Hydrological reporting and analysis for hydropower schemes
Why do I need to provide hydrological information?
We need hydrological data to see how much water there is in a catchment where a hydropower scheme is proposed and what impact an abstraction will have on the river environment.
What information should you provide?
If your scheme will be abstracting water in line with our flow standards for Zones 2 and 3 then you will usually only need to provide us with:
- a map of the catchment boundary with catchment size and
- river flow estimates in the form of long-term flow duration statistics for your point of abstraction.
If your scheme is in Zone 1 (affecting sites designated for nature conservation, supporting habitat, protected species or salmon spawning areas) or you are proposing an alternative abstraction regime (because your catchment has complex hydrology or for specific environmental protection, recreation or landscape purposes), then for the point of abstraction and any other river reaches where flow sensitive features are present you will need to provide us with:
- a map of the catchment boundary with catchment size
- natural and influenced residual flow duration statistics
- residual flow calculations
- average and dry year time series hydrographs showing natural and influenced residual flow.
These are to show how river flows will be altered in reaches where flow sensitive features are present. We also require you to provide an environmental report that assesses how changes in river flows may affect protected habitats, features and other relevant points within the depleted reach that are sensitive to changes in flow caused by your proposed abstraction for hydropower.
Sources of hydrological data
Most potential hydropower sites will be ungauged. This means that there are unlikely to be any existing flow measurements in reaches affected by a proposed hydropower scheme.
For small ungauged catchments or larger ungauged catchments with simple hydrology, we will accept estimated flow duration statistics generated from commercially available software.
The most commonly used is the Low Flows package provided by Wallingford HydroSolutions.
For larger and more complex gauged catchments we expect developers to use measured flow data in hydrological analyses to provide flow duration statistics and times series hydrographs. We recommend that you seek advice from an experienced hydrologist to do this.
Where a catchment is ungauged but complex due to factors such as the influence of upstream abstractions, reservoirs, artificial drainage or geology, then you should collect site specific flow measurements to inform a detailed hydrological analysis. We recommend that you seek advice from an experienced hydrologist in these circumstances.