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Scour and sedimentation of submarine pipelines: closing the gap between laboratory experiments and field conditions (Keynote)
Get PDFPredicting changes to subsea pipeline embedment due to sediment mobility is critical to many aspects of pipeline design, including on-bottom stability, thermal management, fatigue analysis and flow assurance. Motivated by this requirement, significant advances have been made over the last few decades in un-derstanding the mechanisms of pipeline scour and sedimentation. This has led to the development of predic-tive models and formulas, based predominantly on laboratory experiments. However, despite these developments uncertainties still remain in predicting scour and sedimentation in actual field conditions. One reason for this continued uncertainty is that previous laboratory experiments have often focused on idealised testing conditions, consisting of uniform sandy sediments and steady or stationary near-bed current and wave velocities. Although these idealised conditions enable systematic studies, they are not representative of the range in marine sediments and metocean conditions observed in practice; hence extrapolation is necessary. A second reason for uncertainty is that there has only been limited comparison of laboratory results with field data, and so quantitative validation is lacking. Noting these areas of uncertainty, in this paper we review a col-lection of recent studies completed at the University of Western Australia (UWA) which each aim to close the gap between laboratory experiments and actual field conditions, and therefore reduce uncertainty in predicting changes in scour and sedimentation in the field. These studies focus on three aspects of work: (i) the effect of variations in marine sediment properties on the rate of pipeline scour; (ii) the effect of time-varying seabed velocities on pipeline scour; and (iii) comparisons of laboratory based estimates of scour and sedimentation with field data. In each study an emphasis is placed on developing reliable predictive models and formulas that better represent field conditions, or are validated against field observations. It is argued that these models allow for improved predictions of pipeline scour and sedimentation, and may be used to form a rational design approach for subsea pipelines
Improving urban resilience to flooding: a vital role for civil engineers
No full textBeing resilient against flooding is a key challenge for urban communities – and one for which civil engineers can play a vital role. Manuela Escarameia of HR Wallingford highlights findings of two themed issues of the Institution of Civil Engineers’ journal Water Management on the topic.
Much has been written in recent years about resilience in many sectors of society and, equally, many definitions of resilience have been suggested.
In the context of urban resilience to flooding, the following definition by van Veelen et al. (2015: p. 50) is arguably the most appropriate: ‘Resilience [is] the capacity of a system to buffer natural variations, recover from disturbances and return to its previous state without experiencing changes to the system as a whole.’
However, when certain thresholds are reached (‘tipping points’) systems are no longer able to recover and need to adapt to face changing circumstances.
This is what civil engineers need to bear in mind when designing and managing infrastructure that limits personal and economic damage from flooding
Methods of assessing flood resilience of critical buildings
No full textAn overview is presented of recent advances in the assessment methods and mitigation solutions for the performance of critical buildings during flood events. This draws on research focusing on critical urban infrastructure, which is defined as assets that are essential for the continuity of economic activities in cities and for the basic living needs of the urban population. These assets include networks as well as buildings, the latter (termed ‘critical buildings‘) having an important role in protecting equipment and personnel associated with the networks. Examples include power stations, transport control centres, communication hubs, fire stations, shelters and hospitals. Unlike domestic constructions, due to their specificity, these buildings cannot easily be categorised in terms of type of construction or age, and have to be treated as individual buildings. Three methods are presented as a framework with a logical progression for the assessment of building flood vulnerability and the identification of improvement measures: the ‘quick scan’ method, the ‘selection and evaluation tools for flood proofing of buildings‘ and the ‘individual building flood damage tool’. It is expected that building owners, insurance companies, local authorities and agencies with urban flood management responsibilities will benefit from the application of the framework and tools presented
Real-time flood inundation forecasting and mapping for key railway infrastructure: a UK case study
No full textFlooding events that impede railway infrastructure can cause severe travel delays for the general public and large fines in delayed minutes for the rail industry. Early warnings of flood inundation can give more time to implement mitigation measures which help reduce cancellations, delays and fines. Initial work is reported on the development of a real-time flood inundation forecasting and mapping system for the Cowley Bridge track area near Exeter, UK. This location is on one of the main access routes to South West England and has suffered major floods in the past resulting in significant transport impacts. Flood forecasting systems in the UK mainly forecast river level/flow rather than extent and depth of flood inundation. Here, the development of a chain of coupled models is discussed that link rainfall to river flow, river level and flood extent for the rail track area relating to Cowley Bridge. Historical events are identified to test model performance in predicting inundation of railway infrastructure. The modelling system will operate alongside a series of in-situ sensors chosen to enhance the flood mapping forecasting system. Sensor data will support offline model calibration/verification and real-time data assimilation as well as monitoring flood conditions to inform track closure decisions
Impact of soil treatment on internal erosion resistance and hydro-mechanical characteristics of a silty soil
Get PDFThe aim of this paper is to examine the impact of soil treatment on the internal erosion and the hydro-mechanical characteristics of a silty soil. The study is focused on the treatment by kaolinite, bentonite, lime and cement, with different amounts and curing periods. A new enhanced Hole Erosion Test was developed especially to study the internal erosion of treated soils using high hydraulic shear stresses.
