Blog - At the mercy of the weather gods: marine surveying in Wales - Kieran Craven (GSI)

Planning

Planning marine surveys is hard. Surveys have to be organised months in advance, but weather conditions dictate everything on the day. Too windy, and the swell picks up. While the boats we use have equipment (inertial measurement units) that track the motion of the vessel, large waves and the bubbles that come with that disperse the sound waves from the multibeam and leads to “noisy data”. Weather down time is a frequent occurrence.

The way around this is to plan multiple targets that take all weather conditions into account. The predominant wind direction in Ireland and the UK is from the southwest. Choose your primary targets, then choose some more in bays and inlets that face the northeast. Select some targets in shallow water, some in deep. Try to have multiple places to go, so if the wind changes direction and gets stronger, there’s always something to attempt to increase the chances of a successful survey. Thus far, we’ve been lucky!

Previous Years

We have now just completed our third season surveying in Welsh waters. In 2018, the RV Keary operated around Anglesey (Figure 1). Initially targeting wrecks to the south west of the island, the south-westerly winds picked up and the boat was forced to move to the northeast. Sheltered conditions here allowed us to continue data collection, with all bathymetry gridded up to 10 m, 5 m and 2 m resolutions. Finer resolutions can be generated, especially for wrecks which we generally grid at 0.25 m down to 0.10 m. The Puffin Island 2 m data has now been combined with CHERISH LiDAR data to produce one of our seamless onshore-offshore maps (Figure 2).

Bathymetry coverage from KRY18_CHERISHFigure 1: Bathymetry coverage from KRY18_CHERISH

Seamless onshore-offshore map of Puffin Island. 2 x vertical exaggeration. Red is high elevation, changing towards blue for deeper areas.Figure 2: Seamless onshore-offshore map of Puffin Island. 2 x vertical exaggeration. Red is high elevation, changing towards blue for deeper areas.

In 2019, The RV Keary returned to Wales, this time moving south and targeting the Sarn Badrig reef in Cardigan Bay along with other key CHERISH terrestrial sites (Figure 3). The weather this year was kind and allowed us to operate on the exposed western shore. Sarn Badrig is extremely shallow and during low tide the RV Keary shifted locations to St Tudwal’s Islands to continue data collection. The offshore regions of Dinas Dinlle and Rhosneigr were surveyed to tie in with the onshore work of our Welsh colleagues.

KRY19_CHERISH survey sites with bathymetry surveyed.Figure 3: KRY19_CHERISH survey sites with bathymetry surveyed.

2020 Survey

This year, the plan was to extend the work started in 2019, with Sarn Badrig and the South Sands around Menai Strait being our primary targets (Figure 4). However, as these are vulnerable to south-westerlies, a number of reserve areas were identified, extending from north of Anglesey right down to Pembrokeshire. The survey was planned around large spring tides, to take full advantage of deeper water over the shallow targets.

Plan for 2020 surveying with priority (orange) and reserve areas (pink), alongside existing multibeam coverage (blue and green). Target wrecks are spots and stars.Figure 4: Plan for 2020 surveying with priority (orange) and reserve areas (pink), alongside existing multibeam coverage (blue and green). Target wrecks are spots and stars.

Luckily, the weather gods were kind to us for a second successive year and the RV Keary focussed on the priority targets. We surveyed the wreck of the “Bronze Bell” (Figure 5) and extended the bathymetry around Sarn Badrig (Figure 6). Here, there’s a shallow ridge that extends offshore for about 15km and this is the site for a number of historic shipwrecks, including the Diamond and Bronze Bell. The seafloor map will act as context for the surveyed shipwrecks and will help update the nautical charts for the region. At Dinas Dinlle, bathymetry coverage now includes the mythical palace of Caer Arianrhod (Figure 7).

Figure 5: Multibeam bathymetry around the wreck the "Bronze Bell", including Carrara Marble, anchors and cannon. Red is shallow, getting deeper towards blue.

Figure 5: Multibeam bathymetry around the wreck the "Bronze Bell", including Carrara Marble, anchors and cannon. Red is shallow, getting deeper towards blue.

 

Multibeam converage of Sarn Badrig. Red is shallow, getting deeper towards blue.

Figure 6:Multibeam converage of Sarn Badrig. Red is shallow, getting deeper towards blue.

Bathymetry off Dinas Dinlle. Red is shallow, getting deeper with green. Caer Arianrhod is the oval reef in the south of the multibeam coverageFigure 7: Bathymetry off Dinas Dinlle. Red is shallow, getting deeper with green. Caer Arianrhod is the oval reef in the south of the multibeam coverage We’ve always received a warm welcome whenever we’ve made it over to Welsh waters. With this in mind, on our final day in Wales this year, it was an honour to participate in the sail past in memory of Mark Shackleton, Dock Master at Caernarf

We’ve always received a warm welcome whenever we’ve made it over to Welsh waters. With this in mind, on our final day in Wales this year, it was an honour to participate in the sail past in memory of Mark Shackleton, Dock Master at Caernarfon.