LONDONSUSTAINABLE
DRAINAGE ACTION
PLAN
2016

LONDON SUSTAINABLE DRAINAGE ACTION PLAN

COPYRIGHT
Greater London Authority
December 2016
Published byGreater London Authority
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LONDON SUSTAINABLE DRAINAGE ACTION PLAN

CONTENTSEXECUTIVE SUMMARY

2PART 1: WHY WE NEED AND WANT MORE SUSTAINABLE DRAINAGE 3
Surface water management in London

4

Surface water management challenges

5

What is sustainable drainage?

8

International experience of sustainable drainage

11

The case for sustainable drainage in London

12

Sustainable drainage vision

13

PART 2: THE SUSTAINABLE DRAINAGE ACTION PLAN

19

The Sustainable Drainage Action Plan

20

Understanding the opportunities and benefits of sustainable drainage

21

Delivering sustainable drainage through new developments via the planning system

23

Retrofitting sustainable drainage across London

25

What can you do? Delivering sustainable drainage through domestic
and local neighbourhood measures

56

Funding opportunities and regulatory incentives

59

Monitoring

61

Appendix 1: Action plan by year

62

Appendix 2: References71

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
2EXECUTIVE SUMMARY
London is outgrowing its drains and sewers. The combined sewer system originally built over 150
years ago by Joseph Bazalgette has served us well, but it was designed for a smaller city with more
green surfaces. The combined challenges of London’s growing population, changing land uses andchanging climate mean that if we continue to rely on our current drains and sewers, we face anincreasing risk of flooding.
To make the most effective use of our existing and planned drainage infrastructure and avoid
increased flood risk, we need to change how London’s drainage system operates. Rainwater should bemanaged as a valuable resource rather than a waste product. We need to roll back the tide ofimpermeable surfaces. They should be replaced with ‘sustainable drainage’ systems that mimic theways that nature manages rainwater and add to the services provided by our existing drains andsewers. The need for more sustainable drainage is now widely recognised internationally andembedded in our national and local planning systems including in the Mayor’s London Plan.
This action plan addresses a specific need to promote the awareness, and the retrofitting, ofsustainable drainage systems right across London. It contains a series of actions to make our drainage
system work in a more natural way which will bring a wide range of benefits including: steadily reducing flood risks by easing the burden on our drains and sewers
 reducing pollution of our tributary rivers and streams
 creating more pleasant landscapes, streets and settings for London’s buildings
 providing opportunities to save water providing opportunities for school activities and studies related to the water cycle
The main focus of the action plan is on the retrofitting of sustainable drainage to existing buildings,
land and infrastructure. It is recognised that funding pressures mean there will not be funds
specifically for a large-scale drainage improvement programme. Instead the key is to identify when
and where other planned maintenance, repair or improvement works are scheduled and then to
identify opportunities to retrofit sustainable drainage as part of those works. This way sustainabledrainage can be introduced at a much lower cost. In some cases these measures can save money, forexample where ‘harvested’ rainwater replaces large scale water supplies used for irrigation, toilet
flushing or vehicle/plant cleaning.
The action plan aims to set the direction for the next 20 years, but includes 40 actions specifically forthe next five years. These actions will be implemented, in part by Greater London Authority staff, andin part by others and include a commitment to measure and report progress annually. It is also
important that the awareness of rainwater management is spread more broadly across London’s
institutions and individual Londoners – we can all make a contribution to the vision:
VisionBy 2040, London will manage its rainwater more sustainably to reduce flood risk and improve water
quality and security. This will maximise the benefits for people, the environment and the economy.

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
3

PART 1:
WHY WE NEED AND
WANT MORESUSTAINABLE
DRAINAGE

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
4

Surface water management in London
Surface water is the rainwater that falls on the city’s surfaces; on the ground, streets, pavements,
roofs, parks, and gardens.
Flooding
When this water does not soak into the ground or drain through normal drainage systems, but lies onor flows over the ground instead, it can cause surface water flooding. Whilst London is currently very
well protected against flooding from the tidal Thames, it has a relatively lower standard of protection
against surface water flooding.
The London Regional Flood Risk Appraisal (RFRA) identifies the high potential risk of surface water
flooding in London (GLA, 2014). It notes London’s density of development, high proportion ofimpermeable surfaces and general lack of records as particular problems. The Mayor’s Climate Change
Adaptation Strategy (GLA, 2011) identified surface water flood risk as the greatest short-term climate
risk to London.
In 2007, other areas of the country, including parts of western England, Sheffield, York and Hull,suffered severe flooding. This was initially from surface water as a result of heavy rainfall, and laterfrom rivers as the rainwater naturally moved through the system. London was spared the worst of
those storms. However, it was clear that had these storms been concentrated over parts of London, it
would have caused huge disruption, high economic impacts and long recovery times, especially if
major infrastructure was severely affected. Within London, there have been several localised examples
of surface water flooding - most recently during heavy rainstorms in summer 2015 and 2016.
Widespread use of sustainable drainage systems will help reduce the impact of such heavy storms.
Water quality
The quality of water in London’s tributary rivers is generally poor to moderate. Of 41 London riverwaterbodies monitored for the Thames River Basin Management Plan in 2015, three were classified as
bad, five as poor and 33 as moderate. No waterbodies were classified as good or very good.
Classifications can change from year to year. The overall aim of the EU Water Framework Directive isto improve water quality in rivers and lakes. However, it is clear that there is scope for major
improvement within London. Removing pollutants from surface water discharges will be an importantpart of any improvements. Many sustainable drainage techniques can help to do this. Sustainabledrainage will also help to maintain improved base flows in our tributary rivers, which again will help toimprove the health of those rivers.
Drought
London is often mistakenly perceived as having abundant rainfall. However, London (and indeed thewhole of south east England) is classified as ‘seriously’ water stressed. That means that more water istaken from the environment than the environment can sustain in the long term. Fifty-five per cent of
all the rain that falls in the Thames Valley is abstracted and used. This is more than anywhere else in
the UK, and more than almost everywhere in the world. London is usually relatively resilient todrought and it takes two consecutive drier-than-normal winters to create water supply issues. In 2006

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
5

and 2012, London experienced significant droughts, and in 2012 only avoided serious water
restrictions by the having the wettest spring in a century. Some sustainable drainage techniques
retain water for later use, either directly through rainwater harvesting systems or indirectly throughinfiltration. It is also important that vegetated sustainable drainage systems are drought resilient andthat new green infrastructure sustainable drainage doesn’t need significant irrigation in dry weather.

Surface water management challenges
The frequency and severity of future surface water flooding, drought and poor water quality in
London depend on several different factors. Some of these factors are physical, others are social, andsome are a result of London’s historical development, whilst others are the result of projected future
trends. These are explored further in the following sections.
Physical
The climate of the future is likely to be increasingly different from that of the past. The south east of
England is expected to experience warmer, wetter winters and hotter, drier summers. It is also
expected there will be more frequent and intense extreme weather events, such as heatwaves andheavy rainfall events. By the middle of the century, the probability of a rainstorm likely to overcome
the drainage system will have increased from a 1 in 30 (3.3 per cent) chance to a 1 in 13 (7.7 percent) chance in any one year (UK CIP, 2002).
Like all cities, London has a high proportion of impermeable surfaces, which prevent water fromsoaking into the ground. As well as this, the clay soils found under parts of London reduce the rate of
infiltration, which results in more water at the surface. This is often used as a reason not to installsustainable drainage solutions. However, there are a range of sustainable drainage techniques that do
not depend on infiltration. The soils in most areas have some degree of permeability and should betested in line with best practice (BRE, 2016).
London also has relatively old drainage systems. Routinely built to very high standards, it was
designed to manage lower return period storms than now used and to cater for a smaller population.
In general the drainage system can be split into two distinct systems. In central and inner London
there is a combined sewer system that carries both rainwater and foul water in the same pipework andsewers to the major sewage treatment works of Beckton and Crossness. The key challenge in the
combined sewer area is that rainfall can quickly fill the sewers. This leads to overflows into the rivers(mainly the Thames) of untreated sewage mixed with rainwater. These are known as combined sewer
overflows (CSOs).
In 2014, the Government gave permission for the Thames Tideway Tunnel (TTT). This project isconsidered necessary to address the current problems of combined sewer overflows into the Thames.
These problems are basically caused by the rainwater flowing into the combined sewer network. The
TTT will not increase capacity in the combined sewer system, but will prevent all but the most severe
sewer overflows into the Thames. Thames Water is also progressing towards a planning application
for the Counters Creek Storm Relief Sewer on the Kensington and Chelsea / Hammersmith andFulham border. This will address problems of capacity and sewer flooding in the area.

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
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In outer London, there are mainly separate systems that convey rainwater into local tributary rivers
and foul water to sewage treatment works (see Figure 1). There are two main problems with theseparated drainage systems. Firstly, there are widespread problems of pollution caused by the‘misconnection’ of foul pipes into the surface water drainage system within the separated sewerage
areas. This means that untreated sewage finds its way into local streams. Secondly, there is theimpact of the ‘first flush’ following a heavy rainstorm. This is especially significant following a
prolonged dry period. The storm has the effect of washing urban surfaces into local rivers andstreams. It takes with it a concentrated first flush of organic litter (such as leaves and bird/animal
faeces), human litter/debris, tyre, metal and motor fluids from road surfaces. This has a severe impact
on water quality in those local streams.
It is becoming more complex and expensive to increase the capacity of London’s drainage systems
using traditional underground piped networks, like the Tideway Tunnel and Counters Creek project.
This is due to the necessity for large-scale and widespread excavations in many streets. There is also
the need to work in and around the vast amount of infrastructure that now lies under most streets.

Figure 1: Combined and separated sewer systems. Source: Thames Water

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
7

SocialFlood risk tends to affect poorer communities the most. Poorer people are more likely to live in floodrisk areas. They’re less likely to have insurance to cover any loss or damage. They’re also less likely tohave the means to install flood resilience or adaptation measures. Floods are therefore likely to havemore of an impact on the poorest people in London.
Over the past few decades, more and more front gardens (and to some extent, rear gardens) havebeen paved over with impermeable surfaces. Estimates vary, but two-thirds of front gardens are atleast partially covered by surfacing other than vegetation (London Assembly, 2005). The annual
average loss of vegetated garden land in London is the size of 2.5 Hyde Parks (London Wildlife Trust,
GiGL & GLA, 2010). A recent poll for the Royal Horticultural Society also suggested that almost aquarter of London’s front gardens have been paved over (RHS, 2015). This is placing an everincreasing strain on our drainage systems. It needs to be not only stopped, but reversed, if flood risk is
to be managed.
In the past 25 years, London’s population has grown significantly, by nearly two million people. The
London Plan estimates the population will be over nine million by 2020, and nearly ten million by
2031. The London Infrastructure Plan suggests that by 2050 the population will be over 11 million.
The increase in population will certainly add to the base sewage flows and demand for water supplies.
If planned and designed traditionally, the increased population would also lead to an increase inimpermeable area. Such trends would exacerbate pressures on the city’s drainage and water supply
systems, potentially increasing the risk of flooding and drought.
Thames Water has modelled the impact of London’s projected population growth and climate change
on its foul and combined sewers to understand how they’ll cope with these future challenges. It showsthat for a relatively common rainfall event in 2050 (one expected on average once every other year),some areas of London wouldn’t have enough drainage or sewerage capacity to manage the expectedflows. This would lead to an increasing risk of surface water and sewer flooding.
Figure 2 shows the mapped output of this modelling for the 2050s. Areas in red on the map are where
the projected flows in the system exceed capacity and some flooding would be expected.

