BEEMS Scientific Position Paper SPP063 Edition 2/S

Entrainment impact on organisms at – supplementary note

Not Protectively Marked ii Version and Quality Control

Version Author Date Draft 0.01 B J Robinson 26/09/2011 Submission to EDF as Prel A 1.00 30/09/2011 Comments received from EDF CJLT 01/10/2011 Revised version 1.01 B J Robinson 09/10/2011 Internal QC 1.02 Julian Metcalfe, Steve Milligan 10/10/2011 Submission to EDF as BPE 2.00 11/10/2011 Edition2 with additional information 2.01 B J Robinson 28/03/2012 Internal QC 2.02 Julie Bremner 28/03/2012 Submission to EDF as “approved” 3.00 28/03/2012

iii Table of Contents

Not Protectively Marked ...... i 1 Purpose ...... 6 1.1 Title / topic ...... 6 1.2 Author...... 6 1.3 Purpose ...... 6 2 Summary ...... 6 3 Comparison of the cooling water systems of HP B and HP C...... 7 3.1 Hinkley Point monthly water temperatures ...... 7 3.2 Impact of changed inlet mesh sizes...... 9 4 Entrainment effects ...... 9 4.1 Estimating the abstraction zone ...... 10 5 Relative importance of the sources of production in the Bristol Channel...... 11 6 Phytoplankton entrainment...... 12 6.1 Evidence for phytoplankton entrainment mortality...... 13 6.2 Predicted entrainment impact of HP C...... 13 6.3 Predicted additional impact due to climate change...... 14 7 Zooplankton entrainment ...... 14 7.1 Copepod entrainment...... 16 7.1.1 Evidence of entrainment mortality: Acartia tonsa (adults) ...... 16 7.1.2 Predicted Entrainment Impact of HP C...... 17 7.1.3 Predicted additional impact due to climate change ...... 17 7.2 Mysid Entrainment...... 17 7.2.1 Evidence for entrainment mortality ...... 18 7.2.2 Predicted entrainment impact of HP C ...... 18 7.2.3 Predicted additional impact due to climate change ...... 19 8 Crangon crangon ...... 19 8.1 Evidence for entrainment mortality...... 20 8.2 Annual Impingement and Entrainment Impact of HP C options compared with HP B ...... 20 8.3 Predicted additional impact due to climate change...... 22 9 Sabellaria alveolata ...... 23 9.1 Evidence for entrainment mortality...... 24 9.2 Predicted impact of entrainment of HP C...... 24 10 Macoma balthica and other important macrofauna in Bridgwater Bay...... 24 10.1 Entrainment impact on other important macrofaunal organisms in Bridgwater Bay...... 26 10.2 Predicted additional impact due to climate change...... 27 11 Glass Eels ...... 27 11.1 Evidence for Entrainment Mortality ...... 28 11.2 Predicted entrainment Impact of HP C...... 29 11.3 Predicted additional impact due to climate change...... 30

BEEMS SPP063 (Entrainment) iv 12 References ...... 31

BEEMS SPP063 (Entrainment) v 1 Purpose

1.1 Title / topic

Entrainment impact on organisms at Hinkley Point C – supplementary note

1.2 Author

Brian Robinson

1.3 Purpose

The purpose of this document is to respond to regulators’ comments on this topic as set out in their review of EDF’s draft Hinkley Point C Habitats Regulations Assessment report, which was produced as part of the formal planning process for proposed nuclear new build (NNB) at Hinkley Point. In response to regulators’ subsequent comments this edition 2 includes further clarifications on: a. the predicted effects of climate change on the entrainment impacts at HP C. b. Information about the seasonal succession of zooplankton at Hinkley Point c. Predicted entrainment impacts on the eggs and larvae of Macoma balthica and the other important macrofauna at Bridgwater Bay

2 Summary

In response to consultation feedback, this report provides additional information on the predicted entrainment effects of HP C and builds on BEEMS Technical Report TR148 which provided entrainment impact predictions for fish eggs and larvae. Further information is provided on potential entrainment impacts on: • Phytoplankton • The major components of the haloplankton (copepods and mysids) • Crangon crangon • Sabellaria.alveolata larvae • Eggs and larvae of Macoma balthica and other important invertebrate organisms in Bridgwater Bay (Hediste diversicolor, Hydrobia ulvae, Nephtys hombergii) • Glass Eels ( Anguilla anguilla )

BEEMS SPP063 (Entrainment) 6 The report provides a description of the populations of the above species at Hinkley Point, describes the lifecycle stages that are potentially vulnerable to entrainment and provides a population impact assessment.

3 Comparison of the cooling water systems of HP B and HP C

Proposed cooling water system characteristics of HP C are: • Mean discharge volume: 125m 3 s-1 • ∆T of 11.6ºC (ambient water temperature raised by 11.6ºC) • Chlorination – only if biofouling becomes an issue. If necessary HP C may chlorinate either at 0.2mg l -1 continuously or on a 50% duty cycle. Under current environmental conditions at Hinkley Point the need for chlorination is not considered likely. • Offshore inlet tunnels 3.3km long, unchlorinated under any option • Offshore discharge 2km long • Drum filter screen mesh size 5mm • Transit time from inlet of condenser to outfall approx 18 minutes

Cooling water system characteristics of HP B: • Discharge 33.7 m 3 s -1 at ∆T of 11ºC • No chlorination • Intake 550 m offshore • Discharge: cross shore channel • Drum filter screen mesh size 10mm • transit time from inlet condenser to outfall <3 minutes

3.1 Hinkley Point monthly water temperatures

Table 1 below shows the predicted monthly temperatures at the inlet of HP C that were derived in BEEMS Technical Report TR187 edition 2/S. The table shows mean and 95%ile temperatures for 2020 and 2085 (based upon UKCP09 projections). For entrainment impact purposes it is appropriate to use the 95%ile predictions.

BEEMS SPP063 (Entrainment) 7 Table 1. Predicted monthly temperature at the HP C intakes (from BEEMS Technical Report TR187 Edition 2/S)

Month Predicted HP C inlet mean 1 stdev of UKCP09 Predicted HP C monthly temp. ºC daily sea predicted max daily temp . temp. daily max 95% ile ºC UKCP09. temp. 2020 2055 2085 2070 - increase 2020 2085 2100 2085 ºC JAN 7.8 8.6 9.3 1.1 +2.5 10.0 11.5 FEB 7.6 8.5 9.2 1.1 +3.0 9.7 11.3 MAR 7.9 8.8 9.5 0.8 +2.7 9.5 11.1 APR 10.0 10.9 11.6 0.8 +3.0 11.6 13.2 MAY 13.1 13.9 14.6 0.7 +3.1 14.5 16.0 JUN 16.8 17.6 18.3 0.8 +3.2 18.3 19.8 JUL 19.4 20.2 20.9 0.9 +3.2 21.2 22.7 AUG 20.1 21.1 22.0 0.8 +2.1 21.6 23.5 SEP 18.3 19.4 20.3 0.9 +2.3 20.0 22.0 OCT 15.8 16.8 17.8 1.0 +3.9 17.8 19.8 NOV 12.4 13.4 14.3 1.0 +3.5 14.3 16.2 DEC 9.8 10.6 11.4 1.4 +3.4 12.6 14.2

Table 2 shows the predicted temperatures at the output of the HP C condensers in 2020 and 2085 based upon the specified mean ∆T of 11.6 ºC in the HP C cooling water system. Any organisms entrained through HP C will be exposed to this temperature for an 18 minute transit time from the condenser to the outfall, after which the temperature exposure will drop as heat is lost from the plume and/or the organism leaves the buoyant surface plume. For many, but not all organisms, exposure to temperatures greater than 30 to 33 ºC leads to increased mortality (see section 4 below). The HP C discharge temperature is predicted to exceed 30 ºC as a 95%ile from July to September in 2020 and from June to October in 2085 based upon UKCP09 projections.

