The Election Go Round, The Tamar And The Gorge

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Launceston Flood Authority calls to South Esk to be 
reinstated to fix the Tamar estuary's silt problem
By MATT MALONEY March 28, 2016, 8 p.m.
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Ratepayers Association has been canvassing the idea of reclaiming waterflow for the South Esk River for some years now, with little recognition or credit by The Examiner.

Our summation asks for at least the full flow to be restored to the old Duck Reach Power Station, not just the half flow presently proposed. Presently the proposal is to reduce the intake pipe/tunnel size by half, forever limiting the possible flow.

We also argue for the valves in the dam to become mini-power generators, and although the replacement valves are currently being installed. Presently the 'valve replacement strategy' has bee  suspended so that Trevallyn Power Station is kept operating during the present power crises. 

Moreover, we also argue for generators to be installed in the riverbed itself, so all in all the water for generation is used more than once.

Despite the lessons to be learned from the present management regime there is no sign of the valve being replaced by 'generator valves'.

It may be that Trevallyn Power Station could continue operating, albeit on a reduced basis, but during floods, could be fully commissioned as there would be more water through Cataract Gorge than can be easily managed.

IN SUMMARY: Water flow in South Esk River via Cataract Gorge:

• Water is diverted from the natural course via Cataract Gorge of the South Esk River via the Trevallyn Dam to the Trevallyn Power Station, hence via the Trevallyn Tailrace to the Tamar River. 
• The Trevallyn Power Station is a 'run of the river' power station, meaning that the rate of flow to the power station is regulated by the rate of flow entering the Trevallyn Dam, save for a 0.48 cumec ( has been increased to 2.5 cumec) flow allowed beneath the Trevallyn Dam to flow into the Cataract Gorge section of the South Esk River.
• The intake level at Trevallyn Dam is approx 2.M below the top of the dam, meaning the lower level water remains captured in the dam until it flows under the dam to Cataract Gorge, albeit at a very slow rate of 0.48 cumecs (has been increased to 2.5 cumecs). 
• Prior to decommissioning, the Duck Reach Power Station, diverted water from the South Esk River via a low level dam, at a maximum flow of 4.6 cumec (calculated by maximum cross-section of flume). Apart from a periodic lessening of water flow in the South Esk River between the low level dam and the Duck Reach Power Station (Deadman's Hollow section), all South Esk water continued to flow through Cataract Gorge to Tamar River. 
• The effect of the Trevallyn Dam diversion is that the 'fresh' water entering the dam is all diverted to the Trevallyn Power Station, leaving only 'static' water trapped in the dam to flow via Cataract Gorge, apart from periods of flooding when significant water overflows the dam. 

Providing a power station is constructed at Duck Reach, and even better if mini power stations are built in the Trevallyn Dam wall to replace the manual valves, then:

•  A total of approx 5 cumecs of water could flow through Cataract Gorge, calculated as 0.48 cumec via Dead Man's Hollow and 4.6 cumec max. via Duck Reach Power Station. 

• A flow of approx. 5 cumecs will be beneficial to improving the environmental water flow impacts in Cataract Gorge, without overflowing the causeway at First Basin; and thus 

• Delivering a benefit by lessening of silt in the yacht basin area because less 'flocculation' of clay will occur due the presence of additional fresh water there.

Launceston Flood Authority chairman Alan Birchmore belief that "almost every problem that we've got in the upper reaches is to do with waterflow,” might not be justified if the full spectrum of evidence is taken into account.

Hydro Tasmania installed a dam on the South Esk in 1955 to service the Trevallyn Power Station 

The flood authority's  convincing Hydro to release 25 cumecs of water from the dam over three days in 2013 after the silt raking programs experiment, and to flush out the Tamar’s yacht basin has had contestable outcome. 

The ways the Tamar gets choked by mud and sludge are various and Launceston's stormwater management surely plays a significant part in it. The full consequences of reconfiguring the city's geography needs to be studied from multiple perspectives and involving a broad spectrum of the community.

If the mud is considered "visually un-aesthetic" then maybe we need to learn how change that perception. If the problem is too much sewage sludge, and the toxins that come with it, then maybe an increase in river low will help but all by itself it is unlikely to solve the problem.

Interesting, with an election on the way 'the state of the river'  an  'the Gorge' will get the kind of airing designed to "distract the punter until next time".  We might do well to keep this in mind this election – and maybe Examiner sales may even peak.