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
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Figure 2: Modelled foul and combined sewer capacity for the 2050s. Source: Thames Water

What is sustainable drainage?
Sustainable drainage includes both good management practices, such as retaining permeable surfaces,
and the installation and use of sustainable drainage techniques. Sustainable drainage techniques help
capture, use, delay discharge or absorb surface water. They can also reduce the volume and/or
concentration of pollutants reaching watercourses. Green infrastructure forms of sustainable drainage
also have a wide range of other benefits over and above the direct drainage benefits. This action plan
focuses mainly on sustainable drainage techniques, rather than management practices. It has a clear
preference for green infrastructure sustainable drainage. However, it accepts that in some instances
hard engineered sustainable drainage will be required.
Box 1: Definition of green infrastructure
A network of green spaces - and features like street trees and green roofs - that is planned, designed
and managed to deliver a range of benefits. These include recreation and amenity, healthy living,
mitigating flooding, improving air quality, cooling the urban environment, encouraging walking andcycling, and enhancing biodiversity and ecological resilience. (Green Infrastructure Task Force 2015)

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
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Sustainable drainage techniques
Details on particular techniques can be found in a range of other documents and websites. It is also
possible that new techniques or variations on techniques may be developed in future. Table 1 details
some of the more common techniques that are used. This is not intended to be comprehensive and, ofcourse, any one building or site may successfully incorporate a range of techniques. A particularly
useful reference will be the Sustainable Drainage Manual (CIRIA, 2015). This gives a complete guideto sustainable drainage. It includes a chapter dedicated to the use of sustainable drainage in urban
areas, with a useful range of illustrations. CIRIA has also produced the BeST tool (CIRIA, 2015), whichenables users to quantify the benefits of a range of sustainable drainage techniques. The Susdrain
website (CIRIA, 2016) is a valuable source of guidance advice and discussion within the sustainabledrainage profession.
Table 1: Summary of sustainable drainage techniques
Technique

Summary

Rainwater
harvesting

Capture of rainwater into a tank(s) for use (usually non potable) such as irrigation,
toilet flushing, vehicle or plant cleansing. For some premises the rainwater harvesting
can generate major cost savings on water bills. Care is needed to prevent thedevelopment of bacteria, algae and insect infestation.
Systems are now available to combine rain water harvesting with tanked attenuation.
That means water is stored during dry periods and released ahead of predicted storms.
This ensures that the attenuation capacity remains available when needed.

Green/brown/
blue roofs

Used on flat or shallow pitched roofs to provide a durable roof covering which also
provides thermal insulation, amenity space, biodiversity habitat as well as attenuationof rainwater. The use of roof areas for Solar PV energy generation is sometimes quoted
as a reason for not installing a green roof. However the two uses of a roof can be
combined. There is even some evidence to suggest that by keeping a roof cooler, thegreen roof actually increases the efficiency of the PV panels. Depending on the design,
such roofs can attenuate differing volumes of rainwater. The term ‘blue roof’ is reserved
for those roofs designed to maximise water retention. This is a relatively recent area ofincreased focus and can involve effectively an attenuation tank at roof level. This
reduces or avoids the need for pumping of basement tanks.

Raingardens

Planted areas usually close to buildings (but not immediately adjacent) that allow thediversion of a portion of rainwater from either downpipes or surrounding paved
surfaces. These techniques can be incorporated into the landscaping plans for a site.
They’re most effective if the landscaping regime is designed with the aim of capturing
as much rainfall as possible. Raingardens can either allow infiltration into the ground or
have tanked systems for water retention, depending on the site and soil conditions.
There are also a limited number of vertical raingardens attached to building walls withrainwater downpipes diverted through a stacked series of planters.

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Technique

Summary

Bio-retention

A chain of landscaped features, potentially including reed beds, filter drains, etc.
designed to hold and treat surface water. These are often used where there is a highrisk of low-level pollution, for example from road run-off. However, it does require
areas of open space. Design can vary widely depending on site conditions and available
space. At a small scale this could include flow through planters or stormwater tree pits
(often referred to as Stockholm Tree Pits).

Permeable
pavements /surfaces

Permeable hard surfaces which work in much the same way as traditional impermeablesurfaces apart from the ability to allow rainwater to pass through. Permeable blocks arewell used. Recent innovations have enabled the development of bound granularsurfaces with both high load bearing and high permeability properties. Permeablesurfaces can either allow infiltration into the ground or have tanked systems for water
retention, depending on the site and soil conditions. They are suitable in even themost densely built-up development. However, they’re not well suited to roads carrying
heavy or fast motor traffic.

SwalesDry ditches used as landscape features to allow the storage, carriage and infiltration of
rainwater. Often used as linear features alongside roads, footpaths or rail lines, they
can also be integrated into the design of many open spaces.

Detentionbasin/ponds

Landscape features designed to store and in some cases infiltrate rainwater. Detentions
basins are usually dry, whereas a pond should retain water. These features need areasof open space but can often be combined with other sustainable drainage techniques.

Discharge totidal river/dock/canals

Discharging clean rainwater directly to tidal rivers, canals or docks isn’t normally asustainable drainage technique. Other more productive techniques should be used first.
However, it is generally more sustainable than discharging to the combined or surface
drainage systems. Residual surface water can be discharged to tidal/large waterbodies,in some cases with no limitation on volumes. Some storage may be required to allow for
outfalls becoming tide locked. Care is needed to prevent scour in the receiving
waterbody and potentially to prevent pollution. Consent from the EA, the asset owner
and where applicable the Canal and River Trust will be required.

Storage tanks

Usually but not necessarily below ground level, they attenuate rainwater for later slow
release back into the drainage system. They don’t provide the wider benefits of green
infrastructure sustainable drainage. They can also have the disadvantage that pumping
may be required to empty the tank into the drainage system - especially if the tank is atbasement level (see also Blue roof above). Where tanks are designed for large storm
events, care is needed to ensure that they still perform a useful sustainable drainage
function for low order storms. This action plan therefore recommends the use of theSusdrain Method 2 tank design (Anthony McCloy for Susdrain, 2015).

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Technique

Summary

Geocellularstorage

Similar to storage tanks except that the volume is made up from multiple units rather
than a single tank. Can underlie permeable surfaces.

Oversized
pipingUsing larger than necessary pipework creates more room to store rainwater. Potentiallymore sustainable than storage tanks/geocellular storage if the pipes drain by gravity
and do not require pumping. However, lacks the wider benefits of the green
infrastructure based techniques.

Design forexceedanceThis involves designing areas within a site such that they will flood and hold water
during rare storm events (typically a frequency of once in ten years or longer).

Sustainable drainage maintenance
Maintenance varies for different types of sustainable drainage technique. Overall maintenance needs
are unlikely to be excessive but will be different to traditional engineered drainage systems.
Maintenance requirements such as flushing and unblocking pipe networks may be lower than
traditional drainage systems, but there may be an increase in soft landscaping maintenance. Many
activities such as keeping flow routes clear of debris will remain essentially the same.
As with any operational system, appropriate maintenance is a key part of sustaining operational
effectiveness. Long term maintenance plans for sustainable drainage are equally important tomaintenance plans for other infrastructure. Without appropriate maintenance the effectiveness ofsustainable drainage systems will decrease. This will be particularly important where sustainabledrainage systems are being relied upon to provide a flood risk management role. In most new build
projects the sustainable drainage system is designed with a specific maintenance regime. This is often
controlled via a planning condition. A similar approach should be taken for retrofit projects and would
be a suitable requirement of any funding agreement to implement sustainable drainage.

International experience of sustainable drainage
A number of cities around the world have developed long-term plans to increase the use ofsustainable drainage techniques, including several in the US. One of the earliest adopters wasPortland, Oregon. It has a sustainable drainage plan dating back to the early 1990s that’s proved to
be a great success (City of Portland, 2016). Philadelphia has a 25 year plan, complemented by arange of financial incentives and changes to water bills. It was adopted in 2011. The first years of
implementation have shown significant success in the implementation of a more sustainable drainage
regime (City of Philadelphia, 2011).
New York City has started a programme of installing thousands of small-scale raingardens to collectrainwater, primarily from streets. However, it should be noted that the US context is very different to
the UK. In the US, there are generally fewer organisations responsible for rainwater management.
Drainage responsibilities largely remain with municipal city governments.

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In Copenhagen, Denmark, severe thunderstorms over recent years have caused serious flooding inparts of the city. This has led to a rethink of rainwater management in the city, the use of moresustainable drainage, and the use of specific areas (such as local streets and surface car parks) totemporarily store relatively shallow depths of rainwater. The development of the Copenhagen
Cloudburst Plan is a good example of planning to manage severe thunderstorm events.
In Melbourne, Australia, a wide range of sustainable drainage retrofit projects have been carried out
across the city with the dual aims of improving water quality and reducing flood risk. These projects
have also resulted in improvements to the public open spaces, building settings and urban streets.
International experience suggests that two key things are required for any large-scale sustainabledrainage programme to be successful. First, it must be integrated into city governance and theplanning departments. Second, it must have clear, cross-cutting political support. Through thedevelopment of this action plan, both of these elements are now in place for London.

The case for sustainable drainage in London
Thames Water’s modelling (Figure 2) will be used to help prioritise certain areas or sewer catchments
for future improvements to the existing drainage system. However, given the interconnected nature of
London’s networks, more sustainable drainage is required across all of London. The implementation ofthis action plan will seek to ensure that rainwater run-off is either slowed down or removed from thissystem. That will ensure that in 50-100 years there’ll be no need to replicate or extend the Thames
Tideway Tunnel.
In outer London, during heavy rainstorms, London's tributary rivers absorb large volumes of rainwaterfrom urban areas. This is a natural part of our drainage system but significant quantities of polluting
matter and litter can be washed into the rivers from streets, pavements and road gullies. In extreme
cases, the deluge of pollution can kill fish in the rivers. Sustainable drainage measures can help tackle
this water quality problem by holding back the peak rainwater volumes and reducing the “flushing”
effect on the drainage system. Some sustainable drainage techniques, such as reed beds and filter
drains, can be specifically designed to remove pollutants. Furthermore, because sustainable drainage
systems slowly release water back to the streams and rivers, they can increase the un-naturally lowbase flows that most urban rivers experience and help the overall quality of these watercourses.
Sustainable drainage techniques can therefore have a wide range of water quality benefit. Indeed, in
the USA and Australia it is these water quality benefits that are often the main reason for
implementing sustainable drainage.
It is also clear that adding green infrastructure sustainable drainage (as opposed to hard-engineered
techniques) has many other benefits. These include reducing air pollution, reducing noise, creating
pleasant amenity areas, improving biodiversity, reducing summer urban heat island effects andpotentially providing water for use instead of mains supply. These benefits remain challenging toincorporate into cost-benefit analyses. As a result, sustainable drainage techniques can sometimes
appear to be less cost-effective than traditional engineered drainage solutions. However, twoapproaches offer potential solutions to this problem:

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
13

SuDS-specific tools. CIRIA has done work at a national level to show the relative costs andbenefits of different sustainable drainage options. The Benefits of SuDS Tool (BeST) is an easy
to use means of assessment.



Generic ecosystem services tools. The natural capital approach involves the economic
valuation of natural assets, and the services we get from them (like clean water and flood risk
reduction), for use in decision-making. A range of tools exists to value different natural assets
and ecosystem services (assuming the availability of the necessary data). For example, iTree
Eco estimates the value of some of the ecosystem services provided by individual trees, suchas carbon storage and sequestration. These are likely to develop and improve in future.

Sustainable drainage vision
The use of sustainable drainage systems in London is increasing but is still at a low level. London faces
many challenges in terms of surface water flooding. That, alongside the co-benefits that sustainabledrainage can provide, means the Mayor now wants far more sustainable drainage in London.
By 2040, London will manage its rainwater more sustainably to reduce flood risk and improve water
quality and security. This will maximise the benefits to people, the environment and the economy.

