Flood surfaces are created in FloodAUS to approximate the actual height and shape of the water surface during a flood. Ideally FloodAUS relies on several flood surfaces, the most appropriate being the ARI 20-year, 50-year, 100-year and Probable Maximum Flood. Flood surfaces are also created using ANUDEM® and MapInfo Vertical Mapper®. Flood surface input data are derived from the most recently available flood studies - usually hydraulic modelling studies performed by consulting engineers.

Of the 24 FloodAUS studies completed to date, 15 include flood surface data to the Probable Maximum Flood or Extreme Flood Event level. For 6 study areas the most severe flood for which data were available is the ARI 100-year event.

Flood surface input data are available in a myriad of formats ranging from surface contours, inundation maps and river profiles. In this respect, virtually every study is different.

Levees have an important impact on flood risk. The influence of ring levees on flood risk has been taken into account in 7 studies. Similarly, flood risk is reduced for addresses protected by levees tying into high ground in a further 10 studies.