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Docket OW-2002-0049 DCN# 5-4301 

Turnpenny, A. W.H. 

Fish Returns at Cooling Water Intakes ffc-W 

FAWLEY 

aqpafi e iras©amdh flailb®iratlffiiii®§ L M 

Consultancy Report 

Client: Nuclear Electric pic 

For the attention of: 

Mr C J L Taylor 

CONFIDENTIAL 

23 December 1992 

FISH RETURN AT COOLING 

WATER INTAKES 

AWH Turnpenny 

FCR 023/92 
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SUMMARY 

This Report reviews information from the UK, USA .and Europe relating to fish damage 

associated with impingement on the cooling water intake screens of power stations, types 

of fish return system used and their relative success. On the basis of this information, 

outline design criteria for drum- or band-screen-based fish return system are presented. 

CONCLUSIONS 

1 Impingement of fish on cooling water intake screens causes a variety of externally 

visible injuries, ranging from scale loss, to more serious damage to eyes and fins.. These are 

mainly contact injuries. In species possessing a closed swimbladder (eg. cod family and 

bass), internal damage to this organ could result from pressure reductions associated with 

raising fish to the surface over a period of time which is too short to allow pressure 

adaptation. This is only likely when the intake opening is >5m below the water surface. 

Larval or adult clupeid fish may suffer damage to the auditory bulla system in offshore intake 

systems where the fish .are drawn down 20 m or more below intake level. 

2 Impinged fish may also suffer physiological stress. This can be caused by exercise 

and exhaustion within the turbulent conditions of the screenwells of a power station, by 

osmotic imbalance resulting from disruption of the epithelial layer by abrasion and, during 

periods of biocide application, by the toxicity of the biocide. 

3 Survival of fish for periods of one to four days following impingement has been 

investigated in overseas studies and varies from zero to a hundred per cent, depending on 

species. Demersal and inshore epibenthic species (eg., flatfishes, bass) tend to be most 

resilient, whereas pelagic species (eg. clupeids, anchovies) are most delicate. The resilience 

of the demersal and epibenthic fish may be related to both physical robustness and the fact 

that they make little attempt to swim, once within the screen well, and are thus less subject 

to exhaustion and continued abrasion. 

4 In the USA and France, fish rescue/return systems have been developed to collect fish 

entering the CW intakes and return them to the wild. The simplest systems used collect fish 

following impingement on the screens and attempt to minimise further handling stress by 

careful design of the associated backwash and handling equipment. More sophisticated 

designs prevent impingement and guide fish to extraction areas where they can be pumped 

or lifted out prior to return to the wild. The success of the more elaborate systems is 

moderately good when measured in terms of numbers offish diverted and returned (eg. 50 

to 75% at San Onofre Nuclear Generating Station) but these figures do not take account of 

additional mortalities due to predation at the outfall, which may be high. It is doubtful 

whether any fish return system can hope to achieve >30% success rate overall, for all 

species. 

5 Effective fish protection at water intakes requires attention first at the design and 

siting stage to ensure that areas of high fish concentration are avoided and that intake 

approach velocities are kept below the sustainable swimming speeds of the most important 
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fish species; secondly, behavioural deterrents (eg., based on sound, light or bubble stimuli) 

should be considered as a means of reducing fish entry into the intake; fish return systems 

offer a final level of protection. 

6 Design criteria for a simple screen-based fish return system are presented. This 

involves provision of fish buckets on the screens .and careful design and choice of materials 

to minimise handling damage. Fish are lifted by means of the screens themselves, but 

additional lift may be provided if necessary by the use of screw-impeller fish pumps. A 

simple fish/trash separation pit is described, though it is recommended that this should not 

be used where fish survival is a priority, on account of the additional handling stress. 

7 The choice of return route for rescued fish - either via the CW disch-arge or via a 

dedicated fish return pipeline - depends parti.ally on cost. Where a dedicated return line can 

be accomplished at or below the cost of routing fish into the CW discharge, this is always 

preferable, being free from thermal or biocide related stresses. For typical exposure times 

calculated for passage through CW discharges, including exit of the fish from the plume 

(range 17.5 to 90 minutes), chlorine toxicity is not likely to kill fish. The effects of thermal 

shock are less predictable and it is recommended that site-specific tri.als be performed to 

determine the effects of thermal stress on fish which have already been subjected to the 

stresses of impingement. 

8 There may scope for further reducing fish damage by reducing their residence time 

in screenwells. This might be accomplished by electrical stunning, narcotization (eg. with 

carbon dioxide) or by elimination of light from the screenwell to prevent effective 

orientation. Experimental trials would be required. 

Dr A W H Ty 

for: 

FAWLEY aquatic research laboratories Ltd 

Marine & Freshwater Biology Unit 

Fawley, Southampton S04 1TW 
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CONTENTS 

1. INTRODUCTION 

2 DESCRIPTION OF POWER STATION WATER INTAKES 

3. STRESS AND DAMAGE TO FISH CAUSED BY IMPINGEMENT 

3.1 Damage symptoms of impinged fish 

3.2 Post-impingement survival 

3.3 Physiological stress 

4. FISH RETURN SYSTEMS: OVERSEAS EXPERIENCE 

4.1 SONGS fish diversion system 

4.2 Le Blayais fish/shrimp return system 

4.3 The NEP Brayton Point Angled Screen fish by-pass system 

4.4 Hanford fish return system 

4.5 Summary of fish recovery experience 

5. DESIGN CRITERIA 

5.1 General layout 

5.2 Screen mesh 

5.3 Fish buckets and backwash system 

5.4 Trash hoppers and fish return pipe 

5.5 Fish/trash separation pit and discharge 

5.6 Limitations of the design 

5.7 Scope for further reducing fish damage 

6. FISH RETURN ROUTES 

6.1 Return via the CW discarge 

6.2 Dedicated fish return pipes 

7. CONCLUSIONS 

TABLES 

FIGURES 

APPENDIX: Investigations of fish damage symptoms on Fawley Power Station 

screens 
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1. INTRODUCTION 

The unintentional capture of fish is a virtually unavoidable consequence of abstracting large 

flows of water from rivers, lakes, estuaries or the sea. Whilst most modem intake designs 

are able to take advantage of established design principles and fish protection technologies 

to minimise entrapment of fish, none are wholly effective against all species and life stages 

of fish (Turnpenny, 1988). A possible exception to this are passive screening systems using 

fine meshes, wedge-wire materials or porous filtration media, but whose use is restricted to 

relatively small abstractions of < lmV1 (Turnpenny, 1989). 

The need for fish return systems stems from the inadequacy of primary fish protection. The 

first and potentially most effective measures will aim to keep fish away from the water intake 

point altogether: any fish, once within the engineered system, will be at risk of damage from 

the stresses of passage and contact with surfaces and machinery, in many cases from toxic 

exposure to biocides, and finally from predation at the point of return to the wild. Fish return 

systems will thus have, at best, a limited success rate. 

There has been a limited experience of fish return systems in the UK, installed principally 

at estuarine sites for the return of salmon (Salmo salar) and sea trout (S. trutta) smolts (e.g., 

Uskmouth and Oldbury-on-Severn power stations). A number of other stations (e.g. 

Dungeness 'B', Sizewell 'A') have operated simpler trash return systems which involve 

periodic discharge of the accumulated biological and other debris to the sea, with no 

deliberate attempt to secure the survival of living organisms. The inclusion at the yet-to-becommissioned Sizewell 'B' power stetion of the facility to direct trash either to baskets or 

into the CW discharge, thereby providing the opportunity for fish return, is to be welcomed. 

There has, indeed, been little encouragement by the regulatory authorities in England and 

Wales, with the Ministry of Agriculture, Fisheries and Food (MAFF) on the one hand 

generally in favour of the return of impinged materials to the sea for the benefit of fisheries, 

and the National Rivers Authority (NRA) on the other, reluctant to licence discharges 

containing impinged debris. It is to be hoped that the argument will be decided ultimately 

in terms of which can be shown to be the most environmentally beneficial. 

Overseas authorities have been less reticent about encouraging the development of fish return 

systems. In the United States, the prospect of compensation being levied against fish losses 

(Loeffelman and Tamms, 1991), and the requirement under Section 316(b) of the Federal 

Water Pollution Control Act to implement effective environmental protection systems 

(Langford, 1983) has encouraged the development of primary (fish deterrence) and secondary 

(fish return) fish protection systems for water intakes. In Europe, the French power 

industry, as part of its nuclear expansion during the '70s and '80s, investigated a wide range 

of fish protection systems and has implemented a fish and shrimp return system on at least 

one estuarine site, Le Blayais, on the Gironde (Travade et al., 1983). 

The objective of this Report is to review research into the nature and frequency of fish stress 

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and damage symptoms associated with fish impingement and return in estuarine and marine 

power station cooling water (CW) systems and, from a review of the limited data from 

existing fish return systems, to summarize design criteria for a cost-effective fish return 

system suitable for estuarine and coastal power stations. 

2 DESCRIPTION OF POWER STATION WATER INTAKES 

Details of intake system design differ from plant to plant but, in general, the cooling water 

systems of estuarine and marine power stations conform to one of two types: onshore or 

offshore. The essential differences between these two types of intake are illustrated in Figure 

1. In both types, water is pumped at the landward end from a deep screenwell, which is fed 

by gravity from the sea or estuary. In the offshore design, water enters the screenwell via 

an offshore intake opening, on or above the bed, which feeds into one or more concrete- or 

steel-lined pipes sunk below bed level. Hydraulically, the offshore intake operates on the 

manometer principle. The onshore design differs in two chief respects: firstly, the water is 

canalised, rather than piped, so that a free surface exists; secondly, the passage distance and 

time for fish from intake to screenwell is much reduced. Both types normally feature a 

forebay area, ahead of the screenwell, which introduces a storage volume into the system. 

The exclusion of fish, weed and other debris is normally achieved by at least two levels of 

screening. The primary coarse screens, or trash racks, are located at the most upstream 

point of the intake system and serve to exclude bulky items such as driftwood and barrels. 

