Design and analysis of the Sydney deepwater ocean outfall environmental monitoring programme: a critique

The Sydney Environmental Monitoring Programme (EMP) measured the environmental performance of Sydney's new deepwater sewage outfalls against a wide range of criteria related to impacts on marine ecosystems and on human use of marine resources. It consisted of a number of interacting studies conducted during the period 1989 to 1993. Given that all the studies have now been finalized and the data analysed and presented (see papers in this volume), it is appropriate to review the program as a whole and identify, with the benefit of hindsight, where things could have been done better. This paper focuses mainly on the experimental design and statistical treatment of the studies conducted, although management problems are also briefly addressed. Overall it is concluded that the studies making up the EMP contributed greatly to enhancing our understanding of the marine environment of the coastal shelf off Sydney, an area which had previously received only limited attention. Most of the studies, however, suffered from deficiencies in experimental design, which was difficult to overcome when analysing the data. It will be important, in designing future integrated monitoring studies, to draw on the experience of programs such as this to avoid some of the pitfalls which appear to be inherent in these types of large programs.     

An inverse problem approach to modelling coastal effluent plumes

Formulated as an inverse problem, the diffusion parameters associated with length-scale dependent eddy diffusivities can be viewed as the unknowns in the mass conservation equation for coastal zone transport problems. The values of the diffusion parameters can be optimized according to an error function incorporated with observed concentration data. Examples are given for the Fickian, shear diffusion and inertial subrange diffusion models. Based on a new set of dyeplume data collected in the coastal zone off Bronte, Lake Ontario, it is shown that the predictions of turbulence closure models can be evaluated for different flow conditions. The choice of computational schemes for this diagnostic approach is based on tests with analytic solutions and observed data. It is found that the optimized shear diffusion model produced a better agreement with observations for both high and low advective flows than, e.g., the unoptimized semi-empirical model, K_y=0.075 σ_y^1.2, described by Murthy and Kenney.     

Progress in the numerical modeling of mantle plumes

The mantle plume model, as an integral part of the Earth’s internal convection system, is complementary to the theory of plate tectonics. They together constitute the key configuration of material circulation and energy transport in the Earth’s interior. Seismology, high-temperature and high-pressure mineralogy, geology, and geodynamic numerical modeling have conducted comprehensive studies on the mantle plume model since it was proposed. In particular, numerical simulation, which investigates t...     

Medium-term responses of rocky bottoms to sewage discharges from a deepwater outfall in the NE Atlantic

An investigation on the effects of deepwater outfall discharges on the status of rocky reef communities was carried out. The sanitation system was found to be an environmentally suitable option for the protection of those habitats situated in high energy coastal environments. Sediments occurring between the predominating rocky substrates showed low values of the fine fraction (<63microm) and organic matter content. In addition, high average concentrations of Cd, Hg and Zn were found in these sediments, though these values were similar to those registered in non-affected sites, far away from the outfall. On the other hand, those assemblages typical of hard substrates that settled near the outfall showed an increase in total richness and abundance of macroinvertebrates. Moreover, the average number of species of each taxonomic group, a good indicator of the maintenance of the previous trophic structure, only varied considerably over time at the rip-rap protection. In a global context, those changes were not directly related to the discharge disturbances, but to the natural variability or the successional processes occurring within those communities. Only communities dwelling in the rip-rap protection area were affected by the proximity of the discharges.     

Subtidal assemblages on rocky reefs at a cliff-face sewage outfall (North Head, Sydney, Australia): What happened when the outfall was turned off?

