On harbour siltation in the fresh-salt water mixing region

In this paper a novel series of field measurements are presented, which are the first to elucidate the processes influencing siltation in Botlek Harbour. Botlek Harbour is situated at the limit of saline water intrusion in the Rotterdam Waterway. Normally, after the ebb tide fresher river waters are found in the Rotterdam Waterway at the location of Botlek Harbour. On the flooding tide, the tip of the salt wedge is advected along the Rotterdam Waterway towards the mouth of Botlek Harbour. Hence on flood, a lock-exchange mechanism operates between Botlek Harbour and the Rotterdam Waterway. On the flood tide, when there is a supply of suspended particulate matter (SPM) associated with the presence of the estuarine turbidity maximum (ETM) at the mouth of the harbour, the survey data show exchange of SPM into the harbour. This lock-exchange process is found to be the dominant cause for SPM transport into the harbour. This is further substantiated by an analysis of the mass transport mechanisms. In this analysis, the vertical profiles of the instantaneous velocity, salinity and SPM concentration fields, recorded during the surveys, were decomposed into advective and dispersive transport components. The results of this analysis indicate that the correlation between the lock-exchange mechanism on the flood tide with the availability of SPM for exchange and efficient trapping, dominate the total exchange of SPM (97%). Hence, the increase in measured near-bed SPM concentration within the harbour is ascribed to tidal advection of saline water and the ETM along the Rotterdam Waterway. Tidal advection controls the density difference between the estuary and harbour, as well as the availability of SPM for exchange at the entrance to Botlek Harbour. The location of the ETM at the tip of the salt wedge is a key factor in supplying SPM to Botlek Harbour. Consequently the timing of the availability of SPM at the mouth of the harbour needs to be considered in siltation studies. The survey data suggest that Botlek Harbour basin has a 100% trapping efficiency. Analysis of 5 months of data, from a measuring rig located within the harbour, show excursions of the limit of the salt wedge and ETM. These excursions are likely to affect siltation of upstream harbours. Salinity-induced density gradients control the transport and subsequent trapping of SPM in the estuary in close proximity to the harbour entrance, the exchange of SPM between the estuary and harbour, and the trapping of SPM in the harbour basin.     

On the siltation of the middle Yangtze River

1 Origin, process and method of the research Silt deposition created the fertile Dongting and Jianghan Plains of the middle Yangtze drainage, but has become a main cause of the deteriorating flooding along the middle Yangtze. The history of flood and waterlog of the Yangtze River in last century, esp. the disastrous 1998 flood, has proved that the key to the Yangtze flood control is its middle reach, especially the Jingjiang Segment. To study the silt deposition of the middle Yangtze and …     

The effect of slope length on sediment yield by rainfall impact under different land use types

To evaluate the impact of slope length on sediment yield under different rainfall intensities and land use types on low hill gentle slope, the characteristics of sediment yield process were analyzed based on the field artificial rainfall simulation. For the study, grassland and capsicum slope were taken from Anji county of Zhejiang province, China. Results indicated that rainfall intensity had stronger influence than slope length on sediment yield in south region. For capsicum slope, sediment yield increased quickly with increasing slope length when rainfall intensity greater than 90 mm h^–1. The slope length had no significant effect on sediment yield when rainfall intensity less than or equaled to 90 mm h^–1. For grassland, data from experiments indicated that sediment yield increased slowly with increasing slope length under rainfall intensity less than 120 mm h^–1. There was a decreasing tendency of sediment yield at 6 m slope length under all rainfall events. It was concluded from particle size analysis of erosional sediment that silt and clay particles <0.02 mm were always preferentially transported on both capsicum slope (silt 47.1%, clay 40.9%) and grassland (silt 38.3%, clay 35.9%). We hope these results are useful for soil and water conservation and land management.     

Observations on the effects of sewage discharged into a tidal harbour

Portsmouth harbour, a partially enclosed tidal inlet, receives a large discharge of sewage effluent. Investigations involving the measurement of nutrient concentrations, dissolved oxygen, heavy metals in sediments and faunal distributions have shown that gross effects are confined to an area near the discharge point. Surveys over 3 years have shown most of the harbour to be capable of supporting large mats of macroalgae, probably stimulated by the nutrient in the effluent which is to be removed by 1980.     

