1. Institute of Soil and Water Conservation, Chinese Academy of Sciences and Ministry of Water Resources, 712100, Yangling, Shaanxi, China;
2. University of Chinese Academy of Sciences, 100039, Beijing, China;
3. Institute of Soil and Water Conservation, Northwest A & F University, 712100, Yangling, Shaanxi, China;
4. College of Water Resources and Architectural Engineering, Northwest A & F University, 712100, Yangling, Shaanxi, China;
5. Shaanxi Environmental Protection Group Ecological Construction Management Co., Ltd., 710000, Xi'an, China;
6. Hunan Provincial Water Resources Department, 410000, Changsha, China
Abstract：[Background] Shallow gully erosion is a very common and important type of erosion in the Loess Plateau, and the amount of shallow gully accounts for a large proportion of the total erosion on the slope. Shallow gully erosion is not only the main source of sand production, but also the main cause of low agricultural output and land degradation. Shallow gully is widely distributed, but the measure of it is inefficient. Therefore, there is an urgent need for a quick and easy way to complete this work.[Methods] Google Earth can provide information such as path length, elevation and area for public, so the erosion amount of a shallow gully can be measured by it without GIS software or other tools for secondary processing. As for channel volume measurement, the "Triangular prism method" is feasible, means that the erosion gully can be simplified into a triangular prism whose bottom surface is a triangle with a vertex facing down, the volume of "triangular prism" is the volume of the gully roughly, the resulting value is the amount of erosion. Specifically, the erosion gully surface on the digital map can be divided into rectangular blocks by using terrain tools of Google Earth. We can view each rectangular block as the base of a "triangular prism", then base on the traditional "Triangular prism method" erosion measurement method and use the relevant parameters the Google Earth provides for public, the volume of each "triangular prism" is measured. Finally, superimpose every volume of "triangular prism" all, the total amount of shallow gully erosion can be measured quickly and accurately.[Results] Although Google Earth is deviant in eroded region, but this error can be regarded as a systematic error which can be eliminated mathematically, as for the minuteness error values that still exist after the elimination can be ignored. And the random error of this study is mainly derived from the slight differences in the operation of shadow analysis under Google Earth, for the nature of random error, it can be corrected through repeated calculations. The following is the actual test validation, after the extreme rainfall in Yan'an, 2013, a representative shallow gully erosion in terraces occurred in the Majiagou basin. The relative error of elevation is 23.2%, the relative error of area is 2.7%, the relative error of gully depth is 14.8% and the relative error of shallow gully erosion amount is 4.8% compared with the measured. It shows the accuracy of shallow gully erosion amount measurement method based on Google Earth is meets the requirements of erosion amount measurements in soil and water conservation.[Conclusions] Shallow gully erosion amount measurement method based on Google Earth is a new method of shallow trench erosion measurement, which can provide a technical reference for the investigation and control of soil erosion on slope surface in the Loess Plateau.
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2018, Vol. 16 
