Permeable Groins Research Articles

Groin Opening Effect on Shoreline

An actual scale model of a groin was designed and constructed to investigate the impact of the gap width on the shoreline changes in the close vicinity of the groin. The Surface water Modeling System (SMS) model has been used to simulate the wave hydrodynamics around the groin for about 5 years to study the impact of the proposed groin on the shoreline and wave conditions at various time steps. The model has been calibrated and validated against the collected and measured field data. The dominant wave/current conditions along the North-West coast of Egypt have been considered for various possible configurations of the semi-open groin to identify the appropriate design. Wind and wave data of the El-Dekhila port Meteorological Station (EMS) have been adopted for the period 2010-2014. The results and analysis provide general guidelines for the use of groins with a clear opening in coastal resorts that can be applied to a wide range of wave climates. It has also been found that a groin with a clear opening can help to provide safe swimming conditions with minimum impact on the shoreline if groins were properly studied. Wide gap spacing and permeable groins generally reduce the shoreline changes. It is found that the maximum erosion and accretion depths are almost equal in case of S>0.15 Lg for the cases investigated (Lg is the groin length, S is the gap width). The effective length on the up-drift side is much more than that on the down-drift for the cases investigated in this work. The up-drift is affected up to twice the length of the groin in case of no gap and the length is about 1.1 Lg in case of gap width equaling 0.15 Lg. The variation of the Original Research Article Balah et al.; AIR, 3(4): 427-444, 2015; Article no.AIR.2015.038 428 effective length on the down-drift varies slowly as the gap width varies. The effective length varied from 1.2 to 1.1 as S/Lg varies from 0 to 0.15. It is noteworthy that the variation of the effective length is nearly linear with the gap width in this study.

The Design and Application of Permeable Groynes

Permeable groyne is an innovative type of traditional groynes, Netherlands have accumulated some experiences on this field during the practice on the Rhine and Jamuna river (Bangladesh). This paper summarized the present study results of permeable groynes and inspired by it, proposed an supplementary alternative for the river training work in the Lower Yellow River.

FLOW ANALYSIS AROUND GROYNE WITH DIFFERENT PERMEABILITY IN COMPOUND CHANNEL FLOODPLAINS

Presented herein are the results of an experimental study on the flow characteristics around compound channel floodplain groynes with various permeability and length. Both the permeable and impermeable groynes are considered to clarify the influences of floodplain groynes on flow structure, velocity, and water surface. A channel consisting of a main channel and one floodplain with flat and fixed bed was used. The width of floodplain is the same as the main channel width. Pile groyne models with three different relative lengths relative to floodplain width (Lr), 0.5, 0.75, and 1.0, with three different permeability values (P= area of water crossing the groyne/total projected area of groyne) 40%, 60%, 80% plus an impermeable groyne were used and installed in the floodplain with single arrangement. The 3D flow velocities at both of the horizontal plane above floodplain bed by 0.25 of floodplain water depth (h) and at the main channel centerline in the vertical plane were measured using an Acoustic Doppler Veloci-meter (16 MHz Micro-ADV). The flow pattern around groynes was analyzed in both the horizontal and vertical planes. The results show that, for permeable groynes as the permeability increased the groyne length has limited influence on the flow structure. For the horizontal plane maximum and tip velocities were decreased while the minimum and bank velocities were increased as the permeability increased. Empirical formulas to describe these relations depending on the groyne relative length and permeability were suggested. The influence of permeable groynes installation in the compound channel has insignificant effect on the main channel flow while the impermeable groynes affect greatly the main channel flow structure. Both the groyne permeability and length ratio have obvious effects on the floodplain water depth.

Model Experiments on Control Function of Permeable Groins on Littoral Drift

Model Experiments on Control Function of Permeable Groins on Littoral Drift

STUDY ON THE CHANGE OF RIVER-BED CONFIGURATION CAUSED BY A PERMEABLE GROIN OF STONE GABIONS

This paper shows the experimental results on the river-bed configuration caused by a single permeable groin made of stone gabions. The local scour around the permeable groin is proved to be very small, whereas the bed-configuration of the downstream region far from the groin largely changes forming sand waves. The characteristics of the bed configuration downstream of a single permeable groin are experimentally revealed to be influenced by the permeability and the scale of the groin of stone gabions as well as the flow conditions such as submerged or emerged flow over the groin.

