Keywords

1 Introduction

The construction of dams on rivers to make full use of water resources has brought great benefits, but also blocked the connectivity of rivers and led to the fragmentation of river water ecosystems. In order to compensate for the ecological impact on fish, the first fishway was built at the end of the 19th century to allow fish to cross the barrier and thrive, followed by various fishway arrangements such as Daniel fishway, vertical slot fishway and submerged orifice fishway (Katopodis and Williams 2012). According to the Hydraulic Design Manual (2nd Edition) (GIWP 2014), fish passage widths worldwide range from 1 m to 10 m, while river widths are often several hundred meters or even thousands of meters, for example, the narrowest point of the Yangtze River is 1100 m, so fishway projects are also “needle’s eye”. At the same time, considering that fishway is generally set next to the hydropower station, the fish are easily attracted by relatively high-speed water flow and cross the dam from turbines, causing fish death or injury (Silva et al. 2018); in some river areas, irrigation is the main water consumption project, and its water intake often causes a large number of fish entrainment and casualties.

Therefore, fish barrier measure has been more widely used as an effective artificial intervention, and according to the summary analysis of (Fisheries 2011), they can prevent fish from entering irrigation ditches, power plant tailwaters, streams with sudden changes in flow, turbine tailpipes, rivers with poor spawning gravels, poor water quality or insufficient water quantity, and guide them to fishway, bypass, etc. According to the characteristics of fish barrier measure, it can be divided into two categories: physical barrier and behavioral barrier, which are mainly represented by fish screen, porous dike, barrier net and guide wall. The interception of fish is mainly achieved through small apertures (spacing) or large heights; behavioral barriers mainly stimulate fish through flow, sound, light, electricity and biochemical means and cause avoidance effects (Noatch and Suski 2012). This paper will introduce the fish barrier measures from the aspects of the function principle, applicable conditions and application, and analyze the development trend of fish barrier measure.

2 Physical Barrier

2.1 Fish Screen

The role of the screen for fish mainly includes two parts: blocking and guiding. All fish screens usually have blocking function due to their relatively dense pores, while the guiding function of fish screen is mainly reflected in the fact that some of them can be arranged at a certain angle with the direction of water flow, which can guide fish into the bypass or other safe waters by generating sweeping flow.

2.1.1 Flat Plate Screen

A flat plate screen consists of a series of flat mesh grids that are fixed between support beams or rails and placed at an angle to the direction of the water flow. The water flow will pass through the grids, while fish and debris will be directed to the bypass. To minimize maintenance requirements and maintain efficient operation, any fish retention facility must include effective cleaning measures. For small grids and low debris loads, cleaning measures may require only manually operated rakes, brushes or scrapers. For larger systems, mechanically driven rakes, brushes, or scrapers may be required. Due to their excellent fish retention performance, low operating costs, reasonable cleaning measures and low water depth requirements, flat plate screens are now widely used in small and large irrigation diversions in Washington, Oregon and California, USA, where complete fish retention is required (USBR 2006). The main disadvantages are the accumulated cleaning and maintenance costs over time and the tendency for debris to enter the bypass along with fish and cause clogging.

2.1.2 Drum Screen

Drum screen consists of cylindrical frames covered with mesh (usually woven wire) that are placed at an angle to the direction of flow with the cylindrical axis placed horizontally. The installation can consist of individual screen at smaller diversion sites or, in wider river basins, a series of drum screens placed end-to-end.

The installed screen rotates slowly about its horizontal axis. As it rotates, the front surface of the drum rotates upward and out of water, while the rear surface rotates downward. The rotation picks up any debris on the drum and it is washed off at the back as the water passes through the screen. In order to provide sufficient screen area and optimize self-cleaning capability, drum screens must operate at 65% to 85% submersion and require high water level stability. Most commonly installed in rivers, drum screens are placed in the water at an angle along the axis to generate sweeping velocities to guide fish into the bypass, but are more costly than flat mesh screens due to their relatively complex construction.

