

Species-level evaluation of riparian 

vegetation dynamics using remotely 

sensed imagery from

aerial overflights

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
Species-level evaluation of riparian 

vegetation dynamics using remotely 

sensed imagery from aerial overflights

 Laura Durning, NAU, School of Earth and 

Sustainability 

 Joel B. Sankey, US Geological Survey, SBSC, GCMRC

 Temuulen Sankey, NAU, School of Informatics, 

Computing & Cyber Systems

 Brad Butterfield, NAU, Department of Biological 

Sciences

 Charles Yackulic, US Geological Survey, SBSC, 

GCMRC,

 Paul Grams, US Geological Survey, SBSC, GCMRC

 Tom Gushue, US Geological Survey, SBSC, GCMRC
Project C.2

 Project C.2 Imagery-based riparian vegetation 

monitoring at the landscape scale

 LTEMP Resource and Goal

 Riparian Vegetation

 Maintain native vegetation and wildlife 

habitat, in various stages of maturity, such 

that they are diverse, healthy, productive, 

self-sustaining, and ecologically appropriate.


Presentation Outline

 Remote sensing overflights

 Species-level evaluation of riparian vegetation 

dynamics from remote sensing overflight 

imagery

 Closing thoughts
Remote Sensing

Overflights

 "Historical" overflights  Analog air photos 

since the 1960s (and 

even earlier)

 "Modern" overflights  Multispectral digital 

image mosaics  2002, 2004, 

2005, 2009, 

2013, 2021

Durning, L.E., Sankey, J.B., 

Davis, P.A., & Sankey, T.T., 

2016, Four-band image 

mosaic of the Colorado 

River corridor downstream 

of Glen Canyon Dam in 

Arizona, derived from the 

May 2013 airborne image 

acquisition: U.S. Geological 

Survey Data Series 

1027, https://doi.org/10.31

33/ds1027

.


Air Photos and Multispectral Imagery from 

Overflights of the Colorado River in Grand Canyon

Sankey, J.B., Ralston, B., 

Grams, P.E., Schmidt, J.C., and 

Cagney, L.E., 2015, Riparian 

vegetation, Colorado River, and 

climate: five decades of 

spatiotemporal dynamics in the 

Grand Canyon with river 

regulation: Journal of 

Geophysical Research, v. 

(online), doi: 

10.1002/2015JG002991.
Products from Modern Overflights


Modern Overflight Products

 Imagery and datasets 

available through 

GCMRC website

 Online maps

 Data applications

 Data releases


Modern Overflight Products

Mapbooks

 All projects use these!

 Critical to field data collection

 River navigation

 Citizen science


Modern Overflight Products

 Fish sampling unit system

 Based on shorelines 

derived from imagery

 Used for all fish 

monitoring and 

research

 LCR humpback 

monitoring depends on 

imagery too


Modern Overflight Products

Digital Surface & 

Elevation Models

(DSM & DEM)

 DEM topographic change 

detection

 e.g., sand dunes 

Remote sensing topographic change detection 2002-2013

Sankey, J.B., Kasprak, A., Caster, J., East, 

A.E. and Fairley, H.C., 2018. The response of 

source-bordering aeolian dunefields to 

sediment-supply changes 1: effects of wind 

variability and river-valley morphodynamics. 

Aeolian research, 32, pp.228-245.


Modern Overflight Products

 Geomorphic basemap

Unpublished data, do not cite


Modern Overflight Products

River channel 

changes

 Flowlines 

depicting low-flow 

water's edge (~8,000 

CFS) in 

overflight imagery

 2002, 2004, 2005, 

2009, & 2013

• Sankey, et al., 2015

• Durning, L.E., Sankey, J.B., Chain, 

G.R., and Sankey, T.T., 2017, Water 

classification of the Colorado River 

Corridor, Grand Canyon, Arizona, 

2013—Data: U.S. Geological Survey 

data release, 

https://doi.org/10.5066/F7PZ5799.
Modern Overflight 

Products

Landcover changes

• Image classifications of bare 

unvegetated sand

• 2002, 2009, 2013

RM 45

RM 53

RM 58 RM 62

Sankey, J.B., Chain, G.R., Solazzo, D., Durning, L.E., Bedford, A., 

Grams, P.E., and Ross, R.P., 2018, Sand classifications along the 

Colorado River in Grand Canyon derived from 2002, 2009, and 2013 

high-resolution multispectral airborne imagery: U.S. Geological 

Survey data release, https://doi.org/10.5066/P99TN424.
Modern Overflight Products

Landcover changes – Total Vegetation

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, 42(6), 

pp.739-764.
Modern Overflight Products 

 Landcover changes and Glen Canyon 

Dam and Colorado River hydrology

 Modelled Shorelines

 Geomorphic basemap

 River center-line and river-mile 

system

 Landcover changes

Sankey, et al., 2015

(From Sankey, et al., 2018)


Modern Overflight Products

Tamarisk and Tamarisk Beetle Impacts

2009 2013

2009 2013

Bedford, A., Sankey, T.T., Sankey, J.B., Durning, L.E., and Ralston, 

B.E., 2018, Remote sensing of tamarisk beetle (Diorhabda

carinulata) impacts along 412 km of the Colorado River in the Grand 

Canyon, Arizona, USA: Ecological Indicators, v. 89, p. 365-375, 

https://doi.org/10.1016/j.ecolind.2018.02.026.
Modern Overflight 

Products

Vegetation Species Classification

 Map covers from Glen Canyon Dam 

to Pearce Ferry

 26 species and 7 additional 

generalized vegetation classes

 Overall accuracy 71%

Durning, L.E., Sankey, J.B., Bedford, A., and Sankey, T.T., 2018, Riparian 

species vegetation classification data for the Colorado River within Grand 

Canyon derived from 2013 airborne imagery: U.S. Geological Survey data 

release, https://doi.org/10.5066/P9OUB1RS.


