Abstract
In recent years, the increased incidence of sudden heavy rains in Japan has enhanced the occurrences of surface runoff from sloping farmlands. These runoff events negatively affect the ecosystems as a result of the fertilizer components or heavy metals present in the runoff water that flows into local watersheds. A conventional method for measuring the extent of surface runoff has been to use water-level meters installed at the bottom edge of sloping farmlands. However, such equipment may provide unreliable data because of, for instance, pileup of crop residues and/or soil particles around the sensor. To avoid such a problem, this study proposes a sensing system that uses automatically captured moving images of surface runoff. The system was tested in outdoor artificial sloping fields for more than a year in total. Several sets of images, recorded actual rainfall levels and runoff amounts, were obtained during natural rainfall/runoff events in Ibaraki and Kagoshima prefectures. Particle image velocimetry (PIV) was applied to the captured moving images to estimate the runoff velocities utilizing floating tiny residues as markers of water flow, which are essential for the PIV procedure. The estimated values of runoff velocity reasonably corresponded to the instantaneous rainfall levels and runoff amounts and were relatively close to the velocity measurements obtained using alternative methods.
