象山港多年围填海工程对水动力影响的累积效应

Cumulative influence of long term reclamation on hydrodynamics in the Xiangshangang Bay

由于土地资源开发和围塘养殖等需要,多年以来象山港实施了大量的围填海工程。单个的小面积围填海工程对海湾的影响并不大,但是在较长时间段内,多个围填海工程的累积效应却比较明显。本文在POM(Princeton Ocean Model)模型的基础上,利用动边界处理技术,针对1963,2003和2010年3个不同时期的岸线与地形进行模拟,计算了不同时期的纳潮量和水交换能力。通过对比发现,较长时间段内实施的大量围填海工程对象山港的纳潮量和水交换累积影响明显:从1963年到2003年,大潮纳潮量减少8.9%,中潮纳潮量减少8.7%,小潮纳潮量减少8.0%,全潮平均纳潮量减少8.6%;从1963年到2010年,大潮纳潮量减少12.7%,中潮纳潮量减少12.7%,小潮纳潮量减少12.4%,全潮平均纳潮量减少12.6%;在2003年岸线和地形下,整个港湾交换30,60和90 d后的平均水交换率与1963年相比分别减少5.3%,4.5%和3.9%;而在2010年岸线和地形下,整个港湾交换30,60和90 d后的平均水交换率与1963年相比分别减少7.7%,6.8%和6.1%。

In recent years,reclamation projects present a trend of large scale and wide range due to land shortage and other factors in the coastal areas.One single small area reclamation project may not change the hydrodynamics a lot,but many such reclamation projects during a long time period could accumulatively influence the flow field,tidal prism,water exchange and even the environment.The Xiangshangang Bay is a typical narrow semi-enclosed bay in the north of Zhejiang province with high tidal range,rich biological resources and favourable natural environment.However,due to land resource shortage,mariculture and other needs,many reclamation projects have been implemented in recent years.Based on POM（Princeton Ocean Model） added with soluble tracer transport model,the variable boundary technique is used to establish the three dimensional model for the Xiangshangang Bay.Then the topography and coastline of 1963,2003 and 2010 are simulated.The models are all cold-started,and the tidal prism and dispersion of the soluble tracer are calculated after the hydrodynamics become stable.The same dynamic parameters and initial conditions are used for the three different coastline and topography models and the same boundary conditions are sued to run the models.The simulated results of 2003 were verified with the measurements from three tidal stations and eight current stations,which shows that the simulated results,no matter the tidal level or the flow speed and direction match the observed data well,which means that the model is good enough to simulate the Xiangshangang Bay hydrodynamics and can be used for further research.Tidal prism and water exchange ability is calculated for the three different periods after running the model stablely for 90 days.Comparison shows that the reclamation accumulated in a long period in the Xiangshangang Bay resulted in evident influence on the tidal prism and water exchange ability： from 1963 to 2003,the spring tidal prism reduced by 8.9%,the middle tidal prism by 8.7%,the neap tidal prism by 8.0% and the average by 8.6%;from 1963 to 2010,the spring tidal prism reduced by 12.7%,the middle tidal prism by 12.7%,the neap tidal prism by 12.4% and the averaged by 12.6 %.The whole bay water exchange rate after 30,60 and 90 days under the coastline and topography of 2003 reduced by 5.3%,4.5% and 3.9% than that of 1963,and reduced by 7.7%,6.8% and 6.1% for the 2010 coastline and topography.Compared with 1963,the largest variation of high and low tidal level of 2003 and 2010 is about 10 cm,and the average variation is less than 5 cm.Generally speaking,the high tidal level change is less than the low one.The averaged high tidal level has slightly raised and the low tidal level has slightly reduced.