By Ken Granger
There are still several questions that need answers regarding the costs and benefits of Traveston. In addition to the flood safety issues that have now been well reported, the following come to mind:
1. The Mary River shares the head of its catchment with the Stanley, Brisbane and Pine Rivers. If dams on those rivers are at a low level why would Traveston not also be at a low level - so where is the gain?
2. Being such a shallow impoundment would Traveston not be an ideal environment for blooms of blue-green algae and if it were so affected would that mean that the water could not be used for human consumption without expensive treatment?
3. The final design, and hence cost, of the dam construction can not be known until after the completion of the hydrological and hydraulic modelling and the geotechnical engineering study. If the flood regime and the poor foundation geology cause the cost of the dam to escalate considerably (as it could) will there be a cost-benefit of the dam be acceptable?
4. Will the geotechnical investigation take into account the fact that there have been 32 recorded earthquakes with a magnitude of 3 or greater within 150 km of the dam site - the closes being a magnitude 3.6 event only 30 km from the dam site? Whilst earthquakes of this size would not threaten a dam this seismic record should clearly be taken into account in the design of the dam, especially its foundations. Given the poor geological structures at the dam site this may add considerably to the cost.
2006 July 30, Off Sunshine Coast, Qld, ML 2.9
0145 UTC, 153.89°E, 26.68°S, normal depth [MEL]
(Sunday July 30, 11:45 am AEST)
This moderate earthquake occurred off the coast of Queensland, about 120km northeast of Brisbane.
2005 September 6, Off Fraser Island, Qld, ML 2.6
1501 UTC, 154.55°E, 24.64°S, Normal depth [QLD]
(Wednesday, September 7, 01:01 am AEST)
This earthquake was in the Pacific Ocean, northeast of Fraser Island, and 245 km east of Bundaberg.
2005 September 7, Somerset Dam, Qld, ML 2.2
0918 UTC, 152.62°E, 27.12°S, Normal depth [QLD]
(Wednesday, September 7, 07:18 pm AEST)
This earthquake was 6 km east of Somerset Dam, and 54 km northwest of Brisbane.
2005 January 5, Off Sunshine Coast, Qld, ML 3.6
0831 UTC, 153.4°E, 26.1°S, Normal depth [MEL]
(Wednesday, January 5 06:31 pm AEST)
This earthquake occurred off the Sunshine Coast in southeastern Queensland, northeast of Noosa.
Gayndah, Qld, 1883 and 1935
1883 Gayndah earthquake, ML 5.9
1883 August 28, 16:55 UTC
(Wednesday, August 29, 02:55 am EST)
Buildings in Gayndah sustained considerable damage, with a maximum intensity of MMI 7. Bundaberg and Maryborough suffered minor damage to structures. The earthquake was felt from Rockhampton in the north to Warwick in the south, and as far west as Roma. See Atlas 2 for details and an isoseismal map.
An aftershock followed at 04:20 am EST, and was felt in Rockhampton (250 km to the north) and Maryborough (110 km to the east). This radius suggests an aftershock magnitude of about ML 5.2.
This earthquake occurred two days after the Krakatoa volcano eruption in Indonesia.
1935 Gayndah earthquake, ML 5.2
1935 April 12, 01:32 UTC
(Friday, April 12, 11:32 am EST
stevem
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