NUMERICAL SIMULATION OF SALTWATER INTRUSION IN A LOCK WITH LONG CANAL ADOPTING COUPLED BOX MODEL AND THREE-DIMENSIONAL MODEL

In order to enhance river-ocean connection and improve shipping capacity, plans have been made to build a multichamber lock and a canal to connect the sea and inland lake. The construction will alter the inland topography and the salt distribution in the lake. In the long run, it will influence the surrounding ecosystem significantly. In this research, box model of salt exchange in the lock and three-dimensional model of salt intrusion in canal are set up to predict the salt exchange in lock chambers, water saving basins and the canal. The study shows that the saltwater intrusion in chambers arrives at dynamic balance after several days' functioning of lock, and the salinity in each chamber fluctuates in certain range. However, due to the long distance of canal, saltwater intrusion in the canal is much different from that in lock, and the canal can be divided into three regions according to the intrusion pattern: In the density flow region, salt water is propelled by gravity and goes upstream rapidly. The salinity in this region fluctuates as the opening and closing of lock gate, and comes to dynamic balance at the nearly same time as that in chambers; in the transition region, the impacts of gravity is weaken while the effects of diffusion is becoming stronger, and salt water runs upstream in a moderate velocity. Salinity in this region keeps rising at the beginning of lock's operation, and meets the dynamic balance after a longer time; in the diffusion region, salt water is pushed all by diffusion action, and moves with a much small upstream rate. Salinity in this region becomes constant after a much longer time's slow rising. The study presents a view of salinity variation in locks and its long canal, which is much different form that in locks with short canal. The long cannel slows down the saltwater intrusion from lock to lake, and is helpful for alleviating the intrusion.