To make this happen, we will use both the planning system and retrofitting initiatives, working with anumber of key partners. The following sections describe both current planning policy and existing key
partners and programmes.
National planning policy
Proposals to increase the use of sustainable drainage techniques are in line with England’s planningpolicies, as set out in the National Planning Policy Framework (NPPF). Sustainable drainage is seen asa means by which developments can avoid increasing the risk of flooding elsewhere. Following thegovernment’s consultation ‘Delivering Sustainable Drainage’ (Defra & DCLG, 2014), there is stronger
guidance to support the NPPF in terms of sustainable drainage.
Since April 2015, planning authorities have been responsible for the approval of sustainable drainage
designs for all major planning applications in consultation with the lead local flood authority (LLFA).
In London, the relevant borough is both the local planning authority and the LLFA.
The London Plan
The London Plan’s Policy 5.13 (Box 2) is aimed at ensuring that sustainable drainage techniques areused wherever practical for new developments. This policy has remained broadly unchanged since2004 and is understood to be working well for large-scale development. It is anticipated that in any
future London Plan the broad thrust of the policy will remain.
The policy requires developers to aim for greenfield run-off rates. However, it also recognises that insuch a densely built-up city as London this may not always be possible. In particular, given that thevast majority of development is targeted on brownfield sites.

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The policy contains a hierarchy of broad drainage methods. Methods are preferred that makebeneficial use of any rainfall captured, for example for irrigation or other non-potable uses like vehicle
cleaning. The policy also places a preference for sustainable drainage measures that retain water insurface features over methods than store water below the surface. The policy recognises thedischarge of rainwater directly to tidal rivers or docks can be a sustainable method of managing
rainwater, rather than requiring sustainable drainage features to be incorporated into thedevelopment. The Sustainable Design and Construction Supplementary Planning Guidance (GLA,
2014) gives further detail on the implementation of this policy.
New development will be an important aspect of future sustainable drainage delivery. This action plan
provides a dedicated section and series of actions relevant to the planning system.
Box 2: London Plan Policy 5:13 Sustainable Drainage
Planning decisions
A. Development should utilise sustainable urban drainage systems (Sustainable drainage) unlessthere are practical reasons for not doing so, and should aim to achieve greenfield run-off
rates and ensure that surface water run-off is managed as close to its source as possible inline with the following drainage hierarchy:
1 store rainwater for later use
2 use infiltration techniques, such as porous surfaces in non-clay areas
3 attenuate rainwater in ponds or open water features for gradual release
4 attenuate rainwater by storing in tanks or sealed water features for gradual release
5 discharge rainwater direct to a watercourse
6 discharge rainwater to a surface water sewer/drain
7 discharge rainwater to the combined sewer.
Drainage should be designed and implemented in ways that deliver other policy objectives ofthis Plan, including water use efficiency and quality, biodiversity, amenity and recreation.
Local Development Framework (LDF) preparation
B. Within LDFs boroughs should, in line with the Flood and Water Management Act 2010, utilise
Surface Water Management Plans to identify areas where there are particular surface water
management issues and develop actions and policy approaches aimed at reducing these risks.

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Drain London
In 2008, the GLA, Thames Water and the Environment Agency commissioned a short scoping study tocheck the RFRA findings and to suggest ways of improving surface water flood risk management.
This confirmed that London is at high risk. It suggested that surface water risk mapping should be
carried out across London. The production of a Surface Water Management Plan (SWMP) would be an
important next step. This scoping study coincided with the government receiving the Pitt Review into
the 2007 flooding events. This review identified 14 London boroughs amongst the top 15 local
authorities most at risk of flooding, including surface water flooding.
The GLA then bid to Defra to fund a new project, known as Drain London. This would model surface
water flood risk, and map and produce SWMPs for London. Defra provided £3.2 million on the basisthat this work would cost around £100,000 per borough. The GLA allocated a project manager for
Drain London and Defra delivered the funding in 2010. The project was split into three tiers.
Tier 1 (2010-12)
 Established the modelling and mapping standards.
 Split London into manageable surface water catchments, loosely based on borough boundaries.
 Gathered all known existing data and purchased any missing data (for example, Lidar andGeological datasets).
 Established the borough groupings (originally there were 8 groups, but groups 1 and 2 havemerged and groups 7 and 8 have re-modelled themselves slightly).

Credit: Greater London Authority
Figure 3: Current Drain London Groupings

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Table 2: Current Drain London Group Members
Group

Borough

1&2 NW London

Barnet, Brent, Ealing. Harrow , Hillingdon, Hounslow

3 Central London

Camden, City of London, City of Westminster, Hammersmith &Fulham, Islington, Kensington & Chelsea

4 Lee Valley

Enfield, Hackney, Haringey, Newham, Tower Hamlets, Waltham
Forest5 NE London

Barking & Dagenham, Havering, Redbridge

6 SE London

Bexley, Bromley, Greenwich, Lewisham

7 London South
CentralLambeth, Southwark

8 SW London

Croydon, Kingston , Merton, Sutton, Richmond, Wandsworth

The new Flood and Water Management Act 2010 and the creation of boroughs as LLFAs meant it
became important for each borough and the City of London to have its own surface water mappingand SWMP.
Tier 2 (2011-2012)
This tier undertook the surface water modelling itself and worked with borough officers to produce
SWMPs. The work was split into eight contracts, one for each of the Drain London groups. The work
also delivered Preliminary Flood Risk Appraisals (PFRAs) for each London borough which became arequirement of the EU Flood Directive 2009. The modelling identified areas of flood risk whichcontain a range of critical infrastructure and over one million properties (although most of those
properties are at a fairly low level of risk). It also identified Critical Drainage Areas, which were themain areas that contribute to the areas of highest surface water flood risk.
Tier 3 (2013- 2016)
This tier examined in detail some of the areas that the Tier 2 work highlighted as being at high risk of
surface water flooding. Nearly 30 high flood risk areas and a range of important infrastructure havebeen investigated to date. A range of sustainable drainage demonstration projects were part-funded
by Drain London to show how surface water can be managed more sustainably. Drain London funding
has also been used to monitor the water attenuation performance of experimental and conventional
green roofs at London Underground’s Ruislip depot.
Over five years, the Drain London project has led to a much better understanding of surface water
flood risk. It has also tested a number of approaches to mitigate that risk. These approaches showthat sustainable drainage techniques suitable for all parts of London can help address London’s

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
17

surface water flood risk. Sustainable drainage has been shown to deliver substantial benefits in a
London context. Now the aim is to encourage further uptake of sustainable drainage.

Partner support
The GLA alone cannot implement sustainable drainage on a widespread basis; it will require an
integrated approach from a wide range of partners. The Environment Agency, Thames Water andLondon Councils have all supported the GLA in drawing up this action plan and have committed tosupport a range of the actions. Further advice has been taken from London boroughs, TfL and several
non-governmental organisations and their support will be critical to the success of the actions.
Thames Water
Thames Water owns and manages London’s public sewerage systems. Rainwater is deliberately
designed to flow into the combined sewer system that covers most of central and inner London. Yet inmost of outer London rainwater is also accidentally and incorrectly connected to the foul seweragesystem. As a result, there are some areas where the sewer system has limited capacity. With the
projected large growth of London’s population through to at least the middle of the century, capacity
will come under further pressure. The removal of rainwater from the sewer system would free up
capacity for foul water flows and delay. It might even remove the need for what could be expensive
and disruptive upgrading of parts of the sewerage network.
As a result, Thames Water has allocated funding in the period 2015-2020 for projects that can remove
surface water from the combined or foul sewerage system across its operational area. The programme
is known as “Twenty4twenty” and aims to stop at least 20 hectares of drained land from discharging
rainwater into the sewers. The programme applies not just to London but across the Thames Water
operational area, so some projects may be developed in other towns and cities. However, due to theextent of combined sewers in the capital, at least 50 per cent of the available funding will be put touse in London. This action plan supports this initiative and is keen to see its success used todemonstrate the need for similar funding beyond 2020.
Environment Agency
The Environment Agency is an executive non-departmental public body, sponsored by Defra. It has
principal responsibilities in England to protect and improve the environment, and to promotesustainable development. It takes a strategic overview of all sources of flooding, including surface
water flooding. Over £12million of government investment (via Flood Defence Grant in Aid (FDGiA))
has been allocated to help London boroughs manage surface water flood risk in 35 projects over the
next six years.
London boroughs
London boroughs have been LLFAs since 2010 and are now settled into this role. Each LLFA has or is
producing a Local Flood Risk Management Strategy. These strategies, building on the Surface Water
Management Plans provided through Drain London, are expected to give a prominent role tosustainable drainage as a flood risk management tool. Furthermore since April 2015 boroughplanning departments should be seeking specific input from their LLFAs with respect to sustainable

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
18

drainage measures in ‘major’ planning applications. As awareness of sustainable drainage projects
grows, more schemes are being developed that incorporate sustainable drainage techniques. Manyboroughs are now carrying out localised projects. Most of these follow a similar approach to thisaction plan, with the project being woven into wider objectives of upgrading facilities or improving theappearance and function of buildings and public spaces. The GLA has launched a register to record
such examples across London. It is anticipated this will form a body of evidence about good practiceand opportunities.
Transport for London
TfL is the organisation that implements the Mayor’s transport strategy. It owns around 2,300 hectaresof land across London, including buildings, land attached to Tube stations, railways and highways.
This makes TfL one of London's largest landowners, and it has demonstrated some early sustainabledrainage projects across London. Examples include green roofs at stations and depots andraingardens in the public realm. Given the extent of land that TfL owns and manages it is clear thatfurther sustainable drainage activities are possible in relation to TfL assets. TfL is developing specificguidance to help increase delivery in relation to its assets.
Non-governmental organisations (NGOs)
A range of NGOs have already played an important role in both implementing sustainable drainage
projects and in raising awareness of the need for and benefits of sustainable drainage. Groundwork
London, Thames21, London Wildlife Trust, Wildlife & Wetlands Trust and many locally focused groups
all have important roles to play. Indeed some of these have already delivered sustainable drainage
systems across a range of sites. They have good community engagement strengths and could take anincreasing role in this field. In particular, they can help with implementing local projects where thebrokering of community relationships is essential.

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19

PART 2:
THE SUSTAINABLE
DRAINAGE ACTION
PLAN

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
20

The Sustainable Drainage Action Plan
The aim of this document is to set a long-term strategy and series of actions for increasing sustainabledrainage implementation. The emphasis of the strategy is to use whatever technique, or combinationof techniques, best suits particular buildings, developments, land or neighbourhoods. This action planshould not be used to suggest that particular techniques can or can’t be used. It is intended tocommit a wide variety of organisations to actions that will increase the use of sustainable drainage
over a long time period. To account for longer-term uncertainties, the plan makes firm shorter term
commitments and sets a direction for the longer term. The implementation of the action plan will bemonitored and reported on annually and progress will be reviewed. If necessary, actions will beamended and new actions introduced.
Monitoring
The action plan will be monitored, and progress reported on, an annual basis to allow trend analysis
and exploration of new opportunities. The number of known sustainable drainage retrofit projects will
be reported along with the area drained, volumes, and flow rates where available. Measuring the net
impact of the action plan on surface water flooding, however, is recognised as a difficult task. The
multiple variables of weather, new development patterns, economic trends, water consumption
behaviour and investment in sewerage and drainage infrastructure will all change the net flows in
sewers. Nevertheless, in the interests of having a simple and reliable metric to report, we will workwith Thames Water and others to develop simple, practical measures of the average and/or peak flows
at key points in the sewer network. This will be monitored to determine the overall success of the
programme. We will also develop an online Sustainable Drainage mapping tool, where we will crowd
source information on sustainable drainage projects that get delivered across London.
Glossary
Throughout this action plan, the suggested lead organisations and partners for action delivery arelisted in tables. The abbreviations for these organisations are listed in Table 3.
Table 3: Action plan abbreviations
Abbreviation

Lead organisation / partner

GLA

Greater London Authority

TW

Thames Water

TfL

Transport for London

LA

Local authority

LB/s

London borough/s

LLFA

Lead local flood authority

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
21

Abbreviation

Lead organisation / partner

LC

London Councils

CIRIA

Construction Industry Research and Information Association

EA

Environment Agency

LoDEG

London Drainage Engineers Group

LU

London Underground

DLR

Docklands Light Railway

Understanding the opportunities and benefits of sustainable drainage
There are a wide range of opportunities to manage rainwater more sustainably, and these should betaken wherever feasible. There are, however, often-quoted reasons why sustainable drainage
techniques either cannot be implemented or are limited. This includes the presence of clay soils,
ground contamination, sub-surface utilities and high groundwater. As a result, the Drain London
project has commissioned consultants to map the opportunities for sustainable drainage at a Londonwide scale. The project will highlight any particular locations where there are either very good, ormuch more limited, opportunities. The output from this project will be available later in 2016.
The importance of maintenance has been highlighted in Part 1. However, it is also worth investigating
whether there are any limits on the amount of certain types of sustainable drainage that should be
implemented. For example, a concentration of infiltration techniques could lead to long-term changes
in ground moisture levels, and lots of small-scale storage tanks requiring pumps to release rainwater
following a storm will have an increasing energy requirement. This will be considered in future reviewsof the action plan. However, the position at the start of this plan is that a significant increase in theuse of sustainable drainage is required. As such, in no way should implementation of existing
opportunities be put on hold or resisted awaiting longer-term research.
The actions outlined in this part of the action plan are aimed at understanding these wider andlonger-term implications, and establishing a monitoring framework.