The trash racks typically have bars spaced at ~ 10cm pitch. Smaller items, including fish, 

are removed by finer, mobile screens. The screen aperture is commonly ~ 1cm square, 

formed from woven stainless steel wire or punched stainless panels; Electricite de France 

have adopted finer (2-3mm aperture) woven plastic or wire mesh on some recently built 

stations. The characteristics and mesh size of the screening surface may have some bearing 

on fish damage, and will also determine the sizes of fish excluded. Turnpenny (1981) 

examined the relationship between mesh size and fish exclusion, and a summary of the 

findings for common inshore British species is given in Figure 2. Any small fish not 

retained by the mesh, including eggs and ichthyoplankton, will pass through the cooling 

system and be returned to the wild, though with variable survival prospects (Langford, 

1983). 

The mobile screens to which the fine mesh panels are attached are usually of the dmm or 

band type. Band screens comprise flat panels of screen mesh affixed to vertical belts in the 

manner of a 'caterpillar' track (Figure 3). The water is filtered from outside to in, fish and 

other debris becoming impinged on the inner vertical wall of mesh. The screens are 

continuously or intermittently rotated, so that the fouled surface is raised above water level 

and impinged materials fall by gravity onto ledges or scoops fitted horizontally along the 

bottom of each screen panel. Upon reaching a point close to the top of the rotation path, 

pressurised backwash jets (1-4 bar pressure) spray water through the screen, washing debris 

off into a collection trough or 'tundish', whence the flow of backwash water carries the 

material into a collecting pit lined with a mesh basket. 

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The principle of dmm screens (Figure 4) is similar to that of band screens, but here the mesh 

panels are affixed to a rigid dmm which rotates continuously. Photographs showing details 

of the dmm screen and backwash system at Fawley power station are included in the 

Appendix. 

A third type of fine screen which is less commonly used is the Detford strainer. It is a 

pressure strainer which comminutes the debris and passes it through the CW system. 

Strainers offer no opportunity for fish return. In Britain, strainer systems are fitted at Isle of 

Grain and Brad well power stations. 

At most power stations, chlorine, which is toxic to fish, is injected into the cooling water 

intakes close to the prim.ary screens. Its purpose is to prevent the accumulation of attached 

biofouling organisms (in the UK, principally the mussel, Mytilus edulis) which could 

otherwise reduce flow rate and damage heat exchangers (Whitehouse et a/., 1985). Where 

long inlet tunnels exist, additional injection points may be fitted at intervals along their length 

to compensate for chlorine decay. In France, chlorine is injected at a concentration of 1 mgl" 

'; in Britain, dosing is normally designed to achieve a concentration of 0.2 mg l"1 at the 

condenser inlet, which may require > 1 mg"1 at the injection point, especially for long inlet 

tunnels. Chlorine is usually applied only in the warmer seasons of active mussel growth 

(water temperature >9-10°C) . 

3. STRESS AND DAMAGE TO FISH CAUSED BY IMPINGEMENT 

3.1 Damage Symptoms of Impinged Fish 

There has been a number of investigations of damage suffered by fish as a result 

impingement on mobile dmm or band screens. The most relevant of these to Sizewell is the 

previously unreported study of fish damage symptoms observed by the author and colleagues 

at Fawley Power Station, Hampshire. This is reported in full in the Appendix. 

The study describes damage symptoms, including loss of scales, splitting of fins, 

haemorrhaging of eyes and fins, and protruding or bulging eyes. The species of fish 

examined were bass (Dicentrarchus labrax), herring (Clupea harengus), sprat (Sprattus 

sprattus), pollack (Pollachius pollachius), pout (Trisopterus luscus), whiting (Merlangius 

merlangus) and sand smelt (Atherina presbyter). No flatfish species were included in the 

study, owing to their scarcity in the catch at Fawley. 

Of the fish examined, over 90% exhibited signs of physical damage. The commonest 

symptoms were fin damage (splitting and/or haemorrhaging) and scale loss, though eye 

damage was also common (Table 1). These conditions are all potentially harmful to the fish, 

either through directly impaired function of the damaged part, or through consequential 

physiological disturbance or disease (see the Appendix for a fuller discussion). 

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The types of fish damage in the Fawley study can be described as contact injuries, caused 

by physical contact with the dmm screens, troughs and backwash system. Low pressure 

effects, which can lead to similar eye damage symptoms (Turnpenny, Davis, Fleming and 

Davies, unpublished data) can be mled out in this case, as the fish are at all times below a 

free atmospheric surface at Fawley. 

3.2 Post-Impingement Survival 

A few studies of the survival rates of marine or estuarine species in the period shortly after 

impingement have been reported, though no attempt was made to measure these in the 

Fawley study, due principally to the difficulty of obtaining good control data. This also is 

a shortcoming of some of the investigations in the literature, 

Clark and Brownwell (1973), from studies in the USA, refer to high rates of mortality, not 

immediately after impingement but after a delay of a few hours or more. They mention 

flounder (Pleuronectidae), along with "certain other bottom species" as being able to survive 

impingement where exposure time and other conditions are favourable. 

These findings are given more scientific substance in the environmental monitoring studies 

arising from the Calvert Cliffs nuclear station in Maryland, USA (Burton, 1976). Impinged 

fish were removed to laboratory aquaria and their survival monitored over a 96 h period 

post-impingement (Figure 5). As might be expected, delicate clupeiod species such as the 

anchovy (Anchoa sp.) and menhaden (Brevortia sp.) mostly died over this period, whereas 

the more robust littoral species such as the spot (Leiostomus sp.) and pipefishes (Syngnathus 

sp.) showed good survival. Unfortunately, this experiment was compromised by lack of 

control data using unimpinged fish, so that while high survival rates are meaningful, low 

survival rates must be regarded as unsubstantiated. 

A more rigorous analysis of impinged fish survival was conducted as part of the Hudson 

River (New York) power plant investigations (Muessig et al., 1988). These authors did use 

experimental controls and the findings they present are adjusted for control fish survival. 

Figure 6 gives a simplified representation of their findings for families of fish commonly 

present at UK power stations. This gives a clear picture of decreasing survival rate with the 

progression from littoral and epibenthic species such as the soles, through the demersal 

species such as bass and cod families, to the pelagic clupeids and anchovies. This 

progression concurs with the trend in physical robustness of the animals as befits their habits. 

The only surprise amongst these results is the apparent sensitivity of the eels, a family 

generally renowned for its tolerance of hostile environmental conditions. 

In France, Travade and Bordet (1982) monitored post-impingement survival of estuarine fish 

and shrimps at Le Blayais power station. They placed fish and shrimp species into five 

categories of resistance, as shown in Table 2, based on survival rates 24-h post-impingement. 

As is seen from Table 2, the findings are broadly consistent with those from the US studies, 

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though the high resistance attributed to eel in the French study is more credible. 

It should be noted that in the French study, the backwash jet pressure was 3.5 bar, compared 

with a typical pressure of — 1 bar on UK power stations. Travade and Bordet reported 

comparative trials of 3.5 bar versus 1 bar backwash pressure and showed that, whilst the 

sensitive species did not benefit, a higher proportion of the shrimps and 'resistant' fish 

species were enabled to survive. 

It is not made clear in any of these studies whether chlorine or alternative biocides were 

being applied at the time of the experiments. 

3.3 Physiological Stress 

Fish mortalities due to impingement, whether or not precipitated by physical injuries, are 

ultimately due to physiological stress. A number of possible contributory causes can be 

identified, including: 

exhaustion 

asphyxiation 

osmotic stress 

biocide toxicity 

pressure change 

Exhaustion 

Fish may spend long periods, hours or even days, swimming within the screenwell of a 

power station (Turnpenny and Utting, 1981) and as a result may be exhausted by the time 

that they are impinged. In physiological terms this signifies an accumulation of lactate in the 

blood, generating an oxygen debt. This oxygen debt may take up to 24 hours of resting to 

repay (Batty and Wardle, 1979), during which time the fish is unable attain maximum 

swimming performance and so is at increased risk of predation. It is not clear whether 

exhaustion per se is likely to cause death. 

It is noticeable that certain types of fish, particularly flatfish, make no visible attempt to 

swim once within a screenwell. This has also been noted by other workers (Clark and 

Brownell, 1973) and may contribute towards the higher survival of flatfish species. The 

same may be tme for other inshore epibenthic species, many of which have no sustained 

swimming ability (Turnpenny, 1988). 

The consequences of fish not resisting the flow by swimming may not be restricted to the 

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reduction of oxygen debt: protracted residence in the turbulent waters of a screenwell will 

undoubtedly increase the chance of contact injuries and, where biocides are present, will 

increase the exposure period. 

Asphyxiation 

Fish are likely only to become asphyxiated when they accumulate with other debris in trash 

baskets. On the screens themselves, concentrations of fish are rarely adequate to make 

asphyxiation possible. 

Osmotic Stress 

The osmotic concentration of fish blood lies somewhere between that of fresh and salt water, 

equivalent to about 15%o in herring (Clupea harengus), for example (Blaxter and Hunter, 

1982). Damage to the epithelium, and scale loss, break down the interface between these 

two media and can lead to osmotic dismption. In the author's experience with clupeids 

particularly, this is most serious in hypersaline conditions since osmotic water loss from the 

fish leads to dehydration. This can occur within less than one hour. It is normal practice 

at the Fawley laboratory, when seine netting for marine fish, to transfer them immediately 

after capture into half-strength sea water, where they are held for 24 hours before being 

returned to full-strength sea water. This period allows the majority to recover from 

superficial damage and restore osmoregulatory function. 

Hyposaline conditions can also jeopardize survival. In the Hudson River study, where the 

salinity range was 0.1 to 2 %o, Muessig et al. (1988) found fish survival to be increased at 

the higher salinity values in this range. Low temperatures, below 3°C, were also linked with 

high mortality rates due, the authors suggest, to impairment of osmotic function at low 

temperatures. 

Biocide Toxicity 

As chlorine is the chief form of biocide used at British power stations, discussion will be 

limited to chlorine. 

