1ENVIRONMENTAL REPORT
OCTOBER 2008
1. INTRODUCTION AND BACKGROUND
1.1 Thames Water is applying for a licence to abstract water from the Thames
Tideway at the proposed Beckton Desalination Plant next to Beckton Sewage
Treatment Works (STW) in Barking, East London. The primary function of the
proposed Beckton desalination plant and the distribution pipeline is to provide
potable water to supplement the supply available for London during drought
periods, through desalination of the abstracted Tideway water.
1.2 The proposed water treatment plant represents one element of Thames Water’s
water resource planning programme, addressing the shortfall in potable supply in
the North East of London that may occur during severe drought. Demand in London is forecast to increase steadily over the 25 year planning horizon. In recent years (especially summer 2003) peak demands in parts of London have
been very high and are close to the available resources for supply. This rising
demand is driven by both new residential and commercial developments as well
as increasing per capita usage.
1.3 Thames Water continues to make a major effort to reduce leakage, with
significant success. However, this process takes time and will not offset the
resource deficit in the short term, and it will have less impact on peak demand
than base demand. In the long term the capacity for demand management
measures to contain future demand is unproven. However, demand management
opportunities are being maximised but still resource development is required to
ensure security of supply.
1.4 Thames Water’s strategy, which is outlined in detail within the draft Water
Resources Management Plan (dWRMP) that was published for consultation in
May 2008, is to eliminate the supply-demand imbalance, taking into account
headroom, as soon as is practicable. This will be done through implementation of
a twin track approach which balances proactive demand management and leakage
control activity with further resource development, treatment and distribution
system enhancement.
1.5 The new water treatment plant will produce a potable water supply by treating
brackish water from the tidal reaches of the River Thames using the latest
desalination technology involving the process of Reverse Osmosis. The proposed
development will be capable of supplying some 140 Ml (1 Megalitre (Ml) =
1,000 cubic metres = 1,000,000 litres) of potable water per day over a prolonged
period of drought, equivalent to the water used by approximately 400,000
households. This source will be used to supplement the current resource base for
North East London during drought periods.
1.6 Abstraction from the Tideway will only take place for a 3-hour period of the ebb
tide and will cease after the point of low tide. The salinity of the Tideway is at its
lowest during this period, therefore reducing the plant’s energy usage since water
with a lower salinity requires less energy to treat through the Reverse Osmosis
process. Large buffer tanks were included as part of the Beckton Desalination
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Plant design to provide enough storage to enable a full days raw water
requirements to be abstracted within the two limited available windows for
abstraction each day. An additional reason for restricting abstraction to the ebb
tide is to avoid abstraction of the Beckton STW treated effluent, which passes the
abstraction point after low tide (i.e. on the flood tide).
1.7 Because the water is abstracted from the Tideway and hence is drawing on the
resource of the North Sea, which effectively provides an unlimited supply, the
abstraction of up to 200 Ml/d, which allows for water treatment process losses,
and which will not have any adverse impact on the wider water environment.
Potentially local adverse impacts on fish entrainment will be mitigated through
the installation of protective screens and acoustic deterrents.
1.8 The plant will primarily be used for abstraction during drought periods. However
the plant will also provide resilience backup in the event of a loss of capacity
elsewhere in London due to circumstances out of the company’s control such as
major power outage, pollution or other unforeseen events. There will also be a
requirement for abstraction during the commissioning of the plant and a minimal
requirement to maintain the plant and associated processes in good working
order.
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2. PROPOSAL
2.1 It is proposed that the abstraction will only take place for an approximate 3-hour
period before low tide, during each ebb tide, and will not exceed a maximum flow
of 40,000 m 3 /hr. Therefore the proposed abstraction will be for a maximum of
200,000 m 3 over an approximately 6 hour period within any given 24 hours, but
zero during the other 18 hours. The restriction to the ebb tide is to ensure that the
water of the lowest salinity within the tidal cycle is abstracted as well as ensuring
that effluent from the STW is not abstracted and fish entrainment is minimised.
The requirement for an abstraction of up to 200,000 m3/day arises because this
allows for water treatment process losses at maximum plant output, which are
higher for a desalination plant than for a more conventional water treatment
works.
2.2 The proposed licence limits are as set out below:
Yearly licensed quantity: 73, 000, 000m³ per year
Daily licensed quantity: 200, 000m³ per day
Hourly licensed quantity: 40 000m³ per hour
Pump capacity: 11,112 l/sec
3. STATEMENT OF NEED
3.1 The new resource provided by the Beckton Desalination Plant is required to enhance our resource base to ensure we can meet current and future demands for water in London during drought periods. Forecast demand for London over the 25 year planning horizon shows a steady rise in the need for water even taking into account savings gained from leakage reduction and water efficiency. The desalination plant at Beckton forms the principal element of the supply side programme for future water supply for London.
3.2 This growth is being exerted in the London area by major new housing and
commercial developments particularly in the Kent Thames-side area. Projects such as the Blue Water Park are already giving rise to substantial increases in demand and further increases are projected. Some of this demand can be met by innovative methods such as the recycling of water. However these solutions do not offset the need for the development of new resources.
3.3 Thames Water’s resource strategy for the future includes ensuring that all
sources are used in the most efficient way and that demand management measures including leakage reduction and the promotion of water efficiency are maximised to their full extent. However, the ability of demand management measures to realise long-term reductions in demand is not yet proven and so it is necessary to maintain and where necessary add to the resource base where new sources can be exploited with no adverse environmental impact.
3.4 Thames Water produced its draft Water Resources Management Plan for
consultation in May 2008. After addressing issues raised during the consultation the plan will be finalised in 2009 subject to Defra’s approval. The plan sets out the company’s proposals for ensuring the secure provision of water supplies over the 25-year planning horizon.
3.5 Water Resource Planning has to take account of the uncertainty inherent in
projections of future demand and so an allowance is made for necessary resource provisions to cater for this uncertainty, this allowance is termed ‘Headroom’. The current water resource plan for London shows that existing sources must be retained into the future and that further water resources are required to ensure that available supplies exceed demand taking into account Headroom.
