Design and Testing Specification for a Fish Deterrent 

Bubble Barrier for Heysham Power Stations 1 & 2 

AWH Turnpenny 

& 

PA Henderson 

Client: Mr KS White, Station Mhnager, Heysham 2 Power 

Station 

Report No. FCR006192 

March 1992 

Approve Turnpenny (Managing Director) 

Date:..................... \.r&d@& IQGi2,
SUMMARY 

This Report reviews expedence elsewhere of the use of bubble curtain barriers for 

fisheries applicationsand, in particular, their suitabilityfor excluding fish from water 

intakes. The use of augmentary stimuli, such as underwater strobe lights and sound 

generating systems, aimed at enhancing the effectveness of bubble barriers for fish 

exclusion, is also discussed. 

The Report then provides a specificationfor the design and testing of a fish protection 

barrier system for Heysham Power Stations 1 and 2. 

CONCLUSIONS AND RECOMMENDATIONS 

Bubble Curtains and Augmenting Stimuli 

0 Bubble curtains have been used effectively as fish barriers under certain 

conditions. 

0 For fish protection at water intakes, it is advantageous to angle the barrier 

relative to the flow, so that fish are guided to a safe area at one end of the 

barrier. 

0 Bubble barriers rely primarily on a visual response by fish and so are more 

effectivein daylight. Strobe light systems can be used effectively to improve 

the over day and night, but are likely to be impractical at Heysham due to 

frequent (weekly) inspection and maintenance requirements. 

Vnderwater sound offers a more promising augmentary stimulus, with high 

system reliability and low maintenance costs for a well designed system. 

Combined with a bubble barrier, it should be possible to achieve high 

diversion efficiencies with well-controlled sound distribution. 

Bubble Barrier Design Parameters 

The recommended design parameters for the bubble barrier are as follows: 

barrier line: curved, as shown in Figure 3 

0 barrier length........................ 75m 

0 bubble tube internal diameter.........50rnm 

0 bubble outlet hole size...............0.38mm

0 hole pitch........................... .50mm 

0 

0 air demand............................ 1.5m3min-' 

operating pressure.. ..................276Wa (switch-on), 414Wa (switch-off) 

8 

0 

e 

0 

bubble tube material: semi rigid PVC or alhathene 

delivery tube material: spirally-reinforced PVC hose 

seabed attachment: steel chain and cable ties 

bubble tube purging: via a gate valve attached to the end away from the 
compressor, out of the water 

augmentary stimuli: acoustic, by low frequency (<1OOHz) modulation of the 

air supply, or using an array of electromagnetictransducers behind the bubble 

barrier, fed from an onshore signal generator/amplifier system. 

Experimental Design and Statistics 

The bubble curtain experiment should be undertaken over a minimum twelve 

day period in the months of October or November. 

Tidal and operational conditions permitting, the best period would be the last 

week of October and the first week of November. Once sampling has 

commenced it should be undertaken on consecutive days. This will require 

week-end work. 

It is recommended that two working days be assigned at the beginning of the 

experimentalperiod duringwhich the samplingequipmentwill be installed and 

working methods defined. 

It is recommended that chlorination of the screenwells at an applied dose of 

OSppm should be undertaken for a period of 2-3 hours prior to each trial 

period, to minimisethe adverse effects of fish storageon interpretation of the 

test results. Sodium hypochloritedosing would be adequate for this, if normal 

station chlorination has been suspended. 

To add an augmentary sound stimulus, a second, similar period of testing 

would be required, in which the sound system and the bubble curtain were 

operated simultaneously, again with alternatingdays of operation. This would 

be necessary to ensure that one or other system was not redundant. Ideally, 

a third twelve day period would be used to operate the sound system without 

the bubble barrier, unless it were already decided that a bubble barrier would 

be operated there for other reasons. 

Any trials using a sound system would require an initial survey and a 

minimum of two weeks prior to the trials for installation and testing. A 

temporary system could be installed for the period of the trials only, using 

FAWLEY arl Ud’s mobile fish deterrent caravan. 

There is no requirement for the inner barriers (shown as 2 & 3 on Figure Al) 

to be installed or operational during trials with the outer barrier. It is, 

however, important that operating conditions should be maintained in a 

constant state during the trials, so that if they operational, then they are 

always operational or vice versa. 

0 
C0”TS 

1 Introduction 

1.1 Background 

1.2 Terms of Reference 

2 Review of Bubble Curtain use for Fish Protection 

2.1 Bubble Curtains 

2.2 Bubble Curtains combined with Other Stimuli 

2.3 Bubble Curtains and Augmenting Stimuli: Conclusions

Design Specification for the Heysham Outer Barrier 

3.1 Barrier Line 

3.2 Bubble Curtain Parameters 

3.3 Addition of Underwater Sound Signals 

3.4 Bubble Barrier Design Parameters: Recommendations

Statistical Design for Sampling at Heysham 

4.1 Statement of Problem 

4.2 The Hypothesis 

4.3 Sampling Technique 

4.4 Key Species 

4.5 Experimental Design 

3 

4 
1 INTRODUCTION 

1.1 BackFround 

In 1989, an experimental bubble curtain was installed across No 7D CW intake of 

Heysham 2 Power Station. The original purpose of the barrier was to repel floating 

debris and oil from the intake, and to improve the bottom silt profile. Following 

concern expressed by the MAFF Sea Fisheries Officer (NW District) over fish catch 

at the station, an appraisal of the problem was made by staff of the Fawley Marine 

Laboratory (CEGB Technical Advice Note No. RD/TAN/VlO/015/L88), and it was 

proposed that the effectiveness of the barrier as a fish deterrent should be tested. 

