TERMINOLOGY INDEX

“Flood prone land” is a specific technical term used in the NSW Floodplain Development Manual to refer to all land below the level of the Probable Maximum Flood.

The Probable Maximum Flood (PMF) is described as the largest flood that could conceivably occur at a particular location and is modelled based on Probable Maximum Precipitation which is in turn calculated by methods developed by the Bureau of Meteorology.

A flood control lot is a lot identified as being within the FPA on the Flood Planning Area Map. It is generated by adding a freeboard to the modelled 1% AEP flood surface level. A flood control lot is land or property that is subject to flood-related development controls.

Flood related development controls, specify the special conditions for developing or building on a flood control lot. Typically, these controls include conditions that may require the floor level of new building work to be above a certain level.

A Flood Planning Level (FPL) is the estimated height of a 1% AEP flood event, with freeboard added (see below). It is used as the basis to determine planning controls for flood control lots.

The term “freeboard” is used to describe a safety buffer, to account for unknown factors and uncertainties in the modelling that determines the Flood Planning Level and is typically applied as 0.3 or 0.5m above the 1% AEP Flood Level.

Ponding generally describes relatively still water that remains for a time after a flood event because it is in a low-lying or trapped area and cannot easily drain away.

Mainstream flooding is defined as water that flows over the banks of creeks, river canals and lagoons. In other words, when a creek or river breaks its banks.

Overland flow flooding is defined as surface runoff, typically excess rainfall or stormwater runoff from homes, driveways and other surfaces.