A gully erosion assessment model for the Chinese Loess Plateau based on changes in gully length and area

Gully erosion represents an important sediment source, and gully volume changes can show the contribution of gully erosion to sediment yield. On the Chinese Loess Plateau, where the gully erosion is a serious problem, valley bank gullies are the main gully types in small catchments, and the exploration of a valid method to assess the gully erosion at a large scale is needed. The objective of this study was to develop a model to assess the gully volume using linear and areal parameters that can be determined from high resolution satellite images. A 3-D scanner was used to measure the valley bank gully parameters and the two QuickBird images taken over 6 or 9year periods in two study areas in the central Loess Plateau were used to derive historical linear and areal gully parameters. The results showed that the volume (V, m3) of the 44 valley bank gullies calculated from a 0.15×0.15m digital elevation model was closely related to gully length (L, m) and gully area (Ag, m2). The power function relation between V and L was V=0.6529L2.1622(R2=0.78), indicating the high erosional vulnerability of the area. Compared with the V–L relation, the relation between V and Ag was more pronounced: V=0.2762Ag1.3971(R2=0.91). The relative error and Nash–Sutcliffe efficiency between the measured and predicted gully volumes suggested that the V–Ag relationship had a better predictive ability for gully volume. Another advantage of the V–Ag model is that the gully area can be easily measured from very high-resolution satellite images. Thus, the V–Ag relationship was suggested for modelling the gully volume on the Loess Plateau of China. The gully erosion volume during the periods of 2007 to 2013 and 2004 to 2013 in the two study areas, which was estimated based on the V–Ag relationship and parameters measured from QuickBird imagery, ranged from 0.41 to 36.76m3year−1 and averaged 10.32m3year−1. This study presented a feasible model for assessing gully volume and volume changes over a large scale with high-resolution satellite images.