THE SCOTTISH BEAVER TRIAL

KNAPDALE, ARGYLL: 2009-14

IMPACT ON SCHEDULED MONUMENTS

Longmore House

Salisbury Place

Edinburgh

EH9 1SH

THE SCOTTISH BEAVER TRIAL, KNAPDALE, ARGYLL: 2009-14

IMPACT ON SCHEDULED MONUMENTS

Beaver lodge, Loch Coille-Bharr, Knapdale. May 2014. Introduction In 2008 the Scottish Wildlife Trust and the Royal Zoological Society of Scotland applied to the Scottish Government for a licence to carry out a trial reintroduction of the European beaver to Scotland. The chosen site was Knapdale in Mid-Argyll, which was previously identified by Scottish Natural Heritage as having suitable habitat for beavers. Historic Scotland was consulted in October 2007 by the Scottish Wildlife Trust prior to the submission of the application and we raised concerns about a number of scheduled monuments in the vicinity of the trial area that might be affected by beaver activity, and in particular the Crinan Canal bordering the trial area and Loch Coille-Bharr crannog close to one of the release sites. The Crinan Canal (Scheduled Monument Index Nos. 6500 and 6501) is an historic and well used waterway, mostly consisting of clay-lined earthen banks with intermittent areas of stone pitching revetting the banks. The canal is fed by a system of streams and lochs, mostly unscheduled.

Loch Coille-Bharr, crannog (Scheduled Monument Index No. 10131) is a submerged artificial island presumed to be the site of a late prehistoric – early historic period lake dwelling. The recovery of timber artefacts from the site in 1867 suggests that the lake silts around the site have preserved organic deposits relating to the occupation and use of the crannog. Potential impacts of beaver activity Prior to the commencement of the Scottish Beaver Trial, both the canal and the crannog were considered to be potentially vulnerable to beaver activity: digging of tunnels, construction of channels, dams, lodges, flooding of land resulting from damming, and foraging activities. Beavers are burrowing animals that dig into banks along suitable water courses, lined with deciduous tree cover to build their lodges. They will also utilise suitable islands for shelter and foraging. They create scrapes, slides and bankside lodges in particular areas of their territories and will therefore have an impact upon some banks of watercourses. They dive to shallow depths to dig up tubers of aquatic plants and use nearby bankside mud when building lodges and dams. In the course of constructing these, trees are felled and the timber floated to the required location. In addition to potential direct impacts on the monuments from the above activity, the potential for changes in the water supply to the canal or changes in water levels in Loch Coille-Bharr, which could affect the preservation of organic remains on the crannog site, were also raised at the outset of the trial. However, based upon experience overseas we understand that it is considered unlikely that the beavers will have any significant impact on the water levels in the loch and water flow within the trial area. Beavers generally build dams to raise water levels in smaller water courses and smaller bodies of water for foraging and shelter. This is not considered to be an issue that would affect the overall flow of water to the canal or reduce water levels in a large open water habitat such as Loch Coille-Bharr. There appear to be no documented cases of beavers damaging archaeological sites, but beavers’ use of timber for construction material and underwater foraging prompted concern that any exposed timbers or archaeological deposits on the crannog site could be at risk from disturbance. Historic Scotland therefore commissioned Graeme Cavers of AOC Archaeology Group to undertake a condition survey of the monument. This was carried out in January 2009 at the outset of the trial period to provide a basis for monitoring any impact. Loch Coille-Bharr Crannog: Condition Survey The crannog in the loch first came to light after it was inspected by Mapleton in 1867, who had noted the presence of a stone ‘cairn’ used by anglers (Mapleton, 1870). With the assistance of divers working on the Crinan Canal, Mapleton recorded the presence of areas of walling filling the gaps in the bedrock foundation of the site; ‘very beautiful and well-made walling, varying in height from 4 to 8 feet and slightly rounded in outline, to suit the circular form of the platform’. The divers also encountered numerous timbers, including the remains of a canoe paddle, and bone tools. These organic remains apparently disintegrated on exposure to the air and were retrieved from some considerable depth of mud in the areas surrounding the crannog. Results of the 2009 survey The 2009 survey found the crannog to be located at NR 7788 8949, approximately 14 metres north-east of the tip of southernmost promontory extending into the bay in the south-east corner of the loch. The site rests on a bedrock reef, itself an extension of the promontory separated from the

shore by a depression in the bedrock where the water depth reaches 2.5 metres. The bedrock reef runs NE-SW and slopes down towards the north-east to a depth of 7 metres. Surrounding the bedrock reef are thick lake silts. This location differs from the national grid reference for the site held in the National Monuments Record (ie. NR 7796 8946) which is incorrect. The 2001 scheduling document for the site was based upon the incorrect grid reference and the monument is in the process of being rescheduled to correct the mapping.

Location of crannog (Cavers, 2009) (Reproduced by permission of Ordnance Survey on behalf of HMSO.

© Crown copyright and database right [2013]. All rights reserved. Ordnance Survey Licence number 100017509.)

The crannog itself is completely submerged, with no evidence of the site visible above water and comprises a roughly circular stone mound 9 metres in diameter. The top of the mound was about 1 metre below the surface of the water at the time of the survey. The site is visible as a mound of boulders measuring 1.6 metres high from the lowest point to the highest point. The boulders average 0.4 – 0.5 metres in diameter and, for the most part, show no clear constructional arrangement. Around the edges of the site, however, the ‘well-built walling’ referred to by Mapleton is visible on the west and south sides, where it appears to act as a revetment, filling clefts

in the bedrock, retaining the main boulder mound and creating a stable platform on the bedrock foundation. The revetting walling is well made, standing to four courses on the west side and five courses on the south side, and made of angular stones averaging 0.3 – 0.4 metres across.

