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Methodology to assess coastal infrastructure resilience to climate change
No full textThe section of railway which runs along the coastline of south Devon in United Kingdom, from Exeter to Newton Abbot, is one of the most photographed sections of railway in the world. It was opened in 1846 with embankments and seawalls protecting and supporting the railway, providing the route of an atmospheric railway. Despite regular maintenance however, there has been a history of storm damage, one of the most severe occurring in February 2014. This resulted in the collapse of the line, interruption of all rail traffic into and out of the far South- West of the United Kingdom (affecting parts of Devon and the whole of Cornwall) and significant damage to the region’s economy.
In order to improve the resilience of the line, several options have been considered to evaluate and reduce climate change impacts to the railway. This paper describes the methodological approach developed to evaluate the risks of flooding for a range of scenarios in the estuary and open coast reaches of the line. Components to derive the present day and future climate change coastal conditions including some possible adaptation measures are also presented together with the results of the hindcasting analysis to assess the performance of the modelling system. An overview of the modelling results obtained to support the development of a long-term Resilience Strategy for asset management is also discussed
Insights and future research into the impacts of deep sea mining
No full textThe pressure on resources of rare earth minerals and other resources like phosphate, together with improvements in technology, are leading to increased interest in the mining of deeper waters. This interest in turn has generated concern about the potential environmental consequences of large scale deep-sea mining (e.g. Wedding et al. 2015). A number of environmental impact assessments have recently been made for deep-sea mining projects with varying success in gaining consent. These projects range over water depths of 100-1600m and encompass typical dredging plant as well as the bespoke mining plant for very deep waters. This experience has highlighted several common issues which have arisen during the EIA studies and consent process and which can be expected to arise again in future mining proposals.
This paper will discuss these issues and highlight management and modelling approaches which can be employed to address these issues, improve the reliability of impact assessment, and so improve the likelihood of consent.
In addition this paper will briefly introduce the recently started UK/Brazil-funded MarineE-tech research project studying the formation and processing feasibility of Fe-Mn crusts on seamounts, and the likely environmental effects of mining these environments
Non-dimensional formulization of the critical hydraulic head difference for seepage failure of soil in front of sheet piles
Get PDFFor the excavation of soil with a high ground water level within a cofferdam, seepage water flows through soil under a hydraulic head difference, H, between up- and downstream sides of a sheet pile wall, and seepage failure is often a problem. Seepage failure sometimes occurs even when a cofferdam has been expertly constructed based on a current design method. There still remain various shortfalls in the theory of the seepage failure of soil. In this paper, the prismatic failure concept 2D (pfc-2D) is first presented, which is one of the conventional methods for designing against seepage failure. Next, the non-dimensional formulization of the critical hydraulic head difference against seepage failure, Hc, is discussed especially in two dimensions. When the prototype (real) and model (test) soils are geometrically similar, we discuss whether or not the non-dimensional formulization for the Hc value is possible. The possibilities of the non-dimensional formulizations of the Hc values in the case of the other flow conditions of 2DC, 3D, and AXS flows are also discussed
Scour development around structures with non-uniform cylindrical geometries
Get PDFMany offshore foundations are composed of non-uniform cylindrical geometries such as cones and different diameter composite cylinders. However, little is known about how these types of structure respond with regards to scour under the forcing of a unidirectional current. The present paper describes a series of laboratory experiments that have been performed to examine the effect that the geometry of a marine structure has on the evolution and equilibrium depth of scour under different hydrodynamic conditions. It was found that the hydrodynamic scour response of the non-uniform cylindrical structures is fundamentally different to that of a uniform cylinder
Equilibrium scour prediction for uniform and non-uniform cylindrical structures under clear water conditions
No full textOffshore Gravity Base Foundations (GBFs) are often designed with non-uniform cylindrical geometries. Such structures interact with the local hydrodynamics which amplify the adverse dynamic pressure gradient, which is responsible for all flow and scour phenomena including the bed shear stress amplification. In this study a method for predicting the effect non-uniform cylindrical structure geometries have on local scour around offshore structures under the forcing of a unidirectional current is presented. The interaction of the flow field with the sediment around these complex structures is described in terms of non-dimensional parameters that characterize the similitude of water-sediment movement. The paper presents insights in the influence a form of the Euler number has on the equilibrium scour around uniform and non-uniform cylindrical structures. Here the Euler number is defined as the depth averaged pressure gradient (calculated using potential flow theory) divided by the product of the square of mean flow velocity and the fluid density. The insights are confirmed through a series of experiments where the equilibrium scour was monitored for different types of structures and flow conditions.
The results of this study show that the Euler number is a more appropriate parameter for describing the scour potential of a structure compared to using the equivalent pile diameter. The experimental data show that an increasing Euler number yields an increase in the non-dimensional equilibrium scour. The results of this study also suggest that an increase in the water depth yields a decrease in the equilibrium scour depth for the conical, cylindrical base structures and truncated cylinders and an increase in the equilibrium scour depth for the uniform cylinders which can also be explained in terms of changes in the Euler number. Finally, the Buckingham π theorem in conjunction with the experimental data was used to derive a simple shape correction factor that could be used to determine the scour depth of a non-uniform cylindrical structure based on the equilibrium scour produced for the same flow conditions by a uniform cylinder
Cumulative effects of multiple marine outfalls: issues for coastal zone management
No full textIntroduction. Rapid and large-scale industrialisation of coastal areas is an on-going challenge for both the environment and the design of efficient marine outfalls. National planning strategies (in GCC countries for example) often identify coastal regions in which multiple industries can be developed. Examples include so-called Free Zones and Industrial Cities, and may involve the construction of ports, factories, refineries, power/desalination facilities, etc. Such zoning optimises land use, but can lead to the release of multiple marine discharges within a small area of coastal waters. This raises issues for the environment, regulation, modelling and engineering.
