46
able based on characteristics such as alteration of land cover, surface water quality,
alteration of flow regime, degree of habitat fragmentation, introduced species, and
imperiled native species (WWF 2013).
Process domains are spatially discrete portions of a landscape or river network
characterized by distinct suites of geomorphic processes (Montgomery 1999).
Within a drainage network, individual process domains might be differentiated
based on disturbance regime. Within a mountainous river network, for example, one
process domain at higher elevations might be defined based on the occurrence of
snowmelt-runoff flow peaks, whereas a second process domain might be defined at
lower elevations based on rainfall-runoff flow peaks. Process domains can also be
distinguished based on how river segments resist or recover following disturbance.
Considering a mountainous river network again, one process domain could consist
of steep, narrow valley segments with erosionally resistant substrate such as bedrock and large boulders and channel geometry predominantly formed during large
flows. Another process domain could consist of lower gradient, wider valley segments with mobile alluvium in which channel geometry reflects predominantly
more frequent flows of lower magnitude (Fig. 2.18). Regardless of the specific criteria used to delineate process domains, they are likely to reflect finer spatial scales
than ecoregions.
River style (Brierley and Fryirs 2005) is a geomorphic classification applied at
the reach scale that is similar to process domains in recognizing spatially discrete
reaches that are internally homogeneous with respect to topography, valley geometry, channel planform, and substrate, but differ from other reaches (Fig. 2.19). There
is substantial overlap between the conceptualization of process domains and river
Fig. 2.17 Map of
freshwater ecoregions in
North America. (After
WWF 2013, Fig. 2.1,
p. 10)
2 Rivers as Ecosystems
able based on characteristics such as alteration of land cover, surface water quality,
alteration of flow regime, degree of habitat fragmentation, introduced species, and
imperiled native species (WWF 2013).
Process domains are spatially discrete portions of a landscape or river network
characterized by distinct suites of geomorphic processes (Montgomery 1999).
Within a drainage network, individual process domains might be differentiated
based on disturbance regime. Within a mountainous river network, for example, one
process domain at higher elevations might be defined based on the occurrence of
snowmelt-runoff flow peaks, whereas a second process domain might be defined at
lower elevations based on rainfall-runoff flow peaks. Process domains can also be
distinguished based on how river segments resist or recover following disturbance.
Considering a mountainous river network again, one process domain could consist
of steep, narrow valley segments with erosionally resistant substrate such as bedrock and large boulders and channel geometry predominantly formed during large
flows. Another process domain could consist of lower gradient, wider valley segments with mobile alluvium in which channel geometry reflects predominantly
more frequent flows of lower magnitude (Fig. 2.18). Regardless of the specific criteria used to delineate process domains, they are likely to reflect finer spatial scales
than ecoregions.
River style (Brierley and Fryirs 2005) is a geomorphic classification applied at
the reach scale that is similar to process domains in recognizing spatially discrete
reaches that are internally homogeneous with respect to topography, valley geometry, channel planform, and substrate, but differ from other reaches (Fig. 2.19). There
is substantial overlap between the conceptualization of process domains and river
Fig. 2.17 Map of
freshwater ecoregions in
North America. (After
WWF 2013, Fig. 2.1,
p. 10)
2 Rivers as Ecosystems