Table 2. Predicted HP C monthly discharge temperatures as a 95%ile. Month 2020 2085 HP C Discharge Temp HP C Discharge Temp ºC at ∆T=11.6ºC ºC at ∆T=11.6ºC Jan 21.6 23.1 Feb 21.3 22.9 Mar 21.1 22.7 April 23.2 24.8 May 26.1 27.6 June 29.9 31.4 July 32.8 34.3 Aug 33.2 35.1 Sept 31.6 33.6 Oct 29.4 31.4 Nov 25.9 27.8 Dec 24.2 25.8

BEEMS SPP063 (Entrainment) 8 .

3.2 Impact of changed inlet mesh sizes

For both HP stations the 5 or 10mm inlet mesh will be too large to impinge significant quantities of phytoplankton and zooplankton that will instead be entrained through the station. The proposed change to a 5mm inlet screen mesh for HP C means that a species dependent percentage of small fish and the important shrimp, Crangon crangon , will become impinged rather than entrained. This effect is not built into the calculations presented in BEEMS Technical Report TR148. In general the impact of the changed mesh size will be that the numbers impinged will increase but because these are smaller animals, the impinged will not increase in proportion. The environmental impact will depend on the relative risks and animal sensitivities to impingement and entrainment. A revised impact prediction for Crangon crangon is presented in this note.

4 Entrainment effects

Organisms entrained in a power station can suffer mortalities due to: • Mechanical stress • Pressure change • Temperature shock • Chlorination (if used)

These effects can be synergistic in that for example increased temperature increases the sensitivity of some organisms to chlorination. In general, with the exception of the egg stage, younger stages of organisms are more sensitive than older stages to entrainment effects. Most animals also show lower mortalities if the exposure time to chlorination chemicals is short. For many entrained species the maximum temperature experienced is important and therefore the ambient temperature at the time of exposure is important; animals that will be entrained in winter are far less likely to suffer effects from temperature rise than those exposed in mid summer.

BEEMS Technical Report TR081 provides an extensive summary of the large number of experimental determinations of entrainment mortalities that have been undertaken in the past. Entrainment effects on organisms have been studied using 3 main approaches: • Experiments that attempted to measure mortality directly after passage through operational power plants. These have produced very variable results due to different sampling regimes, different plant layouts and practices, lack of control over environmental parameters, undocumented control mortalities, different water qualities etc. Results are often difficult to interpret.

BEEMS SPP063 (Entrainment) 9 • Laboratory ecotoxicology experiments that attempted to measure impact of temperature and/or chlorination on individual species. Useful for understanding the impact of a single parameter but often miss synergistic effects of other stressors. • Use of Entrainment Mimic Units that simulate the conditions inside of an operating station. In principle the best form of laboratory experiment but there have been few such studies due to the length of time it takes to acquire statistically reliable results and associated cost considerations

BEEMS Science Advisory Report SAR008 summarises evidence that Upper Lethal Temperatures (ULT) for invertebrates are in the range 30-33ºC. More specifically:

ULT ºC Decapods 32.9 Amphipods 34.4 Euphausiacea 25.1

Mayhew et al (2000) report no thermal effect on Gammarids until discharge temperatures exceed 32 ºC. US EPA reports no effect on Gammarids at a ∆t of 10ºC and a discharge temperature (Tf) of 35ºC.

BEEMS Technical report TR081 presents the results and copies of the original reports from a set of UK experiments using an EMU designed to replicate conditions in Sizewell B: • ∆T 12ºC • Chlorination at 0.2mg l -1 TRO at the input to the condensers • Maximum pressure change approximately 2.5bar • Transit time through the cooling water system 10 minutes (including 3minutes after entering condenser) plus normally 15 minutes in the test water to simulate the discharged plume • 10mm inlet mesh

4.1 Estimating the power station abstraction zone

BEEMS Technical Report TR065 estimated the predicted zone that was at risk from cooling water abstraction as roughly equivalent to the plume volume at the 1C contour. TR065 estimated that 1.1% of this plume volume per day would be abstracted by HP C. This figure has been used in this report; however more recent work using particle tracking in a 3D hydrodynamic model has provided evidence that the abstraction zone has been overestimated and is therefore overly precautionary.

BEEMS SPP063 (Entrainment) 10 5 Relative importance of the sources of production in the Bristol Channel

Williams and Collins (1986) have summarised carbon production budgets for the Bristol Channel. Referring to the subdivisions of the Bristol Channel shown in Figure 1, annual primary production was 165 g C m -2 y -1 in the Outer Channel but only 6.8 g C m -2 y-1 in the Inner Channel (excluding a contribution from the Phaeocystis pouchetti bloom which occurred in most years in the Central Channel in June). Peak production in the outer Channel occurred in May/June and June/July in the Inner Channel. Both sub regions had a similar standing crop of phytoplankton but the annual primary production in the Inner Channel was only 4% of that in the Outer Channel due to rapid light attenuation and the rate of vertical mixing in the turbid waters of the Inner Channel. Uncles and Joint (1983) considered that advection and dispersion by currents determined the phytoplankton concentration in the Inner Channel rather than local production. Underwood (2010) considered that production of microphytobenthos (MPB) on the exposed inter-tidal flats is a major source of primary production in the Inner Channel that may exceed phytoplankton production and that resuspended MPB could be a significant contributor to measured chlorophyll a values. Underwood calculated that MPB primary production on the inter-tidal flats was approximately 33 g C m -2 y -1.

Figure 1. Bristol Channel sub regions referred to in this report.

BEEMS SPP063 (Entrainment) 11 The relative Importance of different production sources can best be appreciated by considering measurements of Total Particulate Carbon (TPC) in the Inner Channel in July of 2,800mg C m -3 of which 107mg C m -3 was ‘phytoplankton’ (calculated from chlorophyll a measurements) and 2.8mg C m-3 was zooplankton (Williams and Collins 1986). At its July peak the zooplankton stock was 50mg C m -2 (2.8 C m -3 * mean depth of 18m) compared with typical values from a thermally stratified Celtic sea site of 1000 to 3000 mg C m -2 and 700mg C m -2 in the Outer Channel. Williams and Collins (1986) concluded that the majority of the TPC and chlorophyll a was allochthonous in origin i.e. detritus mostly of a terrestrial origin and that the low values of phytoplankton and zooplankton demonstrated the minor role that the haloplankton plays in this sub region.

