Coastal Management, erosion, flooding and pollution
Coastal management has always been an important activity and is increasingly so as more people live in coastal areas world-wide. It may cover many activities including monitoring and management of flooding, erosion and pollution. WAVENET is a project commissioned by the UK Government that is provding a near shore wave-monitoring network for England and Wales to improve forecasts and management of coastal flooding and erosion risk. As part of this project the Met Office conducted a trial of an HF radar system to evaluate the usefulness of the technology, which has already demonstrated many advantages over traditional wave buoy and satellite measurements. The system chosen by the Met Office was a pair of Pisces Radars and Seaview Realtime Software, which were installed between 2003 to 2005 in southwest Britain overlooking the Celtic Sea.
This large-scale continuous monitoring of wave characteristics will produce a near shore wave climatology to help improve understanding of coastal erosion risk and the design of coastal erosion defence works. It is planned that the data will be used by Flood Managers, Local Authorities, Consultants and other stakeholders in order to assess flood risk and on a longer timescale will be to help design improved flood defence schemes and to provide data for climate change studies.
In Oct 2004 a storm approached the southwest of the UK, The Guardian newspaper recorded the storm (Thursday October 28, 2004) "Coastline lashed by huge waves. Storms pounded Britain last night. An Irish Ferries vessel arrived at Pembroke dock in west Wales at about 2.30pm, but the captain decided conditions were too risky to dock. The Met Office said the winds were expected to peak last night and were not remarkable, but, combined with high seas, they were a potential danger."
Meanwhile on the north coast of Devon and the south coast of Wales, at Castlemartin not far from Pembroke Dock, the two Pisces radars were being used to monitor waves, currents and winds in the Celtic Sea. The maps here show wind, current and wave conditions near the peak of the storm in the early hours of the 28th contrasted with the situation a day earlier. The combination of high tide, high waveheight and strong winds all directed.
Current map Waveheight map/strong Wind map
Figure 1. Top panel shows measurements from 4am 27/10/2004 when winds and waveheights are low, currents are onshore. Middle panels are for 4–5am on 28th when currents are again onshore but much stronger and bottom panel is for 6am when the tide has turned the currents to a more offshore direction.
In Figure 2 the time series of wave, current and wind at one of the mapped locations are shown for a period of nine days including the storm period of interest at the end. The storm events preceding the 26th October had similar winds and waveheights both directed onshore. But, fortunately for the people in coastal communities in South Wales, this period was during neap tides so although onshore wind-driven currents were significantly enhanced (with maxima similar to spring tide levels) they were not as high as on the second period, the 'headline' storm, which was during spring tides.
Figure 2. Time series during storm events in October 2004.
Note that the problems experienced by the ferry were probably associated with the high waves propagating across the entrance to Milford Haven opposing the tidal current rather than any problems associated with the surge which occurred 12 hours later. Without real-time information of co-occurring wave, wind and current events the risk may not have been anticipated.
The attached table is an indication of how the data might be used to issue potential flood alerts. Each row in the data is one hour's measurement at one location. Similar data would be available at all measurement locations (and at more frequent intervals if digital beam-forming were used). This data could be distributed in real-time on our web site, via email or text message. The status indicators are derived by looking at all the components of a storm surge: wind, wave, current, with a red alert given when all combine to drive water onshore.
A wave buoy was operational in the region during this period and measured similar wave parameters but does not provide wind and surface current data. Data from the UK Met Office operational wave and storm surge models were available for this period but only six-hourly (thus missing the key 4–5am period) and providing only depth averaged currents. There is evidence from earlier comparisons that these currents do not adequately describe wind generated currents near the surface. The Met Office 3D operational model is of course better for near surface currents but limited comparisons for an earlier period suggest that it still underestimates the wind impact.
|Wind direction||Wind speed||Current direction||Current speed||Wave height||Wave direction||Devon status||Wales status|
|27/10/2004||8:10||-66.06||10.27||-80.56||0.65||no wave data at this time||GREEN||GREEN|
|28/10/2004||7:10||7.34||16.09||-41.18||0.65||no wave data at this time||GREEN||GREEN|
|28/10/2004||8:10||8.51||14.91||-65.23||0.65||no wave data at this time||GREEN||GREEN|
|28/10/2004||15:10||-21.78||17.50||60.25||0.53||no wave data at this time||GREEN||GREEN|