Firstly, flood risk is defined as the product of probability and consequence, therefore the greater the development behind the levee the greater the risk.

Levees only reduce risk by reducing the probability of flood provided further development does not occur behind the levee.

Secondly, the probability of a flood (over-topping) is reduced if the levee is strengthened or elevated.

However, the levees are at the maximum height (5.2m AHD) which can be supported by the river banks, so reducing the probability of flooding is not an option.

Thirdly, the probability of over-topping is increasing as sea-levels rise and rainfall increases due to climate change, so risk is increasing even without further development.

The fact that levees increase/encourage risk is the levee paradox.

It has been ignored in Launceston by those who should know better but who will not be around to deal with the ramifications of their decisions.

ALL rivers carve channels through their landscapes over millennia, so have the South Esk and North Esk Rivers.

The resultant silt has been deposited in the flooded valley at and below their confluence.

I struggle to comprehend how the commissioning of Trevallyn Power Scheme in 1955 has had such a dramatic detrimental effect on siltation in the Tamar estuary.

And how de-commissioning of the power scheme "would definitely reduce the silt accumulation" in the estuary (Dr Ian Kidd, The Examiner, March 12).

Dr Kidd you stated that combined sewage and storm-water treatment systems work successfully "around the globe but not in upper estuaries" (The Examiner, March12).

Does this mean that combined systems don't exist in upper estuaries elsewhere or that they are not successful in upper estuaries elsewhere?

If the root cause of poor water quality in the upper Tamar estuary has been identified, shouldn't we be moving to fix the root cause rather than considering Band-Aid solutions which may or may not move the problem a little further downstream?