Now deepest secrets of Loch Lomond lie revealed

Published on Monday 14 February 2011 18:22

SCOTLAND'S largest loch has been mapped for the first time in 150 years.

• The loch's south is shallow

The first Loch Lomond depth survey was carried out in 1861, using a simple but remarkably accurate lead-line process by a team of men from HMS Porcupine under the command of a Captain Otter.

Yesterday, Loch Lomond and The Trossachs National Park Authority (NPA) unveiled a comprehensive new navigation chart of the 24-mile-long loch using the latest technology.

The joint project with the British Geological Survey (BGS) included a full depth survey of the freshwater loch using sonar equipment.

But, as a fitting tribute to the early pioneers, several inlets, islands and features have been named after the 1861 team, including McDougall Bank, Chimmo Rocks and Otter Spit.

The new chart is available to loch users and gives a very modern impression of the hazards around Loch Lomond.

COLOUR CODE

1. Multibeam data of the loch shows shallow water in pink.

2. Deep water is dark blue.

3. The southern end is very shallow.

4. The line of islands crossing from SW to NE marks the line of the Highland Boundary Fault.

5. North of this is a deeper basin with water depths of 40-50 metres.

6. In the far north of the loch, there is a much deeper basin with depths approaching 190 metres.

The BGS team spent three months surveying the loch using equipment including two "multibeam echosounder transducers" that transmit and receive millions of soundings every hour.

The information was gathered using satellite positioning (GPS) and a motion sensor that took into account the movement of the boat.

The data has resulted in detailed images that can be used to give a 3D map of geological features of the loch floor.

The BGS team plan to return to Loch Lomond to collect data that will tell them about the rock types and formations below the loch floor.

Alan Stevenson, who led the BGS team, said: "Sonar data has been used for several years to map the geology of the sea floor around Britain, but this was the first time we had used the technique in a loch environment.

"We are very pleased that the information has also helped the National Park Authority to improve their navigational chart for loch users.

"The data we plan to collect from beneath the loch floor will add to the sonar information and help us to understand even more about the present-day loch environment and its geological history."

Graeme Archibald, Ranger Manager for the National Park Authority added: "Comparing the two charts and taking into consideration the level of equipment available to them, the 1861 chart was remarkably accurate, a testimony to their skills as surveyors.

"I take my hat off to both Otter and his crew and the current team that produced this new chart for Loch Lomond."

Loch Lomond is a freshwater loch, lying on the Highland Boundary Fault. It is the largest loch or lake in Great Britain, by surface area - 27 sq miles - and the second largest after Loch Ness, by water volume.

Loch Lomond is 24 miles long and between 0.75 and five miles wide. It has an average depth of 121ft and a maximum depth of about 620ft. It has more than 30 islands, including Inchmurrin, the largest freshwater island in the British Isles.