Groyne

About: Groyne is a research topic. Over the lifetime, 397 publications have been published within this topic receiving 4549 citations. The topic is also known as: groin & Breakwater.

Analysis of a fluvial groynes system on hydraulic scale model

Abstract: The paper presents the results of an experimental investigation of fluvial groynes con- ducted on a mobile bed scale model. The model reproduces a reach of the River Po, Italy, in which a se- ries of groynes have been designed to improve navigability during dry periods. The experiments were conducted using light plastic material. The density and the grain size of the material were calibrated ac- cording to the similarity of the mobility parameter. Focusing on the processes of sediment deposition and transport within the groynes field, the experimental analysis showed the formation of a bar between two consecutive groynes. The formation of the bar is likely to have been related to the suspended load whipped up by the longitudinal vortex responsible for the local scouring around the head of the groyne. This was one of the most important aspects of the investigation; in fact, the formation of a deposition bar starting downstream from each groyne significantly changed the hydrodynamic field between the groynes. The research also investigated localized scouring, the effects of a variety of groyne parameters, and two different foundation typologies, stiff and flexible, realized with rip-rap stones on filtering bal- lasted mats.

Physical modelling of overbank flows with a groyne set on the floodplain

Abstract: If in natural or anthropized rivers, the river cross-section generally gradually and continuously varies, transversal and discontinuous obstacles either natural or artificial may partially or totally block off floodplains. The flow overbanking in the floodplain is therefore contracted by this obstacle which then promotes two recirculation zones of both sides of the obstacle, resulting in a reduction of the flow section and in the generation of strong mass exchange between channels that superimposes to the classical turbulent interactions. New experiments are conducted in two different compound channels: rapidly varied flows in compound channel with a groyne set on the floodplain. Flows with various groyne lengths and total discharges were investigated. Effects on the hydraulic parameters of the superimposition of the two problems that are (i) flow in compound geometry and (ii) rapidly varied flow in the vicinity of a thin obstacle were analysed. Finally, dominance of physical processes in such flow configuration is discussed

Influence of near-shore marine structures in a beach nourishment project on tidal currents in Haitan Bay, facing the Taiwan Strait

Abstract: The Longfengtou Beach in the Haitan Bay, located in Fujian Province of China and facing the Haitan Strait, has been suffering severe erosion due to the construction of seawalls. A simple beach nourishment project implemented has not achieved the anticipated beach restoration. Thus a practical solution has to rely on a combination with near-shore marine structures. In this study, a 2-D calibrated flow model is set up to investigate the effects of three different layouts of near-shore marine structures on the tidal current. It is shown that the breakwaters situated in both the north and south ends play a vital part in the protection against erosion. The offshore breakwaters can serve as a barrier to obstruct the current circulation then reduce the current velocity. The groyne linking the Guimo islet and the coast significantly reduces the south-to-north water exchange through the channel and redirects the current direction nearly perpendicular to the north breakwater, which cuts off the longshore transport that may have a negative influence on the beach, especially, the northern part. It is also noted that the monsoon at the site with different directions increases the current velocity. In general, proper layouts of marine structures can reduce the current velocity thus lead to less intense sand transport near the beach.

Natural Headland Sand Bypassing: Towards Identifying and Modelling the Mechanisms and Processes

Abstract: Natural headland sand bypassing: Towards identifying and modelling the mechanisms and processes contributes to the understanding of the mechanisms and processes of sand bypassing in artificial and non-artificial coastal environments through a numerical modelling study. Sand bypassing processes in general are a relevant but poorly understood topic. This study attempts to link the theory and physics of sand bypassing processes which is significantly important in definition of coastal sedimentary budget and consequently in coastal management. The main questions are how can we model sand bypassing processes and if the modelled sand bypassing processes represent the actual sand bypassing processes. In this study, it is shown that a process-based numerical model can be used to simulate the processes of sand bypassing around groyne and headland structures for both short (several days) and long term (a year) simulations. Result comparisons were made among analytical models, empirical models and field data. In general, the process-based model can produce reasonable results. The results of a hypothetical process-based model for a single groyne case indicated that the shoreline evolution patterns and sand bypassing rates are in agreement with the results of analytical models. The shoreline patterns behind the groyne structure are well predicted by the process-based model and represented the reality. Results of the shoreline pattern behind the groyne obtained from the model with the inclusion of wave-groups is better than the results of the model without the wave-groups. The main components that influence the longshore sand transport, i.e wave heights, wave angles, and sediment grain sizes, contribute to the sand bypassing processes and different sand transport rates at a groyne structure. The results of a hypothetical model for a case of two separated groynes showed that the morphodynamic characteristics of embayed beaches can be predicted by the process-based model. Results obtained from an empirical model are consistent with the results of the process based numerical model. Surf zone rip currents, particularly headland rips, are responsible for the sand transporting mechanism outside the surf zone area. Findings from the field survey analyses at a small nourished embayed beach which is located on the east coast of Malaysia revealed that wave climate seasonality leads to alternating behaviour patterns of the searshore beach profiles. The results of the cross-shore profile variations along the beach showed the classical onshore-offshore movement patterns of sand transport. Beach rotation, as a result of seasonal wave directional changes promoted sand leakage at one end of the embayment. Additionally, results from the sand volume analyses at the southern area outside the nourishment zone positively showed the contribution of sand into this region and thus verified the potential growth of sand southwards around the south headland. For the southern Gold Coast case study, a process-based model of a permanent sand bypassing system was introduced by utilising the concept of a sand bank discharge operation. Prior to morphological model investigation, models were successfully calibrated and validated and model results were compared against the available field data measurements. The results obtained from the morphological models revealed that additional supply of sand from the sand discharge operation contributed to the development of a sandspit. The sand bypassing process began when the sand started to move around a headland as sandwaves. The sandwaves manifested themselves, moving slowly in front of the beach, and creating an elongated sandspit. The sandspit grew bigger and bypassed another headland before finally attaching itself to the neighbouring beach. Results from the qualitative assessment showed that the morphological beach behaviour captured by the process based model represented the actual morphological beach behaviour as in reality. The modelled sand bypassing process in this study is identical to the conceptual model of headland sand bypassing. A final conclusion is that the combination of seasonal wave climates, in particular wave directions, and the sand bank discharge operations determined the succession of the permanent sand bypassing system. In summary, through numerical modelling this study has added to the understanding of coastal processes and the role of geological controls in governing sand bypassing processes and embayed beach morphodynamics. The morphological model developed in this study is useful to increase understanding of the natural sand distribution patterns due to combination of engineering efforts and natural coastal processes.