Attractiveness of a lateral shelter in a channel as a refuge for juvenile brown trout during hydropeaking

Peak power production in hydroelectric storage power plants results in frequent and intense flow variations in the rivers downstream of the plants. Fish populations can be negatively impacted when subjected to these so-called hydropeaking phenomena. In researching mitigation solutions, shelters in the riverbanks of channelized rivers have been identified as a means of protecting fish from excessive flow velocities. These shelters were studied systematically using juvenile brown trout (Salmo trutta fario) in an experimental configuration in which a straight channel was equipped with a lateral embayment. The purpose of the experiments was to generate hydrodynamic hydropeaking conditions in the channel that are undesirable for juvenile trout, thereby causing them to enter the shelter. The flow velocity distribution in the intersection plane between the main channel and the lateral shelter was found to be a significant parameter for attracting fish to the shelter. The utilization rate of trout in the shelter was used as a performance indicator. Using a basic rectangular shelter configuration without forced water exchange between the shelter and the channel, the utilization rate was only 35 %. This rate was more than doubled by introducing a deviation groyne to force water exchange between the channel and the shelter. The position and orientation angle of this groyne were systematically varied to maximize the utilization rate. Maximum utilization rates approaching 90 % were obtained for an optimum configuration in which an island-type groyne was placed in the shelter. The results of the systematic channel tests showed the potential of the shelter to attract fish. Such a shelter could be used in channelized rivers both for morphological revitalization and to improve fish habitats. As a next step in this research, prototype shelters will be built on a natural river and monitored for 2–3 years under a hydropeaking flow regime.

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

Jean-Marc Ribi, Anton Schleiss

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.

Ed. Dittrich, Koll, Aeberle & Geisenhainer (eds)2010

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

Jean-Marc Ribi, Anton Schleiss

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.

2010

Etude expérimentale de refuges à poissons aménagés dans les berges de rivières soumises aux éclusées hydroélectriques

Jean-Marc Ribi

Downstream of hydroelectric storage dams, the rivers suffer from rapid, frequent and intense flow variations linked to the power production constraints. Subjected to this hydropeaking phenomenon, the fish population suffers from a known decline. In the research of mitigation solutions, shelters in riverbanks are a protection measure against excessive flow velocities. This project gives the design basis for such shelters. The research process is based on experimentations with fish swimming in a canal built on purpose with a lateral embayment. The principle is to generate hydrodynamic conditions that are uncomfortable in the canal on one hand and attracts the fish to the shelter on the other hand. The significant parameter is the flow velocity distribution in the intersection between the main channel and the lateral fish shelter. The frequentation rate of fish in the shelter can be considered as the performance indicator. With a length of 12 m and a width of 1.2 m, the canal is supplied with freshwater from a river. At mid-length, the canal holds a one side enlargement of 1.2 m, shaped like a rectangular gap of 2 m long. For each test, after a steady flow of 10 l/s with a mean velocity of 0.1 m/s, 10 to 20 juvenile brown trout are suddenly exposed during 3 hours to a hydropeaking flow of 220 l/s. At that time, the mean velocity in the canal is of 1 m/s. The fish position is observed every 20 minutes and their movements are recorded continuously in the shelter sector. The first tests have been conducted with a basic rectangular shelter configuration. The frequentation rate was only of 35%. This rate has doubled by introducing a deviation groyne that enforced a water exchange between the canal and the shelter. Following this experiment, the position and the orientation angle of the groyne have been systematically varied with the purpose of maximising the frequentation rate. This way, 12 configurations have been tested 3 times each. The flows transiting in the shelter are calculated using a 2D numerical simulation. By analysing the fish positioning, the mean frequentation rate is determined for each configuration. The maximum rate is of 87%, the mean is of 75% and the standard deviation is of 8%. Using video pictures treatment, the preferential fish trajectories are updated and the fish entrance distribution is determined for each configuration at the interface between the shelter and the channel. On the same interface, ultrasonic velocity profiles (UVP) have been measured for the 12 configurations. By associating the fish entries distribution with the velocities distribution, the preferences are globally established. The entrances happen mostly from downstream of the derivation groyne, in a flow shear zone where the velocities are in a range of 0.0 to 0.2 m/s. Finally, the analysis of all the results confirmed the representativity of the configuration that gives the best frequentation rate, for the development of the experimental shelter's prototype to be realised in rivers. It is composed of a groyne shaped like an equilateral triangle. Finally, recommendations are given for the execution of an experimental prototype shelter to be realized in a river for validation tests.

EPFL2011

Etude expérimentale de refuges à poissons aménagés dans les berges de rivières soumises aux éclusées hydroélectriques

Jean-Marc Ribi

EPFL2011

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

Jean-Marc Ribi, Anton Schleiss

Ed. Dittrich, Koll, Aeberle & Geisenhainer (eds)2010

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

Jean-Marc Ribi, Anton Schleiss

2010