Alan Kasprak

U.S. Geological Survey

24 January 2017

The Individual and Additive Effects of Hydrologic Alteration and 

Vegetation Encroachment on Sediment Connectivity in Grand Canyon

with Daniel Buscombe, Joshua Caster,

Amy East, Paul Grams, Helen Fairley, 

and Joel Sankey

USGS Grand Canyon 

Monitoring and Research Center

TWP Project 4.1 Research Flagstaff, Arizona
The Individual and Additive Effects of Hydrologic Alteration and 

Vegetation Encroachment on Sediment Connectivity in Grand Canyon

Most archaeological sites are situated

above HFE stage throughout Grand Canyon...

To preserve these sites through river management:

- Option 1: Flood and bury sites with larger, sediment-rich HFEs

- Option 2: Rely on wind to move sediment from sandbars to sites
The Individual and Additive Effects of Hydrologic Alteration and 

Vegetation Encroachment on Sediment Connectivity in Grand Canyon

Current HFEs only deposit sediment

in sandbars up to ~45,000 ft3 Most archaeological sites are situated /s

above HFE stage throughout Grand Canyon...

To preserve these sites through river management:

- Option 1: Flood and bury sites with larger, sediment-rich HFEs

- Option 2: Rely on wind to move sediment from sandbars to sites
The Individual and Additive Effects of Hydrologic Alteration and 

Vegetation Encroachment on Sediment Connectivity in Grand Canyon

Most archaeological sites are situated

above HFE stage throughout Grand Canyon...

To preserve these sites through river management:

- Option 1: Flood and bury sites with larger, sediment-rich HFEs

- Option 2: Rely on wind to move sediment from sandbars to sites

Current HFEs only deposit sediment

in sandbars up to ~45,000 ft3/s
Glen Canyon Dam – Completed 1963
- Spring/Summer Snowmelt Floods

- Summer/Fall Low Flows

- Loss of Large Floods

- Loss of Low Flows

- Increased Base Flows

Colorado River at Lee’s Ferry
Study Area:

- 16 mile river reach of Colorado River in Grand Canyon National Park

- From 45 to 61 miles downstream of Glen Canyon Dam 
Mapping Sand Along the Colorado River in Grand Canyon – May, 2009

Channel bed mapping with multibeam sonar

Total station surveys of exposed sand

Upstream-looking DEM

*preliminary results, do not cite (black dots are 1/10 mile intervals)
Multibeam Sonar Bed Classification

The intensity of the 

echo returned from 

the bed is related to 

the grain size

Sand Gravel Cobble/Boulder

Validation using underwater camera

Buscombe et al., 2014; JGR-ES

*preliminary results, do not cite
2009 Sand Mapping: Active Channel

Active Channel Sand

...but this only gets us to the 45,000 ft3/s stage.

Historic floods deposited sand up to 210,000 ft3/s 

From multibeam and 

total station surveys

*preliminary results, do not cite
2009 Sand Mapping: Active Channel and Remote Upland Mapping

Active Channel Sand

From classification

of 2009 aerial photos

From multibeam and 

total station surveys in 2009

Remotely Mapped

Upland Sand

*preliminary results, do not cite
Active Channel Sand

2009 Sand Mapping: Active Channel and Remote and Manual Upland Mapping

Remotely Mapped

Upland Sand

Manually Mapped

Upland Sand

From supervised classification

of 2009 aerial photos

From field mapping on 

river trips

From multibeam and 

total station surveys

Mapped every square meter of sand from the channel bed 

to historic flood of record (210,000 ft3/s) over 16 mile reach

*preliminary results, do not cite
Hydraulic Modeling

Magirl et al., 2008

8,000 ft3/s

20,000 ft3/s

45,000 ft3/s

210,000 ft3/s

...and ten

intermediate

flows not

shown here

What area of sand will be exposed for a

given discharge from Glen Canyon Dam?
For every modeled

inundation extent...

...take the map of

total sand

...and cut out anything

that’s underwater

*preliminary results, do not cite
Exposed Sand as a Function of Discharge

8,000 ft3/s: lowest regularly-occurring flows 

in Grand Canyon today

*preliminary results, do not cite



210,000 ft3/s: estimated historic flood

of record in Grand Canyon
More bare sand from 0 – 8,000 ft3/s...

Than from 8,000 ft3/s to 210,000 ft3/s...

