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Performance of GloFAS Flood Forecasts using proxy data in Uganda
Get PDFCapabilities to forecast fluvial flooding are not equality spread across the globe and forecasting systems are especially limited in flood-prone low-income countries (Revilla Romero et al., 2014). The availability of higher spatial and temporal resolution remote sensing data and the increase in post processing technology have opened opportunities for fluvial forecasting at a continental and global scale (Emerton et al., 2016a) (Revilla-Romero et al., 2015). This means flood forecasts are available for regions where previously there were no forecasting capabilities. The availability of flood forecasts for flood-prone low-income countries does not directly lead to action being taken in case of flooding. The forecast based financing program of the Red Cross Climate Centre enables early action to be taken using probabilistic forecast information, with the aim of reducing the impacts of flooding (Coughlan de Perez et al 2015). The program uses a combination of forecast models including the Global Flood Awareness System (GLoFAS) and is active in multiple location including Tongo, Peru and Uganda. There are many factors at play to create an effective early warning system, including the performance of the forecast. Analysing the performance of forecasts is essential for the further improvement and development of an effective early warning system. However, in low-income countries with a low data availability this is a major challenge. This poster shows the performance of the GloFAS forecast using proxy flood event data in the North East of Uganda and poses the question: “How can the performance of forecasts be analysed when data is limited and uncertain?”
Overflowing erosion modelling of embankment and concrete dams: state of the art and research needs
Get PDFOverflowing erosion of embankment dams and levees and overflowing erosion of bedrock downstream of concrete dams (through crest overflowing or spillway flow impact) are of major concern for dam and levee owners. Despite extensive research efforts performed in North America and Europe since the late 1990s, many gaps in knowledge still need to be answered in order to provide engineers with validated numerical tools able to predict the erosion mechanisms to an acceptable level of certainty. As addressing these gaps in knowledge will likely require a substantial and expensive research effort, international research collaboration in this field seems the most efficient way to reach these objectives. In order to structure and launch such international collaboration, an international workshop was organized in Aussois, France, from 11th to 14th December 2017, on behalf of the European Group of ICOLD and the French Committee on Dams and Reservoirs. This paper presents the outcomes of this workshop and includes a presentation of the state of the art in overflowing erosion of embankment dams and levees, overflowing erosion of bedrock downstream of concrete dams, the main knowledge gaps which need to be addressed and the outlines of a future international research project to solve these issues
ARTEMIS developments at HR Wallingford
Get PDFThe ARTEMIS model (Agitation and Refraction with TElEMAC on a mild Slope) from the TELEMAC suite of solvers solves the elliptic mild slope equation using finite element techniques. Its main field of application is wave disturbance studies inside harbours or small bays, often driven by a regional model. ARTEMIS is a well-established model, used in consultancy studies for over 20years.
ARTEMIS was originally developed by the Laboratoire National d’Hydraulique et d'Environnement (LNHE of EDF-R&D). In recent years, with the transfer of the model to open source, development efforts have been open to entities other than LNHE. This paper presents developments of the ARTEMIS model, at HR Wallingford, available or soon to be available in future releases of the TELEMAC system
The role of model complexity in assessing water supply system resilience
Get PDFAssessing water supply system resilience is becoming increasingly important as system pressures, including climate change and population, increase. The resilience of water supply systems in the UK to droughts of differing intensity and duration is now assessed through the simulation of a range of extreme droughts using water resource models. This process can be time consuming, data intensive and in some cases, may not be proportionate to the system response. The drought response surface has become a useful tool in UK water resources planning to quickly visualise modelled outputs, and therefore resilience, to droughts of differing intensity and duration.
Work undertaken as part of the NERC Historic Droughts project has sought to compare results within the drought response surface framework to different levels of modelling complexity. Models of increasing complexity were developed that are rapid, accommodate varying data quality and provenance, and can be applied worldwide.
Droughts were characterised for a range of reservoir systems based on duration and system response in the historic record. Flexible linear and polynomial regression models were trained on historic storage data and increasingly complex inputs – firstly rainfall, then site-translated historic reconstructed streamflow, and finally site-specific historic reconstructed streamflow – to hindcast reservoir storage to 1891. System understanding was important in drought duration selection, which was dependent on the length and distribution of reservoir storage in the observed record. The models permit the input of fuzzy data points, accommodating anecdotal evidence related to drought intensity and duration.
