1642 research outputs found
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Passing vessel and tidal flow impacts on submerged tunnel elements during installation
No full textA number of numerical and physical model studies were used to assist in the design and future construction of the Oosterweel tunnel Project at Antwerp, Belgium.
An immersed tunnel, when completed, will connect left and right bank of the River Scheldt, see Figure 1. The tunnel will consist of 8 tunnel elements, to be immersed in water depths of up to 30m with ebb and flood tidal currents up to 2m/s. The design of the immersion and mooring systems are therefore a crucial part of the installation as well as understanding the effects of passing vessel on it, whilst in a temporary state before final back fill.
The studies investigate the different hydraulic load cases on various tunnel elements (TEs) during and post immersion. The TEs will be placed starting from the Southern bank of the River Scheldt (Linkeroever) with elements suspended from catamaran pontoons during installation process, see Figure 2
Functional behaviour of flocs explained by observed 3D structure and porosity
No full textClay-rich flocculated suspended sediments are an important constituent of estuarine and coastal systems globally. They are responsible for the host, movement and deposition of a variety of pollutants, contaminants and sediment itself. Accurate modelling of the movement of these sediments is crucial for a number of industries including fisheries, aquaculture, shipping and waste management. This requires an accurate and reliable measurements of the physical properties of flocs and their behaviour. Porosity is a key element in floc structures, and this research provides updated 3D quantified porosity and pore space morphological data in relation to influences on floc settling behaviour. We report the questionable relationship between floc size and settling velocity, and explore alternative influences such as floc composition, porosity and pore morphology. These outcomes suggest that a shift in focus from floc size to a combination of factors is necessitated to understand the complex movement behaviour of flocculated suspended sediments
Detailed modelling to evaluate the effectiveness of sediment recycling on coastal habitat
No full textIn many parts of the world, ports and harbours lie adjacent to ecologically important areas of coastal habitat. In such areas port authorities, coastal managers and regulators are required to negotiate the tension between the demands of making ports ever more efficient, with wider and deeper approaches to accommodate vessels of deeper draft and larger handling areas, and the preservation of coastal habitats which are vitally important for bird and fish populations and which help protect the coast from flooding and erosion. The deepening of approach channels and berths usually results in an increased rate of sedimentation and maintenance dredging. There is an increasing recognition that such dredged sediment is a resource which should be utilised beneficially for human development activities and/or enhancement of ecological habitats. One form of beneficial use of dredged material, is termed “sediment recycling” or “strategic placement”. This form of beneficial use consists of the placement of cohesive sediment into the water column or onto the bed in such a way so that currents and waves then transport the released sediment onto the desired habitats. Sediment recycling is less widely practiced because the changes in bed level resulting from placement are generally of the order of a few centimetres/year or less and it is difficult to demonstrate whether such recycling is successful. This paper describes a methodology for the assessment of the effectiveness sediment recycling, implementing the methodology on a case study of a large-scale sediment recycling scheme in the Stour/Orwell Estuary system in the United Kingdom, designed to offset the identified adverse effects of an approach channel deepening on the estuary system. The study represents a major contribution to the consideration of non-direct beneficial use of cohesive sediment. For the first time a methodology for reliably evaluating the effects of sediment recycling, separating the effects of natural changes in morphology from the beneficial use, has been shown to be effective. This method, which is applicable anywhere where there are sufficient data, allows a robust evaluation of the effectiveness of such methods and crucially enables these methods to be tested and optimised using modelling before implementation
Evaluation of a nature-based agitation dredging solution
No full textThe challenge of maintaining harbours and ports while conserving and sustaining coastal habitats, with all the rich resources they provide, requires that port and harbours do more to develop approaches to maintenance dredging that provide benefit to these neighbouring habitats. In this article, we describe an example from Harwich Harbour in the UK where Harwich Haven Authority (the Conservancy Authority) is looking to move to a more nature-based maintenance dredging methodology, using agitation dredging. Using the results of monitoring and sophisticated numerical modelling, we evaluate the likely benefit to the Stour/Orwell intertidal areas arising from the use of the agitation dredging
An approach to overtopping assessment for a resilient railway at Dawlish, UK
