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Research Project: Understanding Water-Driven Ecohydrologic and Erosion Processes in the Semiarid Southwest to Improve Watershed Management

Location: Southwest Watershed Research Center

Title: Using terrestrial LiDAR to measure water erosion on stony plots under simulated rainfall

item LI, L - University Of Arizona
item Nearing, Mark
item Nichols, Mary
item Polyakov, Viktor
item Cavanaugh, Michelle

Submitted to: Earth Surface Processes and Landforms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2019
Publication Date: 11/1/2019
Citation: Li, L., Nearing, M.A., Nichols, M.H., Polyakov, V.O., Cavanaugh, M.L. 2019. Using terrestrial LiDAR to measure water erosion on stony plots under simulated rainfall. Earth Surface Processes and Landforms. 45(2):484-495.

Interpretive Summary: Scientists often want to measure how much soil is eroded during a given period of time for a variety of reasons. In the past this measurement has been made using plots set up with special measuring instruments at the lower end to monitor how much soil leaves the plot over a period of time. It is a laborious and expensive process. In this study we introduce a new way to make an erosion measurement. A Terrestrial LiDAR scanner is an instrument that uses a laser beam to measures distance very accurately, and gives the user the ability to map the elevations of surfaces very precisely. Theoretically, if one can measure a soil surface with a Terrestrial LiDAR scanner at two different points in time and quantify the differences in the elevations measured, one could determine how much the surface eroded between the measurement times. In this experiment we set up a 6 by 20 feet soil box with an instrument that applies artificial rainfall. We used a Terrestrial LiDAR scanner to measure the surfaces of the plot before and after applications of rainfall. We applied the amount of rain that would typically have the ability to erode about as much as one would expect over a ten-year period at this location in southern Arizona. We were able to detect difference in the elevations on the plot of less than a tenth on an inch. We made several recommendations about how many scans need to be done, and in what configuration the scans should be relative to the plot. This new technique may have important applications in the future for monitoring rates of soil erosion.

Technical Abstract: Terrestrial LiDAR scanning (TLS) technology is used to detect terrain elevation changes in order to monitor soil erosion. This study examines the potential use of terrestrial LiDAR to measure erosion on small plots at high resolution. Multi-temporal TLS scans were conducted at six positions around plots (2 × 6.1 m2) with three slope treatments through 11 simulated rainfall applications. Surface elevation changes were quantified by comparing scans between rainfall simulations, and elevation changes greater than the level of detection were used to obtain volumetric change estimations. Erosion mass was estimated both by using soil bulk density and the density of sediment collected in runoff, and then compared to the erosion estimated from the runoff samples. Results showed: 1) with the aid of fixed reference controls in the form of concrete target surfaces of varying roughness, registration accuracy was better than 1 mm and mean level of change detection was less than 2.2 mm; 2) the TLS-estimated erosion accuracy was affected by erosion magnitude, and grid size of 10 mm was found to be appropriate for this scale to estimate the volumetric changes; 3) the number of scan positions could be reduced to three while not significantly impacting volumetric change estimations; and 4) elevating the scanner resulted in much better accuracy for eroded mass estimations. This study suggests that using the LiDAR to monitor soil erosion at the plot scale is feasible, and provides guidance about the level of accuracy one might expect in doing so.