2.1.3 Traveling Screen

Traveling screen is mainly composed of screen panels, ring chains, water injection systems and other structures, and are generally placed upstream of the intake to prevent debris and fish from entering the water. Traveling screen is usually placed parallel to the fluid or at a shallow angle, similar in principle to the two previous screens, providing guidance for fish by generating a good sweeping flow along the surface of the screen, thus reducing fish impingement. As the screen rotates out of the water, debris and fish impinging on the screen are removed by a high-pressure water spray generated by a water injection system to function as an autonomous cleaning screen.

(Black and Perry 2014) conducted more than 100 replicate tests on more than 13,000 fish at impact velocities of 0.3, 0.6 and 0.9 m/s and found that fish survival and interception rates exceeded 95%, demonstrating the efficiency and eco-friendliness of traveling screen. The effectiveness of traveling screen depends on many specific factors, such as fish size, flow rate, location and escape routes (Taft 2000). In addition, the overall cost is relatively high due to the complex structure and the high maintenance costs of the bearings, screen panels, conveyors and other structures for small and medium-sized waters, which require research trials to determine the solution in conjunction with specific detailed conditions when used.

2.1.4 Cylindrical Screen

Components of a cylindrical screen typically include a wire screen with a V-shaped or wedge-shaped cross-section having an internal baffle concept to produce a uniform velocity distribution, a water differential measurement system, and a cleaning system. Brushes on the outside or inside of the cylinder are used to clean debris from the screen surface. It is usually placed on a canal or riverbank track and acts primarily at the intake end of pumping or gravity diversion pipelines for irrigation, processing, cooling, and small hydroelectric supply. Current applications have shown that screens are biologically efficient in preventing entrainment and impingement of large fish and do not cause unusual maintenance problems (Veneziale 1992). However, as with any screening technology, the potential for clogging and biofouling is an issue that needs to be addressed in the design and operation of this technology (Smith and Ferguson 1979).

2.1.5 Inclined Screen

Inclined screen is a fence placed on the inverted slope of the channel, with the screen at an angle to the flow and submerged in the water. In addition to being arranged in the river, it can also be placed near the tailpipe to prevent fish from entering dangerous waters such as turbines. When the flow with fish and debris sweeps over the surface, the sweeping speed is generated along the direction of the surface due to the slope, while the water depth gradually decreases. The sweeping velocity will guide the fish and debris across the surface into the bypass, while the water flows down through the surface into the diversion pipe. The positive slope design tends to allow debris and branches to clog the screen, requiring regular cleaning; the negative slope design needs to ensure that the bypass has sufficient water depth for the target fish to migrate. Currently, some projects are installed with inclined screen in a removable support frame so that the downstream end of the frame can be raised and lowered to follow or adjust for changes in water surface elevation.

2.1.6 Eicher Screen

Eicher screen is a smooth-surfaced oval metal screen placed on a frame and angled toward the bypass, which can be cleaned by rotating and backflushing (EPRI 2013). The screen was designed in the late 1970s by biologist George Eicher to develop a better facility for fish to safely bypass turbines (Eicher 1982). The elliptical design of the fish screen allows it to be installed at an angle in a pressure pipe and to operate at flow rates of up to 2.4 m/s. The first Eicher screen was installed at the Sullivan Hydroelectric Plant in the United States in 1980, and in 1990, the American Electric Power Research Institute (Winchell 1992) conducted a two-year evaluation of the Eicher screen installed at the Elwha Hydroelectric Project in Washington State. The results showed that the survival rate of target fish, including juveniles, exceeded 98.7%.

2.1.7 Modular Inclined Screen

Modular inclined screen consists of an inlet with an bar rack, a stop log, an inclined screen at a small angle to the flow and bypass (EPRI 2005). Developed by EPRI in the 1990’s, the fish screen was designed to accommodate any type of intake and was designed to operate at relatively high water velocities ranging from 0.6 m/s to 3 m/s. (EPRI 1994) conducted biological tests on the guidance efficiency of modular inclined screens at high water velocities range, and the results showed that the guiding efficiency was higher than 98% for most of the target fishes, and the salmon guiding efficiency was always 100%; based on the laboratory test results, (EPRI 1996) conducted a prototype test of this fish screen in the Green Island Hydroelectric Project to evaluate the effectiveness of fish guiding in the field, and the results showed similar to the laboratory results, with the guiding efficiency close to 100%.

