Soil Erosion and Deposition Monitoring System Using an Ultrasonic Sensor
Although erosion and sediment deposition are naturally occurring processes, the rate of these processes has increased due to human influences. When erosion occurs near human development or infrastructure it can cause extensive and costly damage. Monitoring the erosion in at-risk areas could help managers mitigate the erosion problem before damage occurs. Currently, there are limitations to erosion monitoring techniques. Current methods are either invasive to the area, record low frequency measurements, or have a narrow range of measurement. Erosion pins are an example of a traditional erosion and deposition monitoring technique that is highly invasive to the area of interest and is unable to monitor large areas unless many are used which increases the invasiveness. Erosion monitoring methods are typically either limited to one or more of these problems or require very expensive equipment and set ups to overcome these problems. An example of an expensive erosion monitoring system that can overcome the stated limitations is the Terrestrial Laser Scanner (TLS). This system uses a laser to measure distances to the bank non-invasively and at high frequency. The TLS can scan the whole bank, but the system costs close to $10,000. In order to address the limitations of current erosion monitoring techniques, an affordable erosion monitoring system was created to be non-invasive to the area of interest, conduct high frequency measurements, and monitor an area of approximately 2800 square centimeters, all at a cost of approximately $350. The monitoring system uses an ultrasonic sensor that measures the time of reflectance of sound waves to calculate the distance to the area of interest. During storm events, as erosion and deposition occur, the changes in distance can be determined in real time, allowing for erosion and deposition rates to be determined. Currently the system has been deployed to monitor deposition on sandy soil stream banks in the Nebraska Sandhills and erosion on a streambank and field plot in Lincoln, Nebraska. The current system has been proven successful in measuring the erosion and deposition during storm events but does yield some error. When measuring at a distance of approximately 1 m, the error in a controlled lab setting is ± 0.934 mm. The error in the natural environment increased to ± 10.08 mm when subjected to environmental factors such as temperature and humidity. Future work will focus on improving mechanisms that account for the environmental factors to decrease the error. This monitoring system will be able to provide researchers and managers with real time erosion and deposition rates affordably and non-invasively.