# Flood prevention schemes: guidance for local authorities

Guidance on making flood prevention schemes for local authorities.

##### GLOSSARY OF TERMS
 Consequence An outcome or impact such as economic, social or environmental impact. May be expressed quantitatively (eg monetary value), by category (eg High, Medium, Low), or descriptively. Decision/Event/Fault tree Ways of describing a system and the linkages between different parts. Useful for identifying causes, tracing possible sequences of events, and investigating the effects of decisions. Deterministic method Method in which precise, single values are used for all variables and input values, giving a single value as the output. Hazard A situation with the potential to result in harm. A hazard does not necessarily lead to harm. Monte Carlo modelling A numerical technique for assessing the probability of different outcomes from two or more variables. Probability The probability of an outcome is the relative proportion or frequency of events leading to that outcome, out of all possible events. Probabilistic method Method in which the variability of input values, and the sensitivity of the result, are taken into account to give results in the form of a range of probabilities for different outcomes. Probabilistic discounting Use of probabilities and probability distributions in order to account for uncertainty when estimating present values of streams of cost, or benefit, over a period of time. Probability distributions Used to describe the likelihood of different values across the whole range of the variables, eg flood damage, extreme loads, particular storm conditions, etc. Qualitative methods Approaches which use descriptive rather than numerical values for assessment and decision- making. Residual life of defences The remaining time until a defence is likely to fail or no longer achieve minimum acceptable performance criteria in terms of serviceability or structural strength. (Criteria for failure need to be carefully considered.) Return period The average length of time separating extreme events (eg a flood) of a similar magnitude. Residual risk The risk which remains after risk management and mitigation. May include, for example, risk due to very severe (above design standard) storms, or risks from unforeseen hazards. Risk assessment Consideration of risks inherent in a project. Risk management The activity of mitigating and monitoring risks, which predominately occurs after the project appraisal stage. Risk register An auditable record of the project risks, their consequences and significance, and proposed mitigation and management measures. Sensitivity testing Method in which the impact on the output of an analysis is assessed by systematically changing the input values.

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