Related - Floodplain Manager February 2019

Explaining Townsville’s Extreme Rainfall

An extreme rainfall event in Queensland’s north coast caused extensive flooding on the Ross River and in the Townsville area.

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A total of 1,134 mm of rain, which is roughly what would be expected in a year, was received in a period of just nine days in Townsville. The extreme rainfall was the product of an unprecedented monsoonal trough and tropical low. The impact of these weather systems was greater than normal due to the slowed movement of the monsoon trough which caused it to become stationary on the north Queensland coast for 10 days. The flooding on the Ross River and its tributaries exceeded 1% annual exceedance probability (AEP) levels and experts have indicated that flood levels at Ross River Dam, which reached 130 per cent of its full supply capacity, exceeded 0.2% (1 in 500) AEP levels. Some rainfall totals over the Ross River catchment were found to exceed a 1 in 2000 AEP event. There are reports that the gate operating rules for Ross River Dam are designed to minimise downstream damage from a 1% AEP flood by slowly opening the floodgates. However, doing so perhaps makes flooding worse in larger events. The management of the dam gate operation is currently being investigated as more than 300,000 cattle perished in the floodwater (Read here, here, here, here, here, here and here).

Two Men Swept Away in Townsville Floods and Two Boys Drown

Two men, aged 21 and 23, who were reported missing during the Townsville floods were recently found dead in a stormwater drain and two boys drowned in the Ross River weeks after the flood peak had passed.

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The two men, who were also involved in a police investigation for a break and enter in the area, were last seen near flood waters. As they may have died as a result of a police pursuit a coronial inquest has been established.

The bodies of the two boys, aged three and five, were recovered from the Ross River near Cranbrook Park in Townsville. The boys disappeared a few days prior to being found and were seen swimming in the river which had recently been ravaged by the Townsville floods. The boys were known to regularly play in the river and were likely unaware of the potential dangers that remained. The conditions of the environment had likely not settled even weeks after the flood dissipated, resulting in the dangerous swimming conditions.
(Read here, here, here here, here and here).

Townsville Flood Spreads Deadly Bacteria

Two Townsville residents have died as a result of melioidosis, an infectious disease which is caused by bacteria from floodwater.

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There have been at least 13 confirmed cases of the disease in Townsville residents during the clean up after the flood and multiple people have been hospitalised as a result. The bacteria is soil-borne and was carried by the floodwaters and settled in the stirred up mud after the floodwaters receded (Read here, here, here and here).

App Helps in Townsville Flood Damages

Brisbane software company and Microsoft Partner, GIS People, have created an app which is being used to report flood damages in Townsville.

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The app is called RADAR (Record Asset Damage and Restoration) and was created for the Queensland government. It uses location intelligence and machine learning to document and collate information on damages after a disaster. Field workers are able to take photos and videos of damage with smartphones and the data is then collated into a report. The app allows for increased data resolution and more efficient documentation of damages which in turn results in faster processing of insurance and infrastructure damage claims (Read here).

Parramatta’s Flood Risk

A senior NSW State Emergency Service officer has stated that a flash flood in Parramatta could become catastrophic within just nine minutes.

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The senior officer warned that if there is significant rainfall in the catchment, the Parramatta CBD could become hazardous with minimal warning. Due to numerous short streams which discharge to the Parramatta River upstream of the CBD it is difficult to provide accurate forecasts with more than two hours warning time. Parramatta City Council has recently installed a state-of-the art flood warning system to improve warning times by using forecast rainfall and ultrafast hydraulic modeling which it reported on at the 2018 Floodplain Management Australia national Conference. Molino Stewart conducted a flood evacuation assessment for Parramatta City Council in 2018 which confirmed that evacuation is not practical given projected warning times and recommended planning controls for new development to better manage risk to life in extreme floods (Read here, here, here and here).

How Climate Change is Snowballing Weather Events

Slow-moving weather systems and the unusual persistence of converging weather systems in Australia are potentially linked to climate change.

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The recent monsoon low in north Queensland which caused the possible 1 in 500 AEP flood event in Townsville is an example of the convergence of two weather systems. The monsoon low was stationary for a period of 10 days and was fed by northwesterly winds from Indonesia. These events are described as unusually prolonged. The slowing of forward movements of cyclones is a phenomenon which has also been observed and is thought to be due to the effect of climate change on the world’s circulatory winds. If weather systems such as cyclones move more slowly over an area, the length of time and therefore severity of a disaster may increase, resulting in greater damages and costs (Read here).

How Private Precaution Reduces Flood Damage

A new study published in Earth’s Future has investigated the effect of private precautionary measures on reducing flood damage.

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Private precautionary measures such as adapted building use, sealing basements and purchasing flood barriers were found to reduce flood damage to residential buildings by up to 27% in flooded German households. The researchers used flood models which incorporated private precautionary measures to more accurately determine flood loss predictions (Read more here).

Atacama Desert Floods in Chile

The Atacama desert, one of the world’s driest deserts flooded as a result of heavy showers in northern Chile.

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The normally dry river beds were inundated, causing houses to be swept away, leaving over 1,000 people homeless (Read more here and here).

Nature Based Coastal Protection

With the inevitability of rising sea levels, standard coastal flood defences such as concrete walls are expected to become less effective and as a result “nature-based” solutions to coastal flooding are being considered.

