River incision in south-east France: morphological phenomena and ecological effects

Abstract

The historical trend of aggradation in stream beds of Europe';s mountain and piedmont areas has been reversed since the beginning of the twentieth century to a general tendency towards narrowing and incision. After an overview of some causes and geomorphological effects of river bed incision, and a description of some case studies in alpine rivers, this paper aims to assess how the phenomenon affects the ecosystems of alluvial plains. The questions addressed are, in particular, the effect of river bed incision on sediment redistribution during floods, habitat diversity and the water table; and the consequences of these changes for the distribution and diversity of biological communities. The effect of incision on floodplain vegetation, instream invertebrate communities, groundwater and former channel ecosystems and fish communities are considered. It has been found that incision rarely affects the biocoenoses directly, but indirect changes in habitat conditions are significant. At the scale of the whole hydrosystem, the predicted impact of incision is a decrease in habitat heterogeneity, and, thereby, in biodiversity. At the ecosystem scale, the negative effect on biodiversity is higher in habitats that are less connected to the running water of the river. ©1997 by John Wiley & Sons, Ltd.

Towards a better understanding of the today French torrents management policy through a historical perspective

“…Industrial instream gravel mining started during the 1950s to support concrete buildings and road network development. It rapidly increased during the 1970s-1980s [24]. At the same time, embankments were built to protect the increasing population over alluvial fans.…”

Variabilidad espacial de los cambios de cauce en una rambla mediterránea en las seis últimas décadas (1946-2006)

“…In French rivers, channel narrowing in the first half of the twentieth century has been associated with decreased discharge and sediment supply at the end of the Little Ice Age. In contrast, channel reduction in the second half of the twentieth century is considered a human-induced fluvial adjustment (Bravard et al, 1997;Liébault and Piégay, 2002;Arnaud-Fassetta, 2003;Liébault et al, 2005). In Italy, Surian et al (2009) detected small width changes during the nineteenth century, but with no significant trend.…”

“…Causal interpretation has often been addressed through retrospective analyses of anthropogenic actions such as dam construction, reforestation, torrent control works, or river channelization (Bravard et al, 1997;Rinaldi, 2003;Surian and Rinaldi, 2003;Surian and Cisotto, 2007;García-Ruíz and Lana-Renault, 2011). Gravel extraction has also had a profound impact on rivers around the world (Kondolf et al, 2002;Liébault and Piégay, 2002;Surian and Rinaldi, 2003;Piégay et al, 2004;Rinaldi et al, 2005;Wishart et al, 2008;Surian et al, 2009).…”

Fish Passage and Abundance around Grade Control Structures on Incised Streams

“…Extensive channel erosion has also caused dramatically increased sediment loads. The altered flow regimes, loss of habitat, loss of connectivity, and high sediment loads caused by channel incision has led to decreased biodiversity (Hansen, 1971;Shields et al, 1994;Bravard et al, 1997;Cooper et al, 1997;Shields et al, 1998;Raborn and Schramm 2003). Bunn & Arthington (2002) noted that in highly altered environments, invasive species may find it easier to out-compete native species in the new, altered environment.…”