1642 research outputs found
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Applying a multi-scale decoupled modeling approach to evaluation of New Orleans flood defenses
No full textThe Greater New Orleans Hurricane and Storm Damage Risk Reduction System (GNO-HSDRRS) is the comprehensive flood defense system constructed in response to Hurricane Katrina. The GNO-HSDRRS is divided into two sub polders which are the Lake Pontchartrain and Vicinity (LPV) and the West Bank and Vicinity (WBV) projects. In order for the system to meet the allowable overtopping criterion throughout the design life, continual evaluation and costly maintainance is required to combat deficiencies resulting from subsidence and sea level rise. This analysis aims to test a multi-scale decoupled modeling approach to evaluating the health of the GNO-HSDRRS via AdCirc (regional scale) and Proteus (local scale). Using surge elevations and wave characteristics extracted from 152-synthetic storms (Adcirc), overtopping of floodwalls and levees were calculated with empirical relationships from the EurOtop guidance. For a more in-depth evaluation of the localized hydraulic processes involved with overtopping of the GNO-HSDRRS structures, the study will be supplemented with computational fluid dynamics (CFD) simulation by imposing identical conditions in Proteus. Primarily, this will serve as an evaluation of the Proteus code's ability to produce accurate overtopping rates for the New Orleans coastal defenses. Secondly, overtopping rates for more complex levee and floodwall geometries will be evaluated by using Proteus as a design tool. The goal is to identify and optimize potential cross-sections that could reduce flood risk more efficiently
DAMSAT - An operational system for tailings dam monitoring by bringing together remote sensing, meteorological and on-site observations
No full textTailings dams and storage facilities store toxic mine waste and effluent. Failure of a tailings storage facility can cause dramatic local ecosystem damage, water contamination and, if a tailings dam fails, loss of life due to inundation of the downstream area. The failure rate of tailings dams is known to be significantly greater than that of conventional water retention dams, but monitoring all tailings dams and storage facilities through frequent site visits could be an expensive and resource-demanding task.
Monitoring tools based on remote sensing and internet of things (IoT) sensors have the potential to reduce the risk from tailings storage failures by enabling the organisations responsible to conduct some monitoring remotely, and hence direct their resources for detailed monitoring more efficiently.
We present an overview of DAMSAT (Dam Monitoring from SATellites), an operational tool for monitoring tailings dams, tailings deposit areas and water dams. The tool consists of several different modules. Radar and optical satellite remote sensing data, and in situ internet of things (IoT) sensors are used to monitor surface movement and indicators of pollution at tailings storage sites. Meteorological forecasts are coupled to hydrological models in order to forecast changes in water level at the dams. DAMSAT presents the monitoring information together with risk information from hazard, consequence and evacuation models of possible dam failures in one integrated platform. The project is a partnership between UK and Peruvian organisations. This approach, alongside proactive user engagement activities and user requirements analysis, is designed to ensure that the system is developed with the needs of the user community in mind
An agent-based model to predict fish collisions with tidal stream turbines
No full textInterest in marine tidal turbines, particularly in coastal waters, raises concerns about collisions between marine wildlife and underwater turbine blades. Prediction methods for collisions are necessary to evaluate possible consequences for marine animal populations. Existing collision risk models, based on analytical solutions, assume simplistic non-behavioural traits. This paper seeks to advance these collision models to represent real behaviours of marine species by extending an existing numerical Agent-Based Model (ABM) to include predictions of collisions.
The ABM successfully reproduced the results of the Collision Risk Model [1]. The ABM offers the advantage that the distribution of marine animals around the turbine does not need to be specified a priori, but arises from the swimming behaviours of the individuals within the model.
The ABM was applied to predict the impact of different swimming behaviours on collision rates for migrating silver eels passing a tidal turbine in Strangford Narrows. Just 1.1% of eels passing the Narrows were predicted to collide with the turbines. Different vertical swimming behaviours influenced the number of eels leaving the estuary and the number of predicted collisions. Other behaviours (e.g. active turbine avoidance) could be included in the ABM making this a valuable method for assessing turbine interactions
Supporting reduction of risks of tailings dams using earth observation data
No full textTailings dams are earth embankments used to store toxic mine waste and effluent. Their failure, as already seen in January 2019 with the fatal failure of Brumadinho dam in Brazil, can cause loss of life, irreversible damage to ecosystems and large economic damages. In countries with limited resources, it is challenging for the authorities to be able to assess the risk and effectively monitor this type of infrastructure, especially when located in remote areas.
