Data collection
River level data is collected at gauging stations using a
variety of electronic sensors that measure the level of the water.
In the majority of cases, river levels are measured using a shaft
encoder driven by a float and counterweight arrangement. Pressure
sensors that translate water pressure into level are also used.
Rapid fluctuations in water level caused by surface waves are
dampened by placing the level sensor in a stilling well.
Information from the sensor is stored on a data logger, usually at
15 minute intervals. The data loggers are connected to the
telephone network, enabling SEPA to collect the data via a
telemetry system. Most stations are automatically downloaded and
the data is archived once a day.
Once collected from the gauging stations, the unverified data is
exported automatically to the SEPA web site. Occasionally, data for
a site may be unavailable or incorrect. This is generally caused by
a failure in the telephone network, an instrumentation fault or a
failure in SEPA's computer systems. Problems will generally be
resolved within a period of a single day up to a week, depending on
the nature of the problem.
The website updates six times during the day to allow for failed
transmissions – data may therefore be briefly unavailable during
these times.