December 18, 2020
Central Colorado Conservancy, Salida
Trout Unlimited, Collegiate Peaks Chapter
EcoMetrics, Buena Vista
Round River Design, Salida
Supported by: Gillilan and Associates, Buena Vista
Purpose and scope
This study is a holistic riverscape health assessment of a 1.9 km reach of the South Arkansas River from County Road 107 to the confluence with the Arkansas River east of Salida. The purpose is threefold:
(1) to demonstrate the use of a holistic riverscape health assessment in stream management planning,
(2) to identify potential opportunities to restore or conserve stream health and function, and
(3) to provide a rational basis for restoration and/or conservation plans.
This study is a holistic stream health assessment of the South Arkansas River. It builds upon prior work by the South Arkansas Watershed Coalition to identify conservation and restoration potential on the 1.9 km reach through Salida from County Road 107 downstream to the confluence with the Arkansas. This reach is highly modified for past and current land and water uses. Flow regime is significantly diminished due to upstream water diversions. The stream is channelized and often deeply entrenched. Most of stream corridor was converted for ranching and agriculture in the 1800s which is also when the major roads, and rail lines were built across it. Nowadays, the 150-year-old valley-bottom ranching uses are giving way to urbanization. Most of the riverscape has become incrementally constrained by infrastructure and development, leaving less room for ecosystem function. In its static and greatly simplified state, with a shrunken corridor, narrowed floodplain, and diminished flows, riverscape health and resilience are waning. Composite stream health scores on the reach range from C (significantly impaired) to D+ (severely impaired).
Opportunities to improve stream health and resilience depend upon the ability to reverse or mitigate these impacts, the causes of impairment, to restore natural ecosystem processes and give back some space where these processes can operate. The best prospect for meaningful improvement is on the segment of the old Vandeveer Ranch owned by the City of Salida plus the adjacent private properties up- and downstream. Land use on this section of the stream corridor has moved on from historical industrial-scale ranching, the stream is much less entrenched and beginning to recover naturally, and most of the direct causes of impairment can be practically and feasibly mitigated. Past levees and cross-valley road fills can be removed to reverse the impacts of channelization, entrenchment, and floodplain disconnect; and with improved hydrology native riparian vegetation and wetland can be reestablished. Simple treatments can be applied to promote natural fluvial processes such as sediment capture, scour, structural complexity, and riparian forest regeneration. In short, this segment provides a rare opportunity where natural stream ecosystem processes may occur over a broader portion of the historical riverscape without threatening infrastructure or infringing on property owner’s needs. Conservation and process-based restoration of the riverscape aligns well with landowner values of increased natural habitat, floodplain function, open space, recreation, and environmental education. On other segments where stream functions are constrained by land use, development, or infrastructure, marginal stream health gains or limited enhancement benefits might be possible using costly engineering-based or artificial approaches.