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Nature-based solutions involve reinvigorating natural flood-resistant processes and systems such as sand dunes, beaches and wetlands to reduce potential for coastal floods. An example of such defence in action is the Blakeney Freshes nature reserve which is a unique freshwater wetland on the UK east coast. This natural coastal buffer absorbed the impact of breached embankments in a 2013 storm surge, indicating the importance of having a large natural buffer. This nature-based solution also encourages that people look for ways to work with nature, for example, relocating from coastal zones with increasing flood risk (Read more here).

Are Tropical Cyclones Intensifying?

A new study published in Nature investigated patterns of intensification of tropical cyclones.

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The researchers assessed datasets of tropical cyclones in the Atlantic basin and found significant increases in tropical cyclone intensification rates that were consistent with anthropogenic induced climate change. The observed rates were also considered unusual when compared to model-based estimates of internal climate variations, indicating uncaptured variability in predicting cyclones. It was suggested that more reliable data is needed to accurately forecast and detect global trends in tropical cyclone intensification rates (Read more here).

Melting Glaciers Increase Flood Risks

A new report has assessed the Hindu Kush Himalaya (HKH) region’s social and environmental response to climate change.

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There is expected to be a loss of a third of the HKH region glaciers even under the most conservative global warming projection of 1.5°C, the report found. The accelerated glacial melting is likely to increase river discharge and flooding in the region which will have consequences for food security and water supply. Monsoonal rains are already responsible for widespread floods and landslides which will be exacerbated by melting glaciers (Read more here and here).

New Approach to Improve Flood Recovery Projects

The Colorado Department of Transportation has published case studies in flood recovery projects which feature the use of the cost-saving multidisciplinary tools, 2D hydraulic modelling and Matrix riprap.

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The use of 2D hydraulic modelling and spatially explicit analyses allowed bridge designers to more accurately determine where flood protection is needed and optimize design safety features. The use of the matrix riprap technique for embankment protection involves using smaller, locally available rocks which are strategically placed, resulting in an overall cost reduction for riprap installation. The two techniques combined to produce a more cost-effective approach for flood recovery projects with up to US $9 million in savings (Read more here).

Interdisciplinary Research for Better Flood Forecasting

The integration of different disciplines has been emphasised in a recent review as critical for improving the accuracy of flood forecasting models.

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The author discusses the need for input from meteorological, hydrological and decision-making perspectives. The article draws on an initiative called the Flooding from Intensive Rainfall Program which is designed to link data from hydrology and meteorology to improve the identification and characterisation of flash floods. The program has produced novel methodologies and tools, new techniques for monitoring rivers during floods and improved weather forecasts for intense rainfall, among other outputs. The program shows how an interdisciplinary approach can be performed and its innovative application in forecasting and flood modelling (Read more here).

Coastal Flooding Threatens Global Enterprises

Carbon Delta, a research firm based in Switzerland, estimated in a recent study that approximately 16% of global enterprise facilities are under threat from coastal flooding.

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The analysis used the company’s facility database which comprises approximately 600,000 geo-referenced facilities from 22,000 publicly listed companies and integrated it into a probabilistic model to project potential flood damages under climate change. For each of the facilities, the threat of coastal flooding and the financial risks associated with the asset damaged were assessed. It indicated that many of these facilities are located in low-elevation coastal zones which will be significantly more vulnerable to coastal flooding within the next 15 years. The research encourages investment in adequate flood protection measures to minimise asset damage associated with this projection (Read more here).

Flood Models to Aid in Food Security

Risk analytics company, Ambiental, produced detailed flood maps as part of a project to minimise loss from flash floods in Middle Eastern countries.

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Ambiental was commissioned by the Regional Food Security Analysis Network (RFSAN) on the project as part of a humanitarian initiative to improve food security under a climate change scenario. The flood maps are being used to inform the placement of agricultural zones and buildings in areas with minimal flood risk throughout Jordan, Syria, Lebanon and Iraq (Read more here).

International Floods

There were six international floods reported across seven countries throughout January 2019. At least 42 people died and over 10,000 were displaced.

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Internationally significant floods included:

Pakistan

At least 26 people have died after heavy rain brought flash flooding to several provinces of Pakistan. Most people who died were swept away in the flood waters while some were killed as a result of roof collapses from heavy rain. The city of Multan in Punjab was reportedly the worst affected area which received 153 mm in 24 hours (Read more here, here and here).

Peru

As many as 10 people have died after heavy rain caused flooding and landslides across five regions in Peru. Approximately 8,000 people have also been displaced and 1,800 homeless as a result. The regions of Arequipa, Ancash, Loreto, Tacna and Moquegua were affected. The rain also revived a waterfall in Pica which had been dry for almost 10 years (Read more here and here).

Diary

2019 Floodplain Management Australia Conference
Canberra, ACT
14 - 17 May, 20197
website

ASFPM 43rd Annual National Conference
Cleveland, Ohio
19 - 23 May, 2019
website

Resources

A Look Into the Historical Hunter Floods
Hunter Living Histories publishes information on historical floods in the Hunter Valley region (Click here and here).

World’s Watersheds Mapped

Hungarian cartographer’s colourful maps of the world’s tributary streams, rivers and catchments (Website).

Time-Lapse of Townsville Flood Impact
Queensland Rail’s time-lapse of flood forming on train tracks during north Queensland floods (Website).