For some gauging station additional data series are derived on a routine basis from the core NRFA records. The following flow series are commonly calculated by the NRFA:
Gauged Monthly Flows
The National River Flow Archive is able to calculate monthly mean gauged river flow series for analysis and retrievals. In most cases, the series are not held as a separate dataset but are calculated by taking the mean of all the Gauged Daily Flows in each calendar month. Only complete monthly records are used in the derivation of the monthly mean gauged river flow series.
Users should note that while the majority of station on the NRFA hold Gauged Daily Flow time series, for some stations and some period of records only monthly mean gauged river flow are available. In such cases the NRFA holds these Gauged Monthly Flows as the raw data series. This is of particular relevance when considering early flow records (see Long Hydrometric Records). Monthly average values may also be available in cases where there is missing daily data.
Daily Catchment Runoff
The notional depth of water in millimetres over the catchment equivalent to the daily mean flow as measured at the gauging station. It is computed using the relationship:
Runoff in mm = Mean Flow (m3s-1) x 86.4 / Catchment Area (km2)
Runoff is computed on the basis of naturalised flows for the small minority of catchments where daily naturalised flows are available.
Monthly Catchment Runoff
The notional depth of water in millimetres over the catchment equivalent to the mean flow for the month as measured at the gauging station. It is computed using the relationship:
Runoff in mm = Mean Flow (m3s-1) x 86.4 x n / Catchment Area (km2)
where n is the number of days in the month.
Runoff is computed on the basis of naturalised flows for the small minority of catchments where daily, or monthly, naturalised flows are available.
