Background The management of ephemeral gully and gully erosion relies on their survey at regional scale. The remote sensing technique is the primary method for such survey currently, which, however, is hardly able to identify ephemeral gullies or gullies of small size.

Methods This study provided a regional gully erosion survey scheme based on the stratified unequal probability areal sampling used in the First Water Resources Census (2010-2012) for interrill and rill erosion. The main steps of the method include making a survey maps and record forms of sampling units; field survey, such as photo shooting, record form filling, survey map drawing; determination and measurement of gully section; processing and calculation of survey data; and evaluation of gully erosion intensity. This newly developed method was later applied to four counties in Northeasern China, including Liaoyang county and Zhangwu county in Liaoning province, Nenjiang county in Heilongjiang province, and Arun Banner in Inner-Monglia, covering 112 sampling units in total. The 4 counties belong to the mountain to the transition of the piedmont plain platform and hilly region.But Liaoyang is mainly in the typical hilly region, Zhangwu is mainly in the plateau to plain transition, which the platform characteristics are obvious, and Nenjiang and Arong Banner are mainly in the rolling hill region.

Results The results showed that the densities of both ephemeral gully and gully were 1.70, 0.61, 1.51 and 5.04 km/km² in the 4 counties, respectively, classified as the gully erosion grades of moderate, slight, moderate, and catastrophic. The numbers of both ephemeral gully and gully were 14.7, 9.3, 12.4, and 44.0 per square kilometer in the 4 counties, in which the ephemeral gullies accounted for 46.9%, 44.1%, 71.0%, and 66.1%, respectively. The volume of gully erosion were 15 195.8, 11 489.0, 1 886.5 and 14 060.2 cubic meters per square kilometer respectively, which is mainly caused by gullies. It is clearly manifested that more gullies were developed in the hilly regions like Liaoyang and Zhangwu in Liaoning province, compared to the other type, while ephemeral gullies is dominant in the rolling hill regions, such as Nenjing in Heilongjiang province and Arun Banner in Inner Mongolia. These gullies mainly appear in the cultivated lands. The proportions of the farmand varied between 23.3% and 55.5% for the 4 counties, while the numeral percentage in farmland were between 88.8% and 100% for ephemeral gullies, and between 40.1% and 99.1% for gullies. Without appropriate conservation practices, ephemeral gullies can develop into gullies in a short term.

Conclusions  It is critical to take effective actions on the gullies as well as the ephemeral gullies, especially on the cultivated areas. The method provided in this study could assess both ephemeral gully and gully erosion quantitatively and objectively for regional scale, and evaluate contributions of sheet erosion and gully erosion respectively by combining the interrill and rill survey in the same sampling unit.