A much understudied aspect of flood inundation is examined, i.e. 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 paper, we
present the comparison of three treatments of upland flood inundation
using: (a) a one-dimensional (ID) model (HEC-RAS v. 3.1.2) with the
domain defined as series of extended cross-sections; (b) the same ID
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; (c) a two-dimensional (2D) diffusion wave treatment,
again with explicit representation of floodplain structural features.
The necessary topographic and topological data were derived using lidar
and Ordnance Survey Landline data. The three models were tested on a 6
km upland reach of the River Wharfe, UK. The models were assessed by
comparison with measured inundation extent. The results showed that
both the extended cross-section and the storage cell I D modes were
conceptually problematic. They also resulted in poorer model
predictions, requiring incorrect parameterization of the main river to
floodplain flux in order to approach anything like the level of
agreement observed when the 2D diffusion wave treatment was assessed.
We conclude that a coupled 1D-2D treatment is likely to provide the
best modelling approach, with currently available technology, for
complex floodplain configurations.