A number of trials were carried out in 1989 to quantify the fish catch with and 

without the bubble curtain operating. These indicated some reduction of fish catch, 

particularly of clupeid species (sprat and herring) when the barrier was operating, but 

not for other species. It was concluded that the barrier was not positioned optimally 

for fish protection and that better results might be expected with a barrier placed 

further upstream of the screens to influence both Heysham 1 and 2 CW inlets. Since, 

however, a barrier position close to the intakes was considered to be more effective 

for silt and debris control, a triple barrier scheme (Appendii 1: Figure Al) was 

proposed, with an external barrier (No. 1, Figure Al) for fish deterrence, and 

internal barriers (Nos. 2 and 3, Figure Al) in front of the Heysham 1 and 2 CW 

intakes. 

FAWLEY arl Ltd (formerly the Marine Biology Laboratory of NationalPower) have 

been commissioned to advise on the design and testing requirements for the external 

(No 1) fish deterrent barrier. 

1.2 Terms of Reference 

This report comprises two parts: 

Part 1 (Sections 2 & 3) is the design specification for the outer barrier. 

Part 2 (Section 4) is the test programme for the evaluation of the barrier as a fish 

deterrent. 

The terms of reference given by Nuclear Electric were as follows: 

Design Specification for the Outer Barrier 

(i) The specification is to provide the optimised position on the harbour bed for 

the bubble barrier line. 

(ii) The specification is to take into account the following: 

(a) experience of fish response to bubble curtain barriers elsewhere; 

@) currents and flow patterns, at varying tidal states in the CW intake 

approaches (using sub-surface current velocity and direction measurements 

1 
provided by Heysham 2 Power Station (Appendix 1 ); 

(c) any limitations imposed by harbour use and activity. 

(iii) The specification will make recommendations on the design of the bubble 

curtain delivery tube and air flow rates. 

(iv) The specification will make recommendations for the provision of augmenting 

stimuli such as light and sound for fish deterrents. 

Design of Test Programme for determiniryf the efficacy of the installation 

(i) The Test Programme will take into account the following:-

(a) Target fish species 

@) Tidal ajnd diurnal variability of fish 

(c) Seasonal variability of fish 

(d) The most cost effective manning regime for collection, classification, 

quantification and measurement of fish catches. 

(ii) The Test Programme will incorporate data recording proformas and will 

specify recognised statistical techniques for data analysis. 

2 
2 REVIEW OF BUBBLE CURTAIN USE FOR FISH PROTECTION 

2.1 Bubble Curtains 

Air bubble curtains have been used for a wide variety of applications in the sea since 

the turn of this century. Milne (1970) traces their history from 1907, when Brasher 

patented a system, using a bubble curtain, to attenuate waves emanating from 

compressed air discharges associated with sub-sea tunnelling. He describes a long 

subsequent history of bubble curtain research and development, with activitiesranging 

from coastal protection (through wave height alterations); prevention of salt-water 

intrusion into inland canals; containment of oil slicks; prevention of ice formation (by 

causing upwelling of deeper warm water layers); attenuation of blast waves; water reaeration; finally, and most relevant to the present application, their use in fisheries. 

The use of bubble curtains in fisheries has been quite widespread since the 1950s 

(Milne, 1970). Their original application was to limit wave height around nets in bad 

weather, to prevent fish escaping from the nets and to reduce damage to nets. 

Subsequently, bubble curtains have been used as an alternative to nets for herding and 

concentrating fish within a small area, from which they can be more cost-effectively 

netted, or to drive fish inshore, within reach of coastal fishermen. In this method, 

a loop of perforated flexible tube, through which air is blown, is drawn along the sea 

bed in the manner of a purse seine. A typical installation used for sardine fisheries 

is described by Smith (1961). Another application developed in Scotland has been 

the use of bubble curtains to confine farmed fish within sea lochs (Copland, 1977; 

Stewart, 1982). 

Bubble curtains have been seen for many years as a potential solution for fish 

protection at water intakes, though their use has met with varied success. The idea 

is attractive, as large intake areas can be curtained off at low cost and with no 

hydraulic head loss penalty. One of the earliest trials took place at a British power 

station in 1957, when a bubble screen was constructed at Uskmouth Power Station 

to exclude salmon smolts (CEGB, 1957). The screen was 135 m in length, with holes 

at 50 mm centres. 

In the trial, as many smolts were captured with the air supply turned off as when the 

curtain was operational. Unfortunately, the experimentd design was flawed, since 

it was not known how long the fish had been in the screen chambers prior to 

impingement. The trials were abandoned, owing to the small numbers of smolts 

present during the trialperiod. 

Most later applications of bubble screens at power stations are reported from North 

America where, again, little success has been found in site trials. In a four year 

study of behaviourial deterrents funded by the Electric Power Research Institute 

(EPRI) at Roseton Power Station (Hudson River) (Matousek et al., 1988), a bubble 

curtain with no augmentory stimulus produced no fish deterrent effect. Other power 

station trials have been similarly discouraging, withno demonstrable exclusion effect 

(Sonnichsen et aZ., 1973; Lieberman and Muessig, 1978; Patrick et al., 1988). 

A recent UK trial was undertaken by Thames Water at a potable water supply intake 

on the River Thames. The screen has not been rigorously tested, but is believed to 

3 
be effective in reducing coarse fish entrainment (G Armstrong, pers. comm.). 

The apparent lack of success with bubble curtains at water intakes is in marked 

contrast to findings in the laboratory, where very high 'exclusion' rates have been 

achieved in simulated intake conditions. Patrick et al., (1985) recorded exclusion 

efficiencies ranging from 51to 98% for a range of freshwater and estuarine species. 

Exclusion efficiency depended upon light conditions and the species tested. 

