Abstract
The gully erosion process is influenced by both natural conditions and human activities on the tableland region, the Chinese Loess Plateau, which is a densely populated agricultural area with unique topography. For the purpose of assessing long-term gully growth rates, the influencing factors and potential of gully growth, KH-4B satellite images, Quickbird-2 images, and unmanned aerial vehicle (UAV) images were used to assess gully erosion from 1969 to 2019. The effects of runoff, topography and human activities were analyzed with information derived from historical and present images. Ninety-five investigated gullies were classified into four types: 45 growing, 25 stable, 21 infilled and four excavated gullies. The rates (RA) of 45 growing gullies ranged from 0.50 to 20.94 m2·yr−1, with an average of 5.66 m2·yr−1 from 1969 to 2010. The present drainage area, local slope, average drainage slope, annual runoff, and ratio of the terraced area were all significantly different between the stable and growing gullies. The long-term gully growth rate could be estimated using a nonlinear regression model with annual runoff (Qa) and the slope of the drainage area (Sd) as predictors (RA = 0.301Qa0.562Sd, R2 = 0.530). Based on the Sg-A and Sg-Qa relationship that was used to reveal the threshold conditions for gully growth, all growing gullies still have the potential to keep growing, but soil and water conservation measures, including terraces, could change the threshold condition by reducing the effective drainage area. The results of this study could be helpful for preventing further gully erosion by dealing with gullies far above the threshold line.
Highlights
Erosion is the process whereby water accumulates and often recurs in narrow channels and, over short periods, removes the soil from this narrow area to considerable depths, as defined by the Soil Science Society of America
Erosion represents a minimum of 10% to a maximum of 94% of the total sediment yield caused by water erosion [1], which is a major driver of land degradation on the global scale [2,3,4,5]
Flow hydraulics for gully initiation are constrained in field measurements [1,3]
Summary
Erosion is the process whereby water accumulates and often recurs in narrow channels and, over short periods, removes the soil from this narrow area to considerable depths, as defined by the Soil Science Society of America (https://www.soils.org/publications/soils-glossary/#, accessed on 1 October 2021). Erosion represents a minimum of 10% to a maximum of 94% of the total sediment yield caused by water erosion [1], which is a major driver of land degradation on the global scale [2,3,4,5]. Gullies were developed only when the intensity of concentrated (overland) water flows during a rain event exceeded the threshold [1]. Flow hydraulics for gully initiation are constrained in field measurements [1,3]. The critical environmental conditions of gullies were assessed in terms of precipitation [8], topography [7,9], soils and land use [10,11]
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