Assessment Results for Rivers and Streams of the Southwestern States
A. Pervasive disturbances: The most common disturbances based on total stream length in a given region.
Top five overall most pervasive disturbances to all stream reaches, regardless of stream size and across all spatial scales (ranked highest first):
- Road crossing density
- Road length density
- Impervious surface
- Downstream dam density
- Population density
Top three most pervasive disturbances to creeks (watersheds <100 km 2 in area) across all spatial scales:
- Road crossing density
- Road length density
- Impervious surface
Top three most pervasive disturbances to rivers (watersheds >100 km 2 in area) across all spatial scales :
- Road crossing density
- Road length density
- Impervious surface
Top five most pervasive disturbances to creeks, specific to spatial scale:
- Road crossing density in network catchments
- Road length density in network catchments
- Downstream dam density in network catchments
- Impervious surface cover in network catchments
- Impervious surface cover in network buffers
Top five most pervasive disturbances to rivers, specific to spatial scale:
- Road crossing density in network catchments
- Road length density in network catchments
- Impervious surface cover in network buffers
- Impervious surface cover in network catchments
- Low intensity urban land use in network catchments
In the Southwestern States group, 93.1% of streams are classified as low or very low risk of habitat degradation. Local variables, such as water diversion and withdrawal, drought or intensive grazing, will increase risk of degradation to specific locations.
Infrastructure factors (impervious surface, roads and dams) and potential fragmentation of stream watersheds (road crossings and dams) are important landscape factors in this state group.
B. Most severe disturbances (a subset of pervasive disturbances): Disturbances associated with stream reaches in a given region that were scored as having high or very high risk of habitat degradation (red and orange color groups).
Top five overall most severe disturbances to all stream reaches, regardless of stream size and across all spatial scales (ranked highest first):
- Impervious surface cover
- Road crossing density
- Pasture and hay land use
- Medium intensity urban land use
- Road length density
Top three most severe disturbances to creeks (<100 km 2 watersheds) across all spatial scales:
- Impervious surface cover
- Road crossing density
- Medium intensity urban land use
Top three most severe disturbances to rivers (>100 km 2 watersheds) across all spatial scales:
- Impervious surface cover
- Pasture and hay land use
- Road crossing density
