Henry Chapman on surveying on (and under) water

'Kind of tricky'
A major part of this programme involved the investigation of a prehistoric artificial island called a crannog. The fact that the remnants of this rubble-based island are about 30 metres out in the loch presented Time Team surveyor, Henry Chapman, with a challenge.

'The survey of a crannog is kind of tricky,' says Henry. 'It's just like a land survey but involves recording some of the information underwater. The crannog is out in the loch and so it's surrounded by water. The water level goes up and down all the time, so that's of little use to me when trying to record levels. What I have to do is record the bed of the loch to understand the relationship between the crannog and the main landscape.'

Crannog speculation
There is a great deal of speculation as to why prehistoric people built crannogs and how they accessed them. Was it by boat or did they have pontoons or walkways stretching to the shore? Henry hopes his survey will find some answers: 'I'm particularly trying to find anything that could look like a causeway or path. These things can often have a causeway just under the water level, which would make access to the island easier if you knew they were there. However, surveying the whole thing is another matter.'

In practice, Henry has broken down the survey into several areas: 'The approach I'm using is on three levels. I'm trying to create a 3D landscape survey of the crannog itself as it is above water. Then I'm surveying the bed of the loch up to the bank from a boat. And finally I'm doing my normal survey of the main landscape. If I pick up any indications of a possible causeway I can get the divers to investigate it further. Then I want to tie all the information together into one big plan.'

Paddling around
This may sound like a technical nightmare, but Henry has done similar work before and has confidence in his equipment. 'I've done a lot of wetland archaeology in the past, which can involve working in tidal environments like river estuaries and so I'm experienced in paddling around in the water trying to get the archaeology out of the landscape. It's all good fun at the end of the day.'

By the end of Day Three, Henry has successfully identified a causeway. Running between the crannog and the shore, it is about five metres wide and a metre or so higher than the surrounding material on the loch bed.

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