Friday, 10 June 2016

A Carwoola-take on the East Coast Low

I have reported elsewhere - at some length - on our experience of the East Coast Low at Mallacoota.  This seemed quite exciting, although reading that Robertson NSW scored 600+mm of rain over 3 days makes our coastal experience pretty mild.

While we were getting 180mm  down there I kept an eye on the BoM radar from Captains Flat which suggested that Carwoola was getting plenty.  Mallacoota is 'interesting from a radar view as it is just outside 256km from Captains Flat and only just inside 256km from Bairnsdale. In the next image the curved lines are the relevant circles (with the Flat as the LH image).
It did seem that the image from Bairnsdale was a far better representation of what was happening outside the window.

The Captains Flat images were a bit of a worry as I thought our Creek crossing was likely to flood and that run off down the drive might lead to a lot of scouring.   To my pleasure, when we returned home, while the crossing had flooded it had not damaged the surface at all.  The drive had not scoured at all.

In fact the flood had washed away a lot of debris from the March 2016 deluge!  The clear area (marked 1) looked like the area marked 2 before this event.
So what did happen?  Basically we got 118mm of rain, with 88mm coming on Sunday 5 June.  (That was the second highest reading for the area, with the record being 94mm on 12 October 1996.) getting back to June 2016, in contrast Mallacoota scored 180mm.  The 2016 values are contrasted in this chart although note that:
  1. I don't know when the rain started at Mallacoota - it was happening when we arrived - so the amount for the 4th (and indeed the total) is understated by whatever fell before about 2pm on that day; and.
  2. as I didn't get up at midnight to check the gauge at Mallacoota the split between days is estimated and thus a tad 'approximate'.

Having the benefit of an automated system at Carwoola I can show the amount that fell in each 30 minute period.  (The red line in the axis marks the different days.)  It shows the rain starting just about as we left Carwoola and finishing at 10:30 on the Monday.  At Mallacoota the cease-fire was about 1330 (so making the bold assumption that the start of rain was also 3 hours later I didn't miss much).
 Since returning I have exchanged emails with a neighbour and he advised that "Rain here really useful – steady and non-violent.".    That is supported by a chart of rain rates, showing a similar pattern to the chart above and nothing above 25mm per hour.
In contrast, since October 2013, I have recorded rates of more than 100mm per hour on 18 occasions.  The heaviest fall - on 5 January 2015 - achieved 175 mm per hour but was fortunately brief as we 'only' accumulated 16mm in the 30 minute recording period from 1830.

Of course this amount of rain has topped up our dame very nicely.
The hilt of the sword is just visible in this image of our house dam, whereas the whole device was visible 2 weeks ago.  It isn't so easy to see the difference in the top dam but I estimate it has close to an extra metre of depth.

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