We are developing DAMSAT (Dam Monitoring from SATellites), a web-based system for a sustainable and cost effective way of remotely monitor tailings and water retention dams to support early decision making and reduce the social, economic and environmental impacts downstream of potential failures.
DAMSAT monitors the displacement of the structures using earth observation technologies such as Interferometric Synthetic Aperture Radar (InSAR) and Global Navigation Satellite System (GNSS) technologies, combined with real-time in-situ devices. These observations combined with weather forecasting tools allow the issue of alerts for unusual behaviour or weather conditions that could lead to dam failure. These alerts are part of the Disaster Risk Management cycle to trigger the implementation of mitigation measures to reduce the likelihood of failure of the dam or the potential consequences downstream.
In order to have a better understanding of these potential consequences and provide all the information necessary for asset managers to take decisions, DAMSAT also assesses the hazard component of disaster risk due to dam failure using a set of modelling tools. A dam breach simulation model (EMBREA) is combined with a mud flow model to spread the flood hazard downstream of the dam if a failure occurs. The consequences of the flood are assessed in terms of loss of life using an evacuation model, the Life Safety Model. Different flood warning scenarios and evacuation strategies are mapped to inform emergency planning.
DAMSAT is currently being piloted in two mining regions in Peru with the involvement of government organisations and other relevant stakeholders
On environmental contours for marine and coastal design
No full textEnvironmental contours are used in structural reliability analysis of marine and coastal structures as an approximate means to locate the boundary of the distribution of environmental variables, and hence sets of environmental conditions giving rise to extreme structural loads and responses. Outline guidance concerning the application of environmental contour methods is given in recent design guidelines from many organisations. However there is lack of clarity concerning (a) the differences between approaches to environmental contour estimation reported in the literature, and (b) the relationship between the environmental contour, corresponding to some return period, and the extreme structural response for the same period. Hence there is uncertainty about precisely when environmental contours should be used, and how they should be used well. This article seeks to provide some assistance in understanding the fundamental issues regarding environmental contours and their use in structural reliability analysis. Approaches to estimating the joint distribution of environmental variables, and to estimating environmental contours based on that distribution, are described. Simple freely-available software for estimation of the joint distribution, and hence environmental contours, is illustrated. Extra assumptions required to relate the characteristics of environmental contours to structural failure are outlined. Alternative response-based methods not requiring environmental contours are summarised. The results of an informal survey of the metocean user community regarding environmental contours are presented. Finally, recommendations about when and how environmental contour methods should be used are made
Development of a detailed tide and storm surge forecast system for the South West Coast of Ireland
No full textThis paper describes the development and results of a TELEMAC-2D hydrodynamic model set up to potentially provide an operational forecast of tides and storm surges for Tralee and adjacent bays, in South West (SW) Ireland. The TELEMAC-2D model was set up using the latest bathymetry data including high resolution multibeam and LiDAR data. The model was initially forced with TPXO tidal data and wind and pressure data from ECMWF and Met Éireann and calibrated against available gauge data in SW Ireland including Tralee Bay. The initial calibration of the model showed good agreement against the measurements, with the tide and storm surge model predictions, close to, or within the specified minimum target accuracy and forecast delivery times. Following the first of two trial periods in winter 2018/2019 the model boundary tidal forcing was updated to use FES2014, which resulted in closer agreement with tidal predictions. The second live trial period was subsequently carried out during the autumn of 2019. An analysis of the results shows that the hydrodynamic model is in good agreement with measurements. Little difference was observed between the storm surge forecasts using the ECMWF or Met Éireann meteorological forcing, but it was expected that the higher resolution Met Éireann Harmonie data has the potential to provide more detail. This paper summarises the development model setup and results to date
Recirculating flume tank experiments reconstructed in TELEMAC3D-GAIA to model flow and sediment transport processes around an object in sand and gravel mixtures
No full textIn the ever-increasing need for the installation of seabed infrastructures used for example to extract renewable energy and facilitate offshore centralised storage, differently shaped and orientated objects are employed, causing flow diversion and enhanced forcing of the seabed. These processes are detrimental to the integrity of the seabed and infrastructure, including cabling. We currently lack understanding of the enhanced bed dynamics around objects placed on mixed coarse beds. In sand and gravel beds, the shear stress needed to mobilise gravel can be up to 64% less than the shear stress required for pure gravel beds and the corresponding sediment transport rates can be up to three orders of magnitude higher.