For many years, sewage was continuously discharged via inshore outfalls into shallow subtidal habitats around Sydney (New South Wales). In 1990, deepwater ocean outfalls were commissioned and inshore discharge ceased. This study examined the assemblage of organisms found on subtidal cliffs at one inshore outfall to examine differences in, or recovery by, the biota when sewage was no longer discharged. This assemblage was primarily composed of filter-feeding animals (sponges, ascidians, bryozoans, anthozoans) and encrusting algae. Differences and changes in the assemblages at a number of different spatial scales, relative to the assemblages at two reference locations, were examined four times over a 20 month period. Although most taxa showed significant changes over the study period, most of these were unpredictable and varied interactively according to the taxon, plot, depth and location. For most measures, however, the location where sewage had been released lay within the natural variability shown by the reference locations. The implications of these findings are discussed with respect to other studies on the effects of sewage on intertidal and shallow subtidal habitats.     

Metal contamination of sediments associated with deepwater ocean sewage outfalls, Sydney, Australia

The New South Wales Environment Protection Authority has recently completed a programme to evaluate the impact on near-shore shelf sediments, following the commissioning of three new deepwater sewage outfalls off Sydney, Australia. These outfalls discharge a total of around 1300 ML day⁻¹ of primary treated sewage derived from domestic and industrial sources. The study compared three locations that were close to the outfalls (likely impacted) and three locations far from the outfalls (likely non-impacted). Four zones were sampled within each location to provide estimates of spatial variability. Three samples of surface sediment were collected from each zone at six monthly intervals over a three year period which encompassed the commissioning of the outfalls. The results of the study suggest that, associated with the commissioning of the three deepwater outfalls, there has not been a significant effect on the concentration of trace metals in the sediments surrounding the outfalls. The concentrations of trace metals in the whole sediment generally were close to the world-wide background levels quoted in the literature, and generally reflected the distribution pattern of the sedimentary fines (< 62.5 mm). When compared to a number of sediment quality guidelines, the concentrations of trace metals were found to be below a level considered to have the potential to cause biological effects or (in the case of As, Ni, Cr) at a level that could be tolerated by the majority of benthic organisms.     

古ENSO的研究进展

本文对20世纪90年代后期逐渐在古气候学、古海洋学、地质学和古生物学等跨学科交叉领域中崭露头角的热点问题——古ENSO研究的前沿进展做了系统的总结和回顾.从观测和气候模拟两方面对集中于不同时间尺度的焦点问题进行展开,主要包括如下几个时段：早-中全新世的厄尔尼诺的减弱;末次冰期中的ENSO循环及其与高纬气候的联系;以及末次间冰期的ENSO现象.其中对早-中全新世时期的ENSO减弱的相对成熟的“岁差”机制做了详细总结,而对另两个时段的矛盾和问题做了简要整理和概括.建议在今后的古ENSO研究中,除观测外,要注意提高对古ENSO进行动力模拟研究的比重,两者相互配合来增加对ENSO循环和气候背景之间相互作用机理的理解,从而为今后全球变暖背景下的ENSO预测提供有意义的借鉴.     

干式变压器抗震数值建模分析

建立准确描述体系动力特性的有限元模型是应用反应谱理论进行抗震计算的关键,以公司SCB10-800/6.3变压器为例,建立了干式变压器本体及外壳结构的有限元模型,计算了体系的模态并与实验结果进行了比较,分析了建立干式变压器抗震模型的关键问题。     

Chemistry in plumes of high-flying aircraft with H2 combustion engines: a modelling study

Recent discussions on high-speed civil transport (HSCT) systems have renewed the interest in the chemistry of supersonic-aircraft plumes. The engines of these aircraft emit large concentrations of radicals like O, H, OH, and NO. In order to study the effect of these species on the composition of the atmosphere, the detailed chemistry of an expanding and cooling plume is examined for different expansion models.For a representative flight at 26 km the computed trace gas concentrations do not differ significantly for different models of the expansion behaviour. However, it is shown that the distributions predicted by all these models differ significantly from those adopted in conventional meso-scale and global models in which the plume chemistry is not treated in detail. This applies in particular to the reservoir species HONO and H₂O₂.     

