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Ecological Engineering 48 (2012) 25– 29

Contents lists available at ScienceDirect

Ecological Engineering

j ourna l ho me page: www.elsev ier .com/ locate /eco leng

ffect of trash diverters and overhead cover on downstream migrating brownrout smolts

arry Greenberg ∗, Olle Calles, Jonas Andersson, Thérèse Engqvistepartment of Biology, Karlstad University, S-651 88 Karlstad, Sweden

r t i c l e i n f o

rticle history:eceived 22 October 2010eceived in revised form 24 March 2011ccepted 3 May 2011vailable online 2 June 2011

eywords:uidance efficiencyiversionverhead coveramishurbine mortality

a b s t r a c t

Power plant dams constitute barriers for downstream migration by smolts. The purpose of this study wasto measure guidance efficiency of existing trash diverters and the use of overhead cover in combinationwith trash diverters to guide brown trout (Salmo trutta L.) smolts away from turbine intakes into trashspillway gates at two power plants in the Emån River, southern Sweden. A total of 44 trout smolts werecaught, radio-tagged, released at the two power plants and tracked daily for six weeks. The trash diverterat the lower power plant had a significant guiding effect, as the proportion of smolt that entered thespillway gate was significantly greater than the relative proportion of water that flowed through thegate (52% vs 17%). In contrast, there was no evidence of a guidance effect at upper Finsjö, where theproportion of smolts that entered the spillway gate did not differ significantly from the relative proportionof water that flowed through the gate (0% vs 10%). The lack of a guidance effect at upper Finsjö could notbe explained. The effect of overhead cover was tested at the upper power plant as illumination fromoutdoor, overhead lamps at the power station was believed to attract smolts to the turbine intake. Thiswas accomplishing by setting up and removing a tarpaulin placed between the trash deflector and the

turbine intake approximately every 2–5 days for about one month, so that 52.6% of the time the tarpaulinwas in place and 47.4% of the time it was not. The presence of the tarpaulin reduced turbine passage, as31% of the smolts swam through the trash spillway gate instead of the turbines when the tarpaulin was inplace, whereas all smolts entered the turbines when no tarpaulin was used. For fish that passed throughthe turbines, mortality was higher at the upper power plant, equipped with two twin-Francis turbines,than at the lower one, equipped with a single Kaplan turbine.

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. Introduction

Hydropower stations, with their dams and turbines, constitutearriers and sources of mortality for downstream migrating smolts.he actual route selected, which is associated with a certain risk ofortality, is thought to be strongly influenced by flow conditions,here smolts are believed to select the path with the highest flow.

ypically, the fish pass the dams by either swimming through tur-ines, spillways or some type of bypass system (Clay, 1995). Therere essentially two types of turbines, the Francis and the Kaplanurbine, which are used in low-head power plants. Fish passinghrough Francis turbines, which possess many runner blades withittle space between them, typically experience a higher mortal-

ty than fish passing through Kaplan turbines, with its rather fewunner blades and more space between the blades (Montén, 1985).n addition, the risk of being struck by a runner blade increases

∗ Corresponding author. Tel.: +46 54 7001543; fax: +46 54 7001462.E-mail address: Larry.Greenberg@kau.se (L. Greenberg).

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925-8574/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.ecoleng.2011.05.001

© 2011 Elsevier B.V. All rights reserved.

ith increasing fish body size (Clay, 1995; Rivinoja, 2005). Fishay also die or incur damage as they are impinged against the bar

acks that are often placed just upstream of turbine intakes (Callest al., 2010). Spillways are also associated with mortality risks,ither directly due to fish free-falling against concrete structuresefore re-entering the water (Calles and Greenberg, 2009) or indi-ectly due to pressure changes and gas supersaturation (Coutantnd Whitney, 2000).

There are various methods for diverting fish from turbinentakes (Clay, 1995). One such way is use of a ‘behavioral barrier’,

hereby one elicits a behavioral response by the fish, using forxample sound, so that they select a route associated with a lowisk of injury or death. Such methods have had variable success ashey depend on local conditions that permit active choice as wells on the stimulus having a strong and consistent effect. A secondethod of diverting fish is to construct mechanical barriers, using

or example meshed grating or nets to force the fish to swim along aarticular route. Yet another way of preventing fish from enteringurbines is to capture them in traps and transport them past theower plant.

