Geomorphic Changes to the River Channels and Flood Plains of the Colorado River System: The Planned and Unplanned Effects of Water Development

Transcription

1 Geomorphic Changes to the River Channels and Flood Plains of the Colorado River System: The Planned and Unplanned Effects of Water Development Paul Grams U.S. Geological Survey Grand Canyon Monitoring and Research Center photo : Michael Collier

2 Why to the river channels look the way they do and how are they changing? What are the physical attributes of the Green and Colorado River channels and how have those attributes been affected by river management? What management strategies might be used to address some of those impacts and how are they working? photos : Michael Collier, Jack Schmidt, and Paul Grams

3 Geomorphic Attributes of Green-Colorado River system on Colorado Plateau Canyons with large tributary fans and rapids Gravel bars Now capped with fine sediment and overgrown with vegetation 1909 photo by R. Cogswell 1993 photo by P. Grams photo by P. Grams Green River in Canyon of Lodore

4 Geomorphic Attributes of Green-Colorado River system on Colorado Plateau Canyons with large tributary fans and rapids Gravel bars Now capped with fine sediment and overgrown with vegetation 1909 photo by R. Cogswell Lodore, Whirlpool, Split Mountain Canyons 1993 Desolation and Gray Canyons Cataract Canyon Marble and Grand Canyons photo by P. Grams Green River in Canyon of Lodore

5 Geomorphic Attributes of Green-Colorado River system on Colorado Plateau Canyons with large tributary fans and rapids Narrow flood plains Predam flood plain abandoned New inset flood plain established 1890 photo by R. Stanton Lodore, Whirlpool, Split Mountain Canyons Desolation and Gray Canyons 2010 Cataract Canyon Marble and Grand Canyons photo by R. Webb Colorado River in Grand Canyon

6 Geomorphic Attributes of Green-Colorado River system on Colorado Plateau Canyons with large tributary fans and rapids Sand bars Vegetation encroachment on bars no longer inundated 1871 Lodore, Whirlpool, Split Mountain Canyons Desolation and Gray Canyons photo by E.O. Beaman 1993 Cataract Canyon Marble and Grand Canyons photo by P. Grams Green River in Canyon of Lodore

7 Geomorphic Attributes of Green-Colorado River system on Colorado Plateau Canyons with large tributary fans and rapids Sand bars Vegetation encroachment on bars no longer inundated Erosion where there is sediment deficit 1952 photo by K. Frost Lodore, Whirlpool, Split Mountain Canyons 2003 Desolation and Gray Canyons Cataract Canyon Marble and Grand Canyons photo by S. Tharnstrom Colorado River in Grand Canyon

8 Geomorphic Attributes of Green-Colorado River system on Colorado Plateau Meandering reaches and lowgradient canyons Complex channels with islands and side channels Simplified to single-thread channels Former flood plains transformed into abandoned terraces no longer inundated 1917 photo by R.R. Wooley Browns Park, Echo Park, Island Park 1994 Uinta Basin Green River Basin, Canyonlands Glen Canyon photo by P. Grams Green River in Island Park

9 Geomorphic Attributes of Green-Colorado River system on Colorado Plateau Meandering reaches and lowgradient canyons Complex channels with islands and side channels Simplified to single-thread channels Former flood plains transformed into abandoned terraces no longer inundated 1917 photo by R.R. Wooley Browns Park, Echo Park, Island Park 2015 Uinta Basin Green River Basin, Canyonlands Glen Canyon Green River in Island Park

10 Geomorphic Attributes of Green-Colorado River system on Colorado Plateau Meandering reaches and lowgradient canyons Sand-bedded channel Scoured and armored where in sediment deficit Former flood plains transformed into abandoned terraces no longer inundated photo by P. Grams Photo: Glen Canyon Grams et al. (2007) Colorado River in Glen Canyon below Glen Canyon Dam

11 What have been the causes of geomorphic change? Flow and Sediment Disruptions in the Colorado River Basin Water sourced from the high-elevation mountains Fine sediment enters the river in the low-elevation basins All dams disrupt the flow of water The effect of each dam on fine-sediment transport depends on its location in the basin

12 What have been the causes of geomorphic change? Decline in magnitude of annual flood throughout basin Greendale Green River Lees Ferry

13 Colorado Plateau tributaries add sediment without adding much water, causing variable impact below dams Upper Green River: Sand-bedded reaches, far downstream from Flaming Gorge Dam Channel-narrowing with no bed incision and segments of finesediment accumulation Glen Canyon: Sand-bedded reach, immediately downstream from Glen Canyon Dam Channel-narrowing with bed incision Marble Canyon: Debris-fan dominated reach, far downstream from Glen Canyon Dam Channel-narrowing with sandbar erosion

