长江口咸潮入侵变化特征及成因分析

本文基于海洋站潮位观测数据、海平面变化影响调查信息以及长江口水文站径流量数据等，重点分析了2009−2018年长江口咸潮入侵的变化特征及其影响因素，分析结果表明：(1)长江口咸潮入侵季节变化特征明显。咸潮一般从每年的9−10月开始入侵，翌年4−5月结束。3月咸潮入侵次数最多，达12次。2009−2018年，长江口咸潮入侵次数和咸潮持续时间均呈下降趋势，2009年长江口咸潮入侵次数最多，达13次，时间均发生在10月至翌年的4月；咸潮持续时间年际变化较大，2011年咸潮入侵持续时间最长，累计为55 d。2015−2018年，咸潮入侵次数和入侵持续时间均明显减少，2018年没有监测到咸潮入侵过程。(2) 1−4月，长江口处于季节性低海平面期，且同期径流量少，但是受东亚季风影响，持续的增水过程使得增减水−径流量综合影响指数明显偏高，其中1月、2月、3月的影响指数分别为1.5、1.9和1.6，该时段长江口的咸潮入侵过程主要受增减水的影响。5−7月，长江口径流量明显增加，海平面−径流量综合影响指数均小于0，径流的作用强于海水上溯。8月，长江口径流量开始下降，虽然季节海平面较高，但是长江口呈现明显的减水过程，海平面−径流量和增减水−径流量的综合影响指数分别为0.1和−1.6，基本不会发生咸潮入侵。9月，长江口处于季节高海平面期，并且以增水为主，海平面−径流量和增减水−径流量的综合影响指数较大，分别为1.2和1.0，易发生咸潮入侵。10月、11月长江口海平面−径流量的综合影响指数分别为1.5和0.8，径流影响弱于海水上溯，易发生咸潮入侵。(3) 2009−2018年发生的48次咸潮入侵过程有2/3恰逢天文大潮。在某些年份长江口沿海基础海平面偏高，若持续增水恰逢天文大潮，则加剧咸潮入侵的影响程度。

The variation characteristics and causes analysis of salt tide intrusion in the Changjiang River Estuary

Based on tide gauge observation data, sea level change impact investigation information and runoff observation data, the changing characteristics and causes of salt tide intrusions at Changjiang River Estuary during 2009-2018 were emphatically analyzed. Results show that: (1) Seasonal variations of salt tide intrusions at Changjiang River Estuary are obvious, which usually begin from September to October, and end in April or May of the following year. The most frequent occurrence is in March, reaching 12 times. The occurrence and duration of salt tide intrusions marked downward trend as a whole during 2009-2018. The intrusion occurrence was the most in 2009, reaching 13 times, all appeared during October to April of the following year. Annual variation of salt tide intrusion duration was obvious, which was the longest in 2011, reaching 55 days. The occurrence and duration of salt tide intrusions all decreased obviously during 2015-2018, and there was no salt tide intrusion in 2018. (2) From January to April, the seasonal sea level is low, and runoff is small in the Changjiang River Estuary. As influenced by the East-Asian Monsoon, the surge-runoff impact index is high, valued 1.5, 1.9 and 1.6 for January, February and March respectively during 2009-2018. Salt tide intrusion is mainly influenced by surge during this period. For the time of May to July, the runoff increases significantly and becomes dominant, and the sea-level-runoff impact indexes are less than zero. In August, the runoff of the Changjiang River begins to decrease. Seasonal sea level is high, but there is continuous negative surge during this time. Correspondingly, the sea level-runoff impact index is 0.1, and the surge-runoff impact index is -1.6. And salt tide intrusion hardly happens. In September, the seasonal sea level is high, and surge is obvious. The sea level-runoff as well as surge-runoff impact indexes is 1.2 and 1.0 respectively, and salt tide intrusion is very likely to happen. For the time of October and November, the sea-level-runoff impact indexes are 1.5 and 0.8 respectively, and the Changjiang River Estuary is prone to salt tide intrusions. (3) Two-thirds of the 48 salt tide intrusions in the past 10 years occurred in the period of astronomical high tide. The basic sea level is high in some years in the Changjiang River Estuary. In the cases of continuous surge and astronomical high tide, the impacts of the saltwater intrusion will be aggravated.