Dams and floods

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Dams and floods

Posted 27/01/2011 by Bill McCormick

Dam releasing water
The present floods in NSW, Queensland, Victoria and Western Australia have caused substantial damage to life and property. Questions have been raised as to whether the impacts of the floods could have been better mitigated. Are levees or dams the answer?

Both the Federal Government and Opposition have raised possible solutions to this issue in the future.The Coalition has established a task force of Shadow Ministers to examine potential dam sites for flood mitigation and water storage (see useful articles here and here). The Minister for Regional Affairs, Simon Crean, discussed the possibility of constructing levees to protect parts of Brisbane (see useful articles here and here).

The impact of the operation of the Wivenhoe Dam on the level of flooding of Ipswich and Brisbane has been questioned. The Wivenhoe Dam was built for both water storage, 1165 Gigalitres (GL), and flood mitigation capacity, 1450 GL, to protect Brisbane from a flood the size of the 1974 flood. The dam seems to have reduced the flood levels of the Brisbane River in Brisbane (see article here). A SEQ Water Grid spokesperson said that the estimated flow of the Brisbane River during the recent flood would have been 13,000 cubic metres (m3) per second if Wivenhoe Dam did not exist, which compares to the river flow of 1974 floods of 9500 m3/sec. A Courier Mail article stated that:

Total inflow into Wivenhoe Dam at this time was 2.6 million ML a day, equivalent to the dam's entire storage. SEQ Water Grid spokesman Barry Dennien said this compared with a flow of 1.5 million ML in 1974, showing what an extreme event was under way.
The dam was never designed to completely contain such a massive flood and controlled releases were always planned with their quantum depending on the dam levels and the situation of the flooding of tributaries downstream of the dam, such as Lockyer Creek and the Bremer River. However there have been criticisms of the dam operating procedures which, it is argued, caused greater flooding in Brisbane and Ipswich than would have been the case if the dam levels were held at levels substantially below the 100 per cent storage capacity before the heavy rain event. It is claimed that the maintenance of the 100 per cent storage level may have resulted in the need to release 645 GL from the dam on Tuesday night to prevent an uncontrolled release of water from the dam following the dam nearly reaching its maximum capacity (see useful articles here, here and here). Critics have argued that in a La Niña year future flood operation procedures should keep dam storage levels 400-650 GL below the dam’s normal 100 per cent water storage capacity, as at present (see useful article here).

The Commission of Inquiry into the Queensland floods will address this issue as part of its terms of reference.

Implementation of the systems operation plans for dams across the state and in particular the Wivenhoe and Somerset release strategy and an assessment of compliance with, and the suitability of the operational procedures relating to flood mitigation and dam safety.
Lawyers have raised the possibility of insurance companies and /or home or business owners suing the dam’s owner Seqwater and/or the Queensland Government for damages if the Inquiry were to conclude that there was some negligence in the release of water from Wivenhoe Dam causing greater flooding (see articles here and here).

(Image sourced from: http://cache.virtualtourist.com/4936607-General-Brisbane.jpg)

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