The issue: Subsidence, the sinking or lowering of the land surface, is expected to become a greater issue in coastal areas in the coming years. In these areas, subsidence caused by both natural and human induced factors will amplify the effects of sea level rise caused by climate change. These cities will face an increased risk of flooding, salinization of freshwater, storm surges, increased wave action, increased erosion and permanent inundation. These phenomena will especially interest cities located in coastal or deltaic regions which are growing in population: subsidence is triggered in these locations by excessive groundwater extraction and by the weight of newly built infrastructures on soils prone to compaction. The thesis: The present thesis consists of two main goals: firstly, to build an easily searchable database on subsidence related issues for cities around the world and focusing on the analysis of cities in Europe, North America and South America, among those selected by Nicholls et al., (2008) and Hallegatte et al., (2013) in their studies. The database could be used to identify the coastal cities where subsidence occurs, to identify the most commonly occurring causes of subsidence and lastly to investigate the correlation between subsidence rates recorded from in-situ surveys and from satellite platforms. Secondly, to define a methodology to estimate the rate of subsidence in coastal cities, by using geotechnical data collected in two cities built on soft soils, located in the Netherlands: Delft and Rotterdam, where extensive in-situ surveys and satellite data exists. The aim is to build geotechnical models (using the software programs MWell and D-Settlement, provided by Deltares) exportable to cities of similar geology and issues, where limited data is available, to have better predictions of subsidence rates. Results: The database gives a general view of the most commonly occurring subsidence causes in coastal cities and has been sent to the LASII, the UNESCO Land Subsidence International Initiative, so that it can be used to create a worldwide subsidence map. When it comes to the database, comparing subsidence rates from literature was proven to be very challenging, because those rates have usually been measured with different techniques, in different years, for different time spans or refer to different areas of the same city. What this means is that number of comparable rates is very limited and therefore not significant to identify patterns of correlation between subsidence rates recorded from satellite platforms and from the ground. The hydrogeological models are to be used in cities on soft soils in which only limited data is available, to obtain more precise prediction of subsidence rates. To do so for cities on soft soils in which the extraction of water is the driver of subsidence, a MWell model was built for the city of Delft, NL, where piezometric data is available to confirm that the calculated drawdown is realistic. The calculated drawdown was then imported in D-Settlement to obtain a prediction (verifiable with measured rates) of subsidence in the city. The city of Rotterdam, NL was used as a model for cities built on soft soils in which settlement has been caused by the weight of infrastructures. A 1D D-Settlement model was built to model the phenomena. Bibliography: Nicholls, R. J. et al. (2008), “Ranking Port Cities with High Exposure and Vulnerability to Climate Extremes: Exposure Estimates”, OECD Environment Working Papers, No. 1, OECD Publishing. Hallegatte, Stephane, et al. "Future flood losses in major coastal cities." Nature climate change 3.9 (2013): 802.
Negli anni a venire la subsidenza, l’abbassamento del livello del suolo, avrà un impatto significativo nelle aree costiere. In queste aree, le conseguenze dell’innalzamento del livello del mare dovuto al cambiamento climatico saranno amplificate dalla subsidenza, sia naturale che indotta da attività antropiche. Attualmente queste città sono soggette a fenomeni quali inondazioni, sia temporanee che permanenti, alla salinizzazione degli acquiferi costieri e all’aumento dell’attività erosiva delle onde. Questi fenomeni avranno un impatto particolarmente significativo in città costiere la cui popolazione è in aumento: in queste città la subsidenza è causata principalmente dall’eccessiva estrazione di acqua e dal peso degli edifici di nuova edificazione su litologie che sono soggetti a compattazione. La tesi: La tesi ha due obiettivi principali: il primo è la creazione di un database in Microsoft Excel, che raccoglie informazioni relative alla subsidenza in 136 città costiere e l’analisi della subsidenza in città europee e americane. Le 136 città costiere sono state scelte da Nicholls et al., (2008) e poi analizzate da Hallegatte et al., (2013), che le scelsero per la loro importanza socioeconomica e in base alle perdite attese a causa dall’innalzamento del livello del mare. Il database può essere utilizzato per il confronto tra le città e per la ricerca di una correlazione tra tassi di subsidenza misurati da piattaforme satellitari e da analisi geotecniche in situ. Questa prima parte è stata svolta in collaborazione con Laura Pedretti. Il secondo obiettivo è di definire una metodologia per stimare tassi di subsidenza in città costruite su litologie soggette a compattazione per mezzo di modelli idrogeologici. Tali modelli sono stati costruiti utilizzando i parametri geotecnici e la stratigrafia di due città olandesi: Delft e Rotterdam. L’obiettivo è costruire modelli idrogeologici in città in cui una grande quantità di dati idrogeologici sono disponibili, in modo da verificare che essi diano stime di subsidenza realistiche, perché successivamente possano essere esportati in città di cui si conoscono meno informazioni per avere stime di subsidenza. I modelli sono stati realizzati utilizzando software forniti da Deltares: MWell and D-Settlement. Risultati: Il database fornisce una visione d’insieme sulle cause di subsidenza nelle più grandi città costiere ed è stato fornito al LASII, UNESCO Land Subsidence International Initiative, che lo utilizzerà per creare una mappa di subsidenza su scala globale. La comparazione di tassi di subsidenza da satellite e da sondaggi in situ si è rivelata complicata, perché i tassi misurati in periodi differenti, con metodi differenti e talvolta in aree diverse della stessa città. La quantità di tassi effettivamente comparabili risulta dunque troppo ridotta per individuare pattern significativi tra i tassi. Per quanto riguarda la modellizzazione idrogeologica, i modelli sono stati realizzati per una città in cui la subsidenza è dovuta all’estrazione di acqua (Delft, NL) e per una città in cui la subsidenza è provocata dal carico degli edifici (Rotterdam, NL). Per Delft, il software MWell (fornito da Deltares) è stato utilizzato per calcolare il drawdown nella città dovuto all’estrazione di acqua, che è successivamente stato importato nel software D-Settlement (formito da Deltares) per il calcolo della subsidenza. Per Rotterdam, è stato realizzato un modello di D-Settlement 1D per modellizzare la subsidenza dovuta al carico degli edifici nel corso dei secoli. Bibliography: Nicholls, R. J. et al. (2008), “Ranking Port Cities with High Exposure and Vulnerability to Climate Extremes: Exposure Estimates”, OECD Environment Working Papers, No. 1, OECD Publishing. Hallegatte, Stephane, et al. "Future flood losses in major coastal cities." Nature climate change 3.9
Analysis of subsidence in European and American coastal cities and hydrogeological modelling and predictions in soft soils
GIAROLA, ALESSIA
2019/2020
Abstract
The issue: Subsidence, the sinking or lowering of the land surface, is expected to become a greater issue in coastal areas in the coming years. In these areas, subsidence caused by both natural and human induced factors will amplify the effects of sea level rise caused by climate change. These cities will face an increased risk of flooding, salinization of freshwater, storm surges, increased wave action, increased erosion and permanent inundation. These phenomena will especially interest cities located in coastal or deltaic regions which are growing in population: subsidence is triggered in these locations by excessive groundwater extraction and by the weight of newly built infrastructures on soils prone to compaction. The thesis: The present thesis consists of two main goals: firstly, to build an easily searchable database on subsidence related issues for cities around the world and focusing on the analysis of cities in Europe, North America and South America, among those selected by Nicholls et al., (2008) and Hallegatte et al., (2013) in their studies. The database could be used to identify the coastal cities where subsidence occurs, to identify the most commonly occurring causes of subsidence and lastly to investigate the correlation between subsidence rates recorded from in-situ surveys and from satellite platforms. Secondly, to define a methodology to estimate the rate of subsidence in coastal cities, by using geotechnical data collected in two cities built on soft soils, located in the Netherlands: Delft and Rotterdam, where extensive in-situ surveys and satellite data exists. The aim is to build geotechnical models (using the software programs MWell and D-Settlement, provided by Deltares) exportable to cities of similar geology and issues, where limited data is available, to have better predictions of subsidence rates. Results: The database gives a general view of the most commonly occurring subsidence causes in coastal cities and has been sent to the LASII, the UNESCO Land Subsidence International Initiative, so that it can be used to create a worldwide subsidence map. When it comes to the database, comparing subsidence rates from literature was proven to be very challenging, because those rates have usually been measured with different techniques, in different years, for different time spans or refer to different areas of the same city. What this means is that number of comparable rates is very limited and therefore not significant to identify patterns of correlation between subsidence rates recorded from satellite platforms and from the ground. The hydrogeological models are to be used in cities on soft soils in which only limited data is available, to obtain more precise prediction of subsidence rates. To do so for cities on soft soils in which the extraction of water is the driver of subsidence, a MWell model was built for the city of Delft, NL, where piezometric data is available to confirm that the calculated drawdown is realistic. The calculated drawdown was then imported in D-Settlement to obtain a prediction (verifiable with measured rates) of subsidence in the city. The city of Rotterdam, NL was used as a model for cities built on soft soils in which settlement has been caused by the weight of infrastructures. A 1D D-Settlement model was built to model the phenomena. Bibliography: Nicholls, R. J. et al. (2008), “Ranking Port Cities with High Exposure and Vulnerability to Climate Extremes: Exposure Estimates”, OECD Environment Working Papers, No. 1, OECD Publishing. Hallegatte, Stephane, et al. "Future flood losses in major coastal cities." Nature climate change 3.9 (2013): 802.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/11985