The impacts of flood-mitigation structures on floodplain ecosystems: a review of three case studies from Australia and France

ABSTRACT This study is concerned with the physical impacts of flood-mitigation structures on ‘humanised’ and ‘natural’ floodplain ecosystems. The former constitute fertile, well drained and developed surfaces. The latter are mainly degraded wetland areas located in the backwater zones of wide, low-lying floodplains. Three rivers are investigated: the Hawkesbury–Nepean and the Macleay Rivers in New South Wales, Australia and the Durance River in southern France. Their floodplains, flood-mitigation works and floodplain ecosystems are analysed, together with site- and time-dependent differences in their floodplains, their exploitation and their degradation. Conservation of floodplains seeks to reverse wetland degradation, and to increase biodiversity and sustainability, as well as preserving developed floodplains. This study discusses gaps in our biophysical knowledge of ecosystems and the absence of ecological indicators of degradation. It also considers the lack of data on socio-economic values for what are unique, site- and time-specific, biophysical systems. Only when such inadequacies are addressed will the values of ecosystems be fully understood. Then cost-effective management might be possible. These knowledge gaps contribute to the many problems of floodplain management, which are likely to increase when the additional impacts of population increase and global warming become apparent.