3.6 The Company’s overall objective is to attain headroom in all water resources
zones for both average and peak demand scenarios and to maintain this headroom over the 25 year planning period. The Company has adopted a twin-track approach to achieving and maintaining target headroom whereby demand management measures are chosen initially up to the economic level followed by appropriate resource development options. The economic analysis follows the Economics of Balancing Supply Demand (EBSD) process and guidelines. It is used to determine, initially, the least-cost mix of options having regard to environmental implications. Sensitivity analysis and consideration of other factors, such as the need for enhanced leakage, metering & water efficiency programmes, confidence in option delivery and local supply-demand issues, are used to decide upon the preferred plan.
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3.7 Currently London has a significant deficit with respect to Target Headroom. Our aim is to steadily reduce this deficit through a twin-track programme, including leakage reduction and development of resource options, such that surplus is attained by 2014/15 with respect to Target Headroom. Mains replacement with active leakage control forms the principal element on the demand side. This is supported by increased metering and water efficiency activity. The desalination plant at Beckton forms the principal element of the supply side programme for London.
3.8 Assessment of population growth indicates that London’s population will rise
by a further 1 million by 2034/35. A significant element of the forecast growth
in demand is in the north and east of London. 3.9 The programme also includes customer-side management options. Whilst
results of the economic analysis have demonstrated that metering and water efficiency beyond the current levels are not economic, the Company’s preferred approach is to introduce metering across its area where practicable.
3.10 However, despite significant and rapid progress as a result of the demand
management and resource development programmes, our planning
assessments have shown a large supply-demand deficit with respect to Target
Headroom, for example, for 2008/09 it is just under 200Ml/d. A deficit of this
magnitude cannot be removed in the short term by demand management
measures alone, a significant additional water resource is needed.
3.11 The need to meet demand in the short to medium term meant that any scheme or
measure identified would need to be implemented and operational within a
short timescale, which further restricted the scope of the alternatives
considered. This also constrained the scope of alternative locations considered
to those sites already owned by Thames Water, since major land purchases for
the construction of a scheme would be likely to result in this timescale being
exceeded.
3.12 The Beckton Desalination Plant has been subject to delays due to the resolution of the planning permission requirements. However, the Mayor of London has recently withdrawn a legal challenge against the decision to grant planning permission for the plant construction to go ahead. This means that construction of the plant can now continue to enable delivery by March 2010.
3.13 The works will primarily be require for drought use but it will also need to be
made available for use at short notice for resilience purposes. The requirement for use under such circumstances could arise from unforeseen events such as a major power outage, contamination of other water sources or other events outside the company’s control.
3.14 Following completion of construction of the new works a period of abstraction
will be required to commission the new plant and ensure all the processes work satisfactorily. The desalination plant represents new technology for Thames Water and so there will be a greater period of commissioning than for an advanced but conventional water treatment works.
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3.15 The operation of the desalination plant will be governed by an Operating Agreement, which will be agreed with the Environment Agency. The Operating Agreement will set out the detailed operating protocol for the desalination plant including the provisions for its use covering drought, commissioning, maintenance and operational emergencies beyond the Undertaker’s control.
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4. ALTERNATIVE OPTIONS:
4.1 In order to address London’s supply/demand deficit a combination of the following
options was considered:
- Increased leakage control to reduce water lost in the main system (patch
repairs)
- Increased mains replacement to reduce water losses (laying new water pipes to
existing water pipes);
use less water); and
- New water resource development to provide additional sources of water (e.g.
surface or groundwater abstractions).
Each of these options, and the contribution that they could make to meet the deficit
is described in the following sub-sections.
4.2 Leakage control: Significant progress has been made in reducing leakage through
the Victorian Mains Replacement programme, active leakage control and customer-
side leakage reduction. To date Thames Water has invested £400m to replace over
800km of mains and our current mains replacement and the active leakage control
programme is projected to reduce leakage to 685 Ml/d by 2010 and replace a total of
2,168km of mains. Further mains replacement is planned for the future from 2010 to
2020 with 400km of new mains per annum planned for the period 2010-15 and
300km per annum for the period 2015-20 which is projected to reduce leakage to
520 Ml/d by 2019-20.
4.3 Demand is predicted to decline over the next five years as a consequence of Thames
Water’s VMR and leakage control programme, but will begin to level off and rise
thereafter as population growth and per capita consumption outstrip savings in water
through leakage control. Taking account of all existing and committed supply
programmes, together with a range of other supply options that are likely to be put
in place within the short term such as new groundwater schemes, there remains a
significant gap between the amount of water currently available for use by
customers and the amount that might be required in a dry year. Therefore, although
leakage control is a necessary measure, further provisions are required to address
the deficit.
4.4 Demand management and resource development:
A long list of demand management and resource development options were
considered (see table 1), many of which were discounted due to insufficient yield
and / or insufficient viability. It should also be noted that whilst the company’s
existing metering programme includes meter optants (customers who request a
meter) and selected metering (installation of a meter when a property changes
occupancy) it is not possible to increase meter penetration in the next two years to
significantly impact on the deficit. However in our dWRMP we are proposing a 10-
year progressive programme of targeted compulsory metering of households starting
in 2010.
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Table 1 - A summary of the possible options reviewed to reduce the future shortfall:
4.5 The three viable options remaining were:
- Bulk imports from Scotland, imported by sea, in bags;
- Planned indirect reuse at Beckton STW;
- Desalination at Beckton STW; and
- A combined option including a canal transfer from Birmingham, artificial
recharge in south and west London and two demand management measures:
domestic appliances subsidies and greywater recycling.
4.6 A sustainability review of the short-listed options was carried out, based on a
comparative assessment of the economic, environmental and social impacts of the
four alternative process options.
4.7 The treatment of brackish water from the tidal Thames was identified as the
preferred option from this extensive optioneering study on the basis of its ability to
deliver the required volumes of potable water supply within the time period and in
terms of the comparative assessment against the economic, environmental and
social criteria. It is well suited to providing a supplementary source of supply under
dry conditions because it is a physico-chemical treatment process that can be
activated to augment resources during periods of drought. While desalination is not
the least cost option, the risk of failing to meet Ofwat’s short to medium term target
for supply security in London is considered to be lower for desalination than for the
other available options.
