Showing papers on "Groyne published in 2017"
TL;DR: In this article, the authors investigated the sudden expansion of the mixing layer created in the wake of a single groyne using Particle Image Velocimetry (PIV).
27 citations
TL;DR: In this paper, the authors focused on a coastal stretch situated on the southern sector of the SW coast of India, where Sundar and Sannasiraj (2006) proposed a groyne field along with an existing seawall to control severe erosion.
16 citations
TL;DR: In this article, the results of field experiments in a natural river comprising large-scale groyne models populated with rigid and flexible artificial vegetation were reported, showing that vegetation rearranges twin-circulation flow into slow backwater flow.
Abstract: Flow recirculation in groyne fields promotes accumulation of fine sediments and development of riparian and aquatic vegetation. Although flow hydrodynamics in groyne fields is subject of intensive ongoing research, knowledge of vegetation effects on recirculating flow remains lacking. This paper reports the results of field experiments in a natural river comprising large-scale groyne models populated with rigid and flexible artificial vegetation. In the experimental runs population density, submergence ratios, and vegetation types were varied. The results show that vegetation rearranges twin-circulation flow into slow backwater flow. The magnitude of backwater flow is controlled by the bio-mechanical properties of vegetation. The hydrodynamics of the flow interface between the main river and groyne fields was only slightly altered by vegetation. Analytical models of flow at the interface and inside vegetated areas agree well with these experimental results.
15 citations
01 Jan 2017
TL;DR: In this paper, the authors present a new analytical solution for a widely encountered situation where a groyne is constructed close to a river to control sediment movement, which employs Laplace transforms and has the advantage that a solution for time-varying conditions may be constructed from the solution for constant conditions by means of the Heaviside procedure.
Abstract: Analytical solutions to the equations governing shoreline evolution are well-known and have value both as pedagogical tools and for conceptual design. Nevertheless, solutions have been restricted to a fairly narrow class of conditions with limited applicability to real-life situations. We present a new analytical solution for a widely encountered situation where a groyne is constructed close to a river to control sediment movement. The solution, which employs Laplace transforms, has the advantage that a solution for time-varying conditions may be constructed from the solution for constant conditions by means of the Heaviside procedure. Solutions are presented for various combinations of wave conditions and sediment supply/removal by the river. An innovation introduced in this work is the capability to provide an analytical assessment of the accretion or erosion caused near the groyne due to its proximity to the river which may act either as a source or a sink of sediment material.
14 citations
TL;DR: In this article, a finite difference solver of the one-line sediment continuity equation is proposed for the evolution of an initially straight shoreline of a plane beach subject to regular breaking waves at constant angle of incidence in the presence of either a groyne or a continuous single-point feed of sediment.
7 citations
TL;DR: In this paper, the authors provide numerical simulation of flow around a Groyne and models the ratio of the reattachment length, water depth and velocity on the surface of the channel and the shear stress on the bottom of a channel between the different types of Groynes in the same hydraulic condition for all models.
Abstract: This paper provides numerical simulation of flow around a Groyne and models the ratio of the reattachment length, water depth and velocity on the surface of the channel and the shear stress on the bottom of the channel between the different types of Groynes in the same hydraulic condition for all models. Moreover, a comparison between the results have been done and the most efficient type of Groynes which have more influence on the hydraulic parameters is chosen. The open source TELEMAC-3D software is used for this numerical modeling and k-e model was selected for turbulence modeling of the flow simulation. For validation test, our results are compared against three-dimensional computational flow model around a Groyne by Ouillon and Dartus [10] and experimental result of Holtz [5]. This paper provides a good modeling tools to choose the optimum shape and size for Groynes in rivers for bank protection and river stream training.
4 citations
Patent•
26 Apr 2017
TL;DR: The perforated caisson vertical groyne as mentioned in this paper uses self kinetic energy of waves to eliminate the energy, reduces the wave force thereof, reduces groynes back wave height, reduces wave over-topping rate, and reduces the caisson size.
