Flood Modelling

Modelling the behaviour of Flood Events

There are two types of flooding, overland and riverine. Flood modelling is a predictive science and is based largely upon probability in determining estimated flood levels. When we talk about flood events we speak about the probability of a flood event occurring on an annual basis, Annual Exceedance Probability (AEP).

For example, a 1% AEP means that based upon historical events a flood event of this magnitude is probably going to happen once every one hundred years. However, as we are continually reminded, the environment does not conform to mathematical formulas and therefore a 1% AEP will occur whenever nature decides.

Riverine flooding as the name suggests relates to flooding of a river or a creek system. The Wagga Wagga Local Government Area has a well documented history of riverine flooding related to the Murrumbidgee River.

Wagga Wagga City Council has been able to take advantage of this to produce a series of flood models for the Murrumbidgee River to assist in making improved decisions about activities and development on the floodplain.

Overland flooding relates to a localised storm event which can exceed the design capacity of built infrastructure such as stormwater/drainage pipes and pits, storage basins, roads, kerb and gutter and open drainage systems and channels.

Once the capacity of these systems is reached the stormwater follows a natural 'overland' path under the force of gravity usually in an uncontrolled manner. Council has recently modelled the behaviour of overland flooding in the urban areas of the City and is currently in the early stages of producing similar models for the villages of Uranquinty, Ladysmith and Tarcutta.

To view images of the flood modelling for an overland flood event:

1 per cent Overland flood (PDF, 1.9 MB)

10 per cent Overland Flood (PDF, 463.9 KB)

Further information about Councils flood modelling and reports and outputs can be found here Flood Management.