6 Phytoplankton entrainment

There is limited published information on phytoplankton in the Severn Estuary. Rees 1939, Pybus 2007 describe a system with a low diversity of diatoms predominantly comprising: Primarily benthic diatoms • Actinoptychus spp. • Bacillaria paxillifer • Gyrosigma spp. • Melosira arctica • Nitzschia spp.

Planktonic diatoms • Asterionella spp. • Chaetoceros spp. • Ditylum brightwelli • Odontella spp. • Helicotheca tamesis

Williams and Collins (1986) also reported regular blooms of Phaeocystis in June in the Central Channel. Phytoplankton surveys by APEM from Nov 2008 to October 2009 in the vicinity of the planned HP C cooling water system found limited species diversity and abundance. A total of 21 species were found (19 diatoms, the flagellate Ceratium furca and the prasinophyte Halosphaera viridis ). The highest phytoplankton abundance was found in July and consisted mostly of Odontella spp. (note that due to potential problems with net clogging in the high suspended sediment environment at Hinkley Point, the net mesh size was too coarse to capture all phytoplankton species during the APEM surveys) .

BEEMS SPP063 (Entrainment) 12 In the Inner Channel the major part of primary production occurs in June and July (Williams and Collins, 1986)

6.1 Evidence for phytoplankton entrainment mortality

In a series of experiments at Fawley power station Davis (1983) demonstrated that, in the absence of chlorination, primary production was enhanced by increased water temperature up to a discharge temperature of 23ºC but thereafter was progressively inhibited. No significant net loss in phytoplankton productivity was found at discharge temperatures of up to 27ºC. Davis (1983) concluded that the entrainment effects of mechanical damage and thermal shock on phytoplankton were negligible.

Davis (1983) found that primary productivity was reduced by approximately 60% with a chlorination level of 0.2mg l -1 and a ∆t of 10ºC (ambient temperature unspecified). It was not clear if the phyto- plankton cells were killed or temporarily inhibited. For experimental reasons cells had to be cultured in chlorinated water for 3 hours which is not representative of the short exposures in a power station (18 minutes HP C). Such exposure may have increased the measured effects.

EDF (1978) contains results from laboratory experiments on the effects of thermal shock upon the diatoms: • Phaeodactylum tricornutum • Gyrosigma spencerii

Neither species was significantly affected when cultured at 12ºC or 16ºC by thermal shocks of up to 17ºC. Both species were killed at ambient temperatures of 24ºC and a ∆t of 15ºC. Growth was inhibited at ∆t of 10ºC and ∆t of 12ºC. The LT 50 values (temperature lethal to 50% of the species) were 36.5ºC and 37ºC respectively.

The flagellate Dunaliella tertiolecta was more resistant and survived an exposure time of 40 minutes at a discharge temperature (Tf) of 41ºC. After exposure the cell growth stopped for 5 days and then recovered to densities similar to the control within 12 days.

6.2 Predicted entrainment impact of HP C

The maximum predicted discharge temperature of HP C in August 2020 is 33.2ºC as a 95%ile i.e. below the expected LT 50 values. At such a temperature there is a possibility of a small, localised reduction in growth but this may not be noticeable in the enhanced productivity of the warmer receiving waters. In the absence of chlorination the thermal effects of entrainment on primary production would be expected to be negligible.

BEEMS SPP063 (Entrainment) 13 If chlorination at 0.2mg l -1 TRO were employed by HP C, from the available evidence an approximate 60% reduction in productivity would be expected in entrained phytoplankton. Making worst case assumptions that the effected cells were killed and that HPC extracts 1.1% of the plume volume per day (BEEMS Technical Report TR065) then 0.7% of the phytoplankton cells in the plume volume would be killed per day. Assuming phytoplankton is uniformly distributed over the entire Inner Channel, HP C could reduce the Inner Channel phytoplankton abundance by 0.05% per day. The overwhelming majority of phytoplankton production and consumption by copepod zooplankton takes place outside of the Inner Channel and outside of the influence of HP C (Williams and Collins (1985)).

The predicted recirculation of the HP C discharge water into the intakes is slight (BEEMS Technical Report TR135). The reduced phytoplankton abundance in the HP C discharge water should rapidly be restocked from phytoplankton cells from elsewhere in the Channel that are outside of the HP C abstraction zone. Under such circumstances the impact on phytoplankton production would be negligible.

6.3 Predicted additional impact due to climate change

The maximum predicted discharge temperature of HP C in August 2085 is 35.1ºC as a 95%ile.

Such a temperature is below the expected LT 50 values. There would be a small localised reduction in productivity but as stated above the reduced phytoplankton abundance in the HP C discharge water would rapidly be restocked from phytoplankton cells from elsewhere in the Channel that are outside of the HP C abstraction zone. Under such circumstances the impact on phytoplankton productivity would be negligible.

7 Zooplankton entrainment

A grid of 58 sampling sites in the Bristol Channel was surveyed for zooplankton by the Institute for Marine Environmental Research in the period June 1971 to November 1981 (Collins and Williams, (1982), Williams and Collins (1986)).

Table 3. Zooplankton composition of the Inner Channel integrated over 307days from 4/11/1973 to 6/7/1974 from Williams and Collins (1986) % of total mg C m -3 Feeding type zooplankton Holoplankton

Copepoda 60 Omnivores Mysidacea 120 Euphausiacea 32 63%

BEEMS SPP063 (Entrainment) 14

Chaetognatha 16 Carnivores Ctenophora 11 8%

Meroplankton Decapods: Porcellana larvae, 40 Omnivores Pasiphea swado Amphipods: Gammaridea 20 Others (Brachyura, Caridea larvae, 9 21% Cirripedia, indeterminate zoea)

Fish larvae, isopod Eurydice 8 Carnivores 2% pulchra

Total Meroplankton 77 Total Holoplankton 239 Other 19 Total Zooplankton 335

The zooplankton community has also been sampled qualitatively from the intake forebay at Hinkley Point B in conjunction with the monthly fish impingement sampling since January 1982. Burfoot (1995) provides details of the community structure from samples collected between August 1994 and July 1995. Numerically the most abundant zooplankton in the HP B samples were copepods dominated by Acartia spp, followed by mysids dominated by Schistomysis spiritus.

