The month of June 2017 marked 150 years since one of the most disastrous floods to affect NSW in recorded history. The flood peaked at 19.7m at Windsor on the Hawkesbury River, much higher than the 15.1 m reached by the 1961 flood which is the largest in living memory.
Flooding was widespread across NSW at the time with severe flooding recorded in areas around Sydney such as Parramatta, Liverpool, and Bankstown. However, record flooding also occurred to the south in Wollongong, Nowra, and Moruya, as far north as Tamworth and west to the Murrumbidgee River. It is thought that it was caused by an intense east coast low.
The prolonged and intense rainfall over the 22,000 square kilometre Hawkesbury-Nepean catchment had a devastating effect on the particularly vulnerable, bathtub-like floodplain between Richmond and Windsor. Here the river rose more than 19 metres from its normal level just above sea level.
The town of Windsor was almost entirely underwater, and split into two islands. While the people who lived in the Hawkesbury-Nepean had seen frequent flooding, the 1867 flood was unprecedented in scale, and came after a long period of drought, leaving them unprepared. Twenty people were killed in the floods in NSW, of which 12 members were from the Eather family in the Hawkesbury, who were swept away after their house collapsed before the arrival of a rescue boat. Many families huddled together on the rooves of houses until rescued and a special train was dispatched with additional rescue boats from Sydney.
Historians say that settlers in the catchment were warned by the local Darug people against building in the flood-prone area decades before the big flood, warnings that went unheeded. There is sedimentary evidence that at least one flood much larger than the 1867 flood has occurred in the valley under current climatic conditions.
Settlement on the floodplain only expanded in the decades following the big flood, with some houses being built as low as 11m AHD and many built at 14m AHD. Today, the flood planning level at Windsor is 17.3m AHD. The probable maximum flood at Windsor could reach 26 m, completely submerging the town.
In more recent years it was realised that evacuation roads would be cut off by floodwaters at a gauge height of only 14 m, well before a flood similar to the 1867 flood reached its peak. The rescue effort would not be able to cover the widespread extent of flooding and the growing population, even with modern rescue boats and helicopters. The NSW Government's recently released "Resilient Valley, Resilient Communities" strategy (FM May 2017) aims to address these shortcomings, and provide solutions to be better prepared for floods similar to the one that ravaged NSW 150 years ago. (read more here, here and here)