The chance of a flood of a given size (or larger) occurring in any one
expressed as a percentage. For example, if a peak flood discharge of 500
m3/s has an
AEP of 5%, it means that there is a 5% chance (i.e. a 1 in 20 chance) of a
discharge of 500 m3/s (or larger) occurring in any one year. (see also
Australian Height Datum
(AHD) National survey datum corresponding approximately to mean sea level.
average annual damage (AAD)
Depending on its size (or severity), each flood will cause a different
amount of flood
damage. The average annual damage is the average damage in dollars per
would occur in a designated area (e.g. the Innisfail area) from flooding
over a very
long period of time. In many years there may be no flood damage, in some
there will be minor damage (caused by small, relatively frequent floods)
and, in a few
years, there will be major flood damage (caused by large, rare flood
Estimation of the average annual damage provides a basis for comparing the
effectiveness of different floodplain management measures (i.e. the
reduction in the
annual average damage).
average recurrence interval (ARI)
The long-term average number of years between the occurrence of a flood as
(or larger than) the selected event. For example, floods with a discharge
as great as
(or greater than) the 20yr ARI design flood will occur on average once
years. ARI is another way of expressing the likelihood of occurrence of a
event. (see also annual exceedance probability)
cadastral data Property boundary data
catchment The catchment at a particular point is the area of land that
drains to that point.
design floor level The minimum (lowest) floor level specified for a
A hypothetical flood representing a specific likelihood of occurrence (for
the 100 year or 1% probability flood). The design flood may comprise two
single source dominated floods. Development Existing or proposed works
that may or may not impact upon flooding. Typical
works are filling of land, and the construction of roads, floodways and
The rate of flow of water measured in terms of volume over time (i.e. the
water moving past a point). Discharge and flow are interchangeable.
DEM/DTM Digital Elevation Model or Digital Terrain Model
- a three-dimensional model of the ground surface. effective warning time
The available time that a community has from receiving a flood warning to
when the flood reaches them. flood Relatively high river or creek flows,
which overtop the natural or artificial banks, and inundate floodplains
and/or coastal inundation resulting from super elevated sea levels and/or
waves overtopping coastline defences. flood awareness An appreciation of
the likely threats and consequences of flooding and an understanding of
any flood warning and evacuation procedures. Communities with a high
degree of flood awareness respond to flood warnings promptly and
efficiently, greatly reducing the potential for damage and loss of life
and limb. Communities with a low degree of flood awareness may not fully
appreciate the importance of flood warnings and flood preparedness and
consequently suffer greater personal and
economic losses. flood damage The tangible and intangible costs of
flooding. flood behaviour The pattern / characteristics / nature of a
flood frequency analysis
An analysis of historical flood records to determine estimates of design
flood fringe Land that may be affected by flooding but is not designated
as floodway or flood
The potential risk to life and limb and potential damage to property
flooding. The degree of flood hazard varies with circumstances across the
The height or elevation of floodwaters relative to a datum (typically the
Height Datum). Also referred to as “stage”.
flood liable land see flood prone land
Land adjacent to a river or creek that is periodically inundated due to
floodplain includes all land that is susceptible to inundation by the
maximum flood (PMF) event.
The co-ordinated management of activities that occur on the floodplain.
floodplain management measures
A range of techniques that are aimed at reducing the impact of flooding.
This can involve reduction of: flood damages, disruption and psychological
trauma. floodplain management plan A document outlining a range of actions
aimed at improving floodplain management. The plan is the principal means
of managing the risks associated with the use of the floodplain. A
floodplain risk management plan should be developed in accordance with the
principles and guidelines contained in the CSIRO (2000). The plan will
usually contain both written and diagrammatic information describing how
particular areas of the floodplain are to be used and managed to achieve
defined objectives.floodplain management scheme
A floodplain management scheme comprises a combination of floodplain
management measures. In general, one scheme is selected by the floodplain
management committee and is incorporated into the plan.
flood planning levels (FPL)
Flood planning levels selected for planning purposes are derived from a
combination of the adopted flood level plus freeboard, as determined in
floodplain management studies and incorporated in floodplain risk
management plans. Selection should be based on an understanding of the
full range of flood behaviour and the associated flood risk. It should
also take into account the social, economic and ecological consequences
associated with floods of different severities. Different FPLs may be
appropriate for different categories of landuse and for different flood
plans. The concept of FPLs supersedes the “standard flood event”. As FPLs
do not necessarily extend to the limits of flood prone land, floodplain
risk management plans may apply to flood prone land beyond that defined by
flood prone land
Land susceptible to inundation by the probable maximum flood (PMF) event.
Under the merit policy, the flood prone definition should not be seen as
necessarily precluding development. Floodplain Management Plans should
encompass all flood
prone land (i.e. the entire floodplain) flood proofing Measures taken to
improve or modify the design, construction and alteration of
buildings to minimise or eliminate flood damages and threats to life and
limb. flood source The source of the floodwaters. In this study, the
Johnstone River catchment is the primary source of floodwaters.
Floodplain areas that are important for the temporary storage of
floodwaters during a flood.
A flow path (sometimes artificial) that carries significant volumes of
during a flood.
A factor of safety usually expressed as a height above the adopted flood
determing the flood planning level. Freeboard tends to compensate for
as wave action, localised hydraulic effects and uncertainties in the
A flood that has actually occurred.
The term given to the study of water flow in rivers, estuaries and coastal
hydrograph A graph showing how a river or creek’s discharge changes with
hydrology The term given to the study of the rainfall-runoff process in
peak flood level, flow or velocity
The maximum flood level, flow or velocity occurring during a flood event.
photogrammetry The technology used to obtain reliable measurements, maps,
digital elevation models, and other GIS data primarily from aerial
photography. probable maximum flood (PMF) An extreme flood deemed to be
the maximum flood likely to occur.
probability A statistical measure of the likely frequency or occurrence of
The amount of rainfall from a catchment that actually ends up as flowing
water in the
river or creek. stage See flood level.
A graph of water level over time.
The speed at which the floodwaters are moving. Typically, modelled
velocities in a
river or creek are quoted as the depth and width averaged velocity, i.e.
velocity across the whole river or creek section.
water level See flood level.