Statutory guidance

Appendix 1: Hydroelectric power water abstraction levels

Updated 10 April 2024

Applies to England

• Publication for Northern Ireland
• Publication for Scotland
• Publication for Wales

You will need to apply for a licence to authorise the amount of water you can use for your hydropower scheme.

Abstraction licensing is based on the abstraction licensing strategies (catchment abstraction management strategy process). Abstraction licensing strategies (ALS) use the environmental flow indicator to indicate where and when water is available for new abstractions. It sets different percentages of flow that can be abstracted, depending on the sensitivity of an area to abstraction.

The Environment Agency has assigned each water body in England to an abstraction sensitivity band (ASB):

• high (ASB3)
• medium (ASB2)
• low (ASB1)

The amount of water you can use for your hydropower scheme depends on the ASB assigned to your site. You will be allowed to abstract more water at sites with lower sensitivity and less in highly sensitive areas.

In licensing hydropower schemes, the Environment Agency will normally agree:

• a maximum flow (Qmax)
• a minimum flow, the hands off flow (HOF)
• the volume of water you can divert to a turbine

1. What you need to do

Use this guidance to understand the:

• default design flows set for hydropower schemes
• situations where schemes may apply for more water

Ask your permitting officer for details of the ASB that will apply to your scheme.

To confirm that the level of abstraction you are applying for will not damage the environment, including fish and eel populations, you must:

• carry out an environmental assessment
• provide an environmental report

Provide hydrological information in your application for an abstraction (full or transfer) licence or impoundment licence to tell us:

• the amount of water you propose to abstract
• how you will control your abstraction
• any mitigation measures that are part of your operating regime

2. Flows for hydropower schemes

Table A gives the Environment Agency’s starting point for flow management for hydropower schemes. They will start with these flow allocations for all schemes, although they will consider applications for higher levels of abstraction. However, they may also need to set a more protective flow if:

• your scheme could affect a weir pool that is highly important to the status of the water body or wider catchment
• reducing flow is likely to have an impact on fish passage

2.1 Table A: design flows for hydropower schemes

Water body type	Q95 ÷ Qmean value	HOF	Maximum abstraction	Percentage take above HOF
High sensitivity ASB3: Low or medium base flow	Below 0.2	Q95	1.3 × Qmean	35%
High sensitivity ASB3: High base flow	0.2 and above	Q97	Qmean	35%
Medium sensitivity ASB2: Low or medium base flow	Below 0.2	Q95	1.3 × Qmean	40%
Medium sensitivity ASB2: High base flow	0.2 and above	Q97	1.3 × Qmean	40%
Low sensitivity ASB1: Low or medium base flow	Below 0.2	Q95	1.3 × Qmean	45%
Low sensitivity ASB1: High base flow	0.2 and above	Q97	1.3 × Qmean	45%

3. Applying for higher levels of abstraction

If you wish to apply for higher levels of abstraction than those shown in table A, you will need to provide supporting evidence in your environmental report to prove that your scheme will:

• not prevent the achievement of Water Framework Directive objectives at water body level
• maintain or improve fisheries and fish passage
• not have unacceptable impacts on protected sites or species
• not have unacceptable impacts on the rights of other water users, including anglers

The amount of additional flow we may allow above the design flows in Table A will depend on:

• the potential risk to the environment
• the mitigation measures you propose to avoid environmental damage

Examples of mitigation measures include:

• increasing the HOF
• reducing the maximum abstraction level or the percentage abstraction above HOF
• seasonal variations in abstractions
• actively managing the abstraction to maintain flow variability

The following sections show the other levels of abstraction that the Environment Agency may license for different types of scheme. They assess applications individually – the examples are only indicative.

4. On or around weir

These are schemes with turbines sited at or alongside an existing weir where there will be no significant flow depletion within the natural watercourse. These schemes discharge water back into the weir pool. Based on your environmental assessment and any mitigation measures you propose, the Environment Agency may allow abstraction as shown in table B.

4.1 Table B: hydropower schemes at an existing weir (indicative departures from table A)

HOF	Maximum abstraction	Percentage take above HOF
Q95 (or Q97 for very high base flow rivers)	1.3 × Qmean	100%

5. Low head with depleted reach

Diverting water away from the natural river channel may introduce risks for fish passage and ecological connectivity, as well as changing sediment transport. The risks are also higher where:

• the depleted reach contains ecologically and environmentally sensitive features
• you want to take more flow for longer periods of time

Based on your environmental assessment and any mitigation measures you propose, the Environment Agency may allow abstraction as shown in table C.

5.1 Table C: low head with depleted reach (indicative departures from table A)

Base flow type	Q95 ÷ Qmean value	HOF	Maximum abstraction	Percentage take above HOF
Flashy river: fish migration issues	Less than 0.1	Q90	Q40	100%
Flashy river: no fish migration issues	Less than 0.1	Q90	Qmean	100%
Medium base flow	Between 0.1 and 0.2	Q95	Qmean	100%
High or very high base flow	0.2 or more	Q95	Qmean	100%

6. High head

These schemes can create long depleted reaches which increase the risk of environmental deterioration at water body level. The Environment Agency is more likely to agree higher levels of abstraction for hydropower in steep, upland tributaries of low ecological sensitivity with no migratory fish. In less steep or more ecologically sensitive rivers, there is likely to be less scope for departures from the table A values.

Based on your environmental assessment and any mitigation measures you propose, the Environment Agency may allow abstraction as shown in table D.

6.1 Table D: high head schemes (indicative departures from table A)

HOF	Maximum abstraction	Percentage take above HOF
Q95 (Q90 for sites where the wetted area is significantly reduced at flows below Q90)	1.3 × Qmean	Where necessary, maintain the ratio of the downstream (depleted reach) to the upstream flows at the ratio of at least Q80 to Qmean. The flow split can be calculated using the formula: Flow split % = (1 − (Q80/Qmean)) × 100

7. Applying for flow above ‘indicative’ departures

For levels of abstraction outside this guidance, the Environment Agency will consider applications individually, assessing the:

• evidence provided in the application
• environmental sensitivities of the site

8. More information

Use the guidance on new hydropower schemes for more information on:

• the licences and permits you need
• the documents you must prepare
• how to apply to build a hydropower scheme