Two factors may account for the lack of success at water intakes. First, in the wild, 

fish are exposed to a much wider range of stimuli, and the additional stimulus of the 

bubble curtain may be less important than in an experimental set-up. Secondly, and 

probably most important, in most power station trials the bubble curtain has been 

positioned parallel to and directly in front of the coarse screen/trash rack assembly 

(as in the 1989 Heysham 2 trials), where water velocity is already high and fish are 

offered little opportunity to escape. A more sensible approach is proposed by 

Mishchenko and Pestryakov (1986), who suggest that the bubble curtain should be 

placed ahead of the intake and at an acute angle to the flow to encourage lateral 

diversion of fish along the face of the curtain. The principle is similar to that used 

in other fish diversion systems and is illustrated in Figure 1. Since fish are not 

readily able to resolve the true direction of water flow, as they approach the angled 

barrier, they tend to orientate perpendicular to the barrier and swim in a direction 

away from it. To maintain a constant distance from the barrier, they must swim at 

velocity U,,as shown in Figure 1, and consequently move parallel to the face of the 

barrier at velocity U,. In this way, fish are guided to the end of the barrier. 

2.2 Bubble Curtains combined with Other Stimuli 

Much more promising results at power station water intakes have been obtained with 

bubble curtains augmented by sound or light stimuli. 

Lights 

Whereas bubble curtains produce three types of stimulus, namely visual, aural and 

tactile, laboratory experiments have shown that the fish herding efficiency of bubble 

curtains is much reduced in low light conditions or turbid waters, implying that it is 

primarily the visual sense which is important (Blaxter and Parrish, 1965; Patrick et 

al.; 1988). It is often during the hours of darkness that fish impingement at power 

stations is maximal (Turnpenny, 1988) and hence bubble curtains by themselves can 

be expected to have limited protective value for fish over a 24 h cycle. 

Whilst increasing the ambient light levels improves the response of fish to bubble 

curtains, use of artificial illumination brings with it the risk of attracting certain 

species (see review by Turnpenny, 1988). This risk can be minimised by using 

strobe lights employing xenon discharge tubes, operated at a flash rate of 2 200 

flashes mid, which repel rather than attract most Species of fish. Barriers 

comprising a combination of strobe lights and bubble curtains have been used 

successfully both in the laboratory and at power station intakes, with higher rates of 

fBh deterrence than with either stimulus applied alone. The usual arrangement is to . have an array of strobe lights behind the bubble curtain and projecting on to it, so 

that the curtain acts as a diffuser for the light. The following shows the results 

obtained at Roseton Power Station for the three permutations (Matouseket al., 1988): 

4 
Barrier % Fish Exclusion 

Air curtain -0.02 

Strobe 22.6 

StrObe x air curtain 61.8 

An enhanced effect with a bubble-curtain/strobelight combination was also found in 

laboratory trials by Patrick et al., (1985). Performance may depend on site-specific 

factors, however, as is clear fiom the lack of success of a bubble/strobecombination 

tested at Pickering Power Station on the Canadian Great Lakes (Patrick, McKinley 

and Micheletti, 1988). 

The use of artificial lighting has its problems, especially when used in turbid estuarine 

waters. Where the lights are placed above the water, much of the available light is 

reflected from the water surface. To achieve uniform illumination, underwater 

placement of the lights is essential and, generally, a substantial array of lights will be 

required. Once in place, the lights will require regular attention for cleaning of the 

lenses. Where strobe lights are used, the short life time of the flash tubes will 

require that tubes are changed frequently, probably at least once per week. whist 

this may not be difficult on shallow river water intakes, strobe lights are not likely 

to be a practical proposition for an estuarine site, such as Heysham. 

Sound 

One of the more promising recent developmentshas been the use of underwater sound 

to repel fish. Fish are most sensitive to low frequency sounds in the 20-2000 Hz 

range (Hawkins, 1973). To repel fish requires the attainment of high sound 

pressures, which must be well in excess of ambient sound levels within the same 

frequency band. Various pneumatic and percussion devices which repel fish have 

been developed, and high fish exclusion rates have been reported in power station 

applications. A drawback of these devices is that they are prone to mechanical failure 

(Matousek et al., 1988). 

The availability of low frequency, high output electromagnetic and ceramic 

transducers, originally developed for the defense industry, offers a more reliable 

means of generating sound suitable for fish repulsion. Using signal generators and 

power amplifiers, high sound levels (150-170 dB re 1 Pa @ lm) at frequencies of 

<2000 Hz can be generated. High reliability is expected with these devices, which 

are intended to be operated in the sea for periods of years without intervention. In 

1991, acoustic deterrent trials were conducted by FAWLEY arl Ud at Ofdbury-onSevern Power Station,as part of the joint National Power/Nuclear Electric aquatic 

research programme (Thatcher and Irving, 1992). These preliminary scoping trials, 

using a sound signal developed for bass (Dicentrarchus Zabrcwc) exclusion, 

demonstrated a 30%reduction in bass catch. In these trials the placement of the 

transducers was far from ideal and with improved siting, higher exclusion rates 

should be attainable. In similar studies at inland sites in North America, Loeffelman 

et aZ. (1991) have achieved fish diversion efficiencies of 60 to 100%. 

The benefits of combining sound signals and bubble curtains for fish deterrence are 

not evident frompublished work (Patrick, McKinley and Micheletti, 1988; Matousek 

5 
et al., 1988), which has shown no further reduction in fish catch when a bubble 

curfain has been added to an acoustic deterrent. However, there may be some 

hitherto unexplored virtues of this combination. 

Firstly, bubble curtains absorb low frequency sound waves and therefore may offer 

a means of containing the sound field to limit nuisance effects of extraneous sound, 

for example sound transmission through boat hulls in the vicinity. Similarly, any 

unwanted affects on fish behaviour outside the immediate intake area might be 

controllableby this means. 

A second possibility is that a bubble curtain, by limiting sound transmission, might 

be used to manipulate the shape of a sound field to guide fish in the most desirable 

direction, as in the example shown in Figure 1. The use of sound, rather than light, 

is therefore recommended to augment the bubble curtain as a fish deterrent at 

Heysham. 

