CHARLES GILMOUR
How can we possibly consider applying any more pressure to Great Lake?
My father, Don Gilmour, was inducted into the Anglers Hall of fame mainly due to his book writing on the history of trout fishing in Tasmania. He was a good teacher and a great observer.
I have a personal interest in the development of Central Highland hydro storages and their history.
Generally speaking, all the dam systems created for power generation involved damming naturally occurring swamp areas that had small rivers flowing in and out. These areas include the Bronte system, Lake Echo, Little Pine, Arthur’s Lake, Great Lake etc. They were all built around the 30’s, 40’s and 50’s of last century – 60 to 80 years ago.
By definition, flooded marshes and flooding previously existing small lakes often gives the impression of large bodies of water, but they are in fact very shallow.
The height of a wall of a dam is generally the depth of the lake for the first half of the lake decreasing to nothing at the shore furthest from the dam wall.
Great Lake is a typical example. It looks huge. Originally it was a series of five shallow marshes/lagoons that ultimately drained into the Shannon River. Larger dams have been built, to store Great Lake, over the last 80 odd years. At the moment, water does not touch a dam. From a high vantage point you can see the outline of the original five lagoons. To the south of Canal Bay, the widest point of the lake, you can see a rock reef. You could walk across the lake at this point and in fact people have done so. (A rather telling picture would be to have people hold hands all the way across the lake in about Feb next year.)
The massive rock fill dam you see from the highway at Miena was extended by 10m in the early 70’s. It took 25 years of good winters for the water to even touch this new extension. The hydro then drained the Great Lake to carry out repairs. It took 2 years to drain 25 years of rain.
The outlet on the east shore at Elizabeth Bay is unable to take much more water out of Great Lake due to the low level. The outlet on the Shannon is now permanently open to supply water to down stream farmers and communities. Evaporation alone reduces the level by some 200cm a week.
Arthur’s Lake, which is pumped into Great Lake at Todd’s Corner is at a record low and subject to algae blooms. It has been pumped continuously for 2 years.
How can we possibly consider applying any more pressure to Great Lake?
Let’s have a look at the human wish list.
1. A pulp mill – 40 million litres a day
2. A large diameter pipe to Campbell town and Ross
3. Pipes to the Coal River catchment
4. Pipes to the Clyde river catchment
5. Power supply at Poatina
6. Water for Launceston via the Trevallyn dam
Remember it took 25 years to fill the Great Lake from its current height without all these pressures and with normal rainfall and snow.
Ironically, Mother Nature designed Tasmania to allow water to run evenly across the state. The Ouse River system (Clyde catchment) and Shannon system would normally receive all the water from Great Lake and the Western Lakes system. We have diverted these systems from ending up in the south to ending up in the north of the state via Poatina. We are now starting to see the folly of messing about with Mother Nature.
In actual fact, a pulp mill in the north using Great Lake water will actually be robbing drought affected areas in the south.
If Poatina was shut off and Great Lake water was allowed to run free, where it was designed to go – to the Clyde system etc and if Arthur’s Lake run free, the Northern Midlands would have truck loads of water.
Who would lose? The Gunn’s proposed pulp mill. Who would win? The areas that are drought affected who were naturally designed to have the water.
Get a map out and see who’s stealing your water.
It’s called Great Lake not the Greatest Lake!
Charles Gilmour
