High-resolution data obtained from airborne remote sensing is
increasing opportunities for representation of small-scale structural
elements (e.g. walls, buildings) in complex floodplain systems using
two-dimensional (213) models of flood inundation. At the same time, 2D
inundation models have been developed and shown to provide good
predictions of flood inundation extent, with respect to both full
solution of the depth-averaged Navier-Stokes equations and simplified
diffusion-wave models. However, these models have yet to be applied
extensively to urban areas. This paper applies a 2D raster-based
diffusion-wave model to determine patterns of fluvial flood inundation
in urban areas using high-resolution topographic data and explores the
effects of spatial resolution upon estimated inundation extent and flow
routing process. Model response shows that even relatively small
changes in model resolution have considerable effects on the predicted
inundation extent and the timing of flood inundation. Timing
sensitivity would be expected, given the relatively poor representation
of inertial processes in a diffusion-wave model. Sensitivity to
inundation extent is more surprising, but is associated with: (1) the
smoothing effect of mesh coarsening upon input topographical data; (2)
poorer representation of both cell blockage and surface routing
processes as the mesh is coarsened, where the flow routing is
especially complex; and (3) the effects of (1) and (2) upon water
levels and velocities, which in turn determine which parts of the
floodplain the flow can actually travel to. It is shown that the
combined effects of wetting and roughness parameters can compensate in
part for a coarser mesh resolution. However, the coarser the
resolution, the poorer the ability to control the inundation process,
as these parameters not only affect the speed, but also the direction
of wetting. Thus, high-resolution data will need to be coupled to a
more sophisticated representation of the inundation process in order to
obtain effective predictions of flood inundation extent. This is
explored in a companion paper.