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Take the Floods Quiz

Test your knowledge with the floods quiz, 20 multiple choice questions on basic science and engineering concepts of floods, including flood causes and impacts, flood forecasts and warnings, flood management, and the impact of climate change and other factors on flooding in the future. To learn more, read the Understanding Floods: Questions and Answers report.


1. A flash flood is a flood that:

  1. is caused by heavy rain rather than from the flooding of a river
  2. occurs in urban areas
  3. occurs suddenly and unexpectedly and for a short duration
  4. is caused by the blocking of drains.

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c. Flash floods are defined by the speed of flooding, not the source or location of flooding. While flash floods are often caused by heavy rainfall, they can also result from other events, such as drain blockages and bursts or the flooding of a river.

2. A flood can vary in:

  1. size
  2. speed of water flow
  3. duration
  4. all of the above.

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d. The size, duration and water flow speed of floods can vary. The volume, rate of rise and areal extent (i.e. the total area under flood waters) of flooding can also vary.

3. When a river’s water level reaches 10 metres, this means that:

  1. the water level is 10 metres above an arbitrary ‘zero’ level
  2. the water level is 10 metres above mean sea level
  3. the water level is 10 metres above mean sea level or an arbitrary ‘zero’ level
  4. it will flood.

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c. River height is the level of water in a river as measured by a river gauging station and is expressed in metres above either the Australian Height Datum (i.e. mean sea level) or an alternative arbitrary ‘zero’ level, depending on the location.

4. The size of a flood is measured by:

  1. the rate of flow of water in a waterway or river
  2. the level of water in a waterway or river
  3. a river gauging station
  4. all of the above.

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d. The size of a flood can be measured by the highest level that water in a waterway reaches, referred to as the ‘peak water level’ or ‘flood peak’. It can also be measured by the maximum water flow rate in a waterway, referred to as the ‘peak flow rate’ or ‘peak water flow’. Each of these variables can be measured using a river gauging station.

5. Which of the following is associated with a La Niña event?

  1. The Southern Oscillation Index (SOI) is strongly negative.
  2. The ocean surface off the coast of South America is warmer than usual.
  3. There is an increased chance of above average rainfall in eastern Australia.
  4. All of the above.

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c. In a La Niña event, the equatorial ocean surface off the coast of South America is abnormally cool, and the SOI is strongly positive. Trade winds blow strongly across the warm Pacific, picking up plenty of moisture and increasing the likelihood of above average rainfall in eastern Australia.

6. Which of the following potentially affects the size of a flood?

  1. bridges and other structures in waterways
  2. the size and windiness of a river
  3. vegetation in and around a river
  4. all of the above.

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d. Many factors can affect the size of a flood, including rainfall intensity, weather conditions prior to a rainfall event, tidal and storm surges, dams and other man-made and natural water storages, catchment size and shape, soil types in a catchment, vegetation in and around a waterway, the size and windiness of a waterway, levees, bridges and other structures in waterways and catchments, and urbanisation.

7. In Australia, the average annual cost of floods is around:

  1. $3.8 million
  2. $38 million
  3. $380 million
  4. $3.8 billion.

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c. Over the period 1967-2005, the average annual cost of floods in Australia was around $380 million.

8. In Australia, the most expensive natural disaster is:

  1. drought
  2. floods
  3. bushfires
  4. cyclones.

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b. Floods are the most expensive natural disaster in Australia.

9. Which of the following is an environmental consequence of floods?

  1. dispersal of weed species
  2. erosion of soil
  3. release of pollutants into waterways
  4. all of the above.

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d. Floods can have negative environmental consequences, such as soil erosion, release of pollutants and excess sediments and nutrients into waterways and the ocean, dispersal of weed species, and negative impacts on fish and other aquatic life. Floods can also have positive environmental consequences, such as recharging groundwater systems, filling wetlands, moving useful nutrients around the landscape, and triggering breeding events (for example, of water birds).

10. Which of the following is used to estimate which areas will be inundated during a flood, based on river height information?

  1. satellite and radar images
  2. flood maps / floodplain hydraulic models
  3. river gauging stations
  4. all of the above.

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b. Floodplain hydraulic models and flood maps are used to estimate which areas will be inundated based on river height information. Satellite and radar images, rain gauges and river gauging stations are used to estimate river heights.

11. Which of the following statements is false?

  1. Weather forecasts for a small region are more accurate than those for a large region.
  2. Weather forecasts are more accurate in Melbourne than in Darwin.
  3. Forecasts of temperature are more accurate than forecasts of rainfall.
  4. All of the above.

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a. The accuracy of weather forecasts varies depending on lead time, the size of the region of interest, the weather variable being forecast, and the latitude of the region. Generally, temperature forecasts are more accurate than rainfall forecasts; the mid-latitudes are easier to forecast than the tropics; and it is generally easier to forecast rainfall over a large area (for example, a large catchment) than local rainfall (for example, a reservoir).

