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PCO News Newsletter for the South West Regional Monitoring Programme Coastal Issue 5 June 2007 INSIDE... Regional News Feature Article: Contacts h h h Single Beam Bathymetric Surveys © EMU Ltd.

Newsletter for the South West Regional Monitoring ......PCO News Newsletter for the South West Regional Monitoring ProgrammeCoastal Issue 5 June 2007 INSIDE... Regional News Feature

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Page 1: Newsletter for the South West Regional Monitoring ......PCO News Newsletter for the South West Regional Monitoring ProgrammeCoastal Issue 5 June 2007 INSIDE... Regional News Feature

PCO NewsNewsletter for the South West Regional Monitoring ProgrammeCoastal

Issue 5 June 2007

INSIDE...

Regional

News

Feature

Article:

Contacts

Single Beam

Bathymetric

Surveys

© EMU Ltd.

Page 2: Newsletter for the South West Regional Monitoring ......PCO News Newsletter for the South West Regional Monitoring ProgrammeCoastal Issue 5 June 2007 INSIDE... Regional News Feature

Regional NewsRegional News

Cornwall and Isles of Scilly (CISCAG)

North Devon and Somerset (NDASCAG)

Channel Coast Observatory

This month's edition of PCO news comes witha data update sheet to illustrate which datahas been collected and is available. Theattached pdf document details the location ofthe management units around the SW coast,the accompanying spreadsheet describewhich surveys have been completed for eachof these management units.The feature article this month describes thesingle beam bathymetric surveys beingconducted in the SW as part of thisprogramme.

Bathymetric surveys are currently beingconducted in both of the bathy work packagesin this region. Single beam data are beingcollected between Petit Tor Point and RameHead, whilst multibeam data are beingcollected between Portland Bill and Petit TorPoint. The multibeam data will be sent to thePCO, via the Maritime and CoastguardAgency, as a 2x2m grid which will then be puton the website.Topographic surveys are nearly complete,with some data already uploaded to thewebsite.As lead authority on SMP2 Teignbridge DCwill be going out to tender in the next fewweeks to find a consultant for this work.

Bathy surveys have begun on both the northand south Cornish coasts. Data have beenreceived for 19 management units on thesouth coast and are currently being checkedbefore uploading onto the website. Bathy datahave also been collected for the north coastand we're awaiting delivery of these data.The SMP2 process has now commenced withthe Pro ject Appra isa l Repor t nowcommissioned through Coast and CountryPlanning Ltd to evaluate Stage 1 and with aview to seeking Coast Protection Grant in2007/08.The Cornwall Sand Dune and BeachManagement Strategy Study has suffered adelay of about 4 months as a result of surveydata from SWRCMP being delayed/re-

scheduled due to inclement weather etc.

The bathymetric survey has begun on theNorth Somerset Coast. Single beamechosounder data from the Lilstock area havebeen received by PCO and are undergoingquality control checks.The programme for Stage 1 of the SMP isscheduled to begin in October and continueuntil September 2009.In mid June Prof John Pethick presented thefindings of the “Taw/Torridge Estuary:Geomorphology and Management” study tolocal authorities and the general public at twoseparate meetings. To obtain a copy of theexecutive summary of the report pleasecontactAngela Proctor ([email protected])

Work on the CCO website is progressing well.The updated website will act as the first port ofcall for anyone wishing to download surveydata collected as part of this programme. Anew front end is being designed for thewebsite, which will allow users to access datafrom either the south west or the south eastmonitoring programmes.The wave buoy at Slapton Sands came adriftfrom its moorings on 10th June, due to asuspected collision. It was placed back in thewater on the 12th June. We're trying very hardto raise the profile of these buoys with all localwater users to avoid further damage and lossof data, please let us know of anyone you thinkshould be included in this newsletter to helpwith this.

