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Application of wireless tracer GPRS riverbed scour monitoring for disaster warning
Get PDFRiver incision after long-term general scour due to the existence of river-crossing structures, always has a huge influence on riverbed stability and hydraulic structure safety. The severe short-term riverbed general scour, bridge and bend/levee scour, and scour downstream of a grade-control structure (GCS) occurs frequently, causing bridge failures, levee damages, and headcuttings during typhoon-induced floods in the intermittent rivers in Taiwan. For examples, bridge collapse and embankment damage events resulted in the loss of life and vehicles due to falling into rivers in 2008 and 2009. Now, the wireless tracer GPRS real-time scour monitoring technique has been developed to monitor bridge and general scour, bend and toe scour and scouring below GCSs in real time during high flows, with the approach trialled within a gravel-bed reach in the lower Dachia River during 2015. The result indicates that the proposed method has the potential to be used as a tool for the practical application of disaster warning for monitoring the safety of bridge and embankment
Impact of extreme weather on critical infrastructure: the EU-INTACT risk framework
No full textResilience of critical infrastructure (CI) to extreme weather events, such as heavy rainfall, high temperatures and winter storms, is one of the most demanding challenges for governments and society. Recent experiences have highlighted the economic and societal reliance on a dependable and resilient infrastructure, and the far-reaching impacts that outages or malfunctions can have. Growing scientific evidence indicates that more severe and frequent extreme weather events are likely. The EU-funded INTACT project addresses these CI challenges and attempts to bring together cutting-edge knowledge and experience from across Europe to inform the development of best practice approaches in planning, crisis response and recovery capabilities. The project considers the options for mitigating the extreme weather impacts. A key component of the INTACT project is the development of a risk management structure to support decision-making in the case studies. This structure forms part of the overall INTACT Wiki: the main output of the project. It comprises a risk ‘framework’ that sets out how information and guidance can be accessed by CI owners and operators. Within this there is a step-wise risk assessment process based on best practice from the IEC. The risk framework and process presents: structures for models and data requirements for decision making; identifies tools and methods that support decision making; supports analysis of measures to protect CI through simulation; and indicates gaps in modelling and data availability. This paper outlines the components of the risk framework and process, and illustrates its use in a case study dealing with electricity supply and winter storms
The SuDS wheel of fortune
Get PDFDrivers and standards for SuDS - what can we learn from international requirements for the control of surface water runoff from development
CARDigues: an integrated tool for levee system diagnosis and assessment
Get PDFIn December 2007, a French decree related to hydraulic structures (levees and dams) has introduced for owners the necessity to produce a hazard study for each levee system. On the river Loire, three major class A* state levee systems are present and protect three main urban areas, Orléans, Tours and Authion representing some 240 000 inhabitants. Around 40 class B* and C* levee systems are also present on the river Loire and its tributaries representing 600 km of levees and requiring such hazard studies. In order to have a homogenous method to do these specific risk assessment studies on river Loire levees, a new model named CARDigues (for Levee Breach Hazard Calculation) was developed in a partnership with DREAL Centre-Val de Loire, Cerema and Irstea. This model enables to approach the probability of failure on every levee sections and to integrate and cross different “stability” parameters (topography, embedded structures, geology), hydraulic solicitations and observations from visual inspections or instrumentation results considered as disorders (seepage, burrowing animals, vegetation, pipes, etc.). This model and integrated tool CARDigues enables to check for each levee section, the probability of appearance and rupture of five breaching scenarios initiated by: overflowing, internal erosion, slope instability, external erosion and uplift. It has been recently updated and has been applied on several levee systems by different contractors. The article presents the CARDigues model (V28.00) with examples on river Loire and how it is currently used for a relevant and global levee system diagnosis and assessment. Levee reinforcement or improvement management is also a perspective of applications for this model CARDigues. (* levee classes are function of levee height and protected population
Characterisation of flow conditions for contact erosion analysis using PIV
Get PDFThe aim of this paper is to examine the flow characteristics at the initiation of contact erosion.
