Territory Stories

Miscellaneous Correspondence and Data on Alice Springs Flooding 1986



Miscellaneous Correspondence and Data on Alice Springs Flooding 1986


Hamlyn-Harris, D.; Galton, R. P.; Charrington, Rowan; Freyling, Ron


E-Publications; E-Books; PublicationNT; Report no. 33/1986







Publisher name

Northern Territory Government

Place of publication

Alice Springs


Report no. 33/1986

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Attribution International 4.0 (CC BY 4.0)

Copyright owner

Northern Territory Government



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I I I I I I I I I I I I I I I I I I I ANNEX 2 TRANSCRIPT (Detailed minutes of the Region Counter Disaster Planning Committee Meeting - Region 5) Mr. Paige I have brought along an extra diagram. These are some design calculations typical of floods in Alice Springs. What you see is a graph in time versus discharge, the time axis is marked off in hours then superimposed on each other are a series of Hydro photographs starting off with the 1-10 year event which has a 10% chance of occurring and peaks at something like 450 M3/ sec which would have been smaller that 1983, going up to the 1-100 which peaks at 1150 M3/sec. The maximum probable is not there to scare you. That is a theoretical calculation that if you filled the atmosphere to as high as you could with moisture and it all dropped out at one time, this sort of flood would come down the Todd and for obvious reasons practicality we don't even consider that. It would be virtually an act of God. I guess the thing I wanted to introduce first of all in this diagram is the short warning time. If you look at the 200 M3/sec discharge and then look at the 1-100 Hydrograph you will see that this is predicted to occur almost three hours after the start of the flood rise. That is the 1-100 flow. But then look at, keeping the same 200 M3/sec discharge, at the 1-10 graph, you will see that it occurs at 3 and 3/4 hours, so perhaps we have got an hours difference between the 10 year flood and the 100 year flood, so if that is the 10 year flow there, it's the 100 year flow here, just picture us in our forecasting sequence again, we would pick up at this given time that we are reading 200 M3/sec . At that stage we are not too sure if we have got a 1-10 or a 1-100 flow and in fact we have to wait another hour, and in that hour could be equivalent to a 1-50 year, that's how short the warning times are. Now that, has the obvious affect when we start talking something about the welfare issues and the obvious welfare issue is about evacuation and looking after people. If we start looking at the Hydrograph, I think in about three phases we will talk about the rising curve of the Hydrographs on the left side of the peak, the peak itself and the falling cUrve of the Hydrograph. So if we look at the rising curve of a 1-100, we got about 4 hours to peak. During that time what sort of things will happen?