Low Likelihood Flood




<strong>Moreton Bay City Flood Database</strong>
River and Creek Flooding
Version 3.1.0 (October 2023)
This theme shows river and creek flooding caused by long duration heavy rainfall, typically lasting between 1 hour and 1 day. Sometimes this rain falls over a whole catchment or a number of catchments. This extended period of heavy rainfall causes the water levels in the river or creek to rise and escape the main channel. It may take a number of hours or days for these floodwaters to rise, reach a peak and then subside.&nbsp;
<i>Existing Conditions Maximum Scenario:</i>&nbsp;Maximum of modelled flood behaviour in rivers and creeks for different design rainfall events under existing climate and catchment conditions&nbsp;- with and without structure (bridges and culverts) blockage.&nbsp;
<i>Purpose</i>:&nbsp;To determine flood levels and flows for different design rainfall events for design of infrastructure&nbsp;with and without bridges and culverts being blocked by debris.
<i>Methodology:</i>&nbsp;Coupled hydrologic (WBNM) and hydraulic (TUFLOW) modelling using a two-dimensional regular grid, 1D culvert structures, 2D bridge structures and a design burst rainfall approach&nbsp;based on Australian Rainfall and Runoff 2019 guideline (ARR2019). Blockage calculated based on ARR2019 recommendations.&nbsp;<i>Refer technical publications available from Council's website for further detail.</i>&nbsp;
<i>Flood Height:&nbsp;</i>Indicates the approximate water surface level of potential inundation during a computer-modelled flood event, expressed in metres above mean sea level. This dataset represents the flood height values as contour lines using a contour interval of 0.2m.
<i>Modelled Probability:</i>&nbsp;The dataset includes three possible flood events of different probability.
<i>Likelihood: Likely</i><i>Annual Exceedance Probability (AEP): 5%</i><i>Average Recurrence Interval (ARI): 20 Year</i>
<i>Likelihood:&nbsp;Possible</i><i>Annual Exceedance Probability (AEP):&nbsp;1%</i><i>Average Recurrence Interval (ARI):&nbsp;100 Year</i>
<i>Likelihood: Unlikely</i><i>Annual Exceedance Probability (AEP): 0.1%</i><i>Average Recurrence Interval (ARI): 1,000 Year: 0.1% Chance of Flooding in Any One Year</i>
<i>Version Notes&nbsp;3.1.0</i>&nbsp;- First edition of Generation 3 models, incorporating 2019 LiDAR, ARR2019 for Hydrology and TUFLOW HPC for Hydraulic modelling. All ARIs and all aspects. (BCR 5yr, 10yr, 50yr and 2000yr runs completed by CMB). BYR and MAR no structure blockage only. MAR ARR hazard calculated using WaterRIDE. (October 2023)
<i>Version Resolution: 2.5m</i>
<i>Data Reliability: A&nbsp;</i>
<i>Indicates the flood data is of the highest available standard and has been prepared using the most recent flood model and input data&nbsp;</i>
<i>Further Information:&nbsp;</i>For additional information on flooding in the Moreton Bay Region please see Council's website:&nbsp;<a href="https://www.moretonbay.qld.gov.au/Services/Property-Ownership/Flooding">https://www.moretonbay.qld.gov.au/Services/Property-Ownership/Flooding</a>
<strong>Moreton Bay Regional Floodplain Database</strong>
Overland Flow Flooding
<i>Version 1.25.0 (April 2025)</i>
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<i>Methodology:</i>&nbsp;'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 and small property intersects using spatial analysis and manual techniques.<i>Existing Conditions Scenario:</i><strong>&nbsp;</strong>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.<i>Purpose:</i>&nbsp;To determine flood extent along overland flowpaths in areas outside the extent of the river and creek flood modelling. Suitable for public dissemination.<i>Flood Extent:</i><strong>&nbsp;</strong>Indicates the approximate extent of potential inundation during a computer-modelled flood event (not actual recorded levels). The inundation area may be less accurate where the property is flat near the outer limit of inundation, or where the ground surface has been modified since being surveyed.This dataset represents the flood extent as vector polygons without attribution.<i>Modelled Probability:</i><strong>&nbsp;</strong>The probability of flooding represented by this dataset is:&nbsp;1% Chance of Flooding in Any One Year<i>Likelihood:</i>&nbsp;Possible<i>Annual Exceedance Probability (AEP):</i>&nbsp;1%<i>Average Recurrence Interval (ARI):</i>&nbsp;100 YearA 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.<i>Version Notes&nbsp;1.25.0 - Sub set of F01 Version 1.24 with areas removed where field Public = N in F00N Version 1.18.8 (April 2025)</i><i>Version Resolution: 1.0m</i><i>Data Reliability: D</i><i>Indicates that Council can only provide an extent but not levels as the flood data is of limited reliability</i>
<i><strong>Further Information</strong></i><i>For additional information on flooding in the Moreton Bay Region please see Council's website </i><a href="https://www.moretonbay.qld.gov.au/Services/Property-Ownership/Flooding">Flood information for residents of Moreton Bay - City of Moreton Bay</a>

Tags: flood, overland-flow
Organization: City of Moreton Bay's Data Hub