A study of the reactivation of landsliding at Barton-on-Sea, Hampshire, following stabilisation works in the 1960s

The mostly clay cliffs of Barton-on-Sea, Hampshire, comprise inhomogeneous strata of the Bracklesham, Barton and Headon Hill Formations, overlain unconformably by Plateau Gravels, and have a long history of erosion and instability. Heavily-engineered stabilisation works involving a 1,500m-long sheet-piled wall and cut-off drain were installed in the 1960s but a number of catastrophic failures of the wall have occurred at locations along the Barton frontage since then. This report is concerned with the failures at Cliff House Hotel / Tom’s Garden and at Hoskins Gap West.Extensive monitoring of the cliffs over the past sixty years has produced a large and diverse dataset which has been compiled, analysed and assessed in this report. This includes inclinometer, piezometer and rainfall records, topographic surveying, aerial and ground photography, borehole and exposures logs, consultants’ reports, engineering drawings and newspaper articles. This report identifies characteristics of the key periods of activity at the two locations and compares and contrasts them. Maps of the areas of activity, cliff-top retreat, revetment movement and drainage patterns are provided. Fieldwork undertaken for the project includes the logging of three cliff exposures and the surveying of four cross-section profiles. Drawing on the information available it charts the progress of instability in the two study areas, suggests possible mechanisms for the failures and offers a prediction of future activity based upon the mechanisms described