珠江河口磨刀门口外东西两汊实测分流比分析

磨刀门是珠江河口八大口门中泄洪量最大的口门,口外已形成稳定的东西两汊滩槽格局及中心拦门沙。两汊的分流比是磨刀门河口治理的重点关注问题。根据磨刀门河口及口外东西两汊2015年9月10～11日大潮同步水文观测资料,分析了东西两汊实测流速、流向及分流比特征。结果表明:东西汊总体以往复流为主,在转潮过程会出现一定的旋转流;落潮时表层流速大,底层流速小;涨潮时底层流速大,表层流速小,在转潮时刻会出现短暂表落底涨的现象;西汊的落潮量分流比大于东汊,且净泄量分流比为66%,是磨刀门入海口的主要泄水通道;而东汊的涨潮量分流比大于西汊,是磨刀门入海口的主要涨潮通道。因此,在磨刀门口外治理规划时,需重点考虑东西两汊的自然演变及分流比情况,保证其泄洪纳潮的功能。

Analysis on measured discharge ratio of east and west branches outside Modaomen entrance of Pearl River estuary

Modaokou entrance is the largest among the eight entrances of the Pearl River estuary in terms of flood discharge. Two branches (east and west) and a central sandbar outside of Modaokou entrance are rather stable. The discharge ratios of the two branches are crucial to the estuary regulation of Modaokou entrance. According to the synchronous hydrologic data obtained during the spring tide from September 10th to 11th of 2015 at outside of Modaokou entrance and anabranch, we analyzed the characteristics of measured flow velocities, flow directions and discharge ratios. The results showed that reciprocating flow is the major form of river flows for the two branches, and rotary current appears sometimes during the turning of the tide. During ebb tide, surface flow velocity is high while the bottom is low; during rising tide, flow velocity is high at the bottom and low on the surface, and a temporary phenomenon of "velocity on surface increases while decreases at the bottom" appear at the turning of tide. Discharge ratio in west branch is larger than that of the east branch during ebb tide with net discharge ratio of 66%, which is the main drainage channel of Modaokou estuary to the sea; discharge ratio in the east branch is larger than that of the west branch during rising tide and the east branch is the main tidal channel. In order to ensure the flood discharging and tide inflowing abilities of anabranch, the anabranch evolution processes and discharge ratios should be taken into consideration when developing plans for the two branches.