Typical values for the acute (24-48h) median lethal toxicity of chlorine are as follows 

(Emberton and Turnpenny, 1981): 

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Family LC50 (mg 1) 

Cyprinidae 0.03 - 0.23 

Salmonidae 0.05-0.13 

Pleuronectidae 0.03 - 0.25 

Gasterostidae 0.09-0.13 

Anguillidae 0.25 - 0.30 

These LC50s are well below the applied doses at most power stations and therefore, when 

chlorine is being applied, there is a severe risk of chlorine toxicity, especially for those 

species which extend their residence in the screenwells by swimming. It fortuitous that most 

of the fish are caught at times of the year when the CW tunnels are not chlorinated (see 

Figure 10), thus the conflict will occur only during the warmer months, when few fish are 

impinged. 

Pressure Change 

Pressure changes associated with the intakes of CW systems arise only in offshore intake 

systems, especially where deep tunnels are employed. In such systems, fish drawn in at 

intake level are subjected to pressure increase as they follow the descending limb of the 

intake, and pressure decrease as they rise towards the surface at the inshore end. Onshore 

intakes, having a surface free to the atmosphere, impose no such pressure changes on fish, 

though pump suction may draw fish down by a few metres within the screenwell itself. 

Depth, and hence pressure change are normal features of life to which fish are 

physiologically adapted (see Davies, 1988 review). An increase in depth of 10m is equivalent 

to approximately 1 atmosphere (1 bar) pressure increase. Much of the fish's body is fluid 

and thus will not suffer volume changes as a result of depth changes. However, the gases 

in the swimbladder ( a gas-filled stmcture which functions as a buoyancy controller and 

auditory resonator) will expand and contract with pressure decrease and increase, 

respectively. Gas content in the swimbladder can be adjusted either by secretion/ resorption 

by the blood, or by gulping or expelling gas via the gut. Gadid fish (cod family) and 

others, including bass (Dicentrarchus labrax), possess the former mechanism and are known 

as physoclists. Physoclists require long periods to adjust gas volume and rising fast in a 

water column may mpture the swimbladder. For example cod (Gadus morhua) and saithe 

(Pollachius virens) require five hours for swimbladder adjustment for every halving of 

hydrostatic pressure (Tytler and Blaxter, 1973). It has been shown experimentally that for 

shorter timescales than this, most physoclists can withstand up to a halving of the 

acclimation depth, but no more, before the swimbladder ruptures (Turnpenny, unpublished 

data). Physostomes, those species which regulate gas volume via the gut, can lose gas 

within seconds and depressurisation is less of a problem. Benthic species such as the 

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flatfishes possess no swimbladder and are thus not subject to this problem. Swimbladder 

damage will lead to immediate buoyancy control problems which will leave fish less 

manoeuvrable and possibly more vulnerable to predation. 

The risk of swimbladder damage for physoclists within offshore intake systems is not as great 

as might be expected, since although fish may be subjected to rapid ascent (up to 30m in 

30-40 s at some sites), they will have been exposed to a comparable pressure increase in the 

descending limb of the tunnel at the offshore end a few minutes previously. Over this period 

they will not have had time to adapt physiologically to the pressure change: thus, the 

swimbladder will be compressed on descent and will simply expand to its initial volume on 

reascent. 

An associated phenomenon has been described in herring (Blaxter and Hoss, 1979). In this 

species and other clupeids, the swimbladder is connected to the auditory bulla system via a 

gas duct. In fish of 12 to 15 cm in length, increasing the pressure rapidly from 1 to 3 bar 

(equivalent to 20 m depth increase) causes mpture of the pro-otic membrane within the bulla. 

Smaller fish are less sensitive to this effect, though larval herring of < 30 mm length may 

be at risk since the swim bladder has not yet been formed and hence they have no adaptive 

capacity. The function of the bulla is primarily auditory, though pressure discrimination may 

also be a function. 

Other forms of pressure-related damage are known amongst fish. Haemorrhaging of the 

eyes is frequently ascribed to pressure reduction effects (Davies, 1988), though our own 

studies at Fawley have indicated that mechanical damage is more commonly the cause and 

that this symptom caused by low pressure is only found under some of the more extreme 

conditions associated with passage through low-head hydroelectric turbines. It is unlikely 

to occur as a result of pressure changes of the range and speed found in CW intake systems. 

In conclusion, swimbladder damage is only likely to occur amongst physoclistous species, 

and then only where fish are taken from an initial water depth at the intake opening of 

greater than 5m (i.e., at a pressure of 0.5 bar above atmospheric) and brought up to the 

surface. Larval or adult clupeid fish may be risk of damage to the bulla system in cooling 

systems where the fish are drawn down 20m or more below intake level. 

4. OVERSEAS EXPERIENCE OF FISH RETURN SYSTEMS 

Various technologies have been incorporated into intakes and screening systems to reduce 

fish damage, and to improve the prospects for fish returned to the sea. Experience of marine 

systems has been gained mainly in the USA, by New England Power (NEP), Southern 

California Edison (SCE) and Battelle, and in France by Electricite" de France (E de F). Four 

systems will be described briefly: in-plant fish diversion schemes operated at San Onofre 

Nuclear Generating Station (SONGS), Southern California, and at Brayton Point, 

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Massachusetts; a fish return system operated in France at Le Blayais Power Station on the 

Gironde Estuary; finally, a freshwater fish recovery system at Hanford on the Columbia 

River. 

4.1 SONGS Fish Diversion System 

The SONGS fish return system (Love et al., 1987) accommodates a flow rate 52 mV1 taken 

from 1 km long offshore tunnels. The water enters a forebay and fish are guided by a 

system of concrete guide vanes (flow-straighteners) and plastic louvres. The guidance 

principle is based on fish avoidance of water turbulence generated by the louvre slats (see 

Turnpenny, 1988). The louvres themselves are fitted to a travelling b.and screen, so that they 

are self-cleaning. On encountering the louvres, fish swim along the face of them to a quiet 

zone, which is a concrete-lined basin measuring 4.9 m x 4 m. A fish lift, comprising a 

metal basket with a water-tight lower half and perforated upper half, is activated periodically. 

Upon reaching the upper limit of its travel the basket tips, spilling the fish into a sluice 

channel. Simultaneously, additional water flushes the channel, discharging the fish via a 

pipeline which enters the sea at 6 m depth, some 400 m offshore. 

Tests to examine the efficiency of the SONGS system show variable diversion capability. 

These have been reported regularly in annual environmental reviews of the plant's operation 

since 1984 (Southern California Edison Company, 1985 et seq.), and typically range from 

around 90% for the top species (eg. northern anchovy) to one-third for less responsive 

species (eg. queenfish). Annual averages for all species have been around 75% in good 

years, falling to 50% in less successful years. The reasons for this variability are not clear. 

Experiments have also been conducted to measure 96-h survival rates of returned fish, by 

placing an encircling net around the fish outfall. These survivals are extremely variable (no 

figures published), depending on species and size of fish and indicate that, overall, a rather 

small percentage of fish are able to survive 'rescue'. It is further noted by the researchers, 

that fish emerging from the outfall are often subject to heavy predation pressure by schools 

of predatory fish. The net benefits of the SONGS system are therefore not as high as the 

diversion efficiency figures would imply. 

4.2 Le Blayais Fish/Shrimp Return System 

The system operated by E de F at Le Blayais (Travade, 1982) is intended to cope primarily 

with shrimp return but is effective in reducing mortality of most fish caught, though not 

delicate species such as sprat, herring and shad. The system is a modification of standard 

dmm screen technology, and uses low pressure (1 bar) backwash jets to remove organisms, 

followed by a high pressure (3.5 bar) jet to remove more consolidated debris. The screens 

themselves are fitted with a fine mesh (2-3 mm) plastic mesh with helps to reduce 

impingement damage. 

A rotating trough edge also helps to reduce damage to fish. The troughs from each dmm 

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section feed via plastic-lined gulleys into a common discharge pipe from which the organisms 

are flushed back to the estuary. The system is apparently effective and easy to maintain. 

However, E de F biologists suspect (F. Travade, pers. comm.), from their observations at 

the outlet, that predation pressure from piscivorous birds and fish is high, .and thus the net 

benefit of the system is reduced. 

4.3 The NEP Brayton Point Angled Screen Fish Bypass System 

This study is described by Davis et al. (1988). The equipment was fitted to Unit 4 of the 

power station, which has a design flow of 17.3 mY1. The behavioural principle is similar 

to that of the SONGS system, in that band screens are used, aligned at an angle (25°) to the 

incoming flow, but in this system, there is no louvre assembly in front of the band screens. 

The fish are by-passed to a slot at the downstream end of the screens, where Hidrostal Model 

L12F 30 cm diameter screw-impeller centrifugal pumps are used, rather than a fish-lift, to 

return fish to the sea. 

In addition, the band-screens are fitted with buckets to maintain in water any fish that are 

impinged. These are then washed off with a "low-pressure" (details not supplied) backwash 

spray to a dedicated fish return pipe. 

The efficiency of the system has been evaluated and survival rates 48 h after handling 

measured. Diversion efficiency was 76%, though allowing for mortalities, only about one 

third of fish entering the system were returned live, via the diversion system back to the sea. 

This compares with about 20% expected survival for the return of impinged fish. 

4.4 Hanford Fish Return System 

This freshwater fish recovery system was investigated by Battelle (Page et al., 1979) at 

Hanford Generating Project (HGP) on the Columbia River. The system uses travelling band 

screens fitted with fish buckets. These are backwashed by first a low-pressure spray to 

remove fish, then a high pressure spray to remove debris. The system is therefore much the 

same as that used at Le Blayais, but adapted for band rather than dmm screens. Efforts were 

made to minimise screen penetration by fish, by using a fine screen mesh (3.2 mm aperture) 

and fitting sponge-rubber seals around the edges of the screen to prevent leakage. 

To measure the 96 h survival rates of fish recovered by the system, the fish were sluiced via 

a 15 cm PVC pipe to a swimming pool. Survival of salmon fry was 95%, with 'virtually 

no latent mortality'. Survival for all fish species (unspecified) was 85%. The authors make 

no comment about survival rates on returning fish to the wild. This aspect was apparently 

not investigated. 

