. The scour area of the permeable groyne formation is perpendicular to the scour I (ATLG I) = 0,4800 m2 with benchmarks ATLG I < SeDKP and scour II(ATLG II) = 0,6000 m with benhmarks ATLG II < SeDKP and the average slope of the river bed that occurs and the average slope of the river bed that occurs (Ids TL) = 0,0097 with benchmarks IdsTL < SeDKP so that the balance of the river bed is achieved and the hypothesis is accepted

Investigating the Performance of Enhanced Permeable Groins in Series

The enhanced permeable groin is a novel eco-friendly and cost-effective technique for bank protection and restoration of meander bends. The behavior of bed deformations due to the distance between the structures has to be studied to design enhanced permeable groins in series properly. In this study, scour morphologies around enhanced permeable groins in series, characterized by four different distances and located in a 180° mild flume bend, for clear water conditions were investigated. The analysis indicated that scour geometrical patterns such as the maximum scour depth nearby the structures and the maximum deposition height between them are strongly affected by the distance between the groins. The results revealed that the maximum scour depth around the structures increases with the distance between structures, the scour holes develop towards the outer bank and create a series of pools that can lead to the bank collapse. All experiments, carried out with different structure distances, demonstrated that the location of thalweg effectively shifted towards the middle of the channel and near the inner bank for high and low particle Froude numbers, respectively. As a general result, a distance between enhanced permeable groins equal to four times the effective length of the structure is recommended for a 180° mild flume bend for the investigated particle Froude numbers. Finally, a general design guideline is presented to a proper design of enhanced permeable groins in series.

Bank Protection Structures along the Brahmaputra-Jamuna River, a Study of Flow Slides

The planform of the Brahmaputra-Jamuna River followed its natural path in Bangladesh until the construction of bank protection works started to save Sirajganj from bank erosion since the 1930s. Several so-called hardpoints such as groynes and revetments were constructed in the period 1980–2015 and the Jamuna Multipurpose Bridge was opened in 1998. The Brahmaputra Right Embankment and other projects had saved the western flood plain from inundation during monsoon floods. These river training works experienced severe damage by geotechnical failures, mostly flow slides. A flow slide is an underwater slope failure because of liquefaction or a breaching process in the subsoil or a combination of both. The design of most of these training works did not consider the risk of damage by flow slides. All descriptions of the observed damages show that scour phenomena in the channel close to a river training work are a cause of flow slides, besides pore water outflow. The research question was: how can the design of river training works be improved to reduce the risk of damage by flow slides? The main part of the investigation was focussed on reducing local scour holes near river training works. The most promising results are river training works with gentle bank slopes, permeable groynes, bed protections in dredged trenches with gentle side slopes, and methods to increase locally the bearing capacity of the subsoil. It is recommended to increase the knowledge of the failure mechanisms in the Brahmaputra-Jamuna River by improved monitoring in the field, the setup of a database with descriptions of all observed flow slides and the circumstances in which they occur. In addition to these recommendations, a field test facility is proposed to verify the knowledge of the failure mechanisms in that river. These activities will optimise the design of new river training structures with a very low risk of damages by flow slides and geotechnical instabilities and they will contribute to an improvement of the current design guidelines for river training structures.

Design and Performance of Permeable Groins on a Low-Energy Natural Beach

Beach erosion, ubiquitous of sandy coasts around the world, can be exacerbated or mitigated with the use of hard engineering solutions including groins. The use of groins has been discouraged in many countries despite its capability to reduce sand losses. This study aims to design a 15 m permeable groin that allows sediment bypassing. Field experiments were conducted on a low-energy, sea-breeze dominated micro-tidal beach at the northern Yucatan peninsula during both mean and extreme wave conditions. Firstly, a short-term experiment consisted in monitoring the structure performance for 24 h during typical sea breeze conditions and the subsequent beach recovery after the structure removal. Secondly, a multi-day (60 days) experiment was conducted to investigate the performance of a single- and double-groin system during both mean and local storm conditions. Beach surveys were conducted to evaluate the beach response. Shoreline variability shows sediment accretion on the east side of the structure during sea breezes, whereas during NNW storm events, the accretion occurred on the west side. Importantly, on a scale of days, sediment bypassing occurs, and hence a net accretion was measured at both sides of the structure. During this time, a second structure was deployed 30 m apart to test the performance of a double-groin system, finding a net shoreline advance at all beach transects. Thus, low-crested short-length permeable groins are found to be a suitable emergency mitigation measure against beach erosion in micro-tidal environments causing moderate shoreline change.

