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Title: Exploring the impact of uncertainty of river morphology on flood inundation modelling
Author: Wong, Jefferson See
ISNI:       0000 0004 5992 6035
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2016
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Our landscape is constantly evolving, and so to are our rivers. These changes can be perturbed due to many factors, including land use and climate change. But also changes in river morphology is a dynamic process that constantly evolves, particularly during extreme flood events. This can result in significant changes in channel morphology over short periods of time. Rivers, and the amount of flow they can convey within bank before their channel capacity is reached, is critical to predicting the extent of flood inundation in both rural and urban areas. An important research question is therefore to what extent are fluvial geomorphological changes critical to the prediction of flood inundation extents during and between events? Furthermore how uncertain are these processes and so can their effects be quantified within a risk based framework? This PhD tries to answer those questions using state-of-the-art flood simulation techniques that also comprehensively characterises the inherent uncertainties involved. Most flood modeling studies ignore the potential for morphological changes to alter channel conveyance and bed roughness, in and between large events. Furthermore the overall bedload and geomorphological catchment processes upstream are rarely considered, particularly within an uncertainty analyses framework. The research here within uses the following approaches to characterize this in 3 core results chapters: Chapter 4 uses simple approach to quantifying the potential changes in channel erosion that occur in flooding events to see the sensitivity to the resultant flood inundation extents predicted for the Cockermouth 2009 November flood event. Chapter 5 applies a catchment scale landscape evolution· model CAESAR-Lisflood to two catchments upstream of Cockermouth within an uncertainty analyses framework. This explored the use of uncertain data in• constraining the model simulations for the period of record available. Chapter 6 uses the constrained (behavioural) model simulations found in chapter 5 to simulate flood events at Cockermouth to see the impact of dynamic geomorphological changes during flood events to the predicted extent of flood inundation and flood depths. The results showed that by the inclusion of sediment transport this greatly changed flood dynamics both in terms of water depth and flow volume, with a wider bound of uncertainty quantified in the flood predictions generated. This has important implications for understanding and predicting flood risk across a range of catchments, particularly those that are more susceptible to ongoing geomorphological changes. Futhermore with the inclusion of sediment transport and the consideration of morphological changes, the uncertainties inherent in the observation data which were used to constrain the catchment behaviour had been accounted for and propagated to the downstream reach. This research showed that the prediction uncertainty bounds had been significantly widened in flood inundation extent, flood volume, and water depths. This reveals that the importance of connectivity between catchment dynamics and downstream behavior and flooding at reach scale cannot be examined in isolation from upstream. Hence, it is important and necessary for flood inundation modeling to consider the associated uncertainties from geomorphological impacts and incorporate both hydrodynamic and morphodynamic aspects for subsequent flood risk assessment.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available