Resilience Glossary: K – O





A product that is approved or accredited for a particular use e.g. flood gate barrier.



Spectrum of known relevant information.


Knowledge uncertainty

Uncertainty due to lack of knowledge of all the causes and effects in a physical or social system. For example, a numerical model of wave transformation may not include an accurate mathematical description of all the relevant physical processes. Wave breaking aspects may be parameterised to compensate for the lack of knowledge regarding the physics. The model is thus subject to a form of knowledge uncertainty. Various forms of knowledge uncertainty exist, including:
Process model uncertainty – All models are an abstraction of reality and can never be considered true.
They are thus subject to process model uncertainty. Measured data versus modelled data comparisons give an insight into the extent of model uncertainty but do not produce a complete picture. Statistical inference uncertainty – Formal quantification of the uncertainty of estimating the population from a sample. The uncertainty is related to the extent of data and variability of the data that make up the sample.
Statistical model uncertainty – Uncertainty associated with the fitting of a statistical model. The statistical model is usually assumed to be correct. However, if two different models fit a set of data equally well but have different extrapolations/interpolations then this assumption is not valid and there is statistical model uncertainty.


Land use planning

The development of land use strategies to best meet people’s current and future needs, according to the land’s capabilities. Urban, city, or town planning, deals with design of the built environment from the municipal and metropolitan perspective. Regional planning deals with a still larger environment, at a less detailed level.


Legal uncertainty

The possibility of future liability for actions or inaction. The absence of undisputed legal norms strongly affects the relevant actors’ decisions.



A general concept relating to the chance of an event occurring. Likelihood is generally expressed as a probability or a Frequency.


Limit state

The boundary between safety and failure.



Refers to environmental factors such as high river flows, water levels and wave heights, to which the flooding and erosion system is subjected.


Low lying areas

Low lying areas are defined here as “areas with artificially maintained levels in watercourses, where peak water (river or tide) levels are higher than the surrounding land levels”.


Manual defence

A manual defence is any method of flood protection that requires human interaction in order to be successfully implemented.

Centre for Resilience


A map is a simplified depiction of a space which highlights relations between objects within that space. Most usually a map is a two-dimensional, geometrically accurate representation of a three-dimensional space. Maps are a common instrument to illustrate flood related information. Depending on the information that is to be shown different notations are in use.


Marine flood

The inundation of land areas along the coast by sea waters over and above normal tide actions (OED and Evelpidou).


Mean sea level

The sea level halfway between the mean levels of high and low water (OED)



The action of reducing the severity, seriousness or painfulness of something. (OED)



An abstract construct to represent a system for the purposes of reproducing, simplifying, analysing, or understanding it. The definition of a model can be broadly divided into perceptual, conceptual and procedural models.


Model, Conceptual

The mathematical description of a perceptual model is a conceptual model. It is a construct of mathematical and logical statements that describe a complex system in quantitative terms; a carefully constructed, but sharply limited simulation of nature. It includes hypotheses and assumptions to simplify the processes.


Model, Perceptual

Summary of our (personal) perceptions on how a system responds. Perceptual models are frameworks representing how a given theorist views the phenomena of concern to a discipline. People receive information, process this information, and respond accordingly many times each day. This sort of processing of information is essentially a perceptual model of how things in our surrounding environment work. The perceptual understanding of systems is far greater than most material model implementations.


Model, Procedural

Converts a conceptual model essentially to a computer code for example the replacement of differentials of the original equation by finite-difference or finite-volume equivalents.



Modelling is the process of imitating a real phenomenon or process with a set of mathematical formulas. In principle, any phenomena that can be reduced to mathematical data and equations can be simulated on a computer. But, as natural phenomena are subject to an almost infinite number of influences the trickiest task developing useful simulations is to determine the most important factors.


Morphological change

Morphology is the study of shapes or forms and morphological change in rivers, estuaries and coasts relate to changes in their shape.



A mixture of lime or cement or a combination of both with sand and water, used as a bonding agent between bricks, stones, etc.

Municipal master plan

A spatial plan at a municipal level.


Natural disaster

Natural hazards are naturally occurring physical phenomena caused either by rapid or slow onset events which can be geophysical (earthquakes, landslides, tsunamis and volcanic activity), hydrological (avalanches and floods), climatological (extreme temperatures, drought and wildfires), meteorological (cyclones and storms/wave surges) or biological (disease epidemics and insect/animal plagues).

IFRC (International Federation of Red Cross and Red Crescent Societies)

Natural variability

Uncertainties that stem from the assumed inherent randomness and basic unpredictability in the natural world and are characterised by the variability in known or observable populations.


Non-interruptible supply

Backup power supply that, in case of power failure or fluctuations, will be able to continue functioning independently of the downed power grid. This is usually in the form of a battery back-up system or fuel powered generator.

Centre for Resilience

Non-structural mitigation measures

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


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.


Numerical hydraulic modelling

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