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22

Table 4: London-Wide Actions
No.

ActionLead
Organisation

Partners

Timescale

1

Publish the results of the
London-wide Sustainable
Drainage Opportunity Model

GLA

TW

2016

EA
LC

2

Raise awareness of the needfor, benefits of and deliveryof sustainable drainage
within London

GLA

LBs

2016 onProject deliveryorganisations
Nongovernmentalorganisations

3

Deliver a programme ofsustainable drainage
demonstration projects

TW
LBs
GLA
Nongovernmentalorganisations

2015 – 2020

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
23

Delivering sustainable drainage through new developments via theplanning system
This is an area of the action plan where there is already significant activity. This is not surprising as
implementing sustainable drainage on new development is often cost-neutral and can even offer costsavings compared to conventional drainage techniques. Furthermore, as mentioned in part 1, nationaland London-wide planning policies have promoted and required sustainable drainage for many years(the London Plan has contained a Sustainable Drainage Hierarchy since 2004).
Evidence from the strategic planning applications referred to the Mayor shows that most applications
over recent years have included proposals to significantly reduce rainwater discharge. These
reductions are often to greenfield run-off rates but almost always achieve at least a 50 per cent cut inthe site’s previous peak run-off. The relatively small proportion of development that is proposed on
greenfield sites has generally been able to retain greenfield run-off rates. There’s been a lack ofmonitoring of smaller-scale development proposals. However, it’s expected that these would show
generally fewer proposals for sustainable drainage, particularly at the household level.
There is an indication that in some cases the design of attenuation features to reduce peak flows forlarger events may mean reductions for lower return period events are not significant. This ishighlighted by the two concept designs shown in Fig 4 below. In future, there’ll be a clear preference
for the Method 2 design, to ensure the attenuation benefits are realised for the majority of storms.

Figure 4 Susdrain Method 2 attenuation tank design
With the changes to the NPPF Guidance in April 2015, the delivery of sustainable drainage for major
new development is set to increase significantly. This means that planning applications for major new
development are now referred to LLFAs for their comments. Developers have to give increased
attention to the drainage arrangements for these new developments. There’s also an expectation thatsustainable drainage techniques will be used unless there are clear grounds for not doing so.

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
24

The London Plan
We will work with Drain London partners, and the development and drainage industries, to test
whether any changes are required or would be desirable in order to inform future reviews/replacementof the London Plan. Of particular relevance to this research is the recently revised SuDS Manual(CIRIA, 2015). This contains specific guidance relating to sustainable drainage measures for large
urban areas.
Much of the new development in London will be dispersed in small-scale developments, which will be
individually dealt with through the normal planning process. There will also be significant
concentrations of new development within the London Plan opportunity areas. These areas offer thescope for strategic level redesign of drainage regimes, to include sustainable drainage systems within awider Water Sensitive Urban Design approach. This action plan commits the GLA to examine each of
the Opportunity Area Development Frameworks, as they come forward and identify the mostappropriate drainage strategy for those areas. For some opportunity areas there are particularly
important opportunities to improve the sustainability of the regime. This includes the Vauxhall NineElms, Battersea and Old Oak Common opportunity areas. In such cases a more detailed Integrated
Water Management Plan is being delivered.
This section of the action plan aims to support London boroughs in their planning role. It serves tocoordinate experiences and monitoring of sustainable drainage delivery. That way best practice can beestablished and shared.

Table 5: Actions
No.

ActionLeadorganisation

Partners

Timescale

4

Maintain a strong London
Plan policy to support
sustainable drainage in new
development

GLA

5

Collate information onsustainable drainage
delivered through theplanning system

GLA

LBs

2017 on

6

Provide strategic guidanceon sustainable drainage
requirements for major
development locations

GLA

Partner LBs

Continuous

Continuous

TW
EA

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
25

No.

ActionLeadorganisation

Partners

Timescale

7

Provide detailed Integrated
Water Management Plans
for specific opportunity
areas

Development
partners

GLA

Continuous

EA
TW
LBs

Retrofitting sustainable drainage across London
Through the planning system, new development will deliver steady incremental increases in theamount of sustainable drainage techniques implemented across London. However, new development
typically affects only around 0.5 per cent of land each year. Therefore, any step change in the use ofsustainable drainage requires that existing land and buildings are retrofitted with more sustainabledrainage measures.
The remainder of this action plan examines a range of key land uses in the public and private sectors.
Different elements of the public sector own, manage, and control enormous amounts of land,buildings and infrastructure throughout London. The main sectors are examined below but include
education, housing, transport and health land use sectors. Large commercial sector ownership andmanagement is also hugely significant across London. This action plan seeks to influence thoseorganisations controlling larger plots of land, such as major commercial owners and large format shops
and businesses. Whilst sustainable drainage measures should be considered by all property
owners/managers, this action plan must target efforts. At present, working with larger organisations,
including those in the NGO sector is the main focus. This could be reviewed in future years.
It is fully recognised that all public sector organisations are under tight budgetary control, andcommercial organisations will need to prove a good business case for investment. Other than theThames Water ‘twenty 4 twenty’ programme there is limited funding specifically available formeasures like retrofitting of sustainable drainage as a one-off project. However, there are funds
available for more multi-functional projects that bring a wide range of public benefits. One example isgreen infrastructure sustainable drainage projects.
This action plan proposes to offer guidance and influence existing expenditure plans that public sector
and commercial organisations will already have. We expect that where there are opportunities toincorporate sustainable drainage as part of other required maintenance, repair or improvement offacilities, these options should be duly considered and implemented if practical. There may still besome initial extra cost involved in such measures. However, this will be marginal in most cases andthere may be opportunities for some sustainable drainage options to offer cost-savings, either atinstallation stage and/or in terms of maintenance and operational requirements. Sustainable drainage
opportunities can also often allow the integration of drainage with a range of other objectives. For

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
26

example, greenspace management, water demand, noise reduction, air quality improvement or
improved visual appearance.
To realise the opportunities that do or will exist, organisations must be aware of the importance ofsustainable drainage and its relevance to their operations. It is also necessary for the relevantorganisations to share, at least at a general level, their planned investment programmes. This will allow
enough lead-in time to identify and incorporate sustainable drainage techniques without significant
additional cost or time implications.
Each broad land use sector is now considered in turn. However, we recognise there’ll be many cases
where one land use sector needs to work with another in order to deliver the most effective
sustainable drainage solution. Examples include drainage from a highway diverted onto adjacentparkland, or drainage from a residential area diverted onto an adjoining school playing field.

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
27

Education sector

Credit: Wildfowl & Wetlands Trust
Figure 5: Coppetts Wood Primary School SUDS for schools
Table 6: Education sector options and opportunities
Likely sustainable drainage
options

Likely opportunities to implement
sustainable drainage

Green/brown/blue roofs

Major roof repairs, refurbishment or building
extensionRaingardens, flow through planters,
stormwater tree pits and downpipe
diversion

School extension or refurbishment, or some minor
works/landscaping improvement

Permeable surfacing

Resurfacing of car parks or hard surfaced
playgrounds

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
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Likely sustainable drainage
options

Likely opportunities to implement
sustainable drainage

Attenuation tanks/geocellularstorage

Resurfacing of car parks or hard surfaced
playgrounds – may be combined with permeablesurfacing

Rainwater harvesting

School extension or refurbishment, or some minor
works

Swales, bio-retention

Playing field/landscaping enhancements

Ponds, wetlands

Within landscaping around the school. Ponds canprovide valuable educational opportunities

The education sector has a wide range of buildings and premises. This includes primary and secondary
schools in both the public and private sector, and higher and further education establishments. A
high proportion of these buildings have flat roofs, which may prove suitable for green roof
technologies. Perhaps most significantly, many schools, colleges and universities have outdoor
spaces/playgrounds, playing fields, and/or car parking areas. These offer the potential for significant
surface water storage and infiltration via a range of possible techniques. In general, education
premises in outer London tend to have bigger external spaces. That means they have a wider range ofsustainable drainage retrofit opportunities than schools in more densely built-up parts of London. For
some schools/colleges there may be limited opportunities.
It is notable that with London’s continued growth, there will be significant growth in the education
sector. The London Infrastructure Plan is projecting the equivalent of up to 550 new schools andcolleges in London by 2050. In reality, much of this capacity may be accommodated by expanding
existing schools/school sites. This presents both a challenge and an opportunity for introducing moresustainable drainage. On the one hand, more densely developed school sites will mean that current
areas of open space (whether hard surface or soft landscaping) will be reduced and some scope forsustainable drainage may be lost. On the other hand, the capital investment in those premises
provides exactly the mechanism necessary to change the drainage regime of the school site. If
planned and designed as part of an overall upgrade or extension of the school, the implementation ofsustainable drainage measures can be achieved at minimal, or even zero, extra cost. The provision ofgreen roofs has the additional benefit that the long-term maintenance and repair costs of the roof
should be reduced.
Drain London has already worked with a number of secondary schools across London at risk of surface
water flooding. This work has demonstrated that there are significant opportunities for surface water

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
29

storage or diversion through the use of green roofs, raingardens, swales, detention basins andwetlands.
The ‘SuDS for Schools’ programme (run by the Wildfowl & Wetlands Trust in partnership with theEnvironment Agency and Thames Water) has also provided a range of sustainable drainage techniques
at ten schools within Barnet, Enfield and Haringey. This has demonstrated that schools have huge
potential for sustainable drainage measures. It has also shown that the implementation of thesemeasures can be linked to water cycle topics on the national curriculum and provide good examples
for students to study. One of the important conclusions from this work was that even where external
space was limited there was still some scope for measures like raingardens.
In recent years, the Water for Schools Programme (run by the London Sustainable Schools Forum:
http://www.londonsustainableschools.org/water-for-schools.html) has implemented two pilot
rainwater harvesting schemes. These have captured water for use in the school toilet systems, leading
to savings on water bills. This work also demonstrated that taking a comprehensive look at watersupply systems in schools is a good way to identify leaks and faulty or inefficient plumbing appliances.
The repair and upgrade of these plumbing systems led to significantly greater water savings andnotable cost savings on annual water bills. On their own, such rainwater harvesting systems would
take several years to pay for themselves. However taken as part of a wider refurbishment or extensionof a school, this should be an incremental cost with payback in a shorter time period.
Actions
This section of the action plan sets out a programme of activities to engage with, advise, and lobby
key decision makers in the education sector to promote and deliver more sustainable drainage
throughout the sector. The key theme is that retrofitting sustainable drainage should form part ofalready planned maintenance, repair and improvement programmes. Once opportunities have been
identified with large education sector providers, other smaller-scale opportunities can be examined.