4.8 Bulk sea import was considered the least favourable option due to high costs,
significant environmental impacts and the fact that it is an unproven technology.
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There were concerns regarding public acceptability of the planned indirect reuse
option, and a comprehensive communications plan would be required to assure
consumers, which could take a number of years to implement. A programme of
catchment studies and increased catchment control would be required, which could
also affect the certainty of delivering the supply shortfall within the required
timescale. The combined option was disregarded because it would yield insufficient
supplies and there were potential cumulative environmental and social impacts.
4.9 The desalination plant, known as the Beckton Desalination Plant, will be able to
provide the North East of London with a supply of up to 140Ml/d. Leakage control
will continue to play an important part in achieving the supply-demand balance.
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5 DEMAND MANAGEMENT 5.1 To provide our customers with the service they expect, our water resources
strategy represents a balanced approach, which looks to enhance our resource base by implementing demand management measures in the short and medium term, while in the long term securing our position through the development of additional environmentally sustainable resources. Demand management measures include leakage control, metering and the promotion of water efficiency to our customers.
6 PROGRESS ON LEAKAGE REDUCTION
6.1 Leakage control has been and remains the highest priority for the company.
Activity throughout the last few years has been at exceptional levels and we
continue to deliver the components of our leakage strategy as set out in our 2004
SBP. Where possible delivery has been accelerated to exceed our plan with
expenditure on leakage control now higher than at any time in the past.
6.2 The company’s leakage strategy incorporates a balanced programme of:
Network upgrade (mains replacement targeted to give maximum benefit to
leakage, both the immediate benefit of leakage reduction and the ongoing
benefit from reduction in bursts and leaks breaking out in the future);
Fast track programme of pressure management;
Zonal reconfiguration (to improve the configuration of the network at
zonal level to optimise trunk main routes, pumping regimes and zonal
pressure management);
Find and fix activity (including further refinement of the district metering
system through reduction of DMA size and number of meters and
improved knowledge of night use and base levels); and
Trunk Mains leakage (including installation of further trunk main metering
and installation of further chambers for Sahara surveys).
6.3 This strategy has been developed not only to deliver sizable leakage reductions
but also to ensure, through replacing the oldest most fragile mains, which are
so sensitive to climatic extremes, that these reductions are sustainable.
6.4 Full details of the latest leakage strategy are provided in the company’s draft
Water Resource Management Plan, May 2008.
6.5 Last year significant leakage reductions were delivered with annual average
leakage for 2007/08 of 713 Ml/d, 77 Ml/d lower than the level reported for
2006/07 and almost 150 Ml/d below the level in 2005/06.
6.6 The graph below shows the progress that has been made over the period 2004-
2008 in London. The graph shows that as well as successfully recovering
seasonal increases in leakage, amounting to some 200 Ml/d, the company is
now making significant reductions to the underlying trend in leakage.
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6.7 During 2007/08 the company spent £74.2m on detecting and repairing leaks
(including expenditure on customer side), with a further £268.6m spent on
trunk mains leakage, mains replacement, pressure management and zonal
reconfiguration. Most of this expenditure has been concentrated in London.
The number of FTE employed on leakage detection remained high
during the year 2007/8 at 463, resulting in similarly high numbers
of leaks being detected.
Active leakage repair levels continue to be at high levels. During
2007/08 a total of 35,197 active repairs were completed, the
majority of which were in London.
Similarly, the number of customer side leak repairs completed has
remained at high levels, with a total of 15,435 being delivered
during 2007/08.
In addition, a total of 18,665 visible leaks were repaired on the
Company’s mains network, with repair times being maintained at
their lowest level since reporting started in 2002.
Mains replacement programmes, both DMA based network
upgrade and street based burst driven, have been accelerated and
continue to be delivered ahead of the programme set out in our
WRP04. Under the DMA based network upgrade programme
construction of 527 km of new mains has been completed in
2007/8, 60% more than last year and significantly ahead of the
target of 264km. The street-based mains replacement programme
has delivered a further 101 km of new mains against the target of
29 km set out within the Final Determination.
400
500
600
700
800
900
1000
01 Apr 04 01 Apr 05 01 Apr 06 01 Apr 07 01 Apr 08
R e
p o
rt e
d L
e a
k a
g e
M l/
reconfiguration schemes delivered a total leakage benefit of
14.9 Ml/d against the target of 9.2 Ml/d.
Significant trunk mains leakage savings continue to be delivered
with a total of 119 repairs being completed during 2007/08. 46
further survey chambers have been constructed for the purpose of
undertaking leakage surveys on additional trunk mains and 180
trunk main leakage surveys have been completed.
6.8 The latest progress on leakage and the Leakage Action Plan is reported within
the Quarterly Leakage Progress Report. 7 METERING POLICY
7.1 Thames Water is committed to a twin track approach to managing the supply
demand balance, whereby demand management measures are implemented in parallel
with supply side schemes. Metering is an important demand management tool and a
metered charge is the fairest way to pay for water. Meters are currently installed on
new or converted properties, where a swimming pool is owned or a sprinkler is used,
or when requested by the customer (optant). Additionally, in the period from 2005/06
to 2009/10 there is a significant programme of selective metering on change of
occupier. Forecasts allow for a 5% saving in water use when households opt for a
meter, 10-20% saving for selectives.
7.2This strategy is forecast to result in 62,770 optant meter installations and 64,282
installations on change of occupier in the period 2005-06 to 2009-10, resulting in a
domestic meter penetration of 27%. Three years into the period, we are on target to
deliver the change of occupier targets. The number of meter optants has been in
excess of those predicted in the strategy. We are already above the target for the
period having installed 67,534 meters.
7.3 Looking ahead, Thames Water has been identified by the Environment Agency as
being in an area of 'serious water stress'. Beyond 2009/10, we have set out a case
within our Water Resources Management Plan, to begin a 10-year programme of
targeted compulsory metering, which will raise penetration to 54% by 2015 and 80%
by 2020. We intend to meter the remaining domestic properties on a common supply
basis. Targeting in the first instance will be focused on those zones of greatest supply
demand deficit. Identifying areas of high discretionary use and areas where low
incomes and thus affordability may be an issue will also be undertaken to inform the
roll-out. The Company also intends to introduce meter technology (such as automatic
meter reading) and through this trial the possibilities of alternative tariff structures to:
i) mitigate affordability impacts where possible and ii) increase demand savings. The
trials would be in the period to 2015 with implementation, subject to agreement with
the Regulators thereafter.
