Policy paper

London abstraction licensing strategy

Updated 19 May 2025

1. About the licensing strategy

This strategy sets out our approach to managing new and existing abstractions and impoundments within the London catchment in the Thames river basin district.

Our approach ensures that we:

• meet river basin management plan objectives for water resources activities
• avoid deterioration within this catchment

These are requirements as stipulated by the Water Environment (Water Framework Directive) (England and Wales) Regulations 2017 (referred to as the WFD Regulations 2017, or WFD). We apply this approach to the water body in which the abstraction or impoundment is located.

It also applies to:

• all downstream surface water bodies that may be affected by any reduction in abstraction related flow
• adjacent groundwater bodies affected by any reduction in groundwater level

The strategy also sets out local approaches to the sustainable management of water resources in collaboration with partners.

Our guidance on managing water abstraction gives the technical explanation, legal and policy requirements behind the abstraction licensing strategies (ALS).

Please see our guidance if you need to:

• check if you need a licence to abstract water
• check if you need a licence to impound water
• apply for an abstraction or impounding licence

We continuously update our assessment tools. Because of this some details in this document, for example ‘hands off flow’ (HoF) values, may be out of date. You can contact the Environment Agency for the latest data.

1.1 Collaborative and sustainable water management

Our long term goal is to develop a stronger catchment focus for water resources. We are working with abstractors and catchment groups to:

• develop local solutions to existing pressures
• to prepare for the future

Catchment groups may include a variety of different partnership groups such as:

• abstractor groups
• local catchment partnerships
• priority catchment groups
• environmental groups

Regional water resources groups are taking forward strategic multi-sector regional plans which consider environmental needs for long term planning. We are working with these groups to improve the connection between regional planning and catchment scale planning and delivery. There’s more information on regional planning in our National Framework.

This strategy is a tool to make informed decisions on the choices abstractors make about their use of water. We want this strategy to help abstractors plan their water use and become more resilient in the face of climate change.

2. Catchment overview

2.1 Landscape and land use

The catchment (including Central London) covers an area of nearly 1,400 km². The London catchment covers tributaries of the River Thames, with most of the area enclosed within the M25 (stretching to Hoddesdon in the north and to the North Downs in the south). The Estuary and the area upstream of Teddington Lock are assessed under the Thames catchment abstraction management strategy. 

Most of the catchment is urbanised, with suburban edges where towns are divided by farmland, parkland, and woodland. There are many Sites of Special Scientific Interest (SSSIs) in the catchment area and a few sites that are designated under the Conservation of Habitats and Species Regulations 2017 (known as Habitats Regulations 2017): Lee Valley Park, Wimbledon Common and Richmond Park.

The typology (and other features) of the catchment area can be explored using Magic Map (for extent of the catchment area, see Maps 1 to 6).

2.2 Water resources

The hydrology across most of the catchment is influenced by the impermeable London Clay. In these areas, rivers like the Brent and Crane are very responsive to rainfall. The urban extent in this catchment also has a significant impact upon the hydrology: in addition to the overlying London Clay, the hard, impermeable urban surfaces and the dense surface water drainage network are further drivers of rapid runoff. Flows and water levels increase quickly following heavy or prolonged rainfall as water cannot percolate through the London Clay or urban cover.

This also means that water does not recharge the chalk aquifer (henceforth referred to as the ‘Chalk’) beneath the London Clay. As a result, the Chalk groundwater aquifer in these areas is confined (henceforth referred to as the ‘Confined Chalk’). The Confined Chalk underneath London is designated as a principal aquifer. The groundwater within the waterbody flows towards central London. The source of this groundwater comes from the unconfined upstream areas north and south of London, mainly outside the London ALS catchment.

The South London Rivers – the Hogsmill and the Wandle – have sources that interact with the Chalk groundwater. As a result, this groundwater aquifer in these source areas is considered unconfined. Rainfall falling onto the North Downs can penetrate the soils, recharging the Chalk aquifer. The rising groundwater table forms the headwaters of these watercourses. Map 5 shows the geology of the ALS area.

2.3 Climate change

Climate change is likely to affect the quantity and seasonal availability of water resources within the catchment. The Environment Agency climate impacts tool provides a simple description of current and potential future challenges.

The projected climate change impacts on rainfall and river flow for the London region by the 2050s are for:

• rainfall to decrease by up to about 24% in the summer but increase by up to about 11% in the winter
• low flows to be up to about 39% lower and peak river flows to be up to about 2% higher

2.4 Partnership working

Catchment partnerships are active in this catchment, which bring together stakeholders from a range of backgrounds. They aim to develop collaborative approaches to water resources management and planning, as well as address issues in the catchment. For more information, see:

• Beverley Brook Catchment Partnership
• Brent Catchment Partnership
• Crane Valley Partnership
• Hogsmill Catchment Partnership
• London Lea Catchment Partnership
• Ravensbourne Catchment Improvement Group
• River Wandle Catchment Partnership

3. Water resource availability in the London catchment

3.1 Surface water availability

The method for calculating the water resource availability is explained in managing water abstraction. Water availability is calculated at selected assessment points (APs). The maps show the water availability calculated at the AP – local water availability may differ.