14 Lower floods narrower channel Brown s Park Impacts of channel change Change in channel complexity and habitat Loss of open sand for recreation Disconnection between channel and former flood plain Change in riparian communities Loss of flooded bottomland habitats for fish Creation of new flood plain (often dominated by non-native tamarisk) Establishment of gravel-bedded channels for trout fisheries Grand Canyon Andrews (1986); Lyons et al. (1992); Orchard and Schmidt (1998); Allred and Schmidt (1999); Merritt and Cooper (2000); Grams and Schmidt (2002); Grams and Schmidt (2005); Walker (2017)

15 Management Strategies: Are Controlled Floods (high flows) the answer? Paul Grams U.S. Geological Survey Grand Canyon Monitoring and Research Center photo : Michael Collier

16 Below Glen Canyon Dam: Sediment budget affected by disruption of sand supply and change in flow regime Paria River Glen Canyon Dam Colorado River at Lees Ferry, AZ Marble Canyon ~ 6% of pre-dam sand supply Grand Canyon ~ 16% of pre-dam sand supply Little Colorado River 85 to 95% reduction in supply coupled with ~20% reduction in mean annual flow sediment deficit Topping et al. (2000)

17 Pre-dam Post-dam I Post-dam II: Restricted hydropower operations High Flow Experiments (HFEs) triggered by sand supply from Paria River Pre-dam: Annual floods Abundant sand supply Large sandbars Pre-HFE Post-dam I: Daily small floods Limited sand supply Eroding sandbars Unplanned floods (spills) Post-HFE Science and Management Questions: With frequent HFEs, will sandbars increase in size and abundance? Will frequent HFEs cause sand supply in channel to decrease and exacerbate sediment deficit?

18 What are the high-flow experiments (HFEs) doing? Eroded sandbar before HFE HFE inundates sandbar Debris Fan Sandbar following HFE HFEs transfer sand from channel and lowelevation parts of eddies to sandbars along channel margins

19 November 2016 High-flow Experiment Sandbar Deposition River Mile (RM) 119 R HFE Deposition 11/07/ /13/2016 River Mile (RM) 122R HFE Deposition 11/07/ /13/2016

20 November 2016 High-flow Experiment Sandbar Deposition 11/06/2016 HFE Deposition filling gullies 11/13/2016 River Mile (RM) 23L

21 What are the HFEs doing? 11/17/2014 5/7/2015 9/23/2015 Most sandbars erode to near pre- HFE size within 6 to 12 months. Grams et al. (2018)

22 What are the HFEs doing? Preliminary data do not cite Consistently rebuilding sandbars Sandbars consistently erode following HFEs But, sandbars are consistently larger than in periods without the HFEs Erosion continues in years without HFEs Grams et al. (2018)

23 HFE-deposited sand also moves upslope to cultural sites Sankey et al. (2018a,b)

24 Will HFEs continue to be effective? Sand Supply in Grand Canyon: Paria River ± 3 million metric tons sand accumulation Glen Canyon Dam + 2 ± 5 million metric tons net balance Little Colorado River ± 2 million metric tons sand erosion Alternating segments of significant sand accumulation and erosion Overall accumulation (but not significant) No evidence for overall net evacuation or accumulation Depends on continued sand inputs from Paria and Little Colorado rivers Depends on frequency of years of high release volume (equalization years) that export more sand

25 What are the HFEs not doing? RM 194 L Not depositing sandbars substantially larger than observed in past HFEs? Not depositing sandbars at substantially more locations than observed in past HFEs. Response likely constrained by HFEs that are all within narrow range of magnitude and duration. Response may also be constrained by hydrograph shape. Not removing vegetation or causing channel width to increase Are they benefiting other resources? 4/20/ /20/2016

26 What are the effects of HFEs on other resources? Recource Positive Adverse Recreational trout fishery Native fish (humpback chub) Spring HFEs may cause increases in trout population because of food base response None identified (but populations have been stable and increasing) Strong perception among anglers that fall HFEs are bad for the trout fishery* None identified (increases in trout may be threat) Riparian vegetation None identified None identified Aquatic food base (aquatic invertebrates) Spring HFEs scour macrophytes in growing season stimulates desirable invertebrates Fall HFEs scour macrophytes in winter season no benefit to desirable invertebrates

27 What are the effects of HFEs on other resources? Recource Positive Adverse Recreational trout fishery Native fish (humpback chub) Spring HFEs may cause increases in trout population because of food base response None identified (but populations have been stable and increasing) Strong perception among anglers that fall HFEs are bad for the trout fishery* None identified (increases in trout may be threat) Riparian vegetation None identified None identified Aquatic food base (aquatic invertebrates) Spring HFEs scour macrophytes in growing season stimulates desirable invertebrates Fall HFEs scour macrophytes in winter season no benefit to desirable invertebrates

