Programme design

A wide range of coastal process data is needed for shoreline management. Ideally, regular surveys of the various variables should be conducted at consistent (dense) spatial and (frequent) temporal scales. This idealistic approach cannot be sustained or justified financially however, and a reasoned method of sampling must be designed to provide best value for money.

The survey programme has been designed on a risk basis, developed from a conceptual model of data requirements. More data is generally required at those sites that are most vulnerable or heavily managed. Although the spatial and temporal coverage of data collection varies across the region, the risk-based approach has been applied consistently across the region.

The risk categories considered in programme design are:

• Exposure to wave attack
• Vulnerability to flooding
• Management strategy
• Coastal geomorphology and geology
• Defence type
• Application of GIS to development of risk model
• Limitations of risk model

Each of the risk categories has been considered separately, before drawing the data together within a weighted risk model. Extensive use has been made of a review of existing local and long-term programmes, to determine weightings. The well-developed programmes have been fine-tuned over a period of many years and demonstrate best value through their long-term development and use of the data in practical management of the coast. Particularly good examples of best-practice data collection and analysis have been demonstrated by Bournemouth BC, Canterbury CC and New Forest DC, over many years.

The basic risk assessment model is very simple, but provides a clear separation of management risks and the relative need for monitoring at different sites. When considered together, the risk categories can be analysed in various combinations to determine those types of frontage where monitoring is most needed. A weighted approach, based upon the numerical indices derived for each category, was used to determine the most effective programme. Thresholds have been determined for each index category, and the required level of monitoring defined. The model has been validated against the existing long-term local programmes. The programme has been further refined by consultation with each of the programme partners. Very few changes have been made to the original estimate and the approach also seems to tie up well with the historical approach to monitoring at the well-established programme sites.

Descriptive examples of outputs of the risk-based approach are shown below.

Exposed sites with active beach management and vulnerable features e.g. Medmerry (Sussex) shingle beach may require frequent and intensive monitoring. Low exposure, hard-cliff sites, with a do-nothing strategy e.g. Beachy Head (Sussex) need less intensive coverage, but some strategic data is needed to support other down-drift sites within the process unit e.g. Eastbourne (Sussex). Bathymetric surveys may be needed annually in areas of low tidal range and active submerged surficial sediments e.g. Bournemouth (Dorset), whilst areas that have a beach toe that dries at low water on a hard rock platform e.g. Hythe (Kent) will not benefit from frequent bathymetric surveys. Each site has been reviewed on the basis of exposure and the general dynamics of the local system.