Department of Civil and Environmental Engineering, Tokyo Metropolitan University, 1-1, Minami-Osawa, Hachioji, Tokyo 192-0397, Japan.
Sci Total Environ. 2021 Jan 20;753:142025. doi: 10.1016/j.scitotenv.2020.142025. Epub 2020 Aug 27.
The seasonal and fortnightly erosion and sedimentation pattern as well as the bonding characteristics of the mud deposit at the estuarine turbidity maximum (ETM) zone of the macrotidal Chikugo River estuarine channel were studied during 2005-2008 using the periodical topographic surveys and mud sampling along with continuous monitoring of water level, turbidity and flow velocity. The results revealed that the estuary was influenced by the tidal forcing during the dry season. This tidal forcing accelerated the net landward sediment transport and sedimentation takes place in the estuarine channel. On the contrary, the river discharge dominated the estuary during the rainy season which eroded those mud deposit in the estuarine channel and exported to the downstream and the sandy base layer appeared at the bottom. During the dry season, a mud deposit of 1.5-1.8 m thick was formed which was characterized by 90% of mud (fine silt and clay) and 10% of fine sand. The high viscosity ratio and loss on ignition of this mud deposit revealed that its consolidation begins at the early stages of deposition due to thixotropy and the presence of organic matter. This consolidation process in the natural environment will be several times higher than that of the disturbed mud, which will help the sediment surface to maintain stability against erosion even at high velocities. Moreover, the consolidation of the mud deposit has a strong impact on the seasonal changes in estuarine morphology other than external forcing such as river discharge, tides, wind and availability of sediments.
2005 年至 2008 年期间，利用定期地形测量和泥样采集以及连续监测水位、浊度和流速，研究了大潮河流河口的最大浑浊带（ETM）区的季节性和 fortnightly 侵蚀和淤积模式以及泥沉积物的粘结特性。结果表明，河口在旱季受潮汐力的影响。这种潮汐力加速了净向陆的泥沙输运，导致河口河道发生淤积。相反，雨季河流流量占主导地位，侵蚀了河口河道中的泥沙，并将其输送到下游，在底部出现了沙质基底层。旱季形成了 1.5-1.8 米厚的泥沉积物，其特征是 90%的泥（细砂和粘土）和 10%的细砂。这种泥沉积物的高粘度比和烧失量表明，由于触变性和有机质的存在，其固结在沉积的早期阶段就开始了。这种自然环境中的固结过程比受干扰的泥要高几倍，这将有助于沉积物表面在高流速下保持稳定，防止侵蚀。此外，泥沉积物的固结对河口形态的季节性变化有很大影响，而不仅仅是河流流量、潮汐、风和沉积物可利用性等外部强迫因素。
