Applying a Hand-Held Laser Scanner to Monitoring Gully Erosion: Workflow and Evaluation

Rebecca Bartley,Thomas Lowe,Anne Kinsey-Henderson,Scott N Wilkinson,Aaron Hawdon

doi:10.3390/rs13194004

Abstract

Detailed understanding of gully erosion processes is essential for monitoring gully remediation and requires fine-scale monitoring. Hand-held laser scanning systems (HLS) enable rapid ground-based data acquisition at centimeter precision and ranges of 10–100 m. This study quantified errors in measuring gully morphology and erosion over a four year period using two models of HLS. Reference datasets were provided by Real-Time-Kinematic (RTK) GPS and a RIEGL Terrestrial Laser Scanner (TLS). The study site was representative of linear gullies that occur extensively on hillslopes throughout Great Barrier Reef catchments, where gully erosion is the dominant source of fine sediment. The RMSE error against RTK survey points varied 0.058–0.097 m over five annual scans. HLS was found to measure annual gully headcut extension within 0.035 m of RTK. HLS was, on average, within 6% of TLS for morphological metrics of depth, area and volume. Volumetric change over a 60 m length of the gully and four years was estimated to within 23% of TLS. Errors could potentially be improved by scanning at times of year with lower ground vegetation cover. HLS provided similar levels of error and was relatively more rapid than TLS and RTK for monitoring gully morphology and change.

Highlights

Erosion mapping and load monitoring have indicated that that the majority of fine sediment exported is derived from eroding subsoil in features such as gullies and streambanks, with gullies contributing approximately 40% of the fine sediment exported from river basins draining into the Great Barrier Reef (GBR)
Given the density of vegetation cover in the gully, such point counts provided confidence that the 10 cm and 30 cm MinZ DEMs derived from the held or mobile scanning systems (HLS) workflow were detecting the ground surface in all but the rarest of instances
A previous erosion pin study at this gully [13] determined that annual changes in cross section profiles downstream of the headcut were between 2.2 and 7.2 mm for gully walls and 3 mm for gully floors in gullies without check dams, confirming that it would take more than the 4 years at our study site to reliably detect changes in the gully below the headcut unless we were able to improve the precision of HLS

Summary

Introduction

Erosion from gullies is traditionally measured in terms of growth in length, area or volume using airborne LiDAR, Terrestrial Laser Scanning, Real-Time-Kinematic (RTK). Each method has unique advantages and limitations in terms of capital and ongoing cost, collection time per unit area, accuracy, repeatability and coverage [1,2,3,4,5,6,7,8,9]. Erosion mapping and load monitoring have indicated that that the majority of fine sediment exported is derived from eroding subsoil in features such as gullies and streambanks, with gullies contributing approximately 40% of the fine sediment exported from river basins draining into the GBR lagoon [3,4,5]. As elsewhere, accurately measuring gully morphology and erosion rate is required to inform programs that target and evaluate gully erosion control and ensure the gully treatments are targeted and cost-effective

Methods

Results

Discussion

Conclusion