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Hydrodynamic impact and power production of tidal turbines in a storm surge barrier
To estimate the impact on energy production and environment of tidal turbines placed in the Eastern Scheldt Storm Surge Barrier a Computational Fluid Dynamics (CFD) study has been carried out on the additional head differences induced by the turbines. The CFD model focusses on a single gate opening of the Storm Surge Barrier and includes half of the adjoining gates on either side. In this 40 m wide Gate a 1.2 MW array existing of five Tocardo T2 tidal turbines has been installed as part of a demonstration project in 2015. Transient computations of the barrier with and without the turbine array were carried out for a range of quasi stationary tidal phases. The turbines are resolved in detail as rotating equipment: real-time rotation of the turbine blades (involving the displacement of the mesh nodes in an unsteady setting) is implemented, and torque and thrust for the prescribed speed of rotation is provided as output. The results for velocity, power and thrust are compared with field experiments to validate the model. Based on these computations an estimate of the effect of turbines on the discharge capacity of the storm surge barrier is given. This information will be used to parameterize the tidal turbines in the far-field hydrodynamic model of Eastern Scheldt estuary for the ultimate assessment of the effect of tidal turbines on energy production and on the environment.
Pilot field implementation of suction dredging for sustainable sediment management of dam reservoirs
The buildup of sediment deposits in reservoirs is a long-standing problem with serious consequences on the reservoirs’ functionality and the ecology of their river systems. In the last two decades, hydraulic dredging has been used as a more viable engineering solution to restore reservoirs’ sustainability. This study proposes a novel ejector-pump dredging system (EPDS) that solely utilizes hydraulic dredging for removal and transport of the sediments deposited at the reservoir’s bed. Unlike conventional dredging methods, air is injected into the header pipeline to create a turbulent three-phase flow regime that enhances the solids suspension and continuous flow in the system. Introducing air effectively reduces the critical value of the deposition velocity of the dredged solids and transports them in a slug flow regime. This technique minimizes the tendency of the sediment to settle, and therefore eliminates system plugging. A laboratory prototype of the proposed system has proven the efficacy of removal and transport of mixed-size sediments up to 150 mm. Field trials have further shown the feasibility of the proposed system. Removal of large sediments with productivity approaching 70 m3=h was made possible using the suction-type EPDS. The hopper-type EPDS enabled carrying the dredgedmaterial for up to 1,000mwithout resorting to a booster pump. The developed system was successfully used as part of an integrated dredging management program carried out for the Oouchibaru, Saigo, and Yamasubaru dams in the Mimi River basin, Japan. The very low turbidity levels recorded during the sediment dredging and transport operations of EPDS are indicative of the eco-friendly performance of the system.
Temporal development of backward erosion piping in a large-sScale experiment
This paper presents a large-scale backward erosion piping experiment aimed at studying the erosion rate. This temporal aspect of piping complements previous research that focused on the critical head. To study the progression rate in realistic conditions, an experiment was carried out on a 1.8 m high levee with a cohesive blanket on a sandy foundation. The pipe was guided along a row of pore pressure transducers in order to measure its temporal development. Pipe development in space and time was successfully derived from pore pressure changes, showing an average progression rate of 8 m=day during the progressive erosion phase. The results show a relation between upstream gradient and progression rate. Furthermore, analysis of the eroded sand mass shows a relatively large pipe volume compared to existing lab tests, and an approximately linear relation between pipe length and volume. The results and insights from this study can be used to validate and improve transient piping models, leading to more accurate dam and levee safety assessments.
Adaptive asset management for flood protection : the FAIR framework in action
Uncertainties about climate change consequences, changing societal requirements and system complexity require flood protection asset managers to continuously evaluate their asset management policies and practice to manage risk and improve the resilience of their assets. However, there are many challenges in doing this, with asset operators often facing conflicting interests and major uncertainties about the future needs for asset performance. In the EU Interreg IV FAIR project, flood protection asset owners and operators, with scientific partners from the North Sea Region of Europe collaborated to develop practical guidance for adaptive asset management of flood protection infrastructure. The central component of this guidance is the FAIR framework, presented here. The framework combines insights and principles from ISO 55000 on asset management and ISO 14090 on climate adaptation with asset operator experiences to provide a practical guide for integration of asset management considerations within both strategic and operational contexts via a tactical handshake. This is a means to avoid the common lack of connection between strategic plans and operational practice. The applicability of the framework is illustrated with examples from Pilot Cases within the FAIR project, in which its value in terms of improved asset management and reduced costs has been demonstrated.