8 WATER EFFICIENCY
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8.1 Future domestic water consumption will be affected by Thames Water’s customers becoming more efficient in their use of water. This is largely in response to our promotion of water efficiency. Thames Water' s commitment to the promotion of water efficiency to its customers has been demonstrated for a number of years. Our Water Efficiency Plan sets out our intention of making information available to our customers about water efficiency, promoting the labelling of low water use appliances, and ensuring that our own buildings are as water-efficient as is practicable. Our water efficiency policy is based upon partnership with our customers, offering them practical advice on measures that can be undertaken to reduce water wastage in both the home and garden, but which would not affect their standard of living.
8.2 Against a backdrop of rising demand and Government house building plans,
the past few years have seen a growing recognition of the need to use our water resources more wisely. Whilst attention remains on reducing leakage and installing meters, water efficiency has achieved a higher profile and has consequently risen up the political agenda
8.3 Recently TW has recognised the need to strengthen its water efficiency
programme. This follows the 2006 drought in SE England, scrutiny over water company water resource proposals, higher expectations of water industry regulators and other stakeholders as well as changes in the political agenda with respect to water efficiency. Our water efficiency programme was the largest to date in 2006 and included an enhanced water efficiency campaign linked to the drought, liquid assets audit and retrofit activities with public sector and domestic households and further domestic studies to support development of the business case for further water efficiency in the next AMP period. The water efficiency programme continues to build on previous activities, effectively targeting sustainable behavioural change amongst consumers, and encouraging the increased prevalence of water efficient technologies and practices. This is complemented by continuing development of our educational and community partnership activities, we are planning to conduct three further domestic audit trials upon 3,000 households this regulatory year, and conduct over 16,000 commercial audits by 2010.
8.4 Our public education programme seeks to develop new and more innovative
ways of promoting water conservation. We see the role of the water audit as playing a crucial part in raising awareness and identifying areas where household water wastage can be reduced, particularly non-essential water use at times of peak demand. We aim to reduce domestic and commercial water wastage and discretionary use by targeting our water efficiency activities at the following areas of water use; household water use, school water use, commercial water use and communities of interest. The communities of interest have an existing relationship that values water in a specific context, over and above essential water use, that we can build upon to reinforce water efficiency messages – namely groups involved with sport, faith, the environment and gardening. Partnerships are key to the effective delivery of our water efficiency projects and messages. We use these and a variety of other tools, including the website, to drive water efficiency progress in these areas. Within each of these areas we aim to structure our approach in line with stakeholder preferences and, as far as possible, to have quantifiable outcomes.
9 WATER RESOURCE STRATEGY
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9.1 The success and economic viability of demand management measures in containing demand is unproven, and as such, a water resource strategy based solely on demand management is high risk, which we consider is unacceptable for our customers. We support the adoption of a more balanced approach which recognises the value and importance of demand management initiatives (as outlined above), but also accepts the need to retain existing resources and develop new resource options since it is the only certain way of maintaining and improving upon the reliability of supplies to our customers.
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10 ENVIRONMENTAL EFFECTS
10.1 The impact of the abstraction on the aquatic ecosystem has been fully assessed
within an Environmental Impact Assessment (EIA), which was conducted as part of
the planning application for the proposed Beckton Desalination Plant. The key
potential impact of the abstraction on the aquatic ecosystem of the Thames Tideway
relates to the entrainment of fish and shrimps.
10.2 Thames have worked closely with Jacobs Babtie Aquatic (JBA) and the
Environment Agency to identify sustainable measures to mitigate the impact of the
abstraction upon fish entrainment. In addition to conducting a number of baseline
fish surveys, Thames Water commissioned a pilot trial and a series of laboratory
studies to evaluate the effectiveness of various mitigation measures and inform the
mitigation design.
10.3 A summary of the conclusions of the Environmental Statement and supporting
technical reports with respect to the impact of abstraction on entrainment of fish and
the proposed mitigation measures are set out below. Also outlined are details of the
post commissioning fish-screen monitoring programme to be undertaken.
10.4 Fish entrainment: Fish entrainment was identified as a key potential impact
associated with the planned abstraction at Beckton. In order to establish the likely
impact of the abstraction on fish populations, it was first necessary to understand
the baseline status of fish populations (species and life stages) present within the
proposed intake locality and the differences in species and quantities occurring
close to the riverbed and the water surface to inform intake design.
10.5 A detailed programme of field surveys was conducted by JBA during August –
September 2002 and May 2003. There were no nationally important species
recorded during the survey, however there were species present that are unlikely
to be present in other waterbodies (other than the Tideway) within the London
area. This is reflected in the designation of the Thames Tideway as a non-statutory
Site of Nature Conservation Importance. In total, fourteen species of finfish and
three crustacean species were recorded during the survey. Of the finfish species,
three were pelagic and eleven were demersal / epibenthic species 1
(see Table 5-1
for a list of species recorded).
10.6 Location of intake: To enable comparison of the likely catches for a near-surface
intake and a bottom intake, two sampling techniques, a bass trawl and a surface
water trawl, were employed. Results of the trawls showed that a surface intake of
water would be expected to catch approximately 20% fewer fish overall compared
to a bed-mounted intake and the catch composition would be dominated by
pelagic species. Thus a near-surface intake was chosen for TGWTP in order to
reduce the potential for fish entrainment. Furthermore, as the fixed intake would
be mounted on a platform attached to the existing Beckton jetty, there would be
minimal disruption to the riverbed and associated benthic communities. 1
Pelagic species live throughout the water column; demersal species live in the lower water column and epibenthic species live on or near the estuary bed.
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Table 10-1. Finfish and Crustacean Species Recorded from Trawl Surveys (Scott
Wilson Kirkpatrick and Co Ltd (2004)).
