Scale and resolution problems can also arise in defining the flow domain for both surface and subsurface flow processes. Surface processes will normally require only the definition of topography of the domain, but subsurface processes require the geometry of the various soil and geological layers in the system and the subsurface boundaries of the domain.

Surface topography is often derived by utilizing remote sensing (Wilson, 2004) and although one of the most important inputs into most distributed models, topography is often seen as the factor with the least uncertainty. Various studies have shown that small errors in flood plain topography can have significant effects on flood inundation model results (see e.g. Aronica et al., 1998; Bates et al., 1997; Nicholas and Walling, 1998; Quinn et al., 1995; Wilson, 2004). Such errors can be especially significant if they are related to embankment height or channel depth. Additional models have to be developed to determine e.g. flow paths for rainfall runoff.

Obtaining information on subsurface structure is much more difficult and is likely to be associated with much greater uncertainties in both geometry and characteristics. The sensitivity of groundwater flow predictions, for example, to the conceptual geological model of the flow domain has been demonstrated (McKay? and Fredericia, 1995).

References

Aronica, G., Hankin, B. and Beven, K.J., 1998. Uncertainty and equifinality in calibrating distributed roughness coefficients in a flood propagation model with limited data. Advances in Water Resources, 22(4): 349-365.

Bates, P.D., Anderson, M.G., Hervouet, J.M. and Hawkes, J.C., 1997. Investigating the behaviour of two-dimensional finite element models of compound channel flow. Earth Surface Processes and Landforms, 22(1): 3-17.

McKay?, L.D. and Fredericia, J., 1995. Distribution, origin, and hydraulic influence of fractures in a clay-rich glacial deposit. Canadian Geotechnical Journal, 32(6): 957-975.

Nicholas, A.P. and Walling, D.E., 1998. Numerical modelling of floodplain hydraulics and suspended sediment transport and deposition. Hydrological Processes, 12(8): 1339-1355.

Quinn, P.F., Beven, K.J. and Lamb, R., 1995. The Ln(a/Tan-Beta) Index - How to Calculate It and How to Use It within the Topmodel Framework. Hydrological Processes, 9(2): 161-182.

Wilson, M.D., 2004. Evaluating the effect of data and data uncertainty on predictions of flood inundation, University of Southampton, Southampton, 276 pp.

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Risk and Uncertainty (Description and Definition)