Spatiotemporal Evolution of Runoff and Sediment of the Taohe River and Its Driving Analysis

In order to explore the spatial and temporal changes of runoff and sediment in the Taohe River and its driving mechanism,Spearman correlation coefficient method,Mann-Kendell mutation test method and ordered clustering method were used to analyze the changes of runoff and sediment discharge and their driving factors in four hydrological stations along the Taohe River from 1957 to 2016.The results showed that the correlation between runoff and sediment of the four hydrological stations along the Taohe River was significant,and the correlation coefficient was 0.728-0.984.The runoff and sediment transport in the interval showed an increasing and decreasing trend.The decrease rate of runoff was 133.82%-216.17%higher than that of Xiabagou station,and the decrease rate of sediment transport was 250.49%-4766.33%higher than that of Xiabagou station.The mutation year of the Taohe River runoff occurred in 1986,and the maximum decrease was 35%.The water-sediment relationship curves of different periods showed that the sediment discharge of the four stations changed abruptly around 1990,and the maximum reduction before and after the mutation was up to 73%,and the sediment discharge in the river channel decreased significantly.The research showed that human activities were the main driving factors for the change of water-sediment relationship in the Taohe River.

Can the Grain-for-Green Program Really Ensure a Low Sediment Load on the Chinese Loess Plateau?

The Chinese Loess Plateau is the most seriously eroded area in the world and contributes the vast majority of the sediment that goes into the Yellow River.Since the 1950s,progressive soil and water conservation measures have been implemented—in particular,large-scale ecological restoration has been ongoing since 1999—resulting in a significant reduction of the sediment load.However,the mechanism of the sediment transport dynamics is not fully understood due to multiple and complicated influencing factors including climate change and human activities(e.g.,ecological restoration).A challenging question,then,arises:Is the current low sediment level a“new normal”in this era and in the future?To address this question,we selected a typical loess hilly region where considerable ecological restoration has been implemented,and which is regarded as the site of the first and most representative Grainfor-Green program in the Loess Plateau.We investigated the evolution of discharge–sediment relationships in the past decades(1960–2010)and their association with the soil and water conservation measures in this area.The results showed that there was a distinct change in the regression parameters of the commonly used annual discharge–sediment regression equation—a continuously increasing trend of parameter b and a decreasing trend of parameter a,accompanying the ecological restoration.The increase in exponent b(i.e.,a steeper slope)implies a potential lower sediment load resulting from low discharge and a potential higher sediment load resulting from large discharge.This finding may question the new normal of a low sediment level and implies the potential risk of a large sediment load during extremely wet years.