Rising Waters

The Hawkesbury-Nepean Valley is fed by five major tributaries and the effects of flooding can be fast and far-reaching to the surrounding flat plains.

The Hawkesbury River, on which Thompson Square is situated, is one of the most significant fluvial systems on the eastern coast of Australia.

The Hawkesbury-Nepean Valley covers approximately 425 square kilometres of flood plain. It is an area that is prone to rapid inundation, causing both erosion of river banks and the deposit of silt.

Archaeological investigations previously completed at the site of the Hawkesbury Regional Museum indicate that initial deposition of alluvial sand deposits, found in the soil profile, began approximately 150,000 years ago.

During the late eighteenth century, 1798-1799, New South Wales was in drought. Locally, it was broken by a devasting flood in March 1799. Rising by roughly 15 metres, the river banks could not contain the vast rapidly flowing waters. The Government Store, which was located on the riverbank, was washed away, along with houses, livestock, and provisions. Warnings prior to the flood from the Boorooberongal had gone unheeded. The early settler’s clearing of the land for agricultural purposes also contributed to the effects of flooding along the Hawkesbury River.

The Hawkesbury River again broke its banks in 1800 and inundated the settlement’s crops. This trend continued in 1801, 1806 and 1809. The pattern of rising flood waters was understood by the Boorooberongal. They were well versed in the changing natural environment of the region, interacting with the seasonal cycles by relocating when flood threatened. By comparison, the colony mostly experienced discomfort, deprivation of basic amenities and great loss at each flooding occurrence.

The largest recorded flood occurred in June 1867. The waters rose to over 19 metres above normal levels – its height is represented by the pole above you. This flood was widespread and catastrophic, with many people losing their homes, their livelihoods, and their lives.

Since 1867, the area has experienced many more floods. From 1799 to 1978, there were forty-four major floods (above 10m) recorded for the Windsor area.

The masonry design located on the bridge abutment represents the layers of soils uncovered during the archaeological salvage – from the sand body to current day. The blue lines, based on historical data, represent the voluminous flood history of the area over thousands of years.

Windsor’s Recorded Flood History

Below is a representation of recorded levels of flooding for Windsor from 1799 to 2020.

1799   10.5m
1806   12.9m
1809   14.7m
1816   14.1m
1817   14.4m
1819   12.9m
1857   10.4m (July), 11.9m (August)
1860   8.8m (February), 11.8m (April), 11.1m (July), 11.4 (November)
1861   8.8m
1864   15.1m (June), 11.4m (July)
1867   19.7m
1868   9.5m
1869   11.6m
1870   9.0m (March), 14.1m (April), 11.2m (May), 8.5m (November)
1871   11.7m & 8.5m (May)
1873   13.1m (February), 9.0m (June)
1874   8.7m
1875   12.3m
1877   9.6m (May), 8.6m (July)
1878   8.5m
1879   13.6m
1889   12.2m
1896/7 – Windsor Bridge Raised
1890   12.3m
1891   11.2m
1892   8.5m
1893   9.0m
1894   10.1m
1895   9.7m
1898   10.1m
1899   8.6m
1900   14.5m
1904   12.7m
1911   8.3m
1913   8.5m
1815   8.0m
1916   11.0m
1922   9.6m
1925   8.6m (May), 11.5m (Jun)
1929   8.0m (February), 8.6m (October)
1934   9.3m
1943   10.3m
1945   8.5m
1949   12.1m
1950   9.6m (June), 8.4m (July), 9.8m (October)
1951   9.3m
1952   9.5m (June), 11.8m (July), 9.6m (August)
1954   8.8m
1955   9.9m
1956   13.8m (February), 8.7m (June)
1960 – Warragamba Dam Completed
1961   15.0m
1962   8.6m
1963   8.7m (April), 9.0m (June), 9.6m (August)
1964   14.6m
1967   9.0m
1969   10.2m
1974   8.7m (April), 10.4m (May), 9.6m (August)
1975   11.2m
1976   9.4m (January), 8.0m (March)
1977   8.9m
1978   14.5m (March), 9.7m (June)
1984   8.3m
1986   11.4m
1988   12.8m (May), 10.9m (July)
1989   9.2m
1990   8.7m (April), 13.5m (August)
1992   11.0m
2020   9.2m