Spatial variation of Ephemeral Gully in the Loess Plateau

Ephemeral Gully（EG） erosion is one of the main erosion types in the Loess Plateau. It is important to know the spatial distribution of the EG at the regional scale for land management and EG prevention. This study aimed to identify EG distribution by using high accuracy field measurement using GNSS RTK and visual interpretation based on sub-meter Google Earth images. GIS spatial analysis was utilized to explore the spatial patterns of EGs distribution. A total number of 137 units were systematically selected in the Loess Plateau as survey areas. Parameters such as EG length, EG density, land use of the hillslope where EG existed, etc. were obtained and analyzed. The results showed that:（1） there was no significant difference between EG length obtained from the visual interpretation based on sub-meter resolution images and those from field measurement, which made the former method applicable for a quick survey of EGs at regional scale.（2） On Loess Plateau, 33.6% of the watersheds had EGs. The average EG density of the sampled watersheds with EGs was 3.41 km/km~2, and the maximum density was 21.92 km/km~2. Averagely there were 65 EGs per square kilometers, with an average length of 63.31 m. The critical length of hillslope for EG occurrence mainly ranged from 40 m to 60 m, with an average value of 56.20 m. The highest EG density was found in Wuqi and Zhidan County in the northwest of Yan′an, and Jingbian County in Yulin. The average EG density in the Loess Hilly and Gully Region was 5.32 km/km~2, and the EG erosion intensity was extremely strong. In the Loess sorghum gully region, the average EG density was 2.07 km/km~2, and the EG erosion intensity was moderate.（3） The portions of EGs located in cropland, grassland, and forest land were 38.3%, 35.3%, and 22.8%, respectively. After the Grain for Green Project, more efforts should be paid to the prevention of EGs that were remained on cropland. The threat from cropland EGs remained seriously in some areas, such as the central and northwest of Yan′an City, Shaanxi Province in the middle and upper reaches of Beiluo River, at the junction of Dingxi City and Huining County, Baiyin City, Gansu Province, Suide County, Shaanxi Province and Luliang City, Shanxi Province on both sides of the Yellow River in the lower reaches of Wuding River, etc. This study may provide scientific support for the further management strategy of EGs prevention in the Loess Plateau.