Wednesday, February 23, 2011

Information from ACTEWAGL about inflow/outflow

Through the Canberra Times, I have discovered that ACTEWAGL have been releasing 130 megalitres a day for the year so far to keep the main dam at a safe level. This effectively doubles the inflow that I have measured, but I suspect that that is not the full picture. I believe that there must be further significant releases occurring from the other two dams. Why do I think this, even though ACTEWAGL say that these dams do not usually have such releases? Simply because inflows have been relatively low. I think that there must be continuous 'dribble' releases from the smaller two dams that probably again amounts to around 100 megalitres or so.

However, if that is not the case, we have had 14,000 megalitres from 176.2 mm of rainfall. That is again lower than I would have expected. Remember that the average rainfall for Canberra is 612 mm, with the average runoff 180,000 megalitres. Thus, I think that there must be something else going on - either in the hydrology or in the water management system.

Tuesday, February 8, 2011

Canberra rainfall for January

For January, we had around average rainfall, 54 mm.

My usual method of determining inflow will not work, as Canberra dams are sitting at 100 per cent. Thus, while I can set a minimum for the amount of inflow based on water usage and the fact that we briefly dipped below 100 per cent in early January, I cannot know what the real inflow. I will thus make an estimate, based on 300 megalitres of inflow per mm of rainfall - so around 16,000 megalitres.

We have had significant rainfall in the first week of February already - 56 mm. So we are on track for an above average rainfall for the first part of the year at least.

It may be that it will not be until La Nina ends that I will be able to make some more accurate measures of inflow. It will be interesting to see what the ratio of megalitres to mm is, giving me some more information about the hydrology of the Canberra area at the moment.