An up to date description of the monthly zooplankton succession at Hinkley Point is described in BEEMS Technical Report TR-S 210. The report provides descriptions of the number and species of zooplankton found in the 2010 monthly ‘entrainment’ sampling at Hinkley Point B. Entrainment sampling at HP B is undertaken by Pisces Conservation as a separate task during the monthly impingement monitoring programme at the station. Two plankton nets of 700um and 150um mesh are placed in the HP B cooling water intake forebay in front of the main circulating pumps for 1 hour. The nets are deployed 2 hours before low water on the ebb tide. The sampling is qualitative in that no estimate is available of the volume of water that passes through the nets due to the turbulence in the forebay. Nevertheless the sampling is considered to provide a good representation of the relative zooplankton abundance by month

The year 2010 was chosen for comparative purposes with the quantitative monthly plankton sampling undertaken from February to June 2010 in Bridgwater Bay. (Ichthyoplankton results from these surveys have been presented in BEEMS Technical Report TR083a. These samples have also recently been reanalysed in order to provide quantitative zooplankton abundance estimates.

BEEMS SPP063 (Entrainment) 15 The results support the pattern previously reported in the scientific literature of a zooplankton community numerically dominated by a seasonal succession of mysids (predominantly Mesopodopsis slabberi and Schistomysis spiritus ) and the copepoda Eurytemora affinis and Acartia spp .

7.1 Copepod entrainment

Collins and Williams (1982) characterised the Bristol Channel and Severn estuary via the numerically dominant copepod populations. A strong linkage between the assemblages and salinity was found. The main species found were: • Acartia spp . • Calanus helgolandicus • Centropages hamatus • Eurytemora affinis

The Inner Channel was found to be an intermediate zone between true estuarine and estuarine and marine characterised by salinity ranges of 27 to <34 and dominated by Acartia spp. Burfoot (1995) presents the results of zooplankton sampling in the forebay at Hinkley Point B for the period Aug 1994 to July 1995. Acartia spp. were the dominant copepods (>50% by number). All 4 of the copepod species above were found. They each had 3 abundance peaks per year in February, June and October with the June peak being the largest.

Williams and Collins (1985) show that Acartia production occurs in the Central Channel and then a part of the population migrates to the Inner Channel. Burkill and Kendall (1982) calculated that the production/biomass (P/B) ratio of the copepod Eurytemora affinis in the Inner Channel was approximately 33 yr -1 i.e. 8.6% per day. This value was not atypical for copepods found in similar temperatures. Annual P/B ranges for Acartia spp. were reported as 17-58 yr -1 with higher figures of up to 257 yr -1 reported for tropical latitudes (Burkill and Kendall 1982). As a first approximation, in a steady state system, P/B ≈ natural mortality. A natural mortality of 33 yr -1 has therefore been used in this assessment.

7.1.1 Evidence of entrainment mortality: Acartia tonsa (adults)

A.tonsa Upper Lethal Temperature: 37-39ºC (BEEMS Technical Report TR081)

Table 4. Results from laboratory experiments on the effects of ∆T on Eurytemora velox (EDF 1978); ∆t Mortality Discharge temperature Tf 12 ºC 40% 24 ºC 12 ºC 80% 26 ºC

BEEMS SPP063 (Entrainment) 16 12 ºC 100% 28 ºC 15 ºC 100% Not dependent upon Tf

EMU experiments with A. tonsa (Bamber and Seaby 1994a) These tests used 3 minutes exposure to temperature and chlorination and then held the animals in the test water for 15 minutes. The ambient water temperature was 15ºC. Conclusions from the EMU experiments; • mortality due to pressure effects 10% • ∆t 12ºC (discharge temperature Tf = 27ºC) no effect • Chlorination mean mortality 13.5% (0.14 to 0.25mg l -1 dose) • predicted power station effect with chlorination: 20% mortality • From other studies calenoid copepods are tolerant of Tf = 31ºC • results are representative of other adult calenoid copepods

7.1.2 Predicted Entrainment Impact of HP C Making the following assumptions: • 1.1% of plume volume entrained per day (TR065) • Entrainment mortality 20% (from EMU experiments – see section 4) • Ratio of plume volume to volume of Inner Channel = 7.2% • Copepods uniformly distributed throughout the Inner Channel

The entrainment mortality in the summer at Hinkley Point will represent 0.016% of the Inner Channel population per day. Williams and Collins (1985, 1986) show that the population of Acartia spp is distributed over the entire Central and Inner Channels in spring/summer and therefore the predicted entrainment mortality due to HP C is less than 0.004% of the Bristol Channel population. Given the natural productivity of the species this would be considered a negligible impact.

7.1.3 Predicted additional impact due to climate change TR-S 210 shows that the main period of copepod abundance at Hinkley Point is from February to May with less than 1.6% of Acartia spp. abundance occurring in June. The predicted HP C discharge temperatures from February to May would be 21.3 to 26.1ºC in 2020 and 22.9 to 27.6ºC in 2085. These temperatures are all below the reported 31ºC that Acartia spp. are tolerant to (see section 7.1.1). Bamber and Seaby (1994a) also determined no increased mortality at temperatures of 27ºC. On the basis of this evidence there will be no additional mortality to Acartia spp. from entrainment in HP C due to climate change.

7.2 Mysid Entrainment

The main mysid species found in the Inner Channel and in the Hinkley Point forebay (Collins and Williams 1982, Bamber and Henderson 1994) are shown below:

BEEMS SPP063 (Entrainment) 17

Species % of annual Peak abundance numbers sampled Schistomysis spiritus 66% September/October Mesopodopsis slabbereri 20% August/September Gastrosaccus spinifer 11% April/May & November Neomysis integer 4% March

S. spiritus produces 3 generations per annum. Plankton monitoring data at Hinkley Point only show the autumnal recruitment. Females are pouch bearers and migrate offshore to release their young. Males remain in the offshore nursery areas to await the females. Mean natural mortality has been estimated for another common, temperate latitude mysid, Metamysidopsis elongata, as 0.04 d -1 adults, 0.06 d-1 juveniles and 0.013 d -1 for brood pouch young (Clutter and Theilacker 1971) Mysids are part of the hyperbenthic community and are normally found within 1m of the sea bed. Maximum concentrations are found just below the low water mark in summer and near to the 5 to 10m contour in winter. They indiscriminately feed on fine particulate matter including detritus, algae, zooplankton and sand grains (Mauchline 1967). Mysids are good swimmers and can maintain 10 body lengths s -1. They can maintain their position even in strong currents by sheltering on the seabed. Mysids are an important part of the diet of C.crangon and fishes in the 3-15cm length category.

7.2.1 Evidence for entrainment mortality Mysids are sensitive indicators of water quality and are frequently used in ecotoxicology tests.

Results from US power plant entrainment experiments with mysids

Species % Entrainment Survival at Reference discharge temperature Tf Tf<30C 30C-32C >32C Neomysis mercedis >90% 30% 0% Mayhew et al (2000) N.americana 80% - 10% US EPA (1977)

In an operating plant with chlorination, 100% mortality of mysids was recorded at discharge temperatures >27ºC (Clark and Brownell 1973).

In the absence of better data, 100% entrainment mortality for mysids was assumed as a worst case for HP C.

