Thursday 13 October 2005
TAMAR RIVER SEDIMENTATION
Mr FINCH (Rosevears) - Mr President, I must beg the forbearance of members of the Chamber because I am going to again raise the question of the silt problem in the upper reaches of the Tamar River.
I would like to bring to members' attention a response I have received from the Leader to questions I asked in August about water flows and silt build-up. At that time I sought the Government's view on whether water flows down the Cataract Gorge had any influence on siltation in the upper Tamar and on whether the Government could do anything to increase water flows through Cataract Gorge. The Government's response confirms my view that the problem in the upper Tamar is complicated and many-faceted and there is no single or simple solution. In fact it may well be that just about every suggested solution to silt problems might have undesired consequences. The Government acknowledges that heavy rainfalls in the Esk catchments move silt down the Esk rivers and also scour the bed of the upper Tamar, moving silt down the river. Tidal movements then bring the silt back just as quickly and deposit it as high as tidal movements allow. I will quote from the Leader's response:
'Whilst there are a few individuals who believe that the Trevallyn Dam has somehow been responsible for the levels of silt in the Upper Tamar, the reality is that it is natural geography and geology of the area that has provided a flood plain together with the processes of tidal flows that generates the ongoing levels of silt in the Upper Tamar River.'
I am grateful for the Leader's response and a very clear statement of the Government's view of the problem. The Government view does coincide very much with that of a long-time observer of the Tamar whose analysis I sought - and I speak of Charles Smith. He says that, because of the virtually level gradient of the Tamar, sedimentation due to tidal movements cannot be stopped and that the only way of maintaining the desired depth of water is by removal of the sediment at the rate of deposition. That of course means almost continuous dredging.
Mr Smith says for practical reasons there is little hope of reducing erosion significantly in the North and South Esk catchments. However, that does not mean, Mr President, with respect to the member for Rowallan - I will send him a copy of Hansard - that we should not be doing everything we can to make sure that forestry and farming operations do not make erosion worse. You may have seen the satellite photographs of Bass Strait river mouths published after the floods at the end of August, and that would suggest that erosion is a problem in most northern river basins. That is a picture taken from a satellite of the mud flowing out into Bass Strait, an interesting photo.
Mr Smith comments on other suggestions to alleviate the upper Tamar problem. He says diversion of the North Esk from Henry Street to Stephenson's bend - which I have mentioned here before - may in fact increase silting in the Home Reach area due to reduced flow and the loss of any flood scouring from the North Esk. He says that proposals to build weirs on the North Esk and upper Tamar overlook the fact that very efficient silt traps would be established by doing so, and he adds, hearteningly for the Government, that the Trevallyn Dam acts as a settling pond, trapping sediment, except during the floods of course. So there we are, Mr President, back at square one.
We can but continue a dredging program and try to keep erosion in catchments to a minimum. I might say that when we attended the meeting of UTRIA - Mr President, you may recall and so might the member for Windermere - we were told about three investigations that were going on and those reports are due to be released probably in a few weeks. I shall endeavour to minimise my contributions to the upper Tamar debate unless, of course, there are developments that the Council should be informed about.