黄河银川平原段河岸摆动速率变化及原因

Lateral shift rate variation of the river banks in the YinchuanPlain reach of the Yellow River and its causes

研究选取黄河银川平原全长196 km的河段,以1975年、1990年、2010年和2011年四个年份的卫星影像数据绘制的左右河岸线,与设立的平均间隔为1.3 km的153个河道固定横断面的交点位置的变化,估算了1975-1990年、1990-2010年和2010-2011年三个时期的河岸平均摆动速率。结果表明,该河段左岸以向右摆动为主,在上述时期左岸总的平均摆动速率分别为36.5 m/a、27.8 m/a和61.5 m/a;右岸在1975-1990年以向右摆动为主,此后则以向左摆动为主,其摆动速率分别为31.7 m/a、23.1 m/a和50.8 m/a。在1975-2011全部36年间,左右河岸的年均摆动速率分别为22.3 m/a和14.8 m/a。河岸摆动速率在A、B、C三个河段相差悬殊,在1975-2011的36年间,左岸向左和向右的平均摆动速率之比分别为1:7.6:4.6和1:1.7:3.8;右岸向左和向右的平均摆动速率之比为1:1.8:1.2和1:5.6:17.7。显然,无论左岸右岸,它们在A段的摆动速率最小,向左摆动速率最大的出现在B段,而向右摆动速率最大的则是C段。河岸摆动速率在时序上的增大现象主要受制于人类筑坝蓄水等引起汛期流量的逐渐减小,而空间变化主要受制于河岸物质组成的区域差异。

It is important to examine the lateral shift rate variation of fiver banks in different periods. One of the challenges in this regard is how to obtain the shift rate of fiver banks, as gauging stations are deficient for the study of river reaches. The present study selected the Yinchuan Plain reach of the Yellow River with a length of 196 km as a case study, and searched each point of intersection of 153 cross-sections （interval between two adjacent cross-sections was 1.3 km） and fiver banks in 1975, 1990, 2010 and 2011, which were plotted according to remote sensing images in those years. Then the shift rates for the points of intersection during 1975-1990, 1990-2010 and 2010-2011 were calculated, as well as the average shift rates for different sections and different periods. The results show that the left bank of the river reach shifts mostly to the fight, with the average shift rates being 36.5 m/a, 27.8 m/a and 61.5 rn/a in the three periods, respectively. Contemporarily, the right bank shifts mostly to the fight in the first period, while it shifts to the left in the second and third periods, with the average shift rates being 31.7 m/a, 23.1 m/a and 50.8 rn/a in the three periods, respectively. The average shift rates for the left and right banks during the period 1975-2011 are 22.3 m/a and 14.8 m/a, respectively. The bank shift rates for sections A, B and C are different. The shift rate ratio of the left bank in the three sections is 1：7.6：4.6 for shift to the left and 1：1.7：3.8 for shift to the fight, while that of the fight bank is 1：1.8：1.2 for shift to the left and 1：5.6：17.7 for shift to the right during the period 1975-2011. Obviously, the average shift rate is the least in section A, while it reaches the maximum in section B for shift to the left and in section C for shift to the right. The temporal variation of the shift rate is influenced by human activities, while the spatial variation is controlled by the local difference in bank materials.