No full textFollowing regular disruptions to the Southwest rail network, especially during the storm events of 2014, Arup was appointed by Network Rail (NR) to complete a feasibility review, optioneering and single option development for the Dawlish railway section from Colonnade to Coastguards (C2C) including Dawlish Station and Dawlish Water River basin. The objective of the project was to assess resilience options to wave overtopping, determine feasibility of each option and analyse their respective advantages to select the most appropriate option. The criteria included resilience performance, sustainability, buildability, programme, adaptation and whole life cost. This paper focuses on wave overtopping as a key driver of the design process with important lessons learned from a large physical modelling campaign. A staged approach was developed; it involved development of specific criteria for the assessment of the wave overtopping performance; analytical estimations of overtopping performance based on Eurotop, 2018; testing in a 2D physical model to assess the sensitivity to varying seawall configurations; testing of the initial scheme in a 3D physical model; design optimisation in the 3D physical model; tests of the existing/’do nothing’ in 2D or 3Dto highlight the benefits of the proposed scheme; development of an adaptive design
Damage progression of low-crested rubble mound with single layer and core
No full textA damage progression model for armour and core stones is developed to predict the temporal and cross-shore variation of a low crested rubble mound erosion under irregular wave action. The numerical model predicts the damage of a low crested rubble mound with one armour layer and core. Experimental data in a wave flume are used to calibrate the cross-shore model. The protective effect of the armour layer on core stones decreased as the armour layer was damaged and its alongshore averaged thickness become thinner. This study elucidated the armour and core stone interactions
Variations in vertical seawall geometry and the effect on wave overtopping discharges
No full textWith sea level rise and the potential impacts of climate change, wave overtopping of seawalls around the UK is of increasing concern and importance. This paper briefly describes the current information available to designers and engineers for predicting overtopping discharge of vertical or steeply sloping structures. Three physical model experimental studies undertaken for Arup are described and the measured discharges used to investigate the influence of the different structural elements. The majority of the elements reduced mean overtopping discharge compared to a simple vertical wall. A set-back wall, even a small one, was the most effective element. The three studies also highlight the value of physical modelling in accurately quantifying the overtopping for the different structure configurations, particularly for more complex structures
Relaxation of anti-COVID-19 measures reveals new challenges for infectious disease outbreak forecasting
No full textSince early 2020, countries around the world have seen unprecedented government-imposed restrictions and behavioural changes that have changed the transmission dynamics of infectious diseases. These changes have posed unique challenges for routine seasonal infectious disease forecasting systems, which have seen the relevance of their rich long-term pre-COVID-19 datasets for prediction questioned in this new era
Adapting reservoir flushing strategies to changing hydro-climatic conditions
No full textSustainable use of water reservoirs is threatened by sediment accumulation. The loss of storage volume can be prevented or limited by appropriate sediment management strategies that work for a variety of expected conditions. The paper presents the development of a reservoir flushing strategy, tested against water and sediment inflow that might occur over the centuries. A typical length of water and sediment record of 50 years to represent the range of variability within a year is used and extended by deducing longer term inter-annual variability from suitable indicators (sediment cores in natural lakes, tree-ring chronologies, etc.) It was concluded that over the past centuries, water inflows in a period of 50 years could typically vary by about 10% while sediment inflows could vary by about 20%. The resilience of flushing rules derived solely on the recorded data set over centuries-long periods was tested using a long-term computer simulation of reservoir sedimentation. The simulations showed that some modifications to the rule would increase its performance over centuries-long period. Although the approach was derived for a specific project, it is based on some generally applicable parameters such as the discharge at which operation stops and moving average of the annual peak flow
Interactions between climate change, urban infrastructure and mobility are driving dengue emergence in Vietnam
No full textDengue is expanding globally, but how dengue emergence is shaped locally by interactions between climatic and socio-environmental factors is not well understood. Here, we investigate the drivers of dengue incidence and emergence in Vietnam, through analyzing 23-years of monthly district-level case data spanning a period of significant socioeconomic change (1998-2020). We show that urban infrastructure factors (sanitation, water supply and long-term urban growth) predict local spatial patterns of dengue incidence, while human mobility is a more influential driver in subtropical northern regions than the endemic south. Temperature is the dominant factor shaping dengue’s geographical distribution and dynamics, and using long-term reanalysis temperature data we show that recent warming (since 1950) has generally expanded transmission risk throughout Vietnam, and most strongly in current dengue emergence hotspots (e.g. southern central regions and Ha Noi). In contrast, effects of hydrometeorology are complex, multi-scalar and dependent on local context: risk increases under both short-term precipitation excess and long-term drought, but improvements in water supply largely mitigate drought-associated risks except under extreme conditions. Our findings challenge the assumption that dengue is an urban disease, instead suggesting that incidence peaks in transitional landscapes with intermediate infrastructure provision, and provide evidence that interactions between recent climate change and mobility have contributed to dengue’s ongoing expansion throughout Vietnam