The State Emergency Service (SES) developed the Tasmanian Strategic Flood Mapping (TSFM) with the help of external engineering specialists. The Tasmanian and Federal Governments funded the project.  The mapping uses robust methods based on national and international standards.

The flood mapping uses

• past rainfall records and river heights to estimate the likelihood of given levels of floods
• information about local flood history, and
• computer-generated flood modelling – which simulates how water moves through rivers and overland.

Consultants WMAWater prepared technical reports and flood studies for 28 river catchments with the SES.

The flood studies provide information on flood water

• extent
• level/ depth, and
• velocity (speed of the water).

This helps to understand and define flood hazard within the catchment.

External experts peer reviewed the mapping and related materials. For more information, see the technical reports and flood studies for each catchment.

Flood models and the flood mapping

The flood mapping based on computer flood models. Flood models are simplified but likely representations of reality. They help to better understand flooding. Natural flood events may vary from the models, but the models were checked against past flood events to make sure they are realistic.

Flood models are computer simulations that predict how water will behave during different flood scenarios. They include data such as

• rainfall
• terrain
• river systems, and
• infrastructure.

if there is a certain amount of heavy rain in the river catchment.  This information helps SES and others better understand

• what properties and other assets might flood, and
• how dangerous that flooding could be.

SES uses this information to

• inform people if a flood is likely to affect them, and
• plan how SES will help local communities when there is a flood. 

Flood maps are visual tools created from these flood models. The flood mapping shows the likely impacts of a flood event of a particular scale, known as a “design flood event.”

SES has design flood events for floods that have

• a 2%, 1% and 0.5% chance of happening any year (Annual Exceedance Probability(AEP)) based on past rainfall records
• a 1% chance of happening in the climate expected in 2100.

Our models are robust. They indicate how floods are likely to behave. This includes their extent, depth, and speed. However, real flood events may not match the model exactly because of natural variations such as:

• Rainfall falling unevenly across the catchment
• Differences in river levels and how wet the ground is before a flood
• Snowmelt adding extra water to rivers
• Tidal effects in coastal areas

While these factors cause differences, the model still gives a reliable picture of how a flood is likely to develop.

Based on established methods

Flood specialists use established methods to prepare flood models. These methods make some assumptions. All flood models have limitations, but they provide a likely scenario of what a flood event of a particular scale will look like on the ground.  This helps everyone to better manage flood risks.

There is more technical information on how the flood models were developed.

Local council detailed flood mapping

Local council flood study maps typically have more detail. If your local area is covered by a detailed flood study, use it.

The Tasmanian Strategic Flood Maps provide a broad, regional scale understanding of flood risk across the state. Local council flood studies focus on specific areas. They often

• use more locally specific data
• provide a higher level of detail.

However, not all areas are covered by local flood studies. Some local flood studies may

• be outdated
• not include your area of interest, or
• use a different methodology than the SES modelling.

To understand the relevance and status of local flood studies for your area, contact your local council. Where no local studies are available, use the Tasmanian Strategic Flood Mapping.