10.7 Fish screens: To further mitigate the entrainment of fish, passive wedge-wire
cylinder (PWWC) fish screens will be fitted to the abstraction intakes at Beckton
Desalination Plant. These are fine-meshed screens formed by winding triangular-
profile wire around a cylindrical former, leaving narrow slots through which
water, but not most fish or other coarse debris, can pass. These screens meet
Environment Agency Best Practice guidance (Turnpenny & O’Keeffe, 2005) for
small intakes where juvenile fish may be present.
10.8 The aperture size of the PWWC screens needs to be small enough to prevent
significant levels of fish entrainment, but not so small as to cause risk of blockage by the high detritus loads that are sometimes carried by the Tideway. Build up of detritus on the screens can lead to the development of high velocity hot spots that can cause injuries to fish. Accumulated material can also present a risk of contact injuries to fish. It is therefore important that the construction material is resistant to biofouling. Pilot trials were commissioned at Beckton Jetty in order to firstly test that PWWC screens were operable at Beckton and secondly to evaluate the performance of the different PWWC screen materials and aperture sizes with regards to biofouling, blockage risk and protection against fish entrainment.
10.9 The pumping pilot trial measured the rates of fish egg and fry entrainment
through 3 mm versus 5 mm slot-width screens and an unscreened ‘control’ intake and also compared performance of stainless-steel mesh versus a copper-nickel (90%Cu:10%Ni) alloy screen material in terms of biofouling. Measurement of fish entrainment was undertaken during the summer months (June – August) when fish eggs and larvae are most abundant, therefore ensuring the highest risk period
Fish Type Scientific name Fish Type Scientific name
Epibenthic / demersal Pelagic
Flounder
Poor cod
Red gurnard Aspitrigla cuculus Chinese mitten crab Eriocheir sinensis
Pouting Trisopterus luscus
Roach Rutilus rutilus
3-spined stickleback Gasterosteus
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was captured. Most young stages would not reach Beckton before June and by the end of August they would have grown to a point where they can more readily escape an intake (Turnpenny et al. March 2005). The assessment of resistance to biofouling was conducted for a full year in 2004 to cover the full seasonal range of conditions.
10.10 The results of the trial indicated that there was not a significant difference
between the various screens and the control in terms of fish entrainment (Turnpenny et al. March 2005). This is believed to be due to high natural variability and chance effects, and it should certainly not be inferred from this that screens would not offer effective exclusion as the study was timed to assess the very early life stages of fish. Indeed, residual effects of entrainment may arise from fish and crustaceans that are small enough to pass through the fine screen fitted at the intake openings (e.g. planktonic lifestages), however the EIA has deemed these residual effects to be insignificant. This conclusion was based on a comparison of the mortality rate (due to egg and larval fish entrainment) for a screened intake, which was estimated to be 0.08% of the population per day, with the natural mortality rates in fish over the first few weeks of life, which can exceed 5% per day (Scott Wilson Kirkpatrick and Co Ltd, 2004). Screens of 3 mm and 5 mm aperture will provide effective positive exclusion for fish that have passed through the early development stages. The screens fitted to the TGWTP intakes will be 3 mm aperture screens since these are the (informal) Best Practice standard adopted by the EA in England and Wales.
10.11 The results of the biofouling assessment indicated that all screens tested would
operate within specification (Turnpenny et al. April 2005). However, the 3 mm copper-nickel alloy screen was shown to have the smallest degree of biofouling, with a much slower build up compared with the other screens tested and that there was a greater potential for blockage by biofouling on the stainless steel screens (Turnpenny et al. April 2005). Therefore, 3mm copper-nickel alloy screens will be fitted to the Beckton Desalination Plant intakes. In addition, an air-burst backwash facility will be installed on the intake screens to further minimize any
build up of debris. The backwash system will be operated on a timed cycle to
clear the screens of any accumulated debris prior to each abstraction period. This
also accords with EA Best Practice.
10.12 Although the intake screens offer effective protection to the majority of benthic
and demersal fish, delicate pelagic species are at risk of damage from contact with
the screens. A number of studies have examined the survival rates of marine and
estuarine species shortly after impingement (see table 5-2). A study by Seaby
(1994) illustrated that survival rates for all of the flatfish were between 80 and
100% whereas none of the sprat and herring (i.e. the pelagic species) survived.
Table 10-2: Fish survival rates following impingement (Seaby, 1994). No. of fish tested 24 hr survival rate (%)
Flounder 15 100
Plaice 4 100
Sole 129 96.1
Cod 47 93.6
Bass 37 89.2
Dab 10 80.0
Whiting 203 47.8
Sprat 94 0.00
Herring 5 0.00
Shrimp 635 94.3
19
10.13 Thus it is important that the water velocity passing through the PWWC screens
is sufficiently low to reduce the likelihood of fish becoming pinned to the screen surface and damaged. Intake through-velocities at Beckton Desalination Plant will be maintained below 0.15 ms-1, which is in line with manufacturers design guidance for this type of screen and to EA Best Practice recommendations for juvenile fish screening. Although through-slot velocities will be controlled to minimize impingement, the addition of an Acoustic Fish Deterrent (AFD) system at Beckton Desalination Plant is considered necessary in order to provide further protection against contact damage. This is important considering a significant proportion of the fish at risk of entrainment / impingement are pelagic species and AFD systems have been shown to be particularly effective at repelling these species.
10.14 Acoustic Fish Deterrents (AFDs): AFDs are designed to deflect fish away from
the intake by generating a repellent sound field and are most effective at
deflecting species with sensitive hearing such as the pelagic clupeid species.
Previous studies have shown AFDs to reduce entrainment of clupeid fish by 85-
99% (Turnpenny et al. 1995, Maes et al. 2002). Benthic species, however, are
acoustically less sensitive and therefore it is not expected that the AFD would
exclude as large a proportion (see table 10-3). Although previous studies have
shown that the reduction in entrainment for acoustically less sensitive species can
still be significant (Maes et al. 2004). It is perhaps worth noting that because the
proposed Beckton Desalination Plant intake will be a surface water intake, the
proportion of benthic fish at risk will be much lower than pelagic species.
