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Impact of hydraulic model resolution and loss of life model modification on flood fatality risk estimation : case study of the Bommelerwaard, The Netherlands
Flood simulations are important for flood (fatality) risk assessment. This article provides insight into the sensitivity of flood fatality risks to the model resolution of flood simulations and to several uncertain parameters in the loss of life model used. A case study is conducted for river flooding in a polder in the Netherlands (the Bommelerwaard) where the Dutch approach for loss of life estimation is applied. Flood models with resolutions of 100, 25, and 5 m are considered. Results show locally increased mortality rates in higher resolution simulations nearby structures including road embankments, dikes, and culverts. This causes a larger maximum individual risk value (annual probability of death for a person due to flooding) which has consequences for safety standards based on the individual risk criterion. Mortality rate in the breach zone is also affected by representations of buildings as solid objects versus as roughness elements. Furthermore, changes in the loss of life estimation approach via alternative ways of including people's behaviour, building characteristics, and age of the population, have a significant impact on flood fatality risk. Results from this study can be used to support future risk assessments and decision making with respect to safety standards.
Woods versus waves: wave attenuation through non-uniform forests under extreme condition
Worldwide, communities are facing increasing flood risk, due to more frequent and intense hazards and rising exposure through more people living along coastlines and in flood plains. Nature-based Solutions (NbS), such as mangroves, and riparian forests, offer huge potential for adaptation and risk reduction. The capacity of trees and forests to attenuate waves and mitigate storm damages receives massive attention, especially after extreme storm events. However, application of forests in flood mitigation strategies remains limited to date, due to lack of real-scale measurements on the performance under extreme conditions. Experiments executed in a large-scale flume with a willow forest to dissipate waves show that trees are hardly damaged and strongly reduce wave and run-up heights, even when maximum wave heights are up to 2.5 meters. It was observed for the first time that the surface area of the tree canopy is most relevant for wave attenuation, but that the very flexible leaves hardly add to effectiveness. Overall, the study shows that forests can play a significant role in reducing wave heights and run-up under extreme conditions. Currently, this potential is hardly used but may result in considerable cost savings in levee designs.
Geomorphological disaster in Chamoli, Uttarakhand, India : a challenge of finding a balance between infrastructural development and social and environmental protection
Any intervention to a natural system for the sake of economic growth and prosperity shall objectively be weighed vis-a-vis consequences and benefits as well as any nation’s specific priorities and demands. In this note, we have attempted to revisit the recently occurred geomorphological disaster in Chamoli in Uttarakhand (India) by synthesizing available materials and information. We have also briefly revisited some similar disasters that took place during the last decade in the region. We have not intended to connect the problems with global processes (like climate change) and have not attempted to reveal a “butterfly effect”. The purpose here in this note is to reiterate the necessity of emphasizing finding out a win-win situation (yes, it is possible) between infrastructural development, environmental protection and human security in the Himalayan region.
Sediment characteristics and intertidal beach slopes along the Jiangsu Coast, China
Tidal flats play an important role in promoting coastal biodiversity, defense against flooding, land reclamation and recreation. Many coastal tidal flats, especially the tide-dominant ones, are muddy. However, the number of studies on the profile shape and surficial sediment distribution of muddy tidal flats is small compared to sandy beaches. Based on high spatial-resolution measurements along the tide-dominant Jiangsu Coast, China, we analyzed the morphology and sediment characteristics of the unvegetated intertidal flats along the Jiangsu Coast. The Jiangsu Coast can be divided into an eroding northern part (north coast) and an accreting southern part (south coast). The beach slope of the north coast shows a southward flattening trend, apart from some outliers related to rocky parts of the coastline. We found alternating very fine and coarse sediment (depending on the local clay content) for different locations along the north coast, which can be explained from consolidation and armoring-induced erosion resistance. In the south coast, we found gradual coarsening of bed surface sediment and gradual flattening of beach slopes to the south. This seemingly unexpected pattern is explained by the flood-dominant current causing landward sediment transport, larger tidal range in the south part, sheltering effect of the Radial Sand Ridges, and contribution of different sediment sources, viz. the Abandoned Yellow River Delta and the Radial Sand Ridges. In the cross-shore direction, the sediment grain size decreases landward. Waves are only of secondary importance for the sediment dynamics at the unvegetated tidal flats along the Jiangsu Coast.
