Aerial Photography to Detect Rill Erosion

Abstract

ABSTRACT COLOR and color-infrared (CIR) air photo trans-parencies were investigated as a means of gathering data necessary to assess erosion. An eroded hillside was photographed at three scales to determine the size of ero-sion features that were detectable and the effect of sur-face conditions on the interpretations. Implement pat-terns from chisel plowing, harrowing, double-disk drill-ing, and combining were visible to the naked eye on 1:4,000 scale images. All except the harrowing pattern were also visible on 1:8,000 scale images. The most com-mon erosion feature, rills, was measurable at a minimum width of 38 mm (ground distance) on 1:2,000 scale CIR imagery with a 50X pocket microscope. The number of rills seen depended on scale, interpreter-film type com-bination, soil surface wetness, plant cover, and viewing instrument. The best viewing instrument was a variable power stereoscope. The best result, 85 percent of ground-measured rills, was obtained with 1:2,000 scale CIR film exposed over a dry surface soil. Color and CIR aerial photographs can yield sufficient detail to rank eroding areas according to rill density and width. They are ex-pected to be a useful tool for erosion quantification in the Palouse region of the Pacific Northwest.