Paleofloods and historical floods of the Ardèche River, France

Abstract

[1] Better understanding of flood occurrences and long-term, floodplain planning, and flood risk assessment is achieved by integration of gauged, historical, and paleoflood data. The Ardèche River is ideal for this historical flood-paleoflood study because its historical flood levels record dates back as early as A.D. 587 and useful data date back to A.D. 1522, its systematic gauging record is over 100 years long, and the geologic and geomorphic settings are optimal for paleoflood studies. Three sites provide three different thresholds for flood stages and SWD accumulation. According to our onedimensional (1-D) step-backwater calculations these three thresholds are 5200-5700 m 3 s À1 , 4900-5400 m 3 s À1 , and 3600-4000 m 3 s À1 recording 6, 9, and 19 large Holocene floods, respectively. Dating the deposits enabled a correlation with the historical record. These paleoflood studies indicate that there are long gaps in flood occurrences on the Ardèche River; the floods are not randomly distributed in time but are clustered. They also indicate that the recent nineteenth century floods were the largest at the millennial timescale.

Integrating ecology with hydromorphology: a priority for river science and management

“…Eco-hydromorphic variation has been studied over a wide range of spatial and temporal extents } the latter often in the course of long-term monitoring, such as flow gauging (Sheffer et al, 2003), retrospective aerial photograph/map analyses of geomorphology (Tiegs and Pohl, 2005) and annual river bird surveys (Carter, 1989). Long-term monitoring can provide invaluable information about the behaviour of river systems, as can palaeohydrological investigations that extend the study of river variability over hundreds or thousands of years, or even into longer geological and evolutionary time-scales (Sear and Arnell, 2006).…”

The Palaeoflood record of the Gardon River, France: A comparison with the extreme 2002 flood event

“…In addition to the recent floods, unit 11 dated to the Little Ice Age (LIA), units 4 and 6 were dated to 2850±45 BP and 2260±40 BP respectively. The adjacent Ardèche basin also witnessed paleofloods in these periods (Sheffer, 2003;Sheffer et al, 2003b), with paleoflood clustering dated to 2170 BP and 2705 BP, as well as during the LIA.…”

“…In humid regions exposed deposits are not readily preserved however, caves may record this information (e.g. Kite and Linton, 1993;Springer and Kite, 1997;Sheffer, 2003, Sheffer et al, 2003b. In the case of the Gardon River the protected sites mainly include caves and alcoves in the canyon walls.…”

“…In this study the conventional and AMS methods were used to date radiocarbon samples found in the SWD sequence. The paleoflood methods of separating slack water deposits and dating by radiocarbon used in this study is thoroughly discussed by Sheffer (2003) and Sheffer et al, (2003b).…”

Quantitative historical hydrology in Europe

“…Moreover, the age uncertainty of numerical dating (radiocarbon respectively optically stimulated luminescence methods) used in palaeoflood studies may be refined based on known documentary floods (Medialdea et al, 2014). The SPHERE project has revealed the complementary of palaeoflood and historical flood information with major gain on the quality of past flood records in terms of time and discharge, as is demonstrated in the studies performed for the rivers Gardon (Naulet et al, 2005;Sheffer et al, 2008), Ardèche (Sheffer et al, 2003;Naulet et al, 2005), Llobregat (Thorndycraft et al, 2005), and Guadalentin (Benito et al, 2010;Medialdea et al, 2014). Recent palaeoflood reconstructions from floodplain sediments have analysed geochemical proxies from continuous alluvial records and investigate local documentary flood data to calibrate the palaeohydrological records (e.g.…”