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.

Numerical Simulation of Flow Patterns and Mass Exchange Processes in Dead Zones

Abstract: Contaminants and nutrients transport in streams and rivers is significantly affected by the presence of dead zones that are due to geometrical irregularities, that may have both natural and anthropic origins. Dead zones are characterized by mean flow velocity in the main stream direction approximately equal to zero and by exchange processes of solutes with the main stream. This paper presents the preliminary results of a numerical study undertaken to investigate the fundamental flow phenomena around and inside a simplified geometry, representative of flow in natural rivers with dead zones. Exchange rates between the dead zone and the channel were calculated resulting in a good agreement with previous literature experimental values for the same geometry. Keywords: Environmental Fluid Mechanics; Numerical Simulation; Mass exchange; Dead zones; Verification. 1. INTRODUCTION Solute transport in streams and rivers is strongly related to river characteristics, such as mean flow velocity, velocity distribution, secondary currents and turbulence features. These parameters are mainly determined by the river morphology and the discharge conditions. Most natural channels are characterized by relevant diversity of morphological conditions. In natural channels, changing river width, curvature, bed form, bed material and vegetation are the reason for this diversity, whereas in rivers which are regulated by man-made constructions, such as spur dikes, groins, stabilized bed and so on, the morphological diversity is often less pronounced and, thus, flow velocities are more homogeneous. In natural channels, some of these morphological irregularities, such as small cavities existing in sand or gravel beds, side arms and embayments, can produce recirculating flows which occur on different scales on both the riverbanks and the riverbed. These irregularities act as dead zones for the current flowing in the main stream direction. In regulated rivers, groyne fields are the most important sort of dead zones. Groyne fields can cover large parts of the river significantly affecting its flow field. Dead-water zones or

Flow exchange between a channel and a rectangular embayment equipped with a diverting structure

Abstract: In the framework of a research project focusing on mitigation measures for hydropeaking, a lateral embayment in riverbank is studied as a fish shelter. With the goal to find attractive configurations of shelter, systematic experiments with wild juvenile brown trout (Salmo trutta fario) were carried out in a flume supplied with freshwater from a natural river. The experimental is equipped with a rectangular lateral embayment. In order to follow the fish trajectories, their movements were recorded continuously by video camera during every test, and their positions were periodically observed. In order to link the swimming trajectories of the trout with the flow conditions, 2D simulations were computed to obtain the diverted discharge in the shelter, and systematic UVP measurement of the velocity field was performed. The flow velocities were analysed in the vertical interface between the shelter and the flume. Comparing the velocity patterns with the fish trajectories, the attractiveness of different configurations of fish shelters could be analyzed. The first tests reveal that a very basic shelter configuration, with low water exchange between shelter and channel, is not interesting for fish. When forcing a water exchange By introducing a deviation groyne into the shelter with the aim to force the water exchange, the frequentation rate can be increased significantly. The fish can easily detect the refuge by the exchange flux when searching its way upstream. The shelter attractiveness was optimized by testing different groyne orientations, in order to create an expanded velocity field close to the exit and entrance sections. Important is a high velocity field leaving the refuge at its lower end but also a backwater zone near the groyne. The high velocity field attracts the fish and the close backwater zone allows the fish to enter the shelter. For the best configuration, more than 80% of the fish found the shelter by swimming mainly from downstream, during the next 20 minutes after the beginning of hydropeaking.

Experimental study of the hydraulic behaviour of inclined groyne systems

Abstract: This paper presents the results of an experimental study on the behaviour of inclined groynes and a short discussion on the optimization of groyne systems It supplements a paper presented at the XI Coastal Engineering Conference (London, 1968) In the present paper both studies are applied to the design of a groyne system looated to the south of the Tagus estuary (near Lisbon)j where a serious erosion has been under way.

Detached-eddy simulation of turbulent coherent structures around groynes in a trapezoidal open channel

Abstract: The hydrodynamics in a straight open channel with a multiple-embayment groyne field was investigated using the detached-eddy simulation (DES). A series of short groynes were included on a 1:3 side slope of the channel. This work focuses on the turbulent coherent structures around groynes on an uneven bottom. Flows around groyne fields are characterized by massive separation and highly unsteady vortices. DES can capture a wide spectrum of eddies at a lower computational cost than the large eddy simulation (LES) or direct numerical simulation (DNS). In the present work, a zonal DES model (ZDES) was used to simulate the flow around groynes. The ZDES model is a modified version of the DES designed to overcome the model-stress depletion (MSD) of the RANS/LES hybrid model. The vortex system consists of the horseshoe vortex (HV) formed at the base of the obstructions, the necklace vortex (NV) that wrapped the groyne tips near the free surface, and the shedding vortex (SV) underneath the free surface. The effects of the incident flow and local topography on the vortex evolution were investigated by analyzing the mean flow structures and the instantaneous turbulent flow fields. Some important vortices cannot be captured because of the averaging process, while some flow structures cannot be observed in the instantaneous flow. The mean flow is only a reflection of the averaging process when complex vortices are present.