有限单元法非均匀剖分对数值模拟影响研究

本文研究了有限单元法非均匀剖分对直流电阻率法数值模拟结果的影响.通过非均匀剖分对半空间地质体的视电阻率异常与均匀剖分的视电阻率对比,分析这种模拟方法的可行性,研究计算结果差异产生的原因.通过相邻单元的不同边长比例剖分的对比,研究在误差允许范围内非均匀剖分的单元边长比例极限.计算结果表明,测线方向非均匀剖分是误差产生的主要原因,XYZ三方向非均匀剖分所带来的误差总和是各方向非均匀剖分产生误差之和;当测线方向剖分单元不均匀剖分比例小于0.49∶0.01时,由于非均匀剖分产生的误差在容许范围内.     

An overview on the seismicity of Cuba

The seismicity of Cuba is briefly presented together with a few fundamental neotectonic elements of the adjacent Caribbean region. The Cuban seismicity catalogue has been extended back to 1528 and it shows that the largest earthquakes occurred in 1766 and 1852 (I = IX MSK). Two types of seismicity (intraplate and interplate) can be distinguished in Cuba. Western and Eastern Seismotectonic Units correspond to intraplate type and the Southeastern Seismotectonic Unit to interplate type. Western Cuba is characterized by a low frequency of earthquake occurrence. Distribution of epicenters is not regular and the most important events mainly concentrate along two regional active fault system (Nortecubana and Surcubana). Due to the lack of seismic stations in this region, the characterization of seismicity is frequently done on the grounds of historical data available from 1693. The main seismogenic source for Cuba is the Bartlett-Cayman fault system, but inland there are other active structures. Some issues about historical and present day Cuban seismological research are also showed.     

Three-dimensional numerical thermal and rheological modelling in the central Fennoscandian Shield

A three-dimensional model for the central Fennoscandian Shield was constructed for analysing the thermal, the rheological and the structural conditions in the lithosphere. The mesh covers a rectangular area in the southern Finland with horizontal dimensions of 500 km × 400 km and a depth extent of 100 km. Structural boundaries are derived from the several deep seismic soundings carried out in the area. Constructed model is first used in the calculation of the thermal and the rheological models and secondly in analysing the stress and the deformational conditions with the obtained rheology. Thermal and structural models are solved with the finite element method. The calculated surface HFD is between 40 and 48 mW m⁻² in the Proterozoic southern part and below 40 mW m⁻² in the older and northern Archaean part of the model. The calculated rheological strength shows a layered structure with two individual rheologically weak layers in the crust and strong layer in the upper part of the lower crust. The minimum brittle–ductile transition (BDT) depth is around 10 km in the southern part of the model while in the north and north-eastern parts the BDT depth is around 45–50 km. Comparison with the focal depth data shows that as most of the earthquakes occur no deeper than the depth of 10 km are they located in the brittle regime. Resulting stress conditions and possible regions of deformation after the model is subjected to pressure of 50 MPa reveals that the stress field is quite uniformly distributed in different crustal layers and that the elastic parameters control more the state of the stress than the applied rheological structure. In the upper crust, the stress intensity has values between 42 and 45 MPa whereas in the middle crust the values are around 50 MPa. Comparison of the 3-D model with earlier 2-D models shows that some differences in the results are to be expected.     

Three-dimensional numerical thermal and rheological modelling in the central Fennoscandian Shield

A three-dimensional model for the central Fennoscandian Shield was constructed for analysing the thermal, the rheological and the structural conditions in the lithosphere. The mesh covers a rectangular area in the southern Finland with horizontal dimensions of 500 km × 400 km and a depth extent of 100 km. Structural boundaries are derived from the several deep seismic soundings carried out in the area. Constructed model is first used in the calculation of the thermal and the rheological models and secondly in analysing the stress and the deformational conditions with the obtained rheology. Thermal and structural models are solved with the finite element method. The calculated surface HFD is between 40 and 48 mW m⁻² in the Proterozoic southern part and below 40 mW m⁻² in the older and northern Archaean part of the model. The calculated rheological strength shows a layered structure with two individual rheologically weak layers in the crust and strong layer in the upper part of the lower crust. The minimum brittle–ductile transition (BDT) depth is around 10 km in the southern part of the model while in the north and north-eastern parts the BDT depth is around 45–50 km. Comparison with the focal depth data shows that as most of the earthquakes occur no deeper than the depth of 10 km are they located in the brittle regime. Resulting stress conditions and possible regions of deformation after the model is subjected to pressure of 50 MPa reveals that the stress field is quite uniformly distributed in different crustal layers and that the elastic parameters control more the state of the stress than the applied rheological structure. In the upper crust, the stress intensity has values between 42 and 45 MPa whereas in the middle crust the values are around 50 MPa. Comparison of the 3-D model with earlier 2-D models shows that some differences in the results are to be expected.     

