In accordance with the initial proposals of the project, the broad constraint on site location to the western seaboard of Scotland is derived from the occurrence of well established terrestrial limits of late Quaternary glacial readvance events along this coastline (See Figure. 2.1.).
An initial reconnaissance visit was undertaken, in order to identify a suitable off-shore site for data collection. A set of criteria for each sea loch had to be fulfilled, in order to provide optimum efficiency for geophysical surveying. This was especially important
Figure 2.1. Limits of the Loch Lomond and Wester Ross Readcvances in North- West Scotland (After Robinson and Ballantyne, 1979; Sissons,
Chapter 2. Field Methodology 29
considering the distance of the field areas from St.Andrews, and the temporal and financial logistics of setting up a multi-disciplinary study.
The primary consideration for site location is the ease of boat access to the water body, with preference given to lochs that possess functional slipways or piers. Such entry points have to be easily accessible to the general public or by prior arrangement with the owners. These access points should ideally be serviceable at all stages of the tide so as not to unduly restrict survey runs to specific tidal states.
Due to an insurance restriction on the survey vessel (a 5.5 m dory: See Section 2.3.1.), such that it cannot be used for survey work in wind conditions greater than Force 4 (8 ms-1), it is necessary to locate areas that possess the calmest possible water conditions. The orientation of each loch and the configuration of the surrounding topography must also be considered as they significantly affect the degree of protection offered against the prevailing southerly to westerly winds. These latter two factors thus dictate the maximum size of fetch at each locality, the fetch being the unobstructed distance of sea over which wind may blow. The height of wind-generated waves is directly proportional to the fetch (Bearman, 1989), and so true open sea areas (i.e. those with the greatest fetch) are to be avoided as they tend to have the most unpredictable wave conditions.
After taking into consideration all of the logistical parameters involved in offshore fieldwork, the final choice of field location was based on the extent of onshore mapping of any glacial limits. As can be seen in Figure 2.1, limits for the Loch Lomond and Wester Ross Readvances1 restricted the possible survey areas to Loch Ewe and all sites south. The southern limit of interest was defined by the work of Boulton et al. (1981) who surveyed the area from Loch Nevis to Loch Ailort. It was not deemed necessary to duplicate previous work. The Isle of Skye, however, was considered a worthy target particularly in view of the recent reassessment of the onshore Loch Lomond glacial limits by Ballantyne (1989) and Benn (1990).
Chapter 2. Field Methodology 30
Applying the criteria, as defined above, the following lochs (Grid References given in square brackets) were assessed for their suitability for study (See also Figure 2.1.):
Loch Ewe [NG180880]: Several access points are available, via a jetty at Naast on the western shore and jetties at Aird Point and Tournaig on the eastern shore. The narrow neck at the mouth of the loch and its north-south orientation provides protection from severe conditions throughout. However, the previously defined Wester Ross glacial limits suggest that the off-shore limit is outwith the loch and so in open water (Robinson & Ballantyne, 1979; Sissons, 1981a; Sissons & Dawson, 1981). Thus, the primary survey area is exposed to a fetch of over 50 km and unpredictable sea conditions are to be anticipated.
Loch Gairloch [NG170870]: Access is via a slipway at Gairloch village. The open mouth, east-west orientation and a fetch in excess of 70 km all suggest impractical survey conditions for a small boat. In addition, the off-shore Wester Ross limit is again believed to be in the more exposed open sea area at the loch mouth water (Robinson & Ballantyne, 1979; Sissons, 1981a; Sissons & Dawson, 1981).
Loch Torridon [NG170860] & Upper Loch Torridon [NG180850]: Several access points are present along both the northern and southern shores, with two slipways at Shieldaig, a jetty at Torridon (to which it would be difficult to return the boat at high and low water so restricting surveys to the mid-tide/mid-tide period) and a sheltered pebbly beach at Inveralligin from which a boat could be launched. The north-west - south-east orientation, the peninsula of Applecross to the south-west, and the narrowing of the shores between the outer and upper lochs, all provide for a sheltered locality. Possible Wester Ross limits have been identified both on the northern shore of Torridon and on the northern part of Applecross, but they suggest that the off-shore limits are in the exposed Inner Sound to the west of the loch mouth (Sissons, 1981a).