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4.5 Summary of Fish Recovery Experience 

Although it has been shown that fish rescue systems can remove fish from water intakes with 

less damage than is caused by conventional trash screening equipment, the efficiency of such 

systems is open to question and in some cases lower than published findings suggest when 

additional mortality due to predation pressure on returned organisms is taken into account. 

Two basic types of fish return system can be distinguished: those which rely upon travelling 

dmm or band screens to remove the fish from the CW flow, and those which use by-passes 

to guide fish along the screen face to some form of fish lift. Of the two, the screen-based 

system is much the simpler, requiring little modification to conventional trash screening 

equipment. It is difficult to make useful comparisons of fish survivals between the two 

systems because of the different fish species involved in the studies reported. Comparative 

trials at Brayton Point indicate that the survivals are somewhat lower (20% versus 30%) with 

the screen-based system but the small increase in survival with the by-pass system would not 

appear to justify the greatly increased cost. 

With either type of system, net survivals of returned fish may be low, although some of the 

more robust species may survive well. 

5. DESIGN CRITERIA FOR A SCREEN-BASED FISH RETURN SYSTEM 

With the reported success of fish exclusion methods (acoustic detenent methods for example 

reportedly giving 60 to 100% fish diversion for relatively small capital investment: 

Loeffelman et ah, 1991), a cost-efficient approach would be to install primary protection of 

this type as the main line of defence, backed up by a screen-based fish return system. This 

would be based on conventional dmm or band screen equipment, from which the fish would 

be removed and returned to the wild via either the main CW discharge or a dedicated fish 

return channel. 

In this Section, the main elements and design criteria of such a low-cost fish return are 

described. The example used employs band screens but should work equally well with dmm 

screens, so long as they provide sufficient lift to create adequate fall on the fish return path. 

The design proposed also includes a rudimentary fish/trash separator, though if consents 

can be gained without providing this facility, the degree of fish handling will be reduced and 

fish are likely to be returned in a less damaged state. 

5.1 General layout 

A sketch of the general layout is given in Figure 7. The principle is as follows. Material 

(fish, other organisms, trash) is filtered by the band screens and falls into collecting buckets 

containing water at the bottom of each screen panel. On reaching the backwash point, this 

material is flushed out into hoppers feeding the trash return pipeline. The height to which 

the screens lift material and the height of the backwash hoppers is designed to allow gravity 

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fall of the material along the pipeline to the trash/fish separation pit. This material is 

conveyed in the backwash water, augmented by an additional carrier flow from a pumped 

supply to ensure good pipeline flushing. Additional lift can be provided, if necessary, using 

a fish pump. 

In this case, the CW discharge is used as the route for returning fish back to the estuary or 

sea (though see Section 6). The fish/trash separation pit is located alongside the CW 

discharge seal-pit. Water and material arriving from the bandscreens is discharged over a 

set of sloping tines, allowing coarse material to slide along the bars and into trash basket, 

which is hoisted out periodically for emptying. 

Smaller material drops through the tines and into the base of the pit with the water flow and 

is discharged into the adjacent seal pit. 

5.2 Screen Mesh 

Figure 2 shows screen mesh sizes required for the exclusion of various fish species and 

different sizes. 

The screen mesh size fitted to the dmm or band screens should be small enough to prevent 

'target' fish penetrating the mesh. For example, a mesh size of < 8 mm is required to 

exclude bass >50 mm length. 

Reduction of mesh size to 3-4 mm would help reduce fish damage further, but it should be 

noted that small mesh sizes will increase the risk of screen blockage, especially by 

ctenophores ('comb jellies'). This has been a frequent problem in France (F. Travade, pers. 

comm.), where small mesh sizes are used, but no problem in England and Wales, where an 

8-10 mm mesh size standard has been adopted. 

5.3 Fish Buckets and Backwash System 

Collecting troughs attached to the band screen face should be of the 'fish bucket' type 

(Figure 3). The requirements are that: (a) the troughs should retain water up to the point in 

the cycle where the organisms are flushed out; (b) the backwash jet pressure at the point of 

fish removal should be kept at or below 1.0 bar. The fish buckets should be constmcted of 

epoxy- or plastic-coated mild steel, to give both high strength .and low fish abrasion 

characteristics. 

5.4 Trash Hoppers and Fish Return Pipe 

There is a requirement to avoid abrasion of fish on the return pathway. This is best met by 

using smooth faced plastic pipework and gulleys of GRP or PVC constmction. A minimum 

internal diameter of 30 cm is recommended for the fish return pipeline. 

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Sharp bends in the return pipeline should be avoided. Experience elsewhere has shown that 

fish try to swim back upstream if they encounter turbulence. A minimum bend radius of 

3 m is recommended to avoid this problem. 

The volume of water used for fish return need not fully flood the pipeline but should 

maintain a minimum depth of 10 cm along its whole length. The use of a secondary pumped 

carrier supply to augment the backwash water supply is recommended. 

5.5 Fish/Trash Separation Pit and Discharge 

It is recommended that two such pits be provided to allow for uninterrupted function when 

trash baskets are removed for emptying. A suitable means of diverting flow from one to the 

other would then need to be provided. 

Fish/trash separating tines should be fixed at 10-15 cm centres (Figure 8). A 10 cm pitch 

will allow the majority of fish to fall through, though a 15 cm pitch would be required to 

allow larger flatfishes such as flounder to penetrate. Some experimentation may be required 

to achieve the optimum spacing. This, would, however increase the proportion of undesirable 

anthropogenic material being returned to the estuary. The provision of an optional solid 

cover that can be fitted over the tines is to be recommended, as a means of disabling the fish 

return system and allowing all material to enter the trash baskets. 

The slope of the tines should be around 15° to the horizontal (Figure 8). 

The discharge from the separation pits(s) should enter the CW discharge seal pit via an outlet 

in the side wall. This arrangement is preferable to direct injection into the outfall tunnel as 

it provides better access for removing blockages. The interior of the pit and the discharge 

pipeline should be coated or of plastic construction to minimise fish abrasion. Interior, 

vertical and horizontal comers should be rounded (minimum 30 cm radius) to ensure a 

smooth water flow. 

It may be necessary to elevate the base of the pit above deck level to prevent backing up of 

water from the seal pit on extreme high tides. This should be taken into account when 

calculating the required fall from the screen hoppers. 

5.6 Limitations of the Proposed Design 

It is envisaged that many of the fish returned from the screens will be dead or moribund and 

unlikely to recover upon return to the estuary. Nevertheless, it is expected that a large 

number of the more valuable species, including juvenile bass, eels, sole and other flatfish, 

as well as crustacean species, would survive return to the wild, at least when the system was 

not being chlorinated, making the scheme worthwhile. 

The effect of returning dead or moribund fish to the wild may be of concern. Floating fish 

attract predators, notably gulls (but also larger fish) which, in populated areas, can become 

a nuisance to local residents. However, it would be unusual for large quantities of fish to 

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be emerging from the discharge at any one time: the fish would emerge individually, at the 

same rate as they are becoming impinged. It would under these circumstances be a simple 

matter to disengage the fish return system and divert all the material to the trash baskets. 

The likelihood of dead fish becoming washed ashore and attracting public criticism is 

generally negligible, on account of natural predators and detritivores. 

5.7 Scope for Further Reducing Fish Damage 

Protracted residence of fish in screen wells is a major contributor to damage symptoms, 

especially for larger specimens of strongly-swimming species. It also increases physiological 

stresses associated with exhaustion or biocide toxicity, thereby putting the fish more at risk 

from predation upon being returned to the wild. 

In-plant fish by-pass systems help to reduce the residence time but, otherwise, designers of 

fish return systems seem to have paid no attention to this problem. 

There may be little scope for reducing the residence time of fish within screenwells but some 

experimentation could prove worthwhile. Possible experiments include: 

- use of pulsed electric fields to stun fish (health and safety implications may preclude 

this) 

- n.arcotization of fish by pulsed injection of, eg., carbon dioxide into the screenwells 

- exclusion of light from screenwells to confuse fish orientation. 

None of these appears to have been tested and simple experiments on an existing screenwell 

might quickly yield results. 

6 FISH RETURN PATHWAYS 

Two options exist for the return of fish and other organisms to the sea: they can be returned 

via a dedicated return pipeline or they can enter by the main cooling water discharge at the 

seal pit or surge shaft. 

6.1 Return via the CW Discharge 

The main reason for adopting this route would be to save on cost. Where it would be more 

costly to route material via the CW disch.arge than to constmct a dedicated return pipeline, 

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because for example of the length of the pipe mn, then a dedicated fish return discharge will 

always be preferable, owing to the potential physiological stress imposed by chlorine toxicity 

and/or elevated water temperature in the CW discharge. 

This Section examines the risks associated with biocide toxicity and thermal stress, by 

considering exposure levels and times in relation to dose-response data. 

Exposure Times within the CW Discharge 

Let us assume that the fish are to be discharged from the fish recovery system to the CW 

system via a seal pit or a similar chamber. The time of exposure to the CW effluent will 

comprise three elements; first, the time taken to leave the seal pit (tj); secondly, the transit 

time along the discharge culvert (t2); finally, the time taken for the fish to swim out of the 

plume (t3). 

The time, t, for the fish to leave the seal pit depends on the mixing characteristics of the 

water entering the pit with respect to the water contained in the pit, and whether or not the 

fish actively swim to maintain their position in the flow. Because the fish will tend to avoid 

being displaced downstream, a simple calculation of the dilution rate of the seal pit contents 

will not suffice and the question must be resolved empirically. The clearance of fish from 

screenwells offers a close analogy. From experiments carried out at Dungeness 'A' power 

station (AW H Turnpenny, unpublished data held in the FAWLEY arl Nuclear Electric 

Archive), it was shown that marked dead fish (adult sprat: Sprattus sprattus) were cleared 

at a rate of 60% in 8.5 minutes. It was estimated from exponential decay patterns which 

followed the entry of pulses of live sprats from the sea that live fish were cleared at a rate 

of 60% per hour, though some fish remained in the screenwells for up to five hours 

(Turnpenny and Utting, 1980). No data were obtained for other species, but it can be 

assumed that flatfish and other epibenthic species would be cleared at a rate somewhere 

between that of dead fish and that of live sprats. For the present purpose, the following 

average clearance rates (t,) will be assumed, assuming epibenthic fish and shrimps to resist 

impingement only slightly longer than dead fish: 

Pelagic and demersal fish t, = 60 min 

Epibenthic fish and shrimps; t, = 15 min. 

