Network connectivity refers to the longitudinal (upstream to downstream) and lateral (channel to floodplain) connectedness of the river corridor, considering pathways for movement of biological organisms and other organic material through the stream and riparian corridors. These plant and animal migration pathways determine species distribution, habitat use, and energy flow. Longitudinal barriers like dams, weirs, culverts, and dry-up points may impede migration of fish and other aquatic species and can interrupt the flow of detritus, woody material, and other organic matter. Lateral barriers such as invasive riparian vegetation and alterations to floodplain hydrology may isolate stream corridors from adjacent upland habitat, limiting the exchange of energy and migration of organisms between terrestrial and aquatic systems. Flood hazards are often created or exacerbated in areas with poor longitudinal and lateral connectivity.
On the flip side, interruptions of connectivity can be used to support endangered species and controlling invasive species. For example, Colorado Parks and Wildlife (CPW) often relies on diversion dams to control invasive aquatic species or isolate a native fish population.
Analysis of network connectivity should begin with a comprehensive review of all available related data. Decisions regarding assessment level and data analysis should be made based on SMP goals.
Surrounding land uses
Barriers to migration or materials flow
Potential Data Sources
Remote desktop surveys using aerial imagery to assess surrounding land uses, percent development, and impervious surfaces
Remote desktop surveys using aerial imagery to identify degree of aquatic habitat loss and migration/dispersal barriers
Field visits to verify identified terrestrial barriers
Field visits to identify structural aquatic passage barriers and other existing infrastructure
Interviews with regional aquatic biologists about aquatic connectivity issues
Tips for Success
Barriers can often be identified using Google Earth or similar aerial imagery. These barriers can include dam/reservoir operations, watershed-scale land-use activities, riparian land cover conversion, urbanization, channelization/levees, and channel structures such as dams, weirs, culverts, or diversions.
This variable may be broken out into three categories:
- Buffer capacity rates the degree to which the supporting land area supports healthy stream and riparian functioning by buffering potential stressors just outside of the riparian zone. Reductions to buffer capacity include high-intensity land use or development, impervious surfaces, bare soil, and structures.
- Terrestrial connectivity extends the buffer zone, rating impairment to migration and dispersal of terrestrial organisms based on loss of habitat and dispersal/migration barriers within a “habitat connectivity envelope.”
- Aquatic connectivity rates the severity and proximity of barriers to migration of aquatic organisms between the reach and adjacent segments of the stream and its tributaries.
Not all SMPs include connectivity in their stream health assessments. However, network connectivity is an important factor of overall stream health and may be evaluated with minimal expenditure of resources.
Conducting diversion infrastructure assessments can provide additional information about longitudinal/aquatic connectivity in a system and potential opportunities for addressing barriers to passage of aquatic organisms.
Yampa River Health Assessment and Streamflow Management Plan
Assessment Level: Level 3
To rate the network connectivity variable (referred to as “Landscape”), the Yampa River Health Assessment and Streamflow Management Plan relied on desktop review and remote survey of aerial imagery, examination of existing data sources, and communications with a regional aquatic biologist, but augmented this information with field visits to identify or confirm physical barriers. Three sub-variables (buffer capacity, terrestrial connectivity, and aquatic connectivity) were scored by experts and integrated into the Functional Assessment of Colorado Streams (FACStream) assessment framework.