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Evolution of pneumatic tsunami simulators - from concept to proven experimental technique
No full textThis paper describes the evolution through three generations of pneumatic Tsunami Simulators for physical model tests of realistic tsunami. The pneumatic method, originally developed for tidal modeling in the Fifties, has been modernized to generate extraordinarily long waves in a controlled manner, with accurate reproduction of recorded free-surface tsunami field data. The paper describes how the simulator designs were developed and how they performed in the laboratory. Example results are presented from selected research studies that have validated their performance and then used to quantify tsunami effects. Having described each of the first, second, and third generation Tsunami Simulators, the paper discusses how to calibrate the wave generation control to model tsunami with model periods 20–240 s duration (equivalent to 2–20 min duration in prototype at 1:50 scale), many of which are far too long to “fit into the test flume.” The evolution of a composite approach to wave calibration is described with examples from second and third generation devices, demonstrated by successful simulation of both the 2004 Boxing Day, and the 2011 Great Eastern Japan (Tohoku) Tsunami at 1:50 scale
Managing groundwater supplies subject to drought: perspectives on current status and future priorities from England (UK)
No full textEffective management of groundwater resources during drought is essential. How is groundwater currently managed during droughts, and in the face of environmental change, what should be the future priorities? Four themes are explored, from the perspective of groundwater management in England (UK): (1) integration of drought definitions; (2) enhanced fundamental monitoring; (3) integrated modelling of groundwater in the water cycle; and (4) better information sharing. Whilst these themes are considered in the context of England, globally, they are relevant wherever groundwater is affected by drought
Probabilistic seasonal dengue forecasting in Vietnam: A modelling study using superensembles
No full textBackground: With enough advanced notice, dengue outbreaks can be mitigated. As a climate-sensitive disease, environmental conditions and past patterns of dengue can be used to make predictions about future outbreak risk. These predictions improve public health planning and decision-making to ultimately reduce the burden of disease. Past approaches to dengue forecasting have used seasonal climate forecasts, but the predictive ability of a system using different lead times in a year-round prediction system has been seldom explored. Moreover, the transition from theoretical to operational systems integrated with disease control activities is rare.
Methods and findings: We introduce an operational seasonal dengue forecasting system for Vietnam where Earth observations, seasonal climate forecasts, and lagged dengue cases are used to drive a superensemble of probabilistic dengue models to predict dengue risk up to 6 months ahead. Bayesian spatiotemporal models were fit to 19 years (2002–2020) of dengue data at the province level across Vietnam. A superensemble of these models then makes probabilistic predictions of dengue incidence at various future time points aligned with key Vietnamese decision and planning deadlines. We demonstrate that the superensemble generates more accurate predictions of dengue incidence than the individual models it incorporates across a suite of time horizons and transmission settings. Using historical data, the superensemble made slightly more accurate predictions (continuous rank probability score [CRPS] = 66.8, 95% CI 60.6–148.0) than a baseline model which forecasts the same incidence rate every month (CRPS = 79.4, 95% CI 78.5–80.5) at lead times of 1 to 3 months, albeit with larger uncertainty. The outbreak detection capability of the superensemble was considerably larger (69%) than that of the baseline model (54.5%). Predictions were most accurate in southern Vietnam, an area that experiences semi-regular seasonal dengue transmission. The system also demonstrated added value across multiple areas compared to previous practice of not using a forecast. We use the system to make a prospective prediction for dengue incidence in Vietnam for the period May to October 2020. Prospective predictions made with the superensemble were slightly more accurate (CRPS = 110, 95% CI 102–575) than those made with the baseline model (CRPS = 125, 95% CI 120–168) but had larger uncertainty. Finally, we propose a framework for the evaluation of probabilistic predictions. Despite the demonstrated value of our forecasting system, the approach is limited by the consistency of the dengue case data, as well as the lack of publicly available, continuous, and long-term data sets on mosquito control efforts and serotype-specific case data.
