FLOOD MAPPING
Over 46,000 Logan properties have been affected by the Flood mapping crisis, which has resulted in skyrocketing insurance, falling property values and development restrictions.
KEY INFORMATION
OVER 46,000 LOGAN PROPERTIES AFFECTED
LCC INCORRECTLY EQUATES "HYDRAULIC LIKELIHOOD" WITH "FLOOD RISK"
"FREQUENCY-ONLY" MATRIX HAS INFLATED "HIGH-RISK" PROPERTY NUMBERS THAT SHOULD BE CLASSIFIED AS H1 LOW HAZARD PROPERTIES
RESULTED IN SOARING INSURANCE PREMIUMS AND SAFE LAND RENDERED UNINSURABLE
The flood map created by the Logan City Council shows high risk across tens of thousands of properties, when the flood study shows zero water.
In Logan’s flood risk matrix, all 5% AEP scenarios are automatically classified as HIGH RISK.
It doesn’t matter that the modelling shows:
-
0.0m water depth
-
0.1 m/s velocity
-
Hazard Category H1 (the lowest hazard level)
H1 is generally considered safe for people, vehicles and buildings. Yet the map still labels these areas HIGH RISK because high flood risk is defined as deep or fast flowing OR high frequency (5% AEP).
This “risk map” was not legally required.
In fact, the Brisbane City Council map that Logan says this approach is based on isn’t even called a risk map ... it’s called a Flood Awareness Map.
Even more concerning is that the public flood portal itself was never mandated. Yet now insurance companies can see properties labelled HIGH flood risk. The flood study maps could have simply been published with the studies and made available through council offices or libraries.
View the images below to compare the Flood Risk Map with the modelling.
WHAT DOES THIS MEAN?
The classification appears to be based on frequency alone, not on the actual flood behaviour.
Risk-based flood mapping is supposed to combine: Hazard × Likelihood which is the foundation of ISO 31000 risk assessment.
An ISO 31000 compliant risk assessment is required as part of the SPP – why was this not followed?
Look at the purple areas on the map - those are H1 flood conditions, the lowest hazard level.
Now imagine if the system actually applied risk × frequency. Many of those areas would likely appear yellow as low risk, not high risk.
IN SUMMARY
Council appears to have mapped hydraulic likelihood and labelled it “flood risk.”
Hydraulic modelling is not the same as risk.
Risk must consider: how likely flooding is X how dangerous that flooding actually is
Right now the map appears to be showing likelihood alone.