28 What are the effects of HFEs on other resources? Recource Positive Adverse Recreational trout fishery Native fish (humpback chub) Spring HFEs may cause increases in trout population because of food base response None identified (but populations have been stable and increasing) Strong perception among anglers that fall HFEs are bad for the trout fishery* None identified (increases in trout may be threat) Riparian vegetation None identified None identified Aquatic food base (aquatic invertebrates) Spring HFEs scour macrophytes in growing season stimulates desirable invertebrates Fall HFEs scour macrophytes in winter season no benefit to desirable invertebrates

29 What are the effects of HFEs on other resources? Recource Positive Adverse Recreational trout fishery Native fish (humpback chub) Spring HFEs may cause increases in trout population because of food base response None identified (but populations have been stable and increasing) Strong perception among anglers that fall HFEs are bad for the trout fishery* None identified (increases in trout may be threat) Riparian vegetation None identified None identified Aquatic food base (aquatic invertebrates) Spring HFEs scour macrophytes in growing season stimulates desirable invertebrates Fall HFEs scour macrophytes in winter season no benefit to desirable invertebrates Fall timing of HFE s optimizes for sediment, but is not benefiting the aquatic ecosystem

30 Pitfalls of resource-driven restoration/rehabilitation that is caused by fragmented character of system coupled with resource-based policy (e.g. endangered species) Current HFE protocol is a sediment-driven mitigation strategy. Just because it s been difficult for scientists to demonstrate with data the importance of flood timing to the ecosystem, doesn t mean timing is unimportant the apparent nationwide importance of high flows in spring (March, April, May) also indicates that the timing (not just magnitude) of high flows is critical." Grams et al. (2018) Spring HFE led to good bugs. Kennedy et al. (preliminary data, do not cite) Preliminary data do not cite Although fall HFEs build sandbars, there is mismatch between sandbar size and visitor use

31 Acknowledgements Daniel Buscombe, Thomas Gushue, Daniel Hamill, James Hensleigh, Joseph Hazel, Matt Kaplinski, Erich Mueller, Robert Ross, David Rubin, Joel Sankey, Jack Schmidt, David Topping, Robert Tusso, Scott Wright, References Allred, T. M., & Schmidt, J. C. (1999). Channel narrowing by vertical accretion along the Green River near Green River, Utah. Geological Society of America Bulletin, 111(12), Andrews, E. D. (1986). Downstream effects of Flaming Gorge Reservoir on the Green River, Colorado and Utah. Geological Society of America Bulletin, 97(August), Grams, P. E., & Schmidt, J. C. (2002). Streamf low regulation and multi-level f lood plain formation : channel narrowing on the aggrading Green River in the eastern Uinta Mountains, Colorado and Utah, 44, Grams, P. E., & Schmidt, J. C. (2005). Equilibrium or indeterminate? Where sediment budgets fail: Sediment mass balance and adjustment of channel form, Green River downstream from Flaming Gorge Dam, Utah and Colorado. Geomorphology, 71(1 2), Grams, P. E., Schmidt, J. C., & Topping, D. J. (2007). The rate and pattern of bed incision and bank adjustment on the Colorado River in Glen Canyon downstream from Glen Canyon Dam, Geological Society of America Bulletin, 119(5/6), Grams, P. E., Tusso, R. B., & Buscombe, D. (2018). Automated Remote Cameras for Monitoring Alluvial Sandbars on the Colorado River in Grand Canyon, Arizona. U.S. Geological Survey Open-File Report , Lyons, J. K., Pucherelli, M. J., & Clark, R. C. (1992). Sediment transport and channel characteristics of a sand-bed portion of the Green River below Flaming Gorge Dam, Utah. Regulated Rivers: Research & Management, 7, Merritt, D. M., & Cooper, D. J. (2000). Riparian vegetation and channel change in response to river regulation: A comparative study of regulated and unregulated streams in the Green River Basin, USA. Regulated Rivers: Research & Management, 16, Orchard, K. L., & Schmidt, J. C. (1998). A geomorphic assessment of the availability of potential humpback chub habitat in the Green River in Desolation and Gray Canyons, Utah. Logan, Utah: Utah State University. Sankey, J. B., Kasprak, A., Caster, J., East, A. E., & Fairley, H. C. (2018). The response of source-bordering aeolian dune fi elds to sediment-supply changes 1 : E ff ects of wind variability and river-valley morphodynamics. Aeolian Research, 32(February), Sankey, J. B., Caster, J., Kasprak, A., & East, A. E. (2018). The response of source-bordering aeolian dune fi elds to sediment-supply changes 2 : Controlled fl oods of the Colorado River in Grand Canyon,. Aeolian Research, 32(February),