2.3 Bubble Curtains and Augmenting Stimuli: Conclusions 

0 For fish protection at water intakes, it is advantageous to angle the barrier 

relative to the flow, so that fish are guided to a safe area at one end of the 

barrier. 

0 Bubble barriers rely primarily on a visual response by fish and so are more 

effective in daylight. Strobe light systems can be used effectively to improve 

the over day and night, but are likely to be impractical at Heysham due to 

frequent (weekly) inspection and maintenance requirements. 

0 Underwater sound offers a more promising augmentary stimulus, with high 

system reliability and low maintenance costs for a well designed system. 

Combined with a bubble barrier, it should be possible to achieve high 

diversion efficiencies with well-controlled sound distribution. 

6 
- 

3 DESIGN SPECIFICATION FOR THE HEYSHAM OUTER BARRIER 

3.1 Barrier Line 

The chief requirements for the outer barrier line are: 

1 that water velocity on the vector perpendicular to the barrier (see Figure 1) 

should be low enough for fish to escape; 

2 that the fish can be guided by the barrier to a place of relative safety; 

3 that the barrier should not interfere with harbour activities. 

The first two of these requirements can be met by selection of the appropriatebarrier 

line. Figure A1 and Table AI of Appendix 1 give the flow direction and velocity

data provided by Heysham 2 Power Station. In Table 1, the velocity values of Table 

A1 (shown in ft s-') have been converted to cm s-'. The mean velocity across the 

points shown as 1.1to 1.6 (Figure Al) is calculated to be 16.2 cm s-l. Table 2 gives 

maximum approach velocities that will allow fish of different species and age classes 

to escape, based on swimming performance criteria (Turnpenny, 1988). Previous 

investigations of seasonal fish catch (see Section 4)have shown that the months of 

highest fish catch are October and November. Hence, maximum importance is 

attached to meeting fish requirements during this period, when water temperature is 

expected to be above 7.5"C (Figure 2). Referring to Table 2, for most species, fish 

of all age groups should be capable of escape at or above this temperature. Those 

which might not swim fast enough to escape are shown in bold typeface (0-group 

pout, plaice, dab and sole). At lower temperatures (see 2.5"C column of Table 2), 

more species would be susceptible to capture, though only as the 0-group age class 

(i.e. less than one year old fish). 

To improve the chance of fish escaping from the intake currents, the barrier line 

should be slanted relative to the flow direction to achieve the effect shown in Figure 

1 (e.g. line lo>)rather than 1(a) in Figure A1 ). Fish detecting the barrier are then 

expected to orientatethemselves perpendicular to the barrier line, rather than parallel 

to the flowstreamlines, swimmingin a direction away from the barrier. In this way, 

their movement has a velocity vector parallel to the face of the barrier (UJ,as well 

as one perpendicularto and away from the barrier line. The minimum fish swimming 

speed required to maintain a constant distance ahead of the barrier is U,. For an 

angle 01 relative to the flow streamlines (see Figure l), the two velocity vectors are 

given by: 

- and u3 U,.sin 01 (2) 

For the barrier line l(b), a = 12", hence U2 = 15.8 cm s-' and U,= 3.4 crn s-'. 

With this arrangement, the fish would tend to move along the face of the barrier in 

a north-easterly direction, passing further into the harbour. The barrier length on this 

line is 591x1,hence the maximum time to traverse the barrier would be of the order 

of 28 min. As the fish escape velocities are based on swimming speeds which can 

be sustained for at least one hour (Turnpenny, 1988), this should present no 

7 
difficulties for those species for which figures are not shown in bold typein Table 1. 

Larger fish which are strong swimmers will tend to swim parallel to the face of the 

screen and traverse it much more rapidly. 

In the example of line l(b), the angle of the barrier gives a minimum swimming 

velocity required to avoid penetrating the barrier of U2 = 15.8 cm s-l, only slightly 

lower than the flow velocity. For angles of a > 12, the required escape velocity 

becomes progressively lower, as shown in Table 3. 

In order to achieve a velocity enabling all fish to escape at water temperatures 2 

7.5"C, a 60" barrier angle would be required, but this would more than double the 

required barrier length, to 134 m. Even this barrier line would not enable all fish to 

escape at lower water temperatures. As it would result in at least a doubling of cost 

for a small benefit, such an extended barrier would not in our view be worthwhile. 

To achieve optimum results, it would be advisable avoid contact of the barrier lie 

with the dolphin structures located in the water inlet, as these will introduce breaks 

in the bubble curtain integrity. It is not essential for the barrier line to be straight 

and we would recommend a curved line, as shown in Figure 3. The length of this 

line would be approximately 75m. 

3.2 Bubble Curtain Parameters 

Hole Size and Spacing 

Design details for the bubble curtain are taken mainly from Copland (1977), who 

tested a range of design parameters. Those given here were found to most effective 

for a bubble barrier operating in the sea at 10m depth. Holes in the air tube should 

be 0.38mm diameter. Hole separation (pitch) should be 50 mm. The pitch of 16.5 

cm indicated on the drawing supplied to us (Figure Al) is considered to be excessive 

for fish exclusion purposes. Hole spacing for a bubble curtain is analogous to the 

mesh size of a fish net (Stewart, 1982), hence the need for a closer hole spacing. 

Tube Diameter and Air Supply 

A tube internal diameter of 50mm is recommended for the 75m bubble curtain length, 

to ensure an even air distribution. The air compressor should be set to cut in at a 

pressure of -275kPa, and to cut out at -420 Wa. With the hole size and spacing 

given above, the air supply requirement at this pressure is approximately 0.02m3min-l 

per metre of barrier. Thus for the proposed 75m line, an air supply of 1.5m3min-l 

will be required. 

Efficient plumbing of the air supply is essential if energy losses are to be avoided. 

Sharp bends should be avoided, swept bends being used in preference. Abrupt 

changes in pipe diameter should also be avoided. 

