Counters Creek storm relief sewer
Why we need the
Counters Creek
storm relief sewer
The problem
The sewer network we operate today
has been much improved and vastly
extended over the years and remains
in good condition, but it is under
increasing pressure from climate
change, population growth, and the
paving over of green spaces that
provide natural drainage.
Many areas of outer London have
been developed with separate sewers
to take foul waste and rainwater. In
much of inner London and some other
urban areas, the sewer system has
always been combined, meaning that
foul sewage from kitchens and toilets
mixes with rainfall.
This means that, during a heavy
storm, the flow in the sewer is much
greater and can reach maximum
capacity. Our sewers are designed
to cope with the majority of storms
but occasionally rainfall can be so
heavy that it overwhelms the system,
causing sewer flooding. This is a
particular issue for our Counters Creek
sewerage catchment in west London.
Sewer flooding is one of the worst
experiences our customers can face
and it is unacceptable. It causes
significant social, economic and
environmental impacts to residents,
businesses and communities.
Why we need the Counters Creek
storm relief sewer
Our statutory responsibilities
Thames Water is the statutory sewerage undertaker for the
London Area. We have a statutory duty under the Water
Industry Act 1991 to provide, improve and extend a system
of public sewers, and to effectively deal with the contents
of those sewers. The duty is enforceable by the Secretary of
State and the industry’s financial regulator, Ofwat.
There is a large ‘cluster’ of flooded properties that sit within
the boundaries of both boroughs and the properties share
many similar characteristics. They are generally located in
low lying areas, where there are no local water courses and
there is a very high density of properties with basements.
The storms of 2007
The Counters Creek catchment
After the storms of 2007, which severely tested our
sewerage network, we completed a detailed review of
the flooding that affected many local properties in the
Counters Creek area. The catchment is large and served by
a number of interconnecting sewer systems developed over
many years.
Counters Creek is one of the lost rivers of London and
is situated on the boundary of the London Borough
of Hammersmith and Fulham and the Royal Borough
of Kensington and Chelsea. This former river and its
catchment is now part of the sewerage network, draining
surface water from buildings and roads, as well as foul
water from toilets, bathrooms and kitchens.
There are approximately 44,000 properties with basements
in the Counters Creek area, of which some 30,000 lie within
the London Borough of Hammersmith and Fulham and the
Royal Borough of Kensington and Chelsea. Many of these
basements were converted following the construction of
the Thames Barrier which reduced the risk of river flooding
in the early 1980s.
There are over 1700 properties across parts of the London
Borough of Hammersmith and Fulham and Royal Borough
of Kensington and Chelsea that are subject to sewer
flooding. We believe that the number of properties subject
to flooding exceeds this figure, as we are still receiving new
reports of flooding and our modelling assessment predicts
many more properties are at risk of sewer flooding in these
boroughs. In some areas customers have been flooded up
to six times in recent years.
Key factors contributing
to sewer flooding
We have a statutory duty to address and resolve the
problems of sewer flooding experienced in the Counters
Creek catchment area.
There are several key factors contributing to sewer flooding
in the Counters Creek area which make it unique in the
Thames Water region.
• A significant proportion of properties have basements.
The basements were generally built down to the same
level as the sewers. The area has the highest density of
properties with basements per square kilometre in the
UK and basement developments are continuing.
• The catchment has lost a great deal of open space
over the last 40 years and now has a high coverage
of impermeable surfaces (e.g. buildings and roads),
resulting in more rainwater entering the sewer network.
• There are no other local watercourses in the area to
divert surface water so all storm waters have to be taken
away by the sewer system.
• The entire sewer network in the Counters Creek
catchment takes both wastewater from properties and
rainwater water, making it prone to flooding following
heavy rain.
2 Counters Creek storm relief sewer
Investigating the extent of
flooding and underlying causes
We have learned a significant amount about the sewerage
network in the Counters Creek catchment since the
widespread flooding in July 2007. Since then, we have
completed detailed research of both the number of
customers affected and the underlying causes.
The purpose of this research was to:
• Identify the number of properties affected by
sewer flooding
• Understand the causes of flooding to
customers’ basements
• Identify alternative solutions that reduce the risk of
flooding more sustainably for the future
• Design a programme of work that offers the most
protection to customers, but which is still affordable
We have completed over 3,000 door-to-door surveys taking
physical measurements of basements and sewer level and
ground level assessments.
Top floor
Ground floor
Basement
Sewer
Figure 1: How basement flooding occurs.
