Use of systematic, palaeoflood and historical data for the improvement of flood risk estimation. Review of scientific method

The catastrophic floods recently occurring in Europe warm of the critical need for hydrologic data on floods over long-time scales. Palaeoflood techniques provide information on hydrologic variability and extreme floods over long-time intervals (100 to 10,000 yr) and may be used in combination with historical flood data (last 1,000 yr) and the gauge record (last 30-50 yr). In this paper, advantages and uncertainties related to the reconstruction of palaeofloods in different geomorphological settings and historical floods using different documentary sources are described. Systematic and non-systematic data can be combined in the flood frequency analysis using different methods for the adjustment of distribution functions. Technical tools integrating multidisciplinary approaches (geologic, historical, hydraulic and statistical) on extreme flood risk assessment are discussed. A discussion on the potential theoretical bases for solving the problem of dealing with non-systematic and non-stationary data is presented. This methodology is being developed using new methodological approaches applied to European countries as a part of a European Commission funded project (SPHERE).