Extreme value analysis of storage allowed for water company levels of service to be considered, therefore providing a description of the system response of an event in terms of the customer experience. Drought response surfaces produced under increasingly complex inputs were compared with those produced through water resource modelling to demonstrate the implications of different levels of modelling complexity. While simple, statistical modelling approaches that do not incorporate physical parameters should not replace deterministic system modelling, they allow for identification of periods and systems of interest that can focus further, more detailed analysis using more complex models and may have particular applications in data and model poor regions
Summary of research work about erodibility of grass revetments on dikes
Get PDFGrass prevents erosion of the subsoil and is an effective control measure for overflowing water as well as overtopping waves. This form of protection has long been used for agriculture drainage channels and on the slopes of dikes. Dutch river dikes usually have clay layers covered with grass on the crest and on both the landward and seaward slopes. Lake and sea dikes with hard revetment in the wave impact zone of the seaward slope also have a grass cover on the crest and the landward slope on a clay type of soil. For grass covers, relatively large forces are required to break up clay aggregates within the soil, while smaller forces may suffice to transport pure sand and small clayey aggregates. Therefore, at the onset of dislocation, a grass cover will experience considerable forces, which may be described by turbulence, especially on steep slopes. From 2007-2014 about 50 experiments at several locations on Dutch and Belgian dikes were conducted with the wave overtopping and also run-up simulator for assessing the erodibility of grass revetments. Based on these prototype tests the cumulative overload method has been developed, a model that predicts the damage of grass mats and failure of dikes provided the load of the wave run-up and/or wave overtopping and the erodibility of the soil are known. This paper discusses engineering methods for predicting the erodibility of grass revetments as well as the erosion of grass at transitions, e.g. at the edges of roads, transitions from hard to grass revetments and objects on dikes, for example trees
An overview of levees and reservoirs in England
Get PDFThe Environment Agency regulates 2039 reservoirs in England under the Reservoirs Act, 1975, which includes all bodies of water over 25,000m3 above ground level. With 759 different owners for these reservoirs, there is considerable diversity in the way they are managed. Water companies own the majority (~one third), closely followed by private landowners and farms. It is an aging portfolio, with the average age being 125 years old and the oldest being 800 years old. Of the ~5million properties at risk of flooding, 1million are identified as at risk from flooding from a reservoir (www.gov.uk/check-flood-risk). This is a conservative estimate due to the calculations being based on the unlikely scenario of a complete failure of a reservoir. In the future the flood maps will categorise reservoir flooding into categories of risk (high, medium and low), providing managers and emergency responders with a more informative understanding of potential impact to support such decisions as evacuation.
In regards to linear raised flood defences there is an estimated 9000km in England (EA National Strategy, 2011) which mainly consist of soil embankments (levees), but also include linear defences such as flood walls. These de-fences protect properties from fluvial and coastal flooding, where 2.4million properties are at risk (www.gov.uk/check-flood-risk). These defences, alongside their point structure assets such as flood gates have recently been collated into one national database of information called AIMS – the ‘Asset Information Management System’.
There has been considerable research and development considering overflow in the past decade, enabling the use of fragility based tools for national investment planning and specific modelling tools for overtopping. Consideration of surface protection has recently been reviewed and future research in grass/surface protections and soil is under consideration. Closely connected to this research we have also been considering transitions, animal disturbance, design (steep faces) and the connected failure mechanisms leading to breach
Numerical modelling of skimming flow over small converging spillways
Get PDFRecently, a significant number of embankment dams have been considered unsafe due to inadequate spillway capacity and predicted overtopping during extreme flood events. The use of stepped overlays for overtopping protection has proven to be cost effective and has gained acceptance worldwide, particularly in the USA. An interesting alternative configuration to the typical stepped spillway of constant width is the use of converging chute walls. This spillway typology enables the increase of the crest length in relation to the chute width at the toe, allowing a decrease of the head above the crest, for identical discharge, and complying with possible width constrains at its downstream end. However, a wall deflection induces undesired cross-waves by increasing the flow depths in the vicinity of the wall, which should be taken into account for design purposes.
This study presents a 3D numerical study using the Computational Fluid Dynamics (CFD) code FLOW-3D®, with simulations performed using a RANS approach coupled with the RNG k-ε turbulence modelling. Some main flow characteristics along the converging spillway, for smooth and stepped inverts, were evaluated and compared with those previously acquired on a physical model with a 1V:2H sloping chute, typical of the downstream slope of small embankment dams. The results show that, in general, a good agreement was found between numerical and experimental data along the nonaerated flow region, on both smooth and stepped inverts, namely regarding flow depths in the chute centreline and at the chute sidewalls, as well as velocity profiles in the chute centreline
Scour at cable protection rock berms - Model test observations
No full textRock berms or concrete mattresses have traditionally been applied for protection of shallow buried, surface laid or crossing pipelines and cables. In most cases the installed protection has worked satisfactorily, but under certain adverse conditions, field evidence has shown examples of severe scour both at mattresses and rock berms.
The paper presents and discusses physical model tests of rock berm scour in combined waves and current. Both single and double berm configurations were studied. The conclusions from the tests were two-fold addressing: 1) Scour development caused by rock berm(s), and 2) Structural robustness of the rock berm when subject to wave action and seabed model scale effects.
The model tests support field evidence that scour is prone to develop in strong current environments and when the protection is aligned oblique or perpendicular to the prevailing currents. The tests also demonstrate larger structural integrity of wide crested berms as opposed to sharp crested berms
Interoperability in physical model testing
Get PDFThe funders of research programmes, such as Horizon 2020 are increasingly requiring that the resulting publications and data are made openly available. The EC, for example, requires FAIR (Findable, Accessible, Interoperable, Reusable) data management. This is promoted through a set of principles and guidelines for experimenters to follow. These respect the technologies and intentions at each organisation, whilst providing positive practices to ensure that the experimental data produced is interoperable and reusable. The recommendations respect the wide variety of data management options for formats and structures; metadata, vocabularies and ontologies; and licenses and embargo periods. Where appropriate, specific technologies have been offered. They do not seek to impose an unrealistic set of rules and regulations which must be followed, rather they offer a set of sensible, modern principles and resources to move the community forwards together and bring it in line with other similar communities currently iterating their own data management practices. They also dovetail with the use of data repositories for the storage of data and papers