Riparian Remote Sensing in the Colorado River and Grand Canyon Region

Science Center Objects

Riparian vegetation has increased dramatically along the Colorado River downstream of Glen Canyon Dam since the closure of the dam in 1963. The spatial patterns and temporal rates of vegetation increase occur due to changes in river hydrology, dam operations, and climate. The increase in vegetation, particularly onto otherwise bare sandbars, has impacted recreational, geomorphological, biological, and cultural resources along the river. Some of the riparian vegetation is non-native, invasive Tamarix that has recently been subject to herbivory and defoliation by the northern tamarisk beetle which has been in the Grand Canyon region since approximately 2009. We use remote sensing of very high resolution multispectral imagery and lidar acquired from fixed-wind airplanes and helicopters to monitor and research the short- and long-term dynamics of riparian vegetation and associated environmental science issues in the region. 

Image taken from above depicting the confluence of the Colorado River and the Little Colorado River.

High resolution, multispectral imagery acquired in May of 2013. Image location is the confluence of the Colorado River and Little Colorado River. (Credit: Laura Durning, USGS. Public domain.)

Background & Importance

The Grand Canyon Monitoring and Research Center (GCMRC) of the U.S. Geological Survey (USGS)’s Southwest Biological Science Center is the primary science provider for the Glen Canyon Dam Adaptive Management Program (GCDAMP). In support of that mission, GCMRC periodically collects airborne image and lidar data for the Colorado River corridor within Arizona, allowing scientists to study the operational effects of Glen Canyon Dam on the corridor’s natural and cultural resources. The segment of the Colorado River that flows through Glen, Marble and Grand Canyons is characterized by steep terrain and a predominantly narrow, sinuous riparian corridor, making many areas logistically difficult to study. These remote sensing data are used for environmental change detection analysis of the riparian ecosystem. The complete GCMRC remote sensing image archive includes four dates (2002, 2005, 2009 and 2013) of high spatial resolution multispectral image mosaic datasets since 2002, as well as a longer-term record of analog and film-based aerial photography.

General Methods

We use remote sensing change detection of data from the GCMRC archive to monitor and research the short- and long-term dynamics of riparian vegetation and associated environmental science issues in the region. Our methods include multispectral image classification, and lidar and multispectral data fusion to produce landcover data products that are analyzed with map-based change detection and interpreted as a function of other environmental geospatial datasets.

Lidar data collected using a helicopter (top panel) and the resultant image of a stretch of the Colorado River (bottom panel)

Helicopter acquisition of lidar data in summer of 2013 over the Colorado River (top panel), and the resultant lidar data used for riparian research and monitoring (bottom panel).(Credit: Joel Sankey, USGS. Public domain.)

Important Results

Riparian vegetation has increased dramatically along the Colorado River downstream of Glen Canyon Dam since the closure of the dam in 1963. The spatial patterns and temporal rates of vegetation increase occur due to changes in river hydrology, dam operations, and climate. The increase in vegetation, particularly onto otherwise bare sandbars, has impacted recreational, geomorphological, biological, and cultural resources along the river. Some of the riparian vegetation is non-native, invasive Tamarix that has recently been subject to herbivory and defoliation by the northern tamarisk beetle which has been in the Grand Canyon region since approximately 2009.

Looking down on the Colorado River, an image of healthy tamarisk in 2009 and dead tamarisk in 2013,

Panels A and B are high resolution, multispectral imagery at the Kanab Creek confluence with the Colorado River in Grand Canyon showing dense stands of tamarisk vegetation that was green and healthy in May 2009 (panel A), but brown and defoliated in May 2013 due to herbivory by the tamarisk beetle (panel B). Panel C shows a lidar and multispectral image-based classification of tamarisk defoliation (“Tamarisk Decline” in legend) due to the tamarisk beetle along the Colorado River in Glen Canyon. (Credit: Joel Sankey, USGS. Public domain.)