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
30

Table 7: Education sector actions
No. Action

Leadorganisation

Partners

Timescale

8

GLA

TW

2017

Produce guidance and goodpractice examples of sustainabledrainage applicable to theeducation sector

EA
Local authority
education
depts.
SuDS for
SchoolsSusdrain

9

Identify opportunities andfunding for sustainable drainage
retrofit at the same time asplanned maintenance, repair andimprovement public sector
schools

GLA

Local authority
2017
education
depts. and otherpublicly fundedschools

10

Identify opportunities andfunding for sustainable drainage
retrofit at the same time asplanned maintenance, repair andimprovement works in higher
education establishments

GLA

Highereducation
providers

2017

11

Identify opportunities andfunding for sustainable drainage
retrofit at the same time asplanned maintenance, repair andimprovement works in private
sector schools

GLA

Private sector
education
providers2019

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31

Housing sector

Credit: Groundwork
Figure 6: Groundwork estate retrofit project in Hammersmith & Fulham
Table 8: Housing sector options and opportunities
Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Green/brown/blue roofs

Major roof repairs for residential buildings.
Small scale repairs to garages, sheds andother structures

Raingardens, flow through planters,
stormwater tree pits/diversion of
downpipes

Landscaping enhancements

Rainwater harvesting

Major refurbishment programmes for larger
buildings/estates

Swales, bio-retention, ponds, basins andsoakaways

Refurbishment and landscaping
enhancements dependent upon space andground conditions

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
32

Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Oversized pipes, attenuation tanks,
geocellular storage

Refurbishment and landscaping where spaceis limited or ground conditions for infiltration
unfavourable

Permeable surfacing

Resurfacing of footpaths, hard surfaces or car
parks

This section focuses on the larger providers of housing. This includes housing associations, local
authority social housing and large-scale private rented sector providers.
With over four million homes, the housing sector represents a large proportion of London’s total
surface area. Recently, the number of new homes has been growing at around 30,000 per year.
However, it is generally recognised this must increase to around 50,000 per year to keep up with
continued population growth and with the backlog of demand that already exists.
A key consideration for the housing sector is that properties tend to have a long life span. There arestill a large number of Victorian brick-built homes in use today. Many are well over 100 years old andmake up some of the most sought-after properties in London. Many of the early public sector
housing estates built after the First World War are almost 100 years old. The large tracts of outer
London built during the inter-war years are now 80 years old and look set to remain a key part of
London housing for the foreseeable future. This longevity means that it is important to getsustainable drainage measures built into the design of new housing. It also means that if sustainabledrainage can be retrofitted to existing stock, it should provide benefits for the long-term. Conversely,
the fact that buildings are generally long lasting is an indication that they can be maintained without
the need for frequent major repairs. Therefore the opportunities to retrofit sustainable drainage will
generally occur infrequently for any given building.
An initial distinction should be made between properties with pitched roofs and those with flat roofs.
Flat-roofed properties may be suitable for a green/brown/blue roof. Such roofs can have valuable
benefits in improving the insulation of the buildings, keeping them both warmer in winter and cooler
in summer. A well designed green/brown/blue roof can also reduce long-term maintenance andrepair costs of flat roofs.
Addressing the retrofit of London’s housing stock is likely to be challenging given the diversity ofownership and management. A large proportion of the housing stock is owned either by
individuals/families, or by owners of small and dispersed property portfolios. There is a range ofrelatively easy measures which can be applied to such properties, especially those with garden areas.
These are covered in the ‘What can you do? Delivering sustainable drainage through domestic andlocal neighbourhood ’ section.

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
33

Many municipal or housing association residential estates have relatively large areas of communal
open space. These can often provide good opportunities for retrofitting rain gardens and diverting
downpipes into those raingardens. For example, the Neighbourhoods Green initiative aims to raise
the profile of open space for social housing residents. It works with social landlords to raise the qualityof their design, management and safe use. Sustainable drainage is considered as part of this work
(National Housing Federation 2011).
However, care is required to avoid areas too close to the buildings themselves, to avoid the risk ofdamp or changes to the ground conditions surrounding foundations. Also, areas that are likely tocontain numerous services should generally be avoided due to the large increase in costs that moving
or protecting such services is likely to incur. The architectural design of some estates included theprovision of concealed downpipes. In other words, it’s not clear exactly where the downpipes are as
they are hidden beneath the facade of the building. In such cases, alterations to divert such
downpipes will be slightly more complex and costly. However, in general this shouldn’t be an
insurmountable difficulty.
Nevertheless, there are still likely to be major opportunities to create raingardens in communal
housing areas. Recent demonstration projects in Enfield, Hammersmith and Fulham, Haringey andNewham have shown a variety of sustainable drainage techniques being implemented. Such schemes
divert rainfall from downpipes and also provide more diverse and attractive landscaping for the
residents or potentially small food growing areas. In general such projects are relatively cheap.
For residential locations next to the Thames, tidal rivers or docks, a relatively easy approach is todivert rainwater into the river or dock. This is not normally considered to be a form of sustainabledrainage. However for the heavily urbanised areas of London it is a more sustainable approach to
managing rainwater that would otherwise be carried into the combined sewer system. This method of
rainwater management is usually relatively easy to introduce together with other renovations of abuilding. But it will need to accommodate the regular tidal fluctuations. It may also be necessary tostore or discharge to the surface water sewer during high tide periods.
The GLA runs the RE:NEW programme which is mainly aimed at improving energy efficiency in
London’s housing stock. It could also consider opportunities to improve water and drainage efficiency.
Actions
This section sets out a programme of activities to engage with, advise and lobby the key decision
makers in the housing sector in order to promote and deliver more sustainable drainage in the sector.
The key theme is that retrofitting sustainable drainage should form part of already planned
maintenance, repair and improvement programmes. Once opportunities have been identified with thelarger social landlords, other smaller-scale opportunities will then be examined.

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Table 9: Housing sector actions
No. Action

Leadorganisation

Partners

Timescale

12

GLA

TW

2017

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the housing
sectorEA
LA housing
depts.
Susdrain

13

Identify opportunities andGLAfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works in thesocially rented housing sector

Housing
associations
LA Housing
depts.
GLA Re:New

2017

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Transport sector

BeforeAfter

Credit: Greysmiths Associates
Figure 7: Derbyshire Street pocket park, Tower Hamlets
Table 10: Transport sector options and opportunities
Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Rainwater diversion from gullies to street
trees or swales, or potentially to nonhighway land

Maintenance of road gullies/drainage, ormore substantial capital works enabling alarger scale diversion

Street Trees, stormwater tree pits

New or replacement street trees

Permeable surfacing

Resurfacing of car parks, footways, cycle
paths

SwalesLandscaping enhancements

Rainwater harvesting

Refurbishment of bus/rail depots, especiallywhere there is a requirements for water for
cleansing

Raingardens

Landscaping enhancements around buildings
and transport assets

Green/brown/blue roofs

Refurbishment of buildings and depots

The transport sector has many and varied opportunities to introduce sustainable drainage, andimportantly is a sector with regular, if limited, funding for capital and maintenance works. This action

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
36

plan recognises that most of the transport sector’s linear assets (roads and railways) offer limited
scope for sustainable drainage. Rail and Tube lines can often run in cuttings, making it difficult todivert rainwater away from them: indeed such cuttings are often at some level of flood risk due totheir low topography. Similarly, major road underpasses can often be prone to flooding. Perhaps the
only realistic options for heavily urbanised roads are the creation of permeable parking areas and thediversion of rainwater into stormwater tree pits. Some good examples of such ‘Stockholm’ tree pits
have recently been built in London. It is generally accepted that permeable surfacing is not suitable
for any but the lightest trafficked road surfaces. Transport for London (TfL) is running a permeableroad surfacing trial during on a section of the A127 in east London. Initial results confirm previous
concerns that permeable surfaces are not able to manage large traffic flows without rapid
deterioration. Instead the focus must be on highway land away from the carriageway and potentiallydiverting surface water into adjacent low impact spaces.
Whilst acknowledging the above constraints, many linear assets have large tracts of land alongsidethem, such as road verges, footways and trackside vegetation. In the case of rail and road routes
through outer London, there are often areas of parkland, greenbelt, or indeed farmland alongside
several miles of road or railway. These offer the potential for rainwater to be diverted into such areas
for sustainable drainage. This could reduce flood risk to the transport asset and potentially to thewider neighbourhood. There are also lots of opportunities to design sustainable drainage into trafficcalming measures, examples of which are increasing in London.
Diffuse pollution from transport infrastructure is a huge factor affecting the quality of London’s rivers.
Major roads are likely to generate significant amounts of pollutants that can be washed into receiving
drains and waterbodies during heavy rainfall. The ability to treat surface water from road or rail
corridors using infiltration or bio-retention sustainable drainage techniques is therefore a good
opportunity to reduce the pollution loading for watercourses and groundwater.
In common with many other buildings, transport sector buildings can lend themselves togreen/brown/blue roofs and also realise the benefits of insulation and reduced long-term
maintenance. London Underground has constructed a green roof at its Ruislip Depot. Where suchbuildings are being upgraded or extended, there are likely to be opportunities to incorporate somesustainable drainage measures at little extra cost.
There are often reports of surface water flooding at main line rail termini, given the size of the roof
area of these stations. However, it should also be noted that these and some other transportbuildings may be of historical and architectural significance. This means they may not be suited togreen roofs and or other sustainable drainage techniques.
More modern or utilitarian buildings may be better suited to green/brown/blue roofs. Buildings suchas maintenance depots or bus garages can be well suited for rainwater harvesting schemes for vehicle
cleansing, thus reducing water bills. The West Ham bus depot is a good example, as it incorporates agreen roof with a rainwater harvesting system that is used to supply water to wash the bus fleet.

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Many outer London rail and tube stations have station car parks. These areas may be suited for
permeable surfacing or sub-surface storage if the car parks are resurfaced or redeveloped.
Actions
This plan sets out a programme of activities to engage with, advise and lobby the key decision makers
in the transport sector, in particular with the Mayor’s own agency TfL (for example, through the
Mayor’s Transport Strategy), to promote and deliver more sustainable drainage throughout the sector.
The key theme is that retrofitting sustainable drainage should form part of already planned
maintenance, repair and improvement programmes.
Once opportunities have been identified with the main sector providers, other smaller-scale
opportunities will then be examined.
Table 11: Transport sector actions
No. Action
Leadorganisation
14 Produce guidance that
TfL
includes good practice
examples of sustainabledrainage in the streetscapepublic realm
15

Prepare a standard for
retrofitting green
infrastructure

LU

16

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
TfL owned/managed
transport assets

GLA

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
other highway authorities’transport assets

GLA

17

Partners

Timescale
2016

2017

TfL

On-going

LU
DLR
LondonOverground
Highwaysauthorities
Highways
England2017

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Health sector© Medical Architecture 2015
Figure 8: Green roof at Springfield Hospital, Wandsworth
Table 12: Health sector options and opportunities
Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Green/brown/blue roofs

Major roof repairs, refurbishment or building
extensionRaingardens and downpipe diversion

Hospital extension or refurbishment, or someminor works

Stormwater tree pits

New or replacement street trees, car park remodelling/landscaping

Permeable surfacing

Resurfacing of car parks

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Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Swales, bio-retention

Extension or major refurbishment where
hospital has extensive undeveloped grounds

The NHS, and indeed private sector health providers, has a wide range of premises across London.
Some of these are relatively small, for example some doctors surgeries, and offer only limited scopefor sustainable drainage. However, other premises such as major hospitals are large buildings offering
a range of opportunities for sustainable drainage, both at roof level and within the grounds. A highproportion of health sector buildings have flat roofs that may prove suitable for green/brown/blueroof technologies. These also offer the potential added benefits of improving insulation and reducing
long-term maintenance costs. In some parts of London, hospitals are set in extensive grounds andhave large car park areas. Such sites offer considerable opportunities for the storage, infiltration or
diversion of rainwater away from sewers. Some even have the capacity to absorb rainwater fromsurrounding streets and neighbourhoods. There is also evidence that pleasant natural surroundings
correlate with improved health and recovery (MEBIE2 study: Natural England 2014).
Drain London has worked with 11 major hospitals to assess surface water flood risks. This has
illustrated some ways in which flood risk can be mitigated, at the same time as improving theresilience of the hospital’s operation. Examples include locating critical equipment and utilities above
potential flood levels or by diverting potential flood water away from the most sensitive areas. This
work also highlighted that there are opportunities for green roofs, permeable car parking areas andrain-attenuating landscaping to be incorporated into periodic major maintenance.
Actions
This section of the plan sets out a programme of activities to engage with, advise and lobby the key
decision makers in the health sector in order to promote and deliver more sustainable drainage
throughout the sector. The key theme is that retrofitting sustainable drainage should form part ofalready planned maintenance, repair and improvement programmes.
Once opportunities have been identified with the large health sector providers, other smaller-scale
opportunities will then be examined.