Underwater photograph of revetment walling (Cavers, 2009) The boulder mound is otherwise featureless, although around the edges of the site to the north and east several large boulders may represent ruinous remains of further retaining walling. On the north side several large boulders have slipped down the sloping bedrock into deeper water suggesting that portions of the site may have been lost to collapse. Although several large boulders were observed around the base of the bedrock reef, there was no evidence of any further stone structure around the crannog itself. If it exists it is buried beneath lake silts. Surrounding the bedrock reef are featureless expanses of lake silts, with no evidence of structures of stone or timber visible. No attempt was made in the course of the survey to uncover structures in the silts and if the timbers and other material referred to by Mapleton still exist, these are now covered by silt. At the end of the headland to the south-west of the crannog, a short section of boulder construction may represent the remains of a pier, though the antiquity of this feature could not easily be established as the location has for many years been used by local anglers. No timbers of any form were noted on or around the crannog. If organic deposits exist on the site, these are buried beneath the mound of boulders or in the silts surrounding the bedrock shelf.

Several species of aquatic plant were noted growing on and around the crannog, though these were all superficial in nature and did not have extensive root systems.

Location of Loch Coille-Bharr crannog: beneath the water at the right hand edge of photograph, 14 metres from the end of the tree-covered promontory which has become home to family of beavers. May 2014.

2009 Survey plan (Cavers, 2009)

Condition of the crannog and potential impacts The crannog is generally well preserved. The survival of stone construction in submerged areas of a crannog site is unusual and the quality of construction of the revetment walls goes some way to explaining their survival. The survival of organic deposits on the site could only be confirmed by excavation of the boulder mound or the lake silts surrounding the bedrock reef. If timbers and other organic deposits are preserved in the silts around the site, which seems probable if the site was occupied as a dwelling, it is likely that it is here that any damage to the archaeology is likely to occur. It should be noted, however, that there is no obvious current threat to these deposits. Although aquatic plants have been noted as a potential threat to submerged waterlogged wood, the plant coverage around the site does not appear extensive enough to warrant concern. The sparse plant growth and superficial root systems noted in the course of the survey also suggest that the threat from foraging activity by beavers is small despite the palatability of some of these species (Willby et al. in prep.). Archaeological significance of the site The Loch Coille-Bharr crannog is an unusual site in having well-preserved evidence for stone construction. The majority of the ‘highland’ type stone and timber crannogs are ruinous, with no evidence of the deliberate placement of boulders apparent on surface examination. The Loch Coille-Bharr site is amongst a number of artificial islet structures in mainland Argyll which are apparently built entirely in stone. Recent research has also identified good examples of stone revetted mounds in Loch Leathan and Loch Seil. The internal structure of these stone islets is unknown and it is unclear whether the organic deposits encountered during underwater excavations of ‘highland’ type crannogs should be expected to survive on an otherwise entirely stone mound (Cavers, 2003 and 2009). It is possible that when the stone mound was built the level of the Loch Coille-Bharr was lower than today. This would certainly have made the construction of the revetting walls easier. Such a reduction in the water level could have meant that the site may originally have been built on the end of a promontory or very nearly connected to the headland to the south. Sites such as Loch Coille-Bharr blur the distinction between crannogs, island duns and stone built enclosures of the later prehistoric and early historic periods in western Scotland. Conclusions and future monitoring The atypical and robust nature of the crannog, the sparse and superficial aquatic plant growth on the monument revealed by the 2009 survey, together with the knowledge of how typical beaver activity may affect the loch water level, combine to suggest that the introduction of beavers is unlikely to have any impact on the Loch Coille-Bharr crannog, providing the current water level in the loch is maintained in the expected range. For this reason a further detailed underwater survey during the trial period was not considered necessary. However, should the beavers remain in the loch after the trial period, then periodic monitoring of the condition of the submerged crannog site in Loch Coille-Bharr should be undertaken. With regard to the Crinan Canal, we are not aware of any adverse impact on the scheduled monument or its associated watercourses during the five year trial period. If, following consideration of the results of the trial, the more widespread reintroduction of beavers in Scotland is undertaken, provision for appropriate monitoring and action plans should be made for

any instances where a sensitive archaeological site is thought to be under direct threat from beaver activities. Dam removal or proactive mitigation measures such as fencing or netting or the relocation of beavers might be required in some circumstances. References Cavers, M. G. 2003. The Argyll Crannog Survey. University of Nottingham, unpublished report. Cavers, M. G. 2009 Loch Coille-Bharr Crannog: Condition Survey. Unpublished AOC Archaeology

Group Report no. 21248. Mapleton, R. J. 1870. ‘Notice of an artificial island in Lock Kielziebar, in a letter to Mr Stuart,

secretary’. Proc. Soc. Antiq. Scot. 7; 322-324 Willby, N. J., Perfect, C. and Law, A. (in prep.) The Scottish Beaver Trial: Monitoring of aquatic

vegetation and associated features of the Knapdale lochs 2008-2013. Scottish Natural Heritage Commissioned Report.

Acknowledgments The above report draws heavily on the survey and research of Graeme Cavers, AOC Archaeology Group. Thanks are due to Simon Jones, Scottish Beaver Trial Project Manager and Roisin Campbell-Palmer, Royal Zoological Society of Scotland for supplying background information on beavers and particularly to Roisin for her assistance in visiting the trial site. Heritage Management West Team Historic Scotland November 2014