26 L. Greenberg et al. / Ecological Engineering 48 (2012) 25– 29

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Fig. 1. Diagram showing the power plant intake canals at upper and lower Finsjö

When it concerns behavioral barriers, these can be used to eitherttract or divert fish. A number of studies have shown that down-tream migrants react to or are affected by illumination (Lariniernd Travade, 1999; Kemp et al., 2008; Kemp and Williams, 2009).or example, Kemp and Williams (2009), who worked with severalpecies of juvenile Pacific salmonids, showed that more individu-ls approached, and either passed or rejected an artificial channelith a submerged weir when the area was artificially illuminated

han when it was not. Based on this result, Kemp and Williams2009) suggested that the design of fish passages may need to takento account the response of fish to illumination. Even use of over-ead cover in the design of fish passage facilities may be warrantedKemp et al., 2005, 2006). Kemp et al. (2005, 2006), for example,howed that approximately 75% of chinook salmon (Oncorhynchusshawytscha Walbaum) avoided covered channels in controlled lab-ratory tests.

In many cases, bypass facilities have been implemented with-ut evaluating their effectiveness or if effectiveness has beenvaluated, guidance efficiency has been shown to be low (Kempt al., 2008; Larinier, 1998). Moreover, many of these diver-ions are expensive. Here we evaluate the use of two relativelynexpensive measures, trash deflectors and overhead cover, touide brown trout (Salmo trutta L.) smolts away from turbinentakes. We test whether guidance away from turbine intakes cane increased by simple modifications of extant trash deflectorystems and by use of overhead cover at the often illumi-ated canals just upstream of turbine intakes. This study wasonducted at two power plants, upper Finsjö with two twin-rancis turbines and lower Finsjö with a Kaplan turbine, inhe Emån River, southern Sweden. We also expected mortal-

ty for the fish that passed through the Frances turbine to beigher than for those fish that passed through the Kaplan tur-ine.

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the location of the turbine intakes, trash gates and where the fish were released.

. Materials and methods

.1. Study area

The study was conducted in the Emån River (57◦07′59′′N;6◦30′00′′E), a lowland river dominated by forest and agricultural

and, with a catchment area of 4472 km2. The mean annual dis-harge is 30 m3 s−1 and generally varies between 6 and 107 m3 s−1.he river has been regulated for approximately 100 years and has

long history of supporting a recreational and commercial fisheryKlippinge, 1999). This study was conducted at two hydroelectricacilities in Finsjö, situated approximately 30 km upstream of thealtic Sea. Upper Finsjö is separated from lower Finsjö by an 800-m

ong stretch of slow-flowing, deep water.The power plant at upper Finsjö has a total capacity of 14 m3 s−1

nd is equipped with two twin-Francis units from 1919 (i.e., fourunners). The power plant at lower Finsjö has twice that capac-ty, using one large Kaplan runner. Trash racks are present at bothower plants, with 20 mm spacing at upper Finsjö and 30 mmpacing at lower Finsjö. As is the case for most power plantsn Sweden, the area around the power plant station is illumi-ated with outdoor, overhead lamps. There are no devices guidingownstream-moving fish, but there are 1-m deep, angled trasheflectors at both power plants, and these were used to lead fisho the trash gates adjacent to the turbine intakes (Fig. 1). To evalu-te the functionality of the trash deflectors as fish guiding devices,olf traps (Wolf, 1951) were constructed at the trash gates of

he two power plants. At upper Finsjö, the entrance to the trashate was about 30 cm above the opening to the trap, whereast lower Finsjö the opening to the trap was at the same level

s the trash gate. The gates at upper and lower Finsjö are 1.9 mnd 3.5 m wide, respectively, and water is discharged at the sur-ace.

L. Greenberg et al. / Ecological Engineering 48 (2012) 25– 29 27

Fig. 2. The fate of smolt at upper and lower Finsjö from 23 April to 22 May 2007. Fish indicated by “survived” successfully passed the power stations, based on movementpatterns. Fish indicated by “probably dead” also passed the power station area but then remained in one location until the study was terminated. Some fish were retrieveda er pla

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nd found to be “Dead”. Others were collected in the wolf traps after passing a pow

.2. Method

Field work was conducted between 10 April and 1 June 2007.he wolf trap at upper and lower Finsjö was emptied daily from5 April to 30 May and 14 April to 1 June, respectively. Additionalmolts were collected from a trap situated near the mouth of theiver at Em. From the trap collections, smolts > 150 mm long werearked with radio-transmitters, modell F-1545 (ATS, Isanti, USA),hich weighed 0.9 g and had an estimated lifespan of 55 days. The

adio-transmitters were surgically implanted in the body cavityJepsen et al., 2002), after anaesthetizing the fish with MS-222. Afteragging, the fish were placed in a perforated container in the rivero recover, before releasing them in the evening in the power plantntake channel (Fig. 1). The fish were released between 23 April and1 May.

Position of the radio-tagged fish was identified using four strate-ically placed loggers and antennae (Advanced Telemetry Systems,H, USA, receiver model R2100, DCC and 4-element Yagi antennae).wo loggers and antennae were placed at each power station canalo increase precision in identifying location. Manual tracking waslso conducted daily from 23 April to 1 June.