2.1.8 Porous Dike

Porous dike is a short dike structure made of gravel with certain voids, which can prevent fish from entering power plant intakes and causing economic and ecological losses. (Anglin et al. 2012), the Wisconsin Electric Power Company built a porous dike around the cooling basin of the Port Washington Power Station to prevent the entry of fish, and the results showed that it performed beyond expectations, not only successfully limiting fish entrainment during intake withdrawal, but also reducing the downtime of the plant due to algae problems. Compared to fish screen, porous dike has the advantage of being structurally simple, stable and reliable, and the aperture size does not have to be smaller than the smallest local fish size, which are often afraid to pass through due to their dense and massive structural characteristics (Taft 2000).

However, the results of some experimental studies have shown that some fish can be trapped in the pore space or entrained in the pumping flow, algae and shellfish can clog the pore space and shellfish can grow in it, and when the water passes through the pore space, head loss occurs due to viscous dissipation, which is not conducive to the use of water energy. In view of these unfavorable aspects, its application is not widespread and needs to be verified in targeted tests before use.

2.1.9 Barrier Net

Barrier net is mainly composed of fixed anchors, net surface, support piles and floats. Data from the study results indicate that the fish interceptor nets were successful in reducing the number of fish entering the inlet (Michaud and Taft 2000; Reider et al. 1997). Although barrier net is more economical than other measures, they have problems such as the tendency of the mesh to be clogged and cause overall sinking, the difficulty of cleaning the net after algae accumulation, poor stability at high flow velocities, and ice clogging of the net in winter; therefore, the fish interception efficiency is higher when the flow velocity is low (less than 0.3 m/s), the temperature is suitable, and the debris load in the water is light (Taft 2000).

2.2 Guide Wall

Guide wall consists of a series of partial-depth panels or fish fences anchored to a river, reservoir or canal. These structures are designed for fish that are accustomed to surface migration in the water column (e.g., salmon). The concept of guide wall originated when dam operators observed fish aggregating along gravel fences, similar to the fences of guide walls. The angle between the guide wall and the incoming flow direction is generally less than 45° to ensure that the flow velocity along the guide wall direction, pointing to bypass, is greater than the vertical flow velocity, but because it is not a full-depth design, there is a large vertical flow velocity, which is prone to turbulence and affects the fish blocking effect. The influence can be eliminated by keeping the included Angle with incoming flow less than 15° and increasing the guide wall depth (Liedtke et al. 2009; Mulligan et al. 2018). The device is still in the experimental stage and is currently installed at Bonneville Dam, USA (Mulligan et al. 2017).

3 Behavioral Barrier

Behavioral barrier refer to fish barrier measures that produce stimuli to target fish through flow fields, sound, light, electric fields, bubble curtains, and biochemistry to provide a repellent or attraction effect. The use of behavioral barriers typically provides lower capital and operating costs, but because target fish are often diverse and lack adequate behavioral studies, most behavioral barriers are less effective than physical barriers to partially reduce fish entrainment.

3.1 Angled Bar Rack and Louver

Angled bar rack and louver consist of a series of vertical fence-like slats placed on a rack that span the channel in a diagonal pattern and end at the inlet of the fish bypass. The main difference between louver and angled bar rack is that the louver slats are oriented 90° to the flow while angled rack slats are angled 90° to the rack frame and their orientation to the flow will be dependent upon the angle of the entire rack structure (Shepherd et al. 2007). As fish approach the slats, turbulence will drive them to swim in the direction of the rack and thus into the bypass channel. Studies have shown that its efficiency in guiding fish reaches about 80–95%.

Since the angled bar rack and louver rely heavily on fish response to turbulent flow, its efficiency may be relatively low and unstable when river flow conditions change or when non-target fish are encountered, and it may not be effective in blocking juvenile fish when the slat spacing is too large, while too small spacing is likely to cause injury to weak fish that hit the fence.