Materials 

The pipeline and fittings should be manufactured of materials resistant to corrosion 

in sea water. Semi-rigid alkathene or PVC plastic, of the type used for domestic 

underground water supply, is suitable for the bubble curtain tube. Care should be 

taken to avoid using plastics which deform when heated for connection to the 

compressor as these may collapse and restrict the air flow. The supply from the 

8 
compressor to the bubble curtain should be of larger diameter than the bubble tube 

itself to reduce frictional losses. An internal diameter of at least 50mm is 

recommended. Kink-proof reinforced PVC tubing would be suitable. The diameter 

should be stepped down in two or more stages to avoid abrupt changes of diameter. 

Weighting Down the Tube 

If plastic tube is used, it will need to be weighted down to hold it in place on the 

seabed. A robust way to do this is to bed the tube into a steel U-section channel laid 

onto the seabed. Cross members (e.g. 0.5 m lengths) attached at intervals, 

perpendicular to the tube axis, help to stabilise the assembly to prevent rolling of the 

channel. The tube is attached by means of strong plastic cable ties. 

It is understood, however, that for the Heysham installation, it must be readily liftable 

for dredging operations. Attachment to a steel chain may be suitable for this purpose. 

It is possible that the upward orientation of the holes may be difficult to maintain by 

this method. This should not seriously affect the barrier, unless the holes become 

blocked by sediment. 

Provision for Purging the Lime 

If the barrier is switched off for any reason, it is likely that water and silt will enter 

the air-line, which will be difficult to purge via the normal air outlet holes. A purge 

valve should therefore be fitted. For this purpose, it will be necessary to bring the 

end of the air-line opposite to that attached to the compressor out of the water, and 

to terminate it with a valve, e.g a gate valve. On starting up the system, the valve 

should be opened to allow compressed air to purge water from the line, then closed. 

3.3 Addition of Underwater Sound Signals 

Modulation of the Air Supply 

Our original suggestion for a low cost option of providing an additional sound 

stimulus to the barrier by modulating the air supply has not been tested and would 

require trials at our Fawley laboratories to determine the feasibility of the approach. 

Such trials would need to be undertaken during the summer of 1992 in order to be 

ready for autumn field trials. The basic idea would be to utilise an electromagnetic 

solenoid valve to pulse the airflow in such a way that the noise was transmitted along 

the entire length of the bubble barrier. The following questions would need to be 

investigated: 

i) Can signals produced in this way be used to deter fish? 

ii) Are they effective on the target species? 

iii) Can adequate sound pressures be generated to exceed ambient noise levels in 

Heysham Harbour? 

iv) Will modulating the air supply in this way detract from bubble propagation? 

v) Will the sound generating equipment operate reliably in continuous service? 

The advantages of this approach, if it worked, would be low capital cost and low 

installation and maintenance cost. Essentially, it would add to the basic bubble 

curtain hardware only an electromagnetic modulator valve and a simple electronic 

9 
driver system. 

Electromagnetic Transducers 

An alternative to this approach would be to place an array of electromagnetic 

transducers in the water, behind (i.e. downstream of) the bubble curtain. These 

would best be deployed from a floating boom located parallel to, and from a few 

metres downstream of the barrier line. The transducers would be suspended 

midwater, with supply cables feeding back to a dock wall control centre containing 

the signal generator, amplifier and filter system (see Thatcher and Irving, 1992). 

This would take advantage of an acoustic deterrent signal development programme 

being sponsored corporately for 1992by Nuclear Electric (contact: Mr C J L Taylor, 

Barnwood, Location 106), in which signals suitable for fish deterrence are to be 

identified. A survey of the intake area would be required to determine the number 

of transducers necessary to produce a uniform sound field across the barrier and to 

establish ambient background sound spectra. 

3.4 Bubble Barrier Design Parameters: Recommendations 

The recommended design parameters for the bubble barrier are as follows: 

0 

0 

0 

0 

0 

0 

0 

0 

0 

a 

0 

0 

barrier line: curved, as shown in Figure 3 

barrier length.. ..................... .75m 

bubble tube internal diameter.........50mm 

bubble outlet hole size...............0.38mm 

hole pitch............................ 50mm 

operating pressure.. .................. 276kPa (switch-on), 414Wa (switch-off) 

air demand............................ 1.5m3min-' 

bubble tube material: semi rigid PVC or alkathene 

delivery tube material: spirally-reinforced PVC hose 

seabed attachment: steel chain and cable ties 

bubble tube purging: via a gate valve attached to the end away from the 

compressor, out of the water 

augmentary stimuli: acoustic, by low frequency (<1OOHz) modulation of the 

air supply, or using an array of electromagnetic transducers behind the bubble 

barrier, fed from an onshore signal generator/ampMer system. 

10 
4 STATISTICAL DESIGN FOR SAMPLING AT HEYSHAM 

4.1 Statement of Problem 

To determine whether the proposed bubble barrier in front of Heysham 2 Nuclear 

Power Station will reduce the number of fish captured on the intake screens. 

Additional fsh deterrent methods might also be operational, the efficiency of the 

different components of the fish deterrent system will not be individually identified. 

4.2 The Hypothesis 

For both the total fish catch and individual species the null hypothesis is that the 

bubble screen produces no significant reduction in the catch of fish on the screens. 

4.3 Sampling Technique 

Fish and debris washed from the four Heysham 2 drum screens will be intercepted, 

probably using baskets placed in the screen washing channels running from the 

individual screens. The fish catch will be sorted to species and the number and weight 

of individual species caught per unit time recorded. Samples of fish will also be 

measured (standard length) to show the sizes and approximate ages of fish caught. To 

determine whether the bubble screen reduces the fish catch the rate of capture of fish 

will be determined with the bubble screen both on and off. 

4.4 Key Species 

It is important to ensure that the experimental design is capable of assessing the fish 

deterrent capability of the bubble screen for key species. Key species are defied 

either by their high abundance in the area, conservation value or importance to 

fishermen. 

