Lesley Rickards, British Oceanographic Data Centre, UK

The UK permanent tide gauge network was set up as a result of severe flooding along the east coast of England in 1953. The network comprises 43 gauges (see table) related through the national levelling network to Ordnance Datum Newlyn. Data are collected, processed and banked centrally by the Proudman Oceanographic Laboratory (POL) to provide long time series of reliable and accurate sea levels. The data are used for tidal analysis and prediction, oceanographic research, coastal defence and storm surge warning systems.

The Tide Gauge Inspectorate based at POL is responsible for the operation, maintenance and development of the tide gauge network. With the need to improve data acquisition and the ability to identify and respond to faults in the network, a centralised data collection and monitoring system was designed and developed called DATARING (Data Acquisition for Tidal Applications by the Remote Interrogation of Network Gauges). This is an interactive data logging and transmission system which uses the public switched telephone network for communication. A microprocessor controls the processing, storage and transmission of data at the remote site. Data are normally supplied from at least two independent sea level sensors and are processed and stored in buffer memories. These can be interrogated, and the stored data rapidly transferred to a computer at POL for subsequent processing. Any problems arising at the remote sites can therefore be quickly identified by the interrogating computer and appropriate action taken to minimise data loss.

The Storm Tide Warning Service at the Meteorological Office, Bracknell, has access to the tide gauge network through DATARING. However, it additionally requires continuous, real-time transmission at the four most critical stations on the east coast to monitor tidal levels in the North Sea. A system called DATAFLOW (Direct Acquisition of Tidal Amplitudes for Flood Level and Overflow Warnings) was therefore developed to transmit data along dedicated telephone lines to the Meteorological Office where they are compared with predictions in real-time.

The British Oceanographic Data Centre (BODC) has a special responsibility on behalf of POL for the remote monitoring and retrieval of quarter hourly sea level data from the National Tide Gauge Network. Daily checks are kept on the performance of the gauges and the data are downloaded weekly. These are then routinely processed and quality controlled prior to being made available for scientific use. Data from 1993 onwards have been processed using the BODC in-house EDTEVA software, and are readily available. The situation with older data is more varied, for some sites, the data have been reviewed and are available from the BODC databank. For others, work is still necessary to reformat from old data formats used on previous computers, visually inspect data, compile benchmark details, and check datum information. The attached table shows the sites which comprise the UK national network, and the time periods where data have been collected.

In addition to maintaining a databank of the 15 minutes values, several databases are available containing information about surges, maximum and minimum levels, mean sea levels, etc.

Data from the three GLOSS sites on the network, Newlyn (241), Stornoway (238) and Lerwick (236) are available online from the POL/BODC Web pages. These data are also included on the WOCE Sea Level CD-ROM. Each month, these data are also passed on to the WOCE ‘fast-delivery’ Data Assembly Centre.

Recently information about the UK national network tide gauges has been passed on to the EU COST project, EOSS (European Sea Level Observing Programme). EOSS is concerned with the establishment of a European Sea Level Network, and a questionnaire was distributed to determine the sea level measurements currently made across Europe and also to establish the various agencies requirements for sea level data. In addition, EOSS should allow agencies to co-operate more fully in the exchange of data. The information supplied to EOSS includes details of the tide gauges, what parameters are measured, benchmark and levelling details, details of GPS measurements at tide gauge sites, photographs of gauges/benchmarks, sketch maps showing the locations of gauges and benchmarks. This will soon be available on the Web.