Abstract: The invention discloses a perforated caisson vertical groyne. The perforated caisson vertical groyne comprises a caisson and a breast wall, wherein separation walls or separation plates are arranged in the caisson to form multiple cells; a caisson hole is formed in a wave surface exterior wall at the upper part of the caisson; the cell behind the caisson hole serves as a wave eliminating chamber; sand is filled in the other cells of the caisson besides of the wave eliminating chamber; the wave eliminating chamber is provided with a top plate; the top plate is provided with multiple water inlets; the breast wall is arranged at the top of the top plate; an inclined surface is arranged on a wave side of the breast wall, and is provided with multiple water outlets; and the water outlets are communicated with the water inlets formed in the top plate through pipes. The perforated caisson vertical groyne uses self kinetic energy of waves to eliminate the energy, reduces the wave force thereof, reduces the groyne back wave height, reduces the wave overtopping rate, reduces the caisson size, reduces the work amount, saves investments, is convenient to construct, can fully use self kinetic energy of water, saves the energy, and protects the environment.
3 citations
23 Jun 2017
TL;DR: Munna Point is a popular recreational beach in the Noosa River which has been maintained by regular nourishment for over 20 years as discussed by the authors, however, the long-term costs were high and efforts were eventually suspended resulting in the loss of the beach.
Abstract: Munna Point is a premiere recreational beach in the Noosa River which has been maintained by regular nourishment for over 20 years As longevity of each nourishment was less than 6 months, the long-term costs were high and efforts were eventually suspended resulting in loss of the beach In an effort to reinstate the amenity and provide a more stable beach, a groyne field accompanied by nourishment was proposed To provide a low-impact, low-risk and low-cost solution, the groynes were designed with a low crest using sand-filled geotextile containers To achieve the design, containers and scour mattresses were filled in-situ using a dredge, which was an innovative application of a methodology typically adopted for much larger containers The first 3 groynes have successfully been installed as part of the first stage and 12 months of monitoring subsequently undertaken The groynes have clearly been effective at extending the longevity of the nourishment and the wider intertidal profile has remained very stable The beach is now successfully enhancing the amenity of the community and experiencing a high level of usage
2 citations
01 Jan 2017
TL;DR: In this paper, the effects of removing riverbank protections on bar formation were investigated in a mobile-bed flume with three variables of a bank protection removal; length, location and flow asymmetry.
Abstract: Over the past centuries natural riverbanks have been transformed into banks with artificial revetments or sheet piles to protect them from erosion, which led to disappearance of important river features for flora and fauna. River restoration projects show that the removal of man-made bank protections may lead to the formation of bars (e.g. Van den Berghe et al., 2012; Schirmer et al., 2014). Habitat diversity in rivers may be enhanced through the formation of river bars with preferably diversity in bar height, size and location. This research aims at gaining knowledge into the effects of removing riverbank protections on bar formation to enhance habitat diversity. Mobile-bed flume experiments were performed in the Fluid Mechanics Laboratory of Delft University of Technology. The experiments were focussed on bar formation related to three variables of a bank protection removal; length, location and flow asymmetry. Geometrical and morphodynamic characteristics were selected for the experiment having a bar mode of one to obtain a system with alternate bars (Crosato and Mosselman, 2009) and showed gravel-bed river similarity based on bankfull river characteristics of Parker (2004). The experimental flume consisted of a 6.2 metre long and 0.2 metre wide straight channel with 0.5 metre wide floodplains on the sides. On both sides of the channel, bank protection could be removed over a limited length with optionally a groyne upstream. After seven hours at the end of each test, photos of the bed topography were taken and the longitudinal bed profile was measured. Bar wavelengths and bar heights in each experimental test were determined from detrended bed profiles. The bar height was divided in two classes: low and high. The areas of low bars, high bars, floodplains and the deep channel were determined from photos of the final bed topographies. Bar types were indicated with terminology from Duro et al. (2015) as forced, free or hybrid. Removal of bank protections resulted in lateral erosion of channel banks over a limited length. The eroded bank line moved in downstream direction, which agrees with the downstream meander migration observed in field and laboratory investigations by many authors (e.g. Odgaard, 1987). Scour holes developed downstream of the widened section, due to turbulent eddies forced by the channel geometry. In the widened reach, flow decelerated which resulted in a lower sediment transport. Consequently, sediment was deposited in the widened reach and caused rising of the mean bed level along with formation of bars. In areas with higher flow velocities an increased sediment transport deepened the channel. When the riverbanks were fixed, relatively low, small, side bars were formed in the channel. In general, the total bar area and bar height increased for an increase in channel widening, due to the removal of bank protection. An increased bank protection removal length up to nine times the channel width or an upstream asymmetrical flow forcing, i.e. groyne, increased the total bar area, whereas a bank protection removal at three different locations with a total length of nine times the channel width did not significantly increased the total bar area. It is recommended to remove riverbank protections over a length of at least nine times the river width on both sides of the river with optionally a groyne upstream as a measure to enhance habitat diversity. It is also valuable to remove the bank protection on one side of the river only. It is advised to construct a groyne upstream of the bank protection removal to increase habitat diversity. This research led to results that can be used in further research. It is advised to conduct larger scale experiments and eventually move to the field.