Examination of the screen catch data and has identified the following as key species: 

Bass Dicentrarchus labrax - occasionally caught sport fish 

Silver eel Anmilla anguilla - abundant October and February 

Sand goby Pomatoschistus minutus - abundant November 

Herring Clupea harenrrus - abundant November to February 

Hooknose Aponus cataFhractus - abundant November 

Poor cod Trisopterus minutus - abundant October to January 

Pout Trisopterus luscus - abundant November to January 

Sprat Smattus sprattus - abundant November to January 

Whiting Merlangius merlanpus - abundant September to December. 

Brown shrimp CranEon crangon - abundant October to January 

11 
4.5 Xxperimental Design 

Time of Year 

As shown in Figure 4 the annual pattern of fish capture at Heysham is highly 

seasonal. More than 90% of the total annual catch by either weight or number of 

individuals occurs between October and April and the maximum rate of capture has 

been observed to occur in the months of October and November. An examination of 

the seasonal pattern of occurrence of the key species indicates that this sampling 

period coincides with the periods of maximum abundance of all the key species with 

the possible exception of bass. In the case of bass, the recorded rates of capture are 

too low to reach a conclusion on seasonality. However, information from other sites 

indicates that bass capture rates are usually greatest in the autumn. 

Tidal Factors 

As shown in Figure 5 the rate of fish capture is inversely related to tidal height. Thus 

it is important that the sampling strategy ensures that samples are collected over the 

low water period when most of the fish arrive. Further, the sampling design must 

ensure that fish capture rates for periods with and without the bubble screen are 

controlled for tidalheight. It is proposed that a standard six hour samplingperiod be 

employed with low water at approximately at the end of the third hour of sampling. 

This strategy will maxirnise the number of individuals vulnerable to capture while 

minimising the sampling effort. 

Diurnal Factors 

Little is known about diurnal patterns of capture. While at somepower station intakes 

the rate of fish capture is greater in the dark this is unlikely to be a significant feature 

at Heysham. This is because of the on-shore position of the intakes; in power stations 

with this type of configuration tidal factors tend to dominate short-term temporal 

variation. It is recommended that day length be added to the data set so that any trend 

attributable to this variable can be removed from the data. 

Fish Storage 

A factor which will tend to reduce the distinction between fish catches with the 

deterrent systems off or on is the presence of fish between the barrier and the intake 

screens which have entered during the preceding period. This storage effect can be 

minimised by the following measures. 

Firstly, fish present in the screenwells can be purged from the system by chlorinating 

the screenwells for a period of 2-3hours immediately prior to each trial period. The 

required chlorine concentration is of the order O.5ppm applied dose. Sodium 

hypochlorite is suitable for this purpose, if normal station chlorination has been 

suspended. 

The second measure is to switch on the deterrent system, not at the beginning of the 

6 hour test period, but at the end of the preceding control period. 

12 
Screen Bias 

It has been noted previously that fish capture rates tend to increase from screen 8d 

to 7b.This is probably related to the orientation of fish in relation to the breakwater 

wall. It is proposed that the samples from all four screens are bulked for each 

sampling period to remove screen bias. This recommendation assumes that all 4 

pumps will be operating during the experimental period. If this is not the case care 

must be taken to ensure that the same screens are sampled during the periods when 

the bubble screen is on and off. 

Uncontrolled Factors 

Weather conditions such as wind, rain or changes in the flow of local rivers may 

effect local fish abundance. A weather record and the salinity and temperature of the 

extracted water should be recorded for each sampling period. While it is likely that 

uncontrolled factors will be assumed to contribute to the error-term in the analysis of 

variance, it might become necessary to exclude some samples if they were to be 

collected during unusual weather conditions. This would be the case if periods with 

comparable environmental conditions were not sampled with the bubble screen both 

on and off. 

Temporal Arrangement of Sampling Periods 

To avoid bias linked to uncontrolled factors, and the change in tidal range linked to 

the spring-neap cycle the following arrangement of sampling periods is proposed. A 

single sampling period ( of six hours duration) will be undertaken each day to cover 

the low water period for which the majority or all of the period is during daylight. 

The entire experiment should be undertaken on consecutive days with the bubble 

screen operating every other day. This scheme is summarised in the following table. 

Bubble screen on 

Day 1: Sampling period 1 

Day 3: Sampling period 3 

I1 * - - ' *-- * *

11 Day n-1: sampling period n-1 

Bubble screen off 

Day 2: Sampling period 2 

Day 4:Samplingperiod 4 

.......... I

1 Day n: Samplingperiod n 

Estimated Number of Sampling Periods 

Given a balanced experimental design as described in 4.5 the effect of the bubble 

screen can be assessed statistically using a standard t-test to compare the means of 

fish caught with and without the bubble screen. 

13 
When sample sizes are equal and the null hypothesis is that the means are the same 

(Section 4.2), 

where XI is the mean number caught per period with the bubble screen working 

X2 is the mean number caught per period without the bubble screen 

varl is the variance of the catch with the bubble screen working 

var2 is the variance of the catch without the bubble screen 

and n is the total number of sampling periods. 

The number of sampling periods required for the experiment depends on the 

significancelevel chosen, the degree of differencebetween the means we require to 

detect and the variance in the rate of capture between periods. It also depends on the 

effort we are able to expend, but we shall assume for the present that this is not 

limiting. The least significant difference, LSD, is the least difference between two 

means for which it would be concluded that they were significantlydifferent. For the 

proposed experiment a significancelevel of 5%is appropriate so the LSD is defined 

as 

LSD - tmOs[n]r(l/n(varl+var2)) 

Thus given an estimate of the variances we can estimate the LSD for different It. 

During October 1985three consecutive24hr samples were collected from the screens 

of Heysham 1. Assuming that half of the observed daily catch would have been 

caught in a six hour sampling period centred on iow water, this suggests that the 

mean and variance of our proposed sampling scheme would have been 480 and 4938 

respectively. Similar calculations for three samples taken in November 1985give an 

estimated mean and variance of 176 and 5001 respectively. 

