HR: 17:35h
AN: H34B-06    [Abstracts]
TI: Optimal Use of ALSM for Modelling Urban Flood Inundation
AU: * Brasington, J
EM: jb10016@cam.ac.uk
AF: University of Cambridge, Department of Geography Dowing Place, Cambridge, CB2 3EN United Kingdom
AU: McMillan, H
EM: hkm21@cam.ac.uk
AF: University of Cambridge, Department of Geography Dowing Place, Cambridge, CB2 3EN United Kingdom
AB: Significant advances in flood management have been achieved through the use of a new generation of 2d flood inundation numerical models. These offer the potential to predict the local pattern and timing of flood depth and velocity, enabling informed flood risk zoning and improved emergency planning. With the availability of high resolution DEMs derived from ALSM, these models could theoretically now be routinely parameterised to incorporate the topographic complexity of urban areas, offering the potential to account for flow patterns at the scale of individual buildings. Currently, however, computational constraints on conventional finite element codes typically require model discretization at scales well below those achievable with ALSM and are thus unable to make optimal use this new data stream. In this paper we review two strategies that attempt to address this mismatch between model and data resolution in an effort to improve urban flood forecasts. The first of these strives for a solution by simplifying the mathematical formulation of the numerical model by using a computationally efficient 2d raster storage cell approach coupled to a 1d channel model. By contrast, the second method employs a morphological analysis of ALSM data to determine a sub-grid scale model of topographic complexity. This is then applied in coarse resolution simulations to represent the first order effect of the loss of available storage due to sub-grid scale topographic features. These two strategies are evaluated through numerical experiments simulating the pattern of flooding in the city of Cambridge UK, following a major storm in October 2001. For this, ALSM data were acquired with an Optech ALTM 3033 with a point spacing of 0.25m and simulations are evaluated through comparison with an observed flood envelope digitised from photography flown at the flood peak. Results from both approaches are encouraging, with inundation forecasts using the reduced complexity model comparing well with both the observed flood patterns and a 2d CFD simulation yet offering significant gains in runtime efficiency. The sub-grid parameterization model is also shown to improve low-resolution simulations without contributing significant computational complexity, but cannot match the predictive performance obtained by explicitly incorporating urban features in the topographic boundary condition.
DE: 1817 Extreme events
DE: 1821 Floods
DE: 1847 Modeling
DE: 1849 Numerical approximations and analysis
DE: 1855 Remote sensing (1640)
SC: Hydrology [H]
MN: Fall Meeting 2005