There are 12 APs in the London ALS:

• AP1 Hogsmill: covers the reaches of the River Hogsmill which flows into the non-tidal River Thames (it contains the heavily modified Hogsmill water body) – upper parts of this AP are in connection with the unconfined Chalk
• AP2 Beverley Brook: covers the majority reaches of Motspur Park to Thames, and Pyl Brook at West Barnes (heavily modified) – the upper part of the catchment includes some unconfined Chalk, but the water table is too low to interact with the head of the Beverley Brook
• AP3 Wandle: covers the majority reaches of the River Wandle (heavily modified) – upper parts of this AP are in connection with the unconfined Chalk
• AP4 Pool: covers the reaches of the River Pool (heavily modified), prior to its confluence with the River Ravensbourne
• AP5 Quaggy: covers the majority reaches of the River Quaggy (heavily modified), prior to its confluence with the River Ravensbourne
• AP6 Ravensbourne: covers the reaches and tributaries of the River Ravensbourne (heavily modified) – when groundwater levels are exceptionally high, upper parts of this AP are in connection with the unconfined Chalk
• AP7 Middle Lee: covers the reaches and tributaries of the River Lee from the London catchment boundary at Glen Faba to just after Enfield Lock (heavily modified), including the Nazeing Brook and Cobbins Brook
• AP8 Lee (Chalk Bridge): covers the reaches and tributaries of the River Lee from just after Enfield Lock to besides Banbury Reservoir (heavily modified), including the Ching Brook (heavily modified)
• AP9 Lower Lee: covers the reaches and tributaries of the River Lee from just besides Banbury Reservoir down to Bromley-by-Bow (heavily modified) where it meets the tidal River Thames, including the Moselle Brook (heavily modified), the Pymmes Brook (heavily modified), the Salmons Brook (heavily modified) (and their heavily modified confluence), the Turkey and Cuffley Brook, and the reaches and tributaries of the Small River Lee
• AP10 Upper Crane: covers the reaches of the Yeading Brook (heavily modified) up to the point that it becomes the River Crane
• AP11 Lower Crane: cover the reaches of the River Crane from the end of the Yeading Brook up to the tidal River Thames
• AP12 Brent: covers the reaches and tributaries of the River Brent (heavily modified) – includes the artificial Bentley Priory and Welsh Harp water bodies

3.2 Water resource availability colours and implications for licensing

The water resource availability is calculated and the colour assigned at four different flows:

• Q30 – the flow of a river which is exceeded on average for 30% of the time, therefore you would expect the river flow to be lower than Q30 on 256 days in an average year, that is, a higher flow
• Q50 – the flow of a river which is exceeded on average 50% of the time, therefore you would expect the river flow to be lower than Q50 on 183 days in an average year
• Q70 – the flow of a river which is exceeded on average for 70% of the time, therefore you would expect the river flow to be lower than Q70 on 110 days in an average year
• Q95 – the flow of a river which is exceeded on average for 95% of the time, therefore you would expect the river flow to be lower than Q95 on 18 days in an average year, that is, a low flow

We use the following colours below to represent different surface water availability at these flows.

Water available for licensing

Green

There is more water than required to meet the needs of the environment.

New licences can be considered depending on local and downstream impacts.

Restricted water available for licensing

Yellow

Full licensed flows fall below the environmental flow indicators (EFI).

If all licensed water is abstracted there will not be enough water left for the needs of the environment. No new consumptive licences would be granted. It is likely we will be taking action to reduce full licensed risks. Water may be available if you can ‘buy’ (known as water rights trading) the entitlement to abstract water from an existing licence holder.

Water not available for licensing

Red

Recent actual flows are below the EFI (or have been overridden by a downstream AP where flows are below the EFI).

This scenario highlights water bodies where flows are below the indicative flow requirement to help support a healthy ecology in our rivers. We will not grant further licences in these water bodies.

We are currently taking action in these water bodies. Water may be available if you can buy (known as water rights trading) the volumes equivalent to recently abstracted from an existing licence holder.

3.3 Water availability maps

The water availability colours for the London catchment are presented in maps 1 to 4.

Table 1. Summary of Maps 1 to 4 water availability at each assessment point by flow category

AP name	Q30	Q50	Q70	Q95
1 Hogsmill	Water available	Restricted water available	Water not available	Water not available
2 Beverley Brook	Water available	Water not available	Water not available	Water not available
3 Wandle	Water available	Restricted water available	Water not available	Water not available
4 Pool	Water available	Water available	Water not available	Water not available
5 Quaggy	Water available	Water available	Water not available	Water not available
6 Ravensbourne	Water available	Water available	Water not available	Water not available
7 Middle Lee	Water not available	Water not available	Water not available	Water not available
8 Lee (Chalk Bridge)	Water not available	Water not available	Water not available	Water not available
9 Lower Lee	Water not available	Water not available	Water not available	Water not available
10 Upper Crane	Water available	Water not available	Water not available	Water not available
11 Lower Crane	Water available	Restricted water available	Water not available	Water not available
12 Brent	Water available	Water not available	Water not available	Water not available

Map 1. Water resource availability colours at Q30 for London ALS

This map demonstrates that at Q30 surface water is available across the catchment except in AP7, AP8, and AP9. These AP are in the northeast of the catchment, on the River Lee. In these AP, water is not available. The map additionally shows that surface water in the central London section not covered by an AP is available.

© Environment Agency

Map 2. Water resource availability colours at Q50 for London ALS

This map demonstrates that at Q50, restricted water is available in the APs in the west of the catchment. These are APs for rivers that flow into the freshwater and transitional water River Thames in the west of this catchment (the Thames in the centre and east of the catchment is tidal). The exceptions are AP2, AP10 and AP12, were surface water is not available. For the APs in the southeast of the catchment, being the River Ravensbourne and its upstream tributaries (AP4 to 6), water is available. There is no in the northeast of the catchment, on the River Lee (AP7 to 9). The map additionally shows that surface water in the central London section not covered by an AP is available.

© Environment Agency

Map 3. Water resource availability colours at Q70 for London ALS

This map demonstrates that at Q70 surface water is not available across the catchment. The map additionally shows that surface water in the central London section not covered by an AP is available.

© Environment Agency

Map 4. Water resource availability colours at Q95 for London ALS

This map demonstrates that at Q95 surface water is not available across the catchment. The map additionally shows that surface water in the central London section not covered by an AP is available.

© Environment Agency

3.4 Groundwater resource availability

Abstracting groundwater can impact on overlying surface water bodies and groundwater dependent ecosystems. This impact is measured at the surface water AP. We cannot grant new groundwater licences where abstraction is reducing flows to below the indicative flow requirement to help support a healthy ecology. This is based on Q95 flows.