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Table 13: Health sector actions
No. Action

Leadorganisation

Partners

Timescale

18

GLA

NHS

2017

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the healthsectorEA
TW
Susdrain

19

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
the NHS estate

GLA

NHS Trusts

2018

20

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
the private sector healthproviders’ estate

GLA

Health providers 2019

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Retail sector

Credit: Marks and Spencer
Figure 9: Green wall and green roof on an M&S store, Sheffield
Table 14: Retail sector options and opportunities
Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Green/brown/blue roofs

Major roof repairs, store extension or
refurbishment

Raingardens, flow through planters,
downpipe diversion

Roof repairs, minor alterations, landscaping

Permeable paving

Resurfacing of car parks and pedestrian areas

Stormwater tree pits

Street tree planting, landscaping of car parks

Attenuation tanks, geocellular storage

Remodelling of car parks or large pedestrianareas, maybe linked to permeable paving

Design for exceedance

Temporary storage of surface water in remodelled car parks, service yards, landscaped
areas

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Supermarkets and large-scale retail units have large, generally flat or shallow sloping roofs. There may
be good opportunities to introduce green/brown/blue roofs onto some stores, although it is generally
anticipated that these will be limited, since the relatively lightweight retail unit roof construction often
lacks the structural support required for such a roof. However, a new lightweight green roof
technology will be tested by London Underground that is 40 per cent lighter than conventional green
roofs. These may be appropriate for the retail sector in future.
Huge opportunities do however exist to divert downpipes into raingardens or rainwater storage areas
within the grounds or car parks of the stores. These measures could be incorporated into theresurfacing of a car park or into improved landscaping for stores. Resurfacing of car park areas alsooffers a good opportunity to store or infiltrate rainwater. Permeable supermarket car parks have been
introduced in a number of locations nationally with very positive results. Care will be needed wherestores have been built on previously contaminated ground. It is also unlikely to be practical tointroduce permeable surfacing to delivery yard areas due to the likely damage caused by the
manoeuvring of delivery vehicles.
Car parks, yard areas and landscaping can be designed so that they can temporarily hold rainwater inlonger term return periods (say once every ten years). This can offer a simple and cost effective way of
reducing flood risk at locations with large roof areas/car parking areas.
Shops in town centres are generally of smaller building footprints and not surrounded by large carpark areas. There will therefore be limited opportunities for major sustainable drainage retrofitting
here. Instead, sustainable drainage will generally take place in more comprehensive redevelopment.
That means opportunities will be picked up via the planning system or upgrades and improvements tothe public realm, where stormwater tree pits and raingarden planters may be ideal solutions.
Actions
This section sets out a programme of activities to engage with, advise and lobby the key decision
makers in the retail sector in order to promote and deliver more sustainable drainage throughout thesector. The key theme is that retrofitting sustainable drainage should form part of already planned
maintenance, repair and improvement programmes.

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Table 15: Retail sector actions
No. Action

Leadorganisation

Partners

Timescale

21

GLA

TW

2017

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the retail sector

EA
BIDs
Susdrain

22

23

24

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
the major supermarkets
estates

GLA

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
DIY and other large format
retailers’ estates

GLA

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
retail estate owners’
proposals

GLA

Supermarkets

2017

LBs

DIY stores andother large
format stores

2017

LBs

Retail estate
owners
BIDs

2018

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Recreational land / other open space and sports stadia

Credit: Greater London Authority / Environment Agency
Figure 10: Swales installed at Mayesbrook Park, Barking and Dagenham
Table 16: Recreational land options and opportunities
Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Swales

Maintenance of grounds

Bio-remediation, detention ponds,
wetlands, de-culverting

Upgrades to facilities, landscaping projects

Rainwater harvesting

Refurbishment of buildings and depots

Green/brown/blue roofs

Refurbishment of buildings and depots

Permeable surfacing for car parks

Resurfacing of car parks

Stormwater tree pits

Tree planting

Storage tanks/geocellular storage

For large roof or paved areas

The public sector owns and manages large areas of open space and recreational land. This includes
parks, gardens, sports pitches, and (mainly in outer London) a number of golf courses. These help

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form part of London’s ‘green infrastructure’. Much of this land will drain naturally, either via
infiltration or to tributary streams. These land uses offer good opportunities to absorb or hold more
rainwater from adjoining areas and potentially to improve the quality of the water entering thesewatercourses. During upgrading or remodelling works, these spaces could be designed to hold more
surface water using relatively natural means. Given the record rainfall in several parts of the country
over recent years, it’s time to be more proactive in our approach to storing water in such open spaces.
We know that where heavy clay soils are present, there will be limitations to infiltration techniques.
Also, that where open spaces are particularly heavily used, the ground can become compacted andrainwater runs off at high rates, not unlike hard surfacing. Nevertheless open spaces provide
opportunities for a wide range of sustainable drainage techniques. It is also increasingly common for
sports pitches to be synthetic, for example football pitches and tennis courts. This offers a chance toconsider diverting rainwater into surrounding landscaped areas or into geocellular units below theplaying surface.
Besides the London boroughs, there are a number of other agencies that own and/or manage open
space in London. The City Corporation owns iconic spaces, such as Hampstead Heath, Epping Forest
and a range of commons. The Royal Parks Agency owns and manages the eight Royal Parks in
London. Finally, the Lee Valley Regional Park Authority owns and manages a significant amount ofland in the Lee Valley. These agencies can all play an important role to help improve the managementof rainwater in London.
A range of open spaces is also owned and managed privately either by not-for-profit sports clubs andassociations, or on a commercial basis. Again, golf courses in outer London are relatively common but
there are also many other sports facilities that offer sustainable drainage opportunities. Even whereplaying surfaces are impermeable, there are often large surrounding areas capable of storing and/or
infiltrating surface water.
Major sports grounds have a combination of hard surfaced stadia, circulation space and car parks, aswell as the playing surfaces themselves. Here, it’s worth considering rainwater harvesting, since thepitches will require irrigation and there is a requirement to flush large numbers of toilets. This could
offer reduced water bills. There are examples already, like Arsenal’s Emirates Stadium and Tottenham
Hotspur’s training facility in Enfield.
Open spaces require management and maintenance and are occasionally remodelled. This means that
there are a range of opportunities to introduce more sustainable drainage. There are a number ofgrant programmes aimed at funding improvements and changes to such open spaces. When suchprogrammes are being considered, this is a good opportunity to design in sustainable drainage
measures and locations to retain and infiltrate rainwater.
The GLA manages the All London Green Grid, which is a policy framework to promote a network of‘green infrastructure’ across London. The Green Infrastructure Task Force looked at how a morestrategic and long-term approach to green infrastructure investment and delivery can be encouraged.
There are also a number of non-governmental organisations that promote a more sustainable water

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environment, including sustainable drainage, such as Thames21, Groundwork and London Wildlife
Trust. These organisations provide important networks through which to promote sustainabledrainage opportunities.
Actions
This section sets out a programme of activities to engage with, advise and lobby the key decision
makers in the open space/recreational sector in order to promote and deliver more sustainabledrainage throughout the sector. The key theme is that retrofitting sustainable drainage should form
part of already planned maintenance, repair and improvement programmes.
Table 17: Recreational land actions
No. Action

Leadorganisation

Partners

Timescale25

GLA

Londonboroughs

2017

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the open
space/recreational sector

NGOs
LandscapeInstitute

26

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works in parksand open spaces

GLA

Royal Parks
Corporation of
LondonLee Valley
Regional Park
Authority
Londonboroughs
London Playing
Fields
Association
Major sports/stadia owners

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Other public sector buildings

Credit: Greater London Authority
Figure 11: TfL offices at 55 Broadway, Westminster
Table 18: Other public sector land options and opportunities
Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Green/brown/blue roofs

Building extension or refurbishment, majorroof repairs

Raingardens and downpipe diversion

Major roof repairs

Permeable surfacing

Resurfacing of car parks

Rainwater harvesting

Refurbishment, may also be worthwhile as astandalone investment

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Whilst certain public sector functions have been highlighted earlier, both national and local
government, as well as a range of other public agencies, own and/or manage a significant number ofother buildings and areas of land. These are typically offices, but may also include supplies depots,
waste management sites, vehicle depots, museums, galleries and community centres/halls.
The guidance and best practice proposed for other sectors is likely to cover the range of other public
sector buildings and land. For example, there are likely to be opportunities for green/brown/blueroofs to be incorporated into some buildings, particularly those with flat roofs. This would offer
additional insulation and reduced maintenance costs. For offices and other buildings with highoccupancy rates or high non-potable water demand, putting in a rainwater harvesting system mayprove cost-effective, particularly for toilet flushing. For depots, some waste management sites andvehicle holding sites, the use of rainwater harvesting for site, plant or vehicle washing purposes may
prove cost-effective.
Actions
This section sets out a programme of activities to engage with, advise and lobby the key decision
makers in the wider public/governmental sector in order to promote and deliver more sustainabledrainage throughout the sector. The key theme is that retrofitting sustainable drainage should form
part of already planned maintenance, repair and improvement programmes.
Given that this action plan already contains a range of engagement activities with other public sector
agencies, the actions here are delayed for some years. However, those other discussions may in due
course, reveal a range of public sector opportunities.
Table 19: Other public sector land actions
No. Action

Leadorganisation

Partners

Timescale27

Examine local authority
development proposals,
capital and revenue
programmes for sustainabledrainage opportunities

GLA

LBs

2018

28

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
the central government
departmental and quango
estates

GLA

Centralgovernment
depts. andquangos

2018

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Commercial office sector

Credit: Greater London Authority
Figure 12: Rain garden at John Lewis Headquarters, Victoria
Table 20: Commercial office sector options and opportunities
Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Green/brown/blue roofs

Major roof repairs, office extension or
refurbishment

Raingardens and downpipe diversion

Roof repairs, major and minor refurbishment
and landscaping works

Direct discharge to tidal rivers or docks

Roof repairs, minor refurbishment work,
resurfacing work

Permeable car parks, tree pits

Resurfacing and landscaping of car parks

Rainwater harvesting

Refurbishment, may also be worthwhile as astandalone investment

Commercial offices face many of the same opportunities and constraints as public sector offices.
However, offices in town centre and central London locations will generally offer limited sustainabledrainage opportunities due to the density of development. In contrast, offices in out-of-centre
business parks may offer many opportunities in their surrounding car parks and landscaped grounds.