NUMERICAL CALCULATION OF FLOWS BY A RUBBLE MOUND GROIN BY A COMBINED MODEL OF A POROUS FLOW MODEL WITH A NONDARCIAN RESISTANCE LAW AND A 3-DIMENSIONAL LES MODEL

This study present a combined numerical model of a porous flow model that employ a non-Darcian resistance law and a 3-dimensional Large Eddy Simulation model in order to investigate 3-dimensional and temporal structures of flows around a rubble mound groin. A model's accuracy is cross-checked by comparing numerical results to observed results of an existing experiment, and model's results show good agreement in terms of time- and depth-averaged sense. Calculation results also imply that a permeable groin restricts growth of secondary flows in a constriction section. However, a combined model is not able to produce unsteady characteristics of flows that are caused by small scale and structured turbulences in a down-stream region of a groin.

FLOW AND BED DEFORMATION IN AN OPEN CHANNEL WITH A PERMEABLE RUBBLE MOUND GROYNE

In this study, a numerical analysis and a laboratory experiment were carried out in respect to an open channel flow field with a movable bed in which a permeable groyne was installed. By comparing the agreement between the analysis and the experiment, the influence of the permeable groin to the open channel flow and movable bed erosion were discussed. The numerical method was expected to provide knowledge to the design of river structure such as permeable rubble mound groyne.

Effects of Groyne Layout on the Flow in Groyne Fields: Laboratory Experiments

This research is aimed at finding efficient alternative designs, in the physical, economical, and ecological sense, for the standard groynes as they are found in the large rivers of Europe. In order to test the effects of various groyne shapes on the flow in a groyne field, experiments were performed in a physical model of a schematized river reach, geometrically scaled 1:40. Four different types of schematized groynes were tested, all arranged in an array of five identical groyne fields, i.e., standard reference groynes, groynes with a head having a gentle slope and extending into the main channel, permeable groynes consisting of pile rows, and hybrid groynes consisting of a lowered impermeable groyne with a pile row on top. Flow velocities were measured using particle tracking velocimetry. The design of the experiment was such that the cross-sectional area blocked by the groyne was the same in all cases. Depending on the groyne head shape and the extent of submergence variations in the intensity of vortex shedding and recirculation in the groyne field were observed. The experimental data are used to understand the physical processes like vortex formation and detachment near the groyne head. It is demonstrated that the turbulence properties near and downstream of the groyne can be manipulated by changing the permeability and slope of the groyne head. It is also observed that for submerged conditions the flow becomes complex and locally dominated by three-dimensional effects, which will make it difficult to predict by applying depth average numerical models or by three-dimensional models with a coarse resolution in the vertical direction.

EXPERIMENT AND ANALYSIS ON FLOW FIELD AROUND AND INSIDE A PERMEABLE GROIN

A permeable groin constructed with natural stones would be a nature-friendly river structure with minimum negative impact on natural environment. For making suitable design of the structure, hydrodynamics of the flow inside and around the permeable groin was investigated in the present study. Physical models of the permeable groin were installed in an open channel with various dimensions, porosity and rubble diameters. A numerical model was developed in order to simulate a two-dimensional flow field both in the open channel and the porous body. A flow resistance inside the groin was formulated by applying a non-Darcian formula that has already been verified in the authors' previous study on a rubble mound weir. Effects of grain diameter, porosity, geometry of the groin on the flow structure and flow force were discussed based on the experimental and the numerical data.