7.2.2 Predicted entrainment impact of HP C

Assuming: • 1.1% of plume volume entrained per day (TR065)

BEEMS SPP063 (Entrainment) 18 • Entrainment mortality 100% • Ratio of plume volume to volume of Inner Channel = 7.2% • Mysids uniformly distributed throughout the Inner Channel

The additional mortality in the Bristol Channel from entrainment losses in HP C would be 0.08% d -1 (predominantly to juveniles). Comparing these losses with the natural mortality of mysids reported in Clutter and Theilacker (1971) of 4% d -1 (adults) to 6% d -1 (juveniles) it is reasonable to conclude that there would be a negligible increase in mysid mortality due to HP C entrainment.

7.2.3 Predicted additional impact due to climate change In the above assessment we have assumed a worst case 100% mortality of entrained mysids during the period February to November when there is a succession of mysid species. The predicted higher temperatures due to climate change would therefore have no additional impact.

8 Crangon crangon

Using morphometric measurements Henderson et al (1990) have determined that the Bristol Channel C.crangon population (east of the line Nash Point to Porlock Bay) is distinct from its south- western sea neighbour. C.crangon is impinged at HP B throughout the year with peak abundance in the period July to November and minimum in April/May. In Bridgwater Bay C.crangon (mostly juveniles) migrate with the rising tide onto the high intertidal flats. At low water the population is concentrated near the low water mark and HP B catches are largest; typically 7 times those at high water (Henderson and Holmes 1987). Spawning takes place twice a year in January and late spring/early summer; the females migrate offshore to the west to release their eggs. Mature males remain offshore to mate with returning females. The January spawning leads to egg hatching at the end of March/early April with metamorphosis and settlement on the intertidal area in early to mid May. The early May spawning hatches in early June with settlement in mid July (Henderson 1990). Henderson and Holmes 1987 report that C.crangon larvae have not been found in the monthly plankton sampling at HP B. This is in agreement with Williams and Collins (1986) who found highest density of C. crangon larvae in the Outer Channel. The size of the annual recruitment is therefore determined by environmental factors outside of Bridgwater Bay and the influence of HP B or HP C. The lifecycle stages of C.crangon that are vulnerable to impingement and entrainment are juveniles and predominantly mature females that utilise the lower parts of Stert flats.

C.crangon is an important component of the diet for most fish within Bridgwater Bay and is unique in being the only crustacean that is abundant throughout the year (Henderson et al 1992).

With a 10mm inlet screen mesh at HP B approximately 39% of C. crangon that are drawn into the cooling water system are impinged and the rest are entrained and pass through the condensers (figures calculated using typical length frequency distribution of C.crangon (Oh et al 1999) and

BEEMS SPP063 (Entrainment) 19 impingement probabilities from Henderson and Holmes (1987)). With the proposed 5mm mesh of HP C approximately 90% of the animals will be impinged and 10% entrained.

8.1 Evidence for entrainment mortality

Bamber and Seaby (1994b) have produced results from EMU experiments using C.crangon larvae. These experiments showed no effect from pressure, mechanical damage, direct effects for a ∆T of 12ºC nor from chlorination. The work did show that elevated temperatures increased the animal’s sensitivity to chlorine. Typical power station mortality with chlorination was estimated to be 25% (at a discharge temperature of 23ºC).

No results from juvenile or adult C.crangon are available. Freitas et al (2007) estimated a maximum temperature for C.crangon to survive of 30ºC based upon physiological considerations. However this estimate is not the same as the critical temperature for survival in a 20 minute entrainment exposure. BEEMS SAR008 summarises thermal ULT for invertebrates as falling within the range 30-33ºC and for decapods as a mean of 32.9ºC. In July or August there may therefore be some thermally induced mortality from HP C. The EMU derived 25% mortality applied to larvae but C.crangon larvae are not abstracted in any significant numbers at Hinkley Point (they have not been detected in the entrainment samples and only recorded in small numbers in the offshore sampling programme). In principle it would be expected that juveniles and adults would be less sensitive to chlorine but in the absence of additional data the 25% mortality has been used in entrainment calculations for HP C with chlorination.

8.2 Annual Impingement and Entrainment Impact of HP C options compared with HP B

Impingement and entrainment losses have been calculated based upon the following assumptions: • HP B and HP C impingement from BEEMS Technical report TR148 • HP C will have a Fish Recovery and Return system with a 20% mortality for impinged C.crangon (TR148) • C.crangon e ntrainment mortality in HP C at current ambient temperatures: 25% with chlorination, 0% no chlorination (Bamber and Seaby (1994b)) • Approximations to C.crangon size structure and length weight relationship: weight=0.0008*(carapace length) 3.07 (Both from Oh et al 1999). • Inlet mesh selectivity (Henderson and Holmes 1987)

BEEMS SPP063 (Entrainment) 20 Table 5. Predicted losses of C.crangon due to impingement and entrainment at HPB and C in 2020 Station Impinged Loss Loss Entrained Loss Loss Total Loss Tonnes Millions Millions Tonnes Millions Millions Tonnes Millions HP B 4.9 4.9 3.8 7.7 0 0 4.9 3.8 HP C 10mm 19.1 3.8 3.0 29.9 0 0 3.8 3.0 mesh, No Cl HP C 10mm mesh 19.1 3.8 3.0 29.9 7.5 1.6 11.3 4.5 Cl at 0.2ppm HP C 5mm mesh, 44.1 8.8 4.06 4.9 0 0 8.8 4.06 No Cl HP C 5mm mesh, 44.1 8.8 4.06 4.9 1.2 0.07 10.0 4.13 Cl at 0.2ppm

Henderson and Holmes (1987) estimated the C. crangon adult population size on the 20km 2 of Stolford flats to be in the range 3 10 6 to 5 10 7 with a geometric mean of 1.22 10 7 individuals. The adults have a mean weight of approximately 1g and the population estimate was therefore approximately 610kg/km 2. Henderson et al (2006) estimated the mean Production/Biomass ratio in the area over the period 1981-2004 to be 2.92 i.e. the estimated annual production at Stert flats was 1781kg/km 2. The estimated production from the 48km 2 of Stert and Berrow flats was therefore approximately 85T and 356T for the 200km 2 of the Bristol Channel inter-tidal flats.

Station Predicted % loss of Bristol Channel Annual C. crangon Production HP B at present 1.1% HP C (5mm mesh) with no chlorination 1.1% HP C (5mm mesh) with chlorination 1.2%

There is therefore a negligible difference between the total predicted losses from HP C (with its 5mm inlet mesh) and the existing HP B station. If HP C needed to chlorinate, losses could be further reduced from those shown above by adopting a 50:50% chlorination duty cycle. Under such circumstances the total losses would reduce to 1.1% of the Bristol Channel production.

These losses need to be seen in the context of the natural mortality of C.crangon . Henderson et al (2006) estimated the mean natural mortality of the Bridgwater Bay population over the period 1981 to 2004 to be 2.92 y -1 i.e. 95% per annum. The instantaneous natural mortality of juvenile, newly settled shrimps which form the majority of the animals abstracted by the existing HP B is much greater. The existing Bristol Channel C.crangon population is considered to be density limited with a relatively stable adult standing stock (Henderson et al 2006) and the evidence from the HP B impingement surveys is that the C.crangon production/biomass ratio has increased over the past 27 years. It is therefore concluded that HP B has had no measurable effect on the C.crangon

BEEMS SPP063 (Entrainment) 21 population locally or in the wider Bristol Channel and that the predicted virtually identical annual C.crangon impingement/entrainment losses from HP C will also have negligible effect.

