A preliminary investigation into the impact of initial conditions on flood inundation predictions using a time/space distributed sensitivity analysis

A new high space/time resolution distributed sensitivity analysis is presented and used to examine the impact of simple variations in initial conditions on inundation predictions derived from a two dimensional finite element model of river channel/floodplain flow. Specifically changes in the specification of the floodplain topographic surface and the upstream boundary condition are considered for two flood events. Model response to uniform variation of both parameters is shown to be both non-uniform and complex. The space/time distributed surface of model sensitivity is shown to be consistent within treatments but with significant variations in response shown between treatments and between storm events. It is shown that there is no simple mechanism generating this complex response, although significant inter-storm variations in the two dimensional auto-correlation surface calculated for the sensitivity data are shown to exist. It is suggested that this latter class of analysis provides a possible means of investigating the generating mechanism further.