The effect of gauge length on axially incident P‐waves measured using fibre optic distributed vibration sensing

Distributed vibration sensing, also known as distributed acoustic sensing, is a relatively new method for recording vertical seismic profile data using a fibre optic cable as the sensor. The signal obtained from such systems is a distributed measurement over a length of fibre referred to as the gauge length. In this paper, we show that gauge length selection is one of the most important acquisition parameters for a distributed vibration sensing survey. If the gauge length is too small, then the signal‐to‐noise ratio will be poor. If the gauge length is too large, resolution will be reduced and the shape of the wavelet will be distorted. The optimum gauge length, as derived here, is a function of the velocity and frequencies of the seismic waves being measured. If these attributes vary considerably over the depth of a survey, then the use of different gauge lengths is recommended. The significant increases in data quality resulting from the use of multiple gauge length values are demonstrated using field data.     

The length of day since 1656

Observed values of the difference between the time determined using the rotation of the Earth and a uniform time scale are available since 1627, with useful observations becoming available in 1656. These early data were recorded with low precision and must be smoothed numerically in order to be useful for the derivation of estimates of the difference between the actual length of the day and the standard 24 h, known as excess length of day, or the Earth's rotational speed. Modern data requires no smoothing. The observational data have been adjusted to be consistent with one estimate of the lunar acceleration and smoothed so that the internal and external precision of the observations are approximately equal. The final values along with the derived excess length of day are presented and their spectra are discussed.     

Numerical modelling of circulation and dispersion processes in Boulogne-sur-Mer harbour (Eastern English Channel): sensitivity to physical forcing and harbour design

The MARS-3D model in conjunction with the particle tracking module Ichthyop is used to study circulation and tracer dynamics under a variety of forcing conditions in the eastern English Channel, and in the Boulogne-sur-Mer harbour (referred to hereafter as BLH). Results of hydrodynamic modelling are validated against the tidal gauge data, VHF radar surface velocities and ADCP measurements. Lagrangian tracking experiments are performed with passive particles to study tracer dispersal along the northern French coast, with special emphasis on the BLH. Simulations revealed an anticyclonic eddy generated in the harbour at rising tide. Tracers, released during flood tide at the Liane river mouth, move northward with powerful clockwise rotating current. After the high water, the current direction changes to westward, and tracers leave the harbour through the open boundary. During ebb tide, currents convergence along the western open boundary but no eddy is formed, surface currents inside the harbour are much weaker and the tracer excursion length is small. After the current reversal at low water, particles are advected shoreward resulting in a significant increase of the residence time of tracers released during ebb tide. The effect of wind on particle dispersion was found to be particularly strong. Under strong SW wind, the residence time of particles released during flood tide increases from 1.5 to 6 days. For release during ebb tide, SW wind weakens the southward tidally induced drift and thus the residence time decreases. Similar effects are observed when the freshwater inflow to the harbour is increased from 2 to 10 m³/s during the ebb tide flow. For flood tide conditions, the effect of freshwater inflow is less significant. We also demonstrate an example of innovative coastal management targeted at the reduction of the residence time of the pathogenic material accidentally released in the harbour.

     

Numerical modelling of circulation and dispersion processes in Boulogne-sur-Mer harbour (Eastern English Channel): sensitivity to physical forcing and harbour design

The MARS-3D model in conjunction with the particle tracking module Ichthyop is used to study circulation and tracer dynamics under a variety of forcing conditions in the eastern English Channel, and in the Boulogne-sur-Mer harbour (referred to hereafter as BLH). Results of hydrodynamic modelling are validated against the tidal gauge data, VHF radar surface velocities and ADCP measurements. Lagrangian tracking experiments are performed with passive particles to study tracer dispersal along the northern French coast, with special emphasis on the BLH. Simulations revealed an anticyclonic eddy generated in the harbour at rising tide. Tracers, released during flood tide at the Liane river mouth, move northward with powerful clockwise rotating current. After the high water, the current direction changes to westward, and tracers leave the harbour through the open boundary. During ebb tide, currents convergence along the western open boundary but no eddy is formed, surface currents inside the harbour are much weaker and the tracer excursion length is small. After the current reversal at low water, particles are advected shoreward resulting in a significant increase of the residence time of tracers released during ebb tide. The effect of wind on particle dispersion was found to be particularly strong. Under strong SW wind, the residence time of particles released during flood tide increases from 1.5 to 6 days. For release during ebb tide, SW wind weakens the southward tidally induced drift and thus the residence time decreases. Similar effects are observed when the freshwater inflow to the harbour is increased from 2 to 10 m³/s during the ebb tide flow. For flood tide conditions, the effect of freshwater inflow is less significant. We also demonstrate an example of innovative coastal management targeted at the reduction of the residence time of the pathogenic material accidentally released in the harbour.     