These calculations suggest that without a bubble screen operating it would be prudent 

to assume a mean catch of 300 fish per period with a variance of 5000. We it is 

likely that the variance in the number of fish captured when the bubble screen is 

operational will be lower, at the planning stage it is prudent to assume a similar 

variance. 

14 
Number of sampling 

periods n 

4 

8 

12 

16 

20 

32 

t for n sampling periods LSD 

and 5%significance level 

2.13 106.5 

1.86 65.8 

1.78 51.4 

1.75 43.8 

1.72 38.5 

1.7 30.1 

From this table it can be seen that to detect a 10% reduction in catch due to the 

bubble screen, given a mean catch rate of 300 per period, would require sampling 

over a 32 periods (days) of sampling. 

Inpractice, a 20% reduction or more would be environmentally important (difference 

between the means of 60) and this could be detected with reasonable certainty with 

12 sampling periods ( 12 days). 

The same general conclusions for the number of samples also applies to the individual 

key species. 

4.6 Recording Proformas 

Appendix 2 contains sample recording proformas. One set of sheets should be used 

for each six-hour sampling session. The first sheet accommodates a range 

environmental and operational parameters which will assist in interpretation of the 

trials, together with the total hourly catch figures. The second sheet accommodates 

data on fish size so that the approximate age classes of the catch can be determined. 

These proformas are also available as Lotus 1-2-3 spreadsheets. 

4.7 Experimental Design and Statistics: Recommendations 

The bubble curtain experiment should be undertaken over a minimum twelve 

day period in the months of October or November. 

Tidal and operational conditions permitting, the best period would be the last 

week of October and the first week of November. Once sampliig has 

commenced it should be undertaken on consecutive days. This will require 

week-end work. 

It is recommended that two working days be assigned at the beginning of the 

experimentalperiod during which the samplingequipmentwillbe installed and 

working methods defined. 

It is recommended that chlorination of the screenwells at an applied dose of 

15 
OSppm should be undertaken for a period of 2-3 hours prior to each trial 

period, to minimise the adverse effects of fish storageon interpretation of the 

test results. Sodiumhypochloritedosing would be adequatefor this, if normal 

station chlorination has been suspended. 

0 To add an augmentary sound stimulus, a second, similar period of testing 

would be required, in which the sound system and the bu6ble curtain were 

operated simultaneously, again with alternating days of operation. This would 

be necessary to ensure that one or other system was not redundant. Ideally, 

a third twelve day period would be used to operate the sound system without 

the bubble barrier, unless it were already decided that a bubble barrier would 

be operated there for other reasons. 

0 Any trials using a sound system would require an initial survey and a 

minimum of two weeks prior to the trials for installation and testing. A 

temporary system could be installed for the period of the trials only, using 

FAWLEY arl Ltd’s mobile fish deterrent caravan. 

0 There is no requirement for the inner barriers (shown as 2 & 3 on Figure AI) 

to be installed or operational during trials with the outer barrier. It is, 

however, important that operating conditions should be maintained in a 

constant state during the trials, so that if they operational, then they are 

always operational or vice versa. 

16 
References 

Blaxter, J.H.S and Parrish, B.B. (1965). The reactions of marine fishes to moving netting 

and other objects in tanks. Mar. Res., 1960/61. 

CEGB (1961). Preventing the entry of salmon smolt on migration - survey of research 1956­

61. Central Electricity Generating Board, South Wales Division. Operational Report No. 

77. 

Copland, P.J. (1977). Design, developmentand field testing of a bubble curtain. Department 

of Agriculture and Fisheries for Scotland, Working Paper No. 77/14, 10pp. 

Hawkins, A.D. (1973). ’The sensitivity of fish to sounds’. Oceanogr. mar. Biol. Ann. Rev. 

11,pp. 291-340. 

Lieberman, J.L. and Muessig, P.H. (1978). Evaluation of an air bubbler to mitigate fish 

impingement at an electric generating plant. Estuaries 1 (2), pp.129-132. 

Loeffelman, P.H., Klinect, D.A. and Van Hassell, J.H. (1991). Fish protection at water 

intakes using a new signal development process and sound system. Published in 

“Waterpower ’91”,Proc. Int. Con$ Hydropower, Amer. SOC.Civ. Engrs., pp. 355-365. 

Matousek, J.A., Wells, A.W. and McGroddy, P.M. (1988). Field testing of behaviourial 

barriers for fish exclusion at cooling water intake systems. WRI Report No. CS-5995, 

Electric Power Research Institute, Palo Alto, Ca. USA. 

Milne, P.H. (1970. Air bubble curtains and their use in coastal waters. Fluid Power 

International May 1970, pp. 33-36. 

Mishchenko, V.S.and Pestryakov, V.N. (1986). Problem of protecting fish at water intakes. 

Gidrotechhnicheskoe Stroitel’stvo 8, pp. 50-52. 

Patrick, P.H. ,Christie, A.E. ,Sager, D. ,Howett, C. and Stauffer, J. ,Jr. (1985). Responses 

of fish to a strobe light/air bubble barrier. Fish. Res. 3, pp. 157-172. 

Patrick, P.H., McKinley, R.S and Micheletti, W.C. (1988). Field testing of behaviourial 

barriers for cooling water intake structure - Test Site - Pickering Nuclear Generating 

Station. In: ’Proceedings: Fish Protection at Steam and Hydroelectric Power Plants: 

Electric Power Research Institute’,EPRI C8IEAIAP-5663-SR pp.4.13-4.25. 

Smith, K.A. (1961). Air curtain fishing for Maine sardines. US Dept. of the Interior, Fish 

and Wildl. Serv. Commercial Fish. Rev. 23 (3), pp. 1-14. 

