Effects of human activity on erosion, sedimentation and debris flow activity – A case study of the Qionghai Lake watershed, southeastern Tibetan Plateau, China

Abstract

We report the results of a study of the Qionghai Lake watershed, located on the southeastern edge of the Qinghai–Tibetan Plateau, China, designed to investigate the effects of human activity on changes in soil erosion intensity, debris flow activity and lacustrine sedimentation. The results indicate that the mean denudation rate of the watershed was about 0.82 mm/yr during the Holocene. However, since 1952, the rate has increased to 1.82 mm/yr, accompanied by a greatly increased sedimentation rate in Qionghai Lake. The increased denudation rate was accompanied by increases in population and the related intensified exploitation of land resources, including deforestation and an increase in the area of cultivated land. In addition, the increasing rate of denudation and lacustrine sedimentation is closely linked to the increased frequency of flooding and debris flows in the watershed. Based on our results, we estimate that the longevity of Qionghai Lake is about 1200 years in the case of natural evolution; however, this is reduced to 540 years in the context of continued intensive human activity in the region. These findings are important for the mitigation of mountain hazards such as debris flows and for the promotion of sustainable economic development in the Qionghai Lake area. They also provide a basis for obtaining an improved estimate of changes in denudation rate on the southeastern edge of the Qinghai–Tibet Plateau.