Rapid prediction of flood inundation by interpolation between flood library maps for real-time applications

Abstract

It is important that real-time flood forecasting provides information on inundation extents and depths to emergency responders for flood mitigation planning, warning and rescue operations. Conventional hydrodynamic flood inundation modelling is generally not suited for real-time operations because of its large computational demand. The most widely adopted industry practice is to link a pre-canned library of flood maps with river levels and use an interpolation approach to derive flood surfaces and depths based on selected model inputs. However, there is surprisingly scant information in the literature on the procedures and performance of the library interpolation approach. In this study, we describe the library interpolation approach, introduce univariate and multivariate interpolation schemes, and investigate their performance through a case study of a river in Port Fairy, Australia. The MIKE 11/21 hydrodynamic model was used to construct a pre-canned flood inundation library of design events. The hydrodynamic model was also used to generate outputs for four test cases to evaluate the performance of the library interpolation approach. It is found that the accuracy of the library interpolation approach relies heavily on how the map library was constructed, selection of flood drivers, and shape and timing of hydrographs. The widely deployed univariate interpolation scheme based on a single primary flood driver yields results of varied accuracy, depending on the validity of assumptions, often made implicitly, about the inputs of the non-primary drivers. A newly developed multivariate interpolation scheme overcomes this problem. Overall, it is found that the results obtained using the map library interpolation schemes are generally satisfactory, achieving a hit rate of 0.85-0.99 and a critical success index of 0.85-0.99. However, a major limitation of the library interpolation approach is that the shape and timing of the input hydrographs need to be similar to that used in constructing the map library. Further research is needed to mitigate this limitation.