Short-term morphological evolution of an ephemeral gully in the Dry-hot Valley of Southwest China

Abstract

The evolution process of ephemeral gully (EG) is a major content in the study of gully erosion and geomorphology. However, due to the short duration of EG existence, field-based continuous quantitative observation information is still lacking. The objective of this study was to characterize the morphological changes and evolution mechanisms of EG under natural conditions in the Dry-hot Valley. A representative EG was observed from 2016 to 2020 by using laser scanning. Results showed that after four years, the erosion area and erosion volume increased 4.5 and 17.3 times, respectively. The length, width, and depth of the main channel continuously increased over time but the growth rates decreased. During the four monitoring periods, the average growth rates of width were 0.12, 0.26, 0.33 and 0.06 m/year, respectively; the average growth rates of depth were 0.07, 0.08, 0.03 and 0.02 m/year, respectively; and the growth rates of length were 7.58, 1.78, 2.17 and 1.17 m/year, respectively. EG morphological parameters varied at different locations of the hillslope. The cross-section area increased gradually towards downslope, especially in the middle and lower parts of the channel. However, the width-depth ratio of EG decreased gradually from upper to lower parts of the hillslope, and the values were generally greater than 1.0. In addition, the variation of sinuosity, density and tortuosity complexity were influenced by both headward and lateral erosion, which increased and then decreased. The vertical gradient increased significantly and then tends to be stable. The results of this study are helpful to enrich current studies on the evolution process of ephemeral gully.