The Use of Oblique Aerial Photography to Investigate the Extent and Sequence of Landslipping at Stag Hill, Guildford, Surrey

Abstract

Abstract The University of Surrey is situated on the northern slopes of Stag Hill, below Guildford Cathedral, which occupies the summit. During the investigation for the design of the University, it became apparent that the site was underlain by a large landslip, 500 m wide from east to west and extending 160 m from rear scarp to toe. Considerable effort was made to establish its geometry and extent (Skempton & Petley (1967), and Morgenstern & Tchalenko (1967)). In recent years it was realised that because the construction of the Cathedral extended over a long period of time, the likelihood of Stag Hill being covered by oblique aerial photography would be high. Some forty oblique aerial photographs, spanning the period 1949 to 1982, were collected and analysed together with vertical aerial photographs and topographic maps. Although the landslip is visible on vertical aerial photographs, individual elements are not easily identified. Using oblique photography, in particular that in which recognition of subdued topography has been enhanced by low sun angles, up to six phases of landslipping were identified. This paper uses this example to demonstrate the usefulness of aerial photography in site investigation and in particular the value of oblique photography, a topic which receives little attention in BS 5930:1981 considering how cost effective this tool can be.