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强人类活动驱动下珠江磨刀门河口径潮动力的季节性异变特征分析
张先毅, 杨昊, 黄竞争, 傅林曦, 王恒, 刘俊勇, 欧素英, 刘锋, 蔡华阳, 杨清书
中山大学河口海岸研究所
摘要:
人类活动对河口环境的影响日益增大,揭示强人类活动驱动下河口径潮动力非线性相互作用的异变特征,有利于探究人类活动对河口动力地貌演变的影响机制,对河口区水利工程建设及环境保护等具有重要指导意义。本文基于1960-2016年珠江磨刀门河口沿程潮位站(甘竹、竹银、灯笼山、三灶)的逐月高、低潮位数据及马口水文站的月均流量数据,统计分析磨刀门河口在强人类活动驱动下余水位、潮波振幅及其空间梯度(即余水位坡度和潮波振幅衰减率)的季节性异变特征。结果表明,1990年和2000年为磨刀门河口径潮动力的异变年份,1990年前为自然演变阶段,2000年后为恢复调整阶段,1990-2000年为过渡阶段;高强度采砂导致的河床下切使磨刀门河口余水位及余水位坡度显著减小,夏季减小幅度最为明显,沿程平均分别减小0.53m和8.93×10-6;余水位坡度减小导致潮波衰减效应减弱,进而使沿程潮波振幅增大,多年平均增大0.071m;磨刀门河口径潮动力相互作用具有明显的季节性差异,夏季余水位坡度随流量增大在上游抬升明显,冬季余水位坡度在上游显著减小,但在下游略有抬升;随着流量的增大潮波振幅的衰减作用增强,但当流量超过阈值20000m3/s时,余水位坡度引起的底床摩擦增大效应不足以抵消横截面积辐散效应,潮波衰减效应略有减弱。
关键词:  径潮相互作用  余水位坡度  潮波振幅衰减率  强人类活动  季节性变化
DOI:10.11693/hyhz20190900176
分类号:
基金项目:国家重点研发计划项目,2016YFC0402600号;国家自然科学基金项目,51709287号、51979296号;广东省自然科学基金项目,2017A030310321号;广东省水利科技创新项目,2016-20号
Seasonal variations in river-tide dynamics driven by intensive human activities in the Modaomen Estuary of Pearl River
Zhang Zianyi, Yang Hao, Huang Jingzheng, Fu Linxi, Wang Heng, Liu Junyong, Ou Suying, Liu Feng, Cai Huayang, Yang Qingshu
Institute of Estuarine and Coastal Research, Sun Yat-sen University
Abstract:
As the impacts of human activities on estuarine environment increased, it is essential to quantify the alterations in river-tide dynamics driven by intensive human activities, which is particularly helpful for exploring the underlying mechanism of geomorphological evolution as well as guiding the water conservancy planning and environmental protection in estuaries. In this study, we analyzed the seasonal variations of residual water level, tidal amplitude and their spatial gradients (i.e., residual water level slope and tidal damping rate) driven by intensive human interventions based on the observed monthly averaged tidal water levels along the Modaomen estuary (including the Ganzhu, Zhuyin, Denglongshan and Sanzao gauging stations) and the river discharge observed at Makou hydrological station from 1960 to 2016. Results show that the year of 1990 and 2000 can be regarded as the critical points corresponding to the period without (pre-1990) and with (post-2000) intensive human activities, respectively, while the 1990-2000 corresponds to a transitional period. It was shown that riverbed deepening caused by intensive sand excavations tends to reduce the residual water level and residual water level slope along the Modaomen estuary, especially in summer (being 0.53m and 8.93×10-6, respectively). The decrease in the residual water level slope subsequently weakened the tidal damping effect, which results in an increase of the tidal amplitude for the whole channel (increased by 0.071m after intensive human activities). Seasonal variations in the river-tide dynamics in the Modaomen estuary indicate that the residual water level slope in the upstream part increased obviously only in summer with substantial river discharge, while it decreased significantly in the upstream and rose slightly in the downstream part in winter. Although the tidal damping effect will be enhanced with the river discharge, remarkably, it will eventually weaken when river discharge exceeds a threshold approximately 20000m3/s. This has to do with the fact that the damping effect caused by increase of bottom friction due to residual water level slope is not strong enough to compensate the cross-sectional divergence effect leading to an amplification of energy input from riverine forcing.
Key words:  river-tide interaction  residual water level slope  tidal damping rate  intensive human activities  seasonal variation
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