Evaluating the Frequency of Triggered Spring High 

Flow Experiments (HFE’s) Assumed in the LongTerm Experimental and Management Plan 

Presentation to Glen Canyon Dam Adaptive Management Program, 

Technical Working Group 

April 24, 2018 

Phoenix, Arizona 

Paul Grams and David Topping 

U.S. Geological Survey, Southwest Biological Science Center, Grand Canyon 

Monitoring and Research Center 
Building sandbars with HFEs Sand Budget for 2008 HFE in Upper 

Marble Canyon 

Eroded sandbar before 

HFE 

Sandbar following HFE 

HFE inundates sandbar 

• HFEs transfer sand from channel and 

low-elevation parts of eddies to 

sandbars along channel margins 

• Cause net export of sand 

Sand export 

during HFE 

Data from: https://www.gcmrc.gov/discharge_qw_sediment 
Basic concept of HFE protocol in LTEMP: 

Balance sand export during HFEs with Paria Sand 

inputs 

Paria River during flood 

= 

Transport at RM 61 

(downstream end of Marble Canyon) 

SandParia + Sandsmall tribs = Sandexport at 61 mi
 

Sand accounting periods 

Accomplish sand budget balance 

with absolute (long-term) sand 

accounting or relative (short-term) 

sand accounting? 

• Problems with absolute or “long-term” 

accounting: 

• Lack accurate measurements of 

total sand storage 

• Uncertainty in sand budgets 

accumulates over time (several 

years) 

We monitor the sand budget for 

long-term trends in storage, but use 

relative accounting for HFE 

planning. 

2008 to 2012 sand budget for 

Upper Marble Canyon 

Data from: https://www.gcmrc.gov/discharge_qw_sediment 
 

Sand accounting periods 

Short-term relative sand 

accounting: 

• Distinct Spring and Fall accounting 

periods: 

• Can design HFE to “use” only 

recent sand inputs. 

• HFEs are implemented when 

storage in Upper Marble Canyon is 

highest 

• Simple decision process 

• One annual accounting period 

• Would likely end up with more 

sand export before implementing 

HFE 

• Would need decision process for 

deciding whether to implement 

HFE in Fall or Spring 

Plot from LTEMP EIS, Appendix P 
 

 

 

 

Sand accounting periods 

Short-term relative sand 

accounting: 

• Distinct Spring and Fall accounting 

periods: 

• Can design HFE to “use” only 

recent sand inputs. 

• HFEs are implemented when 

storage in Upper Marble Canyon is 

highest 

• Simple decision process 

• One annual accounting period 

• Would likely end up with more 

sand export before implementing 

HFE 

• Would need decision process for 

deciding whether to implement 

HFE in Fall or Spring “... sediment-triggered spring HFEs would be 

Spring HFE’s have been implemented after an initial 2-year delay in order to 

... address concerns raised by the apparent positive avoided since 2008: response of trout to the 2008 spring HFE (Korman et 

al. 2011; Melis et al. 2011)." 

Plot from LTEMP EIS, Appendix P 
Basic concept of HFE protocol in LTEMP: 

Balance sand export during HFEs with Paria Sand 

inputs 

Paria River during flood 

Data from: https://www.gcmrc.gov/discharge_qw_sediment 
Frequency of Spring HFEs 

As estimated in LTEMP 

• Simulations designed to represent 

the full range of historical 

conditions: 

• 21 hydrologic traces 

• 3 sediment traces (low, 

median, high) 

 May be sufficient sediment input 

to trigger Spring HFEs in “26% of 

the years in the LTEMP period”

Estimated number of HFEs to occur during 20-

year implementation of LTEMP 

(“D” was selected alternative)

Plot from LTEMP EIS, Appendix E 
Frequency of Spring HFEs 

Based on observations 

of past 20 years: 

• Compare December – April Paria 

sand inputs with December to 

April sand export from Marble 

Canyon 

 May have been sufficient 

sediment input to trigger Spring 

HFE: “Once since 1998”

Data from: https://www.gcmrc.gov/discharge_qw_sediment 
 

 

 

–

Frequency of Spring HFEs 

Why the difference? 

• Simulations included Paria River 

sand inputs since 1963 

• Fall (summer) sand inputs from 

Paria have been relatively 

consistent 

• Spring (winter) sand inputs were 

at least 3 times greater between 

1964 and 1997 than between 

1998 and present 

 Winter sand inputs are not 

consistent 

Maybe we’ll see a return to larger 

winter floods, or maybe there has 

been a shift in winter 

precipitation...

• Black circles (summer/fall inputs) and red 

diamonds (winter/spring inputs) are data used in 

LTEMP 

• Blue “+” are 1998 2018 data we looked at 

(same) 

Data from: https://www.gcmrc.gov/discharge_qw_sediment 
 

 

 

HFE Design 

April 24, 2018 

Paul Grams 

U.S. Geological Survey, Southwest Biological Science Center, Grand Canyon 

Monitoring and Research Center 

U.S. Department of Interior 

U.S. Geological Survey 
Types of sandbar response to HFEs 

Deposition 

~ 50-60% of sites 

Erosion 

No change 

~ 30-40% of sites 

~ 10% of sites 

Grams et al. (2018) 
Erosion of HFE deposit HFE Response: 2012 to 2017 

11/17/2014 

5/7/2015 

Most sandbars erode near pre-HFE 

size within 6 to 12 months. 

