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The 6M approach to land subsidence
Though global awareness of land subsidence has increased over recent years, subsidence remains an ongoing and largely unsolved problem, which is exemplified by frequent discoveries of apparently new subsiding areas. This means that for many of these areas there is a continuous and growing need to provide guidance to decision makers on how to tackle this global problem. This paper presents a comprehensive, step-by-step approach to address land subsidence, illustrated by best practise examples from around the world. The approach places emphasis on the long-term sustainability of resources, whose development is related to the subsidence problems. We identified 6 steps, collectively referred to as the 6M approach, that are crucial to tackle subsidence: Measuring, understanding Mechanisms, Modelling, Money, Measures and Monitoring. This paper offers guidance for implementing the 6M approach, and the lessons learned from the real-life examples provide valuable information and inspiration for decision makers and experts to address subsidence. The focus is on subsidence in deltaic and coastal areas where subsidence contributes to relative sea level rise. It is expected that the 6M approach will contribute to lowering the threshold to act on subsidence. The 6M approach is also used as a guiding principle for the thematic subdivision of TISOLS, providing a meaningful linkage between subsidence science and the societal response to subsidence problems.
An assessment of present day and future sea level rise at the Dutch coast : Zeespiegelstijging langs de Nederlandse kust en de regionale bestuurlijke consequenties
In this report an assessment of present day and future sea level rise is given, to provide a scientific background in the related public debates. We start with a discussion on the present-day sea level rise acceleration. Subsequently, we discuss the consistency between sea level rise observations and future sea level projections along the North Sea coast, followed by a discussion on different future sea level projections and their interpretations.
Impacts of progressive urban expansion on subsurface temperatures in the city of Amsterdam (The Netherlands)
Subsurface temperatures are substantially higher in urban areas than in surrounding rural environments; the result is a subsurface urban heat island (SUHI). SUHIs and their drivers have received attention in studies world-wide. In this study, a well-constrained data set of subsurface temperatures fromAmsterdam, The Netherlands, is presented. The study demonstrates that, throughmodeling of centuries-long (fromfourteenth to twenty-first century) urban development and climate change, along with the history of both the surface urban heat-island temperatures and ground surface temperatures, it is possible to simulate the development and present state of the Amsterdam SUHI. The results provide insight into the drivers of long-term SUHI development, which makes it possible to distinguish subterranean heat sources of more recent times that are localized drivers (such as geothermal energy systems, sewers, boiler basements, subway stations or district heating) from larger-scale drivers (mainly heat loss from buildings and raised groundsurface temperatures due to pavements). Because these findings have consequences for the assessment of the shallow geothermal potential of the SUHIs, it is proposed to distinguish between (1) a regional, long-term SUHI that has developed over centuries due to the larger-scale drivers, and (2) local anomalies caused by anthropogenic heat sources less than one century old.
Wind effects on the water age in a large shallow lake
As the third largest fresh water lake in China, Taihu Lake is suffering from serious eutrophication, where nutrient loading from tributary and surrounding river networks is one of the main contributors. In this study, water age is used to investigate the impacts of tributary discharge and wind influence on nutrient status in Taihu Lake, quantitatively. On the base of sub-basins of upstream catchments and boundary conditions of the lake, multiple inflow tributaries are categorized into three groups. For each group, the water age has been computed accordingly. A well-calibrated and validated three-dimensional Delft3D model is used to investigate both spatial and temporal heterogeneity of water age. Changes in wind direction lead to changes in both the average value and spatial pattern of water age, while the impact of wind speed differs in each tributary group. Water age decreases with higher inflow discharge from tributaries; however, discharge effects are less significant than that of wind. Wind speed decline, such as that induced by climate change, has negative effects on both internal and external nutrient source release, and results in water quality deterioration. Water age is proved to be an effective indicator of water exchange efficiency, which may help decision-makers to carry out integrated water management at a complex basin scale.
Numerical study of bubble screens for mitigating salt intrusion in sea locks
In order to mitigate the effects of salt water intrusion at sea locks, bubble screens are installed which act as a barrier between the dense sea water and the fresh water inland. In order to optimize the design of the bubble screen, in this study a state-of-the-art numerical model is developed based on the Euler- Lagrange CFD method which is expanded with a simple salt balance and concentration-density coupling. The model has been validated by means of experimental results on a laboratory-scale bubble screen. The liquid circulation and entrainment have been investigated for two types of bubble injection methods. It is found that the bubble screen is successful as a separator of salt and fresh water in an initial period of τsep = 30 seconds but acts more as a mixer at later times due to the swaying of the screen. The rate of the mixing increases with the air flow rate. Two mechanisms of salt intrusion are distinguished; a delayed density current along the bottom and entrained liquid being circulated through the domain back to the screen. An optimum in air flow rate is found at a Froude air number F r air = 0 . 91 . Bubble screen behaviour is also checked at the lock-scale using lock-scale geometry and simulations. The amount of salt transmitted agrees well with the large-scale field tests up until the reported Fr air numbers but Fr air > > 1 need to be tested to check for the optimum as found in the lab-scale tests.