The transit time, t2, along the CW culvert, depends on the water velocity and length of 

culverts. It is assumed that in the absence of light, organisms will not orientate effectively 

in the tunnels and therefore will move, on average, at the .same rate as the water. Typically, 

at full CW discharge, design velocity is 2 m s1, reducing to half this at periods of reduced 

generating load. The length of the CW culverts range from perhaps 200 m to 1000 m, 

giving a range of values of tj from half to full load of approximately 2 to 17 minutes. At 

Sizewell 'A', for example, the culvert length is - 200 m, putting t2 in the range 2-4 

minutes. 

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The time, t3, taken for fish to swim out of the plume depends on their swimming speed 

relative to width of the plume. An order of magnitude estimate will suffice for this purpose. 

Assuming an average fish length of 10 cm and, conservatively, a steady swimming speed of 

1 body length per second (see Turnpenny, 1988), a fish would take 500 seconds to swim 

from the centre to edge of a 100 m plume, perpendicular to the plume axis. Since the fish 

may swim in any direction within the 180° sector, the average time to escape can be 

calculated using the average value of the sine of the angle between the fish and the plume 

between the fish and the plume for 0 to 180°, which is 0.64. Hence, the average time for 

the fish to exit the plume, assuming it swam in a straight line at any randomly-selected angle 

would be 500/0.64 = 780 seconds (13 minutes). A 100 m plume width is large compared 

with thermal plumes in flowing water conditions at most coastal sites, and this will be taken 

as the upper limit for the time that is likely to be spent by a fish in the plume. A 20 cm fish 

in a 10 m plume would, by the same calculation, spend 25 seconds in the plume, which will 

be taken as the lower limit. 

The sum of t, + t2 + t3 gives the overall exposure time, as follows 

Minimum Maximum 

^ (seal pit) 15 min 60 min 

tj (outlet tunnel) 2 min 17 min 

t3 (plume) 0.5 min 13 min 

Total time 17.5 min 90 min 

Chlorine Concentration 

Chlorine concentration (as total residual oxidant: TRO) at the seal pit can be expected to 

remain close to the 0.2 mgl"1 target concentration at the condensers. Typically, this would 

decline to around half this value or less within the first 100 m of the plume (Davies, 1992). 

Chlorine Dose-Response Curves 

Figure 9 summarises exposure times required for 50% mortality at different chlorine 

concentrations for a selection of eight marine and estuarine fish species. Also shown is the 

area enclosing chlorine and exposure time minima and maxima for typical CW discharges, 

as detailed earlier in this Section. 

It is shown that the exposure time and concentration envelope for CW discharges falls well 

below the acutely lethal zone for these fish species. It can be concluded from this 

information that the chlorine will not be acutely toxic to most fish during passage from the 

CW seal pit or surge shaft to the point of exit from the plume, under typical station design 

and operating conditions. 

It should be recalled that in the UK chlorination is normally limited to relatively low periods 

of fish impingement, when the water temperature is > 10°C. Figure 10 shows the monthly 

catch of impinged fish at Fawley power station over a 12 month period and the associated 

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seasonal temperature profile. During the period when chlorine would have been applied, in 

this case May to November, the catch represented only 13% of the annual catch. Typically 

at British stations, less than 20% of the annual impingement total is impinged during the 

chlorination period, so that for 80% of fish chlorine toxicity will not be an issue. 

Temperature in CW Discharges 

Temperature rises (At) at the CW discharge relative to the CW inlet at UK stations are 

generally in the range 8 to 12°C, occasionally reaching 15°C at some nuclear sites 

(Langford, 1990). This At is added to a seasonal temperature profile which, in British coastal 

waters, ranges from a mean winter temperature of 5 to 8°C to a mean summer temperature 

of 14 to 17°C (MAFF, 1981). Thus, the seasonal maximum discharge temperatures will 

normally fall within the range 13 to 20°C for winter and 22 to 29°C in summer. The 

seasonal profile shown in Figure 10 is typical of southern British waters. 

Fish Tolerance of Thermal Shock 

Thermal discharge effects on fish have been reviewed recently by Langford (1990). All fish 

can adapt, in time, to temperature change, though the capacity to adapt depends upon the 

rate of change and is bounded at high temperatures by the ultimate lethal temperature (ULT), 

beyond which no further adaptation is possible. Tolerance of temperature increase is related, 

first, to the temperature increase relative to the temperature to which the fish have been 

acclimatized and, secondly, to proximity to the ULT. 

Few fish species, either temperate or tropical, have ULTs above 38°C. For European 

species, ULTs range from 22 to 32°C in salmonids, to 33 to 42°C in non-salmonids 

(Alabaster and Lloyd, 1980). Thus, it is conceivable that discharge temperatures may reach 

the ULT for some salmomds, though not for non-salmonids. Thermal shock is therefore 

likely to be the main issue for most fish species. 

Despite the extensive literature on temperature effects on fish (Langford, 1990), there is 

surprisingly little coverage of UK marine and estuarine fish, and even less relating 

specifically to short term exposure. The little information which is available relates mainly 

to larval and juvenile fish exposed to combined temperature, chlorine and mechanical stress, 

and indicates high mortality of most species (GESAMP, 1984). Published information 

may, in any case, have little relevance to fish which have already been stressed by 

impingement and subsequent handling. 

In the absence of relevant thermal shock data, it would be advisable to conduct empirical 

trials with the species of interest, based on the At of the station in question and the computed 

exposure time. It would be preferable to conduct such trials using fish that have been 

impinged. 

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6.2 Dedicated Fish Return Pipes 

Adoption of a dedicated route for fish return obviates any problems associated with chlorine 

or thermal stress. The general design criteria are as set out in Section 5.4. 

The outfall from the fish return pipe should be located such as to minimise the chance of reentrapment. It should preferably be submerged at all states of tide but, if not, should be 

arranged so that it discharges into water rather than a drying area of sea bed. 

7 CONCLUSIONS 

7.1 Impingement of fish on cooling water intake screens causes a variety of externally 

visible injuries, ranging from scale loss, to more serious damage to eyes and fins.. These are 

mainly contact injuries. In species possessing a closed swimbladder (eg. cod family and 

bass), internal damage to this organ could result from pressure reductions associated with 

raising fish to the surface over a period of time which is too short to allow pressure 

adaptation. This is only likely when the intake opening is >5m below the water surface. 

Larval or adult clupeid fish may suffer d.amage to the auditory bulla system in offshore intake 

systems where the fish are drawn down 20 m or more below intake level. 

7.2 Impinged fish may also suffer physiological stress. This can be caused by exercise 

and exhaustion within the turbulent conditions of the screenwells of a power station, by 

osmotic imbalance resulting from dismption of the epithelid layer by abrasion and, during 

periods of biocide application, by the toxicity of the biocide. 

7.3 Survival of fish for periods of one to four days following impingement has been 

investigated in overseas studies and varies from zero to a hundred per cent, depending on 

species. Demersal and inshore epibenthic species (eg., flatfishes, bass) tend to be most 

resilient, whereas pelagic species (eg. clupeids, anchovies) are most delicate. The resilience 

of the demersal and epibenthic fish may be related to both physical robustness and the fact 

that they make little attempt to swim, once within the screen well, and are thus less subject 

to exhaustion and continued abrasion. 

7.4 In the USA and France, fish rescue/return systems have been developed to collect fish 

entering the CW intakes and return them to the wild. The simplest systems used collect fish 

following impingement on the screens and attempt to minimise further handling stress by 

careful design of the associated backwash and handling equipment. More sophisticated 

designs prevent impingement and guide fish to extraction areas where they can be pumped 

or lifted out prior to return to the wild. The success of the more elaborate systems is 

moderately good when measured in terms of numbers of fish diverted and returned (eg. 50 

to 75 % at San Onofre Nuclear Generating Station) but these figures do not take account of 

additional mortalities due to predation at the outfall, which may be high. It is doubtful 

whether any fish return system can hope to achieve >30% success rate overall, for all 

species. 

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7.5 Effective fish protection at water intakes requires attention first at the design and 

siting stage to ensure that areas of high fish concentration are avoided and that intake 

approach velocities are kept below the sustainable swimming speeds of the most important 

fish species; secondly, behavioural detenents (eg., based on sound, light or bubble stimuli) 

should be considered as a means of reducing fish entry into the intake; fish return systems 

offer a final level of protection. 

7.6 Design criteria for a simple screen-based fish return system are presented. This 

involves provision of fish buckets on the screens and careful design and choice of materials 

to minimise handling damage. Fish are lifted by means of the screens themselves, but 

additional lift may be provided if necessary by the use of screw-impeller fish pumps. A 

simple fish/trash separation pit is described, though it is recommended that this should not 

be used where fish survival is a priority, on account of the additional handling stress. 

7.7 The choice of return route for rescued fish- either via the CW discharge or via a 

dedicated fish return pipeline- depends partially on cost. Where a dedicated return line can 

be accomplished at or below the cost of routing fish into the CW discharge, this is always 

preferable, being free from thermal or biocide related stresses. For typical exposure times 

calculated for passage through CW discharges, including exit of the fish from the plume 

(range 17.5 to 90 minutes), chlorine toxicity is not likely to kill fish. The effects of thermal 

shock are less predictable and it is recommended that site-specific trials be performed to 

determine the effects of thermal stress on fish which have already been subjected to the 

stresses of impingement. 

7.8 There may scope for further reducing fish damage by reducing their residence time 

in screenwells. This might be accomplished by electrical stunning, narcotization (eg. with 

carbon dioxide) or by elimination of light from the screenwell to prevent effective 

orientation. Experimental trials would be required. 