8.3 Predicted additional impact due to climate change

The peak abundance of C.crangon in Bridgwater Bay occurs from July to November when discharge temperatures in 2085 are predicted to be in the range 34.3 to 27.8ºC respectively as a 95%ile. From June to October there would be a risk of thermally induced entrainment mortality. As a conservative assumption we have assumed that there would be 100% mortality of entrained C.crangon in 2085 with or without chlorination.

The table below shows the impact of this assumption.

Table 6. Predicted losses of C. crangon due to impingement and entrainment at HPB and C in 2085 Station Impinged Loss Loss Entrained Loss Loss Total Loss Tonnes Millions Millions Tonnes Millions Millions Tonnes Millions HP B (theoretical 4.9 4.9 3.8 7.7 7.7 1.6 12.6 5.4 – station would no longer be operational) HP C 10mm 19.1 3.8 3.0 29.9 29.9 6.3 33.7 9.3 mesh, No Cl HP C 10mm mesh 19.1 3.8 3.0 29.9 29.9 6.3 33.7 9.3 Cl at 0.2ppm HP C 5mm mesh, 44.1 8.8 4.06 4.9 4.9 0.3 13.7 4.3 No Cl HP C 5mm mesh, 44.1 8.8 4.06 4.9 4.9 0.3 13.7 4.3 Cl at 0.2ppm

These predicted losses have been expressed as a percentage of the Bristol Channel annual production below and as can be seen the additional impact over that in 2020 is negligible.

Station Predicted % loss of Bristol Channel Annual C. crangon Production in 2085 HP B (theoretical – the station will no longer be 1.5% operational) HP C (5mm mesh) with no chlorination 1.2% HP C (5mm mesh) with chlorination 1.2% Note: The above calculation assumes that annual production of C. crangon remains constant at the 2006 level but it is worth noting that production has risen with rising water temperatures due to climate change over past 30 years. There will, however, be a limit to this effect.

BEEMS SPP063 (Entrainment) 22

9 Sabellaria alveolata

Reefs of the tube building worm, Sabellaria alveolata, are found to the west of Hinkley Point and along the low shore directly in front of the station, as well as on some low shore areas of Stert Flats.

Evidence from laboratory experiments Wilson (1971) is that S.alveloata spawns briefly in July and the larvae spend a minimum of 6 weeks and a maximum of 8 months in the plankton. Field observations on larval settlement have proved variable from year to year but Wilson (1976) detected peaks in September to November and December in Cornwall. Cazaux (1970) reported peak larval densities from October to March on the French Atlantic coast. Dubois et al (2007) report spawning in the Bay of Mont-Saint-Michel in early May with a settlement time of 12 weeks and then September with a settlement period in the 8ºC warmer water of 4 weeks. Larvae settle principally on old colonies and detect the cement used by tube building worms of S.alveolata or S.spinulosa . Natural mortality has been estimated by field measurement by Dubois et al (2007) to be 0.09 d -1 (range 0.089 to 0.097 d -1). These values were in the range of marine invertebrate mortalities described in Rumrill (1990) (mean of 23 species 0.23 d -1, range 0.016 to 0.82). Dubois et al (2007) found evidence for vertical migration with larvae moving towards the surface during the flood tide during the day as well as at night.

S.alveolata growth is promoted by high levels of suspended sediment and higher water temperatures. In the UK it is at or near the northern edge of its thermal range and it can suffer high mortalities in cold winters.

BEEMS SPP063 (Entrainment) 23 9.1 Evidence for entrainment mortality

The planktonic life stage of S.alveoloata is the only stage vulnerable to entrainment. There are no published data on the entrainment mortality of Sabellaria larvae. BEEMS technical report TR153 found no adult mortality for S.spinulosa after a 28day exposure to chlorine at 0.1mg/l at 15ºC -1 ambient. BEEMS Technical Report TR162 reports an EC50 for a 5min exposure at 0.3mg l for the polychaete Phragmatopoma californica ( temperature not specified). In the absence of more data a 50% mortality has been assumed for HPC with chlorination at 0.2mg l -1 TRO.

9.2 Predicted impact of entrainment of HP C

BEEMS SPP066 on modelling the potential abstraction of S.alveolata larvae released from the range of possible sites in Bridgwater Bay by particle tracking predicts a 0.05% chance of larval abstraction per day for the 4 intakes planned for HP C (The potential spawning area in Bridgwater Bay was determined from habitat maps in BEEMS Technical Report TR039). Assuming 50% entrainment mortality, the predicted worst case loss of S. alveolata larvae (assuming chlorination at HP C) is 0.025% per day. In practice the risk of abstraction would be less than calculated because no account has been taken of larval dispersion into the wider channel. Natural mortality is approximately 9% per day (Dubois et al 2007). The resultant increase in natural mortality from 9% to less than 9.025% is considered negligible.

10 Macoma balthica and other important macrofauna in Bridgwater Bay

Monitoring studies conducted in the Severn Estuary suggest that the bivalve Macoma balthica is ubiquitous in intertidal sedimentary habitats between at least Hinkley Point and the Severn Bridge (BEEMS SPP062). Macoma balthica is, along with Hediste diversicolor and Hydrobia ulvae, one of the most dominant benthic species in the area; these three species together constitute 86% of the biomass of benthic organisms on Stert Flats (BEEMS Technical Report TR029). Macoma balthica is found in subtidal and intertidal areas of Bridgwater Bay and is a broadcast spawner. The proximity of HP B and the proposed HP C means that a proportion of the local annual production of M. balthica eggs and larvae are likely to be entrained into the power station cooling water systems and potentially suffer increased mortality.

BEEMS SPP070/S describes modelling by particle tracking of potential abstraction of M.balthica eggs and larvae released from sites in Bridgwater Bay. The instantaneous mortality of M.balthica eggs and larvae due to entrainment by the proposed HP C power station was calculated to be equivalent to 0.0027 and 0.0019 day -1 for planktonic stage lengths of 18 and 25 days respectively;

BEEMS SPP063 (Entrainment) 24 assuming a worst case scenario of no organisms surviving entrainment through the cooling water system.

The natural mortality of M.balthica decreases after larval settlement on the seabed, and Philippart et al (2003) estimate that the natural mortality of the planktonic phase is >0.1 d -1 as opposed to < 0.05d -1 after settling. Such an estimate of planktonic mortality is in broad agreement with the lower end of the estimates for invertebrate meroplanktonic larvae from a wide variety of locations of 0.13 to 0.28 d -1 (Rumrill 1990).