Issues. High pollutant loads along a small section of coastal waters can cause significant local ecological stress, and multiple pollutants can act synergistically on flora and fauna. Pollutants may accumulate locally, particularly if the waters are poorly flushed. The author has studied several sites where multiple thermal outfalls have caused significant seawater warming, effectively raising the ambient temperature over a region. Significant pollutant build-up can reduce the efficiency of outfall designs, by limiting the availability of fresher ambient seawater for dilution.
Communication. The cumulative effects of marine outfalls are often exacerbated by a lack of reliable information-sharing between neighbouring industries, plants and facilities. Data on discharge constituents and release rates is rarely available and so it can be difficult to plan and optimise new outfalls. In extreme cases this can mean that Environmental Impact Assessments and engineering studies for each outfall are effectively carried out in isolation.
Management and mitigation. Several measures may help to mitigate the cumulative effects of neighbouring discharges. Common outfalls are built to release combined wastewater from industrial zones, confining high pollutant concentrations to specific areas. These areas may be identified from baseline marine and/or hydrodynamic model studies as low ecological risk, or as regions of rapid water exchange. Examples along the Gulf include outfalls at Sohar Industrial area (Oman), and Ras Laffan Industrial City (Qatar). Common outfalls can also help to mix “complimentary” effluents. For example warm water discharges from refineries/power stations can be combined with cooler discharges from LNG regasification plants. Smaller volumes of highly concentrated effluent (e.g. wastewater) can be combined with larger cooling water discharges to effectively pre-dilute and reduce harmful pollutant concentrations.
Regional planning studies. Regional planning studies can be supported by hydrodynamic modelling. used to successfully managing the effects of multiple outfalls. Computational modelling studies can be carried out to determine optimum outfall locations, and discharges can then be coordinated appropriately, accounting for in-combination effects. Management plans must be supported by open information sharing between industries / operators, which might be coordinated by the site owner, overseen by the environmental regulator. The author presents examples of such optimisation studies and how environmental impact can be reduced without significant increases to project costs
Local scour around two subsea pipelines in an oscillatory flow
Get PDFIn offshore engineering, wave generated flows are generally modelled as oscillatory flows when flow around small scale cylindrical structures are considered. The understanding of local scour around subsea pipelines under waves is important to ensure the stability of pipelines. In this study, local scour around two identical pipelines in a tandem arrangement in an oscillatory flow is investigated numerically. The flow around the pipelines is simulated by the Reynolds-averaged Navier-Stokes (RANS) equations and the local scour is predicted by solving the conservation equation of the sediment mass. The numerical model is firstly validated against experimental data. Then, the effects of the gap between the two pipelines and the KC number on the scour depth below the pipelines are examined over a wide parameter space
A field erodibility testing device for scour evaluation of bridges
Get PDFEvaluation of scour in cohesive soil requires a good understanding of hydraulic erosion power from stream flow and the erosion resistance of the soil. In order to develop more reliable scour evaluation methods, the US Federal Highway Administration is investigating a few approaches for evaluating erosion resistance of cohesive soil. The In-situ Scour Testing Device (ISTD) produces a horizontal flow to simulate the flood conditions in an open channel and test the soil for erodibility. The erosion head assembly is compact in size and fits into the steel casing commonly used with hollow stem augers in a routine geotechnical subsurface exploration. The ISTD can be deployed to any depth that pier scour may reach to test the local material for erosion resistance. This device is calibrated using lab erosion testing devices and has been tested in the field
Numerical simulation on local scour below a weir using two-phase WC-SPH method
Get PDFIn this study, numerical simulation of the local scour behind a weir due to overflow using a Lagrangian formulation of the Navier–Stokes equations, based on the weakly compressible smoothed particle hydrodynamics (WC-SPH) method, has been done. In this simulation, the advantages of SPH will be exploit-ed to simulate the soil–water interaction. Water is considered as a viscous fluid with weak compressibility and soil is assumed to be an elastic–plastic material. The elastic–perfectly plastic model based on Mohr–Coulomb’s failure criterion is implemented in SPH formulations to model the soil movement. Interaction between soil and water is taken into account by means of seepage force and pore water pressure. Numerical Simulation of local scour behind the weir has been done; the numerical results are then compared with experimental data. The results have shown that the proposed model could be considered a powerful tool to simulate extremely large deformation and failure of soil
Sediment transport and shoreline erosion induced by bichromatic waves with varying group period
Get PDFIn the present paper, large scale experimental data are presented showing sediment transport and beach profile evolution at the inner surf zone, close to the shoreline. Four different bichromatic wave conditions have been generated characterized by a similar energy content but varying the wave group period (frequency bandwidth). The differences in the shoreline evolution and associated sediment transport are explained from the differences in the wave group period. It has been shown that increasing the wave group period promotes a seaward horizontal displacement in the shoreline erosion pattern. The inner surf zone shows larger erosion for increasing wave group periods. However at the swash zone larger wave group periods show a berm located further seaward with a relatively less shoreline retreat. Differences in the beach profile evolution are explained from the bandwidth influence in the propagation of wave groups and associated long wave. Larger wave group periods showed a progressive long wave pattern with the associated long wave out of phase with the wave group envelope. This resulted in negative long-wave induced sediment transport within the inner surf zone. Reduced wave group periods have shown a standing pattern that resulted in long wave motions in and out of phase with the wave group envelope depending on the cross-shore location. Within the inner surf zone this resulted in mostly positive long wave induced sediment transport for reduced wave group periods. It was also shown that the long wave induced sediment transport represented on average 18% of the total mobilized sediment transport