Collaborative provision of a national peak flow data service

High quality and trustworthy data on peak river flows are fundamental for assessing, monitoring, estimating and managing flood events.  In the UK, a national data service provides open access to peak flow data (annual maximum and peaks-over-threshold) with supporting metadata at more than 900 gauging locations.  A collaborative programme of work involves the four main Measurement Authorities (MAs) and the National River Flow Archive (NRFA) which is based at the UK Centre for Ecology & Hydrology (UKCEH).  This partnership and the channelling of peak flow data for the UK through one organisation also promotes sharing of best practice.  Once the data have been generated, they undergo checks by each of the MAs before being sent to UKCEH who undertake a number of complementary automatic and manual quality control checks.  These include the consistency of the data with stage-discharge ratings, the continuity of the digital and pre-digital periods, and the suitability of the data for flood estimation purposes.  Queries that arise during this process are resolved in close collaboration with the MAs.

The data are updated and released annually.  The most recent water year is added to the dataset, and a rolling programme of period-of-record review for a percentage of sites each year captures data reprocessing, newly available data from digitisation and other improvements that have come to light since the initial submission of the data to the central repository.  Following each annual cycle, the data are released in a number of accessible formats, including files which can be loaded directly into the UK’s industry standard Flood Estimation Software (WINFAP), as well as being added to the NRFA website and API.  Each gauging station has a webpage with a wealth of associated metadata and context to aid the community in using the data.

There are however challenges remaining.  These include event independence, concerned with the criteria used to derive peaks-over-threshold data, consolidation of stage-discharge ratings between the MAs and UKCEH, and further digitisation of pre-digital data where physical charts exist.  Running through all of these threads is the quantification of uncertainty in high flow measurement and the challenges in how to communicate this to users.  Initiatives are addressing some of these, but more is needed to ensure that reliable long records are available for reproducible flood estimation and trend analysis.