Flood risk assessment of the European road network
River floods pose a significant threat to road transport infrastructure in Europe. This study presents a high-resolution object-based continental-scale assessment of direct flood risk of the European road network for the present climate, using high-resolution exposure data from OpenStreetMap. A new set of road-specific damage functions is developed. The expected annual direct damage from large river floods to road infrastructure in Europe is EUR230 million per year. Compared to grid-based approaches, the object-based approach is more precise and provides more action perspective for road owners because it calculates damage directly for individual road segments while accounting for segment-specific attributes. This enables the identification of European hotspots, such as roads in the Alps and along the Sava River. A first comparison to a reference case shows that the new object-based method computes realistic damage estimates, paving the way for targeted risk reduction strategies.
EURODYN 2020 : XI International conference on structural dynamics (23-26 November 2020, Athens, Greece)
Subsoil modelling for railway induced vibrations
Nuisance due to railway induced vibrations has been receiving increased attention in the Netherlands, as a recent study has found that a significant part of the population living in the vicinity of railway tracks in the Netherlands, experiences excessive vibrations levels. As a result, the Dutch government has commissioned the design and implementation of a screening model for the estimation of railway induced vibrations at a network level. Within this screening model, attention has been paid to the characterisation of the subsoil. This paper focuses on the methodology developed to perform a semi-stochastic subsoil characterisation, based on publicly available datasets for the Netherlands. The method uses a countrywide cone penetration test database and the Dutch geomorphological map to define, at a specific location, a set of possible subsoil schematisations, their likelihood of occurrence, and the corresponding subsoil parameters. The effect of soil variability on the vibration levels is assessed by computing the transfer function at different distances from the source. The transfer functions are computed with a newly developed finite element model kernel. The kernel is optimised to specifically compute layered half-spaces. The results show that the subsoil schematisation plays a significant role on the vibration level, which shows that it is paramount to perform a correct characterisation of the subsoil when trying to estimate induced vibration.
High-resolution modeling and prediction of urban floods using WRF-Hydro and data assimilation
We assess the impact of increasing the resolution of hydrologic modeling, calibration of selected model parameters and assimilation of streamflow observation toward event-based urban flood modeling and prediction using WRF-Hydro in the Dallas-Fort Worth area (DFW). We use quantitative precipitation estimates at 500-m 1- min resolution from the Collaborative Adaptive Sensing of the Atmosphere radar network for observed rainfall, Stepwise Line Search for calibration, and fixed-lag smoothing for data assimilation (DA). The model domain is a 144.6 km2 area comprising 3 urban catchments in Arlington and Grand Prairie in the middle of DFW. It is shown that event-specific calibration of 6 WRF-Hydro parameters is largely successful in simulating hydrographs at the catchment outlets particularly for the most important rising limbs, but less so for attenuated peaks or fast-receding falling limbs. A spatial resolution of at least 250 m was necessary for the land surface model (LSM) to delineate small catchments and hence to capture catchment-wide rainfall with acceptable accuracy. Simulations at selected combinations of resolutions, 250 and 125 m for the LSM and 250, 125, 50 m for the routing models, showed mixed results. The overall results indicate that, in the absence of resolution-specific prescription and calibration of channel routing parameters, a resolution of 250 m for both the LSM and routing models is a good choice in terms of performance and computational requirements, and that, in the absence of high-quality calibration and continuous simulation of streamflow, DA is necessary to initialize WRF-Hydro for event-based high-resolution urban flood prediction.
Morfologische ontwikkeling Noord-Beveland en Breezand : regio advies kusterosie Banjaardstrand en Breezand
Rijkswaterstaat heeft Deltares advies gevraagd over de morfologische veranderingen van de kust bij het Banjaardstrand (Noord-Beveland) en nabij Breezand (Walcheren). De erosie van het Banjaardstrand wordt veroorzaakt door de voorliggende geul "Schaar van Onrust". De noordzijde van Walcheren grenst aan de grote getijgeul "Roompot Zuid", waardoor grote stroomsnelheden en langstransporten optreden. De knik in de kustlijn net ten oosten van Breezand zorgt ervoor dat Breezand uitsteekt ten opzichte van de omliggende kust. Het uitstekende bolwerk voeroorzaakt hier gradiënten in de stromingen en de transporten, wat leidt tot erosie van het strand.
BOI - Scaling of dimensional parameters in XBeach
The Action Plan for the Safety of Sandy Coasts describes the development of a new dune safety assessment methodolgy for the Dutch coast based on the process-based numerical model XBeach. The Action Plan describes a set of tasks required to enable implementation of this new method for safety assessment of dunes in 2023. In this report a general scaling approach is investigated for the relevant dimensional parameters. For certain parameters alternative and optimized parameters are defined and subsequently implemented in the source code. An additioonal focus of the study was the correct definition of the computational grid when performing simulations on laboratory scales.