Table 10-3: Expected fish deflection efficiencies for an AFD system at Beckton
(Scott Wilson Kirkpatrick and Co Ltd (2004). Fish group Deflection efficiency
Pelagic > 80%
Demersal 50-80%
Epibenthic 15-30%
10.15 Achieving an effective AFD system design is reliant on two main factors: (i)
taking account of the swimming performance of the target species and (ii)
engineering an acoustic field that will repel fish at sufficient distance to ensure
that they can swim away without being entrained. Little information was available
on the acoustic response and swimming speeds of smelt, which are not only a key
species of conservation importance in the Tideway but could also be particularly
susceptible to impingement unless they can be effectively deflected by AFDs.
This is due to their migration characteristics, whereby the young are carried
downstream from their spawning grounds by tidal flushing and are therefore not
actively swimming during this period. Consequently, Thames Water
commissioned a series of laboratory studies to address this knowledge gap and the
resulting data was applied to the design of the Beckton Desalination Plant water
intake to reduce the entrainment of smelt.
10.16 The results of the studies demonstrated that, given an appropriate repellent
stimulus (i.e. an AFD), smelt of all sizes tested would be able to ‘burst-swim’ fast
.
Maintaining the Beckton Desalination Plant intake velocities below 0.15ms -1
will
therefore include a high safety margin for smelt and also protect smaller species,
20
which are likely to have a lower swimming ability. Table 10-4 illustrates that this
margin would protect the majority of species. Juvenile flounder and sole are more
susceptible to entrainment / impingement, only being able to escape intake
velocities of 0.2 and 0.15ms -1
respectively. However these species are also the
more robust species with a high survival rate following impingement (see table
10-2).
) for juvenile and adult fish
escape at different water temperatures (Scott Wilson Kirkpatrick and Co Ltd,
Appendix 8B, 2004).
Sprat & Herring 0.40 0.60 0.64 0.92
Smelt 0.30 0.40 0.40 0.45
Bream - - 0.59
Salmon - - 0.60 0.80
10.17 In previous studies, for example Hanson (1979), a screen operated at a through-
velocity of 0.15 ms -1
achieved optimum performance (in terms of preventing
entrainment / impingement) when the sweeping velocity was above 0.3 ms -1
(Scott
Wilson Kirkpatrick and Co Ltd, 2004). Monitored velocities in the vicinity of the
Becton Jetty during 2003 were analysed to determine the average, minimum and
maximum current speeds relative to low water. The summer months were analysed,
as it is expected that the Beckton Desalination Plant is more likely to be in full
operation during times of low river flow. The analysis shows that between May and
August the mean velocities briefly drop below 0.3 ms -1
prior to low water but on no
occasion in the 3 hour window before low water does the mean velocity drop below
0.15 ms -1
(Beckton Desalination Plant: Analysis of currents at the intake, HR
Wallingford 2008). Although optimum performance of the fish screens is
achieved at velocities of 0.3 ms -1
, the fish screens will remain effective at
preventing entrainment at velocities of 0.15 ms -1
. However, Thames Water will
endeavour to minimize abstraction when water velocities fall below 0.3 ms -1
by
stopping abstraction earlier in the 3-hour window when the plant is not being run
at full flow.
10.18 The AFD system will comprise an array of acoustic transducers, known as
sound projectors, carefully positioned to divert approaching pelagic fish into the
tidal flows passing the plant, and away from streamlines entering the PWWC
screens. As abstraction will take place only on the ebb tide, the sound projector
array (SPA) will be asymmetric, concentrating the sound field on the side of the
approaching ebb tide. The precise number and positioning of the sound projectors
will be determined in a design study using the PrISM™ acoustic model. PrISM
calculates the interactions between the individual sound sources, the riverbed and
the water surfaces and hard structures and ensures the development of the
optimum acoustic levels and gradient around the intake structure. Other elements
of the AFD system include a signal generator, audio power amplifiers (one per
sound projector) and a performance diagnostics unit (figure 1).
21
10.19 The AFD system at TGWTP will operate at least 15 minutes prior to the
commencement of abstraction. Telemetry will be fitted to ensure any faults or
inoperable equipment are readily identified by plant operators or Agency staff.
Figure 1. Schematic of Acoustic Fish Deterrent System
10.20 Hydrodynamics: There will be no significant environmental impact on the
water levels or hydrodynamics of the Tideway as a result of the abstraction itself,
as the quantities of water to be abstracted are insignificant in relation to the total
volume of water that passes the site in the Thames Tideway, even at periods of
low tide. Analysis of flows using HR Wallingford’s model illustrates that for a
low river flow condition the total discharge during the last three hours of a neap
tide is 16 million m³. At one hour before low water the discharge on a neap tide
(i.e. a conservative scenario) is about 1000m³/s. We are proposing the abstraction
of 11.1m³/s (i.e. 1.1%) from the Tideway it is therefore clear that the amount to be
abstracted is insignificant in comparison to the total discharge of the Thames
Tideway. Furthermore, the Tideway is linked to the North Sea, which will provide
an inexhaustible supply of water to the Tideway.
10.21 No other licensed users will be derogated as a result of this proposal as the
abstraction is so small in relation to the volume of water in the Tideway.
10.22 Water quality: Detailed information regarding the impacts of discharge from
the TGWTP on water quality within the Thames Tideway is included within the
associated Discharge Consent Application and the Beckton Desalination Plant ES.
However, a brief summary of water quality impacts is outlined below.
10.23 Effluent produced as a by-product of the membrane filtration process of
Beckton Desalination Plant will mainly consist of a concentrated solution of
dissolved salts with a few additive biodegradeable chemicals, which are unable to
pass through the final reverse osmosis membrane. This effluent will be highly
diluted by mixing it with existing effluent discharges from the STW plant prior to
discharge and will be further diluted in the Tideway. This will ensure that the
dissolved substances within the effluent that originated in the Thames, are actually
discharged at either their original concentration or lower.
10.24 The additive substances represent a very small proportion of the concentration
of the sludge from the treatment process (approximately 4%). Detailed modelling
has been undertaken by HR Wallingford to determine the impacts of returning
Sound Projector
Diagnostic Unit
22
these additive residuals, as well as the original Tideway solids, to the Tideway.
This modelling assessment demonstrated that the effluent will not have a
significant effect upon water quality, salinity or sediment accumulation within the
Tideway or a significant effect upon the aquatic ecology within the Tideway.