Three-dimensional numerical modelling of wind-driven circulation in a homogeneous lake

A three-dimensional numerical model has been developed to study wind-induced circulation patterns in a shallow homogeneous lake with a complex bathymetry. The governing equations are the unsteady Reynolds-Averaged Navier–Stokes equations in which the non-hydrostatic pressure distribution has been included. The model was tested against analytical solutions and laboratory data for wind-induced currents and then applied to Esthwaite Water, a small lake in Cumbria, UK. The model was used to study the main model parameters and to generate typical circulation patterns for a variety of conditions in the lake. Simulations showed that a non-hydrostatic pressure distribution did not have any noticeable influence on the overall circulation pattern in the lake. However, comparisons with field data at some measurement stations in the near-shore region with sharply varying bottom topography showed that the hydrodynamic pressure component had some influence on the vertical velocity profile.     

Well-balanced numerical modelling of non-uniform sediment transport in alluvial rivers

The last two decades have witnessed the development and application of well-balanced numerical models for shallow flows in natural rivers.However,until now there have been no such models for flows with non-uniform sediment transport.This paper presents a 1D well-balanced model to simulate flows and non-capacity transport of non-uniform sediment in alluvial rivers.The active layer formulation is adopted to resolve the change of bed sediment composition.In the framework of the finite volume Slope Llmiter Centred(SLIC) scheme,a surface gradient method is incorporated to attain well-balanced solutions to the governing equations.The proposed model is tested against typical cases with irregular topography,including the refilling of dredged trenches,aggradation due to sediment overloading and flood flow due to landslide dam failure.The agreement between the computed results and measured data is encouraging.Compared to a non-well-balanced model,the well-balanced model features improved performance in reproducing stage,velocity and bed deformation.It should find general applications for non-uniform sediment transport modelling in alluvial rivers,especially in mountain areas where the bed topography is mostly irregular.     

A review of the numerical modelling of salt mobilization from groundwater-surface water interactions

Salinization of land and water is a significant challenge in most continents and particularly in arid and semi-arid regions. The need to accurately forecast surface and groundwater interactions has promoted the use of physically-based numerical modelling approaches in many studies. In this regard, two issues can be considered as the main research challenges. First, in contrast with surface water, there is generally less observed level and salinity data available for groundwater systems. These data are critical in the validation and verification of numerical models. The second challenge is to develop an integrated surface-groundwater numerical model that is capable of salt mobilization modelling but which can be validated and verified against accurate observed data. This paper reviews the current state of understanding of groundwater and surface water interactions with particular respect to the numerical modelling of salt mobilization. 3D physically-based fully coupled surface-subsurface numerical model with the capability of modelling density-dependent, saturated-unsaturated solute transport is an ideal tool for groundwater-surface water interaction studies. It is concluded that there is a clear need to develop modelling capabilities for the movement of salt to, from, and within wetlands to provide temporal predictions of wetland salinity which can be used to assess ecosystem outcomes.     