Overflight – 2021

 General timeframe

 2021-2024 Work plan

 2021 - 1 year for managing contract and acquiring data

 Mission scheduled for May 2021

 2022 - 1 year for building image mosaic & serving it online

 2023 - Image analysis and product generation begin

 Approximately $0.6 million to contract the acquisition

 GCMRC staff support and funding required

 to plan and manage the acquisition

 to process, serve, and analyze the data
 Species-level evaluation of riparian vegetation 

dynamics: analysis of overflight imagery from 

2002, 2009, and 2013
Long-term changes in 

riparian vegetation 

quantified with historic and 

modern overflight imagery 

(1965 - 2013)

Sankey et al., 2015

2010

1890
Changes in riparian vegetation and 

vegetation-sand dynamics quantified 

with modern overflight imagery 

(2002-2009-2013)

 Types of riparian vegetation encroachment onto sand

 "Sustained" – sand in 2002 and vegetated in 2009 & 2013

 "Recent" – sand in 2002 & 2009 but vegetated in 2013

 "Burial and emergence" – vegetated in 2002 & 2013, but 

sand present in 2009.

Unpublished results, do not cite


Changes in riparian vegetation and 

vegetation-sand dynamics quantified with 

modern overflight imagery (2002-2009-2013)
Methods – Species-level Classification of Riparian 

Vegetation

Acacia

Tamarisk

Mesquite

Durning et al., 2018.
Methods – Species-level Classification of Riparian 

Vegetation

Common reed

Sedge

Coyote willow

Baccharis

Durning et al., 2018.
Methods – Geomorphic basemap and inundation zones

Unpublished results, do not cite


Results - Species cover on geomorphic landforms

Seep 

Willow

Tamarisk

Mesquite

Horsetail Acacia

Reed

Arrowweed

Submergent & 

Emergent 

plants

Coyote Willow

Unpublished results, do not cite
Results -

Encroachment on 

geomorphic 

landforms

Sustained 

Encroachment

Recent 

Encroachment

Burial and 

Encroachment

Seep 

Willow

Tamarisk

Coyote 

Willow

Seep 

Willow

Tamarisk

Seep 

Willow

Tamarisk

Arrowweed

Arrowweed

Arrowweed

Arrowweed Arrowweed

Arrowweed

Arrowweed

Unpublished results, do not cite


Methods - Modeling encroachment behavior 

 Focused on the 7 most common encroachment species 

encroachment: Tamarisk, seep willow, arrowweed, coyote 

willow, alkali goldenbush, phragmites, & horsetail.

 Evaluated encroachment rates relative to species cover using 210 

generalized linear models

0.00 0.50 1.00

Alternative Models

- rates of encroachment 

increase linearly with

species cover

- encroachment rates 

"slow" at higher cover

-encroachment rates 

don't change as cover 

increases

Unpublished results, do not cite


Results - Modeling encroachment behavior

 All species in all inundation zones 

showed a quadratic trend.

 Implies that encroachment 

rates slow down as vegetation 

cover increases to high 

amounts;

 for example, plants might run 

out of available space for 

encroachment at high cover,

 or, might reflect successional 

changes among species as 

encroachment and cover 

increase

0.00 0.50 1.00

Unpublished results, do not cite


Results - Modeling encroachment behavior 

0.00 0.25 0.50 0.75 1.00

Recirculation

Channel

Constriction

Gravel bar

Sandbar

Terrace

Veg. Sandbar

Unpublished results, do not cite


Results - Modeling encroachment behavior

 When evaluating encroachment 

within geomorphic landforms see that 

species behave differently on the 

different landforms

 For example:

 Sandbars: quadratic relationships 

for nearly all species

 Channel: linear relationships for 

nearly all species

Geomorphic 

Landforms Intercept Linear Quadratic no selection

Sandbar 1 6

Veg. Sandbar 1 6

Constriction 2 5

Terrace 1 1 4 1

Gravelbar 1 3 3

Recirculation 1 3 2 1

Channel 6 1

Unpublished results, do not cite


Key Points - Changes in 

riparian vegetation and vegetation-sand 

dynamics quantified with modern 

overflight imagery (2002-2009-2013)

 The occurrence and expansion of riparian vegetation from 2002 to 2013 varied 

by species for different hydrologic zones and geomorphic landforms.

 On all geomorphic landforms and within all hydrologic zones common drivers of 

encroachment were seep willow, tamarisk, and arrowweed.

 Sandbars inundated and resupplied from HFE(s) indicate that several of the 

most common riparian species, most notably seep willow, are resilient to burial 

by sand.

Unpublished results, do not cite


Closing Thoughts

 Remote sensing provides a powerful way 

to evaluate environmental changes 

synoptically throughout the entire river 

corridor

 Overflight data are used universally in the 

GCDAMP

 all projects, scientists, managers, and 

stakeholders

 Overflight 2021!!!