23
11.1 Fish entrainment monitoring programme: Post commissioning fish
entrainment monitoring will be undertaken to establish the effectiveness of the
fish screens and acoustic deterrent at mitigating fish entrainment.
11.2 The programme will involve collection of a set of samples from the water inlet
line and examining these in the laboratory to assess numbers and sizes of different
fish species entrained and their Adult Equivalent Values. From these figures, the
total annual entrainment mortality due to operation of the plant will be estimated
using standard procedures. Full details are set out in Appendix A.
11.3 The results of this monitoring program will be reported to the EA and will
inform the need for any modification to the mitigation plan.
24
12 CONCLUSIONS ON ENVIRONMENTAL EFFECTS
12.1 Thames Water has utilized a number of sources of information in order to design
environmentally sustainable intakes at Beckton Desalination Plant that will
minimize fish entrainment and impingement. Various intake design and operating
measures are proposed:
Installation of 3mm copper-nickel alloy PWWC fish screens to minimize fish
entrainment.
to maximize the
ability of fish to escape entrainment and to minimize likelihood of fish
becoming pinned to the screen.
Air-blast backwash facility fitted to the intake screens to remove accumulated
debris that may cause contact damage to fish and also prevent the development
of high velocity hot spots.
Minimisation of abstraction during tidal slack periods (i.e. sweeping velocities
below 0.3 ms -1
) to minimize the entrainment of fish.
Installation of an Acoustic Fish Deterrent system to deflect fish away from the
abstraction intake, reducing impingement risk of delicate pelagic species.
12.2 As outlined in Section 5, the impact of fish entrainment and impingement is
largely mitigated by these proposed measures.
12.3 Although residual effects of entrainment may arise from fish and crustaceans that
are small enough to pass through the fine screen fitted at the intake openings,
these residual effects are considered to be of low magnitude. Furthermore,
Thames Water will undertake post-commissioning monitoring of fish entrainment
rates to confirm the mitigation measures are minimizing fish entrainment effectively
(see Appendix A for details of the monitoring programme proposed). Dependant on
the results of this monitoring programme, the mitigation measures of the abstraction
regime may need to be amended.
12.4 The potential for impacts on Tidal hydrodynamics and water quality resulting from
the abstraction and effluent discharge were also investigated as part of the Beckton
Desalination Plant EIA. Close liaison with water quality specialists and aquatic
ecologists has ensured that any potential impacts identified have been suitably
mitigated with the result that there will be no significant residual impacts.
25
13. CONCLUSIONS
13.1 Thames Water’s planning process has indicated that in a severe drought the
potential exists for an imbalance between supply and demand. A series of
measures are being implemented to eliminate this potential deficit, however in
view of the need to ensure a positive supply-demand balance as quickly as
possible it is necessary for Thames Water to construct a desalination plant with
the capacity to supply some 140Ml/d of potable water over the period of a
drought.
13.2 Desalination has the potential to provide a significant new water resource with
minimal environmental impact. The impact of the abstraction on the water
resources of the Thames Tideway will be negligible as the volumes involved are
so small in comparison to the raw water available. With regards to the potential
impact on fish populations due to fish entrainment, although this is considered to
be a key potential impact of the abstraction, the extensive mitigation measures that
proposed for implementation will ensure that the residual impact is of low
significance.
13.3 The proposed Beckton Desalination Plant is only one of the components of
Thames Water's resource strategy to meet demand arising within London. It is,
however, a vital component and urgently needed. Demand management alone
cannot deliver the required saving in water to meet the projected shortfall in the
volume of water available for use. Additional water resource development is
therefore required.
13.4 The Beckton Desalination Plant represents the best practicable means by which
to guarantee the provision of increased potable supply capacity at the quantity
required and within the shortest timescale to ensure the elimination of the supply-
demand deficit.
13.5 The plant will primarily be used for abstraction during drought periods. However
the plant will also provide resilience backup in the event of a loss of capacity
elsewhere in London due to circumstances out of the company’s control such as
major power outage pollution or other unforeseen event. There will also be a
requirement for abstraction during the commissioning of the plant and a minimal
requirement to keep the plant and associated processes in good working order.
26
Introduction
Fish entrained into the desalination raw water supply must be small enough to
penetrate the 3 mm PWWC screens. For freshwater fish, Turnpenny et al. (2008)
showed that a 3 mm PWWC screen will exclude fish larger than 25 mm total length
and therefore mainly early-stage larval and post-larval fish (“ichthyoplankton”) would
be expected to enter entrainment samples. The means of sampling and sampling
season therefore need to accommodate this.
A national sampling protocol for entrainment monitoring in the context of coastal and
estuarine power plant has recently been drawn up (Turnpenny et al., 2008) and the
methods proposed here are consistent with that protocol
Design of Sampling Programme
For entrainment sampling, the vulnerable period is normally for no more than six
months, which should capture the start of the spawning season (beginning of March)
through to the point where fish have grown beyond the vulnerable size limit (end of
August). Twenty samples should be taken within this period. These should be biased
towards the peak period April-July and it is proposed that sampling dates should fall
as follows:
Table A1: Number of sampling dates per month
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
- - 2 4 4 4 4 2 - - - -
The dates should be chosen to fall within consecutive weeks for the 4-date months
and on alternate weeks for the 2-date months; the days should be chosen within in
each week on a random basis to avoid tidal bias, although it should not be necessary
to sample on weekends provided that there is no bias in the operation of the plant
between weekdays and weekends. Sampling would be undertaken on these dates
subject to plant operating at the time.
Sample Rate and Duration
For ichtyoplankton sampling, a sample stream flow rate of at least10 ls -1
and
is recommended. Samples should be collected over the full tidal
operating period of the plant.
Method of Sampling
Samples should be taken from the raw water supply line on the positive-pressure side
of the pumps. The main supply pumps are designed for 120 mm solids passage and
will not harm a significant percentage of the ichtyoplankton sample (similar in this
respect, e.g., to ‘fish-friendly’ pumps used in AMP4 Thames Fish Screening Project).