Main causes of flooding
We identified the main causes of flooding to be:
a. Deep basements: Some property basement levels were
found to be very close or at the same level as the sewer.
So, as soon as the flow levels rise during heavy rainfall,
the flows back up the connection pipework into the
basement areas, as shown in Figure 1.
b. Inadequate capacity in the sewers: This causes water
levels within the sewer network to rise when it rains.
This rise can result in flows backing up the connection
pipework serving the properties and then into the
basement areas.
c. Large flows from the upper catchment: the deep storm
relief sewers fill up following rainfall from the flows
coming from the upper areas of the catchment, leaving
insufficient capacity to relieve the sewer network in
the lower catchment (Hammersmith and Fulham and
Kensington and Chelsea)
Independent research
In 2008 we began our investigation to understand the
extent of basement sewer flooding in the Counters
Creek catchment area of west London. We established
an Independent Advisory Group of industry experts to
assess and scrutinise our work to investigate and develop a
sustainable and long-term solution.
The group concluded that a combination of measures
was necessary to alleviate flood risk in the Counters
Creek catchment.
We have engaged with the Independent Advisory Group
throughout the development of our proposals and the group
is supportive of our approach and the proposed solution of
constructing a storm relief sewer.
Appraisal of initial options
We assessed the following options in terms of effectiveness
and cost:
• Isolation – Temporarily disconnect the property from
the sewer network during storms (e.g. Flooding Local
Improvement Programme (FLIP) devices)
• Flow transfer – Divert flow to another part of the system
with capacity
• System optimisation – Real time control of sewer levels
• Storage – Where the storm flows are stored in a large
underground chamber and pumped back into the
existing sewer system after storm has passed
• Upsizing – Replacing the existing overloaded sewers with
larger diameter pipework
Counters Creek storm relief sewer 3
• Overflow – Construction of chambers on the existing
overloaded sewers to allow the excess flows to overflow
into the River Thames
storm flows in the sewer network are so significant that
reasonable application of SuDS would not resolve the
flooding problem.
• Sustainable Drainage Systems (SuDS) – Permeable
paving, water butts etc.
However, we agree that SuDS should be developed and
encouraged wherever possible and beneficial, through
collaborative working between all the stakeholders
involved, in order to reduce the risk of future increases in
impermeable areas.
This process highlighted where certain options would not
work locally (e.g. they moved the flooding elsewhere), but
would still be effective at a regional level. In addition to the
hydraulic performance of each option, we considered how
viable they would be in terms of construction practicalities
and their associated costs.
A key part of the process was the investigation of the
potential for sustainable drainage systems (SuDS) across
the Counters Creek catchment to reduce surface water runoff and flood risk.
Using a Geographical Information System (GIS)
assessment, we identified different impermeable areas
(such as roofs, driveways, roads, car parks). We assessed the
potential for a range of different SuDS measures, including
diversion of downpipes to gardens, diversion of highway
run-off to natural land, green roofs, permeable paving and
water butts.
The range of options considered demonstrated that a
number of the options proved to be very expensive to
reduce sewer flooding risk and no single solution could deal
with the problem by itself.
In addition, we realised that we simply could not help a
number of properties without using a catchment-wide
solution to intercept and transfer storm flows. We therefore
investigated the construction of a new storm relief sewer.
The proposed solutions
Through this work we determined that the most cost
beneficial solution would be a programme of flood
alleviation measures including the following:
Sustainable drainage systems (SuDS)
We are piloting different sustainable drainage systems
in three streets locally, with the aim of slowing down
the rate at which rainwater enters the sewer network
when it rains heavily. This involves installing permeable
road surfaces and underground rainwater storage.
Hydraulic investigations have shown that the volumes of
We have not trialled the retrofitting of SuDS solutions
into densely populated urban areas before. We will use
key outputs from these SuDS pilots, such as how well the
different types of SuDS hold back rainwater from entering
the sewers under different rainfall conditions, to inform
future SuDS schemes across our region.
A programme of local sewer improvements
For some of the sewer flooding problems in this area a
local sewer enhancement is required. We need to improve
a number of smaller local sewers in the area to ensure
they have capacity to cope with heavy rainfall. Once we
have a proposed work programme we will consult with the
communities that may be affected.
Installation of anti-flooding devices
Installation of Flooding Local Improvement Programme
(FLIP) devices at some of the properties that have suffered
sewer flooding. These devices are designed to pump
sewage and rainwater from the drains in basements to
the local sewers in the road, and prevent sewage from the
sewer entering the property.