The contribution of urban runoff to organic contaminant levels in harbour sediments near two Norwegian cities

The main aim of the present study was to compare the quality of particle emissions (urban runoff and settling particles in rivers and harbours) to the quality of top-layer bed sediments, for two Norwegian harbours (Oslo and Drammen). A sub-aim was to investigate whether non-industrial urban runoff contributed to the organotin load of sediments, apart from leaching from ship hulls. Time-integrated samples of stormwater runoff were obtained in an innovative manner, by sampling man-holes in the stormwater system. Settling particles were sampled with sediment traps. The study focused on PAHs, PCBs and organotin compounds. Contaminant levels were generally a factor of 2-10 (PAHs) and 3-30 (TBT) lower in emitted riverine and runoff particles than in top-layer bed sediments, except for PCBs in Oslo harbour (only 20-30% lower). Significant levels of tributyltin (TBT; median 140mug/kg) were shown in runoff particles, showing that TBT can also be emitted via urban sources, since the sampled man-holes were not in areas where dry-docking activities take place. Possible land-based TBT sources include long-lasting house paint and use of TBT as PVC stabilizer and timber preservative. Since there are ongoing emissions into the two studied harbour areas, it is concluded that the addition of an actively sorbing capping material such as activated carbon might be the best remediation alternative.     

Small river basin and estuarine sediment fluxes: The magnitude necessary for coastal dispersion and siltation effects on a coral reef

Increasing continental suspended sediment influx to coral reefs is an example of land-sea coupling that requires the identification of sources, magnitude of transport, and controlling processes. In Brazil, a small coastal basin (Macaé River) was identified as a source of suspended sediment to a coral reef on the coast of Cape Armação dos Búzios. Biannual suspended sediment loads were measured at the basin as were fluxes within the estuary and towards the coast during eight tidal cycles. Particle load and yield from this basin were typical of small coastal basins, showing high to moderate slopes and transitional land management. However, the magnitude of the river loads was lower than the sediment transport within the estuary, indicating that the estuary amplifies river fluxes and sustains the transference of suspended sediment alongshore to the coral reef. Nonetheless, the estuary displays both suspended particle retention and export capacity and, therefore, fluxes to the coast and the coral reef occur as episodic events.     

Response of a harbour opened to a sea of variable depth

Wave-induced oscillations in a circular harbour with protruding breakwaters and narrow mouth are analytically investigated by using a variational method. The effects of the bottom topography of the contiguous external sea are studied, especially as far as Helmholtz resonance is concerned; it has been found that the amplitude of the resonance peak is quite sensitive to the depth variation, while the related resonance wavenumber is more stable.     

Heavy metals mobility in harbour contaminated sediments: the case of Port-en-Bessin

Metallic contaminants associated with sediments showed various behaviours depending on physicochemical conditions. A contaminated sediment core from a harbour in the Bay of Seine was sampled to derive information about metal solubilization from anoxic sediment. In these anaerobic surroundings, physicochemical processes depended on the organic matter cycle, on vertical variation of redox conditions and on precipitation conditions of iron and manganese. In the studied core, anoxic conditions were developed at -15 cm depth. A three-step sequential extraction procedure, modified from the BCR method (now the SM&T), was applied to the anoxic sediment in order to evaluate the potential mobility of fixed metals. Zinc was the most labile metal, recovered in the first extraction stages, and was associated with the non-residual fraction of sediment. Lead was the least labile metal, with up to 70% associated with the residual fraction of the sediment. Copper was associated with organic matter, and its mobility was controlled by the concentration and degradation of the organic fraction. Discharge of organic-rich dredged sediments at sea results in degradation of contained organic matter and may affect the environmental impact of these metals significantly. These results therefore help to improve the waste management of such contaminated sediments.     

