Heavy Rainfall on 19 January 2016

Published: 19 Jan 2016

Our rainfall gauge at the Botanical Gardens showed that we received 84.8mm of rain on Tuesday 19 January, peaking at 2pm.  To put this into perspective the average rainfall for the entire month of January is 54mm.

Some interesting stats:

  • The 24 hour rainfall of 84.8mm was calculated at a 1 in 7 year event
  • The peak 1 hour rainfall was recorded at 22.8mm and was a 1 in 8 year event
  • The peak 12 hour rainfall of 82mm, the peak 6 hour rainfall of 63mm and the peak 2 hour rainfall of 38.6mm were all around the 1 in 15 year event range

So this has been a reasonably significant event.

Roading

Despite the heavy rain there was virtually no damage to the roads with the flooding confined to the urban areas and generally just ponding not flowing.  The lack of water flowing and the short time it ponded for was why damage was minimised.

With the lead up to the heavy rain most of the road sumps had been cleared prior to the heavy rain.  Our road maintenance contractor responded to 50 service requests that day, mostly in the afternoon.  The performance by Fulton Hogan and CityCare crews with the response time of 10 to 15 minutes was excellent.

Rural roads were not flooded by the heavy rain although road side drains were often at capacity.  However the water quickly disappeared through soakage to ground or flowing into waterways.   The low level of most waterway, streams and rivers allowed the drainage system to work very efficiently.

Stormwater

Our Level of Service for the residential stormwater system is to deal with a 1 in 5 year event.

There were some significant ponding issues in some locations and also some minor sewage overflows. However the ponding drained away through the network very quickly once the peak rainfall had passed. For example, even though it was still raining the ponding in Canada St had completely gone by 6pm. The clean-up following the event has primarily consisted of clearing of debris and checking sumps and outlets are clear, along with some sewage hosing and lime dosing.

We are looking at each reported ponding, to see if improvements to the network or its maintenance are necessary.

The rain event appears to have been quite varied over the district, with some areas that might be expected to have ponding not affected at all.

We are programmed to CCTV the Canada Street stormwater in March and we will be checking the stormwater hydraulics on the network in the area to see if there are improvements that can be made.

In terms of the sewerage system, there was a vast improvement on issues experienced during similar events in the past.

Considering the scale of the event and the amount of rainfall that fell our systems coped very well and it was business as usual.