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SUMMARY This report presents an up-to-date review of the British Isles (BI) Mean Sea Level (MSL) data set obtained from tide gauges, and of the long-term secular trends in BI MSL. The data are of mixed quality, and not as copious as one would like for scientific analysis given the complexity of long-term sea and land level changes around BI coasts. Nevertheless, the small number of very long records can be studied eVectively, and indicate that twentieth century secular trends in BI MSL are consistent with those obtained from NW Europe as a whole and with the bottom range of estimates for global average MSL change during the past 100 years. Century-timescale low-frequency ‘accelerations’ in MSL of the order of 0.4‐0.8 mm yr’1 century’1 are obtained from the three longest records, which are also similar to estimates from mainland Europe. ‘Sea level indices’ for the BI are constructed which can provide responsible agencies with a guide to the ‘average state’ of BI sea level. Combined ocean tide and storm surge (‘tide+surge’) numerical modelling is demonstrated to be a valuable tool in understanding part of the variability of MSL around the BI, although modelling of long-term changes is limited at present by the lack of adequate meteorological data sets from before 1955. Nevertheless, it is shown that, even if a complete meteorological modelling data set were available, it would not be able to account for all of the MSL variability. Finally, recommendations are made for the development of tide gauge and Global Positioning System (GPS) recording in the BI for the purpose of long-term MSL monitoring in the next century.

The study of the foreshore is of considerable interest to the environmental science community, and the advent of regular SAR imagery from the ERS, Radarsat and JERS satellites has offered the opportunity to monitor continuously this dynamic region. Knowledge of foreshore topography is of use in improving flood prediction models, measuring sediment flux, and assessing the effectiveness of sea defences. Conventional surveying is the expensive, time consuming and often hazardous current technique often employed to obtain these data. The alternative technique presented here involves a semi-automatic process to delineate the shoreline on a number of ERS SAR images, and a model to calculate the sea heights at the time the images were taken. By combining these data a set of quasi-contours is generated, and from these it is possible to devise a digital elevation model of the foreshore. Each of these quasi-contours is associated with the time its image was taken, and it is therefore necessary to interpolate in time and space. Such interpolation allows the creation of time- dependent DEMs which can be used to study the long-term evolution of the foreshore. This paper demonstrates the technique by following its application to the length of UK coastline of most interest to the NERC Land-Ocean Interaction Study Community Programme, the 100km from the Humber estuary to the Wash. The INDUS project funded under the British National Space Centre Earth Observation LINK scheme is further refining the accuracy of the technique and extending its application to cover more of the coastal regions of the UK, as well as establishing the requirements of users.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A test of a storm surge model using the shallow water equations is presented. The model is designed to be run using CMC (Canadian Meteorological Centre) prognostic data. The model incorporates a quadratic bottom friction term and is capable of including advective, topographic and tidal effects. It can simulate a moving land‐sea boundary approximately. The model is applied to the east coast of Nova Scotia for the “Ground Hog Day” storm of February 1976. Meteorological forcing is calculated using subjectively analysed sea‐level pressures. Away from open boundaries, the agreement with observed surge residuals is generally good. However, the results are less satisfactory near the boundaries. CMC meteorological data are found to underestimate the surface wind stress during this period.

Still-water level and currents are important parameters for the design and operation of offshore structures (Marty and Eggar, 1983; Prior-Jones, 1983). Still-water level (swl), due to tide and surge, is required for water depth and deck clearance (‘air gap’) studies, and it also determines the level of attack of waves on the structure. Currents contribute to the forces on the structure and may be as important as waves in coastal regions where wave heights tend to decrease (due to depth-limiting) and tidal currents are strong.