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River sediment supply, sedimentation and transport of the highly turbid sediment plume in Malindi Bay, Kenya

Journal of Geographical Sciences 2013年第3期23卷 465-489页

作者： JOHNSON U. Kitheka South Eastern Kenya University School of Water Resources Science and Technology Department of Hydrol-ogy and Water Resources Management Kitui 170-90200 Kenya

The paper presents results of a study on the sediment supply and movement of highly turbid sediment plume within Malindi Bay in the Northern region of the Kenya coast. The current velocities, tidal elevation, salinity and suspended sediment concentrations （TSSC） were measured in stations located within the bay using Aanderaa Recording Current Meter （RCM-9）, Turbidity Sensor mounted on RCM-9, Divers Gauges and Aanderaa Tempera- ture-Salinity Meter. The study established that Malindi Bay receives a high terrigenous sedi- ment load amounting to 5.7 x 106 ***-1. The river freshwater supply into the bay is highly variable ranging from 7 to 680 m3.s-1. The high flows that are 〉 150 m3.s^-1 occurred in May during the South East Monsoon （SEM）. Relatively low peak flows occurred in November during the North East Monsoon （NEM） but these were usually 〈70 m3.s^-1. The discharge of highly turbidity river water into the bay in April and May occurs in a period of high intensity SEM winds that generate strong north flowing current that transports the river sediment plume northward. However, during the NEM, the river supply of turbid water is relatively low occur- ring in a period of relatively low intensity NEM winds that result in relatively weaker south flowing current that transports the sediment plume southward. The mechanism of advection of the sediment plume north or south of the estuary is mainly thought to be due to the Ekman transport generated by the onshore monsoon winds. Limited movement of the river sediment plume southward towards Ras Vasco Da Gama during NEM has ensured that the coral reef ecosystem in the northern parts of Malindi Marine National Park has not been completely destroyed by the influx of terrigenous sediments. However, to the north there is no coral reef ecosystem. The high sediment discharge into Malindi Bay can be attributed to land use change in the Athi-Sabaki River Basin in addition to rapid population increase which has led to clearance of for

关键词： sediment plume monsoon winds longshore currents Athi-Sabaki River Malindi Bay Kenya

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Experimental investigation of the inhibition of deep-sea mining sediment plumes by polyaluminum chloride

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International Journal of Mining Science and Technology 2024年第1期34卷 91-104页

作者： Fengpeng Zhang Xuguang Chen Jiakang Wei Yangyang Zhang Weikun Xu Hao Li College of Engineering Ocean University of ChinaQingdao 266100China Shandong Province Key Laboratory of Ocean Engineering Ocean University of ChinaQingdao 266100China China Merchants Marine and Offshore Research Institute Co. Ltd.Shenzhen 518000China National Deep Sea Center Qingdao 266237China

Deep-sea sediment disturbance may occur when collecting polymetallic nodules,resulting in the creation of plumes that could have a negative impact on the ecological *** study aims to investigate the potential solution of using polyaluminum chloride(PAC)in the water *** effects of PAC are examined through a self-designed simulation system for deep-sea polymetallic nodule collection and sediment samples from a potential deep-sea mining *** experimental results showed that the optimal PAC dose was found to be 0.75 g/*** with the test conditions without the addition of PAC,the presence of PAC leads to a reduction in volume,lower characteristic turbidity,smaller diffusion velocity,and shorter settling time of the *** indicates that PAC inhibits the entire development process of the *** addition of PAC leads to the flocculation of mm-sized particles,resulting in the formation of cm-sized *** flocculation of particles decreases the rate of erosion on the seabed by around 30%.This reduction in erosion helps to decrease the formation of ***,when the size of suspended particles increases,it reduces the scale at which they ***,the settling velocity of flocs(around 10^(-2) m/s)is much higher that of compared to sediment particles(around 10^(-5) m/s),which effectively reduces the amount of time the plume remains in suspension.

关键词： Deep-sea mining Deep-sea polymetallic nodules sediment plume Polyaluminum chloride Jet impact Particle flocculation

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Influence of bottom and sand curtain on hydrodynamic performance of otter boards

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Aquaculture and Fisheries 2023年第6期8卷 634-643页

作者： Haoran Li Weiguo Qian Wenhua Chu Qing Yun Chunqin Yin College of Marine Sciences Shanghai Ocean UniversityShanghai201306China College of Fisheries Zhejiang Ocean UniversityZhoushan316022China National Engineering Research Center for Oceanic Fisheries Shanghai201306China Laboratory of Sustainable Exploitation of Oceanic Fisheries Resources Ministry of EducationShanghai201306China

Numerical simulation is an important method for calculating the hydrodynamic performance of otter boards used in sea floor *** such simulations have been explored in prior studies,the effects of the proximity of the otter boards to the seafloor and the plume of upward-drawn sediment during bottom trawling have largely been *** this study,we assessed these *** results show that within the angles of attack used during normal operations,the effect of the seafloor bottom boundary of the flow field on the hydrodynamic performance of an otter board is *** found that when the ratio of the distance between the bottom of an otter board and the surface boundary of the flow field to the chord length of the board exceeds 0.4,the influence of the bottom boundary of the flow field on the hydrodynamic performance of the board is *** values of less than 0.4,the seafloor bottom boundary has an increasingly obvious impact on the hydrodynamic performance as this ratio *** also found that the turbid plume of ocean floor sediment raised during bottom trawling has an obvious effect on the lift and resistance coefficients of an otter board at high angles of *** low angles,this effect on the lift-to-drag ratio is reversed and less *** simulation results show that the optimal lift-to-drag ratio decreases with an increase in the sediment concentration;however,beyond a certain threshold,an increasing concentration of sediments was not found to have an obvious impact on the lift-to-drag ratio.

关键词： Otter board Numerical simulation Hydrodynamic performance sediment plume

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