罗源湾海洋倾倒区抛泥过程含沙量增量数值模拟

Numerical simulation of sediment concentration increment during dumping in Luoyuan Bay ocean dumping site

罗源湾及周边海域港口、航道开发利用工程产生大量的疏浚物,为准确掌握罗源湾临时性海洋倾倒区抛泥过程中泥沙运动规律和含沙量增量分布,预测并有效控制倾倒泥沙对倾倒区周边海域环境影响,基于FVCOM数值模式和有限差分理论,建立倾倒区二维潮流动力和悬浮泥沙输移扩散数学模型,分析计算海域潮流动力特征和悬浮泥沙输移扩散情况.经过监测数据率定验证,模型计算结果与实测潮位、潮流过程曲线吻合较好,含沙量曲线与实测值比较接近.利用建立的模型预测倾倒区疏浚泥倾倒过程中含沙量增量及影响范围,倾倒区含沙量本底值为22～58 mg/dm3,单次抛泥7 300 m3时,含沙量增量10 mg/dm3（超一、二类水质标准）,扩散距离小于3.5 km,抛泥1 h后含沙量增量基本降至10 mg/dm3以下,6 h后含沙量增量降至1 mg/dm3以下；连续120 d随机点抛放时,含沙量增量100 mg/dm3（超三类水质标准）的包络面积为1.40 km2,主要分布在倾倒区附近0.74 km范围内,含沙量增量10 mg/dm3的包络面积为9.27 km2,最大扩散距离为3.25 km.最后,结合模型预测结果和海域功能区划要求,建议倾倒施工单位选择落潮时段进行倾倒作业,保证在空间和时间方面均匀倾倒,尽量避免或减少对附近的三都澳大黄鱼繁育保护区产生影响.

The sea port and channel engineerings in and around Luoyuan bay produce a large number of dredged mud. In order to know the movement rules and concentration increment of suspend sediment caused by dumping dredged mud in the temporary sea dumping ground near Luoyuan bay for accurately predicting and effectively controlling the influence of marine environment around the dumping area,we build a two-dimensional tidal current and sediment transport-diffusion model based on the FVCOM model and finite difference method,to simulate and analyse the tidal current and sediment transportation. After monitoring data validation,the calculation results show well consistent with the measured water level and tidal current,and sediment concentration curves fit the measured values. We use the model to forecast the sediment concentration increment and area influenced after dumping. The background concentration value of the ocean area is 22 ～ 58 mg / dm3. For dumping 7 300 m3dredged mud at the central dumping ground,the maximum distance of the sediment concentration increment of 10 mg / dm3（exceeding class I and II of the national water quality standard）is 3. 5 km. The sediment concentration increment of 10 mg / dm3 disappeared an hour later,increment of 1 mg / dm3disappear 6 hour later. While dumping 7 300 m3dredged mud randomly in the ocean dumping area at ebb and flow tide moment for 120 days,the area of sediment concentration increment of 100 mg / dm3（exceeding class III of the natinal water quality standard）is 1. 40 km2within the scope of 0. 74 km near the center of dumping area. The area of sediment concentration increment of 10 mg / dm3is 9. 27 km2 within the scope of 3. 25 km. In conclusion,when considerations both the local marine functional zoning requirements and the results of model forecast it suggested that the ebb tide time be chosen for dumping for better distributions of dredged mud in space and time to reduce the impact on the Pseudosciaena crocea breeding area nearby in Sandu-ao bay.