The total mortality of M.balthica eggs and larvae at the end of the planktonic phase is given by

-M N -1 Mortality 0 = 1- (e ) where M= natural mortality in d and N is the length of the planktonic phase in days

With additional power station entrainment mortality (m), the total mortality is given by -M-m N Mortality p = 1- (e )

The ratio of these 2 numbers gives the change in mortality of the egg and larval phase due to power station entrainment and this is tabulated below for HP C as a function of M between 0.13 and 0.28d -1 (Rumrill 1990).

Table 7. Change in M.balthica mortality at the end of the planktonic phase Natural mortality M Duration of planktonic phase 0.13 0.28 18d 0.51% 0.03% 25d 0.19% 0.004% Note: the above results assume a worst case of 100% mortality of entrained eggs and larvae

Recruitment of benthic organisms is often extremely variable with some species displaying annual variations of up to several orders of magnitude. Beukema et al (2001) describe the results of a 27 year time series in the Wadden Sea from 1973-1999 on bivalve recruitment success. The annual production of M.balthica varied between 40% to +200% of the long term mean. The distribution of results was far from normal with more extreme than close-to-average values. Indeed more than half the years could be classified as clear recruitment failures or outstanding successes. Set against such natural variability, changes in mortality due to power station entrainment of between 0.004% and 0.5% can be considered negligible, having no impact on the recruitment success of the M. balthica population - especially given the likelihood that areas outside of Bridgwater Bay contribute significantly to recruitment in the Bay (SPP070/S)

BEEMS SPP063 (Entrainment) 25 10.1 Entrainment impact on other important macrofaunal organisms in Bridgwater Bay

The intertidal and subtidal ecology of Bridgwater Bay is described in BEEMS Technical Reports TR029 and TR184. Mud-dominated sediment types can be found on the low shore at Berrow Flats and across most of Stert Flats at all elevations leading to relatively homogenous infaunal communities across the mudflat in terms of the dominant species. An increasing trend in taxonomic richness, abundance and biomass with increasing tidal height was noticeable at Berrow Flats, as well as relatively high abundance of organisms adjacent to the River Parret. The three most significant invertebrates in terms of biomass, M. balthica, H. diversicolor and H. ulvae were widely distributed across Berrow and Stert flats. The clam M. balthica was most abundant in the mid- upper shore of Berrow Flats, and in the south-western corner of Stert Flats. The gastropod H. ulvae was more uniformly distributed across the site (BEEMS Technical Report TR029).

Figure 1. Contributions of the three most significant invertebrates in terms of biomass, M. balthica H. diversicolor and H. ulvae, across the intertidal areas of Bridgwater Bay. The size of the symbols is proportional to the summed biomass of all species. Data are taken from the 2008 characterisation

As with the intertidal mudflats, the subtidal infaunal communities of Bridgwater Bay are depauperate. Across the BEEMS 2008-2010 sampling the average species richness and abundance was less than 2 species and 3 individuals per 0.1m -2 respectively, while mean biomass was less than 0.005 g.m -2 (BEEMS Technical Report TR067). Two species of bivalve dominated the biomass, M. balthica (58%) and Nucula nucleus (28%) ; together comprising 85% of the infaunal biomass. There was a trend towards greater abundance and biomass in the nearshore stations, a pattern that was consistent through time.

Table 8 below summarises the reproductive behaviour of the important macrofauna in Bridgwater Bay. The species are found commonly across Stert and Berrow flats and their distribution is broadly similar to that of M.balthica (BEEMS Technical Reports TR184, TR029 ). H.diversicolor eggs and larvae do not have a planktonic phase and are not therefore at risk from entrainment by HP C. H.ulvae and N.hombergii have planktonic phases lasting from 0 to 8 weeks. Both species would be at risk of entrainment but their respective planktonic phases would have moved out of Bridgwater Bay after 6 or 11 days on neaps and springs respectively (SPP070/S).

Table 8. Reproductive behaviour of important macrofauna in Bridgwater Bay (from Marlin database) Species Organism type and Reproductive Planktonic phase and distribution behaviour M.balthica Intertidal and Broadcast spawner 18-25 days subtidal bivalve Deleted: H.diversicolor Intertidal polychaete Eggs laid and develop None in burrows

BEEMS SPP063 (Entrainment) 26 H.ulvae Intertidal gastropod Fertilised eggs Variable: Up to 4 weeks also found subtidally deposited on shells, or completely absent down to 100m. larvae planktonic N. hombergii Polychaete - lives Broadcast spawner 7 to 8 weeks infaunally in muddy sand in the intertidal and shallow sublittoral.

10.2 Predicted additional impact due to climate change

In the above analysis we have already assumed a worst case of 100% entrainment mortality in HP C. The increased temperatures due to climate change would, therefore, have no effect on the predicted population impact.

11 Glass Eels

The majority of any glass eels abstracted by HP C will be entrained as they will be small enough to pass through the 5mm inlet screen mesh (Turnpenny and O’Keefe 2005). Roqueplo (2000) reported that 97% of glass eels were able to pass through a 3mm mesh within 1 minute; the remainder being impinged. Glass eels enter the Bristol Channel in the approximate period February to April. Once they detect that they are in an estuary (possibly from the freshwater signal) they migrate up the estuary using selective tidal stream transport. The presumption in the literature is that in the highly turbid environment of the Severn that glass eels will be distributed throughout the water column on the flood tide and either on or buried into the seabed sediment on the ebb tide. If they migrate with the same efficiency as in the Gironde (Beaulaton et al 2005) the eels will migrate through the estuary at approximately 3 to 4km d -1. The migration routes that glass eels take through the Bristol Channel have not previously been determined because of the experimental difficulty in performing such work in such a large estuary. In much smaller estuaries there is evidence from fishing that glass eels use the full width of the estuary to migrate. It is known that the eels employ selective tidal stream transport to migrate and therefore the use of a particle tracking model may provide some insights into their behaviour. Such a model has been developed within the BEEMS programme but to be initialised it requires information on glass eel distribution across the Channel (spatial, vertical and temporal). BEEMS Technical Report TR-S 211 in preparation at 27/3/2012) describes a survey undertaken in February 2012 to determine the distribution of glass eels within the Estuary. The results from the survey have not yet been analysed statistically but initial suggestions are that:

• Eels migrated up- estuary on the flood tide by day and night • Eels were not in the water column on the ebb tide • Eels migrated preferentially on or near to the surface on the flood tide but were also found in lower densities across the full measured depth range (0, 4 and 7m depending on the available water depth)

BEEMS SPP063 (Entrainment) 27 • They were distributed across the full width of the Bristol Channel at Hinkley Point • That higher densities appeared to occurr in shallower waters close to shore, particularly along the southern shore in the vicinity of the HP B inlet. In such circumstances densities at HP B were greater than at the proposed HP C offshore intakes.

The sampling net had a square opening; 1.5m deep. The statement that eels migrate near to the surface describes those eels that were caught within 1.5m of the surface. It is possible that the majority of such eels occurred at depths of less than 1.5m. However even at 1.5m deep, except at low water, the eels would be above the predicted abstraction zone of HP B and HP C and therefore at low risk of entrainment.