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Given the density of employees, most offices should consider the potential long-term benefits ofreducing water supply costs by using rainwater harvesting systems to supply toilets. These are likely toprove financially viable in many cases.
For office locations adjacent to the Thames, tidal rivers or docks, a relatively easy approach is to divert
rainwater into the river or dock. Not normally considered a form of sustainable drainage, for theheavily urbanised areas of London it’s a more sustainable way to manage rainwater that would
otherwise be carried into the combined sewer system. This method of rainwater management isusually relatively easy to introduce alongside other building renovations. However, it will generally
only be applicable for tidal waterbodies. So there may be a need for storage in high tide conditions.
Offices in less densely built-up areas (typically along arterial roads or within business parks) are likely
to offer major opportunities. These include introducing green/brown/blue roofs, diverting rainwater
downpipes into raingardens or permeable areas, and adding permeable surfacing to car parks.
Together, such measures can provide a significant reduction in rainwater run-off. If combined withother works (such as a wider refurbishment programme, re-roofing, or resurfacing of car park areas),these can be put in at minimal additional initial cost. It is recognised that in many outer areas of
London, the office sector is shrinking. This may mean that there are fewer opportunities for
retrofitting. It may also mean that any conversion to residential premises provides a good opportunity
to introduce more sustainable drainage. Any major redevelopment will be expected to provide
sustainable drainage through the planning system.
For offices in more built-up locations it’s likely the only options may be adding green/brown/blueroofs when major roof repairs are required, or introducing a rainwater harvesting system.
Actions
This section recognises that this is a more diverse sector than some others, and so the timescale forengagement is slightly later than other sectors. The likely guidance and good practice examples will
be similar to those for some other sectors so no specific guidance is proposed.
Table 21: Commercial office sector actions
No. Action

Leadorganisation

Partners

Timescale

29

GLA

Major officeowners/occupiers

2019

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned maintenance,
repair and improvement works
with major officeowners/occupiers

BIDs

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Industrial sector and major utilities

Table 22: Industrial sector and major utilities options and opportunities
Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Green/brown/blue roofs

Major roof repairs, premises extension or
refurbishment

Raingardens and downpipe diversion(potentially to tidal rivers or docks)

Roof repairs, minor works

Permeable car parks, stormwater tree pits

Resurfacing or landscaping of car parks andyard areas

Detention ponds, swales, bio-retention

As part of remodelling work, where land
permits

Rainwater harvesting

Refurbishment, may also be worthwhile as astandalone investment

It is widely recognised that London’s industrial sector has shrunk over past decades. However, inseveral parts of London there is an important remaining industrial sector, some of which is now
expanding and intensifying its activities. Businesses such as distribution and storage facilities should
be considered here too. This section also addresses the premises of the major water, energy andtelecoms utilities. These utilities often have large-scale sites, many of which are likely to remain as
long-term land uses in London. There may be further rationalisation of the telecoms and mail sector
land over the future years given the changes in those industries.
Industrial premises often have large buildings. In common with other large buildings, these may offer
the opportunity for a green/brown/blue roof. However, the roof construction is often relatively
lightweight and may not be able to support a vegetated roof (depending on the availability oflightweight green roof technologies in the future). The diversion of downpipes to raingardens, swales,and detention ponds is likely to be generally feasible. However attention should be paid to potential
for rainwater to come into contact with contaminants, and to consider the possibility of previous
ground contamination.
Resurfacing or landscaping of car park and yard areas will present the opportunity to introduce
sustainable drainage measures, like permeable parking surfaces, at relatively low extral initial cost.
However, if HGVs are likely to use parking or servicing areas, it may not be appropriate to use
permeable road surfacing due to the risk of damage to its surface. Given industrial uses, issues of

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potential ground contamination may limit some of the sustainable drainage techniques available,
notably infiltration techniques.
There are a large number of industrial and utility premises in the London parts of the Thames
Gateway. These may also offer the opportunity for rainwater to be discharged to the Thames or theRoyal Docks.
For industrial premises that use large volumes of water as part of their processes, like for cleansing or
cooling, then rainwater harvesting schemes may prove cost-effective in reducing long-term water bills.
Actions
This section sets out a programme of activities to engage with, advise and lobby the key decision
makers in the industrial/utility sector in order to promote and deliver more sustainable drainage
throughout the sector. The key theme is that retrofitting sustainable drainage should form part ofalready planned maintenance, repair and improvement programmes. Once opportunities have been
identified with the large industrial sector providers, other smaller-scale opportunities will be examined.
Table 23: Industrial sector and major utilities actions
No. Action

Leadorganisation

Partners

Timescale30

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the industrial
sector

GLA

31

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
Thames Water’s estate

TW

GLA

2017

32

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works withinenergy companies’ estates

GLA

Utilities
companies

2018

2018

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No. Action

Leadorganisation

Partners

Timescale

33

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works withintelecoms companies’ estates

GLA

Telecoms
companies

2019

34

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
the Environment Agency’s
estate

EA

GLA

2017

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Agricultural sector

Table 24: Agricultural sector options and opportunities
Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

SwalesLand management grants

Storage ponds

Changes to agricultural practices

Rainwater harvesting

Wherever, cost-effective

Design for exceedance (temporary
flooding of low impact land during heavy
rainfall events)

Wherever, cost-effective

Although London is a relatively densely built-up city, it does have some quite extensive areas ofagricultural land between the urban area and the London boundary. Most of this is protected fromdevelopment by the Metropolitan Green Belt.
Whilst much of this land will drain and infiltrate naturally, modern farming practices can lead toincreased rates of rainfall run-off. Most of London’s tributary rivers originate or flow through these
agricultural areas. As a result, agricultural drainage practices can lead to rainwater rapidly running off
the land into local watercourses and lakes/ponds. This can carry a significant pollutant load fromlivestock and from fertilisers and pesticides applied to crops. As a result, sustainable drainage
measures are valuable tools on agricultural land. They can be used to add biodiversity value tofarmland, improve water quality in watercourses, and hold back potential flood waters before theyreach urbanised parts of London.
There are likely to be relatively easy opportunities to implement sustainable drainage in agriculturalareas. However, there are also likely to be fewer potential funding mechanisms to enable such works
to take place. Most farms already have rainwater harvesting systems in place to provide water for
irrigation or livestock. Also, green/brown/blue roofs are not likely to be viable on many buildings.
Instead, the general focus should be on land management practices.
There has been a recent focus on a catchment management based approach to flood risk
management. This approach, using natural measures is becoming an increasingly important aspect ofcatchment-wide planning and modern agricultural practice. Undoubtedly there will be some scope forthis within the green belt areas of London. It must also be remembered that farms are commercial
businesses providing the most essential of all products, food. Thus there’ll be a continuing need toensure that agricultural land can continue to be productive and not damaged by flooding.

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Actions
This section sets out a programme of activities to engage with, advise and lobby the key decision
makers in the agricultural sector in order to promote and deliver more sustainable drainage
throughout the sector. The key theme is that retrofitting sustainable drainage should form part ofalready planned maintenance, repair and improvement programmes. Given the limitation of the rangeof measures and uncertainty over funding, these actions are focused towards the end of theengagement programme.
Table 25: Agricultural sector actions
No. Action

Leadorganisation

Partners

Timescale35

GLA

National
Farmers’ Union

2020

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
agricultural estates

Farming
representatives

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What can you do? Delivering sustainable drainage through domestic and local
neighbourhood measures

Table 26: Options and opportunities for individuals
Likely sustainable drainage options

Likely opportunities to implement
sustainable drainage

Water butts

Garden improvements

Raingardens and downpipe diversion

Roof repairs, extensions, community
landscaping projects, garden improvements

Green/brown/blue roofs

Major roof repairs, extensions

Permeable driveways

Resurfacing of driveways, patios and otherhardstanding areas

The previous sections have focused on the land uses, owners and occupiers of larger buildings, sites
and areas of land in London. Yet the largest area of land coverage is that of single/small blocks ofindividually occupied residential homes. Each specific home or apartment block can only make a small
contribution to improving the sustainability of London’s drainage system. However, collectively they
could make a major contribution.
Perhaps just as importantly, action at the individual/community level can help to raise awareness ofand demystify London’s drainage issues and the wider benefits of a sustainable drainage approach.
Sustainable drainage measures can be readily introduced in individual homes at minimal cost. Perhaps
the most common example is the installation of water butts. These can easily be installed as a DIY
project in most houses, and can reduce water consumption when irrigating gardens or washingvehicles. Typical water butts cost under £50 and contain approximately 200 litres. Smaller versions arealso available and multiple water butts can be linked to provide additional storage. There is a growing
market for more bespoke water butts that also act as decorative features, garden benches or planters.
For larger gardens, there are also options to install more industrial-scale products. For a water butt tobe effective in rainwater management it must be able to absorb the flow from a storm. In other words,
it must not be full. One way of achieving this is to have an overflow from the water butt discharging
to a flower bed or pond within the garden.
With careful design considerations, some roof downpipes can be diverted into ponds or flower beds
around individual homes. Care is needed not to introduce permanently damp conditions adjacent tobuildings or to change the load bearing characteristics of the soil structure around buildings. This isparticularly important for older houses, which tend to have relatively shallow foundations compared tohomes built under modern Building Regulations.

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Over the past few decades, there has been a trend of paving over front, and to an extent rear, gardens(London Wildlife Trust, GiGL & GLA, 2010). This has led to a huge increase in the area of landdraining into public sewers. Planning changes in 2008 require planning permission for newimpermeable areas of front gardens, this should see this issue controlled and there is a growing
availability of highly permeable hard surfacing. However it’s not clear how effective this planningchange is. This is especially since more areas of back gardens are being made impermeable throughextensions and patios, and these often do not require planning permission.
In any case many paved garden areas already exist and these are relatively easy to convert to moresustainably drainage areas. As the paving systems/driveways become older, owners will consider
renewing them. This is an opportunity to encourage, and possibly incentivise, the re-introduction of
more sustainable drainage. Some London boroughs have led ‘De-pave’ projects to remove small areasof paving, creating landscaping opportunities and allowing more natural drainage.
Some houses and many apartment blocks have flat roofs. When the time comes for a major
refurbishment or repair of those flat roofs, there will be opportunities to introduce agreen/brown/blue roof. This offers associated benefits of improved insulation and long-term
reductions in maintenance costs. This opportunity is covered under the earlier section for the housing
sector, which is aimed at large-scale housing providers.
The Drain London partnership is leading a series of urban greening demonstration projects. These
highlight how streets and neighbourhoods can be modified to provide for more sustainable drainage,
whilst improving the look and amenity of residential areas. The lessons learned from these early pilots
will be communicated into further programmes over the lifetime of this action plan.
There may also be opportunities to divert rainfall into small areas of landscaping or under-used land in
and around local streets and estates, areas such as road and footpath verges. This plan will consider
the need for a Fund for local people to suggest such areas and bid for funds to enable such areas tobecome more sustainably drained. It’s important to remember that not all such areas may be suitable
for retrofitting sustainable drainage measures, and that the landowner’s consent will be required.