We must also account for:

• the available resource in the aquifer
• the impact of abstraction on protected sites
• the risk of saline intrusion

Where the Chalk aquifer is unconfined (namely in parts of the Hogsmill, Wandle, and Ravensbourne catchments), groundwater availability is guided by the surface water resource availability colours. This same principle applies to the areas of shallow deposits, like the Bagshot Formation and the gravels. Map 5 shows geology of the London ALS. Maps 1 to 4 show the surface water resource availability colours in the London area.

Abstractions from the gravels or other deposits where groundwater is in continuity with the surface water will be considered as surface water abstractions. Abstractions from such deposits which do not have direct impact on the river system may be permitted, but may be subject to restrictions such as prescribed groundwater levels (referred to as ‘hands off levels’, or HoLs – see section 4.3). Restrictions will be determined on a case-by-case basis, based upon the nature and scale of the abstraction.

Where the Chalk is confined beneath the London Clay, groundwater availability is regularly assessed. Details on this availability and of the management of the Confined Chalk are detailed in the latest London basin chalk aquifer annual status report. The Confined Chalk is the part of the Chalk aquifer overlain by London Clay (and by the Lambeth Group). It gains water transmitted underground within the Chalk from the North Downs and from the Chilterns.

Water was available for new consumptive abstraction in the 1990s when rising groundwater was identified as a danger to deeper underground structures in Central London. Water levels stabilised in the late 2000s – however, licences for new consumptive abstractions will be limited to areas where groundwater levels are above the Thanet Sands (meaning within the Lambeth Group or into the London Clay base). These areas are identified in the London basin chalk aquifer annual status report

Map 5. Surface geology of the London catchment

This map shows the surface geology of the London catchment. It shows that the catchment is almost entirely upon the impermeable London Clay formation, except where the London Clay is absent in the southernmost sections (at the headwaters of AP1-6) and the very northernmost point (the top of AP7).

© Environment Agency

3.5 Resource reliability

If you want to apply for a licence, it is worth considering the reliability of your surface water abstraction.

By assessing the quantity of water available at different flows it is possible to see:

• when there is a surplus or deficit of water
• the associated reliability of an abstraction

This is an indication only. Actual reliability of a licence will be discussed when you apply.

Map 6 gives an indication of the resource availability for consumptive abstraction in the London area expressed as a percentage of time. In this catchment:

• AP1 Hogsmill: Consumptive abstraction is available at least 30% of the time
• AP2 Beverley Brook: Consumptive abstraction is available at least 30% of the time
• AP3 Wandle: Consumptive abstraction is available at least 30% of the time
• AP4 Pool: Consumptive abstraction is available at least 50% of the time
• AP5 Quaggy: Consumptive abstraction is available at least 50% of the time
• AP6 Ravensbourne: Consumptive abstraction is available at least 50% of the time
• AP7 Middle Lee: Consumptive abstraction is available less than 30% of the time
• AP8 Lee (Chalk Bridge): Consumptive abstraction is available less than 30% of the time
• AP9 Lower Lee: Consumptive abstraction is available less than 30% of the time
• AP10 Upper Crane: Consumptive abstraction is available at least 30% of the time
• AP11 Lower Crane: Consumptive abstraction is available at least 30% of the time
• AP12 Brent: Consumptive abstraction is available at least 30% of the time

Map 6. Water resource reliability of the London ALS expressed as a percentage of time available

This map visualises the resource availability for each as described in section 3.7. The map additionally shows that surface water in the central London section not covered by an AP is available at least 95% of the time.

© Environment Agency

3.6 Other considerations for resource availability and reliability

When we grant a licence, it does not mean that we guarantee a supply of water.

We may have to add constraints to licences such as HoF or HoL conditions to protect the environment and the rights of other abstractors. These conditions specify that if the flow or level in the river or groundwater table drops below what is needed to protect the environment, abstraction must reduce or stop. In dry years, restrictions are likely to apply more often, which will affect the reliability of supply.

Whilst this document may say that water is available for abstraction, this does not guarantee that all applications will be successful. This is because we must determine each application on its own merits, and local factors may mean we are either unable to grant a licence as applied for, or even at all.

New licences within an ALS are usually given a ‘common end date’ (CED), which allows them to be reviewed at the same time.

The next CED for this ALS is 31 March 2037.

3.7 Impoundments

Applications for impounding licences will be dealt with on a case-by-case basis and take into account the requirements of our obligations under the Habitats Regulations (2017) and WFD Regulations (2017). Proposals must also comply with The Eels (England and Wales) Regulations 2009 and the Salmon and Freshwater Fisheries Act 1975.

An impoundment is a dam, weir or other construction in an inland waterway that obstructs or impedes flow. Our assessment of an impounding licence application takes into consideration its potential impacts on the environment (such on as fish and eel migration, on riparian mammals, on plant communities, or on fluvial geomorphology), flood risk, downstream water users and flow modification. In line with current legislation, we do not time limit impounding licences.

You must have an impounding licence before you start to construct, alter, repair, or remove an impounding structure, even in an emergency. However, certain exemptions may apply and if we deem there is little or no impact on the environment and other water users, you may not need a licence. Please contact the Environment Agency if you intend to construct, alter, repair, or remove an impounding structure so that we may advise you whether a licence is required.

There is more information in our guidance on how to check if you need a licence to impound water.

4. How we manage water availability in the London ALS

4.1 Surface water

We assess surface water flows at each AP, which are significant points on a river, often where 2 major rivers join or at a gauging station. An AP can cover multiple surface water bodies.

Where groundwater abstractions directly impact on surface water flows, the impact is measured at the surface water AP. Where groundwater abstractions are from the Confined Chalk, reference should be made to section 4.2.

Section 4.2 gives an indication of:

• how much water is available for further abstraction
• the associated restrictions we may have to apply to new and varied abstraction licences from the main river.

Depending on the nature of the catchment, tributaries to the main river may be subject to different restrictions and quantities. This may be assessed locally on a case-by-case basis. Please note that Section 4.2 is entirely indicative and is only reflective of the water resources situation at the time of publication of this ALS. All values are subject to change depending on the changing water resources situation, or on granted licence applications.

