黄河口尾闾河道近40年河床断面及平面形态调整特点

Variations in planform and cross-sectional geometries of Qingshuigou channel in Yellow River estuary(1976-2016)

清水沟改道及龙羊峡、小浪底水库运用后,黄河口尾闾河道的河床形态发生了显著调整。黄河口尾闾河道河床调整过程总体分为四个阶段,分别为:1976—1980年淤滩成槽阶段,1980—1984年单股入海阶段,1984-1999年主槽萎缩阶段,1999—2016年河床冲刷阶段。研究发现:清水沟改道初期,河床平面形态宽浅散乱,河口迅速延伸,河长从75.1 km增加到93.2 km。1980年后,河道逐渐形成单一顺直的河型,入海口逐渐南偏,河口延伸速率减小。1984—1999年,主槽萎缩严重,平滩面积减小了61%;深泓摆动剧烈,其摆动距离及强度分别为102 m及0.17。小浪底水库运用后,河床剧烈冲刷,平滩水深增加了41%;深泓摆动幅度减小,其摆动距离及强度分别减小至37 m及0.09。此外还建立了1999年后平滩形态参数及深泓摆动强度与前4年汛期平均水流冲刷强度的经验关系,一定条件下可用于反演河床形态随水沙条件的调整过程。

Remarkable channel adjustments have occurred in the Yellow River estuary since the 1996 artificial avulsion from the Diaokouhe course to Qingshuigou course. The channel has evolved through four stages: rapid aggradation, undercutting, shrinkage, and severe degradation. Its geometrical variations indicate that(i) in the initial stage of 1976-1980, the study reach was drastically aggraded, with its length increasing from 75.1 km to 93.2 km;(ii) during 1980-1984, numerous branches near the river mouth were gradually coalescing into a single channel toward the southeast, and channel undercutting was dominant;(iii) after 1984, the channel’s bankfull area was decreased by 61% in severe shrinkage caused by the operation of Longyangxia reservoir, with its thalweg migrating frequently at a migrating intensity and width of 0.17 and 102 m respectively;(iv) during 1999-2016, its bankfull depth was increased by 41% and the migrating intensity and width decreased to 0.09 and 37 m respectively. In addition, we develop empirical relationships of reach-scale bankfull dimensions and thalweg-migrating intensity versus the average flow scour intensity over previous four years, which give satisfactory predictions of channel adjustments highly correlated with the real case.