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Two-dimensional modelling of floods due to levee breaching: Application to Enza River, Italy
No full textAs overflow and overtopping erosion pose significant threats to embankment dams and levees, predicting flow propagation in protected areas is vital for effective flood risk management. In this paper, simplified breach growth laws were integrated with the two-dimensional (2D) shallow water equations solver TELEMAC-2D. We applied this model for simulating the levee breaching and associated inundation that occurred on the Enza River, Italy, in December 2017. We compared the computed and observed flood maps. The study evaluated various empirical breach growth models, finding that models allowing specification of breach time and width performed better than those based on physical characteristics for this test case, though the latter models faced data availability challenges and were affected by the presence of multiple breaches
Nacelle natural frequency data to assess the effectiveness of pre- and post-installation scour protection
No full textAt the case study offshore wind farm 140 wind turbine generators were installed atop monopile foundations. At four monopiles a filter rock layer was installed before the piling operations took place, with an armor layer installed atop this layer after piling (pre-installation) and at six monopiles rock protection was installed after some scour had developed (post-installation). Accelerometers were installed in the nacelle of each wind turbine generator. Natural frequency data have been recorded for 10 years since the installation of the scour protection. The initial natural frequency for the pre-installation foundations was significantly higher (i.e. the pre-installation foundations were stiffer). The natural frequency was observed to increase with time at all locations where scour protection had been installed. It is thought that this was due to the densification of the sand within the rock matrix. These findings have implications for the pile fatigue and the management of the site
Forecasting tropical cyclone surge for humanitarian relief
No full textTropical cyclones, with strong winds and low central pressure, can produce very large coastal surges and have led to the most devastating flooding in history. While forecasting of cyclones and emergency management have improved dramatically, flooding from cyclone surge still represents one of the most serious global natural hazards and present a considerable challenge for humanitarian organisations.
A surge and inundation forecasting system has been developed for the UK Foreign, Commonwealth and Development Office in order to aid the coordination of humanitarian relief. The aim of the forecast is to provide advance warning of the location, extent and severity of flooding and impact on population.
A surge forecast system was developed using the hydrodynamic model, TELEMAC-2D, forced by cyclonic wind and atmospheric pressure fields. A number of constraints and requirements needed to be met to develop a practical and reliable service, including:
• A number of regional TELEMAC2D models were developed covering coastal areas around the globe at risk of flooding from cyclone surge and be of interest to the FCDO and humanitarian agencies;
• The models must adequately resolve the wind and pressure fields of cyclones, coastal bathymetry and topography;
• The models include tide as it is the combination of both tide and surge that determines the elevation of the water and hence the extent and severity of flooding;
• Models must run quickly. The flood advisory bulletin is prepared within one working day and the target for the surge model runtime is less than one hour;
• Probabilistic forecasts involving ensemble modelling have been trialled.
The surge modelling system includes a number of regional TELEMAC-2D models covering areas of the world vulnerable to cyclone surge flooding and of interest to the FCDO. The regional models include tide and atmospheric forcing. Cyclone tracks are obtained from relevant meteorological agencies responsible for forecasting tropical cyclones. Within the modelling system, these are converted into wind and pressure fields to force the model. Model results are extracted along the coastline for input into an inundation model and population exposure analysis. The combined results showing areas forecast to be affected by flooding and the impact on the local population and infrastructure are summarised in a concise bulletin for the FCDO which is then circulated to local and international aid organisations including the UN OCHA and International Federation of Red Cross and Red Crescent.
Since the start of the pilot study in October 2020, the team have responded to tropical cyclones affecting Bangladesh, Central America, Mozambique, Madagascar and the Philippines
Wave loads on pile-supported decks overhanging armoured slopes
No full textDeck structures overhanging rubble mounds are commonly adopted solutions for quay walls for marine terminals in relatively deep water or in geotechnical complex conditions. The interaction of waves with relatively low-lying pile supported decks overhanging wave-absorbing slopes can lead to wave energy amplification and entrapment underneath the deck, which can therefore experience very intense dynamic loading, resulting in significant damage and even structural failure.
