Arrangements for Flood Warning Services in Victoria
February 2001

Non flash flooding can be typically defined as riverine flooding where flooding occurs after about 6 hours from the start of rainfall and the rainfall causes the river or creek to exceed channel capacity. Flooding can also result from water levels in a lake exceeding lake full level (lacustrine), the result of dam failure, storm surge or tsunami.

Flash flooding is defined as 'flooding occurring within about 6 hours of rain, usually the result of intense local rain and characterised by rapid rises in water levels' (Bureau of Meteorology, Weather Services Handbook).

1. Severe thunderstorms: a thunderstorm that produces rainfall of sufficient intensity to cause flash flooding.
2. Heavy rainfall: rainfall of sufficient intensity to cause flash flooding, independent of antecedent conditions, can be the result of a meteorological event other then a thunderstorm.
3. Non intense rainfall: flash flooding can occur during periods of prolonged rainfall resulting, for example, from a slow moving weather system. Stream levels already high, but not yet in flood, can suddenly increase to flood level following a short burst of (but not necessarily intense) rainfall during these situations.

In addition to the fundamentals of flood warning presented previously, the following general principles are to be applied to service development and functioning:

• Flood warning in Australia involves agencies from Commonwealth, State and Local Government, regional authorities and the community.
• Flood warning services are best provided through a cooperative approach involving all these parties. It must also be recognised that all these parties make up the flood warning service whether they be an agency, private entity or individual and they all have some degree of service ownership.
• Effective flood warning services are provided where beneficiaries and agencies have a direct involvement in the provision of the service, and contribute to its cost.
• Effective flood warning services rely on utilising the existing strengths of partner agencies, private entities and communities.
• Free real time access to rainfall, stream level and stream flow data is to be provided for agencies with a flood prediction responsibility in flood warning.

Flash flooding in Elizabeth Street, Melbourne, 17 February 1972. Photograph, 'The Age'

Flash flooding at St Kilda, Melbourne, 7 February 1989. Photograph, 'The Age'

In recognition of the general principles the following applies for non flash flood:

• For rural Victoria the Bureau has the lead role to provide warnings of minor, moderate and major flooding within its available resources. These warnings are disseminated to State agencies, selected private entities, and media.
• VICSES disseminates the Bureau's warnings to Local Government and relevant regional authorities who in turn disseminate warning information (Bureau and local content) in their community. In some cases the Bureau's warnings are issued direct to relevant regional authorities and some councils (Local Government) where time is critical with flooding. VICSES still disseminate the warnings to those same Councils as backup.
• For the Greater Melbourne area Melbourne Water determines flood predictions and prepares the flood warnings but the warnings are issued through the Bureau.
• In circumstances where it is more effective to provide a service by State or Local Government, or regional authority undertaking what would otherwise be a Bureau function, then such arrangements should be formally ratified and implemented. An example of this principle is in the area of Greater Melbourne.

In recognition of the general principles the following applies for flash flood:

• The Bureau of Meteorology has a responsibility within its legislated role and resources to provide predictions of weather conditions that lead to flash flooding e.g. thunderstorms etc.
• Due to the short lead times (less than 6 hours) associated with flash floods, quick and effective response is required at local level. For this reason Local Government has the prime responsibility for flash flood warning and is responsible for providing predictions of stream levels as a result of flash flooding.
• For the urban area of Greater Melbourne where flash flooding can occur across a number of Local Government boundaries Melbourne Water, where appropriate, may be able to provide assistance to Local Government. This assistance includes providing stream level predictions where possible which are presented in flood warnings prepared by Melbourne Water but issued through the Bureau of Meteorology.
• The Bureau of Meteorology can provide specialist advice to Local Government in relation to flood prediction techniques and establishment of flash flood warning systems.