Author : J. V. Hodgkinson F. C. A. Chartered
Accountant : Aug 2006 to November 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
Associated evidence. The North Pine Dam.
You will see the evidence that the North Pine Dam mirrors the pattern and volume of rainfall of the Borumba Dam catchment. In the first instance we will look at the available information from the professionals at SEQWater.
The comparison of rainfall follows :-
A summary of the comparison of three stations in the Borumba catchment now follows :-
The SEQWater Dam statistics of the North Pine now follow :-
The calculation is : 54,750ML X 466 Sq Klms of the Borumba
catchment / divided by the catchment of the North Pine at 348 Sq Klms.
The SEQWater information above shows that there is no flood mitigation in the North Pine Dam with all flood water released in a controlled manner. The photo also shows the flood releases of the 1999 event. A glance at the major rainfall figures above shows a similar pattern to all of the Dams and a substantial volume would have flowed over the Dam. We have sufficient information to examine this aspect.
The Borumba Dam is its own flood mitigation if the Dam wall is raised in accordance with Mr R McMah's contribution. He envisages the Borumba capacity to be in the region of 2,000,000ML capacity.
The attached schedule is a summary of rainfall in that category. Of particular interest is the 1999 rainfall average of 438mm in the North Pine Dam with the photo above clearly showing the flood discharge. The other rainfall events are significantly higher. The higher rainfall can have a much higher impact than a direct correlation.
It is generally recognized that, with its rocky terrain, the Borumba Dam catchment is the most efficient of the Dams. In the area of proof, there is a conflict of information. The Regional Manager at the time advised that the "Peak discharge per day" was 154,300ML. The Department of Natural Resources web-site advises that the total discharge for the month of February 1999 was 167,062ML.
The Qld Government advises that the duration of the flood in the Mary Valley was significantly more than a single day. Examination reveals that the volume of water was most likely to be double the 154,300ML to over 300,000ML.
You will notice that the Dam Manager at the time compared the volume of water in a single day to 1/2 of Sydney Harbour. That converts to 250,000ML a day. However, we should keep in mind that he was making a point.
Using the Dam Manager's advice of the time, the efficiency of the Borumba catchment compared to the rest of the Mary River catchment is above 1.7 times. If the Dept of Natural Resources information is correct, the point is not proven. Refer to my calculations under "Hydrology" button.
With the catchment area of the Borumba being either equal to or more efficient than the North Pine, the Calculation based on the catchment area is stable at 73,314ML.
The evidence points to a very high volume of inflow not retained by the North Pine because of the lack of flood mitigation or retention availability. This is not so in Mr R. McMah's proposition of the expanded Borumba Dam. This will make a significant addition to the 73,314ML already calculated.