1,721,082 research outputs found
Design of water connections to improve the sustainability of an urban constructed wetland system
No full textThe constructed wetland (CW) system is usually regarded as a cost-effective and eco-friendly technology, especially in urban drainage systems, where CWs attenuate flooding, purify pollutants, and support habitats. However, some challenges exist in modeling, evaluating, and optimizing CWs.
First, there are models available for CWs and urban drainage systems separately, but there is a lack of systematic framework for coupling wetland models for urban drainage system applications. Therefore, this thesis develops an integrated modeling framework to simulate various CWs in urban drainage systems. The model framework is based on the SWMM model to simulate simple cases of drainage systems and coupled with the OpenFOAM and modified EFDC models to cope with complex cases of hydrodynamic and biochemical processes, respectively. This modeling framework is more suitable for urban CW systems after simple case validation.
Second, hydrology is the primary driver of mass and energy in CWs and is vital to CWs’ design, operation, and maintenance. However, there is currently a lack of comprehensive understanding of CWs’ responses to changing hydrological conditions. Therefore, this thesis monitors a multistage surface flow CW, evaluates its performance and sustainability in water resources management and water quality improvement under changing hydrological conditions, and proposes recommendations for current urban CWs. A summary of previous cases based on a literature survey is also presented. Simple quantitative methods are used to investigate the feedback of the CWs under changing hydrological conditions and propose simple prediction equations. The insights generated can be used to deepen the understanding of changing hydrological conditions for urban CWs systems.
Third, hydrological connectivity is a critical factor for urban CW systems. Connecting different CWs can have synergistic effects that enhance overall performance and sustainability. However, currently there is a lack of index system to assess hydrological connectivity and how it impacts CW systems' sustainability. Therefore, this thesis proposes a CW management framework that uses an evaluation index system consisting of hydrological connectivity indexes and sustainability indexes. The index system is applied to a case study to analyze the improvement of hydrological connectivity design for urban sustainability. Results indicate that among the three connection modes of dendritic, parallel, and reticulate, the reticulate mode has the best effect in peak reduction. Each of these three connection modes has its focus, with the dendritic mode being more stable and the reticulate mode being more reliable and resilient. It was also found that the CWs located closer to the end of the drainage system are more sensitive and important, while CWs near the source can have a broader range and combination of design parameters. Finally, the optimal CW design parameters are derived based on the sustainability index.
These frameworks, methods, and tools developed to address individual challenges culminate in a comprehensive simulation, evaluation, and optimization framework that can be utilized to improve the sustainability of current CWs practices in urban areas.published_or_final_versionCivil EngineeringDoctoralDoctor of Philosoph
Evaluating and optimizing the design and spatial allocation of green infrastructure in shallow groundwater environments
No full textGreen infrastructure (GI) represent semi-engineered stormwater management practices that have been widely implemented to tackle urban stormwater problems, e.g., urban flooding, non-point source pollution. However, it is challenging to implement GI in shallow groundwater conditions. The impact of shallow groundwater, and the suitable engineering approaches to implement GI in these areas remain to be studied.
First, although shallow groundwater is known to be a challenge of implementing GI, its interaction with GI has not been quantified. This thesis thus performed statistical analyses to evaluate the interaction between porous pavement and shallow groundwater at various temporal scales. The results showed that rainfall remained the key driver of underdrain flow. The impact of groundwater on underdrain flow outweighed that of rainfall when groundwater table was shallower than the underdrain, particularly at finer temporal scales.
Second, although some design recommendations have been given to implement GI in groundwater table, they mostly appear to be empirically based, and their feasibility and effectiveness have not been thoroughly studied. This thesis thus built numerical models of individual bioretention cell and porous pavement and proposed design recommendations through investigating their hydrologic performance in shallow groundwater. The thesis showed that it is generally feasible to implement well-designed GI in shallow groundwater areas. Lower- and higher- permeable media soils are recommended for bioretention cells when groundwater contamination and runoff control are of concern, respectively. Building a thinner pavement, installing an underdrain, and installing an impermeable liner showed some benefits and drawbacks in mimicking natural hydrologic cycle and retaining the performance of porous pavement.
Third, although there are many GI-enabled models, they all have limitations in simulating GI in shallow groundwater at catchment scale. This thesis thus developed a modified SWMM (named SWMM-LID-GW) which considered groundwater table condition into the calculation of GI-related hydrologic processes. Furthermore, this thesis developed a coupled surface-subsurface hydrological model (named SWMM-MODFLOW) which realized the two-way interaction between GI and groundwater at catchment scale. The thesis showed that both models are applicable; SWMM-LID-GW performed significantly better than the current SWMM particularly for shallower groundwater table conditions.
Fourth, when planning GI spatially at catchment scale, maximizing the reductions in runoff and pollution are normally the main objectives. Groundwater dynamics, however, are seldom considered. Thus, this thesis performed scenario-based simulations and algorithm-based optimizations to quantify the impact of spatial allocation of bioretention cells on groundwater table dynamics using SWMM-MODFLOW. It also provided recommendations on the optimal spatial allocation of bioretention cells when their interaction with shallow groundwater is considered. The thesis demonstrated the importance of considering groundwater table condition in GI planning. Apart from the areal coverage of GI, their aggregation level and locations are also vital when groundwater management is of concern.
In conclusion, this thesis demonstrated that the impact of shallow groundwater on the hydrologic performance of GI needs to be carefully considered in the design and planning of GI. A better design and planning strategy of GI can mitigate the impact of shallow groundwater and facilitate the GI implementation in shallow groundwater environments.published_or_final_versionCivil EngineeringDoctoralDoctor of Philosoph
Advancing characterization of rainstorm variabilities for urban flood hazard assessment and mitigation
No full textIntensified rainfall extremes coupled with ongoing urbanization are anticipated to increasingly expose populations to urban flood hazards. However, the pace at which flood hazard assessment theories and practices are updated is not keeping up with this trend. Traditional flood hazard assessments and infrastructure design are typically based on regular-shaped and uniform rainfall patterns with stationary frequencies; the mapping of flood hazards largely depends on riverine flood peaks, and the severity is assumed to align with the return level of the designed rainstorms. Yet, the nonstationary frequency of rainfall extremes is prevalent in a warming climate; complex spatiotemporal variabilities (STV) lead to significant discrepancies in the flooding processes compared to idealized designs. Moreover, the intensely local nature of urban floods necessitates dynamic and distributed estimation of inundation hazards. Consequently, high spatiotemporal-resolution rainfall inputs that accurately represent space-time structures are essential. This thesis seeks to enhance flood hazard assessment and mitigation by advancing the characterization of rainstorm variabilities, encompassing both long-term frequency and event-level STV. Using a multi-source merged gridded dataset, this study first evaluated the non-stationarity (NS) of short-duration rainfall extremes in the rapidly developing Greater Bay Area of China. The findings indicate that NS exhibits significant land cover and duration dependencies, with urban areas experiencing a more pronounced intensification of events over short durations and short return periods compared to rural areas. Besides, urban areas display a higher degree of variabilities in NS across time scales and return periods with higher peak scaling rates. Then, this study tracked rainstorms across various watersheds in Hong Kong using radar data and explored the interplay among rainstorm kinematics, heterogeneity, scaling, and event severity through a vine copula-based model. The prevailing STV challenges the equal-probability assumption in the frequency analysis regarding event severity across scales. The study also demonstrated the integration of rainstorm STV into generating a stochastic rainstorm catalog that reflects the realistic STV distribution over a rural-urban watershed. 