The use of clayey products decreases both the hydraulic conductivity and the coefficient of soil erosion without changing the mechanical behavior. Lime and cement treatment induce a significant improvement of both internal erosion resistance and strength, and also keep the same level of hydraulic conductivity, and may even decrease it in some cases. The magnitude of these modifications is related to the nature and amount of the treatment product, and the curing period. The cross relationships between the hydraulic conductivity, the unconfined compression strength and the internal erosion were also assessed
Application of swat model to estimate the annual runoff and sediment of Duhok Reservoir watershed
Get PDFEstimation of runoff volume and sediment load is a problem that directly affects the performance of dams due to the reduction in the storage capacity of their reservoirs and their effect on dam efficiency and operation schedule. The simulation models can be considered for evaluation of sediment potential if the continuous field measurements are not available. Soil and Water Assessment Tool (SWAT) was applied to estimate the annual runoff volume and sediment load for Duhok Dam Reservoir in north of Duhok/Iraq for the period 1988-2011. The estimated annual runoff volume varied from 2.6 to 34.7MCM. Those values are af-fected by rainfall depth, intensity and runoff coefficient, while the annual runoff coefficient for the studied area ranged from 0.06 to 0.33 (average is 0.19) causing an average runoff volume of 14.3 MCM. The sediment routing indicated that the values of sediment yields varied from 50 to 1400 t/km2/year depending on sub basin properties. The average annual sediment load from the whole watershed was 124.6 *103 ton. The estimated total sediment arrived to Duhok Reservoir for the considered period 1988-2011 was about 2.99*106 ton
Development of a new submersible test to characterise the erosion of soils and sediments
Get PDFUnderstanding the mechanism and behavior of the scour process is a most challenging subject. One part of this challenge is the in situ measurement of soil and sediment sensitivity to erosion (in undisturbed and submersible conditions). To improve this understanding, a new test, the Wheel Erosion Test (WET), was developed. It consists of a wheel rotating upon a layer of sediments located in an aquarium filled in with water. The rotating speed of the wheel and the distance to the sediment bed are the main control parameters. If the bed shear stress produced by the wheel is sufficient, grains are eroded and a scour hole is observed. The dimensions of the scour hole (length, width and depth) can be determined by video camera and acoustic measurements allowing the quantification of erosion strength. A first parametric study on Fontainebleau sand validating the principle of the WET is reported
Stability of wide-graded granular filters under oscillatory flow
Get PDFGranular filters are applied for bed and bank protections and installed at coastal and offshore structures (i) to prevent erosion and (local) liquefaction, (ii) to avoid sinking and sagging of the cover layer into the subsoil, and (iii) to provide a sufficient superimposed load to the subsoil countering failure due to excess pore pressure. Offshore and coastal structures are mainly subject to oscillatory flow driven by wind induced waves. Geotechnical and hydraulic processes are studied and discussed with the key objective of developing hydraulic filter criteria for granular filters in marine environments. The focus of this paper is on the contact erosion at the interface of a wide-graded granular filter and subsoil subject to oscillatory flow perpendicular to the interface. For this purpose, a new test facility is applied for the first time and a new test cell is developed
Direct action self-help (DASH) groups in UK flood risk management
No full textThis paper presents an analysis of the nature and effectiveness of community direct action self-help (DASH) groups and includes a case study analysis of a river conveyance management group and a sea wall management group. DASH groups are found to be motivated by the need to deal with increasing flood risk in the face of reduced public funding, alongside sense of stewardship and community solidarity. Channel maintenance work by a DASH group can be effective and efficient at reducing some aspects of local fluvial flood risk for lower order flood events. Maintenance of existing sea walls by a DASH group may be less efficient because of the need for significant expenditure on materials and only efficacious if the engineering is quality-controlled; its longer term effectiveness is also limited by sea level rise. DASH groups require nurture to be sustainable but can deliver community benefits. Professional FCRM coordination and support of DASH activity was examined using a case study of an Environment Agency (EA) area coordinator and comparisons with alternative approaches. Support of DASH groups by FCRM professionals was found to be essential to avoid unwise activities and involves not only controlling consents, but also providing advice on the nature and extent to which DASH activity might be appropriate and arranging practical support and seed-corn funding. The most effective form of DASH facilitation requires a quality and quantity of involvement that cannot readily be supplied by dispersed arrangements from a number of individuals
Effectiveness of direct action self-help (DASH) groups in local flood risk management
Get PDFA case study analysis of the effectiveness of two community direct action self-help (DASH) groups: a river conveyance management group and a sea wall management group. DASH groups are found to be motivated by the need to deal with increasing flood risk in the face of reduced public funding, alongside sense of stewardship and community solidarity