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Hydrological information

The river flow information required by SEPA is summarised in Table 3, below. Where more than one flow information requirement may apply, please contact us to determine which is applicable.  

The flow information supplied must be sufficient to give us confidence in the accuracy of our calculated flow duration curve for the river. We therefore recommend that you contact us at an early stage in the scheme design, so that:

  • the river flow information collected will be sufficient for our purposes;
  • your assessment of the flow duration curve for the river is consistent with ours; and
  • you are provided with any relevant flow data we hold, to help you assess the available resource.

Table 3: Hydrological information requirements


River Waterbody Status

Scale of impact* 
<500m or <0.35GWh per annum 500m - 1500m >1500m
High status A B B
Less than high status A A B

*impact is expressed as the length of river between the abstraction point and return, or the annual generating capacity of the scheme

Key to different flow information requirements:  

A: LowFlows software estimate (subject to note 3);

B: Licence application requires a minimum of 1 year of monitoring data.

For schemes which fall into category B, and where the applicant does not submit the required flow data, SEPA may choose to determine the application using the LowFlows software and apply precautionary limits when setting mitigation conditions in any licence granted. These precautionary limits are summarised in table 4, below).

Table 4: Precautionary limits

Mitigation flow usually required (percentile)

Precautionary LFE flow to be applied in the absence of flow data










  1. Where there is more than one intake, the distance between the intakes and the turbine tailrace will include the relevant lengths of each tributary. SEPA will accept distances measured using 1:25,000 Ordnance Survey maps, referring to grid references for intakes and tailrace.  
  2. Contact your local SEPA office or for advice on the status of a river water body.

  3. Sites that contain important bryophyte communities, are within or connected to a protected area with water dependent interests, or which are subject to third party interests may require site-specific monitoring. In such cases SEPA should be consulted to determine the flow data required.  

We will not need the information on river flows specified in Table 3 where the applicant has an appropriately located gauging station that provides river flow measurements. Where you have undertaken flow modelling, we will need this to be submitted in support of the application.

For further technical guidance on how this information should be collected, consult Annex A of the ‘Guidance for applicants on supporting information requirements for hydropower applications’.