Blood metal levels and metal-influenced immune functions of harbour seals in captivity

Immunological blood parameters and the effects of environmental pollutants on the immune system are important to assess the health status of seals. Animals living permanently in seal centres are useful for development and validation of diagnostic tools for free-ranging animals. In this study, parameters of cellular immunity as well as metal concentrations in blood and metal influence on cell proliferation of seven seals from a seal centre were investigated repeatedly using multi-element analysis and a lymphocyte proliferation assay. The metal concentrations, except for tin and chromium, were in general comparable to those of free-ranging animals of the North Sea. The unstimulated and mitogen-stimulated lymphocyte proliferation showed strong intra- and inter-individual variability, which reflected variability in activation of the immune status. Furthermore, both immunosuppressive and stimulative influences of metals on lymphocytes were found. Summarising, the methods used in this investigation provided useful information on these animals, and their application to free-ranging animals can be recommended.     

Field investigation of siltation at a tidal harbor: North Port of Incheon,Korea

Ocean Dynamics - To understand siltation processes within the North Port of Incheon, Korea, this study estimated the sedimentation rate and then determined the dominant mechanisms for the...     

Bacteria and organic matter dynamics during a bioremediation treatment of organic-rich harbour sediments

We studied the dynamics of bacteria and organic matter in the Ancient Port of Genoa (Italy) during a bioremediation treatment of sediment (during summer-autumn 1998) in an area characterised by continuous sewage discharge. A strong increase in total benthic bacterial density (TBN) was recorded at the end of the study, from 14 x 10(8) to 58-172 x 10(8) cell g(-1) in different parts of the treated area. The TBN increase was linked to organic matter depletion, from more than 40 to less than 20 mg x g(-1). In order to highlight the main ecological mechanisms involved in bioremediation, a laboratory experiment based on both water and sediment from the basin studied was carried out. We observed an increase in TBN during the first 20 days and a decrease in sediment organic matter (up to about 20%). Increases of organic matter (about 2-fold) and TBN (from 21 to 33 x 10(9) cell l(-1)) occurred in the overlying water, suggesting a strong association between the sediments and water column processes. Hydrolytic activities, which double in the sediment and increase up to a 300-fold in the water, are consistent with the decrease in sediment organic matter and with the water fraction dynamics.     

Reaction of fish larvae to the water of the River Elbe at Hamburg harbour

The River Elbe is one of the biggest streams carrying pollutants of all kinds into the North Sea. However, investigations of direct effects of the Elbe water on river life are not numerous. Early life stages of common whitefish and carp were reared under comparable conditions in water of the River Elbe, and in tap water, respectively. No direct effects on the viability of the fry could be found by observing mortality and growth rates in both treatments. Whitefish larvae were severely infested by parasitic ciliates which were able to build up a dense population in the river water. In these experiments life conditions for the protozoa seemed to be much better than in tap water. Mortality rates of early larvae of common whitefish were lower in the Elbe water than in tap water. Mortality, growth rate and starvation resistance of carp fry was equal in river and tap water.     

Occurrence of anthropogenic and naturally-produced organohalogenated compounds in tissues of Black Sea harbour porpoises

Harbour porpoises are one of the three cetacean species inhabiting the Black Sea. This is the first study to report on polybrominated diphenyl ethers (PBDEs) and naturally-produced compounds, methoxylated PBDEs (MeO-PBDEs) and polybrominated hexahydroxanthene derivatives (PBHDs), in tissues (kidney, brain, blubber, liver, muscle) of male harbour porpoises (11 adults, 9 juveniles) from the Black Sea. Lipid-normalized concentrations decreased from muscle > blubber > liver > kidney > brain for the sum of polychlorinated biphenyls (PCBs) and for the sum of PBDEs. Among the naturally-produced compounds, levels of PBHDs were higher than of MeO-PBDEs, with tri-BHD and 6-MeO-BDE 47 being the dominant compounds for both groups, respectively. Concentrations of naturally-produced compounds decreased from blubber to brain, similarly to the sum of DDT and metabolites (DDXs). Concentrations of DDXs were highest, followed by PCBs, HCB, PBHDs, PBDEs and MeO-PBDEs. Levels of PCBs and PBDEs in blubber were lower than concentrations reported for harbour porpoises from the North Sea, while concentrations of DDXs were higher.