Geomorphic Effects of Dam Operations and Vegetation 

Management for Archaeological Sites

Glen Canyon Dam Adaptive Management Program Annual Reporting Meeting,

January 14, 2020, Phoenix, AZ

Joel B. Sankey (jsankey@usgs.gov)

US Geological Survey, Grand Canyon Monitoring and Research Center, Flagstaff, AZ
Geomorphic Effects of Dam Operations and 

Vegetation Management for Archaeological Sites

Project D.1 Geomorphic Effects of Dam Operations and 

Vegetation Management for Archaeological Sites

• Joel B. Sankey, US Geological Survey, SBSC, GCMRC, Flagstaff, AZ

• Joshua Caster, US Geological Survey, SBSC, GCMRC, Flagstaff, AZ

• Helen Fairley, US Geological Survey, SBSC, GCMRC, Flagstaff, AZ

• Jen Dierker, National Park Service, Grand Canyon, AZ

• Mike Kearsley, National Park Service, Grand Canyon, AZ

LTEMP Resource and Goal

• Archaeological and Cultural Resources

• Maintain the integrity of potentially affected NRHP-eligible or listed 

historic properties in place, where possible, with preservation methods 

employed on a site-specific basis.
The majority of river corridor archaeological sites 

in Grand Canyon are on river sand reworked by 

water and wind.

Hereford and others, 1993

East and others, 2016

Stratigraphy near Palisades Creek, Colorado 

River Corridor

Alluvial/ Fluvial

Aeolian 
The geomorphic condition of archaeological

sites is affected by how Colorado River sand is 

transferred among landforms in Grand Canyon

Kasprak and others, 2018
Many archaeological sites are degraded by gully 

erosion, but windblown river sand can help provide 

a protective cover to preserve sites in place

East and others, 2016

Archaeological Site

Eroding 

Gully
Grand Canyon geomorphic site classification 

Drainage Classification:

Type 1 = low gully impact potential

Type 4 = high gully impact potential

East and others, 2017

Type 3 Type 4

Type 1 Type 2

Kasprak and others, 2018
Grand Canyon geomorphic site classification

Aeolian 

Classification:

 Type 1: > Sand 

availability

 Types 2 – 4: 

Reduced sand 

availability

 Type 5: No river 

sand availability

East and others, 2016; 2017

Kasprak and others, 2018
Using the classifications to monitor changes in 

the geomorphic condition of archaeological sites

East and others, 2016

> 350 River Corridor 

sites being monitored

Classifications are 

efficient, with site 

visits and remote 

observations

Observed changes 

provide clues to site 

condition

...but classification is qualitative and 

must be evaluated against quantitative 

data
Vegetation changes since river regulation

1973

2019

Unpublished results, do not cite
Supplementing site classification monitoring 

with topographic site monitoring

Since 2006, GCMRC has 

monitored a sample of sites with 

ground-based terrestrial lidar

Lidar provides 

a quantitative 

record of 

observed field 

conditions

Surveyed Area

Lidar relief map
Summarize the last 8 years of monitoring in 

a new report (Caster and others, in press):

 survey at 23 archaeological sites

 spanning four HFEs

Unpublished results, do not cite

Grand Canyon topographic site monitoring 

now and in the future
Caster and others (in press) report presents both new and previously 

published data placed within the established monitoring framework:

 Geomorphic classification: Large number of sites

 Ground-based survey: Sub-sample of classified sites

 Survey time interval: Variable based on geomorphic context, NPS 

management priorities, and HFE protocol

 Weather observations: Sub-sample of sites

Grand Canyon topographic site monitoring 

now and in the future Greater sand availability

Unpublished results, do not cite

Greater gully impacts
Grand Canyon topographic site monitoring:

changes in geomorphic condition

Caster and others (in press) report:

 Several monitoring locations were repeatedly surveyed between 2010 & 2018

 DEMs-of-Difference (DODs) to measure topographic change

 Synthesis of previously published data between 2010 and 2016

 New results for change detection after 2016 

Unpublished results, do not cite
Grand Canyon topographic site monitoring:

changes in geomorphic condition

Analyze changes in sediment storage by geomorphic process 

mechanism within the archaeological site... 

Unpublished results, do not cite Aeolian

Aeolian

Aeolian Aeolian
Grand Canyon topographic site monitoring:

changes in geomorphic condition

...and within individual features in the archaeological site

Unpublished results, do not cite
Grand Canyon topographic site monitoring:

changes in geomorphic condition

Caster et al. (in press) monitoring results are consistent with our 

previously published results of how HFEs affect aeolian 

dunefields that contain archaeological sites.

“Sankey et al., 2018. The response of source-bordering aeolian dunefields to 

sediment supply changes: controlled floods of the Colorado River in Grand 

Canyon, Arizona, USA. Aeolian Research 32, 154-169”

•Sediment storage increases cumulatively when HFEs are conducted 

consistently on an annual basis.

