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Contains terms and definitions used in the reference book, the project and the structure of the Ontology.

Browse the glossary using this index

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The ways in which different processes have impacts that may feed back into the underlying conditions for ongoing risk, potentially altering the nature of these conditions.

First flush

High concentrations of pollutants observed at the beginning of a flow event.

Flood management plans

Plans which discuss different aspects of water management (and some of them are flood-related issues) and they are traditionally divided into: integrated water resources management plans, river basin management plans, catchment flood management plans, coastal management plans, disaster management plans and asset management plans. Flood management plans are also referred to as flood risk management plans (FRMPs). Since these plans provide an overview of the framework for evaluating, developing, and implementing various strategies, project and activities they are also sometimes referred to as master plans (or strategic plans).

Flood maps

Maps that typically indicate the geographical areas which could be covered by a flood (during a given return period storm or extreme event) in the absence of control structures. The maps may be complemented by indication of the type of flood, the water depths or water level, and where appropriate flow velocity, plus often simplified hazard categories.

Flood risk

Condition commonly referred to the existence of the possibility that the hydro-meteorological phenomena can cause harm to those elements that are exposed or susceptible to being affected.

Flood risk management

The process of data and information gathering, risk analysis and evaluation, appraisal of options, and making, implementing and reviewing decisions to reduce, control, accept or redistribute flood risks. It is a continuous process of analysis, adjustment and adaptation of policies and actions taken to reduce flood risk (including modifying the probability of flooding and its severity as well as the vulnerability and resilience of the receptors threatened). FRM is based on the recognition that risks cannot be removed entirely but only partially, and often at the expense of other societal goals.


Condition where wastewater and/or surface water temporarily escapes from or cannot enter an urban stream, drain or sewer system and flows with significant depth over the surface, causing disruption to traffic and can enter buildings (see also surface flooding).


The generally flat areas adjacent to a watercourse or the sea where water flows in time of flood, or would flow but for the presence of structures and other flood controls. The limits of a floodplain are notionally infinite, so it is normally defined by the maximum flood extent (associated with a given return period storm (in the absence of flood control structures).


An overwhelming flow of water onto land that is normally dry and which under certain circumstances can cause unprecedented losses and devastation.

Flow simulation

Modelling of flows in drain or sewer systems.

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