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.

KEYWORDS:

• Floodplains
• flood mitigation
• humanised floodplain ecosystems
• natural and artificial wetland ecosystems
• ecosystem values
• management
• Hawkesbury–Nepean River
• Macleay River
• Durance River

Acknowledgments

The author has been interested in flood mitigation for at least five decades. This began with the study of New South Wales rivers in the 1960s and 1970s and the Los Angeles system in the early 1980s, and was followed by more than 20 years of work on the Durance. He has enjoyed the support of Gutteridge Haskins and Davey (1980), the former New South Wales Public Works Department, Sydney Water, the Los Angeles County Flood Control District, Antony Orme (University of California, Los Angeles), the Syndicat Mixte d’Aménagement de la Vallée de la Durance, and friends and colleagues in France, notably Maya Delançon (formerly Direction Régionale de l’Environnement) and Jean-Paul Bravard (Université Lumiere Lyon 2). Peter Johnson helped considerably with the diagrams and tables. Ross Chapman, former Director of the Centre for International Economics, and Professor Stephen Gale have critically reviewed several versions of this paper.