Research On The Changes Of The Hydrodynamic Environment Before And After Reclamation In Luoyuan Bay

Luoyuan Bay is one of the top six deep harbors in Fujian Province. It is located in the northeast coast of Fujian with the only narrow mouth at the northeast corner, which is the only way to connect with open sea. Because Fujian is at the hill country with large tidal flats, reclamation is the most economic way to resolve the land shortage problem and it also can bring the huge profit with the negative impact at the same time. The water environment quality in Luoyuan Bay is descending during recent years for the changes of hydrodynamic environment. These environment problems will be the hidden trouble for the harmonic development of this place.According to the features of Luoyuan Bay, such as the complex terrain, flexural coastline and the large area of tidal flat, 3-D hydrodynamic numerical model FVCOM is used to simulate this place. And in order to ensure the accuracy of this model, the observational data are used to test it.Firstly, I simulate the present situation of hydrodynamic environment in Luoyuan Bay and conclude the tidal, fluid field, residual current, tidal capacity, water exchange rate, etc. Secondly, in order to reproduce the hydrodynamic environment before the top three reclamations, it needs to redesign the numerical experiment at the same boundary and hydrodynamic conditions. Tide, flow field, residual current, tidal capacity, water exchange rate are concluded in this numerical experiment. According to the comparison before and after reclamation, it can be concluded that the main tidal constituents M2 and S2 are generally keep the same, but the sallow water constituents M4 and MS4 are affected greatly. The amplitude of M4 and MS4 increases by 60%, epoch of partial tide increases by 10%,The coefficient of the tidal level shoaling coefficient grows slowly at present situation, and the growing range before reclamation is much larger than present. They are 2.5 times and 2 times compared with the present at line 1 and line 2 separately. The largest growing range is near the Da Guanban and Song Shan area, which means that the non linear effect of tidal is the strongest at there. And the increasing range also depends on how close to the reclamation areas. So the tidal flats have huge influence to the sallow water tidal component. The average flow velocity before reclamation is faster than present situation. The flow velocity area higher than 0.6 m/s distributes as a belt along the northwest deep trough before reclamation, while it is only confined to the east of 119.73°E and shaped as several small blocks after reclamation. Although the range becomes larger during the ebb tide, it is still much smaller than it before reclamation. According to the analysis results from the 8 sensitive flow velocity points in the bay, it can be concluded that the flow direction before reclamation is almost the same as the present, while the speed is faster than present situation. It would be more obviously when it is more close to the reclamation area. The residual current is also stronger than present situation and vertical structure is totally different between before reclamation and present. It flows out at top and in at bottom present, while it is opposite before reclamation. The tidal capacity decreases for the reclamation, which declines 37.87% during the spring tide and 27.74% during the neap tide. The half life time becomes from 12 days before reclamation to 14.3 days at present, which is conformed that self-purification capacity of the bay declines and that would be a disadvantage to the water quality environment. The water exchange rate is different at different layer, bottom is lower than middle, middle is lower than surface and they are all higher before reclamation than present at the same layer.Finally, in order to study the important impact of tidal flat to the hydrodynamic environment at Luoyuan Bay, it is designed another numerical experiment to calculate the varieties in the bay at the condition of no tidal flats at all. It does not use the wet-dry method for there is no tidal flat. The experiment results show that the sallow water constituents have a great change with the amplitude of M4 declining more than 70% and the epoch of partial tide of M4 and MS4 increasing more than 70%, which are greater than before and after reclamation. The flow velocity decreases more than 50% and the direction turnaround time is earlier about 1 hour. The residual current horizontal distribution becomes uniform and weak except for Kemen channel. The vertical distribution of it is quite different from present. The water area in the bay decreases by 45.5% without tidal flat and the tidal capacity declines by 56.45% during the spring tide, 46.23% during the neap tide compared with present. The water exchange rate also decreases 1.02% at the mouth, 12.12% in the bay and 4.57% at the whole area. The half life time delays 8.2 days compared with present. All about above, it can be concluded that tidal flat plays the key role during the hydrodynamic process in the bay.Through the systematic analysis of hydrodynamic environment of Luoyuan Bay, the results show that tidal flats have great influence to the hydrodynamic environment and water quality, which can be the reference to use this rich resource reasonably in Luoyuan Bay.