Extreme wave conditions within the SCOPAC region

The investigation into extreme wave conditions in the SCOPAC region by Professor Andy Bradbury is now largely complete.   

Key conclusions suggest that the central south coast is regularly subject to conditions that are not generally considered in scheme design. Current scheme design does not account for bi-modal conditions, where there is a combination of not only wind waves but swell waves also.  The implication is that greater overtopping and wave run-up on beaches might be expected than traditional design advice might suggest.

Consequently defences in most of the SCOPAC region are not designed to a high enough standard.  Most of the Solent shoreline is unaffected by these conditions as it is protected by the Isle of Wight from swell waves, until you reach Hayling Island where the bi-modal conditions are present.

The conclusions support the need for a change in the design approach where these conditions are present. This is likely to take several years and considerable additional (national) funding to deal with.  

As an interim measure, steps have been taken to modify the CCO website to identify these conditions routinely in real time; follow this link to view data from one of the buoys.

A screenshot from the CCO website

All wavebuoy sites are now enabled with this technology and can be accessed via the realtime wave pages.  This will at least allow partners to identify such conditions in a simple manner. 

This is realistically as much as this project can expect to deliver. The next step is to provide a series of trigger levels which can provide text or email alerts when these conditions occur.

The problem arising from the research conclusions has already been highlighted to the EA Sustainable Asset Management Theme Advisory Research Group (SAMTAG), to a workshop for the EA flood forecasters, and a section of the new CIRIA Beach Management Manual now includes a reference to it.

Some very senior UK coastal engineers have considered this to be a major issue, suggesting that it should be dealt with as a nationally funded EA research project in the “must do” category.  A detailed proposal must now be prepared, but it seems likely that a national programme will emerge from this project.

This is exactly what we had hoped for and demonstrates once again how valuable both the regional coastal monitoring programme and the SCOPAC research programmes are.

The ACCESS project is essentially investigating methods associated with effectively quantifying ‘Assets at risk along the SCOPAC coastline’.

There is a need for more refined assessments to be made of the methodologies currently applied in Shoreline Management Plans and Flood and Coastal Erosion Risk Management Strategies to ascertain coastal erosion risk and identify and value the assets at risk, looking ahead over the next one hundred years. 

The greater the erosion risk to property, the more likely the frontage will obtain the benefit-cost ratio required to achieve a Hold The Line policy, thereby potentially attracting funding for future works.  Still, if methods are under- or indeed over-predicting erosion then there could be significant implications for future policy setting and central government funding distribution.

Coastal and Geotechnical Services, Halcrow and the Channel Coastal Observatory (CCO) are undertaking the work for this project. 

As an introduction to the project, the CCO used a coarse method to identify “hotspots” across the SCOPAC region where more than 40 properties are at risk from erosion and/or flooding within Shoreline Management Plan “Management Unit” boundaries over the next 100 years - see Figure 1 below:

Click on Figure 1 to view an enlarged version

With a focus on sites under threat from instability, erosion and erosion followed by flooding, case studies for each geomorphology type were selected from the list of hotspots, ensuring a variety of examples were taken from across the SCOPAC region.  These include the following case studies identified in the Figure 2 below:

Click on Figure 2 to view an enlarged version

The ACCESS project team are planning to print the document in the Autumn of 2011 and hold a launch event at the National Oceanography Centre inviting Councillors, planners and consultants.

Eastoke deployment 1 -  results to date

On Hayling Island, 10% of the original batch of 300 tracers deployed in September 2010 were detected in June 2011 after 9 months active in the beach. The tracers have moved west between 25 and 1900 metres and continue to move in a westerly direction towards the Langstone Harbour entrance channel.

Eastoke deployment 2 - results to date

Of the 1,000 tracers deployed immediately after the 2011 beach recycling operation at Eastoke, 24% were detected after nearly three months active in the beach.  The tracers remain largely on the nourished frontage, and are following the anticipated pattern of sediment transport. The tracers deployed at the drift divide have dispersed in both directions along the nourished frontage but the centre of the mass of tracers remains near the deployment location, whereas the batches placed further away from the drift divide show a clearer pattern of movement downdrift in both directions.

2010/2011

Professor A Bradbury/Channel Coast Observatory £2,500 (2010/11) and £15,500 (2011/12)