Observations of cross-shore chenier dynamics in Demak, Indonesia
Cheniers are important for stabilising mud-dominated coastlines. A chenier is a body of wave-reworked, coarse-grained sediment consisting of sand and shells overlying a muddy substrate. In this paper we present and analyse a week of field observations of the dynamics of a single chenier along the coast of Demak, Indonesia. Despite relatively calm hydrodynamics during the one-week observational period, the chenier migrated surprisingly fast in the landward direction. The role of the tide and waves on the cross-shore chenier dynamics is explored using velocity moments as a proxy for the sediment transport. This approach shows that both tide and waves are capable of transporting the sediment of the chenier system. During calm conditions (representative for the south-east monsoon season), the tides generate a landward-directed sediment transport when the chenier crest is high relative to mean sea level. Waves only generate substantial sediment transport (direct, via skewness, and indirect, via stirring) when the chenier is submerged during periods with higher waves. The cross-shore chenier dynamics are very sensitive to the timing of tide and waves: most transport takes place when high water levels coincide with (relatively) high waves.
Improving dike reliability estimates by incorporating construction survival
During construction of a dike, slope stability often reaches critical levels, due to the excess pore water pressures in the foundation. The loading condition during construction has similarities with the design conditions during flood loading. Not only in terms of the pore water pressures as the main driving force, but also in terms of criticality of the stability. This paper examines how the information of survival of the construction stage can be used to improve the reliability estimate for a dike in flood conditions, using Bayesian updating. The approach is exemplified for a range of typical dikes and for a case study of a full-scale test embankment. The main result is that the reliability can increase significantly by including the information of construction survival and the uncertainty reduction involved, especially for dikes on soft soil blankets. For the investigated cases, the posterior failure probability was up to several orders of magnitude lower than the prior failure probability. The main factors influencing the degree of reliability update, were the ground conditions and the degree of criticality of the slope stability during construction. In conclusion, using the information of the survived construction leads to improved reliability-based safety assessments of dikes, and consequently to more targeted and cost-effective flood protection.
Comparison of estimates of global flood models for flood hazard and exposed gross domestic product : a China case study
Over the past decade global flood hazard models have been developed and continuously improved. There is now a significant demand for testing global hazard maps generated by these models in order to understand their applicability for international risk reduction strategies and for reinsurance portfolio risk assessments using catastrophe models. We expand on existing methods for comparing global hazard maps and analyse eight global flood models (GFMs) that represent the current state of the global flood modelling community. We apply our comparison to China as a case study and, for the first time, include industry models, pluvial flooding, and flood protection standards in the analysis. In doing so, we provide new insights into how these components change the results of this comparison. We find substantial variability, up to a factor of 4, between the flood hazard maps in the modelled inundated area and exposed gross domestic product (GDP) across multiple return periods (ranging from 5 to 1500 years) and in expected annual exposed GDP. The inclusion of industry models, which currently model flooding at a higher spatial resolution and which additionally include pluvial flooding, strongly improves the comparison and provides important new benchmarks. We find that the addition of pluvial flooding can increase the expected annual exposed GDP by as much as 1.3 percentage points. Our findings strongly highlight the importance of flood defences for a realistic risk assessment in countries like China that are characterized by high concentrations of exposure. Even an incomplete (1.74% of the area of China) but locally detailed layer of structural defences in high-exposure areas reduces the expected annual exposed GDP to fluvial and pluvial flooding from 4.1% to 2.8 %.
Sandy coastlines under threat of erosion
Here, we present a comprehensive global analysis of sandy shoreline dynamics during the twenty-first century. Our probabilistic projections explicitly take into account estimates of future SLR, spatial variations of coastal morphology, ambient shoreline change trends and future changes in meteorological drivers (for example, storm surge and waves). We first evaluate long-term shoreline change which is the result of two components: the ambient shoreline change (AC) driven by geological, anthropogenic and other physical factors and the shoreline retreat due to SLR (R). We obtained AC by extrapolating observed historical trends within a probabilistic framework. We computed R by using a modified Bruun rule together with a new global dataset of active beach slopes. In addition to the long-term shoreline dynamics we also project how maximum erosion from coastal storms may change with climate change. Shoreline change projections are discussed for the years 2050 and 2100 under representative concentration pathways (RCP) 4.5 and 8.5, relative to the baseline year 2010. Our analysis shows an overall erosive trend of sandy beaches that increases in time and with the intensity of GHG emissions.