When water flows through fine soil to a coarser soil layer, changes of the flow properties may occur due to
transition of the pore structure. A pore scale experiment was developed in order to explore the local flow behaviour
which leads to migration of fine particles into a coarse structure. Optical access to the pore structure
was obtained by having a transparent soil model consisting of hydrogel beads. This allowed water to be used as
the fluid phase and resulted in a more adaptable Particle Image Velocimetry (PIV) system. Upward seeded flow
was applied to the test section and illuminated using a low risk Light Emitting Diode (LED) light sheet. After
calibrating the set-up with macroscopic flow rate measured by flow meter, images of the contact zone of coarse
and fine particles were taken with different flow boundary conditions using a high speed camera. Qualitative and
quantitative analysis were carried out to identify spatial variability of the flow conditions which led to initiation
of the fine particle movement. Results show that the local reorientation of the flow will lead to local initiation
of the contact erosion. Major reasons for this behaviour are discussed in this paper
Bridge scour protection
Get PDFBridge scour protection appears to be increasingly needed to protect foundations from more extreme flooding events. However, the invert level at which the protection is installed can have a significant effect upon flow through bridges and associated flooding levels (Figs. 1 & 2).
Methods to assess this will be outlined along with a review of scour protection types, and arrangements which are effective and beneficial
Local scour and flow characteristics around a circular cylinder undergoing vortex-induced vibration
Get PDFVortex-induced vibration (VIV) has been extensively studied and the related findings presented in published literature. However, when the cylinder is placed near an erodible sand bed, interactions between the vibrating cylinder, flow field and local scour evidently will become very complex. The aim of this study is to provide an improved understanding of the interaction between the flow field, free vibrating cylinder and scour by using flow visualization and a new PIV measurement technique. The results show that the amplitude and frequency of the vibrating cylinder are closely related to the depth of the scour hole. Based on the qualitative observation and quantitative measurement of the flow field, vibrating cylinder and scour dimensions, three distinct scour stages are identified in this study. The characteristics of the turbulence intensity, formation and transmission of the vortices in each of these three scour stages are discussed in this paper
Investigation into the multiple recent sinkholes in Pokhara, Nepal
Get PDFSince November 2013, numerous sinkholes have been forming in the Armala area of Pokhara Valley, Central Nepal, posing serious threat to local residents. In order to provide countermeasures for reducing sinkhole risk, detailed investigations into the cause and the formation mechanism of the sinkholes are crucial. Preliminary surveys were conducted in June 2014 and November 2014. Comparison of photos, taken in the two surveys, clearly indicates not only the formation of new sinkholes, but also the re-activation of filled sinkholes. By means of dynamic cone penetration tests and surface wave investigations, qualitative characterization of the soil profile was attained, and shallow weak soil layers which are believed to be the location for future sinkholes could be identified. On the basis of the preliminary field investigation, possible sinkhole formation mechanisms are considered. A risk of sinkhole does not seem to disappear as white turbid water continuously springs. It indicates that the internal erosion of white clayey silt layer is still in progress. In August 2015, a boring was carried out beside one of the largest sinkholes. The overall structure of ground layers was first revealed and a 2.5m high cavity at 7.5-10m deep from the ground surface was found within a thick white clayey silt layer. Further ground investigations including surface wave exploration were conducted in December 2015 and the results are reported
Small-scale physical modelling of scour at bridge piers with light-weight sediments
Get PDFThis study entailed physical model testing to support the design of marine facilities associated with a proposed 36 km long causeway, which is under construction in Kuwait Bay. The marine facilities include 1050 bridge piers, to be built in varying conditions in terms of water depth, soil conditions, current and wave conditions. Seabed levels vary from intertidal to approximately -12 m MSL and three different types of seabed material were observed: cap-rock underlain by sand, silty sand and silty clay. Light-weight sediment physical models with scales 1:20 and 1:37 were used to assess scour potential due to waves and currents at the base of the bridge piers and to guide the design of scour protection (rock armouring of the seabed). The PVC light-weight particles used to model the prototype silty sand had a density of approximately 1200 kg/m3 and a median diameter (d50) of 0.25 mm. Quantitative assessments of the seabed evolution were made with advanced photo-scan techniques. The model results provide insight to the evolution of scour over time and equilibrium scour hole dimensions, which were compared to predictions using empirical formulae. The similitude laws that apply for this type of model and observed model effects are also discussed
Localized fluidization in a granular medium: Parametric study with a physical model of “sand boiling”
Get PDFThe present study investigates steady-state localized fluidization within a granular bed by means of experiments on a physical model using a direct internal visualization by means of combined optical techniques. The experimental setup allows access to a broad range of control parameters with the purpose of extending previous findings on this specific configuration, in particular regarding the critical flow rate needed to generate a chimney fluidization. A saturation of this critical flow rate with bed height is and can be explained by a purely hydrodynamic effect related to the geometry and the permeability of the bed which rule together the development of the upward fluid flow through the initially static granular bed. A quantitative model based on CFD simulations is successfully developed in good agreement with the experimental findings