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‘THE NORTH STREET
Working with
the River in the
North
STREET
QUARTER
The North Street Quarter water
management strategy will not only
complete the town’s flood defences,
protecting North Street and the Pells,
but it will open up the riverside, making
it accessible and visible throughout the
area, for local people and visitors enjoy.
YOU QUARTER WILL NEED EFFECTIVE
SAID: PROTECTION AGAINST FLOODING.’
Since the big floods of 2000, significant research
has been undertaken and reports produced on how
to manage flood defences in the area, mainly led by
the Environment Agency. Our water engineering team
has used this extensive research and implemented
a water management strategy and design, in full
consultation with residents and the statutory
authorities, including the Environment Agency.
Flood defences for the development must recognise
where Lewes is located on the River Ouse. The
catchment area of the river covers over 600 km2. In
the Lewes area, the catchment extends to Slaugham
in the north west and Sheffield Park and the upper
Ashdown Forest slopes towards Crowborough in the
north east.
At times of significant rainfall, huge volumes of water
flow into the Ouse and are carried through Lewes.
The length of time over which it rains, together with
the intensity of the rainfall, will determine when these
flows arrive at Lewes and their associated volume.
Whether or not Lewes suffers flooding is then a
function of how the Ouse catchment handles these
rain events, in terms of flow rates, arrival times
and upstream storage devices. The majority of
the catchment area lies to the north of Lewes (i.e.
upstream) and therefore the improvements made
at these northerly reaches of the catchment will
significantly affect the flood risk at Lewes.
Upstream of Lewes, considerable efforts by the
Environment Agency are being made to encourage
the management of the undeveloped land, arable
acres, woodlands, etc, to be sensitive towards
the way in which rainfall run-off happens, as this
management can, at modest costs, significantly
affect the rate of flow and volumes of flood water
reaching Lewes at the critical time during a flood risk
event.
A university study has produced a flood model that
identifies the benefit of installing various natural
woodland devices to impede and ‘manage’ the
excess flows. All of this will have a positive impact on
flood risk for all the towns along the Ouse, with Lewes
gaining probably most benefit as it is the second
furthest town downstream.
The North Street Quarter Development is in Flood
Cell 4. As part of the development work, we have also
taken the decision to defend Flood Cell 5, which is
outside of the North Street Quarter, but constructing
defences here would complete the Environment
Agency’s plans for this area, so this seems a sensible
addition to our plans to ensure long-term security for
the wider area.
THE RIVERSIDE WALK - LEAFLET 5
‘SOFT FLOODING DEFENCES
The proposed flood defences in the North Street
Quarter are designed for a flood risk level which is
set by the Environment Agency and includes a 30%
additional allowance for the climate change expected
over the coming decades.
To give you an idea how this defence design level
compares with events in recent memory, the 2000
flood, which a lot of people will remember, was
measured as a 0.5 - 0.75% risk of flooding, which
means it was of a size which statistically would only
be expected every 133 – 200 years. The 2000 flood
raised the water level to 5.8m Above Ordnance
Datum (AOD). The design defence level for the
proposed defences is 6.1m AOD (ie. 0.3m higher than
the floods in 2000 – this ‘spare’ capacity is called the
‘Freeboard’).
The flood risk strategy, prepared by the Environment
Agency for Lewes, is to create defensive cells next to
the river (see diagram).
YOU SHOULD BE INCLUDED IN THE
SAID: DESIGN.’
During the consultation programme, residents
suggested that ‘soft defences’ should be included
in the plans, such as floodable public spaces. The
design of the North Street Quarter scheme will meet
the technical requirements of the flood defence
strategy with the added benefit of opening up the
riverbank, linking the town centre with the Ouse and
surrounding countryside.
Rainwater run-off will be managed on the site through
permeable paving and Sustainable Urban Drainage
Systems (SUDS), which use open swales and water
gardens instead of drains. As well as managing the
run off, SUDS helps attract and support more plant,
insect and animal species. Making space for water
and designing attractive features to store water
within the site also helps alleviate the risk of flooding.
Without these measures, water would otherwise
gather behind the flood defences. We will create
ducted outlets, which will allow the tide to take the
water away as it falls, assisting the flow of water into
the Ouse.
The diagram above shows how the North Street
Quarter has planned for the sustainable management
of rainwater as it falls onto the development.
A complementary water strategy, built into the
scheme’s design, will provide attractive water
features within public open spaces, which will also
boost the area’s biodiversity.
WWW.NORTHSTREETQTR.CO.UK
ENJOYING THE RIVERSIDE
The principle public space and riverside features
include:
•
Two-level riverside walks, including promenade
and riverside path, linking the site to Pells, town
centre, Malling Fields and the South Downs
•
Multiple views and pedestrian connections and
stopping places to the riverside throughout the
site
•
Public launch access points for small boats
•
Swales and open water features will be created
throughout the site, creating new landscape and
ecology pathways which encourage connections
for wildlife through the scheme to the river
•
The new health centre will provide services
for 26,000 patients, including public exhibition
space capturing the heritage of the site and
public gardens leading down to the riverside
The documents which have advised
the design include:
• Report by Binnie Black & Veatch 2001 –
Executive Summary on the flooding event – 2000
•
Lewes Flood 2000 – Review of the Recovery
•
Lewes Flood Action – Consultation on flood
defences for mallings Brooks – 2003
•
Lewes District Strategic Flood Risk Assessment
– 2009
•
Flood Risk Assessment for Phoenix Quarter
Development – 2003
•
Flood Risk Assessment for Malling Brooks –
2006, revised February 2009
•
Ouse Catchment Flood Management Plan
•
Flood Management Strategy for ESCC
•
Lewes Flood Plan - 2010
HARNESSING THE POWER OF THE RIVER
The North Street Quarter will be powered by a unique
low carbon district heating system and thanks to
funding from the Department for Energy and Climate
Change, we can use the best available affordable low
carbon design, using the river as the main source of
heating.
WWW.NORTHSTREETQTR.CO.UK
THE DETAILED PLANNING APPLICATION CAN BE FOUND AT:
http://planningpublicaccess.southdowns.gov.uk/online-applications/