Submitted to: ARS Workshop on Real World Infiltration
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/1996
Publication Date: N/A
Technical Abstract: Surface roughness of agricultural fields is utilized to control both wind and water erosion. There is no method that is both simple and accurate for measuring the roughness of a soil surface. Since both roughness and porosity of a surface control the reflection of sound, acoustic level difference measurements (Sabatier et al. 1990), were collected above dry fine (< 0.2 mm) and coarse ( 0.8 mm) textured sands with a variety of roughened surfaces. The theoretical pattern of the sound pressure above each surface was computed as described by Sabatier et al. 1993. Expected roughness effects were computed according to Howe, 1985 and provided by Attenborough,1995. Theoretical level difference curves were fitted to the observed data by selecting flow resistivity and tortuosity values for best fit when measured soil porosity, roughness element size and source-receiver distances for each surface condition were utilized. For the flat surfaces, ,agreement between theory and observation was excellent. For the fine sand which was quite reflective to sound, observed and computed effects of the furrows also matched quite well. In order to match the observed effects of roughness for the coarse sand, which did not reflect sound well, a lower value of flow resistivity had to be used for the coarse sand when it was furrowed than when it was flat. Furrow height and spacing must be measured and provided for the computations. Changes in flow resistivity of soils caused by tillage are detectable with level difference measurements. The computations were very sensitive to the distances between the microphones, speaker, and soil surfaces. Accurate measures of these distances between system components were critical. Simultaneous changes of both surface roughness and porosity could not be detected from a single observation.