Each HoF is linked to a relevant gauging station, which is turn is linked to an AP. The value of the HoF is dependent on the resource availability at that AP. In some cases, additional restrictions may apply to licences where there is a more critical resource availability downstream to protect the ecological requirements of the river and other water users. This has been considered in the figures given in Section 4.2.

All abstraction licence applications are subject to an assessment. This takes account of any local and downstream issues and may be subject to further restrictions.

Section 4.2 sets out the APs in the London ALS area. It shows the potential reliability of a new licence expressed as the number of days water may be available under this restriction during an average year. In cases where there is water available at all flows, we may apply a minimum residual flow (MRF) in the water body to protect very low flows. We will decide this on a case-by-case basis.

Licensing strategy for new and varied licences (please see Section 4.2)

Where the HoF at the AP has been over-ridden by a more restrictive River Thames Q50 flow constraint (AP1, AP2, AP3, AP10, AP11, and AP12), water is likely to only be available in the wetter winter period. It is likely that a storage system would be required to make use of any licence. In addition to the River Thames flow constraint, it is likely that local HoFs will be required on all consumptive surface water abstractions to protect flows in the local watercourse.

The upper sections of AP1 are under greater water resource pressures than the downstream sections. The availability of water as indicated by the AP may therefore be overstating the availability of water in the upper section. Licence proposals impacting these upper sections may therefore be subject to a more restrictive HoF than indicated by Section 4.2 or Maps 1 to 5.

For AP4 and AP5, the HoF is restricted to protect the flows at the downstream Ravensbourne AP6. Due to the size of these rivers and protective constraints, this means the amount of water available to abstract would be extremely low, and that water would only be available in the higher flow periods, typically wet winters.

New consumptive surface water abstractions for the Middle Lee, Lee (Chalk Bridge) and Lower Lee APs (AP7 to 9) will only be considered at time of very high flows. Abstraction at very high flows will not provide a reliable source of water, as they may not occur every year. There are potential flood risks when taking water under these conditions which an applicant will need to consider along with the suitability of the water for the intended purpose. 

The Lee navigation has water requirements that are supplied by several different channels. The quoted figures in Section 4.2 for the Middle Lee (AP7) do not take account of these splits in flows. The HoF value in this AP will be very restrictive of when abstraction is permitted.

In the Middle Lee high flows are diverted down a flood relief channel. The quoted figures in Section 4.2 for this AP7 do not take account of the split in flows between the River Lee and the flood relief channel. The HoF value in the AP will be very restrictive of when abstraction is permitted. 

In the Lower Lee high flows are split between several different channels. The quoted figures in Section 4.2 for this AP9 do not take account of this split in flow down the different channels. The HoF value in the AP will be very restrictive to when abstraction is permitted. 

In the Lower Crane, flow is split between the River Crane and the Duke of Northumberland’s River. The quoted figures in Section 4.2 for this AP11 do not take account of this split in flows. The HoF value in this AP will be very restrictive of when abstraction is permitted.

Abstractions that are considered non-consumptive or small scale consumptive licences that result in an overall net benefit to the water environment may be considered beyond the stated restrictions, subject to a local impact assessment and the need to ensure that there is no deterioration of any WFD water bodies or their associated elements. See the Catchment Data Explorer for more information on water body and associated elements WFD statuses.

Licence variations that could result in an increase in actual abstraction but remain within existing licensed volumes (for example, if the point of abstraction was being changed, or if the purpose of the licence was changing) will be assessed as if were a new licence. We must ensure that such a variation would not result in a deterioration of any WFD water body or their associated elements. This assessment will therefore be in line with our licensing strategy for surface or groundwater abstractions, subject to a local impact assessment.

4.2. Summary of licensing approach for the assessment points of the London abstraction licensing strategy

1. Hogsmill

Restricted water available for licensing: yellow

National Grid reference	TQ177772
HOF restriction (Ml/d)	58.6
Flow value being protected	Q50
Number of days a year abstraction may be available	240
Approximate volume available at restriction (Ml/d)	53.5
Gauging station at this AP	Yes

Addition restrictions: This is the only river in the London ALS that flows into the non-tidal Thames which is heavily over abstracted. The HoF at AP1 has been overridden by a more restrictive flow constraint to protect the Thames. See the Thames ALS for more details.

2. Beverley Brook

Restricted water available for licensing: yellow

National Grid reference	TQ214754
HOF restriction (Ml/d)	55.9
Flow value being protected	Q50
Number of days a year abstraction may be available	178
Approximate volume available at restriction (Ml/d)	55.4
Gauging station at this AP	No – 4km upstream

Addition restrictions: The HoF at AP2 has been overridden by a more restrictive flow constraint to protect the Thames below the Teddington Weir. See the Thames ALS for more details.

3. Wandle

Restricted water available for licensing: yellow

National Grid reference	TQ256743
HOF restriction (Ml/d)	197.5
Flow value being protected	Q50
Number of days a year abstraction may be available	222
Approximate volume available at restriction (Ml/d)	76.7
Gauging station at this AP	No – 4km upstream

Addition restrictions: The HoF at AP3 has been overridden by a more restrictive flow constraint to protect the Thames below the Teddington Weir. See the Thames ALS for more details.

4. Pool

Restricted water available for licensing: yellow

National Grid reference	TQ372725
HOF restriction (Ml/d)	13.7
Flow value being protected	Q61
Number of days a year abstraction may be available	219
Approximate volume available at restriction (Ml/d)	1
Gauging station at this AP	Yes

Addition restrictions: This catchment is assessed as ‘restricted water available for licensing’ to protect the downstream flows of AP6.

5. Quaggy

Restricted water available for licensing: yellow

National Grid reference	TQ395749
HOF restriction (Ml/d)	5.1
Flow value being protected	Q61
Number of days a year abstraction may be available	26
Approximate volume available at restriction (Ml/d)	1
Gauging station at this AP	Yes

Addition restrictions: This catchment is assessed as ‘restricted water available for licensing’ to protect the downstream flows of AP6.

