Abstract:
The Yellow River flows through an extensive aeolian alluvial plain in Ningxia and Inner Mongolia plateau, which extends from Xiaheyan in Ningxia to Toudaoguai in Inner Mongolia. The Hedong sandy land, the Ulanbuh Desert and the Kubuqi Desert all border on the Yellow River. Frequent strong winds and erodible surfaces cause extreme wind-erosion process in the watershed of Ningxia-Inner Mongolia reach of the Yellow River. A large amount of aeolian sediment flows into the main stream and tributaries of the Yellow River by particle saltation and dune avalanche, which result in the continuous elevation of riverbed. Especially since 1986, the combined operation of Longyangxia Reservoir and Liujiaxia Reservoir has decreased the number and discharge of the flood crest, and lowered the erosiveness of the flow in the upper reach of the Yellow River. In this situation, the siltation of the Ningxia-Inner Mongolia reach of the Yellow River is severer and severer. To resolve the silting problem in this reach, it is urgent to estimate the spatial and temporal variations of wind erosion hazards and the quantities of aeolian sediment fed into the river in this watershed. In this study, the models of IWEMS (integrated wind-erosion modelling system) and RWEQ (revised wind erosion equation) were selected to estimate the wind erosion modulus in this watershed. The observed data in the field in 2011 and 2012 were used to calibrate the models, and the calibration result showed that the simulation accuracies of the 2 models were both satisfactory. Using the calibrated models, the wind erosion moduli in this watershed were obtained. The results showed that the wind erosion moduli in this watershed ranged from 0 to 27 780.6 t/(km2·a) in the period from 1986 to 1995, from 0 to 33 673.1 t/(km2·a) during 1996-2002, from 0 to 37 251.3 t/(km2·a) in the period from 2003 to 2007, and from 0 to 16 111.4 t/(km2·a) in the period from 2008 to 2013, respectively. Since 1986, the wind erosion hazards mainly occurred in the sandy lands such as the Ulanbuh Desert, the Kubuqi Desert and the Hedong sandy land. The wind erosion modulus of the Hedong sandy land gradually dropped from 1986 till now, but the wind erosion modulus of the Ulanbuh Desert was increasingly highlighting in this period, and this desert became to the region with severest wind erosion hazard in the whole watershed. The results also showed that the areas having wind erosion risk in the watershed of the Ningxia-Inner Mongolia reach of the Yellow River were diminishing gradually in these years. The average wind erosion modulus of this watershed was also decreasing, and the fitting regression function between average wind erosion modulus and time showed that the slope was high to -182.81. Based on the estimated wind erosion modulus in watershed of Ningxia-Inner Mongolia reach of the Yellow River, the quantities of aeolian sediment blown into the different reaches of the Yellow River were calculated by aeolian sediment transport equations. The results showed that the Shizuishan- Bayangol reach had the highest value, and the average quantity of aeolian sediment blown into the Yellow River was 9.31×106 t/a. The quantity in the Xiaheyan-Qingtongxia reach was lowest, and it was only 7.6×105 t/a. Excluding in Shizuishan- Bayangol Reach, in the other reaches, the quantities of aeolian sediment blown into the river did not show the trend of obviously decreasing with time. Through analyzing the relationship between wind erosion modulus and changes of climate and land use, we found the dropping wind erosion modulus in watershed of Ningxia-Inner Mongolia reach of the Yellow River was mainly affected by the climate change. The study results in this paper are not only meaningful for solving the siltation in Ningxia-Inner Mongolia reach of the Yellow River, but also important to the complete the protection systems of wind-blown hazards in this watershed.