A STUDY OF PERMEABLE GROINS IN SERIES INSTALLED IN A STRAIGHT CHANNEL

Natural vegetation plays important roles on river environment. It is needed to find the way of managing vegetation aiming at the harmony between flood control and environment. Considering the vegetation as groins, we studied the flow and bed topography around permeable groins to determine the structure and arrangement of vegetation groins from the standpoint of both flood control and environment.The experiment showed that the groin interval to length ratio, L/D=2.0 and groin height to water depth ratio, hg/h=0.90 gave good representation for flood control and environment. The three dimensional numerical model provided good explanation for experimental results of the flow and bed topography in the channel with permeable groins in series.

Factors affecting performance of permeable groins in channel bank erosion control

The factors affecting the performance of permeable groins are investigated by an analytical approach supplemented with field observation. These factors are broadly divided into three classes: (1) the properties of the soil where the groin is embedded; (2) the flow characteristics of the river channel that are imposed on the groin; and (3) the makeup of the groins. Factors relating to the properties of the soil and flow are then combined into an expression for the factor of safety against failure by overturning. This enables a deterministic sensitivity technique involving partial differentiation of the factor of safety with respect to each contributory factor to be applied. The results obtained show that depth of the groin is the most critical factor that determines groin stability. The depth is followed by flow velocity and discharge, unit weight of water, unit weight of soil, and cohesion. This order of importance agrees with the analysis of observed groin performance in a pilot project at Kaiama in the Niger delta.

Control of channel bank erosion using permeable groins

An experimental erosion control scheme in the Niger Delta was designed as a permeable groin using timber piles laced with strong cane nets. At the onset of the rains, when external channel water level was only 10 percent of its seasonal peak, a failure of the peripherial groin was recorded, which apparently was due to local sliding in the bank. At peak flood, a timber pile probably buried to a shallow depth failed, making the system of groins ineffective. The failure of the single timber pile resulted in extensive scouring and bed degradation, leading ultimately to the failure of the protective structure. Analyses carried out confirm that depth of embedment of the pile system is the single most important factor ensuring the stability of the groin structure.

Characteristics of flow resistance and permeable velocity on a permeable groyne

Two dimensional experiments with permeable groynes were carried out and theoretical analysis was tried in order to know functions of permeable groynes. We found the fact there are close connection among three factors of mean velocity (U1), permeable velocitythrough groyne (vQ) and separate length (L). vQ is depending on U1 - it takes two fold values correspoding to the same U1 under the certain condition for the porosity of groyne. On the other hand, increase of vQ. reduces L, and L is weakly related in U1.

PERMEABLE GROYNES: EXPERIMENTS AND PRACTICE IN THE NETHERLANDS

This paper reports on model experiments and up to 20 years of practice in nature with a permeable groyne system, consisting of single or double permeable rows of wooden piles perpendicular to the beach, without bottom protection. This system costs only 10 to 25% of the impermeable stone groynes which have for centuries been used in the Netherlands. Model experiments confirm that wave-induced currents in the protected areas are reduced to 65%, and tidal currents even to 50%, depending on the pile screen configuration. Prototype measurements could not lead to straightforward conclusions with statistical significance: the effect of the pile screens on beach evolution is partly merged into natural fluctuations and trends. Wooden pile screens do not prevent the shoreward motion of tidal channels, which can cause washing out of piles. Furthermore, constructional failures, which in the future can be avoided, at some places resulted in negative experience. It is concluded that permeable pile screens deserve serious consideration as a first flexible and cheap phase in combating coastal erosion. Its application however should be based on a thorough analysis of the local coastal current climate.

FIELD TESTS ON TWO PERMEABLE GROYNES

A section of beach on the south coast of England has been under surveillance for five years, from March 1966 until March 1971. During this period, two permeable groynes of the Makepeace Wood type were constructed. Beach cross sectional areas and rates of accretion were compared before and after groyne construction. The groynes caused a buildup in beach levels updrift.

THE EFFECT OF GROYNES ON STABLE BEACHES

The paper describes tests carried out in a wave basin to study the effect of groynes on a beach that was stable for a particular wave climate and a given supply of littoral material. The main conclusion was that on the part of the beach between H.W. and L.W. level the groynes produced no build up. The only build-up that occurred took place seaward of the impermeable groynes. Permeable groynes had little effect either inshore or offshore.