One- and two-dimensional modelling of upland floodplain flows in response to different channel configuration

This research is based on two contexts. First, the .research is concerned with a much understudied aspect of flood inundation: upland environments with topographically complex floodplains. Although the presence of high resolution topographic data (e.g. LiDAR) has improved the quality of river flood inundation predictions, the optimum dimensionality of hydraulic models for this purpose has yet to be fully evaluated for situations of both topographic and topological (i.e. the connectivity of floodplain features) complexity. In this research, we present the comparison of three treatments of upland flood inundation using: (a) a one-dimensional model (HEC-RAS) with the domain defined as series of extended cross-sections; (b) the same 1 D model, but with the floodplain defined by a series of storage cells, hydraulically connected to the main river channel and other storage cells on the floodplain according to floodplain topological characteristics; and (c) a 2D diffusion wave treatment, again with explicit representation of floodplain structural features. The three models were tested on a 6 km upland reach of the river Wharfe, UK. The results showed that both the extended cross-section and storage cell modes were conceptually problematic. They also resulted in poorer model predictions, requiring incorrect parameterisation of the main river to floodplain flux in order to approach anything like the level of agreement observed when the diffusion wave treatment was assessed. The research concludes that a coupled 1 D-2D treatment is likely to provide the best modelling approach, with currently available technology, for complex floodplain configurations. Second, as a substantive issue, the research is concerned with the effects of channel configuration change (i.e. in-channel morphology) and climate change on flood inundation; the aspect on which mush less attention has been paid. The results show that for the 1 in 0.5 flood event in this study reach, there is a rise of 5.7% and 12.2% to the inundation extent due to 2-year in-channel change '(i.e. 10cm rise in bed level) and climate change (i.e. scenario 2050) respectively. The sensitivity of inundated area changes to climate change is strongly conditioned by in-channel sedimentation.