The Frindsbury area, Rochester: a review of historical data and their implication on subsidence in an urban area

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Abstract A sudden subsidence under a footpath which led to the tragic death of a pedestrian was followed by a series of further subsidences over a period of several years, all incidents apparently located within an area no more than approximately 1 km square. The area is one of high density housing of the terraced style which was largely developed in the period 1900-1940. Further housing estates have been added in the period since the 1950s. Increasing public concern over the incidents led to the commissioning of a preliminary study by the Rochester-upon-Medway City Council to collate and assess relevant archival information to determine whether the subsidence occurrences in the area could be related to some common cause. The study included reference to local museums, libraries and societies, visits to the British Library Map Department, a review of the geological literature and a collation of the industrial history of the area. Several potential causes of subsidence were discovered; these included the existence of old water wells and dene holes and, more significantly, extensive excavations associated with brick production at the turn of the century. In addition, a canal had been tunnelled under the area in 1823, subsequently partly infilled and converted to railway use. The probable cause of the incidents at Frindsbury has been attributed to the existence of chalk mines associated with the brickfields and further investigation is now taking place to locate these. Clues to all of the features discussed above were available as open file information in public records. This paper describes how the information was acquired and assimilated and emphasizes the importance of the role of desk study in the initial stages of any development project.