1642 research outputs found
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A two-fluid simulation of tailings dam breaching
No full textThis paper presents the development and application of a dam breach model, EMBREA-MUD, which is suitable for tailings dams. One of the common failure modes for these structures is breaching due to overtopping, which together with the flow of liquefied tailings, is simulated by the proposed model. The model simultaneously computes the outflow of water and tailings from a tailings storage facility and the corresponding growth of the breach opening. Tailings outflows are represented by a separate non-Newtonian viscous layer, which together with a water layer, represent the two fluid components of the model. The third component represents dam material that can be eroded by the shear forces exerted by either water or mud. The water layer also exerts dynamic and erosional forces and can transport solids eroded from either the mud or dam layer. The model was verified against laboratory cases as well as two field cases reported in the literature, the failures of the Mount Polley tailings dam in Canada in 2015 and the Merriespruit dam in South Africa in 1994. The model results agreed well with the recorded narrative of the events, although in the latter case, careful calibration of one of the model parameters was necessary to obtain a good match
Experimental study of local scour around submerged compound piles in steady current
No full textMany subsea structures have non-uniform geometries, which extend only a finite distance above the seabed. To better understand local scour at these structures, this paper presents scour measurements from an experimental study of submerged compound piles comprised of a circular superstructure supported by a circular foundation. The experiments were conducted in the clear-water regime and considered the effect of three different ratios describing the structural geometry: (i) the overall height of the compound structure above the initial bed level to the diameter of the super-structure h1/D1; (ii) the height of the foundation exposed above the initial bed level relative to the overall height of the superstructure h2/h1; and (iii) the diameter of the foundation to that of the superstructure D2/D1. In all cases D2 ≥ D1 and h1 ≥ h2 ≥ 0 (i.e. the foundation and superstructure where never buried). The experimental results indicate that, if all other parameters are held constant, the non-dimensional equilibrium scour depth S0/D2 increases with both h1/D1 and h2/h1, and decreases as D2/D1 increases. To quantitatively explain these trends the experimental results are compared with a range of existing methods to predict scour depth for non-uniform (or complex) surface piercing piles. Of these methods it is found that an effective pile height and an effective pile diameter, computed using simple geometric arguments, give good agreement. The concept of effective height is also shown to collapse time-scale measurements of the scour process convincingly across the full range of experimental results and to explain the extent and shape of the local scour hole reasonably well. Collectively, these findings suggest that the calculation of an effective height may be used to provide a reasonable first approximation to estimate the rate and extent of local scour around submerged compound structures
Internal erosion breach model review and validation
No full textPredicting breach erosion processes is essential for the effective risk management of both dams and levees. Following the success of an earlier initiative to assess the performance of breach models for predicting overflow erosion of dams and levees (i.e. the CEATI Dam Safety Interest Group Breach Modelling Project), a new project has been launched to investigate the performance of industry models predicting breach formation initiated through internal erosion.
The project was initiated by Electricité de France (EDF) and started mid-2019, with a planned duration of ~2 ½ years. The approach being taken is to: review existing IE models with the most promising few (with potential for industry application) selected for closer analysis; review available laboratory, field and case study data in order to identify a number of data sets that can be used for model performance assessment and validation; invite international organisations to participate in programme of model review, testing and validation; implement a programme of both ‘blind’ and ‘aware’ model testing, with results shared and assessed transparently by the international team; review and conclude as to the capabilities and potential of existing internal erosion models.
The overall conclusions from this work will be guidance for industry practitioners regarding the types, availability and likely performance of industry applicable internal erosion breach prediction models.
This paper will present details of the programme in April 2020, almost one year into the 2 ½ year overall programme. At this stage, the initial model and data reviews will have been completed, the working group established and the first phase (of three) of modelling and performance review underway
Industry research into dam and levee breach erosion through coarser grained materials
No full textPredicting breach erosion processes is essential for the effective risk management of both dams and levees. In recent years, a variety of research efforts have improved our knowledge of erosion processes, and in particular validation of the work on headcut erosion through cohesive soils performed at USDA-HERU. A similar level of analysis and validation is required for coarser grained and mixed materials to provide a clearer overview of when breach erosion processes change from headcut through surface erosion to slumping of rockfill.
Since the release of flood water through a breached dam or levee depends both upon the rate of soil particle erosion and the macro erosion process (i.e. whether headcut or surface erosion or some other process occurs) it is important to ensure that conditions for these macro and micro erosion processes are understood in relation to different soil types and conditions, and that any breach prediction models correctly reflect these processes.