6. Ravensbourne

Restricted water available for licensing: yellow

National Grid reference	TQ374769
HOF restriction (Ml/d)	20
Flow value being protected	Q61
Number of days a year abstraction may be available	237
Approximate volume available at restriction (Ml/d)	1
Gauging station at this AP	No

7. Middle Lee

No water available for licensing: red

National Grid reference	TQ378976
HOF restriction (Ml/d)	1,973.2
Flow value being protected	Q5
Number of days a year abstraction may be available	18
Approximate volume available at restriction (Ml/d)	217.2
Gauging station at this AP	No

Addition restrictions: Please see the licensing strategy for this AP explained in Section 4.1.

8. Lee (Chalk Bridge)

No water available for licensing: red

National Grid reference	TQ359916
HOF restriction (Ml/d)	1,839.1
Flow value being protected	Q5
Number of days a year abstraction may be available	18
Approximate volume available at restriction (Ml/d)	217.2
Gauging station at this AP	No

Addition restrictions: Please see the licensing strategy for this AP explained in Section 4.1.

9. Lower Lee

No water available for licensing: red

National Grid reference	TQ382825
HOF restriction (Ml/d)	1,405.6
Flow value being protected	Q9
Number of days a year abstraction may be available	32
Approximate volume available at restriction (Ml/d)	412.3
Gauging station at this AP	No

Addition restrictions: Please see the licensing strategy for this AP explained in Section 4.1.

10. Upper Crane

Restricted water available for licensing: yellow

National Grid reference	TQ103778
HOF restriction (Ml/d)	19.6
Flow value being protected	Q50
Number of days a year abstraction may be available	178
Approximate volume available at restriction (Ml/d)	9.5
Gauging station at this AP	No

Addition restrictions: The HoF at AP10 has been overridden by a more restrictive flow constraint to protect the Thames Upper water body. See the Thames ALS for more details.

11. Lower Crane

Restricted water available for licensing: yellow

National Grid reference	TQ166753
HOF restriction (Ml/d)	24.5
Flow value being protected	Q50
Number of days a year abstraction may be available	175
Approximate volume available at restriction (Ml/d)	13.3
Gauging station at this AP	No

Addition restrictions: The HoF at AP11 has been overridden by a more restrictive flow constraint to protect the Thames Upper water body. See the Thames ALS for more details.

12. Brent

Restricted water available for licensing: yellow

National Grid reference	TQ177772
HOF restriction (Ml/d)	87.7
Flow value being protected	Q50
Number of days a year abstraction may be available	127
Approximate volume available at restriction (Ml/d)	81.5
Gauging station at this AP	No

Addition restrictions: The HoF at AP12 has been overridden by a more restrictive flow constraint to protect the Thames Upper water body. See the Thames ALS for more details.

4.3 Groundwater

Where groundwater abstractions directly impact on surface water flows the impact is measured at the surface water AP. This includes where the impact reduces baseflow. In these cases, restrictions may be applied to licences, such as HoL conditions. The HoL is a groundwater level below which an abstractor is required to reduce or stop abstraction.

The Confined Chalk underneath London is a principal aquifer. This aquifer is artificially managed according to the three below guiding principles:

• to prevent flooding of infrastructure under London, like the London Underground and the foundations of buildings
• to maintain the net groundwater levels above the top of the Chalk layer in order to keep the Chalk fully saturated. This would maintain a stable environment in the aquifer, required for complying with WFD requirements and to reduce the risk of derogation
• to prevent the water levels in the aquifer from moving between geological strata (such as the Chalk, Thanet Sands and so on) to reduce negative impacts on the quality of abstracted water

We base our decisions on water availability within the aquifer using the water table geology map, which is updated as appropriate in the London basin chalk aquifer annual status report. Accordingly, this strategy is flexible, as water can become available to address areas of water table rise. The report is updated regularly. The latest version is available either on our website or by request.

Our licensing strategy for the London Confined Chalk aquifer

Water might be available for consumptive use in the areas where the water table is in the Lambeth Group or into the London Clay (see Figure 1), subject to local assessment. No new consumptive abstraction licences will be granted in areas where the abstraction would result in groundwater levels being lowered into the Thanet Sands or Chalk. Water might be available for further consumptive use in the areas where the water table is in the Lambeth Group or into the London Clay, subject to local assessment.

In areas where the water table is already in the Thanet Sands or Chalk, it is likely that new consumptive abstractions licences will not be granted. These correlate with areas marked ‘no water available’ in the London basin chalk aquifer annual status report.

In the east and southeast of London, where the Chalk outcrops around the brackish River Thames and becomes unconfined, regular water quality sampling conditions may be attached to an abstraction licence document, as the abstraction of groundwater in these areas can increase the risk of saline intrusion. Large groundwater abstractions elsewhere in the catchment – even where from the Confined Chalk – may also require this condition.

New or renewed abstraction licences may have a HoL where, depending on the nature of the induced drawdown, abstraction may have to cease or reduce if it leads to dewatering of the Thanet Sands or the Chalk (where the Thanet Sands strata is locally absent).

As this ALS is only correct at the time of publication, proposals for abstractions from the Confined Chalk may not be granted if new licences for groundwater abstraction have been granted in the vicinity of the proposal. This is even in areas where this document may suggest that groundwater is available. This is because the new abstractions may have influenced the level of the water table and therefore have changed the availability of groundwater (see Figure 1). This is particularly important in managing the Confined Chalk, which is reliant on recharge from outside of the London catchment.

The proximity of a proposed abstraction to an existing or proposed Artificial Recharge Scheme must be considered. Artificial Recharge Schemes abstract water when water from other sources is unavailable. In areas around these schemes there is therefore the potential for significant episodic lowering of the water table, meaning that water may not be available as regularly as a proposal may require. Applications in this situation may be required to alter their installation or operation proposals accordingly – we recommend seeking advice.

New abstraction licences issued will usually have a condition for measuring groundwater levels in the borehole. Licence holders will be expected to collect regular groundwater level readings. This will require new boreholes to be constructed or installed in a manner that will allow groundwater levels to be measured. This will enable the Environment Agency to effectively manage water resources in the London Chalk underground strata.

