1977年以来黄河临河段河岸冲淤变化及河道萎缩速率

不同时段河道的侧向侵蚀/加积面积变化的定量研究可以揭示河道的变化特征。以黄河临河段213 km长的河段为研究对象,利用1977年以来19个时段基于遥感影像绘制的河道平面形态图的面积变化来估算其4个亚河段（S1、S2、S3和S4）在不同时段的河岸侧向侵蚀/加积面积以及全河段的河道平均萎缩速率。研究结果表明,黄河临河段左右河岸在37年间都表现为侧向净加积,其4个亚河段左岸的侧向累计加积面积分别为33.16 km²、49.59 km²、29.52 km²和30.85 km²,其中1995-2000年的加积面积分别占到其总加积面积的85.5%、51.2%、47.2%和104.6%;右岸的侧向累计加积面积分别为30.83 km²、8.74 km²、26.44 km²和18.76 km²,而1995-2000年的加积面积分别占到其总加积面积的57.2%、111.9%、65.7%和61.6%。该河段河道面积1977-2001年具有减小趋势,2001年之后河道表现为侧向侵蚀、加积的交替变化,1977-2014年间河道平均萎缩速率为6.16 km²/yr。该河段河道平面形态值最明显的变化也发生在1990s,与1995年相比,2000年的河道长度增加了5.8%,河道面积减少了39.4%,河道平均宽度减小了42.8%,弯曲系数增加了6.6%。黄河临河段河道形态剧烈变化及河道严重萎缩都发生在1990s,这主要是黄河上游刘家峡和龙羊峡水库联合运行导致汛期水沙量大量减小所致,4个亚河段的河岸冲淤变化还受到局部河岸物质结构、护岸工程及水动力差异的影响。随着2000年后河流综合管理措施的调整,黄河临河段河道的上述变化趋势明显弱化,河流健康程度有所好转。

Variation of channel lateral erosion/accretion and channel shrinkage rate in the Linhe Reach of the Yellow River since 1977

Taking the Linhe reach of the Yellow River with a channel length of 213 km as an example, this paper evaluated the area changes of channel bank erosion/accretion in four sub-reaches (S1, S2, S3 and S4) during 19 different periods on the basis of remote sensing images since 1977. Furthermore, the mean channel shrinkage rate for the whole river reach was obtained. The results show that the left and right banks of the Linhe reach were dominant in lateral net accretion during the period 1977-2014. For the left bank of the four sub-reaches, the accumulative lateral accretion areas during 1977-2014 were 33.16 km², 49.59 km², 29.52 km² and 30.85 km², respectively, while the lateral accretion areas during 1995-2000 accounted for 85.5%, 51.2%, 47.2% and 104.6% of the accumulative values, respectively. For the right bank of the four sub-reaches, the accumulative lateral accretion areas in 1977-2014 were 30.83 km², 8.74 km², 26.44 km² and 18.76 km², respectively, while the lateral accretion areas during the period 1995-2000 accounted for 57.2%, 111.9%, 65.7% and 61.6% of the accumulative values, respectively. The channel area of the Linhe reach was characterized by a reduction tendency from 1977 to 2001, and alternate erosion and accretion after 2001. The channel mean shrinkage rate of the Linhe reach was 6.16 km²/yr during the period 1977-2014. The most remarkable change of channel planform of the Linhe reach also occurred in the 1990s. Compared with 1995, the channel length and sinuosity increased by 5.8% and 6.6% and the channel area and mean width decreased by 39.4% and 42.8% in 2000, respectively. Significant channel planform changes and channel shrinkage for the Linhe reach occurred in the 1990s, which was mainly influenced by the joint-operation of the Longyangxia and Liujiaxia reservoirs since 1986, which resulted in substantial reductions of runoff and sediment fluxes in flooding season in a year. In addition, the bankerosion-accretion for the the four sub-reaches was also affected by the physical properties of local bank, protection engineering of channel bank and hydrodynamic differences. With the implementation of integrated river management measures since 2000, these changes have been significantly weakened and the river's health has been restored.