Experimental study the effect of turbulent flows in bend channels as to a result of vegetation groin structure on permeable type

Highly dynamic changes in flow regimes are caused by relatively high rainfall intensity, so that the excessive flood volume in the last ten years, and it is caused by watersheds experiencing a crisis or degradation due to conversion into economic and non-economic areas which ultimately impacts on river bank and beds by turbulent flow. The use of groin structure as a method of scouring prevention and channel flow control has not been able to fully meet the expectations of scouring prevention. We obtain the effect of changing the turbulent flow regime on the use of groins on the bent channel. Testing was conducted through laboratory experiments in artificial conditions to investigate the relationship between variables by providing certain treatments in several experimental groups with a comparative control of bend channel angle uses 60° with distance variations of groins and discharge; in addition, software Surfer used to describe scour contour pattern. Analysis of changes in flow behavior is done by using Froude (Fr) and Raynolds (Re) number approaches with the effect of turbulent flow on the bent channel scour. The results of the research indicate that the placement of the groins on the river bank channel bend causes a new phenomenon of turbulent flow with shear stress, resulting in local scouring around groin structure and the placement of looser permeable groin gives prevention 81% of river bank scour.

The Effect of Pole Density on Permeable Groin Due to Controlling Longshore Current

Erosion and sedimentation problems that occurs, usually solved firstly by finding the cause of erosion and sedimentation literally, due to determining the action to overcome them. In coastal engineering, there are two approaches that can be used to solve such kind of problems; which are the soft approach, i.e. beach nourishment, vegetation, sand by passing, coastal boundary policy; while the hard approach or structural approach are building breakwater, jetty, groin, sea wall and so on. In structural approach, the uses of permeable groin nowadays is one of the new ways to overcome the erosion and sedimentation problems in beaches. To find out how efficient the permeable groin can control the flow along the coast, so called longshore current, a research needed to be conducted focusing on the effect of pole density at permeable groin itself. The ability of controlling longshore current will be the main analysis, in such various variations of pole densities at the permeable groin. It found out that the pole densities of permeable groin can significantly controlled the longshore current; which is if the pole density become higher than the speed of longshore current can be reduced. It also found out that by implementing 40% of pole density, the longshore current can be reduce up 50% respectively.

Scour around a Permeable Groin Combined with a Triangular Vane in River Bends

AbstractRiver restoration refers to the environmental and ecological aspect of river engineering and aims to improve the natural habitat of a river system using eco-friendly methods. This paper int...

REVISITED HYDRAULIC FUNCTIONING OF PERMEABLE PILE GROINS

Since 1965, a new type of permeable groins (or ‘pile screens’ referred to Bakker et al.,(1984)), which consist of wooden pile rows with a high permeability, have been widely used to protect the coastline from recession in the Netherlands, especially at southwestern coastline. However, the hydraulic functioning of such structures has not been understood well compared to traditional impermeable pebble mound groins. As the wooden pile groins become older and the maintenance costs increase, the issue of their effectiveness has become of importance, while no serious research has been undertaken. This paper tries to tackle this issue. Based on experimental data which was obtained at Delft Hydraulics (Hulsbergen and Horst, 1973), the functioning of pile groins has been revisited and analyzed by an advanced numerical model. The simulations give deeper insights into the effectiveness of permeable pile groins under well controlled laboratory conditions.

In Use of Permeable Groin for Reducing Longshore Sediment Transport at Tanjung Bayang Beach of South Sulawesi

Breaking wave near beaches is the main force to generate longshore currents, which moved the sediment at surrounding area. Due to its negative outcome, which are erosion and sedimentation, the need of longshore sediment transport analysis become very important. One of the tools for solving that problem is by using coastal protection structure such as permeable groin. Permeable groin may reduce the rate of longshore sediment transport respectively by changing the level of permeability of the groin itself.
 The objective of this research was to obtain analytical results of the longshore sediment transport reduction analysis by using permeable groins at Tanjung Bayang Beach of South Sulawesi. Reduction of sediment transport along the beach was analyzed by calculating reduction coefficient, which is the ratio between the longshore current before and after hitting the permeable groins. The result showed that with 40% of permeability, the groin can reduced longshore sediment transport at Tanjung Bayang Beach for almost 50%; from 341.37x103 m3/year to 170.68x103 m3/year.

