Reconnaissance survey of slope instability in the Bath area

The current BGS 1:50,000 scale geological map of Bath (265) shows a large area (45 km2), mainly to the north of the city, identified as ‘foundered strata’ (Figure 1). This area has no other information within it. Unlike areas shown as ‘landslipped’, no attempt has been made to indicate stratigraphy. The ‘foundered stata’ category on the Bath map is unhelpful for map users who are unfamiliar with the geological materials and processes involved, and which have led to this unique categorisation. The reason for the use of the term ‘foundered strata’ stems from the difficulty experienced by the mapping team in differentiating landslipped ground from cambered ground and from ground unaffected by either slope process. The areas contain steep slopes many of which are heavily wooded. Non-wooded areas are subject to agricultural processes which tend to obscure landslides and other slope related and geological features. The purpose of the reconnaissance survey, carried out by the authors by vehicle and on foot, with the assistance of K. Royse (geologist, BGS), was to examine the area categorised as ‘foundered strata’ and to assess the possibilities for re-mapping in order to show the stratigraphy and slope processes. Factors such as tree cover, access, ground conditions were considered. The ability to discern surface features which may be indicative of slope instability was considered. Comparison between the ‘foundered strata’ area and adjacent areas was made. A brief assessment of existing available sub-surface data was made.