17.5 Overbank flood spilling
Flooding did occur throughout the Adelaide region during the 2010–11 year; however this volume could not be quantified in a way that is complete, neutral and free from material error.
The majority of flooding occurred in the north of the Adelaide region during the 2010–11 year. The following figure shows the extent of the 100-year flood peak average recurrence intervals (ARI) calculated in a composite of flood-hazard mapping studies. The composite study area covers only 6.2% of the Adelaide region. The studies are mostly concentrated in built-up areas with a risk of flooding from both watercourses and stormwater.
Map of 100-year flood peak average recurrence intervals in the Adelaide region
Data source: South Australian Department for Water – a composite of flood hazard layers derived from various flood hazard studies.
The volume of overbank flood spilling is expected to be significant. However, its influence on the surface water balance is not expected to be material. This is because a substantial portion of the volume of flood waters spilling overbank is likely to return to the river channel (line item 9.6), which could also not be quantified.