Modelling shoreline evolution to enhance flood risk assessment

Abstract

Traditional flood-risk assessment considers coastal defences to be static features with foreshores represented simply with an assigned elevation and slope. However, beach elevations can vary rapidly over time, perhaps fluctuating seasonally, and often losing or gaining volume over a longer time period. Their dynamic nature ultimately influences the risk of coastal erosion and flooding. In a regional flood-risk assessment, in which beaches offer protection to a variety of backshore features such as seawalls, soft cliffs, and dunes, the ability to represent the beach dynamics fronting these defences is important. At regional scale, it is also necessary to consider the various backshore environments that may be encountered over a long stretch of coastline, and how their individual processes affect flood risk, particularly if they are erodible. An integrated framework of dynamically linked numerical models of coastal processes and statistical analysis methods is being developed to enhance regional flood-risk assessment via consideration of coastal evolution and foreshore morphodynamics. The framework is run entirely from within commercially available geographical information system software where model operation and numerical output is managed; standard geographical information system analysis and database capabilities are therefore also available within the modelling system. This paper outlines the basis of the modular framework, and demonstrates how flood-risk assessment is enhanced.

Regional-scale probabilistic shoreline evolution modelling for flood-risk assessment

“…The model results presented here should not be treated as absolute (due to limited calibration), but instead are comparative relative to each other. The model study is carried out within the GIS framework reported by Stripling et al (2007) and Stripling and Panzeri (2009).…”

“…Recognising the ability of GIS to manage large quantities of data, Stripling et al (2007) examined an alternative approach which linked deterministic numerical models of coastal processes within a GIS framework in order to populate the database directly. Stripling and Panzeri (2009) (Hall et al 2003, Gouldby et al 2008.…”

“…The database now holds significant statistical data fields based on the probabilistic model runs, and can be queried in accord with proprietary GIS methods. (see Stripling et al 2007 andPanzeri 2009), allowing generation of long duration time-series of wave data (over decades) and subsequent derivation of morphologically-averaged conditions.…”

“…indicates the entire extent of the modelled coastline, the initial position of which was extracted from aerial photographs taken in 2003. Wave conditions at the site were derived from a regional-scale shallow-water wave propagation model(Stripling and Panzeri, 2009) and filtered to provide daily morphologically-averaged conditions. Littoral drift volumes were prescribed to provide a marked response by the coastline, purely for demonstration purposes.…”

“…Where there are defences (e.g. at Withernsea and Hornsea) rates of erosion have been locally reduced, and groyne systems have been successful in capturing sand and maintaining beach levelsThe integrated UnaLineaProb and RASP-SU modelling system is now applied to the Holderness Coast within the GIS framework developed byStripling and Panzeri (2009). The UnaLinea model domain covered about 50 km of the coastline.…”