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REFERENCES 

Alabaster, J S and Lloyd, R (1980). Water Quality Criteria for Freshwater Fish. 

Butterworths, London and Boston. 

Batty, R S & Wardle, C S (1979). Restoration of glycogen from lactic acid in the anaerobic 

swimming muscle of plaice Pleuronectes platessa L.. J. Fish Biol. 15, pp 509-519. 

Blaxter, J H S & Hunter, J R (1982). The biology of clupeoid fishes. Adv. mar. Biol 20, 

pp 3-223. 

Blaxter, J H S and Hoss, D E (1979). The effect of rapid change of hydrostatic pressure on 

the atlantic herring Clupea harengus L. II The response of the auditory bulla system 

in larvae in juvenile. J. Exp. Mar. Biol. Ecol. 41, pp 87-100. 

Burton, D T (1976). Impingement Studies II: Qualitative and quantitative survival estimates 

of impinged fish and crabs. In: Semi-annual Environmental Monitoring Report, 

Calvert Cliffs Nuclear Power Plant, Pacific Gas and Electric, March 1976. 

Clark, J and Brownwell, W (1973). Electric power plants in the coastal zone: environmental 

issues. Am. Littoral Soc, Spec. Publ., 7, American Littoral Society, Highlands, NJ 

07732, USA. 

Davies, J K (1988). A review of information relating to fish passage through turbines: 

implications to tidal power scheme. J. Fish. Biol. 33 (Suppl. A), pp 111-126. 

Davis, R A, Matousek, J A, Skelly, M J & Anerson, M R (1988). Biological evaluation of 

Brayton Point Station Unit 4 Angled Screen Intake, pp 3.23-3.42. In 'Proceedings: 

Fish Protection at Steam and Hydroelectric Power Plants'. Electric Power Research 

Institute. EPRI CS/EA/AP-5663-SR. 

Emberton, H and Turnpenny, AW H (1981). Toxicity of chlorinated sea water in relation 

to the culture of eels (Anguilla anguilla L.) in heated effluents. CEGB Report No. 

RD/L/2112N81. 

Langford, TE L (1983). Electricity Generations and the Ecology of Natural Waters. 

Liverpool, University Press, 342 pp. 

Langford, TE L (1990). Ecological Effects of Thermal Discharges. London, Elsevier, 468 

pp. 

Loeffelman, P H and Tamms, K M (1991). Environmental aspects and compliance costs of 

hydropower regulation. In: Proceedings of the Speciality Conference on Energy in 

the '90s. Sponsored by the Am. Soc. Civ. Engrs., pp 243-249. 

Love, M S, Sandhu, M, Stein, J, Herbinson, K T, Moore, R H, Mullins, M, and Stephens, 

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J S, Jr. (1987). Analyses of diversion efficiency and survivorship of the San Onofre 

Nuclear Generating Station fish return system. Unpublished report, Southern 

California Edison Co, Rosemead, USA. 

MAFF (1981). Atlas ofthe Seas around the British Isles. Ministry of Agriculture, Fisheries 

and Food, Lowestoft, NR33 OHT, England. 

Mattice, J S and Zittel, H E (1976). Site-specific evaluation of power plant chlorination. 

J.Wat. Pollut. Contr. Fed., 48(10), pp 2284-2308. 

Muessig, P H, Hutchinson, J B Jr, King, L R, Ligotino, R J .and Daley, M (1988). Survival 

of fishes after impingement on travelling screens at Hudson River power plants. Am. 

Fish. Soc. Mon. 4, pp 170-181. 

Page, T L, Gray, R H, Saroglia, GM & Bronzi, P (1978). Comparative fish impingement 

of Italian and United States Water Intakes: Proceedings of a Workshop. Battelle 

Pacific North West Laboratory, Report No. BN-SA-1040. 

Southern California Edison Company (1985 to 1991). San Onofre Nuclear Generating 

station: Marine Environmental Analysis and Interpretation. Report on 1985 Data. 

Report No. 85-RD-37. 1986 Data. Report No. 86-RD-31. 1987 Data. Report No. 

87-RD-31. 1988 Data. Report No. 88-RD-35. 1989 Data. Report No. 89-RD-ll. 

1990 Data. Report No. 90-RD-50. 1991 Data. Report No. 91-RD-10. 

Travade, F (1982). Survie des organismes entrained sur les filtres rotetifs de la Centrale du 

Blayais. Electricite de France, Report No. HE/31 - 82.04, ARD - E3A08. 

Travade, F and Bordet, F (1982). Etudes experimentales relatives aux entrainments 

d'organismes dans les prises d'eau de la Centrale du Blayais. Resultets de 1981 -

Perspectives. Electricite de France, Report No. HE/31-82.05, 17 pp. 

Travade, F, Bertrand Y and Coulon, G (1983). Etude comparative de deux systems de 

recuperation d'organisms entraines dans les prises d'eau de la centrale du Blayais. 

Electricite de France, Report No. HE/31.83.17, 32 pp + figures + plates + tables. 

Turnpenny, AW H (1981). An analysis of mesh sizes required for screening fishes at water 

intakes. Estuaries 4(4), pp 363-368. 

Turnpenny, A W H & Utting, N J (1981). Tidal factors in fish impingement, CEGB 

Internal Publication RD/L/2109/N8. 

Turnpenny, AW H (1988). The behaviourial basis of fish exclusion from coastal power 

station cooling water intakes. CEGB Research Report No. RD/L/3301/R88. 

Turnpenny, AW H (1988). Exclusion of salmonid fish from water intakes. CEGB 

Research Report No. RD/L/3371/R88. 

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Tytler, P, Blaxter, J H S (1973). Adaption by cod and saithe to pressure changes. Neth. 

J. Sea Res. 7, pp 31-45. 

Whitehouse, J W, Khdanski, M, Saroglia, M G and Jenner, H A (1985). Marine Fouling 

and Power Stations. A collaborative Research Working Group Report, CEGB, EDF, 

ENEL, KEMA. 

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Table 1 Percentage of Each Fish Species Exhibiting Different Damage Symptoms 

following Impingement on Fawley Power Station Screens. 

Species 

Bass 

Herring 

Sprat 

Pollack 

Pout 

Whiting 

Sand smelt 

Scale Loss 

35 

80 

91 

52 

58 

41 

15 

Eye Haemonhage 

0 

60 

28 

33 

16 

11 

47 

Bulging 

Eye 

0 

7 

4 

17 

13 

0 

7 

Fin Damage 

94 

89 

100 

83 

87 

100 

99 

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Table 2 Post-Impingement Survival Rates Recorded for Various Species at Le Blayais 

Power Station on the Gironde Estu.ary (Travade and Bordet (1982). 

Damage Resistance 

Very resistant species 

Resistant species 

Less resistant species 

Sensitive species 

Very sensitive species 

24-hour Survival 

100% 

60-80% 

50% 

10% 

0% 

Species 

Eel, adult 

flounder,lamprey,bass 

Juvenile flounder, sole, adult 

mullet, stickleback 

Palaemon longirostris, 

Crangon crangon 

Gobies 

Shad, sprat, herring, 

anchovy, smelt, juvenile 

mullet, juvenile pipefishes 

FAWLEY aquatic research laboratories Ltd 
FIGURE 1 Comparison of the Main Features of Offshore 

and Onshore Intake Systems (Sectional views) 

(a) Offshore Intake 

Water Surface 

Intake Structure 

Coarse Screen 

Descending 

Limb 

/ Sea Bed 

CW Inlet Tunnel 

Forebay 

i Ascending 

Limb 

(b) Onshore Intake 

Water Surface 

Sea Bed 

Water 

Intake 

Forebay 

Coarse ScreenIco 
P.31 

SCREEN MESH SIZE - mm 

Fig. 2 Square screen mesh apertures required for excluding fish 

of different species and sizes. 
P.32 

Low pressure 

fish washing 

system 

Figure 3 Sectional View of A Band Screen Fitted with 

Fish Buckets 
P.33 

SPRAY 

TRANSVERSE TROUGH 

CHANNEL TO 

^TRASH PITS 

(FROM DRG. SPG/F2 105) OF DRUM SCR 

Figure 4 Sectional View of a Drum Screen 
P.34 

Figure 5 Survival of North American 

Fish Species Following Impingement 

(After Burton, 1976) 

100 

CO 80 

> 

c/) 

^ 60 

CD 

> 

.S3 

E 

o 

40 

20 

\ 

\ 

•X-

\ 

\ 

\ 

J T ~--h ~ 4-- L. 

0 10 20 30 40 50 60 70 80 90 100 

Hours after Impingement 

Trinectes maculatus -Syngnathus fuscus 

Leiostomus xanthurus Anchoa mitchilli 
Fish Return Systems 

Figure 6 Summary of Post-Impingement Survival Rate Findings in Hudson 

River Studies (after Muessig et al., 1988) 

Percent of Fish Alive "96 h post-Impingement 

Family Common Name <10 % 10-50 % 51-80 % >80 % 

Soleidae Soles ' r. ' * JJJ.t Sf $<•£ * rn. 

~ ' l" \ Cr .*' 

Gasterostidae Sticklebacks 

JfffJ 

Gadidae Cod, etc - < it&jg&y 

Syngnathidae Pipefishes 

Percichthyidae Striped bass 

Osmeridae Smelts 

4

 "%\ ^ fSU $1. g£r 

Anguillidae Eels %»* 

Clupeidae Herrings 

Engraulidae Anchovies WWSWffifffWWfJWvi 

Note: shaded areas represent the survival class into which the majority of observation! 

FAWLEY aquatic research laboratories Ltd 
Band 

screen Backwash trough 

Fish/trash separating pit. 

Distance a » height above deck of backwash trough, 

sufficient to provide adequate fall to fish/trash separating pit. 

C.W. discharge 

seal pit 

M i l 

Figure 7 General Arrangement of Fish Return 

System 
P.37 

Plan view 

r. 

