AN ASSESSMENT OF AERIAL LIDAR FOR GEOMORPHIC CHANGE DETECTION WITHIN BOQUILLAS CANYON, BIG BEND NATIONAL PARK, TEXAS

The Boquillas Canyon study area is a roughly 20-mile reach along the Rio Grande within Big Bend National Park in far west Texas. The area has been the location of an ongoing effort by researchers to assess the effectiveness of invasive species removal (Saltceder (Tamarisk spp.) and Giant River Cane (Arundo donax)) and its impact on channel morphology, sediment transport and riparian diversity. Geomorphic Change Detection (GCD) is one of the techniques used to assess the success of the invasive species removal. GCD is accomplished by comparing 3D models of the same sand/gravel bar from before and after the species removal. Net changes in elevation can indicate desired changes in sediment mobility.

We have used several techniques to create the 3D models necessary for this analysis at selected locations within Boquillas canyon. First, we created a network of control points in UTM coordinates throughout the canyon using RTK GPS. Using these control points for georeferencing, we periodically collect 3D data using a laser Total Station, a Real Time Kinematic (RTK) GPS instrument, and ground based LiDAR instrument. The resultant 3D models are limited in extent, but provide fairly high temporal resolution to our growing geomorphic database. The resolution of these 3D models is 0.25 m.

For comparison, we have access to a 2012 aerial LiDAR dataset that was collected from flights over the entirety of the river channel within Big Bend National Park. This project produced a moderately high resolution (1 m) DEM and orthophoto. To assess the accuracy of the aerial LiDAR data, we have compared the elevations to our known georeferencing control points to the values from the 1 m LiDAR derived DEM’s. Results show a range of elevation differences from 7.3 meters to less than 1 cm with a mean of 0.47 m.