The efficiency of the trash diverter as a method of guiding fishnto the trash spillway gate and away from the turbine intake wasested at upper and lower Finsjö. To be able to evaluate this, weompared the proportion of fish that used the trash spillway gatend the turbine intake relative to the amount of water that flowedia these two pathways.

The area immediately upstream of the turbine intake at upperinsjö is illuminated, a consequence of the fact that outdoor, over-ead lamps are used to illuminate the power station for safetyurposes. As outdoor lighting was expected to attract the fishowards the turbine intake, the area immediately upstream of theurbine intake was covered with an opaque tarpaulin. In this way,e could test the effect of overhead cover on the route selected by

he smolts. The tarpaulin was mounted using rope and clamps, sohat it covered the area between the trash deflector and the turbinentake rack (Fig. 1). The tarpaulin was set up and removed every 2–5ays from 23 April until 26 May, so that for five time periods, repre-enting 52.6% the time (about 18 days), the tarpaulin was in place;he remaining 47.4% of the time it was not (6 periods for a total ofbout 16 days).

To test turbine mortality, the turbine passages were classified

s (1) successful passage, (2) death, or (3) probably dead. Fish thatere classified as “probably dead” were tracked to the same place

very day until the study was terminated. The few fish that werelassified as “dead” were verified visually.

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nt and found to be in bad condition (“injured”).

Separate chi-square tests were used to test fish guidance effi-iency at each power station, with the possible routes being via thetrash gate” or via the “turbine”. This was done by comparing theumber of fish that used the trash spillway gate and the turbine

ntake relative to what would be expected if the fish made theirelection based on the relative discharge for the two possible path-ays. For upper Finsjö, the analysis was restricted to data obtainedhen no tarpaulin was in place. A chi-square test was also used to

est the effect of the tarpaulin on guidance efficiency at upper Finsjöy comparing the route selected by the fish when the tarpaulin wasresent vs when it was absent. A probability < 0.05 was consideredo be statistically significant.

. Results

In total, 46 smolts were marked with radio-transmitters, butwo of the fish were excluded as they were observed to have fungalnfections when recaptured in traps. The 44 remaining smolts were53–270 mm long and weighed 31.9–180.4 g. Two of these wereever recorded on the loggers.

The fate of the smolts differed at upper and lower Finsjö. A sig-ificantly larger number of successful passages occurred at lowerinsjö than at upper Finsjö (Fig. 2). This was in large part due to theubstantially higher turbine mortality at upper Finsjö, about 68%s compared to lower Finsjö, where turbine mortality was 31% (17f 25 fish died at upper Finsjö vs 5 of 16 at lower Finsjö; �2 = 16.0,f = 1, p < 0.001).

Fish guidance efficiency differed between the two power plantsTable 1). At upper Finsjö, the trash deflector had no effect, as theroportion of smolt that swam through the trash gate (i.e., caught

n the wolf trap) did not differ from the relative proportion of waterhat flowed through the trash gate and the turbine (�2 = 1.4, df = 1,

= 0.24). At lower Finsjö, the proportion of smolt that entered therash gate was greater than the relative proportion of water thatowed through the gate (�2 = 27.3, df = 1, p < 0.001).

The use of a tarpaulin as overhead cover resulted in a largerercentage of smolts passing through the trash gate rather thanhrough the turbines (Fig. 3). Specifically 31% passed through therash gate instead of the turbine when the tarpaulin was present,hereas all fish passed through the turbine in the absence of the

arpaulin (�2 = 4.57, df = 1, p = 0.033). For the 17 passages for which

ime of passage could be identified (regardless of route selected), 10f these occurred during daylight hours (59%). Four of six occurreduring the day when the tarpaulin was in place and six of 11ccurred during the day when there was no tarpaulin in place.

28 L. Greenberg et al. / Ecological Engineering 48 (2012) 25– 29

Table 1Fish guidance efficiency in relation to discharge (absolute and relative) when using the trash deflector at upper and lower Finsjö. There were two possible routes for thesmolts: through the turbine or through the trash gate, where fish were caught in a wolf trap. The average flow for these two passage routes is given, based on the period 15April to 31 May 2007. Note that data for upper Finsjö are based on the period when no tarpaulin was used.

Station Location Discharge (m3 s−1) % discharge No. smolt % smolt

Upper Finsjö Trash gate 1.4 10 0 0Turbine 12.3 90 12 100

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. Discussion

There was a large difference in mortality between upper andower Finsjö. As shown previously for Emån, mortality was higheror upper Finsjö than for lower Finsjö (Calles and Greenberg, 2009;reenberg and Calles, 2010). A salient difference between the twoower plants is the presence of twin-Francis turbines at upper Fin-jö and a single Kaplan turbine at lower Finsjö. In general, mortalityn Francis turbines is higher than in Kaplan turbines (Montén, 1985;alles and Greenberg, 2009). At upper Finsjö, many of the smoltsere classified as “probably dead”, indicating that these fish wererobably consumed by predators such as pike or killed by the tur-ines and carried downstream.

