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Carboxymethylcellulose as a Newtonian viscous fluid for centrifuge modelling
In geotechnical centrifuge modelling, the unification of time-scaling factors is particularly important for studies regarding coupling consolidation and dynamic phenomena, for example pile installation problems and earthquake loading. A common method to achieve this unification is the use of a substitute pore fluid, which has a viscosity which is larger than that of the prototype pore fluid (generally water). Aqueous methyl celluloses have proven very valuable for this purpose, mainly because the viscosity can be increased while the density remains relatively unaffected and the solution can be characterised as near-Newtonian. In this paper we describe the use of a low molecular weight sodium carboxymethylcellulose (designated lCMC) in 1% to 4% solutions as an alternative to methyl celluloses through physical chemical, (density, temperature dependence) and geotechnical (permeability in sand and friction angle) analyses and describe the experience with this pore fluid at the Delft Geotechnics centrifuge over the past 20 years.
Rainfall nowcasting using commercial microwave links
Accurate and timely precipitation forecasts are crucial for early warning. Rainfall nowcasting, the process of statistically extrapolating recent rainfall observations, is increasingly used for short‐term forecasting. Nowcasts are generally constructed with high‐resolution radar observations. As a proof of concept, we construct nowcasts with country‐wide rainfall maps estimated from signal level data of commercial microwave links (CMLs) for twelve summer days in the Netherlands. CML nowcasts compare well to radar rainfall nowcasts. Provided well‐calibrated CML rainfall estimates are employed, CML nowcasts can outperform unadjusted real‐time radar nowcasts for high rainfall rates, which are underestimated as compared to a reference. Care should be taken with the sensitivity of the advection field derivation to areas with low CML coverage, and the inherent measurement scale of CML data, which can be larger than the application scale. We see potential for rainfall nowcasting with CML data, for example in regions where weather radars are absent.
Morphololgical computation of a cascade system of dams using Delft3D-FM coupled with a real-time control tool
This paper presents a detailed hydraulic and morphological study of a cascade system of dams, located in Marsyangdi River in Nepal. Firstly, a severe morphological problem in one of the dams, namely Middle Marsyangdi Hydropower Project (MMHPP), was studied. We revealed one of the key reasons of the problem, which is related to the ignorance of large- and meso-scale morphological feature of the river while selecting the site. Secondly, the sedimentation process at the reservoir was replicated using a two-dimensional morphological model, namely Delft3D-Flexible Mesh (D-FM) coupled with Real-Time Control (RTC) tool to simulate reservoir gate operation. We attempted to incorporate downstream dam in the model, namely Marsyangdi Hydropower Project (MHPP), to simulate synchronized operation and its morphological impact. The effect of synchronized operation of two dams was assessed by simulating different synthetic flushing scenarios. Sensitivity of two different sediment transport formulae (Ashida-Michiue and Engelund-Hansen) on the model results was assessed as well. Given a rapid modelling exercise of such complex system using D-FM, the results can be regarded as satisfactory. They showed consistent model behaviour and observed trend despite the complexity involved in morphological modelling with synchronized operation of two dams. The study can further be improved in case more data and information are available. The model can also be applied to optimize dam operation considering morphological and ecological impacts on downstream reach.
A new geotechnical centrifuge at Deltares, Delft, the Netherlands
A new geotechnical centrifuge has been commissioned by Deltares, Delft, The Netherlands, as a replacement of the previous facility, which has expended its serviceable life. The new centrifuge is an Actidyn C72-31 beam type centrifuge, and has a 260 g-tonne capacity and a platform radius of 5.0 m. The platform can house test set-ups with dimensions up to 1.2 m × 1.2 m × 1.2 m (length × width × height). The data-acquisition system is supplied by HBM and has 40 channels with a sampling rate of up to 100 kHz. Two high speed cameras and four monitoring cameras are available for imaging. A 4-axis robotic system allows in-flight excavation and installation operations. The centrifuge is fully prepared for later installation of an earthquake simulator. Supporting facilities consist of a clay mixer and a consolidation frame. This paper details the choices made leading to this centrifuge, the specifications of the centrifuge and supporting facilities.
Proceedings of the 4th European Conference on Physical Modelling in Geotechnics - ECPMG 2020 (Lulea, Sweden / Zoom, 7-8 September 2020)
Large‑scale stochastic flood hazard analysis applied to the Po River
Reliable hazard analysis is crucial in the flood risk management of river basins. For the floodplains of large, developed rivers, flood hazard analysis often needs to account for the complex hydrology of multiple tributaries and the potential failure of dikes. Estimating this hazard using deterministic methods ignores two major aspects of large-scale risk analysis: the spatial–temporal variability of extreme events caused by tributaries, and the uncertainty of dike breach development. Innovative stochastic methods are here developed to account for these uncertainties and are applied to the Po River in Italy. The effects of using these stochastic methods are compared against deterministic equivalents, and the methods are combined to demonstrate applications for an overall stochastic hazard analysis. The results show these uncertainties can impact extreme event water levels by more than 2 m at certain channel locations, and also affect inundation and breaching patterns. The combined hazard analysis allows for probability distributions of flood hazard and dike failure to be developed, which can be used to assess future flood risk management measures.
Study of morphological impact and optimization of longitudinal dams in the river Waal by using Delft3D numerical model
Longitudinal dams are proposed to be constructed in the Rhine branches as an alternative or addition to groyne lowering. The measure has been proposed to provide more room for the flood water, as well as to improve navigability. In this study the Delft3D morphological model has been applied to study the morphological impacts of these longitudinal dams, and to optimize them for minimizing inconvenient sedimentation patterns.
Groundwater quality in Dutch water management
Good groundwater quality is essential for numerous receptors in the Netherlands, such as drinking water supply, aquatic and terrestrial ecology, and water supply for agriculture and industry. In the meantime, the anthropogenic use of the water system affects the groundwater quality. We are challenged to use our water resources in a sustainable way. This paper elaborates on a number of examples of our projects on groundwater quality for Dutch water management.
Profiling resilience and adaptation in mega deltas : a comparative assessment of the Mekong, Yellow, Yangtze, and Rhine deltas
River deltas and estuaries are disproportionally-significant coastal landforms that are inhabited by nearly 600 M people globally. In recent history, rapid socio-economic development has dramatically changed many of the world’s mega deltas, which have typically undergone agricultural intensification and expansion, land-use change, urbanization, water resources engineering and exploitation of natural resources. As a result, mega deltas have evolved into complex and potentially vulnerable socio-ecological systems with unique threats and coping capabilities. The goal of this research was to establish a holistic understanding of threats, resilience, and adaptation for four mega deltas of variable geography and levels of socio-economic development, namely the Mekong, Yellow River, Yangtze, and Rhine deltas. Compiling this kind of information is critical for managing and developing these complex coastal areas sustainably but is typically hindered by a lack of consistent quantitative data across the ecological, social and economic sectors. To overcome this limitation, we adopted a qualitative approach, where delta characteristics across all sectors were assessed through systematic expert surveys. This approach enabled us to generate a comparative assessment of threats, resilience, and resilience-strengthening adaptation across the four deltas. Our assessment provides novel insights into the various components that dominate the overall risk situation in each delta and, for the first time, illustrates how each of these components differ across the four mega deltas. As such, our findings can guide a more detailed, sector specific, risk assessment or assist in better targeting the implementation of risk mitigation and adaptation strategies.