Background The river system is an important and very active natural system on the earth, and the change of water and sediment is the direct response of the river system to climate change and human activities. The sediment load dramatically decreased at Tao River watershed, the upper Ganjiang River of China, due to natural and human factors. The objective of this study is to quantify the spatial and temporal variation of runoff and sediment load in the typical watershed in upper reaches of Ganjiang River and their potential causes. Better understanding the dynamic of hydrological processes may provide good reference for soil and water conservation, water resources planning and Ganjiang River basin management.

Methods the Mann-Kendall test and Pettitt test were employed to investigate the temporal trends and abrupt changes of the annual runoff and sediment load at Julongtan gauging station of Tao River watershed from 1958 to 2018. Then the accumulation slope change rates were applied to analyze the relationship of rainfall-sediment during different periods and quantify the drivers of variation of runoff and sediment load.

Results 1) The average annual precipitation, runoff and sediment transport in Tao River watershed were 1 565.5 mm, 6.036 billion m³ and 1.125 million t respectively. 2) The annual distribution of runoff and sediment was basically stable, mainly concentrated in April-June. 3) There was no significant change trend and abrupt change point in rainfall and runoff in the watershedof 61a, but rainfall and runoff fluctuated significantly in 1972 and 1985. The annual sediment discharge had no significant change trend before the 1990s, but has decreased significantly since the 1990s(α < 0.01), and an abrupt change occurred in 2002(P < 0.001). 4) According to the relative change point, the whole period was divided into four connected parts of 1958-1972 (stage A), 1973-1985 (stage B), 1986-2002 (stage C), 2003-2018 (stage D).When the period of 1958-1972 (stage A) with weak human activities was taken as a fundamental baseline, the contribution rate of the human intervention to sediment load in stage B, C and D was 79.14%, 92.05% and 100%. As time went on, human activities causeda greater and greater impact on sediment transport in Tao River watershed. 5) The construction of large-scale water conservancy facilities such as reservoirs and large-scale soil and water conservation measures are the driving factors for the reduction of sediment transport in Tao River watershed.

Conclusions Integrating all these results, this work confirmed clearly that human activities are the main driving factor of variation of runoff and sediment load in the upper reaches of the Ganjiang River basin. The study has important practical significance for accurately evaluating the role of human activities such as hydraulic projects and the sustainable development of watersheds.