Figure 1. Schematic cross-section showing typical geological strata in London and the ideal water table range (not to scale) (Management of the London Basin Chalk Aquifer, Environment Agency, 2022)

This figure presents a simplified, not to scale depiction of the typical geological strata in the London ALS. The layers depicted (from most shallow to deepest) are London Clay, Lambeth Group, Thanet Sands, and Chalk. The figure demonstrates that the top of the water table should ideally be in the Lambeth Group.

4.3.1 Groundwater-based ground source heat pump schemes

Groundwater abstraction licences issued for any ground source heat pump (GSHP) schemes will have attached conditions that will require licence holders to monitor and record water abstraction volume, water levels and temperature of the groundwater on a daily basis. This monitoring is required for licence compliance and to encourage the correct management of GSHP schemes, which in turn is designed to ensure that all GSHP schemes operating under this ALS are efficient, effective, and long-lasting. 

GSHP schemes will need to be installed in accordance with best industry practice. Best practice can be achieved by following the guidance and standards of the Ground Source Heat Pump Association. Note that proposed GSHP schemes will need to demonstrate how their scheme will be compliant with the licence conditions.

Consumptive schemes which consider discharging water to foul sewer or different source of supply are not normally permitted. GSHP schemes are only considered non-consumptive when the total volume of abstracted water is returned to the source of supply (that is, to the same aquifer from which water was abstracted from). For this reason, a GSHP may only be considered fully non-consumptive if it is installed using cased abstraction and injection boreholes. 

If a pump test of a proposed GSHP scheme were to suggest possible desaturation of the Chalk or Thanet Sands, a HoL condition may be applied as necessary. This is to protect the Chalk and Thanet Sands from further desaturation, in line with our principle of keeping the water table above these geological strata (see Figure 1). The HoL requirements on all GSHP licences will be subject to regular review and will be amended as may be required at the time of such reviews.

Where a proposed GSHP is located within areas marked as ‘no water available’ in the London basin chalk aquifer annual status report, even non-consumptive schemes may be rejected. This is to protect the Chalk and Thanet Sands from further desaturation, as the temporal and spatial disparities between the abstraction and reinjection of water may still produce an area of deterioration within these geological strata. Where non-consumptive GSHP schemes in such areas are approved, additional monitoring of groundwater levels may be included as a licence condition. 

The assessment of an application for a GSHP scheme will consider the following:

• any impacts on nearby abstractors and the aquifer from the abstraction and re-injection of groundwater
• the spacing and thermal performance of the system and how that may change over time
• any underground structures and services that could be impacted through the proposed re-injection

There is an expectation that a hydrogeological assessment will constitute part of any application for a GSHP scheme, and we would recommend a thermal modelling report to be included in such an assessment. This would allow insight into the long-term viability of the proposed scheme.

All proposals will be subject to a local hydrogeological assessment, and licences will not be granted if the assessment shows the abstraction to be unsustainable or have unacceptable impacts on the London aquifer or on nearby groundwater abstractions. Potential applicants are encouraged to apply using the enhanced pre-application service. The service provides in-depth advice from Environment Agency specialists which will help you know: 

• if you are likely to get a licence
• what restrictions your licence may have
• how to submit a sound application that contains all necessary information at sufficient detail

4.4 Protected sites

4.4.1 European sites and SSSIs

The Habitats Regulations (2017) provides a very high level of protection to:

• Special Areas of Conservation (SAC), which contribute to biodiversity by maintaining and restoring habitats and species
• Special Protection Area (SPA), which provides protection to birds and their nests, eggs and habitats

Government policy treats Ramsar sites (internationally important wetland sites) in the same way as SACs and SPAs. Ramsar sites, SACs and SPAs are referred to collectively as European sites. SSSIs also carry a high level of environmental importance.

Conservation objectives are the overarching objectives for European and SSSI protected sites to maintain at, or to reach, favourable condition. These are set by Natural England. The process for setting targets that underpin these objectives is described through the Joint Nature Conservation Committee approved ‘Common Standards Monitoring Guidance’ (CSMG). Natural England use CSMG targets to assess the condition of European and SSSI protected sites. Natural England consider these quantitative targets a pre-requisite for achieving the conservation objectives for European or SSSI designated sites. We have a duty to have regard to Natural England’s advice when determining licence applications that may impact on a designated site.

We may need more detailed supporting information when a licence application could impact on a designated feature of a conservation site. This will allow us to complete the required statutory assessment.

The London catchment contains many nationally important SSSIs designated under the Wildlife and Countryside Act 1981. Of these, there are 16 water resource-dependent SSSIs, all of which support an abundance of species. There are 5 SACs – 2 of which are water resource-dependant – and one SPA and Ramsar site in the London catchment. Sites that are dependent on the water resources of the area and could be affected by a change to water levels and water usage are:

• Wimbledon Common (SAC) (comprising Wimbledon Common SSSI): designated for Northern Atlantic wet heath, Erica tetralix (a wetland terrestrial feature) and stag beetles
• Richmond Park (SAC) (comprising Richmond Park SSSI): designated for acidic grassland and collections of invertebrates (mainly saproxylic) and stag beetle (Lucanus cervus)
• Lee Valley SPA and Ramsar Site (partially located in the London ALS): made up of a series of wetlands and reservoirs. It comprises Rye Meads SSSI, Amwell Quarry SSSI, Turnford and Cheshunt Pits SSSI, and Walthamstow Reservoirs SSSI. The latter two of these are within the London ALS. These wetland habitats support wintering wildfowl, in particular gadwall and shoveler. Areas of reedbed within the site also support significant numbers of wintering bittern
• Barn Elms Wetland Centre SSSI: also known as the London Wetland Centre, this wetland provides over 40 acres of habitats including lowland open water, muddy banks, reedbed and grazing marsh. The range of wintering and breeding birds using the site is Favourable, including gadwall, shoveler, little ringed plover, common term, reed warbler, and the now-resident Cetti’s warbler
• Bentley Priory SSSI: comprises an intricate mosaic of unimproved neutral grassland, ancient and long-established woodland, scrub, wetland and open water. This combination of habitats is uncommon in Greater London. Several plant species which are rare or scarce in Greater London are present and the site supports a characteristic breeding bird community The water dependent habitat supports water horsetail, cyperus sedge and greater tussock-sedge, all scarce in Greater London. Also supported is St John’s wort which is classed as rare across Greater London
• Brent Reservoir SSSI (also known as the Welsh Harp): of interest primarily for breeding wetland birds and in particular for significant numbers of nesting great crested grebe. The diversity of wintering waterfowl and the variety of plant species growing along the water margin are also of special note for Greater London. The site supports good numbers of pochard, shoveler and reed warbler
• Cornmill Stream and Old River Lee SSSI: a freshwater habitat with one of the most diverse invertebrate faunas in Essex. The site supports an outstanding assemblage of dragonflies and damselflies (Odonata) – 18 species have been recorded, including 2 notable scarce species. The slow-moving streams support a rich and varied aquatic and marginal flora. Associated with this habitat is one of the richest gastropod molluscan faunas in the county including 2 vulnerable species of freshwater snail and other invertebrates including a rare sawfly and a rare soldier fly
• Chingford Reservoirs SSSI: one of the major wintering grounds for wildfowl and wetland birds in the London area and hold nationally important numbers of some species, including great crested grebe, goldeneye, tufted duck and goosander. The reservoirs also form a moult refuge for large populations of wildfowl during the late summer months
• Epsom and Ashstead Commons SSSI: two commons that support a diverse range of habitats on undulating London Clay. The Stew Pond and recently restored Great Pond date back to the Medieval period of history. Their flora include duckweeds, white water lily, and pondweeds, while the marginal fen flora includes common bulrush, bogbean, trifid bur-marigold, and narrow-leaved water-plantain. Breeding birds associated with open waters at this site include mallard, moorhen, little grebe and kingfisher
• Keston and Hayes Commons SSSI: an unusual area demonstrating an occurrence of heathland vegetation pebble beds that graduates into wetter neutral grassland habitats as it enters into a small valley mire. This species-rich mire is exceptionally rare in London, hosting areas of sphagnum species, a range of bog plants and small amounts of lesser skullcap (a rare plant in the London area). The management of flow through this mire is important for supporting its resilience
• Stones Road Pond SSSI: a large, deep pond and connected terrestrial habitat that support a regionally significant population of great crested newts. During the breeding season the population exceeds 400 to 500 individuals. The site also supports a significant population of smooth newts
• Syon Park SSSI: the only known area of tall grass washland (Tide Meadow) along the Thames in Greater London and the last remaining section that is unbanked. This wet meadow ecosystem is unique in London, and is a host for many wintering birds, invertebrates, plant species (for example, reed sweet grass), and other flora and fauna, including the German hairy snail (of which Syon Park it is only one of a limited number of sites in the UK where this species is found)
• Waltham Abbey SSSI: an area of Alder woodland on damp alluvial soils overlying fluvio-glacial gravel in the valley of the River Lee. The woodland supports the largest heronry in Essex. Maintaining water levels within the site and surrounding watercourses is key to allowing the site to function favourably
• Walthamstow Marshes SSSI: one of the last remaining examples of semi-natural wetland in Greater London. They contain a variety of plant communities typical of a former flood plain location, such as a range of neutral grassland types, sedge marsh, reed swamp, sallow scrub and areas of tall herb vegetation. Associated with this diversity of habitat are several species of plant and insect which are uncommon in the London area

You can get more information on protected sites and species from Natural England.

4.4.2 River Priority Habitats

UK Biodiversity Action Plan Priority Habitats are a range of semi-natural habitat types that were identified as being the most threatened and requiring conservation action. 

See a map of River Priority Habitats around the London catchment. These are river habitats identified as having a high level of naturalness.

The below are some River Priority Habitats within the London ALS: 

• the Cobbins Brook (in AP7 Middle Lee), being an active shingle river habitat
• sections of the River Crane (AP10 and AP11)
• section of the River Wandle (upstream of Wildnerness Island)

Proposed abstraction or impoundment activities that may have a detrimental effect on a River Priority Habitat must include adequate information about the measures proposed to assess and address the risk to ensure protection of the priority habitat in that location. We reserve the right to refuse applications where mitigation measures do not adequately demonstrate protection for these habitats.

4.4.3 Local Wildlife Sites

In addition to the above, Local Wildlife Sites (LWS) are areas identified and selected locally for their nature conservation value. In the Greater London area the Local Authority plans refer to these as Sites of Importance for Nature (SINCs). They are found on both public and private land. A LWS could be a woodland, quiet churchyard, flower-rich roadside verge, hedgerow or a stretch of river. Local authorities seek to protect and enhance LWS at a policy level within their respective local plans. Please consult local authority local plans and development area plans for any specific restrictions on abstractions in place to protect LWS. 

For more information on where LWSs are (and what record centres to contact for data), check the appropriate Local Environmental Record Centre:

• for Essex, Essex Field Club
• for Greater London, Greenspace Information for Greater London
• for Hertfordshire, Herts Environmental Records Centre
• for Surrey, Surrey Biodiversity Information Centre

4.4.4 European eel

European eel are classified as ‘Critically Endangered’ by the IUCN Red List of Threatened Species. As eel are a catadromous fish that migrate to fresh water and complete their lifecycle by entering and moving their way up river catchments, any surface water abstraction points must be screened to prevent glass eel or elver (juvenile eel) being drawn to an intake.

Check the requirements on safe passage for eels.

5. Managing the catchment together

5.1 Action on unsustainable abstraction

Our guidance on managing water abstraction gives details on:

• what an unsustainable abstraction is
• the measures available to resolve environmental issues caused by abstraction

Across the London catchment we are engaged in activities to tackle unsustainable abstraction and to improve flows. These activities include:

• actions under the Water Industry National Environment Programme (WINEP)
• revocations of licences for non-use
• reductions of under-used and unused licenced or permitted abstraction volumes
• changes to permits and time-limited licences where: abstraction quantities are no longer justified – renewal of licence could pose a risk of deterioration in ecological status, and not all sustainability issues in the catchment are resolved

AP1: Hogsmill

The water resource availability colour at Q50 is yellow.

