This dataset, created in June 2013, provides an indication of the likelihood of a flood occurring from overland flow inside the Brisbane City Council local government area. This layer contributes to the overall Flood Awareness Mapping for Brisbane City Council.

Overland flow is excess rainfall that runs across the land after rain before it enters an underground drainage system or a creek/waterway. Overland flow can also rise to the surface naturally from underground or also as a result of creek/waterway bank failure. Overland flow flooding tends to affect localised areas rather than the whole city at once. Overland flow can probably be considered the most frequent type of flooding in Brisbane.

Overland flow tends to occur during high rainfall events. It travels across the land following low-lying, natural drainage paths. Such flooding may occur when underground drainage system exceeds capacity. Overland flow flooding can be unpredictable and occur without warning.

You can identify overland flow by looking at how water may flow across the land around your property. Consider these natural flows when you are looking to renovate, build a fence or put in a shed.

There are three different overland flow flooding impact areas in Flood Awareness Map, namely High, Medium and Low.

The overland flow High impact layer consists of H5 and H6* hazard zones during a 5% Annual Exceedance Probability (AEP) (20 year Average Recurrence Interval (ARI)) flood event. The flood data was sourced from the Citywide Creek and Overland Flow Path mapping study (GHD, 2017).

The overland flow Medium impact layer consists of H3, H4, H5 and H6* hazard zones during a 2% AEP (50 year ARI) flood event (outside high impact area). The flood data was sourced from the Citywide Creek and Overland Flow Path mapping study (GHD, 2017).

The overland flow Low impact layer consists of H2, H3, H4, H5 and H6* hazard zones during a 1% AEP (100 year ARI) flood event (outside high and medium impact areas). The flood data was sourced from the Citywide Creek and Overland Flow Path mapping study (GHD, 2017).

* Hazard ranges from H1 to H6 and is based on the flood hazard, depth and velocity vulnerability thresholds. For more information, refer to Australian Disaster Resilience Guideline 7-3 Flood Hazard (AIDR 2017).