Riverine Flooding

What is 'riverine' flooding

Riverine flooding occurs when excessive rainfall over an extended period of time causes a river to exceed its capacity. It can also be caused by heavy snow melt and ice jams. The damage from a river flood can be widespread as the overflow affects smaller rivers downstream, often causing dams and dikes to break and swamp nearby areas.

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.

1% AEP Design Flood Depth and Extent

A 1% Annual Exceedance Probability (AEP) flood event is equivalent to a 1 in 100 year flood, which is a major rain event that occurs on average once every 100 years (i.e. there is a 1% chance of a flood this size or larger occurring at a particular location in any given year).

However, as we are continually reminded, the environment does not conform to mathematical formulas and therefore a 1% AEP will occur whenever nature decides.

The below images and document outline the flood depths and extent of a 1% AEP Flood in Wagga Wagga.

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Figure 8 - Wagga 1% AEP Design Flood Depths and Extent 2.1 MB Download

Probability of experiencing a given-sized flood in an 80 year period

The following table outlines the probability of experiencing the below flood sizes in an average 80 year lifetime. For reference, the 2012 flood that peaked at 10.56m had an AEP % of approximately 2.85%.