Coastal Wave Network Annual Report Tr 19
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Southeast and Southwest Strategic Regional Coastal Monitoring Programmes COASTAL WAVE NETWORK ANNUAL REPORT 2007 TR 19 01 April 2008 Annual Wave Report 2007 Channel Coastal Observatory National Oceanography Centre European Way Southampton SO14 3ZH Tel: +44 (0)23 8059 8467 Fax: +44 (0)2380 596320 e-mail: [email protected] Web site: www.channelcoast.org Document Title: Coastal Wave Network Annual Report 2007 Reference: TR 19 Status: Final Date: 1 April 2008 Project Name: Southeast and Southwest Strategic Regional Coastal Monitoring Programmes Authors: T. Mason & T. Poate Approved By: A. P. Bradbury Cover photograph by kind permission of EMU Limited Directional Waverider Mk III at West Bay, May 2007 Copyright: EMU Limited Annual Wave Report 2007 Strategic Regional Coastal Monitoring Programmes of England Coastal Wave Network Annual Report 2007 Contents 1. Introduction................................................................................................................. 2 2. Locations .................................................................................................................... 2 3. Instrumentation and data transfer ............................................................................... 3 4. Data recovery rates .................................................................................................... 4 5. Quality Control Procedures......................................................................................... 5 6. Data availability........................................................................................................... 5 7. Site Reports................................................................................................................ 5 Herne Bay ................................................................................................................... 6 Deal Pier.................................................................................................................... 13 Folkestone................................................................................................................. 20 Pevensey Bay ........................................................................................................... 28 Rustington ................................................................................................................. 36 Hayling Island............................................................................................................ 44 Sandown Bay ............................................................................................................ 52 Sandown Pier............................................................................................................ 60 Milford-on-Sea........................................................................................................... 67 Boscombe ................................................................................................................. 75 Swanage Pier............................................................................................................ 83 Weymouth ................................................................................................................. 90 Chesil ........................................................................................................................ 98 West Bay................................................................................................................. 106 Start Bay.................................................................................................................. 113 Penzance ................................................................................................................ 120 Perranporth ............................................................................................................. 127 Minehead................................................................................................................. 134 1 Annual Wave Report 2007 1. Introduction The Strategic Regional Coastal Monitoring Programmes of England have developed a coastal wave network which concentrates on measurements in shallow water where, traditionally, there are very few long-term wave data and where the wave transformation models are generally least reliable. The principle aims of the coastal wave network are to: • generate characteristic nearshore wave climates for design of coastal defences • validate numerical wave transformation models, notably in areas of irregular bathymetry • evaluate the performance of existing beach management schemes A further aim has been to make the measured wave parameters freely and easily available to other users, both in real-time and as quality-controlled archive data. This annual report contains the results of the statistical analysis of quality-controlled data for 2007. 2. Locations The location of the wave measuring sites is shown in Figure 1, with further details in Table 1. The wave buoys are deployed in approximately 10-12m CD water depth There are also four inshore installations, measuring waves in less than 5m water depth. Figure 1 Location of wave measuring sites Approx. Water First Key Site Instrument type Distance depth deployed offshore (km) A Herne Bay Step gauge 0.5m 1 1996 B Deal Pier WaveRadar Rex - - 2005 C Folkestone Directional waverider 12.7 CD 1.5 2003 D Pevensey Bay Directional waverider 9.8 CD 5 2003 E Rustington Directional waverider 9.9 CD 8 2003 F Hayling Island Directional waverider 10.2 CD 7.5 2003 G Sandown Bay Directional waverider 10.7 CD 1.5 2003 H Sandown Pier WaveRadar Rex - - 2006 I Milford-on-Sea Directional waverider 10.0 CD 1.6 1996 2 Annual Wave Report 2007 Approx. Water First Key Site Instrument type Distance depth deployed offshore (km) J Boscombe Directional waverider 10.4 CD 1 2003 K Swanage Pier WaveRadar Rex - - 2007 L Weymouth Directional waverider ~10 CD 1.6 2006 M Chesil Directional waverider ~10 CD 0.5 2006 N West Bay Directional waverider ~10 CD 1.3 2006 O Start Bay Directional waverider ~10 CD 1.6 2007 P Penzance Directional waverider 10.4 CD 1.6 2007 Q Perranporth Directional waverider ~10 CD 1.2 2006 R Minehead Directional waverider ~10 CD 1.3 2006 Table 1 Instrument type and location 3. Instrumentation and data transfer a. Directional wave buoys The wave buoys in the Coastal Wave Network are Directional Waveriders (DWR) Mk III, manufactured by Datawell (Figure 2). They are moored using Datawell’s shallow water mooring, which consists of 2 x 15m bungees buoyed at each section. GPS positions are received by a top-mounted antenna. Sampling rate on the buoy is 3.84Hz. Data are then filtered and down- sampled to 1.28Hz for transmission to the shore station by HF radio link. Figure 2 Wave parameters are calculated Directional Waverider Mk III prior to from the data received at the shore deployment at Minehead (above); station and are derived over a 30 and deployed off West Bay (right). minute sampling period, every 30 Photos courtesy of EMU Ltd) minutes. Processed parameters and directional spectra are transferred from the shore station in near real-time to the Channel Coastal Observatory website for display. An automatic watch is kept on the GPS position, with an alert if the buoy moves outside its watch radius. b. Wave Radar The wave radars are WaveRadar Rex, manufactured by Rosemount (Figure 3). They are downward-looking microwave radars which measure distance to the sea surface. Burst sampling at the Coastal Wave Network radar sites is at 4Hz for ~17.6 minutes, every 20 minutes. Figure 3 WaveRadar Rex, deployed on Swanage Pier 3 Annual Wave Report 2007 c. Step Gauge The Etrometa step gauge at Herne Bay was first deployed in 1996 and has been in near-continuous operation since then. Burst sampling is at 2.56Hz for 20 minutes, every 20 minutes. At present, the Etrometa logging software cannot operate on a Windows-type computer and therefore the wave data are not transmitted to the website. d. Pressure sensor Waves in the Solent are measured using a modified Valeport 730D pressure sensor, mounted on the Royal Lymington Yacht Club Starting Platform. Wave parameters are measured hourly; sampling frequency is 2Hz, over ~17.6 minutes, starting on the hour. The sensor at Lymington was replaced with an Etrometa step gauge in May 2007. e. Data transfer All data from all instruments are time stamped by the shore station computer and the computer clocks are rigorously checked for drift and reset if necessary. Wave parameters can, therefore, be considered as synchronous across all the instrument types and sites. Data are then transmitted to the Channel Coastal Observatory website’s real-time displays. No quality-control is performed on the data displayed on the website, other than flagging for out-of-range values. 4. Data recovery rates The monthly data recovery rates for 2007 are shown in Figure 4, with the annual data recovery rate since first deployed in Figure 5. Figure 4 Monthly recovery rates for 2007 4 Annual Wave Report 2007 Figure 5 Annual recovery rates for 2004 to 2007 5. Quality Control Procedures Archived data are quality controlled for spikes, jumps and out-of-range data, and the thresholds for the spikes etc. are similar to those applied to the WaveNet buoys. No data are removed, but a column of data flags is inserted into the monthly or annual file of parameters. Full details about the flag are contained in the metadata form attached to the archived data parameters. 6. Data availability Annual files containing quality-checked