Application of an ultrasonic sensor to monitor soil erosion and deposition

Abstract

Monitoring erosion at high temporal resolution can provide researchers and managers the data necessary to manage erosion. Current erosion monitoring methods tend to be invasive to the area of interest, record low-frequency measurements, have a narrow spatial range of measurement, or are expensive. There is a need for an affordable system capable of monitoring erosion and deposition non-invasively at high temporal resolution. The objectives of this research were to (1) design and construct a non-invasive sediment monitoring system (SMS) using an ultrasonic sensor capable of monitoring erosion and deposition continuously, (2) test the system in the lab and field, and (3) determine the applications and limitations of the system. The SMS was tested in the lab to determine the extent to which the soil type, slope, surface topography, change in distance, and vegetation impacted the measurements of the ultrasonic sensor. Soil type, slope, and surface topography had little effect on the measurement, but distance and the introduction of vegetation impacted the measurement. In the field during high flows, as erosion and deposition occurred, the changes in distance were determined in near real-time, allowing calculation of erosion and deposition quantities. The SMS was deployed to monitor deposition on sandy streambanks in the Nebraska Sandhills and erosion on a streambank and field plot in Lincoln, Nebraska. The SMS proved successful in measuring sediment change during high-flow events but yielded some error: ±1.06 mm in controlled lab settings and ±10.79 mm when subjected to environmental factors such as temperature, relative humidity, and wind.