Shifting the discharge mindset from harmful to habitat : exploring inventive designs and benefits of underwater discharge structures
A zero discharge seawater desalination approach still appears to be very optimistic, especially when it comes to the large volumes of product water and associated brine (concentrate) that requires appropriate disposal. In addition to this, and although the technology advancements of mining for precious metals from brine show promising potential, it is still a challenge to use a single method to selectively extract valuable minerals from complex brine matrices. These two alternatives, (i) zero discharge and/or (ii) mining for minerals (from brine) may not be the best selections when designing underwater discharge structures (at least for the foreseeable future). With the aim to protect the marine environment, regulations have been set to regulate the brine discharges and defining environmental criteria in the area close to the outfall. It was however noted, that such criteria are often adopted from generic benchmarks and sometimes from unadoptable locations. Robust and in situ research on the effects of the brine effluent on the marine environment is also lacking. Recent surveys, however, suggest that the ecological impact of brine outfalls can be very limited or even result in an improvement of biodiversity and marine abundance on the outfall structure. Such observations suggest that some environmental criteria may be archaic, which may result in needlessly expensive outfall designs. Additionally, the hard substrate that the outfall structure provides appears to be a good habitat for the enhancement of marine growth. We therefore propose, instead of only aiming to minimize impact, also to promote the ecological habitat function by optimizing the design criteria of underwater discharge structures. Our paper presents first guidelines/examples (of shapes and material use e.g., Coating with eco concrete) to promote coral growth, nursery ground for fish, etc. Furthermore, we provide initial ideas for the treatment of the desalination effluent to help the advancement of such marine habitats.
Verwachting waterdiepte Rijntakken
Tijdens de zomer en herfst van 2018 daalde de afvoer op de Rijn als gevolg van aanhoudende droogte. Hierdoor daalde de waterdiepte en kon niet alle vracht worden vervoerd. Voor enkele bedrijven ontstonden flinke problemen doordat de aan- en afvoer van goederen over water stokte. Vanuit de logistieke sector (verladers, bevrachters) zijn er bij aankomende droogteperiodes maatregelen te nemen om beter te anticiperen op verminderde waterdiepte. De huidige voorspellingen die worden ontsloten betreffen echter geen waterdiepte maar waterstand, en bovendien kijken die niet ver genoeg vooruit om adequate tactische en strategische keuzes te maken. Mogelijk dat ook voor de Landelijke Coördinatiecommissie Waterverdeling (LCW), die actief wordt bij dreigende watertekortsituaties, een verwachting in waterdiepte nuttig is voor het nemen van beslissingen met betrekking tot keuzes in waterverdeling. Er is geconstateerd dat tijdens langdurige droogteperiodes met lage rivierafvoeren behoefte is aan een verwachting van de waterdiepte op de Nederlandse rivieren voor een langere termijn van 6-8 weken, en in het bijzonder voor de Rijntakken (Boven-Rijn, Waal, Pannerdensch Kanaal, Neder-Rijn, Lek en IJssel). In deze studie is een procesbeschrijving opgesteld hoe te komen tot een verwachting van de waterdiepte voor de Rijntakken, op basis van bestaande informatie, zowel voor een scenario met een statische bodem als (eerste aanzet) met een dynamische bodem. Zodra een droogte periode zich aankondigt, kan dit proces doorlopen worden en zo een diepteverwachting afgegeven worden. Het proces is eenmalig doorlopen, en er is kwalitatieve beschouwing gegeven van de nauwkeurigheid en betrouwbaarheid waarmee een verwachting kan worden afgegeven. Een verwachting heeft alleen waarde, als deze de juiste informatie levert om een beslissing te kunnen nemen. Er is een beknopte verkenning uitgevoerd naar de toepassingswaarde van de diepteverwachtingen. Dit is gedaan enerzijds via een scan van literatuur, anderzijds door in gesprek te gaan met een klankbordgroep (bijeenkomst) en de transportsector (enquête). Aan de hand hiervan is geconcludeerd dat er behoefte is binnen de natte transportsector naar langere-termijn verwachtingen. Het is aanbevolen om in 2021 als pilot langere-termijn diepteverwachtingen met de statische bodem te gaan afgeven tijdens droogte, en zo te ontdekken of de afgifte meerwaarde heeft. Het stappenplan is hiervoor concreet genoeg en vrij eenvoudig te doorlopen. Belangrijke bevindingen zijn dat (1) in het stappenplan is opgenomen dat afvoerreeksen van de Duitse BfG nodig zijn, omdat die momenteel de beste verwachting geven, dat (2) multibeam-peilingen van de bodemligging op een gegeven moment minder geschikt zijn dan CoVadem-data (die zijn actueler en op een gegeven moment voldoende qua nauwkeurigheid en dichtheid), en dat (3) de wijze waarop een dynamische bodemverwachting wordt meegenomen nog aanvullende analyse vraagt.