Azhikodan Gubash, Yokoyama Katsuhide
Dept. of Civil and Environmental Engineering, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji-shi, Tokyo 192-0397, Japan.
Sci Total Environ. 2019 Sep 20;684:281-295. doi: 10.1016/j.scitotenv.2019.05.289. Epub 2019 May 23.
The spatio-temporal morphodynamics in relation to the fortnightly tidal variations and seasonal river discharge variations in a meandering estuarine channel were investigated. Intensive topographic surveys (longitudinal and transverse) every 3-4 months using a digital sonar system equipped with a differential global positioning system and continuous monitoring of salinity and turbidity with moored instruments were carried out during 2009-2012 in the upstream section of the highly turbid macrotidal Chikugo River estuary, Japan. The results revealed that the tidal flow dominated in the estuary for most of the year except for the rainy season in which river flow dominates. During the low flow season, tidally induced net upward sediment transport dominates and deposition takes place in the upstream section especially in the inner part of the meander. It contributes towards the strengthening of the existing estuarine turbidity maximum (ETM) in the upstream section of the estuary, and the channel capacity reduced gradually during this period. However, large flood events led to the breakdown of this ETM zone in the upstream during the rainy season and exported the sediments to the downstream tidal flat which resulted in the rapid increase of channel capacity. This further exhibited that the ETM zone was migrated to the downstream part of the estuary during the rainy season. There were significant differences in the seasonal trends of morphological evolution in the estuary which further greatly influenced the channel capacity. The drastic changes in channel morphology due to the sediment export by the high river flow during the flood season was approximately recovered through the sediment import by the fortnightly tidal cycle during the dry season over a seasonal basis. The study concludes that the morphological changes in the tide dominated estuaries are strongly influenced by the fortnightly tidal variations as well as the seasonal river discharge variations.
研究了蜿蜒河口河道中与半月潮变化和季节性河流流量变化相关的时空形态动力学。2009年至2012年期间，在日本高浊度强潮筑后河河口的上游段，使用配备差分全球定位系统的数字声纳系统每3 - 4个月进行一次密集地形测量（纵向和横向），并使用系泊仪器对盐度和浊度进行连续监测。结果表明，除了河流流量占主导的雨季外，一年中的大部分时间河口潮汐流占主导。在枯水期，潮汐诱导的净向上泥沙输运占主导，沉积物在上游段尤其是河曲内部沉积。这有助于加强河口上游现有的河口浊度极大值（ETM），在此期间河道容量逐渐减小。然而，大洪水事件导致雨季上游该ETM区域崩溃，沉积物被输送到下游潮滩，导致河道容量迅速增加。这进一步表明雨季ETM区域迁移到了河口下游部分。河口形态演变的季节性趋势存在显著差异，这进一步极大地影响了河道容量。在一个季节内，洪水季节高河流流量导致的泥沙输出引起的河道形态剧烈变化，通过旱季半月潮汐周期的泥沙输入大致得到恢复。研究得出结论，潮汐主导的河口形态变化受到半月潮变化以及季节性河流流量变化的强烈影响。
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