The natural mortality of glass eels (i.e. excluding fishing mortality) has been estimated to be in the range 0.0233 – 0.0049 d-1 (Beaulaton et al 2007)

11.1 Evidence for Entrainment Mortality

Glass eels entrained at HP C would be subject to mortality from:

• mechanical damage from the impellors in the cooling water pumps

• thermal shock (maximum discharge temperature would be in the range 18 to 22ºC during the period when glass eels could be entrained)

• Exposure to chlorination for an 18 minute period inside the plant at 0.2mg l -1 at the inlet to the condenser (If HPC uses chlorination)

Turnpenny (2000) demonstrated that the expected mortality from the above temperature and chlorination regime in combination with a 10mm cooling water inlet mesh would be negligible. Work done by the University of Perpignan in 1977 and ISTPM in 1982 also demonstrated that glass eels do not suffer mortalities nor show any behavioural changes when discharge temperatures are below 30°C or 25°C respectively (cited in Onema 2007). Any glass eel entrainment mortality would therefore only be expected from mechanical damage either in the cooling water pumps or in passage through the 5mm inlet mesh filter and other parts of the cooling water system.

HP C will employ cooling water pumps that are either the same or close equivalents to those designed for Flamanville 3.These pumps were modelled in the STRIKER programme that has been widely applied to other pump mortality calculations (Turnpenny 2000 reproduced in BEEMS Technical report TR081). The predicted mortalities due to the pumps ranged from 1.6% for a 70mm glass eel to 1.8% for an 80mm eel (Appendix 1, Turnpenny pers. comm.).

Roqueplo (2000) reported the results of entrainment experiments performed in March 2000 at le Blayais station on the Gironde estuary. The cooling water system at this station has: • 380m offshore inlets

BEEMS SPP063 (Entrainment) 28 • 3mm inlet mesh • Uses no chlorination. • Multiple offshore discharges heads fed by 2.5km tunnels • The estuary width at the station is approximately 4.5km.

These experiments were undertaken by inserting large numbers of dyed glass eels into the cooling water drum filter (i.e. the eels had to pass through the 3mm mesh to enter the cooling water circuit). The measured transit time from the insertion point to the discharge was 17 minutes. A proportion of the eels were then caught in the immediate vicinity downstream of the discharge zone by a commercial eel fishing boat. A 9% mortality of marked eels was measured 6 hours after capture, rising to 15% after 24hours. This level of mortality remained unchanged after 1 week.

Roqueplo (2000) reported that the experimental eels that did not suffer entrainment mortality did exhibit some behavioural changes; indeed animals with different dye colours showed differential catchability. As with all mark/recapture experiments the experimental animals would have experienced handling stress which could have made the animals more susceptible to entrainment mortality or to being caught in fishing nets.

The results of this experiment are in contrast to those obtained at Cordemais in 1982-83; a large conventional thermal power plant on the Loire (cited in ONEMA 2007). This experiment did not use marked eels and used nets at the discharge to capture entrained eels. The immediate mortality of eels captured in this experiment was 0.9%. No longer-term mortality estimates were made.

The range of available mortality estimates therefore range from 1.8% from pump damage predictions and laboratory experiments to 0.9% to 15% from in situ experiments at French power stations.

11.2 Predicted entrainment Impact of HP C

Assuming: a. 1.1% of the plume volume is abstracted per day (TR065). b. The mortality of entrained glass eels is 1.8% to 15% i.e. the daily mortality is 0.02% to 0.165% of eels within the plume volume. c. that glass eels use the whole Inner Channel to migrate d. That glass eels do not migrate at a depth outside of the abstraction zone of the HP C intakes,

the daily mortality in the Inner Channel due to entrainment would be 0.0014% to 0.012%. (In practice BEEMS Technical Report TR-S 210 indicates that the majority of up-estuary migrating glass eels would be too close to the surface to suffer significant entrainment risk at the HP C

BEEMS SPP063 (Entrainment) 29 intakes and this mortality estimate is probably too conservative). Taking a mean value for natural mortality of 0.01 d -1 (or 0.995%), entrainment through HP C would increase the mortality of glass eels to within the range 0.996% to 1.007% d-1. Such increases can be considered negligible.

11.3 Predicted additional impact due to climate change

At present glass eels are expected to migrate up-estuary past Hinkley Point from February to the end of April. The 2085 HP C maximum discharge temperatures in that period are predicted to be in the range 22.9 to 24.8ºC as a 95%iles i.e. below the temperatures that are reported to cause mortality or behavioural change. On the basis of this evidence we do not expect any additional entrainment impact on glass eels due to climate change.

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BEEMS SPP063 (Entrainment) 33 Appendix A HP C Cooling Water Pump – Predicted mortality for Glass Eels

Hinkley C Pumps- 3.6 m dia Centrifugal Pump STRIKER Centrifugal Pump Passage Risk Assessment Model Note: only information in green cells can be changed by the user; all calculated values are shown in blue

Project name: Hinkley 'C' CW Pumps - Cefas 02/09/11 FIXED TURBINE PARAMETERS (all dimensions in mm except where stated) Rotation rate (rpm) 151 Runner peripheral height (mm) 900 Pump runner diameter (mm) 3600 Number of blades 6 Downstream head (runner centre to upper level - m) -20 Fish Behaviour Assumptions Fish Orientated Randomly? (1=yes, 0=aligned with flow) 1 Distance between blades 1885

Variable Inputs and Intermediate Computed Values VARIABLE TURBINE PARAMETERS Flow rate - Q (cumecs) 30.50 Load % 100

CALCULATED VALUES Relative inflow angle- Beta (deg) 28.2 Runner velocity - U (m/s) 28.46 Inflow area (m^2) 10.179 Inflow velocity - C (m/s) 3.00 Velocity reduction factor 1 Distance between blades 1885 Relative opening - s (mm) 889.9 Relative inflow velocity - w 6.35 Fish orientation length reduction factor 0.785

BEEMS SPP063 (Entrainment) 34 COMPUTED RESULTS: CENTRIFUGAL

Table A

Summary of Predicted Injury Rates for Parr/Smolts According to Fish Length Note: use 'Compound' values shown in right-hand column for total mortality rate. Length values in green-shaded cells may be altered to obtain values for particular fish lengths

Project name: Hinkley 'C' CW Pumps - Cefas 02/09/11 Discharge = 30.5 cumecs Load % = 100

Fish Mutilation Predicted Injuries Due to: Length (cm) Ratio* Strike Shear Pressure Compound 7 0.181 1.12% 0.51% 0.00% 1.63% 8 0.181 1.28% 0.51% 0.00% 1.78% *Note: M reduced to reflect weight of elver Table B

Breakdown of Shear- and Pressure-Related Injuries in Different Zones of the Turbine

% Mortality Turbine Zone Shear Pressure Compound Intake 0.00% 0.00% 0.00% Runner 0.51% 0.00% 0.51% Compound 0.00% 0.00% 0.00% 0.51% 0.00% 0.51%

BEEMS SPP063 (Entrainment) 35