Uncertainty in Flood Risk and its Implications for Management

Student thesis: Doctoral ThesisDoctor of Philosophy


Flooding in the UK is one of the mostly costly natural hazards. Reliable estimation of flood risk is becoming increasingly relevant to flood management practices as the insurance industry, planning decisions and allocation of flood resources are encouraged to move towards a fully risk-based methodology.
This thesis describes the implementation of a flood modelling chain to estimate the flood risk and quantify the associated uncertainty for the city of Carlisle, UK. Observational data from an extreme flood in January, 2005 is analysed to estimate its accuracy, then a method of reducing inconsistencies in the measurements is proposed. The observational dataset is used to condition a hydraulic flood model for the area. The potential benefit of implementing risk-based calibration schemes as an alternative to a global scheme that gives equal weight to all observations is investigated and found to be minimal in this instance.
A flood frequency curve for peak flood discharges in Carlisle is derived using a Bayesian statistical model that combines estimates of historic floods with systematic river gauge data. The uncertainty in the resulting flood frequency curve reflects errors in estimates of peak flood discharge, changes in the channel and floodplain as well as the uncertainty arising from the limited length of the gauge data and compares favourably against the current ‘best practice’ methods.
The flood frequency curve is used to drive the hydraulic model in a series of Monte Carlo simulations to give probabilistic maps of design floods for Carlisle. Spatial dependence between river flows and variability in flood hydrographs are incorporated in the Monte Carlos simulations. The uncertain consequences of the floods are examined in terms of financial risk, and risk to population and property.
A social research project using semi-structured interviews attempts to establish the relevance of the results to urban planning, the insurance industry and flood management resource allocation. Discussion of uncertainty in flood risk in a broad context suggests a high level of awareness, but not prioritisation with no accepted standard of communication.
Date of Award2015
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorHannah Cloke (Supervisor) & David Demeritt (Supervisor)

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