The role of long‐term human impact on avulsion and fan development

Abstract

This study aims to understand (mainly qualitatively) the long‐term role of human impact on avulsion processes and the development of fluvial (mega‐) fans in semi‐arid environments. In this paper we refer to human impact as the direct influences of actions on the river's hydraulics (i.e. flow regulation, flow diversion and channel engineering). In five case‐studies drawn from the Khuzestan plains in southwest Iran we have analysed the setup and triggering conditions of specific avulsions that occurred in the past (timescale of millennia) and identified the role of human interference in their causation. Our analysis is based on the integration of historical, archaeological, geomorphological and geological data. Through this study we demonstrate that avulsions in the Khuzestan plains are the result of long‐term and complex interplay between multiple human‐induced and natural causes. In similar ways human‐induced actions may play important roles during different phases of avulsion development. The ‘success‘ of an avulsion in the post‐triggering phase may be defined by human‐induced setup causes as well as morphodynamic processes. We suggest that present‐day flood events may be partly inherited from long‐term human alterations of the natural processes. These finding could have implications for any fluvial system (e.g. distributive fluvial systems, deltas) where avulsion plays a major role in their development and research tends to emphasize on natural mechanisms. Copyright © 2016 John Wiley & Sons, Ltd.

Humans and the Earth's surface

“…Such changes have provoked significant geomorphic changes in the area (e.g. Heyvaert and Walstra (2016) presented a study on the understanding of the long-term impacts of human activity on avulsion processes and the development of fluvial (mega-) fans in semi-arid environments. In addition, since the 1980s, industrial-touristic infrastructures have developed on the emerging land surface and are associated with growing geomorphic hazards in the coastal zone.…”

“…In 2012-2013, the Huanghe delivered 0.73 Tg (1 Tg = 10 12 g) of POC to the sea, and about 28% of the annual POC flux occurred within a short human induced flood event. Heyvaert and Walstra (2016) presented a study on the understanding of the long-term impacts of human activity on avulsion processes and the development of fluvial (mega-) fans in semi-arid environments. The authors focused upon the analysis of the direct influences on the river's hydraulics (i.e.…”

Where Might the Hands-off Protection Strategy of Anastomosing Rivers Lead? A Case Study of Narew National Park

“…The reach valley conditions accurately listed in Table 2 seem to be preferential for triggering the avulsion process [8,10,12]. However, the historical planform changes indicated contrary findings.…”

“…as an example of an equifinal system, i.e., different combinations of processes or causes produce a similar form [7]. Their origin and development is controlled by the avulsion process, which is the diversion of flow from an existing channel onto the floodplain, eventually resulting in a new channel belt [8][9][10][11][12]. Anastomosing rivers would have been historically common in low-gradient, alluvial valleys worldwide prior to the expansion of agriculture and urbanization, triggering extensive modifications of rivers and their floodplains [13].…”

Human-caused avulsion in the Rhine-Meuse delta before historic embankment (The Netherlands)

“…Many modern fluvio-deltaic environments where avulsion takes place have been increasingly affected by humans over the last millennia. Humans are known to have deliberately triggered avulsion directly, by constructing canals and dams (e.g., Heyvaert and Walstra, 2016), but less is known about unintended avulsion resulting from human impacts in the delta plain and in the hinterland before the avulsion is actually triggered. This is despite the potential importance and impact of avulsion on densely populated deltas worldwide.…”