Project D: Geomorphic Effects of Dam Operations and 

Vegetation management on Archaeological Sites

Joel B. Sankey, Helen Fairley, Joshua Caster

US Geological Survey, Southwest Biological Science Center, 

Grand Canyon Monitoring and Research Center, Flagstaff, AZ
Goals and Objectives

Project Objectives GCDAMP Regulatory Goals:

• GCPA goal: Resource improvement 

• LTEMP and NHPA goal: “Preservation in place.”

• 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. 

Project Objectives:

• Determine whether increasing the frequency of HFEs increases the resupply of river 

sand to archaeological sites in the river corridor and offsets erosion.

• Determine if removal of riparian vegetation located between HFE sediment supplied 

sand bars and archaeologic sites increases the probability of preservation in place.

• Determine if vegetation and biological soil crust cover within archaeological sites that 

are not resupplied with sediment from HFEs help to reduce erosion and increase the 

probability of achieving GCDAMP goals.
Project D: Geomorphic Effects of Dam Operations and 

Vegetation management for Archaeological Sites
Project D: Geomorphic Effects of Dam Operations and 

Vegetation management for Archaeological Sites
Background: Lack of floods and decrease in windblown (aeolian) river sand supply have 

resulted in expanded gullying at archaeological sites from pre- to post-dam time periods

River Mile -0.5

La Rue, 1923

River Mile -0.5

Fairley-Fairley, 2021
Background: Long-term increases in riparian vegetation on sandbars have 

decreased windblown (aeolian) sand supply from sandbars to archaeological sites

River Mile 194, River right

Borden-Weeden, 1973

River Mile 194, River right

Fairley-Fairley, 2021

River Mile 219, River right

Borden-Weeden, 1973

River Mile 219, River right

Fairley-Fairley, 2021
Background: Measuring physical changes to archaeological 

site condition with annual high-resolution lidar

• Lidar surveys are used to measure changes in site 

condition owing to the burial or exposure of 

archaeological sites in sediment
Background: Interpreting physical changes to archaeological 

site condition through decadal geomorphic classifications

• Dam operations 

influence river flow 

elevation, 

sandbars, and 

vegetation growth.

• These factors inturn affect site 

stability through 

burial or exposure

Adapted from

East and others, 

2017

East and others, 2017
Background: Interpreting physical changes to archaeological 

site condition through decadal geomorphic classifications

• Dam operations influence river flow elevation, 

sandbars, and vegetation growth.

• These factors in-turn affect site stability through 

burial or exposure

Adapted from

East and others, 

2017
D.1 Results: Status and trends in archaeological site condition 

through decadal geomorphic classifications

Scale = ~1 m
D.1 Results: Status and trends in archaeological site condition 

through decadal geomorphic classifications

Preliminary results, do not cite
D.1 Results: Measuring physical changes to archaeological site 

condition with annual high-resolution ground-based survey

Preliminary results, do not cite
Preliminary results, do not cite

D.1 Results: Measuring physical changes to archaeological site

condition with annual high-resolution ground-based survey

2020 Photogrammetry 2021 Photogrammetry

4 m

Feature Architecture

30 m

1 m

0.82 m

0.78 m
D.1 Results: Status and trends in archaeological site condition 

with annual high-resolution ground-based survey

Preliminary results, do not cite
LTEMP Vegetation Project (Reclamation TWP projects C.7 

and C.8 led by NPS) 

o Experimental riparian vegetation treatments 

as mitigation for dam operations

1. Control nonnative plant species affected 

by dam operations; including tamarisk 

and other highly invasive species

2. Develop native plant materials for 

replanting through partnerships and the 

use of regional greenhouses

3. Replant native plant species at priority 

sites along the river corridor; including 

native species of interest to tribes

4. Remove vegetation encroaching on 

campsites

5. Manage vegetation to assist with 

cultural site protection
Manage vegetation to assist with cultural site protection

NPS has conducted experimental 

vegetation removal treatments on 

sandbars in Grand Canyon to increase 

the supply of HFE sediment via 

aeolian processes for in-situ 

preservation of archaeological sites in 

dunefields.

Initially Implemented: April 2019

Repeated: September 2020, October 

2021, & 2022...
Manage vegetation to assist with cultural site protection

5 coupled sandbar-archaeological site areas selected based on:

• NPS management priorities

• USGS lidar monitoring data with observed changes in geomorphic condition
Results: Effects of vegetation removal on sediment availability 

and implications for changes in site condition (Area 2)

Preliminary results, do not cite
Results: Effects of vegetation removal on sediment availability 

and implications for changes in site condition (Area 3)

Preliminary results, do not cite
The End