Changes in sediment transport in the Kuye River in the Loess Plateau in China

Abstract

In this paper, the changes in sediment transport over 51 years from 1955 to 2006 in the Kuye River in the Loess Plateau in China are assessed. Key factors affecting sediment yield and sediment transport, such as precipitation depth, discharge, and human activities are studied. To investigate the changes in sediment yield in this watershed, a trend analysis on sediment concentration, precipitation depth, and discharge is conducted. Precipitation depths at 2 Climate Stations (CSs), as well as discharge and sediment transport at 3 Gauging Stations (GSs) are used to assess the features of sediment transport in the Kuye River. The runoff modulus (defined as the annual average discharge per unit area, L/(s .km 2)) and the sediment transport modulus (defined as the annual suspended sediment transport per unit area, t/(yr km 2)) are introduced in this study to assess the changes in runoff and sediment yield for this watershed. The results show that the highest average monthly discharge during the study period in the Kuye River is 66.23 m 3/s in August with an average monthly sediment concentration of 88.9 kg/m 3. However, the highest average monthly sediment concentration during the study period in the Kuye River is 125.34 kg/m 3 and occurs in July, which has an average discharge of 42.6 m 3/s that is much less than the average monthly discharge in August. It is found that both the runoff modulus and sediment transport modulus at Wenjiachuan GS on the Kuye River has a clear downward trend. During the summer season from July to August, the sediment transport modulus at Wenjiachuan GS is much higher than those at Toudaoguai and Longmen GSs on the Yellow River. The easily erodible loess in the Kuye River watershed and the sparse vegetation are responsible for the extremely high sediment yield from the Kuye River watershed. The analyses of the grain size distribution of suspended load in the Kuye River are presented. The average monthly median grain size of suspended load in the Kuye River is largest in February and then decreases until June. In July, the average monthly median grain size of suspended load approaches another peak and decreases until September. Then, the median grain size of suspended load starts to increase until February of the following year. However, the average monthly median grain size of suspended load in the Yellow River at Toudaoguai and Longmen GSs is the smallest between early summer and late fall. The median grain size in the Yellow River starts to increase in November and approaches the largest size in January.