1. photo : Michael Collier
Mitigating Impacts of Changes to the Flow Regime and Sediment Supply on the Colorado River
1. lateral recirculation zones are important because ...
2. we created a physically realistic lateral recirculation zone with mobile bed lab experiment
3. we found that instantaneous vertical flow was important to morphological evolution, as well as time-averaged lateral flow
Paul Grams
U.S. Geological Survey
Grand Canyon Monitoring and Research Center
photo : Michael Collier

2. “redesign of the river channel with dam operations”
Mitigating Impacts of Changes to the Flow Regime and Sediment Supply on the Colorado River
“redesign of the river channel with dam operations”
1. lateral recirculation zones are important because ...
2. we created a physically realistic lateral recirculation zone with mobile bed lab experiment
3. we found that instantaneous vertical flow was important to morphological evolution, as well as time-averaged lateral flow
Paul Grams
U.S. Geological Survey
Grand Canyon Monitoring and Research Center
photo : Michael Collier

3. Overview
Scientific background for high-flow experiments (HFEs) released from Glen Canyon Dam.
How do HFEs work?
What has been the response to repeat HFEs?
What HFEs do and do not accomplish?
1. lateral recirculation zones are important because ...
2. we created a physically realistic lateral recirculation zone with mobile bed lab experiment
3. we found that instantaneous vertical flow was important to morphological evolution, as well as time-averaged lateral flow

4. 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

5. Decline in magnitude of annual flood throughout basin
Greendale
Green River
Cisco
Lees Ferry

6. Lower floods  narrower channel
1911
1952
1999
1998
Brown’s Park, Utah
1871
Glen Canyon, Arizona
1958
2008
1999
Grand Canyon, Arizona
Canyonlands, Utah

7. 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 fine-sediment 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

8. Below Glen Canyon Dam: Sediment budget affected by disruption of sand supply and change in flow regime
Paria River
Glen Canyon Dam
Marble Canyon
~ 6% of pre-dam sand supply
Colorado River at Lees Ferry, AZ
This talk is about how we’re using the framework of the sediment budget in an attempt to restore (or partially restore) sandbars along the Colorado River in Grand Canyon. It’s an example of a case where we’ve integrated the monitoring of sediment flux, with monitoring of geomorphic change, and with a management/decision making framework.
The main subject is what we call the high-flow experiment (HFE) Protocol. Tomorrow, Jack Schmidt will be talking more about how the protocol is implemented in cooperation with the management agencies and how interests other than the movement of sand and building of sandbars are addressed.
For those of you not intimately familiar with the sediment issues in Grand Canyon, a simple summary is that one of the main goals is to manipulate the system that has a very limited sand supply to build sandbars while maintaining as much ability as possible to generate hydropower.
In addition to explaining how the flood protocol works, I’d like to also discuss a bit about the issues and uncertainties that remain when structuring a management strategy around a large-scale sediment budget. This has mainly to do with the spatial and temporal scales over which you try to connect the sediment budget with morphologic change.
Little Colorado River
Grand Canyon
~ 16% of pre-dam sand supply
85 to 95% reduction in supply coupled with ~20% reduction in mean annual flow  sediment deficit
Topping et al. (2000)

9. Pre-dam
Post-dam I
Ratio of observed sandbar area to maximum potential sandbar area (reach-average)
1935
RM:
29-35
0-8
42-49
50-56
60-72
Pre-dam:
Annual floods
Abundant sand supply
Large sandbars
Post-dam I:
Daily small floods
Limited sand supply
Eroding sandbars
Unplanned floods (spills)
About 25% reduction in sandbar area in Marble Canyon (Schmidt et al., 2004; Ross and Grams, 2015)
1952
2003

10. High Flow Experiments (HFEs)
Pre-dam
Post-dam I
Post-dam II:
Restricted hydropower operations
High Flow Experiments (HFEs)
triggered by sand supply from Paria River
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?
Pre-dam:
Annual floods
Abundant sand supply
Large sandbars
Post-dam I:
Daily small floods
Limited sand supply
Eroding sandbars
Unplanned floods (spills)
Pre-HFE
Post-HFE

11. Eroded sandbar before HFE
What are the high-flow experiments (HFEs) doing?
Eroded sandbar before HFE
HFE inundates sandbar
Debris Fan
Sandbars and fan eddy complex
Sandbar following HFE
HFEs transfer sand from channel and low-elevation parts of eddies to sandbars along channel margins

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

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

14. 11/17/2014 5/7/2015 9/23/2015 What are the HFEs doing?
Most sandbars erode near pre-HFE size within 6 to 12 months.

15. What are the HFEs doing? 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

16. Will HFEs continue to be effective?

17. Sand Supply in Grand Canyon: 2012-2017
Will HFEs continue to be effective?
Sand Supply in Grand Canyon:
Glen Canyon Dam
Paria River
+ 5.9 ± 3 million metric tons sand accumulation
+ 2 ± 5 million metric tons net balance
Little Colorado River
This talk is about how we’re using the framework of the sediment budget in an attempt to restore (or partially restore) sandbars along the Colorado River in Grand Canyon. It’s an example of a case where we’ve integrated the monitoring of sediment flux, with monitoring of geomorphic change, and with a management/decision making framework.
The main subject is what we call the high-flow experiment (HFE) Protocol. Tomorrow, Jack Schmidt will be talking more about how the protocol is implemented in cooperation with the management agencies and how interests other than the movement of sand and building of sandbars are addressed.
For those of you not intimately familiar with the sediment issues in Grand Canyon, a simple summary is that one of the main goals is to manipulate the system that has a very limited sand supply to build sandbars while maintaining as much ability as possible to generate hydropower.
In addition to explaining how the flood protocol works, I’d like to also discuss a bit about the issues and uncertainties that remain when structuring a management strategy around a large-scale sediment budget. This has mainly to do with the spatial and temporal scales over which you try to connect the sediment budget with morphologic change.
- 3.9 ± 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

18. What are the HFEs not doing?
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.
Sandbars and fan eddy complex
1996
2004
2008
2012
Example at one site: each HFE built a large sandbar
Bar volume largest in 1996 (highest discharge and longest duration)
Bar area largest in 2012 (more gradual downramp)
Bar less steep in 2012 (more gradual downramp)

19. 4/20/1996 11/20/2016 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
not managing for segments in sediment surplus.
4/20/1996
Sandbars and fan eddy complex
11/20/2016

20. Are dam operations a “tool” for channel design?
HFEs result in sandbar deposition that does not occur during normal operations. Because sandbars inevitably erode, they are only effective if repeated and if sand supply is maintained.
1958
Sandbars and fan eddy complex
But, HFEs as currently implemented, are not expected to recreate pre-dam conditions