Engineers Australia

Slope instability – Managing the risk A regulator’s perspective

Peter R Tobin

Abstract

The Wollongong City Local Government Area has records of slope instability dating back to early settlement. Following very rapid growth of the city in the post war years there was little good developable land left and marginal land became progressively more attractive to developers. In 1974 and 1975 periods of prolonged as well as very intense rainfall resulted in extensive hillside instability. Many houses were lost and litigation followed. As consent authority and without clear guidelines on the development of hillside land Council fared poorly in court.

In response, Council quickly sought and received legal advice with respect to what it needed to do to fulfil its legal responsibilities and duties as the consent authority. The legal advice made it very clear that Council is exposed to actionable negligence where it fails to consider whether the land to be developed has potential slope instability. The legal advice also stated that Council may seek a review by its engineers of the basic facts of the submitted geotechnical information and to set appropriate geotechnical conditions to be applied to the development. On this basis Council is entitled to rely on the submitted geotechnical information and any claim would be unlikely to succeed. It is pointed out that in undertaking this review Council does not have a responsibility to provide professional advice but at the same time must avoid being negligent. The success of Wollongong City Council’s geotechnical review process has been demonstrated by Council’s minimal legal costs on geotechnical aspects of development since the 1970s.