FLOOD MAPS
What are Flood Maps?
Flooding is one of the prominent influences that shape the development of Katherine. Flooding maps developed for Katherine town and rural areas show:
- Probable and possible areas of flooding;
- Likelihood of flood inundation corresponding to the three flood warning categories; and
- Probability of occurrence of a flood (Annual Exceedence Probability).
Flood maps have been produced for insurance purposes and provide a valuable guide to future development possibilities.
What are the Flood Warning Categories?
Flood warnings are issued by the Regional Counter Disaster Controller. The three categories are dictated by the level of Katherine River at Katherine Gorge.
What is Annual Exceedence Probability (AEP)?
A 1% AEP is equivalent to what was previously referred to as a 1 in 100 year flood. This terminology has been abandoned as it often gave a false perception that a flood of that size could only be expected every 100 years. The new terminology better informs readers of the probability of a flood of a certain size to occur in a period of a year. 1%, 2% and 5% AEP flood maps have been produced.
Where does the information shown on the Flood Maps come from?
- Modelled extents of flooding at specific river levels caused by a 100 year Average Recurrence Interval Storm event falling uniformly over the Katherine River catchment;
- Investigating silt deposits by larger past floods in the Katherine River Catchment;
- Post flood event investigations; and
- Flood frequency analysis.
How does Climate Change impact Flood Maps?
Some climate change predictions indicate stronger and more frequent cyclones may be experienced in northern Australia. Cyclones are often the source of flood waters; as tropical cyclones move inland they are often transformed into tropical rain depressions with the potential to deliver large volumes of rainwater over large areas of north Australia, with an obvious consequence of significant flooding potential.
Australian Rainfall & Runoff guidelines produced by the Institute of Engineers Australia are revising the flood frequency methodology to accommodate the climate change factors, which will need to be incorporated into the existing flood maps.
Where can I get more information?
Copies of the Flood Maps are available at: