Hydrological information

The information required by SEPA on river flows is summarised in the table below. Where one of a number of the different flow information requirements may apply, please contact us to determine which is applicable.

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

  • the river flow information collected will be sufficient for our purposes;
  • the applicant's assessment of the flow duration curve for the river is consistent with ours;
  • any relevant flow data we hold can be made available to the applicant to help them assess the resource available.

Table 3: River flow information requirements

Distance measured along the middle of the river channel between the intake structure and the outfall (metres)

Installed capacity (kW)

<15

15 to <100

 100 to <500

>500

<100

A

B

B - C

C - D

100 to <500

A

B - C

C - D

D

500 to <1500

B

B - D

C - E

D - E

≥1500

B

B - D

D - E

D - E

Key to different flow information requirements:

A.  Supporting photographs of indicative flows and measurements of channel width and depth in metres.

B.  Single or multiple measurement of flow – simplified method of measurement (see Annex A).

C.  Single or multiple measurements of flow – use of flow measurement devices (see SEPA guidance ‘WAT-SG-54 Water resource for technical guidance on flow measurement’)

D.  Short periods of logged level data calibrated to flow. 

E.  One year or more of logged data calibrated to flow.
  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. Within the ranges of flows and impacted reaches the level of detail required should be proportionate to the scale of the scheme and the environmental risk.

Please note: Where requirements fall into more than one category, please contact SEPA to find out which is required. The type of measurement will depend on the site location.

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 an applicant has undertaken flow modelling, we will need this to be submitted in support of the application.

Further technical guidance on how this information should be collected is available in Annex A of the Guidance for applicants on supporting information requirements for hydropower applications.

Part 1 of Annex A provides additional background details and guidance on the different flow information requirements. Part 3 of Annex A shows how the hydrological information supplied by the developer is used in defining the mechanisms for protecting the water environment between the intake and the tailrace of the turbine house. This mitigation has to take into consideration both the needs of the aquatic ecology and the water use by third parties.