Potential effects of elevated base flow and midsummer spike flow experiments on riparian vegetation along the Green River
Friedman JM. 2018. Potential effects of elevated base flow and midsummer spike flow experiments on riparian vegetation along the Green River. Natural Resource Report. NPS/NRSS/WRD/NRR—2018/1603. National Park Service. Fort Collins, Colorado
The Upper Colorado River Endangered Fish Recovery Program has requested experimental flow releases from Flaming Gorge Dam for (1) elevated summer base flows to promote larval endangered Colorado pikeminnow, and (2) midsummer spike flows to disadvantage spawning invasive smallmouth bass. This white paper explores the effects of these proposed flow modifications on riparian vegetation and sediment deposition downstream along the Green River. Although modest in magnitude, the elevated base flows and possible associated reductions in magnitude or duration of peak flows would exacerbate a long-term trend of flow stabilization on the Green River that is already leading to proliferation of vegetation including invasive tamarisk along the channel and associated sediment deposition, channel narrowing and channel simplification. Midsummer spike flows could promote establishment of late-flowering plants like tamarisk. Because channel narrowing and simplification threaten persistence and quality of backwater and side channel features needed by endangered fish, the proposed flow modifications could lead to degradation of fish habitat. Channel narrowing and vegetation encroachment could be countered by increases in peak flows or reductions in base flows in some years and by prescription of rapid flow declines following midsummer spike flows. These strategies for reducing vegetation encroachment would need to be balanced with flow needs of other riverine resources. Use of high flows to remove unwanted vegetation is constrained by current operational guidance for Flaming Gorge Dam, which attempts to limit spills (i.e., flows greater than 8600 cfs) that might contribute to cavitation and lead to dam safety concerns. Therefore, reversing vegetation encroachment is more likely to succeed if implemented while plants are still small. Annual monitoring of near-channel vegetation and topography would enable managers to prescribe a timely hydrologic response in case the proposed flow experiments lead to vegetation encroachment and habitat degradation.
- Type
- Published Report
- Authors
- Friedman, Jonathan
- Date of Issue
- 2018-03
- Publisher
- National Park Service
- Units
- CANY , DINO , IMR , NRSS , WRD
- Keywords
- Baseflows, Canyonlands National Park, Colorado pikeminnow, Dinosaur National Monument, elevated baseflows, experimental flows, Flaming Gorge, Green River, Middle Green River, smallmouth bass, smallmouth bass spike flows, spike flows, summer low flows, Upper Colorado River, Upper Colorado River Endangered Fish, Upper Colorado River Endangered Fish Recovery Program
- Subjects
- Ecological Framework: Water | Hydrology | Surface Water Dynamics , Ecological Framework: Biological Integrity | Invasive Species | Invasive/Exotic plants , Ecological Framework: Biological Integrity | Focal Species or Communities | Fishes , Ecological Framework: Biological Integrity | Focal Species or Communities | Vegetation Complex