Impact: Flood

4 December 2024

Oroville Spillway Failures – February 2017

In February 2017, heavy rainfall in the Feather River basin led to outflows
through Oroville Dam. Spillway slab failure occurred  resulting in erosion and damage. Gated
releases ceased for damage assessments and the lake level was allowed to rise
over the emergency spillway crest, that then also experienced significant
erosion. The scenario resulted in evacuation of large numbers downstream in preparation for a failure
event.

Oroville Dam Spillway FailureDownload

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

3 December 2024

Norway Dam Failure – August 2023

Storm Hans was a significant system that impacted Norway and Sweden between 8th -12th August 2023. Estimated damage form the storm is estimated at just under 1 billion euros. A key event during the storm was the overtopping and failure of a dam at Braskereidfoss.

Braskereidfoss hydroelectric dam, owned by Hafslund Eco overtopped during daylight hours on 9th August 2023 when the flood gates remained at 20% capacity, despite increasing water levels overnight. The dam was unmanned and the operations centre in Lillehammer was overwhelmed by multiple situations in the rain event. Attempts to rescue the situation were abandoned as overtopping also inundated the hydroelectric plant, removing back up power systems. During the day, the Norwegian Army was deployed with consideration given to a controlled failure through explosives. The dam overtopped and the embankment subsequently eroded.

A 2018 risk assessment noted the scenario that evolved as a risk and accepted that risk just 7 months prior. There was no technical failure according to the final investigation report with a lack of redundancy, staffing and system testing identified as key elements of a systemic failure. The case study has a full investigative report with over 30 learnings available.

Norway Dam FailureDownload

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

31 January 2024

Nashville Dam Fuse plug Confusion

Heavy rainfall fell in Nashville creek catchment on 16th July 2024 resulting in a high peak, low volume flood. The fuse plug eroded, and the emergency spillway operated as designed protecting the primary embankments. Over floor and infrastructure flooding resulted downstream in Nashville. Antecedent conditions were wet with around 40mm (1.57 inches ) on the 4th, 50mm (1.96 inches) on the 9th and 10mm (0.4 inches) on the 11th , some of the notable totals. Event totals were widely described as around 6 inches (152mm) of rain. Available data shows around 80% of this fell in 1.5 hours between 5:30 am and 7am on the 16th.

There was US national coverage of the ‘dam failure’ resulting from the use of the term secondary dam failure to refer to the fuse plug eroding. The event is useful for learnings regarding communication during natural hazard events as it repeated a similar event in July 2022.

Nashville Dam OutflowsDownload
Nashville Dam OutflowsDownload

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

Slovenia Flooding – August 2023

6-8th August 2023. Slovenia and parts of Austria, Croatia and Italy received record rainfall with an average event total, in Slovenia of 166mm from 115 official Slovenian Environment Agency gauges. Between 65-85% of the country was impacted. A piping event in a flood levee, risks to energy supply, cross border defence implications, and supply chain impacts for the car industry were notable impacts form this event. Learnings for this jurisdiction wide rain events are largely based around planning, continuity, and understanding advance climate risk understanding for integrated economies and businesses.

Slovenia2023Download

Fort Lauderdale Extreme Rainfall

Convective, stationary storms with moist inflow produced over 21 inches (533mm) in 12 hours around Broward County, Florida, according to data from the National Weather Service. Precipitable water was high, and extended wet weather resulted in saturated antecedent conditions for a favorable meteorological environment.

The area around the international airport, and port received the greatest falls with two separate periods of over 4 inches (100mm) in one hour. Standing water varied between 1-2 feet (0.31 to 0.62 metres).  The highest intensities came close to the USA record for 10 minutes with 38mm . The event was estimated at having a 1:1000 annual chance of occurrence.

The international airport was closed for 41 hours and passengers remained on site during this period. 1119 flights were cancelled.

Port Everglades, that manages supplies gasoline for 40% of Florida shut down and within 2 days much of Southern Florida was short of fuel. This took over a week to resolve after a release of emergency fuel by the Federal Govt. Local and Statewide emergency declarations occurred.

A detailed spatial and temporal pattern of the storm is available for modelling along with an economic assessment and mock exercise based on this scenario.

Fort Lauderdale Rainfall April 2023Download