Sonnichsen, J.C.,Jr, Bentley,B.W., Bailey,G.F. and Nakatani, R.E. (1973). A review of 

thermal power plant intake structure designs and related environmental considerations. 

Hanford Engineering Development Laboratory, Richland, Washington, Rpt. No. HEDLTME-73-24. Distributed by National Technical Information Service, US Dept. of 

Commerce, 5285, Port Royal Road, Springfield, Va 22151, USA. 

Stewart, P.A.M. (1982). An investigation intothe reactions of fish to electrifled barriers and 

bubble curtains. Fish. Res. I, pp. 3-22. 

Thatcher, K.P. and fig, P.W. (1992). Fish deterrent trials at Oldbury Power Station. 

National Power/NuclearElectric CommonMarine Programme, Research Report (in Press). 

17 
Turnpenny, A.W.H. (1988). The behaviourid basis of fish exclusion from coastal power 

station cooling water intakes. CEGB RD/L/3301/R88. Central Electricity Generating 

Board, London. 

18 
Table 1 Flow Velocities Measured &toss Points 1.1 to 1.6 (cm s") 

(Figure Al, Appendix 1) 

Position 

Depth (in) 1.1 1.2 1.3 1.4 1.5 1.6 

0 14.9 20.7 9.1 10.1 10.1 9.1 

1.8 20.7 16.5 18.3 20.8 16.5 

3.7 16.5 15.0 20.8 16.5 9.1 

5.5 20.7 16.5 16.5 

7.3 24.9 

Mean velocity = 16.2 cm s*' 

Standard error = 4.7 cm s-' 
Table 2 Maximum Approach Velocities Which Will Enable Fish to Escape at 

Different Water Temperatures (Tmmpenny, 1988). 

I1 

Temp "C 

SDecies 

sprat 

Herring 

Cod 

whiting 

Pout 

Poor cod 

Plaice 

Flounder 

Dab 

Sole 

Bass 

Grey Mullets 

Sand Smelt 

Salmon Smolts 

I Age Group 0 and Older 1 Min. I Age Group 1 and Older 

Length 1 

n.5 17.5 Age 1 

cm s-' -cm cm s-'

30 40 50 60 8 50 64 78 92 

30 40 50 60 12 50 65 80 94 

15 30 40 55 15 30 52 74 95 

10 25 40 50 15 35 55 79 102 

8 15 20 29 20 34 60 83 105 

10 25 35 50 10 26 40 59 73 

8 15 20 30 8 28 48 I 67 92 

10 20 30 40 12 28 46 66 86 

2 10 20 26 10 12 23 34 46 

5 15 20 30 11 22 40 57 72 

20 35 50 66 9 37 59 83 109 

20 35 50 60 10 30 50 69 89 

10 20 130 40 7 24 40 53 70 

Age Group 1and Older Age Group 2 and Older 

80 15 55 68 79 91 

Min Autumn temp. -7.5"C 

ONational Power 1988 

22 
Table 3 Escape Velocities �or Various Barrier Angles �or a Flow Velocity of 

16.2cm s-', and Approximate Barrier Lengths 

Angle (a) Escape Velocity (cm6) Barrier Lengths (m) 

12 15.8 59 

20 15.2 65 

30 14.0 74 

40 1 12.4 87 

50 10.4 110 

60 8.1 134 

1 
7 

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FROM MET. OFFICE 

11 FOR THE SURV�Y PERIOD 

1: 

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ws I 

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w AVERAGE TJZMPERATURE !-' AT HCYSHAW 

MONTHLY MEANS 6 1906- 1954 

6 

4 

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2 

t 

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J F' H A M' J J A S O N 0 

WONTHS 

Figure 2 AnnuaI Cycle of Sea Temperature at Reysham 

(unpublished report by Parker, GCC and Lovejoy,�!., dated 11.1.80: held in the 

Nuclear Electric Archive, FAWLEY arl Ltd) 

c 

f 

cr,

.­

0 

0 0 

0 

0 

0 0 0 0 0 m 0- tn mi F 'r 
FIGURE 5 Tidal Fish Catch Patterns 

Heysham 2 Power Station (Screen 7b) 

November 1989 

......................................................................................... 

....................... 

t-lw.......................................................................................... 

..................... 

_ ............................................................................................................................ &W................... 

. Clupeids 29.11.89 - 1.m ................. ........................................................................................................................ 

_ ......................... L...............

6M) _ ......................... <............................................ 

400 -......................... i................................... 

2(n _........................ 4.................................. 

Od I I I I I I I I 

Time GMT 

Surveys undertakenby Fawley Marine Biology Unit 

Copyright1992 NationalPower 
APPENDIX 1 

Data on Promxed General Arrangement of the Triple Barrier 

and Current Velocity and Direction Data 

as sumlied bv Hevsham 2 Power Station 
-+E­

\ 
. . . , .- __ ­ .. 

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1 iY 
APPENDIX 2 

Sample Recording. Proformas for Fish Barrier Trials at Heysham 
FAWLEY aquatic research laboratories Ltd 

HEYSHAM FISH DETERRENT SYSTEM TRMLS 

Data Recording Proforma Fish Lengths 

Date 

Sample Time 

Sheet-] of 

r Species Length(mm) Species Length(mm) 

I 

I 
FAWLEY aquatic research laboratories Ltd 

HEYSWAM FISH DETERRENT SYSTEM TRIALS 

Data Recording Proforma 

Date 1-1 StaffNames I I 

Start Time U Finish Tlme 1-1 Hours of Daylight 7 1 

(during sampling) 

Off On 

Bubble Curtain 

Physical Measurements 

Water Temperature (C) 1 1 Turbidity (SDextinction, m) 

Salinity 

Tidal State 

(ppt) 

-

17HW Time 1-1 LW Time 1-1 HW Ht(m) { I LW Ht(m) 

CW Pumps Running 

(tick for 'on') 

Sta e One Sta eTwo -1 -1