1986-2013年黄河宁蒙河段风蚀模数与风沙入河量估算

为缓解宁(宁夏)蒙(内蒙古)河段的淤积问题,需要对该河段风蚀灾害和风沙入黄量的时空变化进行研究。该文选取综合风蚀模拟系统(integrated wind-erosion modeling system,IWEMS)和修订版风蚀方程(revised wind erosion equation,RWEQ)对1986-2013年黄河宁蒙河段风蚀模数进行了估算,并结合风沙输移方程,对不同河段的风沙入黄量进行了计算。发现宁蒙河段的风蚀灾害主要发生在乌兰布和沙漠、库布奇沙漠和河东沙地等沙漠区域。自1986年以来河东沙地的风蚀模数逐渐降低,而乌兰布和沙漠的风蚀模数则逐渐凸显,成为宁蒙河段风蚀最严重的区域。1986-2013年间,整个宁蒙河段受风蚀灾害的面积逐渐减小,平均风蚀模数迅速下降,线性拟合函数斜率高达-182.81。风沙入黄量结果显示,石嘴山—巴彦高勒段的年均风沙入黄量最大,高达9.31×106 t/a;下河沿—青铜峡段最小,其值仅为7.6×105 t/a。另外,除石嘴山—巴彦高勒段之外,其余河段风沙入黄量并未呈现出明显的减小趋势。通过对宁蒙河段气象和土地利用数据的分析,发现宁蒙河段的风蚀模数的变化主要受气候条件的影响。该研究结果可为解决黄河淤积问题、完善黄河沿岸风沙防护体系提供参考。

Wind erosion modulus and quantity evaluation of aeolian sediment feed into river in watershed of Ningxia-Inner Mongolia Reach of Yellow River from 1986 to 2013

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.