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 :-
This
shows a high degree of consistency of pattern and volume. The Borumba Dam
recording station is the same in the Summer months where all of the majors occur.
The SEQWater Dam statistics of the North Pine now follow :-
Of interest is the catchment area of 348 sq klms and a yield of 54,750ML. You
will notice that this yield has remained stable whereas the yield from the
Wivenhoe and Somerset has been under consideration for some time.
Catchment variation
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.
Equals 73,314ML.
Flood mitigation
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 Courier Mail article of the 17th February 2007 quoted the 
Dam
manager as saying that it would take 600 to 650 mm of intense rain to fill the
Dam. Its capacity is 214,960ML ( see Dam statistics)
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.
Catchment efficiency
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.
Conclusion
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.