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
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Table 27: Actions for individuals
No. Action

Leadorganisation

Partners

Timescale

36

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the individual
homes, small apartment
blocks or local
neighbourhoods

GLA

NGOs

2017

Consider a grant/incentive
scheme to encourage
individuals or local
communities to implement
their own sustainabledrainage scheme

GLA

37

Londonboroughs

2017

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Funding opportunities and regulatory incentives
The emphasis in this action plan is to find opportunities and techniques for implementing sustainabledrainage techniques that have limited financial impact. As a result, the focus is on identifying
situations where other relevant works are likely to be done, This will mean any extra additional
drainage works will only be a marginal part of a wider project. In some cases, there may be
opportunities to save money either in direct drainage infrastructure provision or over a longer
timeframe. This includes through cuts in water bills, reductions in energy costs to heat/cool buildings,
and/or reductions in maintenance requirements.
There is currently a little-known mechanism where a direct financial benefit can be gained by water
bill customers for disconnecting their property from mains drainage. For Thames Water domestic
customers who can prove they are completely disconnected from the local surface water drainage
system, there is a discount available on the sewerage element of the water bill of around five per cent.
It appears that this provision is little known amongst water customers and take-up in London isminimal. A significant issue is that in a densely built-up city like London, it is generally hard for manysites to be able to store, infiltrate or use all the rainfall that falls on the site during a heavy storm. In
such a case, there will be some discharge of rainwater to the surface water system. There is no
proportional incentive for a partial disconnection from the drainage system.
During 2015, the government consulted on the Charging Guidance for OFWAT (Defra 2015). Thisconsidered the whole charging regime for water supply and wastewater, as well as for surface water.
The consultation recognised the need to manage surface water more sustainably and supported theidea of cost-reflective charging to incentive this. However, it also recognised that parks, open spaces,and some premises with low rateable values, high public benefit, and/or large buildings could be
adversely impacted by a charging system based on the area drained. Such adversely affectedbuildings could include community halls, places of worship, schools and hospitals. The subsequentguidance (Defra, 2016) states that the Flood and Water Management Act 2010 allows watercompanies to offer concessionary schemes for community groups for surface water drainage charges.
The government also plans to review its ‘Guidance to Water and Sewerage Undertakers in relation toConcessionary Schemes for Community Groups for Surface Water Drainage Charges’.
International experience suggests that for the retail and commercial sectors in particular, the use offinancial incentives can be very effective. Philadelphia, for example, introduced a new drainage fee
based on the surface area of a building or area of land. This means that any property with a large
surface area, like a supermarket, that drained to the local drainage system would be faced with a large
extra charge. For such cases, this approach has made it more viable to invest in sustainable drainage
techniques. Indeed, the downspout disconnection programmes of Portland and Philadelphia (US) andToronto (Canada) suggest significant investment in sustainable drainage can be justified once the billpayer is faced with far higher charges to discharge rainwater.

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
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Other public policy/regulatory interventions may also have implications for the management of
surface water. For example, anecdotal evidence suggests the increasing use of parking restrictions
and controlled parking zones, combined with increases in vehicle ownership, may have led toincreased numbers of front gardens being paved over. A review of wider public policy interventions iswarranted to consider if there are any indirect methods of encouraging more sustainable drainage infuture, or if existing policies are unintentionally reducing the take-up of sustainable drainage
techniques. This will be considered as part of future reviews of this action plan.
There is also likely to be an increasing role for the non-governmental sector in promoting andencouraging the use of sustainable drainage techniques. This is expected to increase over the lifetimeof this plan, as the issues become more widely understood and accepted. Similarly, it is an aim of theplan to ensure future projects funded by the GLA group will check for the inclusion of measures tomake drainage systems more sustainable.
Table 28: Funding actions
No Action

Leadorganisation

Partners

Timescale38

Examine methods ofencouraging moresustainable drainage take-up
through adjusting water bill
incentives and Thames Water
investment

GLA

TW

2017 onwards

Lobby for sustainabledrainage to be included inproject funding criteria

GLA group

39

EA

TW

2017-2020

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Monitoring
This action plan sets out an ambitious series of actions to address a topic that is not widely
understood or promoted. Achieving meaningful results will be challenging and it will take several
years to demonstrate real progress. It is therefore important that regular monitoring and reporting of
progress is undertaken. The GLA commits to producing an annual update, reporting progress on eachof the Actions. The monitoring report will be available on-line and may be linked or indeed part ofother GLA monitoring activities. If necessary, the plan will be updated in line with the results of theannual monitoring, with actions amended or new actions introduced. The GLA will also consider any
new metrics or methods of monitoring that might help inform progress.
The GLA will attempt to record the sustainable drainage measures that are implemented, both directly
as a result of this plan and indirectly by building /land owners or via the planning system. This could
potentially be a large task with multiple organisations/individuals carrying out activities. Therefore it
will be challenging to maintain a comprehensive record.
Table 29: Monitoring Actions
No. Action

Lead
Organisation

40

GLA

Produce an annual
monitoring report

Partners

Timescale2017 onwards

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Appendix 1: Action
plan by year
This table shows the same actions already detailed by sector above, but breaks actions down by year.
No.

ActionLeadorganisation

Partners

Timescale

Current/on-going actions
3

Deliver a programme ofsustainable drainage
demonstration projects

2015 – 2020

TW
LBs
GLA
Nongovernmentalorganisations

4

Maintain a strong London
Plan policy to support
sustainable drainage in new
development

GLA

6

Provide strategic guidanceon sustainable drainage
requirements for major
development locations

GLA

7

Continuous

Partner LBs

Continuous

TW
EA

Provide detailed Integrated
Development
Water Management Plans for partners
specific opportunity areas

GLA

Continuous

EA
TW
LBs

16

Identify opportunities andfunding for sustainabledrainage retrofit at the same

GLA

TfL

Continuous

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No.

ActionLeadorganisation

time as planned
maintenance, repair andimprovement works within
TfL owned/managed
transport assets

1

Publish the results of the
London-wide Sustainable
Drainage Opportunity Model

Partners

Timescale

LU
DLR
LondonOverground
GLA

TW

2016

EA
LC

14

Produce guidance that
includes good practice
examples of sustainabledrainage in the streetscapepublic realm

TfL

2

Raise awareness of the needfor, benefits of and deliveryof sustainable drainage
within London

GLA

2016

LBs

2016 onProject deliveryorganisations
Nongovernmentalorganisations

20175

Collate information on
Sustainable drainage
delivered through theplanning system

GLA

LBs

2017 onLONDON SUSTAINABLE DRAINAGE ACTION PLAN
64

No.

ActionLeadorganisation

Partners

Timescale8

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the education
sector

GLA

TW

2017

EA
Local authority
education
depts.
SuDS for
SchoolsSusdrain

9

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement public sector
schools

10

12

GLA

Local authority
education
depts. andother publicly
funded schools

2017

Identify opportunities andGLAfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works in higher
education establishments

Highereducation
providers2017

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the housing
sector

TW

2017

GLA

EA
LA Housing
depts.
Susdrain

13

Identify opportunities andfunding for sustainabledrainage retrofit at the same

GLA

Housing
associations

2017

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No.

ActionLeadorganisation

time as planned
maintenance, repair andimprovement works in thesocially rented housing
sectorTimescale

LA Housing
depts.
GLA Re:New

15

Prepare a standard for
retrofitting green
infrastructure

LU

17

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
other highway authorities’transport assets

GLA

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the healthsector

GLA

18

Partners

2017

Highwaysauthorities

2017

Highways
England

NHS

2017

EA
TW
Susdrain

21

Produce guidance and good GLA
practice examples ofsustainable drainage
applicable to the retail sector

TW
EA
BIDs
Susdrain

2017

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
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No.

ActionLeadorganisation

Partners

Timescale

22

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
the major supermarkets
estates

GLA

Supermarkets

2017

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
DIY and other large format
retailers’ estates

GLA

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the open
space/recreational sector

GLA

23

25

LBs

DIY stores andother large
format stores

2017

LBs

Londonboroughs

2017

NGOs
LandscapeInstitute

26

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works in parksand open spaces

GLA

Royal Parks
Corporation of
LondonLee Valley
Regional Park
Authority
Londonboroughs
London Playing
Fields2017

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No.

ActionLeadorganisation

Partners

Timescale

Association
Major sports/stadia owners
31

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
Thames Water’s estate

TW

GLA

2017

34

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
the Environment Agency’s
estate

EA

GLA

2017

36

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the individual
homes, small apartment
blocks or local
neighbourhoods

GLA

NGOs

2017

37

Consider a grant/incentive
scheme to encourage
individuals or local
communities to implement
their own sustainabledrainage scheme

GLA

38

Examine methods ofencouraging moresustainable drainage take-up
through adjusting water bill

GLA

Londonboroughs

2017

TW
EA

2017 onLONDON SUSTAINABLE DRAINAGE ACTION PLAN
68

No.

ActionLeadorganisation

Partners

TimescaleTW

2017-2020

incentives and Thames Water
investment
39

Lobby for sustainabledrainage to be included inproject funding criteria

GLA group

40

Produce an Annual
Monitoring Report

GLA

19

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
the NHS estate

GLA

NHS Trusts

2018

24

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
retail estate owners’
proposals

GLA

Retail estate
owners201827

Examine local authority
development proposals,
capital and revenue
programmes for sustainabledrainage opportunities

GLA

LBs

2018

28

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within

GLA

Centralgovernment
depts. andquangos20182017 on

2018

BIDs

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
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No.

ActionLeadorganisation

Partners

Timescalethe central government
departmental and quango
estates30

Produce guidance and goodpractice examples ofsustainable drainage
applicable to the industrial
sector

GLA

2018

32

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works withinenergy companies’ estates

GLA

Utilities
companies

2018

11

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works inprivate sector schools

GLA

Private sector
education
providers

2019

20

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
the private sector healthproviders’ estate

GLA

Healthproviders

2019

29

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned

GLA

Major officeowners/occupiers

2019

2019

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No.

ActionLeadorganisation

maintenance, repair andimprovement works withmajor officeowners/occupiers
33

Partners

Timescale

BIDs

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works withintelecoms companies’ estates

GLA

Telecoms
companies

2019

Identify opportunities andfunding for sustainabledrainage retrofit at the sametime as planned
maintenance, repair andimprovement works within
agricultural estates

GLA

National
Farmers’ Union

2020

2020
35

Farming
representatives

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Appendix 2:
References
Anthony McCloy for Susdrain. (2015). Designing Attenuation Storage for Redeveloped Sites. Retrieved
from
http://www.susdrain.org/files/resources/fact_sheets/01_15_fact_sheet_attenuation_for_redeveloped.pdf
BRE. (2016). Digest 365: Soakaway Design.
CIRIA. (2015). Benefits of SuDS Tool (BeST). Retrieved fromhttp://www.susdrain.org/resources/best.html
CIRIA. (2015). The SuDS Manual. Retrieved fromhttp://www.ciria.org/Resources/Free_publications/SuDS_manual_C753.aspx
CIRIA. (2016). Retrieved from Susdrain: http://www.susdrain.org/
City of Philadelphia. (2011). Green City, Clean Waters. Retrieved fromhttp://www.phillywatersheds.org/what_were_doing/documents_and_data/cso_long_term_c
ontrol_plan
City of Portland. (2016). Stormwater Management Manual. Environmental Services. Retrieved fromhttps://www.portlandoregon.gov/bes/64040
Defra & DCLG. (2014). Delivering Sustainable Drainage. Retrieved fromhttps://www.gov.uk/government/uploads/system/uploads/attachment_data/file/399995/R
FI7086_sud_consult_doc_final.pdf
Defra. (2016). Charging Guidance to Ofwat. Retrieved fromhttps://www.gov.uk/government/publications/water-industry-charging-guidance-to-ofwat
GLA. (2011). Managing Risks and Increasing Resilience: Our Adaptation Strategy. Retrieved fromhttps://www.london.gov.uk/WHAT-WE-DO/environment/environmentpublications/managing-risks-and-increasing-resilience-our
GLA. (2014). London Regional Flood Risk Appraisal: First Review. Retrieved fromhttps://www.london.gov.uk/what-we-do/planning/london-plan/london-plan-technical-andresearch-reports#Stub-171933
GLA. (2014). Sustainable Design and Construction Supplementary Planning Guidance. Retrieved fromhttps://www.london.gov.uk/what-we-do/planning/implementing-londonplan/supplementary-planning-guidance/sustainable-design-andLondon Assembly. (2005). Crazy Paving: The Environmental Importance of London’s Front Gardens.
Retrieved from https://www.london.gov.uk/about-us/about-us/london-assembly/londonassembly-publications/crazy-paving-environmental-importance-london%E2%80%99s
London Wildlife Trust, GiGL & GLA. (2010). London: Garden City? Retrieved fromhttp://www.gigl.org.uk/partnershipcasestudy/garden-research/
RHS. (2015). Why we all need Greening Grey Britain. Retrieved fromhttps://www.rhs.org.uk/science/gardening-in-a-changing-world/greening-grey-britain
UK CIP. (2002). London's Warming: The Impacts of Climate Change on London.

LONDON SUSTAINABLE DRAINAGE ACTION PLAN
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