Do high‐resolution fan delta records provide a useful tool for hazard assessment in mountain regions?

The multidisciplinary Fluvalps‐3000 research project focuses on the variability of the Late Holocene and historical fluvial dynamics in alpine catchments. The purpose of this paper is to examine the potential of a 3,600 year‐long record composed from fluvial deposits for flood hazard assessment.

The research is based on a multi‐proxy approach integrating methods of various disciplines as sedimentology, geochronology, pedology, geomorphology, palynology, history, and archaeology. This paper considers particularly the sedimentological and geocronological methods applied to the fluvial records of several key sections of the Lütschine and Lombach fan deltas.

The sedimentary data of the high‐resolution fan delta record show up to seven major aggradation pulses from 3,600 cal yr BP to present. Furthermore, 19 minor burial episodes occur between 3,600 and 1,050 cal yr BP at average intervals between 113 years (Lütschine) and 105 years (Lombach) suggesting that aggradation during the focused period was triggered by centennial flood events. Nine coarse‐grained flood layers of the Lütschine record, deposited during the last 3,350 years by catastrophic flood events at a recurrence interval of 370 years, coincide with positive radiocarbon anomalies and cold phases in the Alps. The solar influence on regional hydrological regime is proposed as the main factor triggering the flooding events. However, the impact of land‐use changes in the region since 2,300 cal yr BP was detected by pollen and geochemical proxy data from fluvial deposits.

According to the results, the 2005 flood may not be considered as one of these mayor catastrophic events, thus providing useful data for future risk assessment by regional and local authorities. The 3,600 year flood history derived from fan delta proxies, presented in this paper, is unique in the European Alps.