Strong anthropogenic activities and climate change have caused distinct hydrology and sediment dynamics in river systems worldwide. Yet, the integrated picture of sediment discharge changes and quantitative attribution of these changes from a basin‐wide perspective were limitedly understood. In this study, we quantified the variations of sediment discharge and in‐reach sediment budget in the Yellow River basin (YRB) during 1956–2019 and examined the underlying reasons. Both streamflow and sediment load in the YRB have substantially decreased during 1956–2000 except the headwater, and the reduction rate increased along the mainstem. However, the streamflow has significantly increased (p < 0.05) since 2000 due to increased precipitation, and the sediment load at most stations tended to stabilize. The contribution of soil conservation measures (SCMs, including check‐dams, terraces, grass plantation, and afforestation) and reservoirs to sediment load reduction was more than 50% in the headwater and middle reaches and over 90% in the upper and lower reaches. The sediment yield coefficient decreased linearly with reservoir capacity and exponentially with the proportional area of SCMs (p < 0.01). With continuous dam construction, the channel erosion in the headwater decreased to nearly zero, and the sediment deposition in the upper and middle reaches increased linearly with storage capacity of reservoirs. In contrast, the sediment deposition in the lower reaches displayed a linear correlation with the concentration of sediment derived from the middle reaches (p < 0.05). This study provides quantitative results for sediment dynamics of entire river system, which facilitates development of sustainable watershed management strategies.
7 September 2017 in Hydrology and Earth System Sciences
Within China's Loess Plateau there have been concerted revegetation efforts and engineering measures since the 1950s aimed at reducing soil erosion and land degradation. As a result, annual streamflow, sediment yield, and sediment concentration have all decreased considerably. Human-induced land use/cover change (LUCC) was the dominant factor, contributing over 70 % of the sediment load reduction, whereas the contribution of precipitation was less than 30 %. In this study, we use 50-year time series data (1961–2011), showing decreasing trends in the annual sediment loads of 15 catchments, to generate spatio-temporal patterns in the effects of LUCC and precipitation variability on sediment yield. The space–time variability of sediment yield was expressed notionally as a product of two factors representing (i) the effect of precipitation and (ii) the fraction of treated land surface area. Under minimal LUCC, the square root of annual sediment yield varied linearly with precipitation, with the precipitation–sediment load relationship showing coherent spatial patterns amongst the catchments. As the LUCC increased and took effect, the changes in sediment yield pattern depended more on engineering measures and vegetation restoration campaign, and the within-year rainfall patterns (especially storm events) also played an important role. The effect of LUCC is expressed in terms of a sediment coefficient, i.e., the ratio of annual sediment yield to annual precipitation. Sediment coefficients showed a steady decrease over the study period, following a linear decreasing function of the fraction of treated land surface area. In this way, the study has brought out the separate roles of precipitation variability and LUCC in controlling spatio-temporal patterns of sediment yield at catchment scale.