Lake Rowallan is situated in the upper reaches of the Mersey River Valley and is the first of two hydro impoundments constructed on the Mersey River.
The dam wall of the Lake Rowallan Dam is leaking. This is an embankment dam (an earth fill dam wall, not a concrete dam) built over 40 years ago.
Apparently the HEC has known of the leak for over 12 months. In winter 2009 the HEC could not use all the water through the power station and the dam spilled. The level of the dam has been reduced from full (spilling) last winter to 8.03 metres below full and steady (neither rising or falling). This has been achieved by running the power station flat out.
The Dam wall leak has not diminished despite the drop in the level of the impounded water by 8.00 metres. The lower level reduces the pressure on the wall and the leak. The hole in the dam wall must be getting larger. I am told the hole is at the base of the wall. This is significant.
The Hydro has been doing extensive investigations into the dam wall including seismic tests, excavating and drilling into the wall, some 15 holes both from the top and at the base to try and work out what is in the wall.
Apparently the documentary specifications of the fill within the dam wall, that is the composition of the wall, has either been lost or was never recorded. Hence the investigation.
The Rowallan Dam wall is apparently leaking to the West of the spillway. Some time ago subsurface drainage was installed along the base of the dam wall.
It seems the Rowallan Dam leak is being kept a secret by the Hydro.
There are many people up there working on the problem and I guess they must have been sworn to secrecy. Apparently the following firms have been working on the project: Shaws, Treloars and Richardsons Engineering.
When you read about dam failures you find that they can fail rather rapidly. Embankment Dam walls can fail. The best example is the Teton Dam. On June 5, 1976, Teton Dam, a 123-meter high dam on the Teton River in Idaho, failed, causing $1 billion in damage and leaving 11 people dead. Over 4,000 homes and more than 4,000 farm buildings were destroyed as a result of the Teton Dam failure. Have a look at the Teton dam failure: HERE
Note this happened within a half an hour.
The public interest of the people living downstream on the Mersey River seems to be of so little consequence that the Minister (David Llewellyn) and the Hydro have deemed their lives not worth considering via a proper and reasonable warning about the potential for a collapse of the Lake Rowallan dam wall.
The Lake Rowallan Dam wall site has been gated off and to move onto site you must be inducted.
It is rumoured that next year the HEC plans to demolish much of the Lake Rowallan dam wall and rebuild the wall.
I cannot understand this, as there has been no mention of this very expensive project in Government estimates and nothing in the media about the potential loss of electrical power to the grid and the enormous cost of such an undertaking.
It seems the HEC has done surveying to ascertain what would actually happen in the event of a catastrophe. But they have not made this surveying report public.
I cannot understand how the Minister could not advise the people of Tasmania. Aren’t they people in his electorate? Of course I do not know whether the Minister David Llewellyn knows about this dam wall leak. But it is hard to imagine he does not know.
Lake Parangana is almost full, so if the Lake Rowallan dam wall let go the 11 kms of water backed up behind the Lake Rowallan dam wall would, I expect, go straight over the Lake Parangana Dam wall and on down to Kimberley, Mersey Lea and Latrobe.
I wonder what does a 20 metre high wall of water 11 kms long actually does when it hurtles down a river such as the Mersey. I would like to know how many houses, farms, people and so forth would be affected.
I find it totally reprehensible and deeply shocking that this matter has not been disclosed and the public warned about the state of the Lake Rowallan Dam.
It is great that MHA Kim Booth has sought to expose this matter.
I refer readers to the following paper:
The University of New South Wales
SCHOOL OF CIVIL AND ENVIRONMENTAL ENGINEERING
BIBLIOGRAPHIC DATA SHEET ISSN 0077-880X
1. UNICIV Report No. R-399
2. ISBN: 85841 366 3
3. Date: 7 June 2001
4. Title and Subtitle:
THE TIME FOR DEVELOPMENT AND DETECTABILITY OF INTERNAL EROSION AND
PIPING IN EMBANKMENT DAMS AND THEIR FOUNDATIONS
5. Author(s): Robin Fell(1), Chi Fai Wan(1), John Cyganiewicz(2) and
METHODS FOR ESTIMATING THE PROBABILITY
OF FAILURE OF EMBANKMENT DAMS
BY INTERNAL EROSION AND PIPING IN THE FOUNDATION
AND FROM EMBANKMENT TO FOUNDATION
Robin FELL and Chi Fai WAN
UNICIV REPORT No. R-436 JANUARY 2005
THE UNIVERSITY OF NEW SOUTH WALES
SYDNEY 2052 AUSTRALIA
ISBN: 85841 403 1
Have a look at the Teton dam failure: HERE
Note this happened within a half an hour.
On June 5, 1976, Teton Dam, a 123-meter high dam on the Teton River in Idaho, failed, causing $1 billion in damage and leaving 11 dead. Over 4,000 homes and over 4,000 farm buildings were destroyed as a result of the Teton Dam failure.
Just think after looking at the slides of Teton, how would the Mersey catchment look. What would the consequences be for the people and the environment?
But the HEC reassures us all. If I lived near the Mersey River I would not be reassured.