Effects of gully head height and soil texture on headward erosion characteristics and topography evolution

Abstract: Gully head erosion has become one of the most serious types of land degradation in the Loess Plateau region of China. Soil erosion from head-cutting has posed severe damage to the natural environment, while soil degradation is ever deteriorating in recent years. This study aims to investigate the effects of gully head height and soil texture on the erosion process and the microgeomorphology during spatial evolution of channel morphology. A three-dimensional laser scanning was used to capture high-precision micro-geomorphology, thereby representing the morphological changes and development process of erosion gullies. A response relationship was established between the sand yield and topographic factors under the headward erosion of the gully head. An indoor test was carried out to explore the effects of different gully head heights (5, 10, and 15 cm) on the erosion sand yield, gully retreat distance, and gully morphological development under silty loam and loamy sand textures using three flow rates (2, 4, and 6 L/min) for water release scour. The results showed that: 1) There was more fluctuation of soil loss in the study areas, while less resistance to the erosion, as the head height increased. The erosion rate of loamy sand was higher than that of silty loam in the various soil textures. Furthermore, the loamy sand loss fluctuated more than the silty loam, while the erosion rate of loamy sand was also significantly larger than that of silty loam. When the height of gully head is 15 cm and the flow rate is 6 L/min, the headward erosion rate of loamy sand is the highest, which is 19.45 cm / min. 2) There was a sharp increase in the rate of gully head headward erosion, where the scouring water accelerated the denudation of surface erosion, particularly when the gully retreat distance reached the location where the surface erosion occurred on the upstream slope of the gully head. 3) The width-to-depth ratio of the channel increased gradually in the cross section under the same gully height, with the increase of water flow. The depth of headcut erosion was great at the head of the gully under silty loam. The maximum width-to-depth ratio of the cross-sectional channel in the loamy sand was more than three times that of silty loam. It indicated that the silty loam was more prone to undercutting erosion, whereas, the loamy sand was more prone to lateral erosion. Meanwhile, the width-to-depth ratio of the cross-sectional channel was the smallest, when the gully retreat distance of the gully head was 75 cm. 4) In addition, there was also a better linear correlation of four microtopographic or topographic factors with the sediment yield, including the fluctuation, roughness, cutting depth, and slope. Consequently, the microtopography under the gully erosion can be expected to represent the size of sand production, further to estimate the quantity of sand yield. The finding can provide a potential promising reference for the soil and water conservation under the erosive action of flushes and gullies on the Loess Plateau of China.