Loch Kishorn [NG180830]: Onshore mapping suggests that neither Wester Ross nor Loch Lomond limits are present in this area. This water body was therefore not reconnoitred.
Loch Carron [NG190830]: Onshore mapping suggests that neither Wester Ross nor Loch Lomond limits are present in this area. This water body was therefore not reconnoitred.
Loch Duich [NG880250]: This water body affords access to Loch Long to the south and Loch Alsh to the west. Two slipways were identified at Dornie at the head of Loch Duich, with a further two at a fish farm at Letterfeam on the south-western shore. Permission to use all slipways was obtained. The north-west - south-east orientation, the surrounding mountainous topography (no area less than 400 m) and the location of the Isle of Skye to the west, all provide excellent protection from the prevailing winds. Owing to extensive afforestation, the Loch Lomond limit is ill defined in this area, but recent work does suggests that a Loch Lomond glacier front was located in the vicinity of Dornie at the mouth of Loch Duich (J.Tate, 1992 pers. comm.}.
Loch Hourn [NG180800]: Despite the east-west orientation, the sheltered conditions, short fetch and possible Loch Lomond ice limits on both shores (Boulton et al., 1981), Loch Hourn had to be disregarded due to its inaccessibility by road. This is particularly important as the survey vessel has to be towed to any chosen site.
Loch Sligachan [Skye - NG150830]: A slipway adjacent to the jetty for the Balmeanach ferry; gives possible access to the loch but there may be a problem during summer months due to competing ferry services. The loch's location on the eastern coastline of southern Skye provides it with excellent protection from wind induced waves due to the presence of the Cuillin Hills to the south-west. Loch Lomond limits are well defined on both shores with the suggested off-shore limit of the Sligachan and Glamaig glaciers occurring in the relatively sheltered waters between the Narrows of Raasay and Caol Mor (Ballantyne, 1988, 1989, 1990; Benn 1989, 1990; Benn et al., 1992).
Loch Ainort [Skye - NG150820] & Loch na Cairidh [NG150820]: Three possible slipways are present, on the south-western shore at a Marine Harvest fish farm. Permission to use any of these was granted. Probable water conditions are similar to those at Loch Sligachan, as Loch Ainort is also protected by the presence of the Cuillin Hills. Lochs Ainort and Cairidh are also sheltered to the north-east and the north by the
Chapter 2. Field Methodology 32
island of Scalpay only 1 km off the coastline. Again, on land limits of the Ainort glacier are well defined on both shores (Ballantyne, 1988, 1989, 1990; Benn 1989, 1990; Benn
etai., 1992). .
Loch Slapin [Skye - NG150810]: An adequate slipway exists at a fish farm on the western shore. Permission to use this was obtained. Loch Slapin is protected from westerly winds by the southern margin of the Cuillin Hills. However, the north-south orientation of this loch makes it vulnerable to southerly winds with a possible fetch of over 200 km. No substantial barrier exists between this part of Skye and southern Ireland. Consequently, severe sea conditions might be anticipated. The on land glacial limits are well defined and suggest that the Slapin glacier front terminated near the head of the loch (Ballantyne, 1988, 1989, 1990; Benn 1989, 1990; Benn etai., 1992).
Loch Scavaig [Skye - NG140810]: A possible entry point to this water body exists at Elgol but the slipway is very narrow making entry difficult. The only protection from westerly winds is provided by the island of Soay, whilst the open nature of the north-south orientated loch leave it fully exposed to the North Atlantic. Again this would suggest that, at the very least, weather and sea conditions would be unpredictable. On land glacial limits suggest that both the Coruisk and Creitheach glaciers would have terminated near the mouth of Loch Scavaig (Ballantyne, 1988, 1989, 1990).
Having assessed the relative merits and limitations of each loch for the project's requirements, Loch Ainort was chosen from the above list as being the most suitable area for study. This loch possessed a large, high resolution onland database with well defined limits on both shores (See Section 3.2.). Therefore it would represent a good test case of the effectiveness of geophysical techniques in identifying and hopefully supplementing sub-aerial data.
Chapter 2. Field Methodology 33