Page 28 - Updated SuDS Design & Evaluation Guide-Newham V3 Spreads

In most locations the water table is likely to studies and LLFA detailed requirements can
Local SuDS requirements
be found at depths of less than 3 metres.
Ground water source protection zones are
found in the northern part of the borough.
Fig.5 Newham’s main made ground
(grey/grey hatched) and source
protection zones (shades of pink)
The combination of these factors may limit
potential for infiltration drainage. However,
given the high variability in ground conditions
found across the borough, it is recommended
that developers carry out thorough ground
investigations to establish the potential for
23 infiltration. It should be noted that none of
the above prevents use of SuDS within a
development, if integrated into the design at
an early stage. In any case, above ground no
infiltration SuDS measures can still be used in
areas of contaminated ground provided that
barriers to contain contaminants, such as
impermeable liners, are used to protect
groundwater.
Local SuDS specific requirements
Newham has developed a number of
documents in connection with local flood risk
assessment and management. Main
requirements applicable to major
development are fully embodied in Newham’s
local policy (Newham Local Plan 2018).
Links to relevant Newham policy, flood risk
Newham Council SuDS D & E Guide
requires that greenfield runoff calculations
be found on Newham webpage as below:
LB Newham Flooding Webpage
Flood Risk and Sustainable Drainage:
Requirements and Guidance for Planning
Application
Newham Local Plan
Newham LLFA drainage pro-forma
Highlights of main requirements:
• All major development is required to
restrict post development runoff to
greenfield runoff rates unless it can be
demonstrated that site conditions prohibit
the ability to do so.
• All development must restrict runoff
discharge within or to Critical Drainage
Areas (CDA) to greenfield rates or below.
N.B. there are 15 CDAs in Newham.
• Discharge to tidal water (i.e. River
Thames, Lea and Roding) will need to
take account of the effect of “tide
locking”, storm surge or submergence of
the outfall, in order to prevent flooding.
An appropriate allowance in terms of
onsite storage should be built into the
drainage strategy.
• Discharge to tidal water may not be
restricted to greenfield provided scour/
erosion would not result, however a level
of attenuation will be expected - normally
a 1 in 30 attenuation - to create SuDS
features that provide additional benefits.
Application of Greenfield Runoff Rates
To enable consistency of assessment
between planning applications, Newham
LLFA, in its Statutory Consultee function,
© 2020 McCloy Consulting & Robert Bray Associates Newham Council SuDS D & E Guide
site specific evidences and mitigation
should be performed using the IH124 method
as supported by the HR Wallingford UK SuDS
online greenfield runoff rate estimation tool.
Under the same concern greenfield
calculations should adopt the default
parameters (e.g. soil type) as provided by the
UK SuDS tool as characteristic of the
application site location.
Newham LLFA will not object to greenfield
runoff calculations based on Flood
Estimation Handbook (FEH) methodology,
provided that the results are demonstrated to
be largely consistent with IH124 methodology
output from UK SuDS online tool and
representative of the application site in a
pre-development greenfield condition.
Newham LLFA does not accept the following
approaches:
• urban soil types for Greenfield runoff
estimation
• applying urban catchment parameters to
runoff estimation
Local LPA and Stakeholder Engagement
In addition to LLFA the Environment Agency
and Thames Water must be consulted with
concern of flood risk, discharge consents,
building in proximity to flood defences
structures and watercourses.
London City Airport (LCY): Under concern of
risk management (i.e. bird strike) LCY may
object to development proposal deemed
potentially to increase of bird presence in the
airport safeguard area. Whilst this concern
should be heeded and early consultation with
City Airport is advised, LCY’s general concern
should never be used to scope out
requirement of green infrastructures, such
SuDS, nor LCY’s objection accepted without
requirements provided to be evaluated by
Newham Local Planning Authority.
London City Airport guidance on biodiversity
and safeguarding
Pre-planning advice
Newham LLFA can provide pre-application Local SuDS requirements
advice for developments as part of a pre-
application consultation agreement with
Newham Local Planning Authority.
Please note that a fee specific to LLFA
services is required:
Pre-Application Advice Guidance Note &
Charging Schedule
LLFA advice can include providing specific
information on local flood risk, review of
information provided by developer relevant
to the SuDS design and making
recommendations on compliance with local
and national policies.
The above could be arranged by contacting 24
Newham Planning Authority development.
control@newham.gov.uk
Adoption of SuDS
Newham will not adopt SuDS unless
undertaken by LB of Newham on council
owned land. Applicants should therefore put
in place arrangements for maintenance and
end of life replacement of SuDS. Details must
be provided to the LLFA to add to its asset
register. There are other Risk Management
Authorities, such as Thames Water or TFL
that may be willing to consider adoption of
SuDS. Early engagement with the relevant
party is critical to ensure their requirements
can be achieved.
© 2020 McCloy Consulting & Robert Bray Associates