The following information has been provided by the Victorian State Emergency Service (SES).
A Flood Watch notifies the community of a potential flood threat from a developing weather situation. It is generally issued 24-36 hours before any likely flooding, and is aimed at giving the community a 'heads-up' that flooding is possible.
If a Flood Watch is issued and you are living, camping or working along rivers or streams, you should regularly check weather forecasts, rainfall totals and river levels and be ready to take action.
Flood Warnings are issued when flooding is about to, or is already happening.
They predict the flood size (minor, moderate or major) and estimate the time that the river height will reach certain river gauges. When flood warnings are issued, people in low-lying areas prone to flooding need to activate their flood emergency plan immediately.
When a Minor Flood Warning is issued, the following may be expected:
- Water levels reach the top of the river banks
- Low lying areas along the waterway are inundated by flood water
- Minor roads may be closed and low level bridges submerged
- Livestock and equipment along the waterways are moved to higher ground
In addition to the above, the following may be expected when a Moderate Flood Warning is issued:
- Water levels overtop river banks and inundates low lying areas
- Flood water starts to approach buildings and infrastructure
- Some properties may be inundated by rising flood water, requiring evacuation
- Caravan parks on waterways may be inundated
- Main traffic routes may be closed by flood water
In addition to all of the above, the following may be expected when a Major Flood Warning is issued:
- Water levels overtop river banks and causes extensive inundation on the floodplain
- Farmland is inundated, stock and equipment losses may occur
- Residential and commercial properties are inundated
- Properties and towns may be isolated
- Major traffic routes may be closed
- Evacuations may be required
Types of flooding
In riverine flooding, relatively high water levels overtop the natural or artificial banks of a stream or river. The nature of riverine flooding can vary significantly in terms of cause, timing and depth between different locations. Coastal rivers with short, steep headwaters often have floods that rise and recede quickly. Inland floods with low gradients have floods that move slowly down the river, sometimes lasting for several months.
Flash flooding occurs when soil absorption, runoff or drainage cannot adequately disperse intense rainfall, and is usually caused by slow-moving thunderstorms. Flash floods are generally defined as developing in six hours or less from rainfall to the onset of flooding.
Although dam failures are rare, their effects can be significant. In Victoria dam safety is monitored, and warning arrangements are in place to warn downstream residents of potential dam failure threats. Should dam failure occur, significant downstream flooding can involve potentially swift flowing water and high amounts of debris.
Storm surge occurs when sea levels are elevated above the usual tidal limit due to the action of intense low pressure systems over the open ocean. The low pressure causes sea level to rise as there is less air pressing down on the sea. Combined with gale force onshore winds, this can lead to flooding of low-lying coastal land.
Overland flow is water that runs across the land after rainfall, either before it enters a watercourse, after it leaves a watercourse as floodwater, or after it rises to the surface naturally from underground. Rain overflowing from gutters or drains can also become overland flows as it travels over the land, through buildings and along roads as it makes its way towards a watercourse (creek or river).
Sandbags will not stop the water completely but can reduce the amount of water entering your home. The Victorian SES Sandbagging Quick Reference Guide provides valuable information in preparing for floods.
The Australian Government has developed an Emergency Survival Checklist to assist you to prepare for the unexpected.
Australian Red Cross
The Australian Red Cross offers a range of valuable resources designed to help people to better prepare, respond to and recover from emergencies.
Resources are available for households, seniors, people with disabilities, parents of young children, psychosocial preparedness and coping with anniversaries.