U.S. Department of the Interior

U.S. Geological Survey

Cultural Site Monitoring in Glen and 

Grand Canyons

Brian Collins

U.S. Geological Survey, Menlo Park, California

with Skye Corbett, Helen Fairley, Amy Draut, David Bedford, Joel 

Sankey, and Joshua Caster

U.S. Geological Survey, Menlo Park, California, Flagstaff, Arizona, and Santa Cruz, California

Presentation at the GCMRC 2015 Annual Reporting Meeting, Phoenix, Arizona

January 20, 2015
What do we know about archaeological site 

change in Grand Canyon?

(Collins et al., in review)
 Are cultural sites eroding or changing faster or in a significantly 

different manner than they would if Glen Canyon Dam was 

operated differently than it has been?

 Are archaeological sites eroding?

 If so, then how fast are archaeological sites eroding?

 What does it take to cause erosion?

 If discrete events cause erosion, then what is the frequency of these events?

 Can meteorological effects be distinguished from dam operational effects?

 Have HFEs impacted archaeological site erosion thus far?

What do we know about archaeological site 

change in Grand Canyon? [2014]
Cultural Monitoring Overview Questions [2015]

 Are cultural sites eroding or changing faster or in a significantly 

different manner than they would if Glen Canyon Dam was 

operated differently than it has been?

 Is the magnitude of aeolian transport to, and deposition at, sites from river 

sand bars sufficient to offset erosion, and thereby protect archaeological 

resources?

 In areas with active aeolian deposition, do sites that are subjected to 

significant gullying (i.e., >30cm downcutting) undergo net topographic 

lowering such that the physical and informational integrity of 

archaeological resources are impacted?

 Are archeological sites in Glen Canyon significantly more eroded (e.g. are 

gullies more incised) compared to those found downstream from Lee’s 

Ferry where the fine-grained sediment supply is larger?
Today

 Update on site specific studies

 How do actual sites respond?

 Do they confirm what we are 

learning at the landscape scale?

 Monitoring

 Existing methods – terrestrial lidar

 New methods in Glen Canyon – airborne lidar

 Glen Canyon

 Geomorphologic analysis

 Short-term change detection

 Long-term gully erosion 

characterization

 Grand Canyon

 Short-term change detection

 Comparison to 7-yr trends

New data from 2012, 2013, 2014

4 new sites in Glen Canyon

(Collins et al., in review)
Geomorphological studies at 

archaeological sites in Glen Canyon

 Application and comparison 

of methods

 Terrestrial lidar

 Airborne lidar

 Airborne photogrammetry

 Topography and 

geomorphology at 4 sites

 Dual terrestrial-airborne gives 

unprecedented data coverage

 USGS SIR 2014-5126

(Collins et al., 2014, High resolution topography and geomorphology at 

select archeological sites in Glen Canyon National Recreational Area, 

Arizona, USGS Scientific Investigations Report 2014-5126, 31p., 

http://dx.doi.org/10.3133/sir20145126)
Short-term changes in Glen Canyon

 Goal: Identify rates and causes 

of change at arch. sites

 Put regional observations into 

context

 Sequential terrestrial lidar

 High resolution change maps

 Four sites

 Sept. 2012 - Nov. 2013

 Brackets November 2012 HFE
Topographic changes: AZ:C:02:0032

• 120 m2 (1.5%) 

of surface 

change in arch. 

site

• Most (81%) 

from bank 

erosion

• Ave. change 

depth = -11 cm

Colorado River

talus slope

Colorado River

talus slope

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
AZ:C:02:0032 – gully bank erosion

Profile view looking up-gully

2013

2013

2012

gullying widening

19 cm of gully 

widening

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
AZ:C:02:0032 – gully undercutting

Colorado River 2012 Colorado River 2013

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
AZ:C:02:0032 – dam operation effects

4/4/1996; 8,300 cfs

4/21/1996; 16,500 cfs

11/19/2012; 23,200 cfs

 Rise and fall of water level leads 

to gravitational terrace bank 

instability and erosion

Oblique photos and flow interpretation courtesy 

of NPS - Mark Anderson and Thann Baker

Colorado River

3/17/1996; 9,500 cfs

View rotated 45° from plan

1996 HFE; 45,000 cfs 2012 HFE; 43,000 cfs

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
upper terrace

Topographic changes: AZ:C:02:0075

• 212 m2 (10%) of surface 

change in arch. site

• Gullying bank collapse and 

possible aeolian erosion

• Ave. change depth = -19 cm

Colorado River

upper terrace

lower terrace

bedrock platform

bedrock platform

Colorado River

lower terrace

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
AZ:C:02:0075 – aeolian and gully bank erosion

2013

2012

2012 2013

bedrock platform bedrock platform

Profile view looking down-gully

95 cm

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
Topographic changes: AZ:C:02:0077

