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7 - Fluvial Processes and Forms in the Anthropocene

Published online by Cambridge University Press:  20 October 2016

Andrew S. Goudie
Affiliation:
University of Oxford
Heather A. Viles
Affiliation:
University of Oxford
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Summary

Humans have deliberately altered fluvial landscapes, by the building of embankments and levees, the construction of dams and reservoirs, and channelization. Fluvial sediment transport has been modified in two main ways. On the one hand, dam construction has caused much sediment to be trapped in reservoirs. On the other, sediment delivery to rivers has been increased as a result of accelerated rates of soil erosion. Humans have greatly modified channels, though it is not always easy to differentiate between human effects and those of climatic fluctuations and flood events. Much channel change is the inadvertent result of modification of the amounts of water and sediment that come down channels, or the modification of riparian vegetation. River restoration describes a set of activities that help improve the environmental health of rivers and which have an impact on river channels. It has become an important approach to river management since the 1980s. Related to stream restoration and to the developing aversion to hard engineering, is dam removal. In recent years, partly because some old dams have become unsafe, ecologically unacceptable, or redundant, they have been demolished. Floodplain sediments have been generated by human activities in the Holocene. The causes of phases of incision and aggradation are illustrated from three regions: the arroyos of the south west United States, aggradation and erosion in valley bottom of the Mediterranean lands, and the spectacular gullies, lavaka, in Madagascar. Global warming will affect fluvial geomorphology in a range of ways. Increasing temperatures will melt snow and ice and promote greater losses of moisture through evapotranspiration. There will be changes in the amount, intensity, duration and timing of precipitation, which will also affect the size of snowpacks and river flows. Vegetation cover will respond to temperature and precipitation changes, as will land use. Vegetation assemblages will also be affected by an increasing frequency of fires and this may also affect runoff.
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Publisher: Cambridge University Press
Print publication year: 2016

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