12. Which of the following is true? Flood warnings:

  1. should not be released until the information is certain
  2. should indicate what the threat is, what action should be taken, by whom and when
  3. are best if they come from a single source (for example, an internet website)
  4. all of the above.

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b. Flood warnings should provide information on what the threat is, what action should be taken, by whom and when. While it is desirable for flood warnings to be accurate, warnings are predictions about the future, so there is inevitably some uncertainty. Accuracy needs to be balanced with timeliness, to allow enough time for appropriate action. Warnings are most likely to reach different audiences and to be heeded if they come from multiple trusted sources.

13. If you experienced a 1-in-100 year flood this year, what is the chance you will experience one next year?

  1. none
  2. 1 in 10,000 odds (0.01%)
  3. 1 in 1000 odds (0.1%)
  4. 1 in 100 odds (1%).

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d. The chance of experiencing a 1-in-100 year flood in any given year is 1% (or 1 in 100), regardless of when the last 1-in-100 year flood was experienced.

14. If your house is in an area that will be flooded by a 1-in-100 year flood, then the chance that you will be flooded at least once within the next 70 years is:

  1. 1 in 2 odds (50%)
  2. 7-in-10 odds (70%)
  3. 1-in-70 odds (1.4%)
  4. 1-in-100 odds (1%).

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a. If you live in a location that has a 1% chance of flooding in any one year (that is, it would only flood if a 1-in-100 year flood or greater occurred), then the chance of being flooded at least once in a 70 year period is: 100% minus the chance of a flood not happening 70 years in a row, i.e. 1 – (0.99)70 = 0.5 (or 50%).

15. Flood risk refers to:

  1. the chance of a flood occurring
  2. the number of people and properties exposed to floodwaters if a flood occurs
  3. the vulnerability of people and properties that are exposed to floodwaters
  4. all of the above.

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d. Flood risk includes both the chance (or probability) of a flood occurring, and the consequences if a flood occurs. The consequences of a flood are in turn affected by the number of people and properties exposed to floodwaters for a flood of a particular size, and the vulnerability of those people and properties. For example, a river might burst its banks regularly, but if this flooding occurs in an isolated area where there are no people or infrastructure, then the risk is low. Similarly, a river might flood very rarely, but if many people and properties are located near this river and they live in dwellings that are vulnerable to water damage, then the flood risk will be greater.

16. Which of the following can reduce the risk of flooding?

  1. zonings and building regulations for new developments
  2. dams, detention basins and levees
  3. flood awareness and education programs
  4. all of the above.

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d. Flood risk in new developments can be reduced by restricting the location of development (zonings) and placing controls (regulations) on development. In existing developed areas, risk can be reduced by modifying flood behaviour (for example, through dams, detention basins, levees, waterway modifications), property modification measures (for example, land filling, flood proofing, house raising, removing developments), and response modification measures (for example, upgrading flood evacuation routes, flood warnings, flood evacuation planning, flood education programs).

17. The Probable Maximum Flood is:

  1. an estimation of the largest possible flood that could occur at a particular location
  2. the maximum flood experienced in the last 100 years
  3. the maximum flood experienced in the last 200 years
  4. the maximum flood experienced since flood records have existed.

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a. The Probable Maximum Flood (PMF) is an estimate of the largest possible flood that could occur at a particular location, under the most severe meteorological and hydrological conditions as they are currently understood.

18. For good land use planning, buildings should be built:

  1. above the 1-in-100 year flood level
  2. above the level of the Probable Maximum Flood
  3. based on the chance and consequences of a flood for that particular building
  4. above the level of the largest historical flood.

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c. Throughout most of Australia, the 1-in-100 year flood (plus an appropriate additional height, or ‘freeboard’, for buildings) is considered as having an ‘acceptable’ risk for planning purposes. However, good planning should take into consideration both the chance of a flood happening and the consequences of a flood. For example, critical infrastructure such as hospitals and emergency management centres are ideally located in areas that will never be flooded so they can operate during a flood event.

19. In the future, which of the following is expected to increase the risk of flooding?

  1. population growth
  2. urbanisation
  3. climate change
  4. all of the above.

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d. In the future, climate change is likely to result in an increased chance of flash floods and coastal inundation. Australia’s growing population and urbanisation are likely to place increased pressure on our waterways and to increase the chance of flooding in cities and the number of properties and people exposed to floodwaters.

20. In the future, which of the following is unlikely?

  1. There will be an increased chance of flash flooding and coastal inundation.
  2. Flood risk will increase due to population growth and urbanisation.
  3. Improvements in flood forecasting and warning technologies will reduce the impacts of floods.
  4. We will be able to eliminate the risk of flooding.

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d. It is not possible to eliminate the risk of flooding. Indeed, it is likely that flood risk will increase in the future due to climate change, population growth and urbanisation. However, we can better manage flood risk through improvements in flood forecasting and warning technologies, as well as improved land use planning, floodplain management and integrated water management.

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Last updated:
15 March, 2013
Last reviewed:
8 August, 2011

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