Joel B. Sankey, for Project J:

Dave Bedford, Josh Caster, Brian Collins, Skye Corbett, 

Amy East, Helen Fairley

Project J Summary:

Conditions and processes 

affecting sand resources at 

archaeological sites 

January 20, 2015

U.S. Department of the Interior

U.S. Geological Survey
Project J: 2013-2014

Overview questions

 Do cultural sites erode or change faster or in a 

significantly different manner than they would if dam 

operations were different?

 How effective are HFEs at supplying aeolian sand to 

upland landscapes and archaeological sites?
What happens to upland landscapes = 

what happens to archaeological sites

 To understand 

processes and risks of 

site erosion, Project J 

included both site- and 

landscape-scale studies

 Highly likely that yetundocumented arch 

sites are within rivercorridor sand deposits
Aeolian landscapes form downwind of river 

sandbars: “source-bordering dunes”

WIND

Flood-deposited sandbar
HFEs supply new wind-blown sand to 

aeolian dunes where wind direction is 

right...

... but with modern (small) floods, not all 

areas receive sand that got river-derived 

sand in pre-dam time. 
Link between river sediment and 

upland aeolian landscapes

 Aeolian dunes get sand from fluvial (flood) sandbars

 Aeolian dunes without modern sand supply develop 

much more biologic soil crust, become less active

 River-derived sand (fluvial and aeolian) matters to 

hundreds of river-corridor archaeological sites
At landscape scale

 What number and proportion of arch sites potentially 

receive windblown sand from HFEs? 

 Role of aeolian sand in limiting gully erosion?

At site scale

 At sites that receive HFE sand, does aeolian 

deposition sufficiently outpace erosion by rainfall and 

gullying? How well does HFE sand preserve sites?

 How do conditions in Glen Canyon compare with 

those in Marble-Grand Canyon?

Project J: 2013-2014 Research questions
What number and proportion of arch sites 

potentially receive windblown sand from HFEs? 

 7-part classification system

 Evaluated 358 river-corridor 

arch sites, RM 0-240

 Types 1-4 have river-derived 

sediments as substrate

 Ranking means decreasing 

potential for aeolian sand 

supply from recent fluvial 

sandbars

 Modern evaluation from field 

data, 3 earlier time steps from 

aerial imagery

Preliminary results, do not cite (East et al., in prep.)
What number and proportion of 

arch sites currently have 

potential to receive windblown 

sand from HFEs? 

Preliminary results, do not cite (East et al., in prep.)
1984-85

Preliminary results, do not cite (East et al., in prep.)
Classifying 358 sites: takeaway points

 266 sites (74%) have river-derived 

sand as substrate (Types 1-4)

 232 sites in Types 1-3 (65%) are 

downwind of HFE shorelines (45k 

and less), so are potentially 

influenced by sandbars from flows 

of that magnitude

 Type 1 sites have best chance of 

getting aeolian sand, but any of 

Type 1-3 could get some new sand 

(Collins measured new deposition at 

a 2b site)

 From 1973-2014, Type 1 sites 

decreased due to veg growth and 

non-deposition

Preliminary results, do not cite (East et al., in prep.)
Limitations and caveats

 Some Type 1 sites “do better” than others; being Type 

1 doesn’t guarantee the site will have new aeolian 

deposition or stay preserved well, only that it has a 

good sand-supply pathway (high connectivity) from 

HFE sandbars

 We did not quantify relative area or volume of sandbar 

sources and downwind sandy landscapes (sandbars 

can change a lot on short time scales)

 Classification is “living document” – historical 

variability warrants future investigations
How effectively does aeolian sand 

counteract gully erosion?

 Balance between forces forming gullies (rainfall, overland 

flow erosion, base level) and annealing them (aeolian sand) 

– our focus.

 Windblown sand fills topographic lows
We mapped sand activity and gullies in 6 

reaches, to test hypothesis that gullies would be 

less common in active sand

“Active” aeolian sand has 

wind-rippled surfaces, slip 

faces at angle of repose 

(Lancaster, 1994)

Active

Inactive “Inactive” sand (often areas 

without modern sand supply) 

gets covered with biologic 

crust, further decreasing its 

aeolian activity
Aeolian sand activity anneals gullies

 Gullies are more prevalent in inactive sand 

 More gullies terminate in active aeolian sand

From Sankey and Draut, 2014 (Geomorphology): 

gullies occupy much less proportion of the sand area in active sand deposits
Relative abundance of active and 

inactive sand

 Major differences, by reach, in the proportion of 

active aeolian sand

 Greatest arch-site concentrations also occur in 

places with greatest % inactive sand, so greatest 

susceptibility to gully erosion (see also Pederson and O’Brien, 2014)

From Sankey and Draut, 2014 (Geomorphology)
Management implications...