Laboratory experiments were conducted, to better understand the interaction of the enhanced fluid dynamics and bed dynamics around an object, using a 10m long recirculating Armfield flume tank. A submerged cylinder was placed on seven different sand and gravel mixtures, to compare the effective mobility of differently mixed beds. Two unidirectional flow speeds were applied to the bed, experimentally tested to mobilise either just the sand (25.7 cm·s-1), or both the sand and gravel fractions (39.6 cm·s-1). The 3D bed scans gathered using an array of 5MHz SeaTek ultrasonic transducers at several stages of the experiment has allowed a quantification of the affected bed in the wake of the object, through erosion rates and ripple migration rates. Down-core sediment samples were taken, using a syringe. Analyses of the samples revealed the changing coarse fraction with depth as the bed evolved. These laboratory experiments were simulated using a coupled TELEMAC3D-GAIA model. The object in the model simulations was treated as a raised feature on the bed, to prevent the model treating the object as erodible sediment. Comparison of preliminary results from the model simulations and laboratory experiments showed that the overall geometry of the scour was good, but the model underestimated the scour depth and extent. To overcome that problem, increased Turbulent Kinetic Energy around the object, calculated in TELEMAC3D by the k-ε model, was used to improve estimations of the bed shear stress
Investigating the use of joint probability curves in coastal engineering practice
No full textThis paper investigates the inherent inaccuracy in the estimation of various extreme response variables (RVs) for different sea defence structures using joint exceedance curve approaches in common use around the UK. Utilising stochastically generated nearshore datasets that include extreme wave and sea-level conditions determined at regular intervals around the English coastline as part of a previous study, and asset information from the Environment Agency's Asset Information Management System database, this paper assesses 592 sea defence structures and their associated extreme response using different joint exceedance curve approaches when compared against the RV approach. This paper highlights that extreme RVs are often underestimated when using a joint exceedance curve approach, which in many cases can be significant. This suggests that the performance of many sea defence structures are incorrectly estimated. As a consequence, joint exceedance curve approaches may under-design sea defence structures to a greater level than previously indicated, or significantly underestimate extreme RVs when assessing the performance of existing structures
A review of Ackers & White sediment transport predictor
No full textSediment transport predictor based on a review and update of the theory of Ackers and White is proposed. While the core of the theory was retained, the approach to predicting transport rates was updated by introducing some new ideas and modified where opportunities for improvement were identified. A large dataset compiled from the existing literature was used for model calibration and validation. The results show a good improvement compared to the original Ackers and White equation as well as some other total load predictors. Better matching with the observed data is achieved especially at higher slopes (above 1%) and low submergence ratios (below 50) as well as at the extremes of the sediment size scale, where the applicability was extended to the coarse silt region. Predictions for gravel and coarser sediment were also improved
Effect of a skirted mudmat foundation on local scour around a submerged structure
No full textIn this paper, local scour around a subsea structure supported by a skirted mudmat foundation is explored experimentally. For simplicity the structure is represented as a submerged circular cylinder founded on a concentric circular mudmat. The experiments are conducted in the clear-water regime and various geometries are considered by varying the height of the submerged cylinder relative to its diameter , and the diameter of the mudmat relative to the submerged cylinder . The experimental results indicate that the scour process can be categorized into two modes depending on geometry: Mode 1, in which local scour develops immediately at the upstream side of the mudmat; and Mode 2, in which local scour initiates at the downstream side of the mudmat and propagates upstream. For each mode, the rate of scour reduces as the mudmat becomes relatively large (i.e. as increases). This reduction is most significant if the mudmat size is sufficient to swap the mode of scour from Mode 1 to Mode 2. The reduction in scour rate, however, does not coincide with a reduction in maximum scour depth. Instead, the relative scour depth of the superstructure increases as the mudmat becomes larger (i.e. as increases). This trend is quantitatively explained by considering the effective aspect ratio of the combined mudmat and superstructure. Collectively, the results of the present study provide insight into the inherent scour protection provided by a skirted mudmat foundation