Assessment of bank gully development and vegetation coverage on the Chinese Loess Plateau

Gully erosion is a serious environmental problem and the primary source of sediment loss on the Loess Plateau of China, yet previous research focusing on bank gullies is limited. An assessment of bank gully development is needed as a basis for predicting erosion rates under the effects of vegetation cover and land use change. To estimate bank gully retreat rates under different land uses, assess the factors leading to bank gully development and model gully area growth rate at the catchment scale, 30 catchments with an average area of 39.0 ha were selected in the southeastern part of the Loess Plateau. QuickBird images (0.61 m resolution) obtained in 2003 and 2010 were interpreted to delineate bank gully features, and a 5 m resolution digital elevation model was used to extract topographic factors. The results showed that from 2003 to 2010, the maximum retreat rates of bank gully heads in the 30 investigated catchments ranged between 0.23 and 1.08 m yr− 1, with an average of 0.51 m yr− 1. The ratio of bank gully growth area to valley area changed from 0.49 to 9.45%, depending on land use, with average increases of 3.94, 4.00 and 2.09% for the three land use types identified, i.e. mixed use, grassland and forestland, respectively. Correlation analysis indicated that the effects of topographic factors on bank gullies decreased as vegetation coverage increased in upslope drainage areas and that vegetation coverage exceeding 60% in upslope drainage areas can significantly control bank gully development. A model was built to predict the bank gully area growth rate (Ra, m2 yr− 1) with upslope drainage area (Ai, m2), local slope gradient (S, m m− 1) and the proportion of the area with vegetation coverage below 60% in upslope drainage areas (Φ0.6) at the catchment scale. The regression equation is in the form Ra = 0.1540[(Φ0.6Ai)0.24S]3.2588. Compared with previous studies, vegetation is a factor in this model, which would be helpful for assessing the influence of vegetation cover on bank gully development.