Analisa Model Matematik Arus Sejajar Pantai Pada Groin Seri Permeable

This research is the mathematical model has been made with two groins, permeable and impermeable groins, with the variation is in length and distance; 50 meters, 100 meters, 150 meters and 200 meters. A modelling has been done by using the data of physical modeling study by Chen., et al, 2003, and used as input to the simulation of mathematical models using 2D Boussinesq software.Results of the research showed the influence of variation model long distance between the groins, the reduction of longshore current velocity along the coast with an average 59.21% reduction for the double permeable groin with 50 meters long, 76.02% for 100 meters, 79.50% for 150 meters, 80.49% for 200 meters. The reduction of longshore current velocity along the coast are 57.42% for an impermeable groin groin double with 50 meters, 84.61% for 100 meters, 150% for 88.89 meters, and 89.91% for 200 meters. The distance variation between one groin to the other groin has a result that a longer permeable or impermeable groin affects the reduction longshore current velocity along the coast of the Surf Zone with the addition of longshore current velocity reduction occurs along the coast up to 20%. Reduction of longshore current velocity along the coast by the permeable and impermeable groin Permeable and impermeable groins has not been significantly occured in the long-term groin area exceeding Surf zone with an average additional reduction up to 5%. The longshore current velocity approaching the speed of currents along the coast for the existing conditions at a distance up to 2.4 times of length of groins. And the distance between the groins are too close if we compare to the long groins causing the current direction of movement towards the sea (rip Current).

Experimental study of flow characteristics around floodplain single groyne

This study investigated the flow around river’s floodplain single groynes. Two different compound channels with one and two symmetrical floodplains having widths of 1- and 2-times of the main channel width, respectively, were used. Both impermeable and permeable groynes with three different relative lengths (relative to the floodplain width) and having three different permeability values of 40, 60, and 80% were investigated. The 3D flow velocities were measured in the horizontal plane at 0.25 and 0.5 of floodplain water depth (hf), and in the vertical plane at the main channel’s centerline. Therefore, the flow velocities in the longitudinal, lateral, and vertical directions, and the flow water surfaces were measured and analyzed. The results showed that, as the groyne permeability increased up to 60%, a reduction of up to 30% to the maximum velocity and 22% to the tip velocity were observed. The permeable groyne length had limited influence on the flow structure. Both the groyne permeability and the length ratio had significant effects on the floodplain water depth. The scouring and the deposition activities resulting from impermeable groynes can be avoided, should the groyne length be kept below half of the floodplain width.

バンダル型水制群周辺における浮遊砂を伴う流れの特性に関する実験的研究

This paper is intended to investigate the characteristics of suspended sediment transport and flow field surrounding Bandal-like structures. Bandal-like structure is a kind of groin which may be considered as a combined structure consisting of an impermeable groin at the upper part and a permeable groin at the lower part. Bandal-like structure is an indigenous structure used in the Indian Subcontinent for navigation enhancement, bank protection and channel stabilization. Bandal-like structure works well under suspended sediment conditions. It is important to clarify the hydraulic and morphological implications of it in order to understand its performances and working mechanisms. In this study, attempts have been made to seek scientific evidences for Bandal-like structures with a laboratory experimental study on the local flow, suspended load concentration and bed deposition around Bandal-like structures.

THE MAIN PRINCIPLES OF BANK STABILISATION BY THE GROINS

The review of field investigations and simulation results led to the conclusion that efficiency of groins use depends on two main factors: amount of free sediments on the bottom slope and angle of wave approach to the shore. The positive effect of groins use can be achieved when angle of approach is acute and sufficient amount of free material is available. Groins are not effective without additional supply of loose sediments if waves have nearly normal approach to shore and there is a deficit of free sediments. An increase of effectiveness of groins could be obtained by varying of their length, spatial step, and orientation. A reduction of downstream erosion is achieved by shortening the groins and adjustment of their complex to the shoreline contour, beach nourishment at the downstream areas, and using of permeable (30–50%) groins.