Evaluation of gully head retreat and fill rates based on high-resolution satellite images in the loess region of China

摘要

The acceleration of large gully erosion in the loess environments of China is a matter of concern because of the changing land use and urban expansion. This paper evaluates the gully head retreat and landfill rates in the Huoxianggou watershed in the loess region of China for the period between 1969 and 2017. High-resolution satellite imageries and ground truths allowed us to estimate the linear and volumetric change rates of gully head. The digital elevation model (DEM) derived from unmanned aerial vehicle (UAV) was used to calculate the geometric parameters of the gully bottom, and the linear and volumetric gully parameters were obtained using the 1969, 2004 and 2017 satellite images of the study area. We estimated the average annual linear retreat rate (R-l) for the study area between 1969 and 2003; R-l was found to be 1.41 +/- 0.98m y(-1), the average annual volumetric retreat rate (R-V) was 63.79 +/- 96.62m(3) y(-1), the average annual linear fill rate (F-l) was 3.87 +/- 4.09m y(-1), and the average annual volumetric fill rate (F-V) was 1002.46 +/- 1633.87m(3) y(-1). Between 2004 and 2017, R-l was 0.82 +/- 0.80m y(-1), R-V was 1.80 +/- 1.37m(3) y(-1), F-l was 3.86 +/- 4.99m y(-1), and F-V was 708.62 +/- 1787.21m(3) y(-1). We also estimated the retreat and fill rate of gullies within various land use classes. When the land use type near the gully head was road, the volumetric retreat rate of the gully was threefold that of the farmland, and the rate of the gully head landfill was fourfold that of the farmland. Moreover, the volumetric change rate (C-V) and linear change rate (C-l) of all gully heads under the influence of a road, including gully retreat and landfill, had a power exponential relationship (C-V=13.29 Cl2.14, R-2=0.71). The gullies near the roads in the thick loess area were cut at an abnormally rapid rate, which has not received sufficient attention previously. Therefore, the effect of road construction on gully erosion in the loess area of China should be reassessed.