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New ‘Structure-from-Motion’ Sandbar Surveying Method used by Youth Citizen Scientists in Grand Canyon National Park

posted Jul 31, 2015, 12:06 PM by Rebecca Rossi   [ updated Aug 17, 2015, 9:49 AM by Jeannine Huenemann ]
“participating in citizen science has widen my perspective and understanding 
of Grand Canyon and why it is vital to protect it.”

                                                                           -Grand Canyon Youth Participant

Youth citizen scientists collect images and ground control data 
with 'structure-from-motion' sandbar surveying method

Earlier this summer, Utah State University graduate student Becca Rossi rafted and surveyed sandbar topography along the Colorado River with a group of youth citizen scientists from the Grand Canyon Youth program. Her team for this trip consisted of 24 youth, 2 youth coordinators, 6 river guides, and 2 other scientists.

During the two weeks of surveying, the group rafted over 225 river miles of canyons in the Grand Canyon National Park (GCNP) to collect data. Both USU and the Grand Canyon Monitoring and Research Center (GCMRC) will use this data to monitor and record changes in size and stability of sandbar deposits along the Colorado River downstream of Glen Canyon Dam. Sandbars provide habitat for terrestrial and aquatic species, campsites for river rafters and scientists, and an aeolian sediment source for the preservation of archaeological sites.

Sandbar at river mile 119R in Grand Canyon providing
campsite area and riparian habitat

The Glen Canyon Dam Adaptive Management Program has monitored sandbar depletion for more than twenty years through GCMRC. Annual topographic monitoring has focused on sandbar response to high flow experiments (HFEs) released from Glen Canyon Dam at 45 sites throughout GCNP. The Paria and Little Colorado Rivers are the two main sand sources downstream of the dam. With enough monsoonal rain, tributary sand is stored on the channel bed and is then mobilized downstream by the HFEs. These environmental flows aim to maintain and build sandbars within GCNP. Annual monitoring campaigns survey sandbar topography using a total station setup and repeatable control network.

There are roughly 500 large sandbars distributed over the 225 miles of the Colorado river throughout GCNP. The question remains, if the 45 sandbar monitoring sites are representative of the total sediment budget in response to the modified 
dam operations.

Map* of the Colorado River downstream of Glen Canyon Dam with 
locations of the 45 annual sandbar monitoring sites (red triangles).

Sandbar site extension provides an option to test the representation of the 45 monitoring sites, but is costly and time-consuming with the current surveying method. 'Structure-from-motion' photogrammetry (SfM) is a new surveying method that will potentially provide a cheaper and faster way to extend the topographic sandbar survey in GCNP. The method consists of collecting overlapping, oblique imagery with consumer grade cameras mounted on 16 ft poles. To ensure repeatability of the survey, 10-50 ground control points are surveyed across the sandbar surface with a total station. Post-processing of the data consists of creating 3D models of the surface topography using robust pixel-matching algorithms.


Top pane shows blue rectangles that represent the location and 
orientation of images collected 16 feet above the sandbar surface. 

Bottom pane shows the dense point cloud reconstruction, located 
at river mile 8L in Marble Canyon (boats at lower right are 18 ft in length).

The youth citizen scientists collected data at 12 different sandbar sites distributed across Marble and Grand Canyons. Images were taken every 10-15 feet along upstream, downstream, and circular transects on the sandbar surface. Repeat surveys were used to test the variability in camera angle and image spacing between youth crews. While in the field, youth were able to see 3D visualizations of the sandbars they surveyed with the SfM software Agisoft Photoscan Professional. The youth also collected ground control point data with the help of a surveyor, and handheld images from across, behind, and in front of the sandbars.

Youth collecting images with pole mounted camera
at river mile 41R in Marble Canyon

In addition to teaching the youth emerging scientific survey methods, Becca’s research goals included teaching them about fluvial geomorphology in Grand Canyon, and the impacts of Glen Canyon dam on the downstream environment. She also hopes to evaluate the feasibility of using citizen science in future monitoring of sandbars. This is the second of three field work trips that Becca will conduct in GCNP during her time at USU to develop and implement a SfM surveying protocol.

One of the youth on the trip said “participating in citizen science has widen my perspective and understanding of Grand Canyon and why it is vital to protect it.” He especially enjoyed the scientists, saying that “they knew how to have fun and to get the projects done,” and that he “really enjoyed learning about the software that would create the beach models.”

Becca is currently working on her Master’s degree in Watershed Sciences with Dr. Joseph Wheaton, Dr. Paul Grams (GCMRC), Dr. Daniel Buscombe (GCMRC), and Dr. Jack Schmidt (USU). At USU, she is specializing in fluvial geomorphology. This interest has brought her to USU and specifically the Colorado River downstream of Glen Canyon Dam where she is currently working on a thesis investigating sandbar dynamics in response to high flow experiments in Marble and Grand Canyons using emerging 'structure-from-motion' photogrammetry techniques.

Of her experience, Becca says, “the public is often disconnected to science and its importance, and citizen science is a way to bridge this gap. Citizen science is especially important for protecting environments from negative anthropogenic impacts. This experience has not only aided the progress of developing an SfM surveying protocol, but has aided me to contextualize my research into the bigger picture of disseminating scientific knowledge to the public, and more importantly to youth.”

*Modified from Hazel et al. (2010).


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