Moreton Bay Regional Flood Database

Overland Flow Flooding

Version 1.26.0 (April 2025)

This theme shows runoff which exceeds the capacity of the underground drainage system (if present) and which concentrates in surface depressions, yards and gullies, and roadways as it flows down a catchment. Overland flow is generally caused by short and intense bursts of rainfall (typically less than 1 hour in duration). Overland flow can cause flooding that generally lasts only for a limited period of time and will usually dissipate shortly after the rainfall has stopped.

Methodology

'Rainfall on grid' approach applied using a hydraulic model (TUFLOW) and a nested rainfall burst. Model does not include underground structures however rainfall was scaled down to account for the possibility of some run-off being contained within the underground system. A post-process was applied to eliminate areas of shallow depth, low velocity and low velocity depth product.

Existing Conditions FIG FCPR Scenario

Modelled estimate of the extent of overland flow paths following a 1% Annual Exceedance Probability storm outside the river and creek flood extent and with some model errors and small property intersects removed. In addition a 1m internal buffer was applied and objects less than 40m2 removed.

Purpose

To determine flood extent along overland flow paths in areas outside the extent of the river and creek flood modelling. Intended to be used by the Property Analysis Module (StoneGecko). Not suitable for public dissemination.

Methodology

Rainfall on grid' approach applied using a hydraulic model (TUFLOW) and a nested rainfall burst. Model does not include underground structures however rainfall was scaled down to account for the possibility of some run-off being contained within the underground system. A post-process was applied to eliminate areas of shallow depth, low velocity and low velocity depth product. Additional removal of model errors, small and 1m internal buffer then removal of objects less than 40m2.

Flood Data Notes

Describes the expected reliability of the flood data including indication of specific areas where Council is of the opinion that the data has limited reliability and a reason for this limited reliability.

The notes polygon dataset stores spatial definitions of model areas of known lower data reliability or subject to review.

Modelled Probability

The probability represented by this dataset is:

1% Chance of Flooding in Any One Year

Likelihood: Possible

Annual Exceedance Probability (AEP): 1%

Average Recurrence Interval (ARI): 100 Year

A large uncommon flood event that is rarely observed but neverthess still possible. Over a long period of time an event of similar size may occur on average once every 100 years. It is therefore likely an event of this size will occur at least once during a single lifetime. It is less likely, but still possible, for a flood of this size to occur more than once in a single lifetime. A flood event of similar size occurred in the middle and upper reaches of the Caboolture River during January 2011.

Version Notes

1.26.0 - Sub set of F01 Version 1.25 with areas removed where field Public = N in F00N Version 1.18.8 (April 2025)

Version Resolution: 1.0m

Data Reliability: D

Indicates that Council can only provide an extent but not levels as the flood data is of limited reliability

Edit History

No edits recorded for this version.

Further Information

For additional information on flooding in the Moreton Bay Region please see Council's website: http://www.moretonbay.qld.gov.au/Services/Property-Ownership/Flooding