From band 

p^ screens 

From band screens 

Figure 8 A Simple Fish/Trash Separation Pit 
FIGURE 9 Chlorine Toxicity to Marine Fish 

in relation to dose and time in CW discharges 

(Dose/time for 50% mortality) 

Legend 

1. Atherinidae 

2. Anguilla anguilla 16C 

3. Anguilla anguilla 23C 

4. Solea solea 12-14C 

5. Pleuronectes platessa 16-17C 

6. Gasterostidae 

7. Percichthyidae 

8. Clupeidae 

9. Salmonidae 

Exposure Time (hours) 

100 

50 

20 

10 

References 

2 & 3: Emberton & Turnpenny, 1981 

4&5 : Alderson, 1974 2 

Others: Mattice & Zttel, 1976 

1 

0.5 

0.2 

0.1 

Dose-time area 

for CW discharge 

S 

0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 

Chlorine Concentration (mg/L TRO) 

10 

(Test temperature shown, where available) 
FIGURE 10 Seasonal Fish Catch on Fawley Power Station 

Screens in Relation to Water Temperature 

i 

Number of Fish per Month Temperature C 

200,000 

150,000 

100,000 

50,000 

0 

cd 

=3 

C 

cd 

(data from Turnpenny, 1983) 

— 

Nominal Chlorination Period: Contains 13% of Fish Catch 

% 

V 

uary 

n o 

arch 

5 

April 

% 

^ 

June 

July 

gust 

< 

Month 

CD 

.Q 

E 

OD 

Q. 

CD 

tt 

CD 

XJ 

O 

+-1 

o O 

CD 

n E 

CD 

> O 

z 

CD 

n E 

CD 

O 

CD 

D 

20 

15 

10 

- 5 

0 
P.40 

Al.l 

Al INTRODUCTION 

A five month study was undertaken at Fawley Power Station, Hampshire, to investigate and classify the types 

of injuries sustained by several species of fish commonly occurring on the screens. 

This study was carried out in 1987 but has not been reported previously. 

A2 DESCRIPTION OF THE FAWLEY POWER STATION 

The 2000 MWe oil-fired power station at Fawley is situated at the south-western extremity of Southampton 

Water. It uses a maximum of 63m3s"' of cooling water taken from a 900m long dredged channel connected to 

the main body of Southampton Water (Figure Al). 

The cooling water is screened before entering the condenser system, by coarse vertical bars to prevent the entry 

of large objects, and then by fine rotating drum screens with a 9.5mm sqirare mesh (Plates 1 and 2). 

As the screen rotates, fish, weed and debris are caught on steel ledges (Plate 3) and are lifted out of the water. 

Water jets (Plate 4) wash the screen and the debris falls about lm into a transverse metal trough (Plate 5). The 

wash water carries the debris to the end of the trough to a drop of 50cm into a concrete channel (Plates 6 and 

7), at the end of which it falls a further 80cm into a steel basket 1.5m (Plate 8 and 9). These baskets are 

emptied periodically, typically once every eight hours, and debris removed to a landfill site. 

A3 METHODS 

As maximum numbers of fish are caught on the intake screens at or just before low water (Turnpenny and 

Utting, 1981) samples were taken during this period. 

A Nedon ® collecting basket was placed in to the concrete channel just before the trash basket. This enabled 

the fish to be coUected easUy .and ensured the sample was fresh. The entire flow went through the b.asket. 

When the retained material impeded the flow of water the basket w.as removed and the fish extracted. The 

material was returned to the laboratory in water, where specimens of b.ass, Dicentrarchus labrax (L) (Plate 10), 

herring, Clupea harengus (L) (Plate 11), poUock, PoUachius poUachius (L) (Plate 12), pout, Trisopterus luscus 

(L) (Plate 13), sand smelt Atherina presbyter (Plate 14), sprat, Sprattus sprattus, and whiting, Merlangius 

merlangus (L) (Plate 15), were removed for examination. 

These are amongst the commonest species recorded at Fawley (Holmes, 1975). 

Each fish was identified, measured in standard length (SL) aad examined for damage. After preliminiary 

examination the foUowing categories were used, b.ased on categories recogni.sed by DadsweU, Rulif-son and 

Dabom (1986), in studies of fish passage through hydro-electric turbines: 

Scale loss - determined as the percentage of scales missing from the left body side of the fish and 

assessed visuaUy. It was also assessed separately for the five areas shown in Figure A2. 

Fin damage 

i haemorrhage - the presence of blood in the fin membrane; 

ii split - the break of the fin membrane; 

iii short - the absence of aU or part of the fin. 

The.se were recorded as zero, light, moderate or severe, depending on the degree of damage. 
P.41 

A1.2 

Eye damage 

i 'red eye' - the presence of haemorrhaging within the eye; 

ii 'pop eye' - bulging of the eye. 

The damage was recorded on a record sheet (Plate 12). 

A4 RESULTS 

Scale Loss 

AU the species showed scale loss to varying degrees as shown in Table Al. The clupeid species, herring .and 

sprat were more susceptible to loss of scales than the other .species studied. Sand smelt was the species of which 

fewest individuals shed scales. 

For aU the species, area 5 (the region containing the lateral line) showed the greatest degree of loss, although 

the other areas had significant loss (Table A2 and Figure A2). 

Eye Damage 

Herring and sand smelt were the two species most susceptible to eye haemorrhage (Plate 16). Bass, whiting 

and pout were the least affected (Table A3). 

Bulging eyes were not common .amongst the fish studied, (Plate 17, Table A4). 

Pout, poUock and bass aU suffered some fin haemorrhage, with the greatest damage being in pout. The caudal 

and pectoral fins were most vulnerable in pout and poUock, .and the pectoral .and pelvic fins in bass. Whiting 

only suffered haemorrhage in the caudal and pectoral fins, while .ssmd smelt and herring had Uttle haemorrhaging 

and sprat were not affected at aU, (Table A6 and Figure A4 - Plate 18). 

The spUtting of the fin membrane is the major symptom of damage to the fins. All the species had a significant 

incidence of spht fins (Plate 18), .although pout, poUock and whiting had a little .damage to the pectoral, pelvic 

and .anal fins (Table A7 and Figure A5). 

A smaU percentage of bass, herring, pout and sand smelt suffered loss of aU or part of any of their fins, (Table 

A8, Plate 10). 

A5 DISCUSSION 

Scale Loss 

Scale loss occurs naturaUy in fish as a result of abrasion of the body .surface againrf the substratum and sohd 

objects. One consequence is the destruction of the integrity of the epithehum causing disruption of essential 

osmotic differentiation between fish body fluids and their environment. However, provided the area affected 

is not krge, scales rapidly regenerate. For ex.ample up to 73% (Tesch, 1956) of the .scales of brown trout 

(Salmo trutta) may be replacement scales. Kostecki and Kynard (1982) found that scale loss was a significant 

factor in latent mortahty of salmon smolts and clupeids due to ionic/osmotic imbalance. 

Scales can be lost by mechanical abrasion in any part of the impingement process, although the major cause of 

scale loss wiU be contact with the drum screens. Area 5, containing the lateral line, is more susceptible to 

abrasion, probably due to the overaU shape of the fish and the lateral line area protruding. 

Sand smelt have a pelagic habit similar to herring and .sprat; however, they do move inshore into shaUow 
P.42 

A1.3 

waterto breed, where they are likely to suffer abrasion. This may be the reason for the tougher coating of scales 

found in this species. 

Eye Damage 

There appears to be no record of natural occurrence of eye damage such as seen at the power station intake. 

However, there have been observations of bulging eyes in trawl samples and bulging and haemorrhaged eyes 

at turbine sites (Cramer and OUgher, 1964). Although it was thought previously that these were symptoms of 

pressure damage, recent experiments carried out at Fawley on a wide range of fish species involving controUed 

pressure changes have shown that eye damage from this cause is rare. It seems likely that most damage found 

is caused by abrasion and contact with sohd objects. 

The consequences of eye damage have not been investigated but it may be surmised that eye damage wiU impair 

the food searching abUity of fish and the risk of predation, owing to the inability to detect predators. 

There is some evidence that minor corneal abrasions in fish will heal (Ubels and Edelhauser, 1982-83). 

Fin Damage 

Fin damage occurs naturaUy in fish, caused by fin-rot or attack by other fish (Abbot and DiU, 1985; Abbot, 

Dunbrack and Orr, 1985). The immediate consequences wiU include impairment of mobihty and stability . 

Once the fins are damaged, the fish are more susceptible to dise^e and fung.al attack leading to fin-rot. 

REFERENCES 

Abbott J C & DUI L M (1985). Patterns of aggressive attack in juvenile steelhead trout (Salmo gairdneri). 

Can. J. Fish Aquat. Sci., 42 (11), 1703-1706. 

Abbott J C; Dunbrack R L & Orr C D (1985). The interaction of size and experience in dominance 

relationships of juvenile steelhead trout (Salmo gairdneri). Behaviour, 92 (3-4), 241-253. 

Cramer F K & OUgher R C (1964). Passing fish through hydrauUc turbines. Trans. Am. Fish. Soc., 93 pp 

243-259. 

DadsweU M J, Rulifson R A & Daborn G R (1986). Potential Impact of Large-scale Tidal Power 

Developments in the Upper Bay of Fundy on Fisheries Resources of the Northwest Atlantic Fisheries, 

Vol. II, No. 4, pp 26-35. 

Haven K F & Ginn T C (1977). A mathematical model of the interactions of an aquatic ecosystem .and a 

thernral power station cooling system, pp 321-342 In: Jen.sen L D, Ed., Fourth Nation^ Workshop on 

Entrainment and Impingement., Ecolocigical Analysts Inc., MelviUe, NY. 

Holmes RH A (1975). Fish and Weed on Fawley Generating Station Screens. CERL No. RD/L/N129/75. 

Kostecki P & Kynard B (1982). Potential effects of scale loss on mortaUty of Atlantic Salmon smolts and 

juvemle clupeids, hr. Knapp W E, Kynard B (Eds) Potential effects of Kaplan, Ossberger and Bulb 

Turbines on Anadromous Fishes of the Northe^t United States (US Fish & WUdlife Service, Newton 

Corner, Massachusets. 