The importance of explicitly modelling sea-swell waves for runup on reef-lined coasts
The importance of explicitly modelling sea-swell waves for runup was examined using a 2D XBeach short wave-averaged (surfbeat, “XB-SB”) and a wave-resolving (non-hydrostatic, “XB-NH”) model of Roi-Namur Island on Kwajalein Atoll in the Republic of Marshall Islands. Field observations on water levels, wave heights, and wave runup were used to drive and evaluate both models, which were subsequently used to determine the effect of sea-level rise and extreme wave conditions on wave runup and its components. Results show that specifically modelling the sea-swell component (using XB-NH) provides a better approximation of the observed runup than XB-SB (which only models the time-variation of the sea-swell wave height), despite good model performance of both models on reef flat water levels and wave heights. XB-SB has a bias of −0.108 – 0.057 m and scatter index of 0.083–0.639, whereas XB-NH has bias of −0.132 – 0.055 m and 0.122–0.490, respectively. However, both models under-predict runup peaks. The difference between XB-SB and XB-NH increases for more extreme wave events and higher sea levels, as XB-NH resolves individual waves and therefore captures SS-wave motions in runup. However, for even larger forcing conditions with offshore wave heights of 6 m, the island is flooded in both XB-SB and XB-NH computations, regardless the sea-swell wave energy contribution. In such cases XB-SB would be adequate to model flooding depths and extents on the island while requiring 4–5 times less computational effort.
Signal test for acoustic fibre optics for the purpose of monitoring varying salinity
Salt intrusion of surface waters in the Netherlands poses a problem for fresh water resources, for example at intake points of drinking water. Currently, the tools and instruments to monitor and understand salt water intrusions are insufficient. The point sensors of the monitoring network provide valuable information, but only at fixed point locations. RWS is looking for new technology to gather 2D or 3D information about salinity variations in fresh, brackish and salt waterbodies. Two promising techniques are Distributed Acoustic Sensing (DAS) with fibre optic cables and Electrical Resistivity Tomography (ERT). This report describes the results of a laboratory test using DAS.
Signal test for acoustic fibre optics for leakage detection of water bottoms
The goal of this project is to analyse the results of the two large laboratory tests in order to assess whether distributed fibre optic sensing can detect the presence or absence of a clay layer in a water bottom. It is about a ‘signal test’ which must show that variations in lithology of the water bottom have an effect in the measured signal. The experiments for which the distributed fibre optic measurements have been performed consisted of experiments at a scale of 18 m x 5.5 m surface area and 2.5 m depth and for which fibre optics cable for acoustic and temperature measurements has been placed in a send bed of 80 cm thickness and covered with a clay layer of 10 cm. Three situations have been analysed.
Scaling point-scale (pedo)transfer functions to seamless large-domain parameter estimates for high resolution distributed hydrologic modeling : an example for the Rhine river
Moving toward high-resolution gridded hydrologic models asks for novel parametrization approaches. A high-resolution conceptual hydrologic model (wflow_sbm) was parameterized for the Rhine basin in Europe based on point-scale (pedo)transfer functions, without further calibration of effective model parameters on discharge. Parameters were estimated on the data resolution, followed by upscaling of parameter fields to the model resolution. The method was tested using a 6-hourly time step at four model resolutions (1.2, 2.4, 3.6, and 4.8 km), followed by a validation with discharge observations and a comparison with actual evapotranspiration (ETact) estimates from an independent model (DMET Land Surface Analysis Satellite Application Facility). Additionally, the scalability of parameter fields and simulated fluxes was tested. Validation of simulated discharges yielded Kling-Gupta Efficiency (KGE) values ranging from 0.6 to 0.9, except for the Alps where a volume bias caused lower performance. Catchment-averaged temporal ETact dynamics were comparable with independent ET estimates (KGE ≈ 0.7), although wflow_sbm model simulations were on average 115 mm yr−1 higher. Spatially, the two models were less in agreement (SPAEF = 0.10), especially around the Rhine valley. Consistent parameter fields were obtained, and by running the model at the different resolutions, preserved ETact fluxes were found across the scales. For recharge, fluxes were less consistent with relative errors around 30% for regions with high drainage densities. However, catchment-averaged fluxes were better preserved. Routed discharge in headwaters was not consistent across scales, although simulations for the main Rhine River were. Better processing (scale independent) of the river and drainage network may overcome this issue.
Geosynthetic-reinforced pile-supported embankments: state of the art
Geosynthetic-reinforced pile-supported embankments have been increasingly used worldwide to support earth structures. A significant amount of research has been conducted by many researchers and engineers in recent years. This paper provides a state-of-the-art review of this technology, and of important developments and results obtained throughout the years that help to better understand the mechanisms that play an important role in the design, construction, and performance of these systems. This paper begins with terminologies and historical developments. It then focuses on load transfer mechanisms and practical design and proposes topics for future research. The supplemental material gives tips for construction details and instrumentation for performance evaluation.