An assessment of the effect of chemical scavenging within submarine hydrothermal plumes upon ocean geochemistry

Profiles of ²¹⁰Pb over the Endeavour and North Cleft Segments of the Juan de Fuca Ridge are used to model a time scale for the scavenging, by hydrothermal plumes, of reactive elements in seawater. The hydrothermal plumes above these ridge segments are sites of intense scavenging removal of ²¹⁰Pb. At Endeavour, the total ²¹⁰Pb activities within the plume are as low as 8 dpm/100 l and dissolved activities are as low as 3 dpm/100 l. At the North Cleft, which is characterized by higher particulate Fe concentrations, the total ²¹⁰Pb activities are 4.5 dpm/100 l, the dissolved activities are 1–2 dpm/100 l and the ²¹⁰Pb activities are deficient with respect to the activity of the ²¹⁰Po daughter. These are perhaps the lowest ²¹⁰Pb activities ever measured in the deep sea. The large gradient of ²¹⁰Pb between the plume and surrounding deep water suggests that scavenging is focused into the plumes through horizontal transport. The implication, therefore, is that this process might impact the ocean on a scale larger than that local to the ridge crest. By coupling published measurements of particle flux from Endeavour with ²¹⁰Pb activities on particles trapped at that site, the total volume of seawater stripped of ²¹⁰Pb per year for that site was calculated to be 7.4 × 10¹² l/y. Globally, the extrapolated volume flux of seawater stripped of reactive constituents is 5.7 × 10¹⁵ l/y, such that the entire ocean is processed in this manner in 2.4×10⁵ y. The geochemical cycle of elements with ocean residence times much shorter than this (e.g., Pb and Th) will not be greatly affected by hydrothermal scavenging. On the other hand, this process holds significance for the geochemistry of other elements scavenged by hydrothermal plumes, such as P and V, whose ocean residence times are > 10⁴ y.     

Towards non-linear inversion for characterization of time-lapse phenomena through numerical modelling

We compare two geophysical survey measurements of the same type made at different times in order to characterize the change in the geological medium during the elapsed time. The aim of this study is to develop a strategy using a full non-linear inversion algorithm as the interpretation tool. In this way, not only the location and the form of the changes are recovered, but also the changes in the material parameters of the geological medium can be estimated. In order to solve this fully non-linear problem, the so-called ‘multiplicative regularized contrast source inversion’ (MR-CSI) method is employed. The unique property of this iterative method is that it does not solve the forward problem at each iterative step. This makes it possible to use the non-linear inversion algorithm for large-scale computation problems. The numerical results show that by taking into account the non-linear nature of the problem, interpretation of the time-lapse data can be significantly improved, compared with that obtained using linear inversion.     

Experimental and numerical modelling of sedimentation in a rectangular shallow basin

Numerical simulation of flows in shallow reservoirs has to be checked for its consistency in predicting real flow conditions and sedimentation patterns. Typical flow patterns may exhibit flow separation at the inlet, accompanied by several recirculation and stagnation areas all over the reservoir surface. The aim of the present research project is to study the influence of the geometry of a reservoir on sediment transport and deposition numerically and experimentally, focusing on a prototype reservoir depth between 5 and 15 m as well as suspended sediment transport.
A series of numerical simulations is presented and compared with scaled laboratory experiments, with the objective of testing the sensitivity to different flow and sediment parameters and different turbulence closure schemes. Different scenarios are analyzed and a detailed comparison of preliminary laboratory tests and some selected simulations are presented.
The laboratory experiments show that suspended sediment transport and deposition are determined by the initial flow pattern and by the upstream and downstream boundary conditions. In the experiments, deposition in the rectangular basin systematically developed along the left bank, although inflow and outflow were positioned symmetrically along the centre of the basin. Three major horizontal eddies developed influencing the sediment deposition pattern. Although asymmetric flow patterns are privileged, a symmetric pattern can appear from time to time. This particular behaviour could also be reproduced by a two-dimensional depth-averaged flow and sediment transport model （CCHE2D）. The paper presents numerical simulations using different turbulence closure schemes （k-ε and eddy viscosity models）. In spite of the symmetric setup, these generally produced an asymmetric flow pattern that can easily switch sides depending on the assumptions made for the initial and boundary conditions. When using the laboratory experiment as a reference, the most reliable numerical results have been obtai