• 1 m2 (0.04%) of surface 

change in arch. site

• Terrace edge gullying 

erosion

• Ave. change depth = -17 cm

• 425 m2 of change area in 

adjacent parts – mostly 

aeolian

Colorado River

lower 

terrace

upper 

terrace

upper 

terrace

lower terrace Colorado River

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
Summary: short-term changes in Glen Canyon

 All sites show measurable 

changes

 Steep terrace banks subject to 

HFE impacts

 Gullying is active on terraces 

and causing site changes

 Aeolian processes also active, 

but minimal: little expectation 

for gully annealing (no 

widespread source of sand)
Long-term changes in Glen Canyon

 Goal: characterize the 

overall state of gully 

erosion (Are arch. sites 

more eroded here than in 

Grand Canyon?)

 Focus on terrace-based 

gullies

 Airborne lidar of 8.5 river 

miles

 Helicopter-based platform

 July 2013

 Analysis of 400+ drainage 

paths
Results: gully characterization

 192 incised gullies (>20 cm) over 8.5 river miles 

(~23 gullies/mile)

 8% cross known arch. sites

 79% cross sand/terrace deposits

Raw lidar data

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
Glen Canyon gully geometry

 Mean gully width = 5.9 m

 Mean gully depth = 2.2 m

 Insightful for characterizing the current 

state of erosion in Glen Canyon

 Work in progress

 Compare to measured annual rates.

 Compare to Grand Canyon.

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
Short-term changes in Grand Canyon

 Goal: Identify if Type 1 sites are 

responding as hypothesized to 

aeolian sand supply

 Four sites

 Sequential terrestrial lidar

 September 2010 - May 2013

 Brackets November 2012 HFE

 May 2013 - May 2014

 Brackets November 2013 HFE

 Adds to existing change analyses

 5 other data sets, May 2006 -

September 2010
Topographic changes: AZ:C:05:0031

2010-2013

2013-2014

• Reworking of fluvial-sourced sand

• Favorable depositional wind trajectory

• Formation of two gullies in 2013

• 2010-2013

• 20% of area changed w/ -3 cm ave. 

change depth

• 2013-2014

• 14% of area changed w/ 0 cm ave. 

change depth

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
Topographic changes: AZ:C:13:0321

2010-2013

2013-2014

Colorado R.

Colo. R.

• Reworking of fluvial-sourced sand

• Favorable depositional wind trajectory

• 2010-2013

• 40% of area changed w/ -3 cm ave. 

change depth (+4 cm in arch. site)

• 2013-2014

• 23% of area changed w/ -1 cm ave. 

change depth

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
Topographic changes: AZ:B:10:0225

2010-2013 2013-2014

• Massive gullying with aeolian reworking (favorable wind trajectory)

• Gully with steep drainage pathway borders site

• Small changes to arch. site, but significant potential

• 2010-2013

• 30% of area changed w/ -25 cm ave. change depth

• 2013-2014

• 22% of area changed w/ -12 cm ave. change depth

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
Topographic changes: AZ:G:03:0072US

2010-2013

2013-

2014

• Aeolian reworking of (originally) fluvial-sourced sands

• Some gullying, but partially annealed

• Connectivity between river and arch. site over 100+ meters

• 2010-2013: 6% of area changed w/ +3 cm ave. change depth

• 2013-2014: 8% of area changed w/ -1 cm ave. change depth

PRELIMINARY RESULTS – DO NOT CITE (Collins et al., in prep.)
Summary: short-term changes in Grand Canyon

 All sites show measurable 

changes

 General patterns of shortterm sediment transport are 

maintained

 Gullying is active and 

causing site changes

 Aeolian processes are active 

and responsible for gully 

annealing
Cultural Monitoring Overview Questions

 Are cultural sites eroding or changing faster or in a significantly 

different manner than they would if Glen Canyon Dam was 

operated differently than it has been?

 In some cases, the answer is yes (sites within direct impact of high water line; 

sites receiving HFE sand)

 Is the magnitude of aeolian transport to, and deposition at, sites from river 

sand bars sufficient to offset erosion, and thereby protect archaeological 

resources?

 Yes – but all examples are in Grand Canyon.

 In areas with active aeolian deposition, do sites that are subjected to 

significant gullying (i.e., >30cm downcutting) undergo net topographic 

lowering such that the physical and informational integrity of 

archaeological resources are impacted?

 Thus far, only minor evidence of this process - additional monitoring necessary.

 Are archeological sites in Glen Canyon significantly more eroded (e.g. are 

gullies more incised) compared to those found downstream from Lee’s 

Ferry where the fine-grained sediment supply is larger?

 Analysis is ongoing – we now know quantitative overall degree of erosion in Glen 

Canyon. 
Thank you