1 citations
18 Apr 2017
1 citations
TL;DR: In this paper, a hindcast of the Volta river mouth sand spit was performed using the 2DH morphological model XBeach to study the evolution of the sand spit.
Abstract: Groynes were constructed west of the Volta river mouth sand spit in Ghana to mitigate the local average beach retreat of 6 m/year. Even though severe swell events occurred during the construction of the first couple of groynes, the sand spit retreat of about 150 m over less than 1 year was surprising. An in-depth analysis was done by performing a hindcast over that year with the 2DH morphological model XBeach. It qualitatively reproduced the sand spit evolution as measured in situ. The governing processes of the severe erosion of the sand spit, in addition to the effect of the groynes, were identified to be a longshore sediment transport gradient and differences in overwash occurrence. A second hindcast, without groynes, has shown that the groynes were not the main cause. It also demonstrated that the beach, which was to be protected, has clearly benefitted from the construction of the groynes.
01 Jan 2017
TL;DR: Acknowledgements and acknowledgements are given in the following sections: I acknowledgements as discussed by the authors, II acknowledgements, III List of Figures, IV List of Tables, V List of Symbols, VI List of Table, X
Abstract: .......................................................................................................................................... II Acknowledgements ....................................................................................................................... III List of Figures ............................................................................................................................ VIII List of Tables ................................................................................................................................ XI List of Symbols ............................................................................................................................ XII
01 Jan 2017
TL;DR: In the present work, performances of four simple finite difference schemes are compared in simulation of flow around groyne structure and the best model is found out in terms of accuracy and efficiency.
Abstract: The flow processes around a groyne structure is a complex and challenging topic in computational hydraulics and has brought attention of many researchers in the last few decades. In comparison to experimental studies, numerical modeling can provide more details about the flow characteristics at less cost. In the present work, performances of four simple finite difference schemes, i.e., Lax diffusive scheme, predictor corrector scheme, modified predictor corrector scheme and Beam and Warming scheme are compared in simulation of flow around groyne structure. The numerical results are validated with available experimental data and the best model is found out in terms of accuracy and efficiency.
Journal Article•
TL;DR: In this article, a permeable groyne has been introduced, tested and monitored during a 24-hour experiment to find a solution for erosion problems caused by currently applied measurements.
Abstract: The north coast of the Yucatan peninsula in Mexico is vulnerable to strong sea breezes, which in turn causes high waves, driving high rates of erosion due to littoral transport. To find a solution for erosion problems caused by currently applied measurements, a permeable groyne was introduced, tested and monitored during a 24h experiment. Concluded was that the permeable groyne has the potential to reduce downdrift erosion problems due to its permeability. However, long term effects could not be properly assessed and requires a follow-up study. Keywords Permeable groyne, longshore sediment transport, erosion, Yucatan, human intervention, sea-breeze events