A physical model study has been carried out with the aim to explore the relative importance of key parameters and develop new formula for use in the estimation of wave slam forces for design purposes. Different combinations of water level / deck freeboards, wave heights and periods were tested using both regular (monochromatic) and irregular (random) waves. The results showed a relationship between the normalised vertical forces (F*) as a function of the normalised run-up clearance (R*). As expected, once a critical threshold between the freeboard and the run-up has been exceeded, the loads on the underside of the deck start to increase rapidly
Internal pressures in rubble mound breakwaters used in coastal protection - recommendations for assessing wave pressures with CFD models
No full textThis paper discusses the use of 2DVertical Computational Fluid Dynamics (2DV- CFD) numerical wave flumes to inform assessments of suffusion risks in permeable structures protecting land reclamation areas. A typical rubble mound breakwater section is presented and key processes during wave interaction with the permeable structure are discussed. Emphasis is given in assessing the influence of the filter layer / geotextile to wave transmission in the breakwater. Results of pressure transmission in the breakwater are presented and compared with empirical methods. Following the analysis of these processes and CFD model results, recommendations are provided, with respect to best practice and limitations of CFD models for assessing suffusion risks, and for their best use. Recommendation include the use of random waves, to capture the effect of groupiness, recommendations for Darcy-Forchheimer coefficient values (A=150 and B=2 for armour layer and underlayer, use of existing empirical relations for core layer) and the consideration of internal overtopping to estimate water build-up at the landfill. Assessing suffusion risks at the filtering layer with the help of CFD models should be based on estimates of pressure differences rather than calculation of pressure gradients directly from the model
Groynes in coastal engineering a new guide to design, construction, monitoring, and maintenance of narrow footprint groynes
No full textGroynes are cross shore structures designed to control coastal longshore transport that form significant elements of the coastal protection and flood defence schemes around the UK's coast. Prompted by work to capture good practice in timber groyne management, an updated CIRIA guide has recently been published. Having briefly summarized the content of the guide, the paper goes on to examine in more detail some specific aspects where more significant innovations from research and from practice development have been identified. These include: timber groyne distribution around the UK; key factors in setting groyne lengths and spacings; designing for, and adapting to, beach profile fluctuations; ensuring the whole life and sustainability of timber groynes; developments in detailing of timber groyne joints and pile abrasion protection systems
Depositional characteristics of oil-mineral flocs in estuarial and coastal waters
No full textIn recent decades, oil spill contamination has tended to occur more commonly in coastal and estuarial systems around the world, including the waters around the U.K (Manning et al., 2022). The management of such oil spillages, such as the 2010 Deepwater Horizon (DWH) disaster in the Gulf of Mexico, has been a major challenge in coastal and estuarial regions due to the highly sensitive nature of deltaic ecosystems and related public health. Many coastal and estuarial regions tend to have an abundance of clay minerals, and these cohesive particles - which can readily flocculate (e.g. Mehta et al., 2014; Zhang et al., 2018; Spencer et al., 2021; Krahl et al., 2022; Vowinckel et al., 2022) - play an important role in determining the transport of spilled oil contamination and its eventual fate, particularly given that suspended sediment and microbial activities are often prevalent and diverse in natural environments
Discussion: Evaluation of sediment management strategies for Tarbela reservoir
No full textWe are discussing the paper ‘Evaluation of sediment management strategies for Tarbela reservoir’ providing some additional information, based on our studies
Dynamic adaptive engineering pathways for mitigating flood risks in Shanghai with regret theory
No full textUncertainty in sea level rise and future extreme climate events presents a great planning challenge for flood defence in coastal mega cities like Shanghai. While academic literature has largely focused on uncertainty analysis, engineering solution design requires effective uncertainty management. Here we incorporate the regret theory of economics and decision science into the dynamic-adaptation-pathways framework and assess the impacts of high rates of changes on the flood defence systems in Shanghai. Specific options are developed to manage flooding on the Huangpu River from tidal water levels, river flows, rainfall, drainage inflows and combinations of these flood sources including sea level rises of up to 3 m. Dynamic adaptation pathways are developed where the timing of tipping points from one intervention to the next depends on the actual changes in sea level, rainfall and other variables that affect the future design. This framework is potentially applicable for planning ‘no regrets’ flood-defence systems in other low-lying coastal cities
Using a novel mylar film technique to measure the efficacy of scour mitigation methods for offshore wind turbines.
No full textIn recent years research on scour around subsurface structures in the offshore wind environment has gained momentum due to the accelerated demand for renewable energy. This study looks at the use of collars to modify the downflow, the main driver of scour, and reduce the horseshoe and lee-wake vortices, thus reducing local scour depths. For measurement of scour in this study, acoustically transparent Mylar film was applied to the surface of the collar, enabling continuous recording of the scour processes beneath the collar, whilst simultaneously preventing the water and sediment passing through the collar. This enables measurement of scour development throughout the experiments until an equilibrium bed state was developed. Three different collar diameters were investigated at five different heights from the bed with data showing that the larger collars closer to the bed have a higher potential to mitigate local scour depths