Measurement of Ephemeral Gully Erosion

Abstract

ABSTRACT THE Universal Soil Loss Equation often under-estimates erosion on agricultural fields because it does not account for the loss of soil from ephemeral gullies. However, the development of appropriate predictive methodology along with the understanding of the erosional processes are limited by the difficulty of acquiring adequate data on ephemeral gully erosion. This paper describes an aerial photogrammetric method for making accurate and repetitive field measurements of ephemeral gully erosion. Stereo aerial photographs are aquired of a field before and after gully changes caused by erosion or tillage. Data reduction of the stereopairs with photogrammetric procedures provides X, Y and Z terrain coordinates with approximate vertical measurement accuracies of 25 mm and contour intervals of 0.15 m. The methodology was tested on a 5.34 ha field that contained two major gullies with eroded depths approaching 0.5 m. Over nearly three years, soil volume changes in the gullies were computed to give the quantities of soil removed by erosion or filled by tillage. The distribution of the soil volume changes along the gullies portrayed the zones and quantities of deposition as well as erosion. This data base offers considerable potential for studying ephemeral gully erosion and developing predictive methodology.