Fish guidance efficiency at the two power stations differed con-iderably. Fifty-two percent of the smolts at lower Finsjö selectedhe trash gate as compared to 0% at upper Finsjö. This resultontrasts with results from 2005 at Emån, where guidance effi-iency was 14% at lower Finsjö and 50% at upper Finsjö (Calles andreenberg, 2009). For lower Finsjö, this difference between yearsay be related to the dimensions of the trash gate opening and

o trap construction. In 2005, the height of the 3.5 m wide open-ng at lower Finsjö was only 0.2 m instead of being fully open as

as the case in this study. Moreover, the opening of the trap waseneath the trash spillway gate in 2005, and as a result the waterpilled (i.e., free-fell) several meters after passing the trash spillwaypening (Calles and Greenberg, 2009). In this study, the opening tohe trap was at the same level as the trash spillway gate. This dif-erence in trap construction between studies most likely affected

he acceleration of flow and turbulence, which are known to makesh reluctant to enter bypasses (Scruton et al., 2003; Larinier andravade, 1999). For upper Finsjö, the lack of a guidance effect in

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007 is difficult to understand. One could argue that the approx-mately 30 cm free-fall of water over the spillway opening mightave made the fish reluctant to enter the bypass, but this difference

n water level between the spillway opening and the opening of therap was also present in 2005, when fish guidance efficiency was0%. In fact, the between-year difference in fish guidance efficiency

s difficult to explain. Nevertheless, there were differences betweenhe studies. Discharge into the trap was higher in 2007 (1.4 m3 s−1)han in 2005 (0.5 m3 s−1), and the tagged smolts were not releasedt the same locations in the river during the two studies, but it isnclear how these methodological differences explain differences

n fish guidance efficiency.Overhead cover influenced migration path as all smolts that

xited via the trash gate did this when the entrance to the turbinentake was covered, and none did so when there was no overheadover. Without more detailed behavioral studies it is difficult tonderstand how overhead cover affects route selection. Neverthe-

ess, Kemp et al. (2005), in a controlled experimental flume study,ound that chinook salmon showed avoidance behavior prior tontering a covered channel entrance, indicating that the salmonesponded to visual cues. It was unclear whether the salmon wereeacting to a change in light climate associated with the overheadover or to the physical presence of overhead structure. Interest-ngly, avoidance of overhead cover in our study of brown trout wasot restricted to nighttime as 59% of the smolts migrated duringaylight hours and 41% at night. This result was somewhat sur-rising as previous studies had indicated that brown trout andther salmonid smolts predominantly migrate at night (Jonsson,991; McCormick et al., 1998; Olsson et al., 2001). If the smoltsad predominately migrated at night this might have indicatedhat the fish were largely reacting to a change in light climate.owever, relatively speaking, conditions were similar during daynd night as light levels at the turbine intake, due to sunlighturing the day and overhead lamps at night, were higher thannder the tarpaulin. Whatever, the mechanism, several studiesave reported a reluctance by fish to enter covered or darkenedtructures (Glass and Wardle, 1995; Welton et al., 2002), andhis fact may be used in designing diversionary structures formolts.

Our results show that upper Finsjö, and presumably other powerlants with Francis turbines (Calles et al., 2010), are in need of

functioning guidance system. Use of overhead cover and trasheflectors represents an inexpensive measure that could be used

f channel velocities are not too high, so that fish have the pos-ibility to choose alternative routes. Nevertheless, such measureslone are not sufficient, given that 69% of the smolts still passedhe dam via the turbines when the tarpaulin was present. At besthis method could be used as a complement to other remedial

easures. One solution that is currently being tested at upperinsjö is the use of a surface-bypass system with low-angled bar

acks that extend from the bottom of the canal to the water sur-ace. This type of bypass system prohibits smolts from enteringurbine intakes and is expected to successfully lead smolts pastams.

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cknowledgements

Hanna Karlsson, Anders Robertsson and Carl-Johan Månssonre thanked for help in the field. The research presented inhis paper was carried out as a part of the Swedish R&D pro-ram ‘Hydropower—Environmental impact, remedial measuresnd costs in existing regulated waters’, which is financed by Elforsk,he Swedish Energy Agency, the National Board of Fisheries andhe Swedish Environmental Protection Agency. The study was per-ormed under license from the Swedish Animal Welfare AgencyGöteborg, CFN Dnr 62-2007).

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