Hydraulic modelling of fish habitat in urban rivers during high flows

In urban rivers, flow regime and channel morphology are the drivers of physical habitat quality for aquatic species. Peak discharges are increased at high flows as a result of impermeable catchments and channel engineering for flood protection schemes. Hazardous conditions and flashy hydrographs mean that measurement of velocities at high flows is a difficult task. This research uses a three‐dimensional computational fluid dynamics (3D‐CFD) model to simulate hydraulic patterns in two urban river channels. A 3D‐CFD code, called SSIIM, was used to simulate hydraulic conditions in two engineered river reaches of the River Tame, Birmingham, UK. These two sites represent channels with different levels of engineering. Models were calibrated and tested using field measurements. Results show that modelled water surface levels and velocity profiles are well simulated. Calibrated roughness heights are compared with those derived from field measurement of sediment size. Numerical experiments are used to assess the relationship between grid resolution in the vertical dimension and the form of the modelled velocity profiles. Biologists have used laboratory experiments to determine maximum sustainable swimming speeds (MSSS) of fish, often in order to assess what level of a particular pollutant may be tolerable. In this work, simulations of high‐flow hydraulic patterns are used to compare velocity patterns with fish MSSS. Results show that when the water levels rise to fill the first channel of the two‐stage channels at the sites, which occurred 16 times in 2000, MSSS are surpassed in the majority of available habitat, suggesting that excessive velocities at high flows are one factor that limits fish habitat. A comparison between the two reaches shows that there is less available habitat in the more modified reach. Conclusions suggest that an approach that integrates water quality issues and physical channel characteristics must be taken in river rehabilitation schemes, as improvements to water quality alone may not be sufficient to improve habitat quality to the desired level. Copyright © 2002 John Wiley & Sons, Ltd.     

Analysis of fully coupled thermomechanical behaviour around a rigid cylindrical heat source buried in clay

The problem of fully coupled consolidation and heat flow around a rigid cylindrical heat source buried in clay has been studied. The governing equations of the problem are summarized in the paper and a finite element time-marching scheme to obtain an approximate solution to the governing equations is described. The stress–strain behaviour of the skeleton of the saturated soil has been represented by both a linear elastic model and the modified Cam clay soil model. The results of a limited parametric study are presented with the aim of understanding the major mechanisms of soil behaviour close to buried canisters of hot radioactive waste. A range of soil properties has been included in the study, and the effects of soil disturbance during canister emplacement have also been considered.     

A semi-analytic model for contaminant migration in a regular two- or three-dimensional fractured network: Conservative contaminants

A new semi-analytical solution for the transport of a conservative contaminant species in a fractured medium having a regular two- or three-dimensional fracture network is presented. The application of the technique and some of the practical implications arising from an examination of contaminant migration in fractured systems is discussed. Particular consideration is given to the effects of Darcy velocity, fracture spacing, matrix porosity, dispersivity and the mass of contaminant available for transport. The implications of uncertainty with respect to fracture opening size and ground-water velocity is also discussed and it is shown that provided one can obtain a reasonable estimate of the hydraulic gradient and hydraulic conductivity for the rock mass, uncertainty regarding the magnitude of the opening size and the groundwater velocity does not have a significant effect on predicted contaminant migration for the class of problems being considered.     

Ground failure around buried tubes

Summary The hoop forces which develop in circular tubes buried in elastic-plastic ground are investigated. A closed form solution is used to determine the hoop forces which develop when the field stresses in the elastic-plastic ground are initially uniform. The finite element method is used to solve the problem for biaxial field stress. A parametric study is undertaken to assess the influence of tube stiffness and ground strength on the hoop forces, and use is made of elastic stress contours to predict the likely extent of material failure around tubes buried in ground with biaxial prestress.Notation a tube radius - c cohesion - D flexural stiffness of the structure - E _i Young's modulus of structure - E _s Young's modulus of ground - F hoop force (compression positive) - G _s shear modulus of ground - H hoop stiffness of the structure - K coefficient of lateral pressure - N tan²(45+/2) - q ( ₁– ₁)/2 - S _f relative flexural stiffness of the structure - S _h relative hoop stiffness of the structure - t structural thickness - v circumferential displacement - w radial displacement - v _l Poisson's ratio of structure - v _s Poisson's ratio of ground - normal traction acting on the structure - _d deviatoric component of field stress - _h horizontal field stress - _m uniform component of field stress - _v vertical field stress - ₁ major principal stress - ₃ minor principal stress - tangential traction acting on the structure - angle of internal friction of the ground - angle of dilation of the ground     

