In the first years of settlement Adelaide's water supply was obtained directly from the River Torrens, or from shallow wells along its banks. This water became brackish in summer and caused serious health problems due to pollution. In any case the supply was inadequate for fighting the fires which regularly broke out among the wooden buildings which made up most of the city. In 1856 a Waterworks Act was passed providing for construction of a reservoir at Thorndon Park to be fed from a weir in the Torrens Gorge (Fig. 1). This weir, the first major structure of its kind in the colony, was destined to provide a salutary lesson for all those engaged in the construction of similar structures. In July 1858 when the dam was tested, water jets broke out on the downstream side through fissures in the rock foundation. By September of the same year it was clear that the structure was in danger of collapse and would have to be completely replaced. Circumstances leading up to this painful decision are described in the Public Enquiry which took place at that time (Parliamentary Papers Nos. 19 and 73) and it is apparent that geology was a major cause of the failure.