Geoscience Reference
In-Depth Information
12.Riversineventhemostinaccessibleregionsareaffectedtosomeextentbyhuman
activities,ashereintheDarienGapinPanama,anarearenownedgloballyforitsre-
moteness
Direct and intentional modifications to rivers are complemented by the impacts of land use
and land use changes which frequently result in the alteration of rivers as an unintended
side effect. Deforestation, afforestation, land drainage, agriculture, and the use of fire have
all had significant impacts, with perhaps the most extreme effects produced by construction
activity and urbanization. These impacts are diverse and are not all direct. Many aspects
of a dynamic river channel and its associated ecosystems are mutually adjusting, so a hu-
man activity in a landscape that affects the supply of water or sediment is likely to set off
a complex cascade of other alterations. When contemporary climate change is included in
the vast array of human activities that in some way result in changes to rivers, many au-
thorities argue that few, if any, rivers - even in the world's least populated regions - remain
unaffected by human impact. In many ways, therefore, the evolution and development of
rivers is driven as much by social and economic factors as by natural ones.