3.2 Velocity Barrier

When the flow rate is within the range of fish’s favorite flow rate, it can attract fish, and when the flow rate is too large and exceeds the limit of fish swimming speed, it can act as a velocity barrier (Noatch and Suski 2012). Currently, a velocity barrier is mainly used in the upstream fish passage to prevent fish from entering dangerous waters by mistake. Velocity barrier consists of a combination of concrete a weir and an apron, which prevent upstream fish from passing through by creating a smaller depth of water and a higher flow velocity on the apron, while fish cannot jump the height of the weir.

The advantage of the velocity barrier is that it does not have the problem of debris blockage like the others, and the debris and water can flow smoothly downstream through the weir. The disadvantage is that the presence of the weir creates a reservoir upstream, and the backwater effect may cause sediment accumulation upstream, resulting in loss of production and life, and a sufficient head difference is required to maintain good fish blockage. It is currently used at the Coleman National Fish Hatchery and the Vitale Tailrace in the United States.

3.3 Sound

Similar to positive and negative phototropism, fish also have positive and negative phonotropism. It is generally believed that fish are positively phonotropic to the swimming and feeding sounds of their baits and counterparts, and to the courtship sounds of the opposite sex, while they are negatively phonotropic to the negative and escape sounds of their counterparts, the feeding and swimming sounds of predators, and the abnormal sounds from fishing boats and fishing gear (Zhu 2007).

Sound decays slowly in the water, is highly directional, and is not affected by low light levels or water turbidity; light and electricity signals are less comprehensive than sound in these aspects, so sound fish guidance and attracting are more widely used and studied. (Murchy et al. 2017)’s experiments on the dispersal effect of boat engine sound on fish resulted in a combined deterrence efficiency of 90.5% for the target fish, indicating the feasibility of sound barriers.

Although sound has some advantages, it also has limitations and its effectiveness may be influenced by bottom morphology, hydrology and acoustic angle. (Maes et al. 2004) conducted field tests on the deterrence efficiency of infrasound fish barrier systems in power stations and found that their deterrence efficiency was only 60%, proving that they are not suitable to be used as a stand-alone fish barrier measure. Although infrasound has been an effective fish barrier measure in some studies, it does not propagate well in shallow water and hard substrates (Turnpenny and Nedwell 1994). Therefore, it should be used in combination with local specificities and multiple means.

3.4 Strobe Light

Fish are phototropic and produce directional movements after observing light, which can be classified as positive or negative phototropism depending on whether they are approaching or fleeing from the light source (Luo 1980). Using the negative phototropism of fish, they can be repelled to achieve the purpose of fish interception.

In the dark, strobe lights from power plants significantly alter light conditions in dangerous sites such as turbines, stimulating fish to take advantage of their negative phototropism and prompting them to seek bypass in the dark. Existing studies show that strobe lights are effective in stopping fish (Johnson et al. 2005; Noatch and Suski 2012), and fish do not become accustomed to continuous flash exposure, so strobes are effective in the long term, but studies to date have not demonstrated their full reliability as a single measure (Hamel et al. 2008).

In addition, taking advantage of the positive phototropism of fish to certain specific light, fish can be attracted to the inlet of the fish passage, thus increasing the efficiency of operation. Light attracting was first applied in fisheries, where early fishermen used vapor lamps to attract squid, and then gradually applied to fishway attracting systems. For example, (Lin et al. 2019) evaluated the effect of different light colors on attracting fish into fish passage fish collection systems and found that warm white light had an important role in attracting fish. The study showed that since fish are selective to light (Zhang et al. 2019), a comprehensive and specific study of the target fish should be considered when making the design arrangement, otherwise the desired effect cannot be achieved, so a combination of measures should be used to improve the fish attraction effect.

3.5 Electric Screen

Electric screen is a suspended structure consisting of a main cable, sling, horizontal cable, electrodes and struts, and anchor piers that generate an electric field in the water (Wang et al. 2013).

Electric screen has been innovative in its delivery method, and the pulsed electric screen is about 1/40th of the power of the DC screen, while its health effects on fish are minimal and it has some prospects for application (Dong 2007). Pulsed electric screen has been used in China on a certain scale, mainly to prevent fish escape from reservoirs, and was tested with good results (Zhao et al. 2000).

