The January 2011 major rain event was devastating for Toowoomba and the communities along the rivers and creeks as far as Brisbane, but the scale of the event was not unprecedented. The event was not unusual in its size, or volume of water that resulted. It was the location of the heavy rainfall upon previously saturated ground as well as the storm’s intensity and speed that caught Queenslanders out.
Brisbane and its surrounding catchment areas have received major rainfall events multiple times over the last few decades. This is something I didn’t know, until I spoke to a colleague who is a hydrologist. After our conversation I did some research and located all the information I needed about previous flood events at www.bom.gov.au.
Here are a few of the rain events listed on the Bureau of Meteorology website:
March 1992: Major flooding occurred in the upper reaches of the Brisbane and Stanley rivers. No reports of damage were received. Minor flooding occurred in some of the Brisbane Metropolitan Creeks causing minor traffic problems.
May 1996: Brisbane River basin: Heavy rainfalls and flooding were reported throughout the Brisbane catchment during the first week of May with widespread 7 day rainfall totals of up to 600mm. A tidal surge caused by the low pressure system and gale force winds caused higher than normal tides in the Brisbane River which also contributed to flooding in low-lying areas. Runoff from the first peak in the Bremer River combined with the tidal surge and local runoff in the Brisbane City reaches caused higher than normal tides at the Port Office during Saturday 4th and Sunday 5th.
During this event, inflow from the Stanley River and tributaries caused the storage level in Somerset Dam to rise from about 54% to just over Full Supply Level. Moderate flooding in the Upper Brisbane River caused the storage level in Wivenhoe Dam to rise from 57% to nearly 90%of Full Supply Level.
Feb 1999: Significant river rises in the Stanley and Brisbane rivers and tributaries above Wivenhoe Dam resulted from heavy rainfall on 8th February. Moderate flooding developed in the Stanley River and major flooding in the Brisbane River above Wivenhoe Dam. Releases from Wivenhoe Dam commenced on the 9th causing closures of low-level crossings along the Brisbane River downstream of Wivenhoe Dam, with minor flooding between Wivenhoe Dam and Mount Crosby. The same rainfall system caused rapid rises with moderate flooding in Lockyer Creek, Warrill Creek and the Bremer River. The Bremer River at Ipswich peaked just below the minor flood height on the evening of the 9th.
Feb 2001: Rainfall in the Brisbane River during early February varied from 150 mm in the lower reaches of the Brisbane River to nearly 600 mm in the upper reaches of Laidley Creek. The most significant flooding occurred along Laidley Creek with levels some of the highest of record but, fortunately, of short duration.
Minor flooding resulted in the upper reaches of the Brisbane River over the first few days of February and low flows were released from Wivenhoe Dam during the second week in February.
Nov 2008: Intense rainfall occurred overnight on Wednesday 19th November across South East Queensland, particularly in the Ipswich and Lockyer Valley area. This caused local flash flooding overnight with riverine flooding occurring in the Bremer River, the Lockyer, Laidley and Warrill Creeks on Thursday the 20th of November. Major flood levels were reached in the Bremer River and in the Lockyer, Ipswich and Northern Brisbane Creeks.
Oct 2010: Brisbane River catchment: Rainfalls in excess of 200mm in the top of the Stanley River catchment combined with widespread 100mm falls throughout the rest of the upper Brisbane River catchment in the 48 hours to 9am on the 12th of October to produce minor to moderate flooding above Wivenhoe Dam. This flooding provided both Somerset and Wivenhoe Dam with good inflows eventually producing the first large-scale gate operation at Wivenhoe Dam since 1999.
In most of these events and in particular the events in 1999 Brisbane would have been flooded. The 1999 event could potentially have even been more damaging than 2011 for the city of Brisbane if not for the mitigating impact of the Wivenhoe dam.
In these events Wivenhoe Dam worked, and worked well in preventing widespread damage to the city of Brisbane. The rain fell into the catchment and flowed into the dam where the flood water was contained and then slowly released downstream to the city.
In 2011 heavy rain was dumped around several major catchments. Inflows to the Brisbane river occurred not only from the controlled release at Wivenhoe, but also the Lockyer Creek and Bremer River, both of which are uncontrolled and join below the dam wall. Water was even flowing from Beaudesert down through the Oxley Creek system into suburban Brisbane and the Brisbane River.
The Flood Report has suggested that the engineers at Wivenhoe did not follow the operations manual and that alternative actions could have changed the level of flooding in Brisbane by as much as 50cm at the Brisbane City gauge. Even if engineers had closed up all the gates and nothing was released, Brisbane would have still flooded. Roads would have been closed, power would have been cut, and homes destroyed.
Some people who were badly affected may feel inclined to vent their anger and point the finger at Wivenhoe Dam authority figures, but most of us should thank the hydrologists, meteorologists and engineers for the wonderful job they have done in the past to save our QLD towns and cities from the worst of Mother Nature.
As a postscript, in case readers may think that I may have little sympathy for people badly affected by the most recent floods, the images you see in this post are of my house in Oxley which was not covered by flood insurance!
If readers have not yet visited QM&S to see the “Bouncing Back From Disaster” exhibition then we would encourage you to do so to stimulate your own personal reflections about this major flooding event in our lives.