Impact: Thunderstorms

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

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

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