I ADMIRE Mr Ibbotson for having the conviction and resources to restart the debate concerning dams on the Clarence in such a bold way. I learnt some things from his interesting opinion piece, but feel I must correct a number of points and state some facts that have been omitted.
Most of us here in the Lower Clarence floodplain live below the 10m contour and are at the mercy of floods - the price we pay for the benefits I guess. No doubt a structure could be built on the Clarence that would mitigate the impacts of some floods, but not without irreversible consequences. Despite whether Ibbo's dam could stop the floods we experienced this year or not, there are a number of ecological considerations that were not covered in his advert. These relate not only to his dam but any dam proposed for the Clarence.
What he and his supporters fail to appreciate is the Clarence River is a sum of its whole. The Clarence River needs floods. From its headwaters to the mouth it is one functioning ecosystem that has provided and will continue to provide directly and indirectly to the livelihoods and wellbeing of generations of floodplain farmers, fishers and communities of the Clarence Valley. The still functioning Clarence brings essential nutrients, carbon and sediment to the lower river, the estuary, the floodplain and the ocean from upstream.
It does this mostly in times of flood. With a dam we irreversibly cut this flow and impact on the function of the whole river system and its floodplains, both upstream and downstream. Flooding is an essential process of our still-functioning river.
Mr Ibbotson states that his dam will create a "pleasant lake". A look at a topographical map shows that this will be a very large "pleasant lake". About 65km in length if the 80m contour is flooded and over 100km if the 100m contour is flooded. A 100km artificial lake to replace 100km of natural functioning river habitat, home to local fish species found in numbers not known anywhere else in the world. Local fish such as the endangered eastern freshwater cod, bass, eel-tailed catfish, freshwater herring, eels and mullet along with platypus, birds and water plants are all dependant upon on this section of the river and access through it.
The fish are mostly migratory species and are dependent on the natural freshes and floods to move between spawning and breeding and feeding grounds along the length of the river from the estuary to around 800m elevation.
Mr Ibbotson's assertion that "lakes are great" because they attract more wildlife diversity, people and achieve environmental outcomes is difficult to support in the case of his dam.
To raise water levels to the 80m contour a dam of 30m height would be required. To dam to the 100m contour a dam 50m high would be required. The Clarence river gorge, located approximately 150km upstream of the Clarence River mouth, has seven waterfalls of between two and 8m in height and is a natural barrier to these migratory fish on their long (up to 300km) return trips from the estuary. The Clarence Fishtrack study has shown that Australian bass are only able to pass upstream of these falls during flood events that occur on average every 1.25 years when the falls are drowned out.
The legacy of inappropriate land use and clearing in the upper catchments, particularly the Timbarra catchment has provided a huge amount of sediment into the Upper Clarence which is now making its way downstream.
Unfortunately the volumes are so large upstream of the gorge that they are likely to pose a limit on the capacity of Ibbo's dam over time. This sediment, while damaging to our river's deep waterholes, is vital to replenish that which is washed out to sea. If it is trapped behind Ibbo's dam then we could expect increased erosion downstream.
Mr Ibbotson's claim that the tidal section "belongs to the sea" is false. It is simply the tidal portion of the Clarence River, a connected part of the Clarence River ecosystem accessed by some marine and estuary species moving upstream including sharks and dolphins who come up to feed, and freshwater species such as bass, mullet and eels which migrate downstream at times in their life cycle.
To function as the healthy productive estuary that it is, our river relies almost entirely on inputs from upstream. The replenishment of silt, sediment, nutrients and organic carbon and of course fresh water all comes from upstream, most of which would be trapped behind Ibbo's dam and therefore denied to the estuary, floodplain, wetlands, farms, soils, in-stream plants and animals that depend upon this input to replenish that washed out to sea naturally as part of the functioning river.
I hope Mr Ibbotson, after living in our Valley for a bit longer, will grow to appreciate the wonder of the east coast's most pristine large river system. He could use his creative skills and resources to promote a greater understanding of its ecology, its unique species and habitat and its existing tourism opportunities.
The advert points out accurately that the river is stressed through many human interventions. But despite this, it still supports NSW's largest fishing fleet, a viable cane industry, internationally recognised wetlands, a vast diversity of threatened species and a community which is proud of its river.
No other NSW river still does this like the Clarence, but they all used to. The main reason we are lucky enough to live alongside one of the last healthy large river systems in Australia is simply because it has been allowed to run free, to flood and to function as a river should - without dams.
Nigel Blake
Grafton
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