Counters Creek storm relief sewer
To remove one of the key underlying causes of flooding,
we determined that flows in the existing larger storm relief
sewers and trunk sewers had to be collected at key pinch
points to allow the existing systems to drain freely. We
identified that a strategic, catchment wide solution was
needed to pick up, drain and transport the storm flows
away from the clusters of properties at risk of flooding.
This ability to collect and transfer storm flows is a key
element of any overall solution. The other solutions, on
their own or in combination, will not enable us to tackle the
sewer flooding problem.
This established the need for a new Counters Creek storm
relief sewer as part of the above package of measures to
alleviate sewer flooding within the catchment.
Counters Creek storm relief sewer 4
Benefits of the Counters
Creek storm relief sewer
By constructing the new storm relief sewer and lowering
the flow levels during storms, we would be able to provide
relief to the existing sewers. By transferring flows to the
new storm relief sewer, we would remove existing hydraulic
constraints or ‘pinch points’ and reduce the risk of flooding
for a large number of properties.
development to incorporate sustainable urban drainage.
We are also constructing pilot schemes across London
to retrofit sustainable drainage in an urban environment
and then extending the lessons learned to retrofitting
sustainable drainage into existing developments where
possible. These measures are aimed to not only address
climate change by reducing the rainwater entering the
sewer network, but create additional capacity for foul flows
from future developments.
In the future, both climate change with the potential
to impact rainfall rates, and new development with the
potential to increase the amount of foul water entering
the drainage system, could increase the risk of sewers
overloading. To address these we are actively working with
councils and developers to maximise the potential for new
It is essential that we fulfil our statutory duty and ensure
that the sewerage system operates effectively. By
introducing the storm relief sewer, alongside our wider
flood alleviation work and sustainable drainage, we will be
putting in place a sewer network that will be fit for purpose
for years to come.
Shepherd’s Bush
Westfield
Shopping Centre
5
3
Goldhawk
Road
KENSINGTON AND CHELSEA
High Street
Kensington
4
KENSINGTON
Olympia
London
HAMMERSMITH
Stamford
Brook
Ravenscourt
Park
CHISWICK
Gloucester
Road
West
Kensington
Earls
Court
2
Barons
Court
HAMMERSMITH
AND FULHAM
Earls Court
Exhibiton Centre
Fulham
Broadway
South Kensington
Stamford
Bridge
Proposed storm relief sewer
1 Cremorne Wharf Depot, Lots Road, Chelsea
2
Land adjacent to Talgarth Road and Trevanion Road, Hammersmith
3
Maclise Road car park and woodland, adjacent to Kensington
BARNES
Olympia Station
4
5
A section of the car park at Tesco Superstore, Shepherd’s Bush Road
Holland Villas Road at its junction with Lower Addison Gardens
1
Parsons
Green
Counters Creek storm relief sewer 5
Related documents
The following documents are available at our drop-in sessions and to download from the document library on our
website - www.thameswater.co.uk/counterscreek
Phase 1 consultation and engagement process
• Feedback from our phase 1 consultation and
engagement process
• Phase 1 Consultation and Engagement Process
Feedback Report
Project information
• Being a good neighbour
• Environment
• Getting planning permission
• Have your say
• How we chose our preferred sites
• How we would build the proposed storm relief sewer
• Transport
• Timing
• Tunnel drive strategy
Project contact details:
Web: www.thameswater.co.uk/counterscreek
Email: [email protected]
Phone: 0800 316 9800, option 2 Ref: BB968577
Postal address: Counters Creek sewer flooding
alleviation scheme consultation,
Freepost RTHE-CJYYCXCJ, 7 St Peter Street,
Winchester SO23 8BW
Site information
• Cremorne Wharf Depot, Lots Road, Chelsea
• Land adjacent to Talgarth Road and Trevanion Road,
Hammersmith
• Maclise Road car park and woodland adjacent to
Kensington Olympia Station
• Holland Villas Road at its junction with Lower Addison
Gardens
• Tesco Superstore car park, Shepherd’s Bush Road
Site Suitability Reports
• Cremorne Wharf Depot, Lots Road, Chelsea
• Land adjacent to Talgarth Road and Trevanion Road,
Hammersmith
• Maclise Road car park and woodland adjacent to
Kensington Olympia Station
• Holland Villas Road at its junction with Lower Addison
Gardens
• Tesco Superstore car park, Shepherd’s Bush Road