Conclusions: This study shows that by combining detailed Earth observation data, seasonal climate forecasts, and state-of-the-art models, dengue outbreaks can be predicted across a broad range of settings, with enough lead time to meaningfully inform dengue control. While our system omits some important variables not currently available at a subnational scale, the majority of past outbreaks could be predicted up to 3 months ahead. Over the next 2 years, the system will be prospectively evaluated and, if successful, potentially extended to other areas and other climate-sensitive disease systems
Effective Coastal Climate Services—An End-User Perspective for Resilient Infrastructure
No full textThis paper focusses on identifying the responses to coastal climate change that are of interest for decision-making by end users and the delivery and the necessary communication process for this information. The focus is on representation of climate (response) information in a form that provides sufficient clarity in the midst of uncertainty for end-users who are seeking to develop or maintain resilient infrastructure. The paper recommends that the use of the term climate services in situations unrelated to supporting adaptation to and mitigation of climate change should be avoided. Better investment decisions could be made if Bayesian frameworks were used to assign probabilities to RCP scenarios. Associated predictions need to cover all types of climate change influences not just sea level rise and ideally provide concurrent time series to allow evaluation of dependencies. Guidance on climate information published by official bodies needs to adopt a consistent approach, with a clear narrative that describes the transition from science to guidance. The form in which climate services information is needed for the required end user decisions needs careful thought, including appropriate communication of the associated uncertainties using good practices and experiences from related sectors
Briefing: Scour guidance supporting bridge resilience
No full textThis briefing provides a short introduction to a supplement of the Ciria Manual on Scour at Bridges and Other Hydraulic Structures published in 2021. The supplement captures additional knowledge since the scour manual was published in 2015. This note is intended for designers and asset managers of structures in the water environment that may be subject to scour
The feasibility of inter-basin water transfers to manage climate risk in England
No full textClimate change, population growth, and environmental pressures, pose challenges for water resource management. Many countries, like the UK, are projected to experience regional variation in the risk of droughts. One solution is to use inter-basin transfer (IBT) schemes to move water from where it is abundant to where it is scarce. But what are the first steps in studying the feasibility of such schemes as a solution? How can we ensure an IBT brings more resilient water future under the rapidly changing climate and not have a detrimental impact elsewhere? This paper develops and demonstrates a framework for a preliminary climate impacts assessment for IBT schemes. The framework evaluates negative hydrological and ecological impacts of IBTs to the exporting basin. A hypothetical IBT scheme, delivering water from the northeast of England to London in the southeast, is tested. Three transfer scenarios are analysed under 100 future climate scenarios generated from the driest member of UK Climate Projection 2018 (UKCP18). The framework shows there would be no ecological harm for the exporting basin under any scenario. However, the hydrological risk is sensitive to the IBT operation. Constant and low flow operation of the IBT would lead to supply deficits of up to 60% in the exporting basin by the 2080 s. Transferring larger volumes, but only in winter months, allows the IBT to meet the projected water resource deficit in London whilst not increasing hydrological risks in the northeast – even under the driest UKCP18 climate scenario
Satellite data for dam safety monitoring
No full textThe use of datasets from satellites to aid the monitoring of dams has been possible for many years. Within the last five years there has been a rapid development in the type and accuracy of the data available, led by an influx of new satellites and improved access to these datasets. This paper gives an overview of the different types of satellite datasets and satellite infrastructure relevant to dam safety that are currently available, explains the complex processes of converting raw satellite data into useable information and summarises the advantages and disadvantages of each data type along with indications of the level of accuracy and cost. The information presented by the authors is based on experience gained undertaking a 3 year, £4 m, UK-government-funded research project to investigate and combine many types of space data to improve the monitoring of dams
Scour at cofferdam structures on river walls
No full textConstruction activities in rivers and estuaries require cofferdams to be installed to provide a dry working area. Predictions of scour at these temporary structures are made using methods proposed for river abutments in industry guidance with engineering judgement made on the selection of coefficients. The area of the cofferdam and protrusion in the waterway is often larger than the permanent works they are facilitating and they are long, in some instances several hundred metres along the flow direction. Clear-water scour experiments in the General Purpose Flume at HR Wallingford explore the influence of wall mounted cofferdam shape and length, water depth and flow speed on scour. The results provide information of use to engineers working with cofferdams and comments are made on the application of predictive methods
Scour hole collapse at an offshore wind farm foundation
No full textAt an offshore wind farm foundation, where the seabed sediments are mobile, the process of tidally-induced scour removes sediment from around a foundation’s base, creating a steep-sided scour pit. Scour pit slopes are known to periodically destabilise and collapse, with results similar to slope failures observed in terrestrial environments. Until recently these elusive events had not been observed in detail (HARRIS et al., 2019). This is because, unlike their terrestrial counterparts, there are processes that can transport material back up and out of the scour pit, restoring the slope. Capturing these events using discrete surveying techniques is near impossible because the events cannot be predicted and operate on short timescales. Little is known about the prevalence of these events and the driving causes. Here, the authors present an example of one of the rare cases where an event was captured using multibeam bathymetry surveying.
The area of seafloor surrounding the base of an offshore wind farm foundation was surveyed using multibeam bathymetry sonar. The same area was resurveyed the next day. Over this 24 hour period the scour hole at the base of the foundation collapsed, raising the seabed level by as much as 3.3 m, almost half the scour depth (the area in red in Fig. 1). The edge of the scour pit extended >10 m upstream (the area in blue in Fig. 1). The volume of material deposited within the scour pit approximated 400 m3 and was near equal to the volume of material eroded from upstream, i.e. the process was a closed system and little material had yet scoured from the pit following the collapse.
From these two time-steps the frequency and longevity of these events could not be determined. To answer this an echosounder transducer, capable of measuring the level at four fixed points on the seabed, was affixed to a foundation (Fig. 2). The echosounder levels show a reversing rather than monotonic progression with time. The scour collapse events occurred regularly, with a frequency of approximately once every 10 days. The largest collapse events happened during the spring tides. These events typically took place over less than an hour and the scour depth recovered over a period of days.
The weight of the material infilling the scour pit will provide overburden and temporarily stiffen the foundation (MAYALL et al., 2019). The stiffness of the foundation has implications for the longevity of the foundation, with less stiff foundations more quickly reaching the end of their life. The prevalence of these events means that they should be considered during the foundation design process.
The occurrence of these events has implications for the survey design and interpretation. If an infilling event occurred just before surveying, reducing the scour depth, then it could be (incorrectly) assumed that there is minimal scour, altering the decision made about mitigation (e.g. scour protection). Where this process is known to occur the interpretation of periodic surveys should be performed with this in mind