This paper presents an update on progress with a programme of research being implemented by EDF which investigates (i) how macro erosion processes change in relation to soil type and state, (ii) the validity of soil erosion relationships used for coarser and mixed grained erosion and (iii) the performance of breach models in predicting the breaching processes. This research combines laboratory testing at UPM (~1m scale tests), and potentially also at CNR (~2m scale tests), with large scale field tests (2-4m high) to be undertaken at a new test facility being constructed in the River Ebro catchment in Spain near Zaragoza. The work also combines breach model performance validation through a programme of international collaboration and aligns with research into soil erosion currently underway in the USA by the Army Corps of Engineers (ERDC, Vicksburg) and the Bureau of Reclamation (Denver)
Tracking the fine scale movements of fish using autonomous maritime robotics: A systematic state of the art review
No full textThis paper provides a systematic state of the art review on tracking the fine scale movements of fish with the use of autonomous maritime robotics. Knowledge of migration patterns and the localization of specific species of fish at a given time is vital to many aspects of conservation. This paper reviews these technologies and provides insight into what systems are being used and why. The review results show that a larger amount of complex systems that use a deep learning techniques are used over more simplistic approaches to the design. Most results found in the study involve Autonomous Underwater Vehicles, which generally require the most complex array of sensors. The results also provide insight into future research such as methods involving swarm intelligence, which has seen an increase in use in recent years. This synthesis of current and future research will be helpful to research teams working to create an autonomous vehicle with intentions to track, navigate or survey
The ARC-Boat: a remote controlled rapid response scour monitoring platform
No full textThe assessment of scour at hydraulic structures through inspection and monitoring is a key part of scour risk management. Bathymetric data from monitoring or rapid response surveys post storm provide up-to-date information on the channel geometry and maximum scour at structures. The opportunity presents itself for the use of USVs. The ARC-Boat is a 2 m long, remotely operated survey vessel used to collect hydrometric and bathymetric data. It can be deployed close to site without the need for lengthy equipment mobilisation. Operating onshore from safety the surveyors can optimise the data in real-time. The ARC-Boat’s shallow draft and high manoeuvrability enable it to get close to structures which could be hazardous for manned survey vessels. A swath bathymetry system was integrated to accurately measure the bathymetry and morphology around a bridge. The results present significant opportunities for increased definition of erosional and depositional processes that occur around key assets
An overview of current knowledge and challenges in predicting breach through dams and levees
No full textPredicting breach erosion processes is essential for the effective risk management of both dams and levees. This has been recognised for decades, with efforts to develop breach prediction models dating back to the 1960s and 70s. Over the past decades, numerical methods and computing have advanced, but since breach processes depend upon a combination of hydraulics, soil mechanics and structure response, the challenge to accurately predict breach formation for all scenarios has yet to be met.
Research into different aspects of breach, and in particular into the soil erosion processes of different soils in different states, is starting to show how different erosion behaviour can arise for different hydraulic load and soil conditions. This new knowledge and understanding then needs to feed through into predictive and probabilistic models that industry can use in analysing and determining flood risk from breach.
This paper provides an overview of current knowledge and practice in predicting the different types and phases of breach showing how research efforts around the world are progressively piecing together the jigsaw puzzle of processes that affect and dictate how breach initiates, forms and grows through dams and levees. This includes reference to recent and ongoing work in the France, Spain, the UK, the Netherlands and the USA, and shows how these research efforts are feeding into models and solutions suitable for industry application
Novel use of social media to assess and improve coastal flood forecasts and hazard alerts
No full textCoastal communities and infrastructure need protection from flooding and wave overtopping events. Assessment of hazard prediction methods, used in sea defence design, defence performance inspections and forecasting services, requires observations at the land-sea interface but these are rarely collected. Here we show how a database of hindcast overtopping events, and the conditions that cause them, can be built using qualitative overtopping information obtained from social media. We develop a database for a case study site at Crosby in the Northwest of England, use it to test the standard methods applied in operational flood forecasting services and new defence design, and suggest improvements to these methods. This novel approach will become increasingly important to deliver long-term, cost-effective coastal management solutions as sea-levels rise and coastal populations grow. At sites with limited, or no, monitoring or forecasting services, this approach, especially if combined with citizen science initiatives, could underpin the development of simplified early warning systems
Modelling the impacts of Hurricane Ike on the Texas coast using a fully coupled TELEMAC-TOMAWAC-SISYPHE model
No full textHurricane Ike, a category 4 hurricane, made landfall near Galveston, Texas on the 13th of September 2008. A fully coupled TELEMAC-TOMAWAC-SISYPHE model was developed to predict sediment transport and associated morphodynamics resulting from the passage of Hurricane Ike. The predicted hydrodynamics were validated against observed tidal elevations, currents, waves and inundation. The predicted sediment transport pathways and resulting bed elevation change were compared with assessments of coastal impacts associated with Hurricane Ike. The model results show good agreement with observations and demonstrate the ability to predict hydrodynamics, sediment transport and morphodynamics associated with hurricanes using a fully coupled TELEMAC-TOMAWAC-SISYPHE model
