长江口北支平面改善方案对咸潮倒灌的控制效果

为了分析长江口北支外顾园沙3种不同围圈方案对咸潮倒灌的控制效果,基于EFDC二维水盐模型,模拟出方案实施前后南北支流场、盐度场分布以及重要水源地盐度变化。结果表明:(1)工程后北支口连兴港处潮流量减小,且单独圈围方案(方案一)进潮总量最小;(2)方案一流场变化最小,并北岸方案(方案二)、并南岸方案(方案三)导堤内侧深槽流速明显增大;(3)方案三北支高盐水上溯范围最大,而南支水源地盐度下降,陈行水库、青草沙水库、东风西沙盐度值分别下降32.16%,27.90%和13.38%;(4)方案二北支盐度通量与现状最接近,方案三盐度通量减幅最大;(5)南支盐度的整体变幅明显小于北支。3种方案下北支口潮动力有所减弱,且潮流量越大减弱效果越明显,但该削弱作用很有限,故对北支咸潮倒灌控制效果并不显著,还需结合其他工程措施。

Effects of controlling salinity intrusion by improvement projects in North Changjiang branch in estuary

To analyze the salinity intrusion controlling effect by three proposed enclosing schemes for Guyuansha sandbar at offshore of North branch in Changjiang estuary, based on the two-dimensional EFDC flow-salinity model, the variations of the flow field, the salinity field and the salinity in important water sources area of South and North branches are simulated before and after the project implement. The results show that:① tidal flow at Lianxinggang sand bar in the north branch decrease after the project completion, and the total inflow tide is the lowest for P1(the sand bar enclosed) ; ② the flow filed changes smallest for P1 and the flow velocities in the inside deep channel of the guiding levee increase significantly for P2（integration of Lianxinggang sand bar and north bank）and P3(integration of Lianxinggang sand bar and south bank; ③ for P3, high density salinity water in the North branch flows upward mostly while the salinity of water source in South branch decreases, going down by 32.16%, 27.9%, and 13.38% respectively for Chenxing reservoir, Qingcaosha reservoir and Dongfengxisha reservoir; ④ the salinity flux in the North branch is close to the present condition for P2 and it deceases mostly for P3; ⑤ the general variation of salinity in South branch is less evidently than that of the North branch. The tidal dynamic of the North branch will become weaker for all three schemes, and the weakening effects are more evident for larger flow but limited in a certain degree, so other co-action of engineering measures for controlling salinity intrusion are needed.