八达岭基性岩和高Ba—Sr花岗岩地球化学特征及成因探讨：华北和大别—苏鲁造山带中生代岩浆岩的对比

八达岭杂岩侵位于华北北部，由辉长闪长岩岩、石英闪长岩、石英二长岩、二长闪长岩、二长花岗岩、碱长花岗岩和石英正长岩等组成，主要属高钾钙碱性系列。除了含V-Ti磁铁矿的堆晶辉长闪长岩，整套岩石的主量元素变化范围较大，SiO2=46.5%-75.3%,MgO=5.6%-0.2%，中酸性岩石的K2O/NaO为0.59-1.09。碱长花岗岩和少数石英二长岩Ba和Sr含量较低，且具有明显（Eu）负异常。大多数中酸性岩石（高Ba-Sr花岗岩）具有如下显著的微量元素地球化学特征：Ba,Sr和轻稀土（LREE）富集，Y和重稀土（HREE）亏损，LREE/HREE强烈分离，Sr/Y和La/Yb比值较高；在原始地幔标准化的蛛网图中具有显著的Nb,Ta和Ti亏损，不具明显的Sr和Eu亏损。在Harker图解中，基性岩石和高Ba-Sr花岗岩的主量元素相关性明显，两者还具有相似的微量元素和稀土（REE）分配特征，并且，REE,Y,Sr,P和Ti含量从基性到酸性逐渐降低。辉长闪长岩和高Ba-Sr花岗岩的Sr-Nd同位素初始值呈EMI特征（Isr=0.7051-0.7068,εNdi=-8.2-20.2），大致呈负相关。地球化学特征表明基性岩浆为富集的大陆岩石圈地幔部分熔融形成，而高Ba-Sr花岗岩则为基性岩浆通过陆壳混染和结晶分离形成；富P和Ti的副矿物（如磷灰石和的榍石）的分离结晶导致了REE,P和Ti丰度的逐渐降低。另外，华北板块内部和大别-苏鲁造山带基性岩和高Ba-Sr花岗岩分别具有相似的地球化学特征，这表明，上述地区燕山期大规模岩浆活动具有相似的地球动力学机制，大别-苏鲁造山带岩浆岩的地球化学特征并不反映其地幔源区一定受到过来自深俯冲的扬子板块的流体的富集作用。岩石圈的拆沉和减簿作用可能导致了华北板块和大别-苏鲁造山带下古老岩石圈地幔的部分熔融，岩石圈地幔的富集作用可能主要性发生于元古代。     

Comparison of derivative-free optimization methods for groundwater supply and hydraulic capture community problems

Management decisions involving groundwater supply and remediation often rely on optimization techniques to determine an effective strategy. We introduce several derivative-free sampling methods for solving constrained optimization problems that have not yet been considered in this field, and we include a genetic algorithm for completeness. Two well-documented community problems are used for illustration purposes: a groundwater supply problem and a hydraulic capture problem. The community problems were found to be challenging applications due to the objective functions being nonsmooth, nonlinear, and having many local minima. Because the results were found to be sensitive to initial iterates for some methods, guidance is provided in selecting initial iterates for these problems that improve the likelihood of achieving significant reductions in the objective function to be minimized. In addition, we suggest some potentially fruitful areas for future research.     

Consolidation around a heat source buried deep in a porous thermoelastic medium with anisotropic flow properties

A solution is derived for the heat flow and consolidation which occur when a heat source is buried deep in a porous thermoelastic soil having anisotropic flow properties. This solution is used to examine the pore pressure generation and dissipation near both point and cylindrical heat sources. An increase in temperature will tend to generate an increase in excess pore pressure. However, the pore water will tend to flow from regions of high excess pore pressure to regions of low excess pore pressure, and so consolidation will occur, and temperature-generated excess pore pressures will tend to dissipate. Many natural soils exhibit horizontal layering and so have a higher horizontal than vertical permeability. It is shown that in soils the excess pore pressure generated by a heat source is significantly less than that in an isotropic soil having an equal vertical permeability.     

A semi-analytical method for the wave-induced seabed response

A general semi-analytical method is presented for the analysis of seabed response under wave action during a storm. The seabed is idealized as a poro-elastic medium filled with a single compressible fluid with anisotropic flow. The coupled process of fluid flow and deformation of soil skeleton is formulated in the framework of Biot's theory. The analysis for the response of homogeneous seabed of finite thickness under a plane progressive wave is developed first, followed by an extension for the case of a layered seabed. A generalization for three-dimensional response of seabed is also developed for a general wave field which provides the analyses for seabed response under short-crested or standing waves in the vicinity of a structure. Some numerical examples illustrating the proposed analyses are also presented.     

The consolidation of a deep clay stratum subject to an impermeable axisymmetric surface loading

Previous analytic solutions to the problem of the consolidation of a deep clay stratum subjected to a surface loading, have been obtained for the assumed condition of a completely permeable upper surface. This may not be so in many applications, where the foundation causing the loading may be impermeable, and therefore only that part of the clay surface outside the loading is free to drain.In this paper a method is presented which may be used to obtain the time-settlement behaviour of a circular loading applied over an impermeable region of the surface of the clay. The solution technique involves representing the continuous values of fluid flow along the surface boundary as uniform blocks of flow. The solution is found in Laplace transform space and a numerical inversion technique is then used to obtain the time dependent solution.Two types of surface loading are examined; a completely uniform loading and a loading distribution which is approximately that of a rigid footing. For the uniform loading case, comparisons are made with previous solutions (permeable surface) and it is shown that the assumption of an impermeable loaded region leads to significant changes in the time-settlement behaviour of the loading.     

Pollutant migration from deeply buried repositories

Semi-analytic solutions are developed for the migration of pollutants from cylindrical and spherical repositories buried deep in a homogeneous and isotropic soil in the presence of a uniform and unidirectional advection. The techniques adopted involves taking the Laplace transform of the governing equations, finding an analytic solution in transform space and then numerically inverting the transform to obtain the concentrations of the contaminants at selected positions and times. Numerical results are presented, and practical implications discussed.