Guiding Principles for Using Ifsar Aerial Survey for Low Cost Flood Mapping (PAP014404)

Código

PAP014404

Autores

Ben Caddis, Melissa Hovey, Chris Nielsen

Tema

Land use and Floods, landslides and erosion

Resumo

Over the past 10 years, access to aerial survey (such as LiDAR and photogrammetry) has enabled practitioners to substantially improve the accuracy of flood models and associated flood mapping. The availability of these data is typically resulting in one-dimensional (1D) flood models being replaced by fully two-dimensional (2D) or integrated 1D/2D models. Consequently, there appears to be a greater dependence on access to high resolution, high accuracy aerial survey to be able to assess complex flood behaviour. Acquisition of highly accurate aerial survey such as LiDAR or photogrammetry can be prohibitively expensive for a project and, in some cases, can delay the commissioning of studies until funding is available. In many situations, this fails to meet the needs of flood prone communities, subjecting them to on-going flood risk. Therefore, lower cost alternative datasets, such as IfSAR, are often sought to make the flood mapping process viable. IfSAR data are captured from aircraft flown at high altitude, thus resulting in a lower cost for a given area. The lower cost is directly reflected in reduced accuracy of data, which itself affects the accuracy of the flood modelling. The adage, any data is better than no data" has a strong place in the debate of whether or not IfSAR is appropriate for flood modelling application. If these lower accuracy data could be used for broadscale flood mapping, there is potential for flood prone areas to be identified earlier. Higher accuracy survey and modelling could then be targeted to specific areas. At the other extreme, some practitioners are actively using IfSAR survey as a basis for flood modelling and subsequent flood mitigation structure design. The risk here is that authorities and practitioners are placing too much confidence in IfSAR data, generating additional risk due to potential failure or under-design of infrastructure. It is imperative that practitioners draw attention to the limitations of flood maps to ensure they are used appropriately and for their intended use. Flood mapping derived from poor data can have serious, and even fatal, consequences. This is particularly relevant for the analysis and design of flood mitigation structures, such as levees. This paper will provide context to, and describe a set of guiding principles that have been developed for the use of different topographic datasets for flood mapping application. The paper identifies the limitations for different types of aerial survey data. It is intended that these guiding principles can be referenced by authorities worldwide when assessing the feasibility of flood mapping or flood mitigation projects. The guiding principles are based upon three case studies (in Australia and Malaysia) where IfSAR, LiDAR and photogrammetric datasets have been used for flood modelling and the resultant flood mapping and modelling output compared."