The primary focus of the book on extreme and large flood events has been on the provision of guidance necessary for assessment of dams and similar systems. With the publication of the Bureau of Transport and Regional Economics report of 2001 and the recent revision of the NSW Floodplain Development Manual where the extent of flood prone land was noted as being that land below the probable maximum flood (PMF) level, there is a need to upgrade the guidance provided on large and extreme floods in urban areas.

While guidance is provided in the current edition of Australian Rainfall and Runoff for the estimation of large and extreme floods in large rural catchments, this guidance has been focussed on the problem of PMF estimation at dams and other large water reservoirs. In essence this problem can be stated as the estimation of the PMF at a single point in a catchment. This problem needs to be compared to the PMF estimation problem in urban areas which can be stated as the simultaneous of the PMF at multiple points within a catchment.