Electric screen also has some limitations, for example, its cross-sectional flow velocity should be controlled below 0.7 m/s, if the flow velocity is too large, it is easy to increase the possibility of fish passage, and under bad weather conditions, fish riot may occur and “sudden change of fish escape”, and there are limited action area, need for stable power supply, and the effect on small fish.

3.6 Bubble Curtain

Bubble curtain mainly produces bubbles by discharging compressed air in a large amount through holes in the tube. If the fish are far away from the bubble curtain, the fish tend to swim towards the bubble curtain for the purpose of luring (Qiao et al. 2011); however, when the fish are close to the bubble curtain, the “bubble curtain wall” has a visual effect on the fish, an auditory effect when the bubbles are strongly mixed with air and broken, and the bubbles cause a change in water pressure and mechanical pressure vibration (Mao 1985).

The efficiency of bubble curtain as a fish barrier measure is relatively low. Its practical application in power facilities was not effective, and since then, the bubble curtain in these power stations has been removed (Hocutt 1980); (Liu and He 1988) found through experiments that freshwater fish had obvious adaptation to the bubble curtain, and that the bubble curtain had a better deterrent effect in a short time and a poorer effect in a long time. Therefore, the bubble curtain can not fully achieve the effect of fish interception, and comprehensive measures are needed to improve efficiency.

3.7 Other Means

In addition to the above, water quality barriers, pheromones and magnetic fields are also viable experimental fish barrier measures.

Water quality barrier is a fish barrier formed by increasing the concentration of carbon dioxide in the ambient water, thereby preventing fish from breathing. (Theresa et al. 2008) suggest that the downstream migration of invasive fish can be stopped by discontinuing supplemental aeration in the river to create a hypoxic zone.

Pheromone is widely defined as a secreted chemical odor that elicits specific behavioral responses in fish (Sorensen and Stacey 2004). Pheromone plays an important role in reproduction and predator avoidance for fish. Attractive pheromone is usually secreted by sexually receptive individuals to attract the opposite sex. In contrast, alarm pheromone, is often released when the fish’s skin is damaged and can trigger an escape response in conspecifics. Alarm pheromones can be used to exclude fish from specific locations, while attraction pheromones can be used to gather fish away from sources of danger. Study shows that chemicals released by decaying eels trigger avoidance behavior in their own kind (Wagner et al. 2011).

Some fishes are endowed with electro-sensory organs that are designed to provide fish with an advantage in locating prey. However, strong magnetic fields may overstimulate these receptors, achieving deterrent or repulsive effects that may help guide the fish away from undesired locations. For example, a study by (O’Connell et al. 2010) showed that decoy areas containing magnets had a repulsive effect on fish.

All of the above measures are in the experimental stage, with limited application, and their efficiency and stability of fish interception need to be further studied.

4 Conclusion

Table 1. Overview of the main fish barrier measures
Full size table

Through the statistics in Table 1, it is easy to find that the physical barrier has the advantages of high efficiency and good stability, but also has the problems that it is mostly applicable to the waters above the dam, easy to encounter debris clogging and high maintenance cost; while the behavioral barrier has the advantages of space saving, no debris clogging, no head loss, etc., but the effect of fish interception is unstable, easily affected by the water body or other external conditions, and the research results are not yet mature.

Most of the fish barrier measures are currently applied in the upstream of the dam, but the downstream of the dam also has the possibility of fish entering the irrigation canal, tailwater canal, or non-upstream river channel and other dangerous waters, which need efficient fish barrier facilities to guide them into the upstream fish passage.

Although fish barrier measures are used in China, there are few data on their effectiveness and fish survival rate, and there is a lack of sufficient data for reference compared with other countries. In addition, there are few types of fish barrier measures applied in China, and there is a certain prospect of developing efficient fish barrier facilities that are specific to the actual situation in China.

Although some of the fish barrier measures can reach 100% efficiency for some specific fish in the test, considering the diversity of target fish and the variability of hydraulic conditions in the actual application, it is difficult to achieve efficient operation by using a certain fish barrier measure alone, therefore, a combination of hybrid fish barrier measures can be considered, for example, the fish trapping and replenishment spraying system combines the use of auxiliary water systems and acoustic fish trapping means, the bioacoustic fish screen uses a combination of strobe lights, sound barriers and bubble curtains.