How to read the map
Each gauge is coloured by where its level sits against that
gauge's own history, so a small stream and a big river can be
compared. Normal is the agency's typical range for the gauge
(where 90% of readings fall), split at the quartiles where a
long record allows. Very high is at or above the median annual
maximum, a level reached in about half of all years.
View: Rate of rise shows how fast each gauge is rising for
that gauge instead, deeper and larger the faster it rises: a
moderate rise is one it sees in about six events a year, a high
rise about twice a year, a very high rise about once in two
years, over one hour or three. Where a gauge has no 15-minute
record to learn from, the thresholds are estimated from its range.
Hover a gauge for its reading and whether it is rising or
falling; click it for its last two weeks and a link to its
gauge page.
Quality control (on by default) leaves out single readings
that are off on their own and straight back, and marks gauges
whose current reading cannot be trusted (stuck, impossible,
on a different datum, or an unconfirmed sudden jump) as check
data: small, grey and left out of the lists. Tidal gauges, and
river gauges the tide reaches (whose level at high water says
more about the tide than the river), are drawn square and shown
with the Tidal switch. Sluices, pumping stations and reservoirs
are in the options. All readings are the
agencies' provisional real-time data and can be revised.
Catchments
Catchments are shaded by how the whole river system is
responding, not by its highest gauge: each gauge's level (or
flow, where it is rated) is placed on its own scale, from 1 at
its median to 2 at the top of its normal range and 3 at its
median annual maximum, and the catchment's index is the average
of them, with larger rivers counting for more. Click one for how
many gauges are high, the highest of them and its last two weeks.
England: Environment Agency flood and river level data from the real-time data API (Beta), and the Hydrology API, Open Government Licence
Wales: Contains Natural Resources Wales information © Natural Resources Wales and Database Right. All rights Reserved. Open Government Licence for Public Sector Information
Scotland: Contains SEPA data © Scottish Environment Protection Agency, Open Government Licence
Rivers: OS Open Rivers - contains OS data © Crown copyright and database right
Boundaries: ONS, Open Government Licence v3.0
Basemap: © OpenStreetMap contributors © CARTO
Catchments: National River Flow Archive (2014). Hydrometric areas for Great Britain and Northern Ireland. NERC-Environmental Information Data Centre doi:10.5285/1957166d-7523-44f4-b279-aa5314163237