Showing papers on "Groyne published in 2010"

Sediment Exchange between a River and Its Groyne Fields: Mobile-Bed Experiment

Abstract: Experiments have been carried out in a mobile-bed laboratory flume in order to study the sediment exchange process between the main channel and the groyne fields. The flume represented half the width of a schematized river reach with a series of groynes. The experiment was designed to represent typical dimensions of the Dutch River Waal at a geometrical scale of 1:100. The conditions were set to guarantee bed load as well as suspended load sediment transport. Conditions with submerged and emerged groynes were investigated. In addition to traditional measurements, viz., bed-level changes, suspended sediment concentrations, and flow velocities, bed-form propagation was measured in two dimensions using a the particle image velocimetry technique. The results were analyzed with focus on sediment exchange mechanisms and sediment transport patterns. The results demonstrate that under all flow conditions there is a net import of sediment into the groyne fields. The prevailing transport mechanisms vary with the fl...

Analysis of flow around impermeable groynes on one side of symmetrical compound channel: An experimental study

Abstract: This paper presents the results of an experimental study on the influences of floodplain impermeable groynes on flow structure, velocity, and water depth around the groyne(s). A wooden symmetrical compound channel was used. Groyne models with three different groyne relative lengths, 0.5, 0.75, and 1.0, were used on one floodplain with single and series arrangements. Analysis of the experimental results using the measured flow velocity and water depth values showed that flow structure, velocity, and water depth mainly depend on groyne relative length and the relative distance between series groynes. The flow velocity at the main channel centerline increased by about 40%, 60%, and 85%, and in other parts on the horizontal plane at the floodplain mid-water depth by about 75%, 125%, and 175% of its original value in cases of one-side floodplain groyne(s) with relative lengths of 0.5, 0.75, and 1.0, respectively. The effective distance between two groynes in series arrangement ranges from 3 to 4 times the groyne length. Using an impermeable groyne with a large relative length in river floodplains increases the generation of eddy and roller zones downstream of the groyne, leading to more scouring and deposition. To avoid that, the groyne relative length must be kept below half the floodplain width.

Restoration of Koggala lagoon: Modelling approach in evaluating lagoon water budget and flow characteristics

Abstract: Groyne system modification is described related to restoration efforts to Koggala lagoon, Sri Lanka. The large-scale unplanned sand removal at the lagoon mouth shifted the formation of sand bar towards the lagoon and made adverse effects on its ecosystem. After the removal of the natural sand bar, groyne system was constructed to avoid sand deposition in the lagoon and to protect the highway bridge (across the lagoon outlet channel) from the wave attack. The existing groyne system resulted the lagoon mouth being permanently open to sea which in turn led to many environmental problems. Groyne system modification is proposed in this study to reduce the sea water intrusion. Water budget and two-dimensional depth averaged hydrodynamic model were developed for understanding the hydrologic and flow characteristics of the lagoon. Numerical experiments was performed at lagoon mouth area for two cases: (1) existing condition and (2) proposed rubble mound groyne system condition. Comparison of results was obtained for both cases to describe flow pattern at lagoon mouth. Results further showed, the width should be reduced to a maximum of 40 m. Proposed mouth width (40 m) pushed the salting factor towards 0.5 from 0.68. Salting factor reduction with the groyne modification may result a predominant influence of fresh water which may in turn lead lagoon to a fresh water ecosystem.

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.

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.

