Yet more rain threatened as QLD Tropical North Coast drenched again
Fri 30 Mar 2018

Just over two weeks after days of rain produced the worst flooding in years in some rivers from Ingham to Cairns, and especially around Ingham, further heavy rain in the same area over the past week has again caused moderate to major flooding. This time the worst flooding was around Cairns after 100 to 200mm of rain fell in part of the saturated Barron River catchment in only two hours late on Monday 26^th.

Minor flooding began in the Barron and Mulgrave-Russell systems around Cairns as early as Sunday 25^th with rapid rises at upstream gauges. For example the Barron River at Mareeba rose by 7.34m to 10.30m in the six hours to 0130 Tuesday 27^th while its tributary Clohesy River rose 10.35m in under eight hours to be 5¾m above major flood level. These rapid rises upstream of Cairns coincided with a period of intense heavy rain: in the two hours to 2300 26^th Copperlode Dam recorded 189mm, Flaggy Creek 135 and Myola 124 while in one hour to 2200 26^th Mona Mona recorded 87mm. All except Copperlode Dam are on the Barron above Barron Falls which was an awe-inspiring sight when dawn broke. [ABC News] However, the Copperlode downpour flowed down Freshwater Creek to join the Barron above Cairns, adding to the torrent of water that arrived in Cairns before dawn on Tuesday 27^th

The resulting river and flash flooding was the worst in the city since February 2000. As reported on 26 March, extreme flash flooding extended north of Cairns to Port Douglas and into the Daintree. In Cairns itself:

• Caravan parks in Brinsmead and Redlynch had to be evacuated when they were inundated in darkness, with cars and caravans floating about, people screaming for help and rescues made from campervans and caravans afloat. Water subsided quickly, but many people lost property in caravans.
• The Bruce Highway was closed in several places and Captain Cook Highway to the north closed. Cairns residents were asked to stay home, and four high schools were closed.
• The QLD Fire and Emergency Services reported dozens of swift-water rescues on Tuesday 27^th. One man was rescued after clinging to a tree at Yorkey's Knob, north of the city.
• Residents and organisations gave first-hand accounts in this ABC News story.

Elsewhere on the North Tropical Coast:

• Douglas Shire ran critically short of drinking water, with only five hours supply left at one point.
• Tully, Halifax, Cordelia, Taylors Beach and Lucinda were isolated, with three Tully schools closed.
• In addition to many closures north of Ingham, the Bruce Highway was closed at Cattle Creek between Townsville and Ingham, lining up traffic for kilometres.

[ABC News, AAP/SMH, Floodlist]

The flooding this time around was caused by the nearly stationary monsoon trough lying from the southern Gulf of Carpentaria to the Coral Sea. Embedded in the trough, the decaying Ex-Tropical Cyclone Nora intensified rainfall for a while when it moved overland closer to the Tropical North Coast before moving back to the SE Gulf.

Also lying menacingly in the trough, out in the Coral Sea between the QLD coast and New Caledonia, the short-lived TC Iris refuses to go away with current guidance indicating it will bring rain to the QLD Capricorn and/or Tropical North Coasts from late on the Easter weekend. [Andrew Miskelly, BoM, JMA] There is still uncertainty as to what effect ex-TC Iris will have, but as of Friday evening 30^th there are flood watches in place for coastal rivers from the Russell-Mulgrave system just south of Cairns to the Kolan River north of Bundaberg. The effects of Iris were already being felt on Friday 30^th, with many Sunshine and Gold Coast beaches closed by by dangerous surf and strong currents. Despite warnings, 50 people had to be rescued. ABC News reported that conditions were so bad on some Sunshine Coast beaches that lifeguards could not get onto them because beachfronts had been washed away.

The BoM weekly rain map to 0900 29^th shows over 400mm falling along the coastal strip from Ingham to the Daintree, where a number of places have now had two to three times their average March rain. A second large area over 400mm E of Normanton was directly due to the slow-moving ex-TC Nora as it moved east, then west, across the base of Cape York Peninsula. Rain there was particularly intense in the 24 hours to 0900 Tuesday 27^th in the Georgetown/Mount Surprise area. Georgetown recorded 189mm, Mount Surprise (90km to the E) 205, Green Hills (30km WSW) 222 and Abingdon Downs (60km NW) a whopping 405mm. It was Abingdon Downs' highest one-day total since records began in 1945, beating the previous record of 263mm, also in a March in 2016.

During the week to the 29^th, the average of all raingauges across all coastal river systems from the Herbert north to the Daintree River was 390mm. Averages in individual catchments were: Herbert (which includes the town of Ingham) 260mm, Tully 440, Johnstone (Innisfail) 510, Russell-Mulgrave (Babinda and Gordonvale) 440, Barron (Cairns) 360, and Daintree-Endeavour (Port Douglas, Mossman and Daintree Village) 465. The highest 7-day total was 1051mm at Bulgan Creek, 7km N of Tully, a quarter of which (252mm) fell in just three hours to 2300 Monday 26^th with the hour to 2300 producing 100mm. The highest one-day fall was 593mm at the Port Douglas Warner Street gauge for the 24 hours to 0900 on the Monday 26^th, its highest daily total for March since records began in 1887.

Overall, the heaviest rain was from the 25^th to the 27^th with most rivers at moderate or major flood levels at some of their gauging points by the morning of the 27^th. Except in the north, flood peaks were lower than two weeks ago with the Herbert at Ingham Pump Station reaching just under the 12m major level and the Murray at Murray Flats just above the 8m major level, both on Wednesday evening 28^th. The Tully at Euramo sat close to its peak of 8.7m (major level 9.0m) from midday Tuesday 27^th to late Wednesday 28^th while the Johnstone River only saw minor to moderate flooding at a few gauges on Tuesday 27th. Moderate flood levels were also reached in the Mulgrave-Russell and Daintree systems.

Don't believe everything you read Fri 30 Mar 2018 - With few exceptions, it pays to be sceptical when reading, listening to or watching media reports of weather events. The Border Mail and The Maitland Mercury, both Fairfax Media country media outlets, reported that "The rain reached emergency levels on Monday when 100mm was said to fall in one minute". While I don't expect journalists pressed for time to comb through the technical data on the BoM Hydro web pages, the Bureau's tweet at the time clearly said "mm/hr". Common sense could also have suggested the figure looked wrong.

For the record, the heaviest 1-minute rainfall ever recorded in the world, as verified by the World Meteorological Organisation, was 31.2mm on 4 July 1956 at Unionville, Maryland, USA. A well-referenced Wikipedia article gives 38mm in one minute at Barot, Guadeloupe, in the Caribbean, on 26 November 1970, with this research document as its basis. It's a pdf in French, so unfortunately no cheating using your browser to translate. If you're interested in weather extremes, visit the WMO Global Weather and Climate Extremes page, the very good Wikipedia List of weather records, and from the BoM these lists of rainfall extremes for the world (now a little dated) and Australia.