The West Dapto flood of February 1984: rainfall characteristics and channel changes

Abstract

Summary This paper describes the distribution, magnitude and areal pattern of recurrence intervals for a very severe rainstorm centred over the West Dapto area of Wollongong in February 1984. It also examines the impact of this storm on the channel geometry of streams draining the Illawarra escarpment. The storm was the largest 24 hour rainfall ever recorded in temperate Australia, and was very likely in excess of the 200 year event for the Dapto area. However, the localised nature of such storms in the region suggests that Wollongong can expect a major flood (in excess of the 100 year event) somewhere within the city every 25–50 years. Similarly, because the catchment of Lake Illawarra is usually larger than the areal distribution of these very high‐intensity storm centres, the frequency of severe flooding in the lake is bound to be greater than the frequency of any individual storm event. The most pronounced channel erosion (up to a fourfold increase in channel size) resulting from the 1984 storm occurr...