Glossary N - Q

Non-structural flood management measures

Measure taken to protect people or property in order to reduce damage without influencing the current of the flood event. Often used as synonym for passive protection measures.

Source: FLOWS

Non-structural measures include all mitigation measures that are not based on large-scale defences.

Source: Era-Net Crue, 2005

Non-structural responses

Responses to urban flood risk that do not involve fixed or permanent facilities and their positive contribution to the reduction of flood risk is most likely through influencing behaviour, usually through government regulation, persuasion, and or economic instruments.

Source: Ashley et al., 2007

Numerical hydraulic modelling

Calculation / simulation of the flow behaviour of a stream based on different parameters.

Source: FLOWS


Route that a hazard takes to reach Receptors. A pathway must exist for a Hazard to be realised.

Source: FLOODsite


a belief or opinion, often held by many people and based on appearances The act of perceiving a hazard is based on an existing notion, a previously perceived awareness of this hazard or on the experience of its effects, generating hazard awareness.



The degree to which a process or activity succeeds when evaluated against some stated aim or objective.

Source: FLOODsite

Performance indicator

The well-articulated and measurable objectives of a particular project or policy. These may be detailed engineering performance indicators, such as acceptable wave overtopping rates, rock stability, or conveyance capacity or more generic indicators such as public satisfaction.

Source: FLOODsite

Permeable paving

Hard surfaces capable of allowing water to pass through and be retained beneath it.

Source: FLOWS, Cambridgeshire County Council, 2006

Pervious surfaces

Surfaces that allow inflow of rainwater into the underlying construction or soil.

Source: Tourbier/ White, 2007

Pipes and Accessories

A series of conduits and their accessories normally laid underground that convey surface water to a suitable location for treatment and/or disposal. (Although sustainable, these techniques should be considered where other SUDS techniques are not practicable).

Source: Tourbier/ White, 2007

Planning instruments

Planning instruments are maps or plans for formulating future goals in a specific area. It can consist of one or more maps and text.

Source: FLOWS


A series of questions asked of a group of people in order to find out what they think about particular subject or how they will vote in an election.


Precautionary principles

Where there are threats of serious or irreversible damage, lack of full scientific certainty shall not be used as a reason for postponing cost-effective measures to prevent environmental degradation.

Source: FLOODsite


The ability to ensure effective response to the impact of hazards, including the issuance of timely and effective early warnings and the temporary evacuation of people and property from threatened locations.

Source: FLOODsite

Prepardness strategy

Within the context of flood risk management a preparedness strategy aims at ensuring effective responses to the impact of hazards, including timely and effective early warnings and the evacuation of people and property from threatened locations.

Source: FLOODsite

Probability of occurence

Probability of a natural event of a given magnitude being equalled or exceeded in a given period of time.

Source: Int. Symposium Interpraevent, 1992, Bd. 3, p 383

The chance of occurrence of one event compared to the population of all events. Therefore, probability is dimensionless. It is however, often referenced to a specific time frame, for example, as an annual exceedance probability or lifetime exceedance probability.

Source: FLOODsite

Project appraisal

The comparison of the identified courses of action in terms of their performance against some desired ends.

Source: FLOODsite

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