BAMOS - Vol 35 No.1 Autumn 2022 Autumn 2022 - Page 19

Charts of the Past with Blair Trewin

Charts of the Past with Blair Trewin

BAMOS Autumn 2022
19

11 March 1974

The early months of 1974 were some of the wettest on record for Australia , as one of the strongest La Niña events on record brought heavy rain to most of the country . January 1974 brought major flooding to the Brisbane region , and widespread and long-lived flooding in many parts in northern and central Australia .
Coastal northern New South Wales , although it was significantly wetter than average , escaped the worst of the January flooding , but its turn was to come in the second week of March . A low , which became Tropical Cyclone Zoe , developed in the Coral Sea on the 6th , and moved slowly south towards southeast Queensland over the following week , strengthening to a peak intensity of category 3 on the 9th . A moist easterly flow developed between the cyclone and a high pressure ridge over southern Australia , reaching its peak on the 10th and 11th .
Following localised extreme rainfall on the 9th on the Mid- North Coast ( 386 mm at Macksville ), more general heavy falls occurred over the Northern Rivers and the Gold Coast on the 10th and 11th . Coolangatta received 461 mm on the 11th , and numerous other sites had more than 300 mm on either the 10th or 11th , with Woodburn recording 683 mm over the two days and numerous other sites on both sides of the border exceeding 500 mm . Further south , there was also 412 mm on the 11th at Crystal Creeks near Bellingen .
Major flooding occurred in the Northern Rivers , with the Wilsons and Richmond Rivers worst affected , as well as in the Bellinger River . At Lismore , the river reached 12.17 m on the 11th , the equal-highest flood on record before 2022 , and record heights were observed at numerous other points on the river . One death was reported and 1500 properties were evacuated , mostly in Lismore and Murwillumbah , with some evacuations taking place by boat . Brisbane received 265 mm over the two days ( and 420 mm over four ), only six weeks after the destructive January floods , but this time significant flooding was mostly confined to local creeks . In New South Wales , moderate flooding extended as far south as the Shoalhaven .
A second round of heavy rain occurred on the 12th and 13th as Zoe crossed the coast near Coolangatta , the southernmost east coast tropical cyclone landfall of the last 50 years . By then it had accelerated and weakened to a category 1 system , and there was no significant wind damage , but there was still enough moisture for daily rainfall totals above 300 mm in the Gold Coast hinterland ( 349 mm at Alpine Panorama on the Springbrook plateau ), and significant beach erosion . This produced a second flood peak at Lismore although it fell well short of that observed two days earlier . Zoe moved out to sea later on the 13th , bringing the heavy rain to a close . Weekly totals exceeded 800 mm at numerous sites , with the highest being 1045 mm at Doon Doon .
A monsoonal low over the Northern Territory brought a second area of heavy rain and flooding . By the 11th it was weakening , but earlier it had produced widespread multi-day totals above 200 mm , with 212 mm at Delamere on the 9th . Most major roads were flooded and the Katherine River reached its highest level since 1957 .
The story was not entirely one of rainfall . Away from the east coast , it was hot and humid in the east to northeasterly flow , with the 11th being the last of five consecutive days above 40 ° C at Moomba in outback South Australia . Heat also affected a Moomba of a different sort , with more than 400 festival attendees being treated by paramedics for heat-related conditions in Melbourne ( where it reached 33.1 ° C ). March nights were particularly warm in the southeast , with mean minimum temperatures the highest on record for both Victoria and Tasmania .
Synoptic chart for 0000 UTC , 11 March 1974