EnvironmentAgencyThe majority of LiDAR data collected duringthe spring flying period have been delivered tothe Environment Agency where they are beingchecked for coverage and depth achieved.Aerial photography will recommence duringthe next set of spring tides, weather permitting.Raw Infra-red (FCIR) data are beingprocessed for selected areas, to be used forecological mapping. Tenders have beenreceived and interviews held for this work. TheEAare in final negotiations with 2 tenderers.

South Devon and Dorset CoastalAuthorities Group (SDADCAG)

Page 3: Newsletter for the South West Regional Monitoring ......PCO News Newsletter for the South West Regional Monitoring ProgrammeCoastal Issue 5 June 2007 INSIDE... Regional News Feature

Bathymetric SurveysPart 1 - Single Beam Echo Sounder

Bathymetric surveys will be carried out along the whole near-shore coastline throughout the southwest using bothsingle beam and multi beam echo sounders. This article will give an introduction to how single beam echosounders are used within the programme, whilst next month’s feature article will describe the multibeam surveys.

The principal of using an echo sounder for measuring water depth is to transmit acoustic pulses from the oceansurface and listen for their reflection from the sea floor. The time it takes for a pulse of sound to be transmitted andreceived is the time taken for the pulse to travel to the sea floor and return. The time delay between transmit andreceive is used to determine the water depth using the following equation:

As we are interested in only the water depth the equation is divided by 2 since the time delay is for two-way travel.

The echo sounder emits and receives acoustic pulses in a single beam. This means that water depth will only bemeasured in the footprint of this beam. Different echo sounders have varying beam widths: A wide beam allowsfor a large footprint but issues can arise where the sea floor to the side of the survey vessel is higher or lower thanthat directly underneath and the return pulse may not be from the sea floor directly below, this situation mayproduce an inaccurate measurement of the depth at this location. A narrow beam has a small footprint and allowsfor a more accurate depth measurement of the sea floor below, however heave, pitch and roll have a more

significant influence on the survey and must either becompensated for or the surveys conducted on a flat calm sea.

To provide optimum location and depth accuracy, the surveyvessel can be navigated using integrated GPS software. Thisallows a DGPS signal to be input to the echo sounder to provideaccurate xyz data.

For the purposes of this programme the extent of the surveysdepends on the management strategy for the nearby beach. For“hold the line” areas the surveys cover from Mean Low WaterNeaps (MLWN) to 1000 m offshore with profile lines being takenevery 50 m. For other areas the extent is from MLWN to 500 moffshore with profiles spaced at 100 m. The profile lines arelocated so that they correspond with the topographic profiles.The landward extent of the bathymetric surveys to MLWNallows for an overlap with the topographic data which helps tocheck the quality of all the data sets.

The data received at PCO have been processed to remove spikesand are in several formats. XYZ data are of processed locationand depth, ASCII raster files are interpolated using the NaturalNeighbours method and profile XYZ data are of the pre-definedprofiles forced through the raster grid.

Once the data have been received at PCO they are checked andthen transferred to the Channel Coast Observatory for upload tothe CCO website ( ). From there the dataare freely available for download to any interested parties.

www.channelcoast.org

2

tim esp eedd is ta n ce

Above: Raster data from South Cornwall, MU 6D5-17

Page 4: Newsletter for the South West Regional Monitoring ......PCO News Newsletter for the South West Regional Monitoring ProgrammeCoastal Issue 5 June 2007 INSIDE... Regional News Feature

Contacts

If you have any queries about the South West Regional Coastal

Monitoring Programme, or would like further information, please

contact:

Lead Authority (Teignbridge DC): Martin Hutchings

[email protected]

Environment Agency SW: Roy Russell

[email protected]

Regional Co-ordinator: Phil Perkins

[email protected]

or contact the regional data management centre:

Plymouth Coastal Observatory

University of Plymouth

Drake's Circus,

Plymouth,

PL4 8AA

Tel: 01752 232676

[email protected]

SDADCAG

CISCAG

NDASCAG