Glossary of Flood Terms
Glossary of Flood Terms - Case Study - Johnstone River Flooding
Extreme Flooding Case Study Contents...
Glossary of Flooding Terms
annual exceedance probability
Australian Height Datum
average annual damage (AAD
average recurrence interval
(ARI)
cadastral data Property
boundary data
design flood
discharge
DEM/DTM
Digital Elevation Model or Digital Terrain Model
flood frequency analysis
flood hazard
flood level
flood liable land
floodplain
floodplain management
floodplain management measures
flood planning levels (FPL)
flood prone land
flood storages
floodway
freeboard
historical flood
hydraulic
peak flood level, flow or
velocity
runoff
stage hydrograph
TUFLOW
URBS
velocity
When
Good Rivers Turn Bad Contents
annual exceedance probability (AEP)
The chance of a flood of a given size (or larger) occurring in any one year, usually
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 peak
discharge of 500 m3/s (or larger) occurring in any one year. (see also average
recurrence interval)
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 year that
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 years
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 events).
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 big 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 every 20
years. ARI is another way of expressing the likelihood of occurrence of a flood
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 building.
design flood
A hypothetical flood representing a specific likelihood of occurrence (for example
the 100 year or 1% probability flood). The design flood may comprise two or more
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 buildings.
discharge
The rate of flow of water measured in terms of volume over time (i.e. the amount of
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.
flood frequency analysis
An analysis of historical flood records to determine estimates of design flood flows.
flood fringe Land that may be affected by flooding but is not designated as floodway or flood
storage.
flood hazard
The potential risk to life and limb and potential damage to property resulting from
flooding. The degree of flood hazard varies with circumstances across the full range
of floods
.
flood level
The height or elevation of floodwaters relative to a datum (typically the Australian
Height Datum). Also referred to as “stage”.
flood liable land see flood prone land
floodplain
Land adjacent to a river or creek that is periodically inundated due to floods. The
floodplain includes all land that is susceptible to inundation by the probable
maximum flood (PMF) event.
floodplain management
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 the FPLs.
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.
flood storages
Floodplain areas that are important for the temporary storage of floodwaters during a flood.
floodway
A flow path (sometimes artificial) that carries significant volumes of floodwaters
during a flood.
freeboard
A factor of safety usually expressed as a height above the adopted flood level thus
determing the flood planning level. Freeboard tends to compensate for factors such
as wave action, localised hydraulic effects and uncertainties in the design flood
levels
.
historical flood
A flood that has actually occurred.
hydraulic
The term given to the study of water flow in rivers, estuaries and coastal systems.
hydrograph A graph showing how a river or creek’s discharge changes with time.
hydrology The term given to the study of the rainfall-runoff process in catchments.
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 flooding.
runoff
The amount of rainfall from a catchment that actually ends up as flowing water in the
river or creek. stage See flood level.
stage hydrograph
A graph of water level over time.
TUFLOW
Fully two-dimensional unsteady flow hydraulic modelling software
URBS
Hydrological computer model software
velocity
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. the average
velocity across the whole river or creek section.
water level See flood level.