*preliminary results, do not cite

Exposed Sand as a Function of Discharge
*preliminary results, do not cite

We know how much sand is exposed for any discharge

...and we know the discharge every day since 1922 

Exposed Sand as a Function of Discharge
*preliminary results, do not cite

We know how much sand is exposed for any discharge

...and we know the discharge every day since 1922 

We can compute daily exposed sand area for the past 94 years

Exposed Sand as a Function of Discharge
Hydrologic Alteration reduced exposed sand area by 13.5%

*preliminary results, do not cite
Glen Canyon Dam – Completed 1963
1890

1890

2010

2010

1890

2010

A trend toward: 

- Increased vegetation area, particularly along the river

- Correspondingly reduced area of bare sand

Observations of vegetation encroachment following dam construction
2009

1000 m
1965 1973 1984

1992 2002 2009 2013

2009 +26% +18%

+12% +2% +3% +1%

1000 m

Vegetation Encroachment reduced exposed sand area by 20%

 

   

*preliminary results, do not cite
Predam Average: 395,000 m2/day

*preliminary results, do not cite
Postdam Average: 289,000 m2/day

Hydrologic Alteration + Vegetation Encroachment

have reduced exposed sand by 27%

*preliminary results, do not cite

Predam Average: 395,000 m2/day
Predam Average: 3.95 x 105 m2/day Postdam Average: 2.89 x 105 m2/day

Hydrologic Alteration Only

Hydrologic Alteration + Vegetation Encroachment

have reduced exposed sand by 27%

*preliminary results, do not cite
Caster, East et al., 2014

What about the Wind?

Wolman and Miller, 1960
Caster, East et al., 2014

Wolman and Miller, 1960

What about the Wind?

*preliminary results, do not cite
Caster, East et al., 2014

Wolman and Miller, 1960

What about the Wind?

*preliminary results, do not cite
Caster, East et al., 2014

25%

What about the Wind?

The product of wind data and 

sand area provide an estimate of

sand transport rate

throughout the year

*preliminary results, do not cite
Relevance to Glen Canyon Dam Operations

Neither sand nor vegetation are uniformly distributed along the river...

 Opportunities for vegetation removal

 Use stage-discharge models to tailor flows for sand exposure

Kwagunt

Rapids

Nankoweap Delta Area

*preliminary results, do not cite
Relevance to Glen Canyon Dam Operations

Kwagunt

Rapids

Nankoweap Delta Area

*preliminary results, do not cite

Neither sand nor vegetation are uniformly distributed along the river...

 Opportunities for vegetation removal

 Use stage-discharge models to tailor flows for sand exposure

A little(r) flow will go a long way...

83% of all available sand

is at stages < 8,000 ft3/s
...at the right time of year!

Relevance to Glen Canyon Dam Operations

Kwagunt

Rapids

Nankoweap Delta Area

*preliminary results, do not cite

Neither sand nor vegetation are uniformly distributed along the river...

 Opportunities for vegetation removal

 Use stage-discharge models to tailor flows for sand exposure

A little(r) flow will go a long way...

83% of all available sand

is at stages < 8,000 ft3/s
*preliminary results, do not cite

TREND: Generally stabilizing over the last ~15 years

STATUS: Reduced by 27% compared to pre-dam period 

Resource: Exposed Sand for Aeolian Transport
Funding from Glen Canyon Dam Adaptive Management 

Program and National Center for Earth Surface Dynamics 2

Thanks to Kirk Burnett, Laura Cagney, Geoff Chain, Maddie 

Friend, Dennis Harris, Joe Hazel, Matt Kaplinski, Rob Ross, 

Bob Tusso
Alternative Flow Regimes

[effect of discharge regimes on 

sand availability]

- Not much difference 

between each alternative 

scenario

...because no alternative 

provides for daily 

maximum flows < 8,000 

ft3/s, with the exception of 

alternative F

8.23 maf year, one year analysis

*preliminary results, do not cite
Argonne National Lab – Flow Factor

[influence of discharge on sand availability for

wind transport]

Major Differences:

1. Discharges < 8,000 ft3/s are 

not constant in terms of sand 

exposure

2. Differences in the importance 

of 8,000 ft3/s to 31,500 

ft3/s discharges

3. Discharges > 31,500 ft3/s 

may matter

*preliminary results, do not cite