Photogrammetric analysis tools for channel widening quantification

Authors: QIN, CHAO - Northwest Agricultural & Forestry University; Wells, Robert - Rob; MOMM, HENRIQUE - Middle Tennessee State University; XU, XIMING - Northwest Agricultural & Forestry University; Wilson, Glenn; ZHENG, FENLI - Northwest Agricultural & Forestry University

Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2019
Publication Date: 8/1/2019
Citation: Qin, C., Wells, R.R., Momm, H.G., Xu, X., Wilson, G.V., Zheng, F. 2019. Photogrammetric analysis tools for channel widening quantification. Soil and Tillage Research. 191(August 2019):306-316. https://doi.org/10.1016/j.still.2019.04.002.
DOI: https://doi.org/10.1016/j.still.2019.04.002

Interpretive Summary: Accurate soil erosion monitoring is important to improve soil erosion prediction accuracy and performance of erosion prevention measures. The manuscript describes several approaches to determine channel width from photographic images. Images were collected above a small soil flume in the laboratory that was designed to promote width expression due to changes in flow rate, channel slope, and soil. The images were analyzed based on color (single image and image pair) and elevation (image pair) discontinuity. Compared with each other, they show relative errors between 0.3% and 7.0% from 0 to 420-s experiment time. Accumulated sediment discharge showed a significant positive linear relationship with channel widths obtained using the images. Soil loss estimated with the paired images color method resulted in a 3.1% difference compared to manual sampling method. Results provide a valuable confirmation that soil erosion monitoring programs utilizing imagery are far less costly in both equipment and personnel, while providing similar results to proven technology.

Technical Abstract: Accurate soil erosion monitoring is important to improve soil erosion prediction accuracy and performance of erosion prevention measures. The objectives of this study are to describe and evaluate methods for monitoring and data post-analysis concerning channel widening in the presence of a non-erodible layer. Technology was developed to capture 5-cm spaced cross-sections along a soil flume at 3-s time intervals. Two off-the-shelf digital cameras were positioned 3-m above the soil bed and controlled by a program to trigger simultaneously and download images to the computer. Methods utilizing color difference in images and elevation difference in DEMs were applied to detect discontinuities between channel wall and bed. Channel widths were calculated by differentiating the coordinates of surface discontinuities. A volumetric method was used to calculate flow velocity with measurements of flow depths obtained from ultrasonic depth sensors. Sediment concentration was determined by manualsampling. The results showed that different channel width calculation methods exhibited comparable outcomes and achieved satisfactory accuracy. Sediment discharge showed a significant positive linear correlation with channel widening rate, while exhibiting a 5 to 25-s time lag compared to the peak channel widening rate. Total sediment discharge calculated by photogrammetry was 3.1% lower than that calculated by manual sampling. Flow velocity decreased with time and showed a significant negative power correlation with channel width. Advantages of described methodology include automated high spatial and temporal monitoring resolution, comprehensive data post-rocessing, and the potential to be generalized to large scale river/reservoir bank failure monitoring.