Tesch F W, (1956). Uber Unterschiede in der Haufigkeit des Auftrertens von regenerierten Schuppes bei der 

BachfereUe (Salmo trutta fario L.) unter verschiedenen unweltverhaltaissen. Biol. 
P.43 

A1.4 

Travade F (1981). Survie des Organismes Entraines sur les FUtres Rotatifs de la Centrale du Blayais. 

Electricite de France, HE/31-82.04, ARD-E 3 A 08. 

Turnpenny A W H & Utting N J (1981). Tidal factors in fish impingement, CERL No. RD/L/2109N81. 

Turnpenny AW H (1983). Swimming performance of juvenUe sprat, (Sprattus sprattus L), and herring, 

(Clupea harengus L) at different .salinities. J. Fish Biol., 23 pp 321-325. 

Ubels J L & EdeUiauser H F (1982). Healing of corneal epithehd wounds in marine .and freshwater fish. 

Curr.Eye Res. 2(9) 613-620. 
P.44 

APPENDIX 

Investigations of Fish Damage Symptoms on Fawley Power Station Screens 

CONTENTS 

Al 

A2 

A3 

A4 

A5 

Introduction 

Description of the 

Methods 

Results 

Discussion 

References 

Tables 

Figures 

Plates 

Fawley power station cooling water intake system 

1 - 8 

1 - 5 

1 - 19 
P.45 

Table A1 

Bass 

Herring 

Pollock 

Pout 

Sand Smelt 

Sprat 

Whiting 

Average Percentage of Fish 

with Scale Loss (%) 

35.2 

80.3 

5 2 

58.8 

14.5 

91.3 

41.4 

Number of Fish 

Examined 

18 

100 

12 

100 

67 

27 

9 

Table A 2 

Bass 

Herring 

Pollock 

Pout 

Sand Smelt 

Sprat 

Whitina 

Percentage of Fish with Scale Loss 

Areas of Scale Loss 

1 2 3 

55 

89 

67 

66 

7 

9 2 

44 

27 

86 

67 

73 

10 

96 

55 

33 

89 

42 

62 

25 

100 

44 

4 

44 

90 

50 

67 

20 

100 

55 

5 

88 

100 

67 

94 

71 

100 

77 

Number of Fish 

Examined 

18 

100 

12 

100 

67 

27 

9 

Table A 3 

Bass 

Herring 

Pollock 

Pout 

Sand Smelt 

Sprat 

Whitina 

Percentage of Fish with Red-Eye 

Numbtt of Red-Eye 

0 

100 

40 

67 

84 

53 

72 

89 

1 

33 

17 

11 

38 

12 

11 

2 

27 

16 

5 

9 

16 

0 

Num .ber of Fish 

Examined 

18 

100 

12 

100 

67 

27 

9 

FAWLEY aquatic research laboratories Ltd 
P.46 

Table A4 

Bass 

Herring 

Pollock 

Pout 

Sand smell 

Sprat 

Whitinq 

Percentage of Rsh with Bulging-Eye 

Number of Bulging-Eye 

0 

100 

93 

83 

87 

93 

96 

100 

1 

0 

5 

17 

9 

5 

4 

0 

2 

0 

2 

0 

4 

2 

0 

0 

Number of Rsh 

Examined 

18 

100 

12 

100 

67 

27 

9 

Table A5 

Bass 

Herring 

Pollock 

Pout 

Sand smelt 

Sprat 

Whiting 

Percentage of Rsh with som 

form of Fin Damage (%) 

94.4 

89 

83 

87 

98.5 

100 

100 

Number of Fish 

Examined 

1 8 

100 

12 

100 

67 

27 

9 

Table A6 

Bass 

Herring 

Pollock 

Pout 

Sand smelt 

Sprat 

Whiting 

Percentage of Fish with Haemorrhaged Fins (%) 

Dorsal Caudal Pectoral Pelvic Anal 

6 

0 

8 

9 

0 

0 

0 

11 

1 

33 

69 

1 

0 

33 

28 

4 

33 

45 

1 

11 

28 

0 

17 

.9 

0 

0 

0 

6 

1 

8 

20 

0 

0 

0 

Mumber of Rsi 

Examined 

18 

100 

12 

100 

67 

27 

9 

FAWLEY aquatic reserach laboratories Ltd 
P.47 

Table A7 

Species 

Bass 

Herring 

Pollock 

Pout 

Sand smell 

Sprat 

Whiting 

Percentage of Fish with Split Fins 

Dorsal 

39 

64 

50 

39 

49 

88 

67 

Caudal 

67 

51 

50 

47 

75 

72 

78 

Pectoral 

33 

56 

8 

18 

75 

64 

0 

Pelvic 

28 

60 

8 

64 

76 

11 

[Anal 

33 

65 

8 

8 

46 

80 

12 

Number of Fish 

Examined 

18 

100 

12 

100 

67 

27 

9 

Table A8 

Species 

Bass 

Herring 

Pollock 

Sand smell 

Sprat 

Whiting 

Percentage of fish with Sortened Rns 

Dorsal 

0 

5 

0 

3 

0 

0 

Caudal 

0 

1 

0 

6 

0 

0 

Pectoral 

0 

0 

0 

4 

0 

0 

Pelvic 

6 

0 

0 

2 

0 

0 

Anal 

12 

0 

0 

0 

0 

0 

Number of Fish 

Examined 

18 

100 

12 

67 

27 

9 

FAWLEY aquatic research laboratories Ltd 
P.48 

•V:?] SALT MARSH 

"(OO IcV 

SUBSTATION 

POWER 

STATION 

2 3 LAND 

CHIMNEY 

.A 

COASTGUARD 

TOWER 

FIG. 1 MAP OF FAWLEY POWER STATION INTAKE AREA 
P.49 

Pout 

\ 

Fig. 2. , Pout, Trxsopterus luscus, showing the 5 area 

s assessed for scale loss, 
P.50 

Percent 

100 

50 

O . 

Herring 

Jn,. lin ll ,II...IIII,„ in m 4 

Pollock 

Percent 

.Sand smelt 

Sprat 

loo 

Whiting 

,

*'l'^r|.t^.»,•,•,•,•.•r•^•. .,*,.,•.•,•.•,• • 

!

,K,4l4,4,4W.|.;,;4;>K>x,,v,;.v s 

' Wfiia^- M I I.', f .f4'*!4.'4V. 4 4 i.C|. 

Fig. 3 Amalgamated histograms for the percentage of fish with scale loss, 

showing area 1 (heavy stippling), area 2 (diagonal shading),area 3 

(horizontal shading), area 4 (light stippling) and area 5 (vertical 

shading). 
P.51 

Percent ^Q O 

50 

Dorsal Caudal Pectoral Pelvic Anal 

piiLimiiiiiiiipiiiil 

pin 

Percent IOO 

50 

0 t— 

Bass 

Herring 

Pollock 

Pout 

Sand smelt 

Sprat 

Whiting 

Pig. 'i '< TVmalgarnated histograms for the percentage of haemorrhaged fins, 

showing dorsal fin (vertical shading), caudal fin (light stippling), 

pectoral fin (horizontal shading), pelvic fin (diagonal shading), 

and anal fin (heavy stippling). 
Percent 

100 

Dorsal Caudal Pectora l Pelvi c 

P.52 

Anal 

Bass 

50 

„! j ",'„in!hii 'I, 

"||, ,1 ' l i 

' I ' I 

mm U !i 

li'VWi'iy 

fwVJ J'"1 I'll 

100 

50 

^M , 

rann 

IP 11 ,nii 11

 h. 

JL 

1 

11,1; 

"i, ' 'i 1, ' hi i, 

i ii'l |':i < in i 

, "11 1 n,i , ii"' ' 

Percent 

Herring 

Pollock 

SSSSSS^SSSSSSSMSa 

Pout 

Sand smelt 

Sprat 

Whiting 

^^^^^^PgJP^^J ^ 

Fig. 5 Amalgamated histograms for the percentage of split fins showing 

dorsal fin (vertical shading), caudal fin (light stippling), pectoral 

fin (horizontal shading), pelvic fin (diagonal shading) and anal fin 

(heavy stippling). 
P.53 

Plate 1. Fawley Power Station drum screens. 
P.54 

Plate 2. Drum screen mesh (^ metre rule for scale). 
P.55 

Plate 3. D.rum screen steel ledges. 
P.56 

Plate I4. High pressure jet wash. 
P.57 

•afe^iaj*.. vi> 

Plate 5- Transverse metal trough (^ metre rule for scale). 
P.58 

Plate 6. Drop from the metal trough into the concrete channel. 
P.59 

Plate 7. Concrete channel (-J metre rule for scale) 
P.60 

Plate 8. Metal basket (J metre rule for scale). 
P.61 

Plate 9. Raised metal basket. 
Bass 

P.62 

miiflrHi!!! Ihl 

100'rfm.'no 120 

IIII 

0 

Plate 10. Bass, Dicentrarchus labrax. 

Herring 

5I0 6I0 7lO 8lb O 9lO T ioo. 

Plate 11. Herring, Clupea harengus, 
P.63 

Plate 12. Pollock, Pollachius pollachius, on a record sheet. 

Pout 

]|]!![l!llll!|ini|llll|lill|iiiniHUiHiiiiii|ii|i||H^ 

ido-Jm iio do i • wo ITO 260 

Plate 13« Pout, Trisopterus luscus. 
P.64 

Sandsmelt 

m 

K>'**lf0 120 130 140 150 160 170 180 

' ^ % • . 1 

Plate 1^. Sand smelt, Atherina boyeri. 

Plate 15. Whiting, Merlangius merlangus. 
P.65 

Plate 16. A specimen of herring, Clupea harengus. showing 'red eye1. 

Plate 17. A specimen of pout, Trisopterus luscus. showing 'pop eye'. 
Pout 

P.66_ 

• * 

Plate 18. A specimen of pout, Trisopterus luscus. showing haemorrhage and 

splitting of the caudal fin. 

y V2mm lb 20 30 40 

Plate 19. A specimen of whiting, Merlangius merlangus, showing splitting 

of the caudal fin.