The 'Indicative Suitability' relates only to the quality of flow data at the station, it does not take into account the relevance of catchment descriptors (particularly URBEXT and FARL). Broad guidance in the FEH and subsequent research is to not use stations for transfer of data for QMED if URBEXT is more than 0.025 or FARL is less than 0.95. The actual choice of stations as a donor station for QMED or for a pooling group may also depend on the availability of suitable stations for selection, and hydrologists may have to balance similarity of catchments and flow statistics against quality of flow data. Hence, these comments are indicative, to help hydrologists make their own decisions. Research is ongoing, and users should consider the latest research and guidance.
The original criteria used by the HiFlows-UK project for determining indicative suitabilities was:
- 'Indicative Suitability for QMED': Accept the station if QMED is likely to be within 30% of its true value.
- 'Indicative Suitability for Pooling': Accept the station if either the highest AMAX flow or the 8 year event is likely to be within 30% of its true value.
Recent reviews have modified the criteria for pooling slightly, as follows:
- 'Indicative Suitability for Pooling': Accept the station if AMAX3, or AMAX2 for stations with a record length of less than 13 years, is likely to be within 30% of its true value; assessors must also consider the accuracy of the data at AMAX1. AMAX1 is the highest in the series of annual maxima, AMAX2 the second, AMAX3 the third.
A List of useful definitions are provided as part of the NRFA Glossary here.