The preferred sampling location would be on the jetty, downstream of the inlet
manifold; this ensures a mixed sample from all PWWC intake heads. A suitable
tapping and 100 mm valve should be supplied at a suitable safe access point; drainage
will also be required at this point.
27
Sampling is achieved by directing the discharge from the valve through a conical
plankton net (minimum 500 mm diameter at mouth, minimum 1.5 m length)
suspended in a tank of water (figure A1). An in-line electromagnetic flowmeter is
used to measure the volume sampled.
Figure A1 Schematic of sampling arrangement
Sample Processing
Samples should be fixed and returned to the laboratory for taxonomic analysis and
counting as per standard ichthyoplankton methods if necessary using a rafter counting
cell or a marked and measured rotating groove under a binocular microscope. Often
density of the different items will make necessary some sort of calibrated
subsampling. The whole sample must be inspected and less abundant taxa sorted
before subsampling.
The following observations should be recorded for each species in all cases:
• Date of capture.
• Species name.
• Total number of specimens over the sampling period (raised from subsamples
if necessary).
• Total length for all fish or a subsample of 200 fish if more than 200 present.
However, if a sample of fish is homogeneous and contains uniform sizes, for example
a shoal of herring has been taken, then such a large subsample may not be needed.
Data Analysis
Deck level
Flow-
meter
28
Data should be bulked for each month of sampling. The following is applied to each
species of fish for which more than ten individuals were captured in the months
samples.
After quantifying the fish, the average age in days from birth should be determined
using age-length keys, and the average age of fish collected in each month should be
computed. The Adult Equivalent Value (AEV) should then be computed for each
species as described by Turnpenny and Watkins (2006) and raised from the sample
volume for the month to the total volume abstracted by the plant for that month. The
annual AEV catch is then calculated by summating values for individual months.
Please note that the entrained material will not be examined for the presence of shad
eggs as there is no evidence at present to suggest that shad are spawning in the
Thames estuary. No shad larvae or ichthyoplankton have been found in the area
during a number of surveys in recent years, although adults are often caught in the
area (Technical Note: Assessing the risk of shad egg entrainment, McCoy, 2008).
However, if a breeding population of shad develops upstream, the planned
ichthyoplankton entrainment surveys at Beckton will provide one of the first
indications by identifying larval shad within the entrained material. Upon
identification of larval shad or any other indications of shad spawning, a reassessment
of the risk to the shad population will be undertaken by TWUL in consultation with
the EA.
The Programme Duration will initially be for one year after which it will be reviewed
with the EA.
29
References:
Hanson, B. N., (1979) Studies of three cylindrical profile-wire screens mounted
parallel to flow direction. Passive intake screens Workshop, Chicago, Illinois,
December 1979. Johnson Division UOP Inc., Surface Water Screen Department, New
Brighton, Minnesota, USA: 97-107.
Maes, J., Turnpenny, A., Lambert, D., Nedwell, J. R., Parmentier, A and Ollevier, F.
(2002). The impact of cooling water abstraction on fish at the Electrabel power plant
Doel (Belgium) after installation of a fish guidance sound system. Journees d’Etude
du Cebedeau, 55: 75-78.
Maes, J., Turnpenny, A., Lambert, D., Nedwell, J. R., Parmentier, A and Ollevier, F.
(2004). Field evaluation of a sound system to reduce estuarine fish intake rates at a
power plant cooling water inlet. Journal of Fish Biology, 64: 938-946.
Scott Wilson Kirkpatrick and Co Ltd (2004). Thames Gateway Water Treatment Plant
at Beckton Sewage Treatment Works Environmental Statement.
Scott Wilson Kirkpatrick and Co Ltd (2004). Thames Gateway Water Treatment Plant
at Beckton Sewage Treatment Works Environmental Statement – Appendix 8B.
Turnpenny A., Fleming, J., Thatcher, K., Wood, R (1995). Trials of an acoustic fish
deterrent system at Hartlepool Power Station. Fawley Aquatic Research Laboratories
Ltd, Client Research Report to Nuclear Electric plc, No. FCR 163/95.
Turnpenny A., Johnson D., Chapman R., Clough, S. (March 2005). Trial of Passive
Wedge-wire Cylinder Screens at Beckton Jetty Part 1: Fish Entrainment. Jacobs
Babtie Aquatic, Consultancy Report to Thames Water Utilities Ltd.
Turnpenny A., Johnson D., Chapman R., Clough, S. (April 2005). Trial of Passive
Wedge-wire Cylinder Screens at Beckton Jetty Part 2: Biofouling. Jacobs Babtie
Aquatic, Consultancy Report to Thames Water Utilities Ltd.
Turnpenny A., Clough, S., Holden, S., Bird, H., Lee-Elliott, I., O’Keeffe, N.
(2003) Beckton Desalination Project: Baseline Fish Surveys, Autumn 2002-
Spring 2003. Fawley Aquatic Research, Consultancy Report to Thames Water
Utilities Ltd. FCR no: 395/03.
Turnpenny, A.W.H. and O’Keeffe, N. (2005). Best Practice Guide for Intake and
Outfall Fish Screening. The Environment Agency, R & D Contract No. W6-103, Final
Report. The Environment Agency, Bristol, UK.
Turnpenny, A.W.H. Bromley, R. & Coyle, S. (2008). AMP4 Lower Thames Water
Intake Investigation. Jacobs Engineering UK Ltd, Client Report to Thames Water
Utilities Ltd Veoila Water Partnership No. B0116300/B0140900
Turnpenny, A.W.H., Colclough, S.C. and Elliott, M. (2008). Sampling to estimate
annual impingement and entrainment amounts, types and rates. British Energy
Estuarine and Marine Science Programme, unpublished.
30
Turnpenny, A.W.H. and Watkins, A. (2006). Equivalent Adult Analysis of Fry
Entrainment at the Thames Gateway Water Treatment Plant. Jacobs Babtie Aquatic,
Consultancy Report to Thames Water Utilities Ltd.
Clough, S., Turnpenny A., Lee-Elliott, I., Hinks, C. (2003) Beckton desalination
plant: the burst and endurance swimming capacity of smelt (osmerus eperlanus).
Fawley Aquatic Research, Consultancy Report to Thames Water Utilities Ltd. FCR
no: 380/03.