Author : J. V. Hodgkinson F. C. A. Chartered
Accountant : Aug 2006 to April 2013
The principal thrust of this
This is my review based on official
statistics and documents. It is done in conjunction with Ron McMah, grazier
of Imbil and Trevor Herse, retired of the Gold Coast
Note : December 2009
The appendix to our alternative proposal provides a clearer view of pumping requirements
The water involved is:
Borumba dam expansion : Additional 52,000ML. No pumping requirements. Hydro power available for delivery of existing yield of 35,000ML to the Mary Valley together with any further allocation out of the additional 52,000ML.
Release of the 93,000ML unallocated in the Wivenhoe/Somerset system. Pumping required for the initial 1,500,000ML and replenishing of 760,000ML and 560,000ML. This is the only pumping required in the period 1888 to 2009.
Release of the additional 80,000ML identified while considering raising the Wivenhoe Dam wall. The following is relevant.
Minister Hinchcliffe has left to the last of what he describes as "The second key constraint". It is contained in pages 3 and 4.
It bears the label "Impact on flood immunity downstream from Wivenhoe Dam"
The general overview of the linking with the Borumba Dam is to store water in it for later return to the Wivenhoe/Somerset. It is an adjunct to storage space in the dam system permitting better control over ecological and water distribution rights.
It can be done, with or without the use of the flood compartments.
There is a provision in the Water Resource (Moreton) Plan to permit this operation of transfer and later return.
The Government's decision to allocate 66% of all water through the Wivenhoe/Somerset system is the Primary key constraint. It has been given priority on the HOME PAGE. There appears to be no other constraint.
For clarity, the overall position is this:
The Borumba Dam is expanded to 2,000,000ML
Dealing with the Expanded Borumba first.
The QWC commissioned hydrology report states:
If this were the case, then there would be no need for the Traveston or the McMah plan as it means that an additional 2,000,000ML is available every 3.7 years on average.
The reality is that in most cases, the Borumba expanded to 2,000,000ML would fill to 25% or 500,000ML based on stream flows. The current yield will increase by 50,000ML to 71,000ML. It mitigates the flooding in Gympie and allows the Mary River to run free.
This leaves approximately 1,500,000ML spare capacity.
Use of that capacity without the use of the flood compartments or change to the operational level.
With this spare capacity, the dam managers have the ability to keep the wivenhoe/Somerset at 50% or lower without use of the altered operational requirements or the flood compartments. With the Wivenhoe at 1,165,000ML plus the Somerset at 380,000ML capacities, the joint capacity is 1,545,000ML. 50% of this figure is available for pumping without interference. = 772,500ML. At 40% level, the figure is 927,000ML.
A simple example of the backup facility in operation is that our current dam levels are at 75%. A reasonable rain depression, covering both catchments, will provide around 50% fill (1996 minor type, see next photo) and thus has 25% going over the spillway uncontrolled to the detriment of Moreton Bay. By controlling the dam levels at 50%, all of this flood water would be retained giving us a further benefit of 386,000ML stored in the Borumba on such an occasion.
A further illustration would occur if the
dams were full and followed closely by another such as occurred in April 1988
and April 1989. The storage in Borumba would benefit by the volume pumped in the
one year gap.
The event to which this article refers did not have any water from the main tributaries being the Upper Brisbane River and the Stanley River. The rain depression did not come far enough west to fully engage the catchments, with the minor 16% flow being trapped in the dams.
While the last period without these random
but vital events, gave the impression of a drought, they are not uncommon
as their name suggest. Our attention should be turned to harvesting them when
they are prevalent. For example, the short life of the Wivenhoe from 1986 to
2001 saw 6 of these events not only fill the dam from scratch to overflow but
refilled it 4 more times, 3 to overflow. These overflows collectively are in the region
of being well in
excess of 2,000,000ML plus. The starting point is April 1988 and April 1989
scratch to overflow and approximating 1,500,000ML.
This method is used until the Borumba is full. The Wivenhoe/Somerset dams then have no where to store overflow water.
Using this method in the short life of the Wivenhoe, at February 2001 both dams would have been full and the "drought" period to 2007 covered with ease without the expensive grid system.
This method releases the 80,000ML held in reserve "in case". It can be allocated. Together with the additional yield of 50,000ML from the Borumba expanded to 2,000,000ML, the collective total is 130,000ML surpassing the Traveston as now constituted.
The cost of the dam wall and pumping requirements on engineering advice of the Government and others is $1.9 billion with the Traveston stage 1 and 2 but not stage 3 estimated to be $2.6 billion.
Use of the flood compartment and change to the Operational level
That leaves the speed at which it can occur. The dam managers and those in control of dam safety should consider any use of the flood compartment together with the size of pumps used. Change to the operational level will allow some scope. Dam safety requirement is at EL 74Metres above sea level and reduces the flood compartment to approximately 1,000,000ML in the Wivenhoe.
If what one reads is correct, that drought and floods are to be larger, longer and more frequent, the use of additional storage is essential.
Extensive work on pumping requirements
Extensive work has been done on pumping volumes and requirements. In the area of engineering and pipeline requirements, I was assisted by an engineer who name appears on the Wivenhoe Dam plaque. He is retired and prefers and enjoys his anonymity. They are contained within pages 20 to 41 in my alternative to the Traveston lodged with the Coordinator General under the EIS (Environmental Impact Statement).
His workings have been on view for two years without critical comment of any kind.
Refer to FINAL SOLUTION tab