41
logical timescales of tens of thousands to millions of years. Natural forms of disconnectivity can thus be persistent, impassable barriers over timespans relevant to
human and biotic communities, but can also effectively slow rather than completely
stop connectivity.
In summary, understanding and maintaining river health relies on understanding
the processes that create and maintain natural levels of connectivity and being able
to characterize natural levels of connectivity.
2.5.2 Complexity
Complexity has at least two meanings within river science. The first refers to complex behavior and the presence of nonlinear dynamics, self-organization, and emergent properties (Werner and McNamara 2007; Phillips 2014). The second uses
complexity to describe spatial heterogeneity, or the degree to which a river corridor
deviates from a straight, uniform canal. Complex behavior and spatial heterogeneity
are commonly interrelated (Phillips 2007; Peipoch et al. 2015), but this discussion
focuses on spatial heterogeneity.
Spatial heterogeneity in a river corridor occurs at diverse spatial scales from a
channel unit or patch of sediment up to the entire longitudinal profile or river network (Fig. 2.16). At any of these scales, heterogeneity results from discrete patches
with differing characteristics. These patches can be described in terms of patch richness (the number of patches present), patch frequency (the number of each patch
Fig. 2.15 Schematic illustration of the three primary dimensions of connectivity: longitudinal,
lateral, and vertical, here superimposed on an upstream view of East Inlet Creek in Rocky Mountain
National Park, Colorado, USA
2.5 The 4Cs of River Health
logical timescales of tens of thousands to millions of years. Natural forms of disconnectivity can thus be persistent, impassable barriers over timespans relevant to
human and biotic communities, but can also effectively slow rather than completely
stop connectivity.
In summary, understanding and maintaining river health relies on understanding
the processes that create and maintain natural levels of connectivity and being able
to characterize natural levels of connectivity.
2.5.2 Complexity
Complexity has at least two meanings within river science. The first refers to complex behavior and the presence of nonlinear dynamics, self-organization, and emergent properties (Werner and McNamara 2007; Phillips 2014). The second uses
complexity to describe spatial heterogeneity, or the degree to which a river corridor
deviates from a straight, uniform canal. Complex behavior and spatial heterogeneity
are commonly interrelated (Phillips 2007; Peipoch et al. 2015), but this discussion
focuses on spatial heterogeneity.
Spatial heterogeneity in a river corridor occurs at diverse spatial scales from a
channel unit or patch of sediment up to the entire longitudinal profile or river network (Fig. 2.16). At any of these scales, heterogeneity results from discrete patches
with differing characteristics. These patches can be described in terms of patch richness (the number of patches present), patch frequency (the number of each patch
Fig. 2.15 Schematic illustration of the three primary dimensions of connectivity: longitudinal,
lateral, and vertical, here superimposed on an upstream view of East Inlet Creek in Rocky Mountain
National Park, Colorado, USA
2.5 The 4Cs of River Health