1 Spatial Modelling of the Terrestrial Environment - Georeferencial

Flood Inundation Modelling Using LiDAR and SAR Data 95
Figure 5.3 Assignment of an ‘effective’ friction value for each element of a finite-element
mesh using the vegetation height data shown in Figure 5.2c and the friction mapping algorithm
of Mason et al. (2003). For each mesh node, an instantaneous friction factor is calculated at
each timestep, given the frictional material in the neighbourhood of the node and the current
water depth and flow velocity there. A node’s neighbourhood is defined as a polygon whose
vertices are the centroids of the elements surrounding the node. Sub-regions of connected
regions in the vegetation height map are formed by intersecting the node polygon map with
the vegetation height map. Each sub-region in a polygon may contain either sediment or one
of the three vegetation height classes. If a sub-region contains vegetation, its region’s average
vegetation height is attributed to the sub-region (from Mason et al.,) 2003. c○ John Wiley &
Sons, Ltd.
in order to rigorously test and refine such schemes and discriminate between competing
approaches. Whilst we should not expect the method proposed by Mason et al. (2003) to
fully overcome the problem of specifying and calibrating frictional resistance, it may be
able to substantially reduce the predictive uncertainty associated with friction estimates for
floodplain areas and hence allow the remaining sources of uncertainty to be more rigorously
analyed.