Fish behavior during hydropeaking in a channel equipped with a lateral shelter

Abstract: In the framework of a research project focusing on mitigation measures for hydropeaking, a lateral embayment at the channel bank is studied as a fish refuge. Systematic experiments with different refuge configurations were carried out. The basic configuration is rectangular with a length of 2 m and a width of 1.2 m installed at the right bank of a 12 m long and 1.2 m wide flume supplied with freshwater from a natural river. In order to trigger water exchange between the flume and the rectangular refuge a wall acting like a groyne was installed inside the refuge protruding slightly in the main channel. Position, inclination and protrusion rate of this groyne were varied systematically in order to obtain an optimal water exchange and the best attractiveness of the shelter for fishes during hydropeaking. Each configuration was tested three times with juvenile wild brown trout (Salmo trutta fario) (0+ and 1+), with 2 different groups of 10 and the combined group of 20 brown trout. They where exposed during 3 hours each time to a hydropeaking flow of 220 l/s in the main channel. During every test, the movements of the fish were recorded continuously by video camera and their positions were observed every 20 minutes. 6 series of 20 fishes were used for 36 sequences corresponding to the 12 configurations tested. For each configuration the analysis of the fish positions gave a global frequentation rate as well as the favorite staying places in the shelter. Some in- and outgoing fish trajectories were obtained by the treatment of video pictures. A particular focus was given to the interface section between the refuge and the main channel in order to relate the spatial distribution and the frequency of fish passage from up- and downstream into the shelter. In order to link the swimming trajectories of the trout with the flow conditions, systematic measurement of the velocity field was performed using UVP technique. The flow velocities were analysed in several horizontal and vertical transects across the refuge and flume. Comparing the velocity patterns with the fish trajectories, the attractiveness of different configurations of fish refuges could be analyzed. The tests reveal that a very basic refuge 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, its frequentation can be increased significantly. The fish can easily detect the refuge by the exchange flux when searching its way upstream. The refuge attractiveness can be optimized by testing different groyne orientations, creating an expanded velocity field close to the exit and the entrance. 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 refuge by swimming mainly from downstream, 20 minutes after the beginning of hydropeaking.

Rockfill embankment construction on tailings — realistic, cost-effective and reliable application at Xstrata, Mount Isa, Australia

Abstract: Mount Isa Mines Ltd (MIM), Queensland, Australia, was formed in 1923 when a discovery of silver lead ore was made. At the beginning, the production was focused on lead-zinc-silver mined underground with little focus on copper. Currently, copper is mined in two underground mines and lead-zinc is mined in two open cuts and an underground mine. It was not until June 2003 that Xstrata officially took control of Mount Isa Mines Ltd. In general terms, the geology of the mining area is comprised mainly of Urquhart shale and Spear siltstone. The history of the Xstrata Mount Isa Mines tailings storage facility (TSF) stretches back to the 1930s with the construction of the No. 1 tailings facility. The current tailings storage facility has two existing and five decommissioned dams. The existing dams, Nos. 7 and 8 comprise five external walls with nine internal groynes covering an estimated area of 1,300 hectares. Current operational capacity, as of Q2 2009, was approximately 16 million cubic metres with more capacity identified in late 2009 with the utilisation of the western and southern evaporation ponds. The current tailings strategy is to continue depositing wet tailings via a gravity outfall line to two of the existing tailings dams, and to also raise dam walls and groynes as they become necessary. The existing strategy proved to be usable for 2–4 years by which time an alternative outfall should be established. Although a conventional geotechnical design was used to construct a groyne on the tailings of one of the tailings dams, recently the groyne has been constructed using the ‘ice-breaker’ technique utilising the waste rock available from the nearest open cut to the tailings area. The lesson learnt from the success of the construction trial of the groyne will be applied next year to the proposed high groyne on the tailings as part of the future tailings placement. By doing so, the life of the existing tailings dams will be extended by postponing the need for a pumped outfall, and hence reducing future operation costs. This is in addition to the benefit of consuming waste rock close to the source, resulting in reduced operating costs to the open pit. The paper presents various aspects of the project. These include a brief on the current and future tailings strategy, the proposed conventional geotechnical design and the economic and safe construction technique used instead to construct the groyne. A summary of the geotechnical modelling results are also presented. To demonstrate the financial benefit, the paper provides cost and time comparison between the conventional design, if adopted for construction, and the realistic and successful construction trial approach.

Analysis of bathymetry change around groyne system on Ishinomaki Coast

Abstract: ABSTRACT Coastal protection has been an interesting case to study. Groyne, as mean of coastal protection structures, has been applied in many cases in the world. In Japan, it is applied to protect sediment deposition in Ishinomaki Coast and also others coastal. The purpose of this study is to analyze influence of groyne system on Ishinomaki Coast using bathymetry data sheet from 1990 to 2006. Analyzing using standard deviation presents how significant sea bed level change to mean elevation. Using Least Square Method, it can also represent changing bottom rate along those years.