Impact: Flash Flood

4 December 2024

Cyclone Marcia – February 2015

Cyclone Marcia (Marcia) formed on 18th February 2015 and intensified rapidly, crossing the coast near Shoalwater Bay, Qld. as a rare Category 5 cyclone. (USA Cat.4). Marcia remained a category 3 far inland on 20th February and after several hours of heavy rainfall, intensities increased with around 250mm of rain in 3 hours over the western slopes of the Calliope Range (Official report).

Multiple record flood height were observed along Bell, Callide, Grevillea, and Kroombit Creeks. Callide (Gated) and Kroombit Dams both observed floods of record with erosion to the toe of Kroombit Dam with 10000-year levels level observed. Environmental monitoring equipment was damaged with one gauging station and building (Stepanoffs) never located.

There was significant flood impacts to residential areas and infrastructure throughout Callide Valley.

Cyclone_MarciaDownload

21 July 2024

Typhoon Hagibis

Typhoon Hagibis impacted Japan in October 2019 with significant infrastructure damage, flooding and disruption to the hosting of the Rugby World Cup. Hagibis is estimated by EM-DAT to be the 3rd costliest (inflation adjusted) on record in the Pacific region since 1991. The event occurred whilst Japan was hosting the Rugby World Cup and preparing for the Japanese Grand Prix. Significant rainfall resulted with over 922mm (36.2 inches) at Hakone, near Tokyo. 99 fatalities occurred with 73% of those greater than 65 years of age.

HagibisDownload

20 July 2024

Wisconsin Dam Failure

July 5th, 2024. Five and a half Inches (140mm) of rain fell over the Manawa City Dam, a small, gated dam in Waupaca County, WI. The speed of the event saw the right abutment overtopped that subsequently failed through erosion. Unofficial data from Manawa shows rainfall of 4.12 inches (105mm) in 1 hour with 1.69 inches (43 mm) in 20 minutes. The timeline provided at the post event public meeting by the City of Manawa advises the gate openings were set on forecast rain of around 1.25 inches, that morning. The flood wave inundated homes and impacted the functioning pf the wastewater treatment plant. Post even issues include public safety, sightseeing management and exposure to bacteria from sediment. Manawa City has around 1400 inhabitants. The impoundment held 1078 acre feet or 1329ML, at full supply.

Wisconsin Dam FailureDownload

31 January 2024

Pennsylvania Thunderstorm and Major Flash Flood

Fatalities during storm when significant rainfall fell in a short period washing cars off the road. The cars had not entered floodwaters. 33mm was recorded at one station in five minutes.

Pennsylvania Flash FloodDownload

30 January 2024

South Korea Infrastructure – July 2023

Goesan Dam is about 15000ML in volume and is in the upper reaches of the Han River catchment that eventually flows through Seoul. It has a catchment area of 671 km2. The issue for the dam was that the calculated inflows exceeded the design outflow capacity of the gates by some margin (10.5%), hence the warnings of potential dam safety issues conveyed in the media and picked up internationally as the level exceeded 136.93 EL, the maximum planned flood level.

Elsewhere, a levee at the Miho River collapsed allowing rapid inundation of a 685-metre-long road tunnel with 14 fatalities. There was significant criticism of emergency managers with the likely failure identified 1 hour prior. A key focus of the police investigation was management and maintenance of the embankment that resulted in convictions related to its construction.

Sth Korea InfrastructureDownload

Auckland Rainfall Emergency

Generated by convective activity associated with an Atmospheric River, heavy rainfall occurred in Auckland on 27th January 2023. Event totals of over 250mm were widespread with over 40mm in 15 minutes at the peak of the event. Over 1300 homes were flood damaged. Infrastructure impacts included the closure of, and flooding of Auckland Airport terminal. There was limited public information throughout the event which led to significant criticism of politicians and emergency managers. The case-study provides great learnings for compound impacts, risk appetite, process, training, roles and responsibilities ,and planning for unusual, but credible natural hazard events.

Auckland Rainfall EmergencyDownload