66
Construction of major transportation corridors such as railroads and large roads
can involve moving large amounts of sediment and disrupting native land cover,
especially in high-relief terrain. These changes can result in continuing hillslope
instability and associated changes in water, sediment, and nutrient yields to river
corridors (e.g., Larsen and Parks 1997).
3.1.3 Introduced Upland Species
Introduced upland species, typically plant species, can change relations among precipitation inputs, infiltration, runoff, and evapotranspiration, and thus change water,
sediment, and nutrient yields and, in the case of woody plants, large wood yields to
river corridors. Examples come from regions with introduced tree species, such as
Chile and New Zealand, where forested streams with introduced tree species have
less large wood and/or less geomorphically effective large wood (e.g., Evans et al.
1993; Baillie and Davies 2002; Ulloa et al. 2011). Introduced insects such as the
woolly adelgid (Adelges tsugae) or emerald ash borer (Agrilus planipennis) in
North America, both of which kill large numbers of trees, can substantially alter
evapotranspiration and water fluxes, with resulting changes in stream flow.
Widespread tree die-off from insect infestation also alters inputs of large wood and
nutrients to river networks (e.g., Ford and Vose 2007).
3.1.4 Water Diversions
People have transferred water from one drainage basin to another for centuries in
some parts of the world (Liu and Zheng 2002). Long-distance water transfers are
now becoming increasingly widespread as the technology to facilitate such transfers, and the economic incentive to support them, develop (Wohl 2011). The most
obvious effect of a water transfer is to decrease flow in the source basin and increase
flow in the receiving basin, with a cascade of secondary effects on transport of sediment and nutrients; complexity; and connectivity in source and receiving basins
(Fig. 3.4). The details of these effects depend on what proportion of total flow is
diverted and how that flow is transferred to the receiving basin (e.g., whether the
flow is transferred throughout the year or for a limited period) (Ryan 1997; Wohl
and Dust 2012).
3.1.5 Urbanization
Urbanization commonly includes changes in land cover, topography, and species
within the urban area. Among the most extensively documented effects of urbanization are a substantial increase in the volume of water delivered to river
3 Human Alterations of Rivers
Construction of major transportation corridors such as railroads and large roads
can involve moving large amounts of sediment and disrupting native land cover,
especially in high-relief terrain. These changes can result in continuing hillslope
instability and associated changes in water, sediment, and nutrient yields to river
corridors (e.g., Larsen and Parks 1997).
3.1.3 Introduced Upland Species
Introduced upland species, typically plant species, can change relations among precipitation inputs, infiltration, runoff, and evapotranspiration, and thus change water,
sediment, and nutrient yields and, in the case of woody plants, large wood yields to
river corridors. Examples come from regions with introduced tree species, such as
Chile and New Zealand, where forested streams with introduced tree species have
less large wood and/or less geomorphically effective large wood (e.g., Evans et al.
1993; Baillie and Davies 2002; Ulloa et al. 2011). Introduced insects such as the
woolly adelgid (Adelges tsugae) or emerald ash borer (Agrilus planipennis) in
North America, both of which kill large numbers of trees, can substantially alter
evapotranspiration and water fluxes, with resulting changes in stream flow.
Widespread tree die-off from insect infestation also alters inputs of large wood and
nutrients to river networks (e.g., Ford and Vose 2007).
3.1.4 Water Diversions
People have transferred water from one drainage basin to another for centuries in
some parts of the world (Liu and Zheng 2002). Long-distance water transfers are
now becoming increasingly widespread as the technology to facilitate such transfers, and the economic incentive to support them, develop (Wohl 2011). The most
obvious effect of a water transfer is to decrease flow in the source basin and increase
flow in the receiving basin, with a cascade of secondary effects on transport of sediment and nutrients; complexity; and connectivity in source and receiving basins
(Fig. 3.4). The details of these effects depend on what proportion of total flow is
diverted and how that flow is transferred to the receiving basin (e.g., whether the
flow is transferred throughout the year or for a limited period) (Ryan 1997; Wohl
and Dust 2012).
3.1.5 Urbanization
Urbanization commonly includes changes in land cover, topography, and species
within the urban area. Among the most extensively documented effects of urbanization are a substantial increase in the volume of water delivered to river
3 Human Alterations of Rivers