The above licensing resource assessment is based upon the downstream abstraction pressures within River Thames, not at Hogsmill AP, however, there is evidence to suggest that there are flow pressures being experienced in the upper reaches, above AP1, near Ewell and Epsom which supported by chalk-fed baseflow sustaining the headwaters of the Hogsmill. As part of the WINEP, SES Water and Thames Water concluded an investigation into the impacts of water company abstractions on the upper reaches of the Hogsmill River. The options appraisal process identified a programme of works for implementation, including abstraction reduction and river restoration measures.

AP3: Wandle

The water resource availability colour at Q50 is yellow.

Following investigations into the impacts of water company abstraction on the Carshalton and Croydon branches of the River Wandle, Thames Water and SES Water have carried out an appraisal of several options. The implementation of these options is intended to mitigate the impacts on flow and flow-dependent habitat exacerbated by abstraction impacts, by using recirculation, habitat improvement and changes to current structures and operations. SES Water are improving the connectivity of the Wandle at Shepley Mill weir structures alongside other river restoration initiatives. Thames Water are planning to carry out river restoration measures in the Beddington Park area and under separate work they have removed the tilting weir at Goatbridge, improving fish passage and habitat.

AP7, AP8 and AP9: Middle Lee, Lee (Chalk Bridge), and Lower Lee

The water resource availability colour at Q30 is red.

There is an investigation being undertaken by Thames Water Ltd to understand the influence of public water supply abstraction on the Lower Lee river system.

AP10 and AP11: River Crane

The water resource availability colour at Q50 is red and yellow respectively.

The Environment Agency investigated what actions may ensure a more consistent flow in the River Crane, including a review of the operation of Mereway Weir. The hydrological regime for the River Crane is at Does Not Support Good WFD status, which means that there are issues with flow in certain parts of the river. This investigation sought to establish whether flow in the Lower Crane could be improved without negatively impacting the requirements of the Duke of Northumberland’s River (the water in this river is distributed from the River Crane at Mereway Weir). The investigation concluded that flow could be improved in the Lower Crane without significant impact on the Duke of Northumberland’s River. As a result, a fish pass was installed adjacent to Mereway Weir to provide a sweetening flow to the Lower Crane. Analysis of the effectiveness of this fish pass – as well as the exploration of other actions that may improve flow in the Crane – is ongoing.

5.2 Water rights trading

We want to make it easier to trade water rights. A water rights trade is where a person sells all or part of their water right, as defined by their abstraction licences, to another person on a permanent or temporary basis. In many cases a trade will involve a change in abstraction location or use which we will need to approve through the issue or variation of abstraction licences.

In licensing trades, as with new abstraction licences, we need to make sure that we do not cause any deterioration in water body status within the water bodies where the trade will take place and to downstream water bodies.

This section provides a guide to the potential for trading in water bodies of a particular ALS water resource availability colour, as shown on Maps 1 to 4.

Water available for licensing

Green

There may be opportunities to allow trades of recent actual abstraction and licensed abstraction. But little demand for trading is expected as water is available for new abstractions.

Restricted water available for licensing

Yellow

There may be opportunities for licence holders to trade up to their full licensed quantities. But the quantities of water available to trade may be restricted once levels of actual abstraction reach sustainable limits. We will not permit water rights trades in water bodies where we are taking action to prevent deterioration. The exception to this is if the trade is consistent with achieving water body objectives.

Water not available for licensing

Red

We will only trade recent actual abstraction but no increase in recent actual abstraction is permitted in the water body. Licensed abstraction will be recovered for the environment.

To find out more about water rights trading, use our guidance on trading water abstraction rights.

6. Glossary

Abstraction: Removal of water from a source of supply (surface or groundwater).

Abstraction licence: The authorisation granted by the Environment Agency to allow the removal of water.

Assessment point: A significant point on a river, often where two major rivers join or at a gauging station.

Catchment: The area from which precipitation and groundwater will collect and contribute to the flow of a specific river.

Catchment based approach: Partnership working at the river catchment scale to deliver a range of environmental, social, and economic benefits while protecting our precious water environments for the benefit of all.

Chalk: The geological layer of permeable chalk which serves as an aquifer.

Confined Chalk: The geological layer of chalk (which serves as an aquifer) when it lies beneath the layer of impermeable London Clay.

Consumptive abstraction: Abstraction where a proportion of the water is not returned either directly or indirectly to the source of supply after use. For example, for the use of spray irrigation, general agriculture, domestic use, public water supply and water bottling.

Discharge: The release of substances (for example, water, treated sewage effluent) into surface waters.

Environmental flow indicator: Flow indicator to prevent environmental deterioration of rivers, set in line with new UK standards set by UK Technical Advisory Group.

Fluvial geomorphology: An understanding of the processes of water and sediment movement in river catchments and channels, and their floodplains, together with the landforms produced by those processes.

Groundwater: Water that is contained in underground rocks.

Hands off flow: A condition attached to an abstraction licence which states that if flow (in the river) falls below the rate specified on the licence, the abstractor will be required to reduce or stop the abstraction.

Hands off level: A condition attached to an abstraction licence which states that if the water level (in the river or groundwater aquifer) falls below the level specified on the licence, the abstractor will be required to reduce or stop abstraction.

Impoundment: A structure that obstructs or impedes the flow of inland water, such as a dam, weir, or other constructed works.

Non consumptive abstraction: Abstraction where a significant proportion of the water is returned either directly or indirectly to the source of supply after use. For example, for hydropower.

Surface water: This is a general term used to describe all water features such as rivers, streams, springs, ponds, and lakes.

Water body: Units of either surface water or groundwater which we use to assess water availability.

Water Environment (Water Framework Directive) (England and Wales) Regulations 2017 (referred to as the WFD Regulations 2017): Regulations that provide a framework for managing the water environment in England and Wales.