•HFEs do not directly inundate most of the dunefields that contain 

archaeological sites, however, HFEs resupply the dunefields with sand by 

rebuilding upwind sandbars

•Aeolian dunefields that contain archaeological sites were resupplied with 

windblown sand from HFE deposits in half of the instances monitored after 

the 2012, 2013, 2014, and 2016 HFEs

•Frequency of sediment resupply by HFEs is analogous to resupply of 

sandbars by HFEs

•Sediment storage decreased with 1-year hiatus from HFE in 2015.
Grand Canyon topographic site monitoring

Adding to our sample size

 Since 2016 we have added 

new archaeological site 

monitoring locations

(white boxes)

By expanding our sample size we can:

 More accurately link geomorphic 

classification with topographic change

 Make more robust inferences about 

changes to site condition Unpublished results, do not cite
Grand Canyon topographic site monitoring

Evaluating changes to geomorphic site classifications

 Changes within the geomorphic classifications can be assess to predict 

future results within all surveyed areas

 Aeolian classification changes from 1996 to 2014

 Drainage classification changes from 2000 to 2016

No Change = 

Site condition has not 

changed

Decrease = Decreased 

erosion potential; less 

degraded site condition

Increase = Increased 

erosion potential; more 

Unpublished results, do not cite degraded site condition
Grand Canyon topographic site monitoring

Evaluating changes to geomorphic site classifications

 Of the newly surveyed archaeological sites, more than half changed in 

either aeolian classification (1996-2014) and drainage classification 

(2000-2016)

No Change = 

Site condition has not 

changed

Unpublished results, do not cite
Grand Canyon topographic site monitoring

Evaluating changes to geomorphic site classifications

Decrease = Decreased 

erosion potential; less 

degraded site condition

Unpublished results, do not cite
Grand Canyon topographic site monitoring

Evaluating changes to geomorphic site classifications

 Some sites are predicted to be in a more degraded state

Increase = Increased 

erosion potential; more 

degraded site condition

Unpublished results, do not cite
Vegetation removal experiments

In April, 2019 the NPS implemented 

experimental vegetation removal 

treatments on several sandbars in 

Grand Canyon to increase the 

supply of HFE sediment via aeolian 

processes to dunefields that host 

archaeological sites

GCMRC is monitoring the outcome 

of the vegetation treatments relative 

to future HFEs
Vegetation removal experiments

LTEMP vegetation removal treatment conducted April, 2019 

by NPS with Ancestral Lands Conservation Corps tribal crews
Vegetation removal experiments

5 areas selected based 

on:

• NPS management 

priorities

• Sandbars

• Campsites

• Arch. Sites

• Lidar monitoring 

data

• Observed changes 

in geomorphic 

condition from site 

classification and 

lidar monitoring

Unpublished results, do not cite
Vegetation removal experiments

Area 1 Vegetation canopy height

Unpublished results, do not cite

Lidar survey 

prior to 

removal 

(2017)

Lidar survey 

after to 

removal 

(2019)

Before removal After removal
Vegetation removal experiments

Unpublished results, do not cite Vegetation canopy height

Area 1
Vegetation removal experiments

Unpublished results, do not cite

Area 2
Vegetation removal experiments

Unpublished results, do not cite Vegetation canopy height

Area 2
Vegetation removal experiments

Area 2

1 week prior to 

removal

2 weeks after removal 1 month after removal

2 months after 3 months after 6 months after

Unpublished results, do not cite
Vegetation removal 

experiments

Area 3

1 week prior to 

removal

2 weeks after removal

Unpublished results, do not cite

1 month after removal

2 months after 3 months after 6 months after
Implications and Future Work

• In April, 2020 the NPS will revisit the sites and conduct maintenance and 

additional experimental vegetation removal treatments to increase aeolian 

sediment supply to several dunefields that host archaeological sites

• GCMRC will monitor the outcome of the treatments relative to future HFEs 

in ongoing monitoring of the geomorphic condition of archaeological sites
Work Cited

Caster, J., Sankey, J.B., Fairley, H., Kasprak, A., in press, Terrestrial Lidar Monitoring of the Effects of Glen Canyon Dam Operations on the Geomorphic Condition of 

Archaeological Sites in Grand Canyon National Park 2010-2018: U.S. Geological Survey 

Open-File Report number pending

East, A.E., Collins, B.D., Sankey, J.B., Corbett, S.C., Fairley, H.C., and Caster, J., 2016, 

Conditions and processes affecting sand resources at archeological sites in the Colorado 

River corridor below Glen Canyon Dam, Arizona: U.S. Geological Survey Professional 

Paper 1825, 104 p., accessed at https://doi.org/10.3133/pp1825

East, A.E., Sankey, J.B., Fairley, H.C., Caster, J.J., and Kasprak, A., 2017, Modern 

landscape processes affecting archaeological sites along the Colorado River corridor 

downstream of Glen Canyon Dam, Glen Canyon National Recreation Area, Arizona: U.S. 

Geological Survey Scientific Investigations Report 2017–5082, 22 p., accessed at https://doi.org/10.3133/sir20175082

Hereford, R., Fairley, H.C., Thompson, K.S., and Balsom, J.R., 1993, Surficial geology, geomorphology, and erosion of archeologic sites along the Colorado River, eastern Grand 

Canyon, Grand Canyon National Park, Arizona: U.S. Geological Survey Open-File Report 

93–517, 46 p., accessed at https://doi.org/10.3133/ofr93517

Kasprak, A., Sankey, J.B., Buscombe, D., Caster, J., East, A.E. and Grams, P.E., 2018. 

Quantifying and forecasting changes in the areal extent of river valley sediment in 

response to altered hydrology and land cover. Progress in Physical Geography: Earth and 

Environment, p.0309133318795846, accessed at 

https://doi.org/10.1177/0309133318795846