9/23/2015 

Grams et al. (2018) 
 

HFE Response: 2012 to 2017 

Unpublished data, do not cite 

Data from: https://www.gcmrc.gov/discharge_qw_sediment 
–

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Sandbar monitoring 

New analysis of sandbar trends 

based on grouping of bars by 

morphology and average response 

• Groups 1a and 1b: 

relatively large and mostly open bare 

sandbars 

Strongest response to HFEs 

• Groups 1c and 3: 

heavily vegetated bars Unpublished data, do not cite 

Less dynamic around HFEs, tend to 

accumulate over time 

• Groups 2 and 4: 

Mostly smaller bars adjacent to debris 

fans (don’t project into eddy)

Tend to be most stable 

HFEs still improve condition by filling 

gullies and burying/removing debris 

Data from: https://www.gcmrc.gov/discharge_qw_sediment 

Mueller et al. (2018); unpublished data, do not cite 
 

 

 

 

HFE Design Experiments 

• Extended duration HFEs 

– Up to 8-10 days (compared to 4 days as currently implemented) 

– Only if there is “enough” sand

– If enough sand, could build larger and more numerous bars 

– LTEMP simulations estimated conditions might occur 5 times in 20 years, 

LTEMP ROD allows 4 implementations 

Makes sense to test when 

conditions occur. 

• Monitoring needed for comparison with 

other HFEs 

• Monitoring sand concentration 

• Sandbar monitoring at all sites with 

complete surveys 

• Daily surveys at selected sites to measure 

changes in deposition rates during HFE 

0

10,000

20,000

30,000

40,000

50,000

-10 -5 0 5 10 15 20

1996

2004

2008

2012

DISCHARGE, IN CUBIC FEET PER SECOND

TIME, IN DAYS RELATIVE TO DEPARTURE FROM NORMAL DAM OPERATIONS

1996 HFE was 8 days, but was not designed to 

match recent sand inputs 

Data from: https://www.gcmrc.gov/discharge_qw_sediment 
 

 

 

HFE Design Experiments 

• Proactive HFEs 

– Spring HFE released regardless of sand 

trigger in advance of summer equalization 

flows 

– Goal is to create some high-elevation sand 

deposits in advance of erosion that will 

occur during sustained high releases. 

– LTEMP simulations estimated conditions 

might occur twice in 20 years 

Makes sense to test when 

conditions occur. 

• Monitoring needed for comparison with other HFEs 

• Monitoring sand concentration 

• Sandbar monitoring at all sites with complete surveys 

• Compare deposition with other HFEs 

• Measure summer erosion (what is the size of bars following 

equalization compared to before the proactive HFE?) 

Data from: https://www.gcmrc.gov/discharge_qw_sediment 

2011 

equalization 

flows 

Conditions in 2011 “inspired” idea 

for proactive Spring HFE – large 

sand inputs during previous fall 

followed by equalization flows 
 

 

 

HFE Design Experiments 

• Changes to hydrograph shape 

(lower downramp rate) 

– Deposition at range of 

elevations, instead of 

focused at elevation of peak 

stage 

– Expected to produce 

sandbars that have lower 

slope on bar face 

– Tested in 2012 

• Limited monitoring 

indicated some bars did 

have lower slopes 

0

10,000

20,000

30,000

40,000

50,000

-10 -5 0 5 10 15 20

1996

2004

2008

2012

DISCHARGE, IN CUBIC FEET PER SECOND

TIME, IN DAYS RELATIVE TO DEPARTURE FROM NORMAL DAM OPERATIONS

• Bars still eroded, but lack 

enough measurements to 

compare erosion rates. 

Since all releases above powerplant capacity count towards the HFE duration, lower 

downramp comes at expense duration of peak sand concentrations. Best experiment might 

be to follow a “regular” 96-hour HFE with slow downramp as part of extended duration HFE 

test. 

• Monitoring needed for comparison with other HFEs 

• Sandbar monitoring at all sites with complete surveys 

• Compare deposition with other HFEs 

Data from: https://www.gcmrc.gov/discharge_qw_sediment 
 

HFE Design Experiments 

>8,000 cfs 

>25,000 cfs 

1996 post-HFE 

>8,000 cfs 

>25,000 cfs 

2008 post-HFE 

>8,000 cfs 

>25,000 cfs 

2012 post-HFE 

>8,000 cfs 

>25,000 cfs 

2004 post-HFE 

Surveys before and after 2012 HFE at 3 large reattachment bars 

• Bar volume largest in 1996 (highest discharge and longest duration), area 

above 8,000 cfs stage largest in 2012 (gradual downramp) 

• Slope from bar crest to 8,000 cfs level less steep than other floods 

Unpublished data, do not cite 
 

 

HFE Design Experiments 

• Low-magnitude HFE (HFE at or near 

powerplant capacity of 31,500 cfs) 

– Not identified as “experiment” in LTEMP.

– Allowed by HFE protocol 

– But they have not yet occurred 

Is there interest in comparison with 

larger HFEs if a low-magnitude HFE 

does occur? 

• Monitoring needed for comparison with other HFEs 

• Sandbar monitoring at all sites with complete surveys 

• Compare deposition with other HFEs