Simulation of the Impact of Breakwaters on Hydrodynamic Environment in Laizhou Bay, China

The construction of two sand breakwaters in Guangli Port might cause changes to the marine environment of Laizhou Bay.Tidal flow field and conservative substance transport are simulated by a two-dimensional hydrodynamic model MIKE21 to assess the impact of breakwaters on the hydrodynamic environment.The results show that the construction has minor influences on the tidal currents.The changes mainly occur in the region near the port(about 20 km^(2) in area).The directions of currents during flood tide and ebb tide veer less than 20 degrees,and a maximum change in speed of(0.87±0.1)m s^(−1) occurs in between the breakwaters during ebb tide.However,the self-purification ability of Laizhou Bay is significantly reduced according to the conservative substance transport model,especially in the southwest(about 100 km from the Guangli Port to the estuary of Xiaoqinghe River),where the water exchange rate decreases by 10%–20%.The breakwaters slow down the northward current during ebb tide,which causes the accumulation of pollutants.

Distribution Characteristics and Controlling Factors of Heavy Metals in Surface Sediments from the Bay-Island-Estuary System(BIES):A Case Study in Coastal Waters of Fujian Province,China

Based on the contents of six heavy metal elements in surface sediments from coastal areas of Fujian Province,the distribution characteristics and controlling factors of six heavy metals in a bay-island-estuary system(BIES)were studied.This paper focuses on the influence of the hydrodynamic environment,and systematically discusses how grain size compositions,chemical environment,tidal current,ocean circulation and human activities influence the distribution and transportation of the heavy metals.The results indicated that the distribution and migration of Cu,Pb,Zn and Cr elements were mainly controlled by natural factors such as regional geological background,grain size compositions,and tidal residual currents.In contrast,As and Hg was mainly affected by human factors such as agriculture and industrial manufacturing.In the BIES,where the chemical environment exerted limited influence,the accumulation and migration of heavy metals are mainly influenced by human activities and enhanced by estuary processes as well as the complex sedimentary dynamic environment caused by many bays and islands.

Computational investigation on hydrodynamic and sediment transport responses influenced by reclamation projects in the Meizhou Bay,China

Reclamation projects are the main method of coastal exploitation,and the hydrodynamic environmental effect,together with the sediment transport response of the reclamation project,is important to the project’s site selection and environmental protection.Herein,a 3D numerical model based on the finite volume community ocean model(FVCOM)is applied to simulate the changes in the Meizhou Bay’s hydrodynamic environment and sediment transport after a reclamation project.The reclamation project greatly alters the shape of the shoreline and narrows the bay,leading to a significant change in its hydrodynamic environment and sediment transport.After the project,the clockwise coastal residual current in the corner above the Meizhou Island gradually disappears.An obvious counter-clockwise coastal residual current emerges around the rectangular corner.The tidal prism decreases by 0.65×10^9 and 0.44×10^9 m^3 in the spring and neap tides,respectively.The residence time presents a major increase.These changes lead to the weakening of the water exchange capacity and the reduction of the self-purification capacity of the bay.Currents in the tidal channel weaken,whilst currents in the horizontal channel strengthen.The strength and scope of particle trajectories around the horizontal channel and the Meizhou Island enhance.The suspended sediment concentration(SSC)increases in the majority of the Meizhou Bay but decreases in the lateral bay.The eastern corner of Z2 shows a tendency to erode.The western region of the Meizhou Island,the upper portion of the rectangular corner and the western corner of Z4 show a tendency to deposit.The reclamation project increases the maximum storm surges by 0.06 m and decreases the maximum significant wave heights by 0.09 m.

Seasonal nutrient distribution in the Rupsha-Passur tidal river system of the Sundarbans mangrove forest,Bangladesh

Introduction:The Rupsha-Passur River System(RS)is one of the biggest and important river systems in the Sundarbans estuarine ecosystem.It is the largest fresh water supplier into this mangrove forest.A comprehensive study was undertaken to evaluate the tidal and seasonal variations in nutrient concentrations(nitrate,phosphate,sulphate and ammonia)of the RS during October,2010(Post monsoon),February,2011(Dry winter)and August 2011(Monsoon).In-situ measurement and laboratory analysis were conducted to measure nutrients and other physico-chemical parameters at discrete water layers of five study points under different tidal cycles.Results:Following post monsoon,NH3–N concentration showed seasonal variation with increasing trend(0.0703 to 0.0803 mg/L)in dry winter and then significant dropping(0.013 to 0.019 mg/L)in monsoon period.During field observation,no significant tidal variation in ammonia concentration was identified among the study sites.Post monsoon and winter time observation recorded lower SO4 content(7.301 to 37.508 mg/L)at all the sampling stations while in monsoon period,most of the stations showed higher concentration up to 126.92 mg/L.Contrary to post monsoon season with comparatively higher PO4–P value(0.314 to 1.347 mg/L),winter and monsoon period sampling indicated low phosphate concentrations(0.045 to 0.5 mg/L)in the Rupsha-Passur RS.Most of the study sites showed considerable tidal changes in phosphate value during post monsoon and monsoon season while only two stations went through tidal fluctuation in sulphate content during monsoon period.Concentrations of NO3–N were found to fluctuate between 0.083 and 1.233 mg/L with no distinct seasonal distribution pattern.Tidal variation of NO3–N in the experimental sites was not so prominent during post monsoon period as of winter data.Conclusion:Present study will serve as a basis for future hydrological and environmental studies in the world’s largest Sundarbans intertidal mangrove forest.Study results indicate how nutrient dynamics of such diversified estuarine system are influenced by varying weather conditions.Daily fluctuations in nutrient concentrations and other physicochemical properties due to semidiurnal tidal activity were also figured out through the study.Information generated from the research works will guide all concerned for any future conservation and management initiatives for the world heritage site.

Numerical Simulation of Dissolved Oxygen Supersaturation Flow over the Three Gorges Dam Spillway

The dissolved oxygen concentration in a flow changes with distance downstream of the spillway crest and depends on the geometric configuration of the spillway and the hydraulic and operating conditions.A mathematical model was developed to simulate the turbulent structure of the flow over the spillway of the Three Gorges Dam at the 145 m reservoir water level to study the aeration characteristics and the gas transport.The model was calibrated and verified with measured data.The analysis of distribution of the aeration and the dissolved oxygen showed that the downstream water level,upstream dissolved oxygen content,and the flow discharge all affect the dissolved oxygen saturation downstream of the sluicing dam.The simulation provides guidance for controlling the dissolved oxygen supersaturation and environmentally friendly operation of the Three Gorges Dam.