 HFE sand sources mean greater aeolian sand activity in 

dune fields immediately downwind of sandbars (Draut, 2012)

 Gullies can form in active sand, but are more likely to 

anneal instead of getting progressively larger

 So, yes, HFEs can reduce gully extent in areas with 

upwind sandbars

Management actions that 

increase deposition of active 

aeolian sand area can 

limit/reduce gully erosion.

Gullies will not last long in 

places like this.
At site scale, for Type 1 sites:

Is aeolian sand supply enough to outpace 

erosion and enhance site preservation?

 Measure rainfall, wind at weather stations at 4 sites

 Terrestrial lidar scanning in 2013-14 (and 2006-10)

 Stationary cameras for daily record of site conditions
At four Type 1 “best case scenario” sites, what processes 

contribute to site stability or erosion, and at what rates?

Site C:05:0031 - Gullies from monsoon storms (rainfall as intense as 75 mm/hr) 

8/22/2013, 3 p.m. 8/23/2013, 7 a.m.

9/11/2013, 3 p.m. 9/12/2013, 7 a.m.

Preliminary results, do not cite (J. Caster)
At four Type 1 “best case scenario” sites, what processes 

contribute to site stability or erosion, and at what rates?

Site C:05:0031 - Gullies that formed in monsoon season 2013 partially annealed during 

the spring 2014 windy season.

3/9/2014, 1 p.m. 5/1/2014, 1 p.m.

Preliminary results, do not cite (J. Caster)
Are Glen Canyon sites significantly more 

eroded than those downstream from Lees Ferry 

where sand supply is greater?

 Measure site topography with lidar (airborne & terrestrial), compare with 

previous data in Marble-Grand Canyon

 Compare weather records – does Glen Canyon get more rain?

Sankey and Draut, 2014 (Geomorphology)
Glen Canyon vs. Marble-Grand Canyon

 Glen Canyon area gets similar or slightly less rain, and less intense 

rain, compared to Marble-Grand Canyon 

 Rainfall differences cannot explain the major gullying there

3-year record 

(2007-2010), 

GCMRC and 

NOAA stations

60-year record 

(1952-2012), 

NOAA stations

Preliminary results, do not cite (Caster et al., in prep.)
Why such intense gullying in Glen Canyon?

 Glen Canyon morphology promoted formation of large, predam 

flood terraces and does not include large fan/eddy complexes to 

store modern sandbars (aeolian sand sources)

 Dune fields were apparently not well-developed even predam –

few dunes, wind scoured river terraces today 

 Substantial incision of bed (lowering of base level; Paul Grams’ 

work) would exacerbate gully formation

 Near-absence of tributary sediment supply would discourage 

annealing

 So arch sites in GLCA seem at exceptional risk of gully erosion, 

very low potential for aeolian annealing
Summary – Project J Findings

 There are individual reaches with particularly high density of 

archaeological sites that are especially susceptible to gullying 

(Furnace Flats, Granite Park). These are large, old flood deposits 

with little modern sand supply (little active aeolian sand)

 Glen Canyon is especially susceptible to gullying due to unique 

geomorphology, where aeolian processes are not a major player 

and there is little modern sand supply

 Among Project J reaches, the proportion of active aeolian sand 

area is lower than in less-regulated Cataract Canyon

 So, we infer that gully development and the risk of gully erosion 

exceeds what would occur without river regulation
Summary – Project J Findings

 The number of sites with potential to receive windblown sand 

decreased from 1973 to 2014.

 Management actions that increase deposition of active 

aeolian sand area can limit/reduce gully erosion.

 HFEs can reduce gully extent in areas with upwind sandbars.

 Sites with greatest potential to receive windblown HFE sand 

still undergo gully erosion on seasonal time scales. In the 

next talk, Brian will show examples of how this translates into 

changes at individual sites.