3000 scenarios were drawn from the catalog to conduct numerical experiments using a full 2D shallow water equations-based inundation model. The intricate joint probability structures of rainstorm severity and STV variables tend to obscure the mechanistic impact of individual factors on flood response, resulting in the inconsistency between the exceedance probabilities of the rainstorm and flood variables, particularly between rainstorm intensity and flood hazard index (with Kendall's tau being 0.22). Notably, significant underestimation of inundation hazards may occur when street-level inundation hazards are represented by watershed-level hazards for the same return period, again underscoring the fallacious outcomes of the equal-probability assumption across scales. Additionally, this thesis assessed the performance of a typical nature-based solution, the flood retention lake (FRL), within the same watershed. The results reveal a pronounced nonlinearity with rainstorm severity, characterized by an L-shaped band of satisfactory effectiveness on the duration-return period diagram. Furthermore, the performance of multiple FRLs in various geographic configurations shows contrasting results from hydrologic and hydrodynamic perspectives, emphasizing the importance of clear objectives in the strategic blueprints prior to optimization.published_or_final_versionCivil EngineeringDoctoralDoctor of Philosoph
Reaction-diffusion models for geological patterns : new insights and potential applications
No full textPattern formation is a ubiquitous phenomenon in nature, arising from reaction-diffusion processes in systems away from equilibrium. These patterns can be found in a wide variety of systems, including chemistry, biology, ecology, geology, and materials science. Reaction-diffusion equations have been used to model a wide variety of patterns, and they have the potential to be used to understand the formation of geological patterns in rocks.
This thesis proposes a generalized reaction-diffusion model that can be used to describe a wide variety of geological patterns. The model is based on the Cahn-Hilliard, Allen-Cahn, and cnoidal wave equations, which are well-established models for describing phase separation and localization phenomena. The generalized model includes additional terms that can account for the effects of fluid flow, stress, and other factors.
The derived models have been used to investigate the formation of three types of geological patterns: Liesegang patterns, dendritic growth, and mineralized veins. The results show that the models can reproduce the characteristic features of these patterns. The model also reveals the role of different factors, such as diffusion coefficients, supersaturation, stress, and heterogeneity, in determining the appearance of the patterns.
The results of this study provide a new theoretical framework for understanding the formation of geological patterns. The model has the potential to be used to improve our understanding of mineral distribution, develop new methods for controlling pattern formation, and develop new computer-vision techniques for field exploration.published_or_final_versionCivil EngineeringDoctoralDoctor of Philosoph
Characterization of near-wake structures around wall-mounted prisms and its implications to wind force generation
No full textThe presence of large-scale coherent structures in the wake of a generic wall-mounted prism has attracted great attention for several decades due to its close association with numerous engineering problems. In wind engineering, this flow is related to the spatio-temporal evolution process of three-dimensional and complex wind flow field around a building, which in turns governs the relationship between the fluctuating velocity field and wind loading, and the ventilation and pollutant dispersion around and behind the building.
The major task of this study is focusing on how to identify and extract the energetic large-scale coherent motions with a relatively pure physical meaning. The inherent chaotic feature of the highly three-dimensional and turbulent wake flow causes huge troubles to the seeking of a proper solution due to frequency modulations, phase jitter, and oscillations. This study takes advantage of the original proper orthogonal decomposition (POD) technique to overcome the difficulties and effectively extract the energetic coherent wake structures by introducing various POD variants.
The planar time-resolved particle image velocimetry (PIV) technique is adopted to obtain the time-varying turbulent wind velocity fields around wall-mounted prisms of seven different geometries. Synchronized measurement of fluctuating wind pressure on the prism faces is also conducted in several cases. As the supplement to the limitation of planar PIV velocity fields, CFD (Computational Fluid Dynamics) using large-eddy simulation (LES) is also performed to obtain the three-dimensional velocity fields around a short square prism.
The current study mainly investigates the following areas: (i) the definition, identification, and significance of transient extreme wake events derived from these energetic large-scale anisotropic coherent structures; (ii) the physical understanding of antisymmetric and symmetric coherent motions and their association with typical Karman vortex shedding and arch-type vortex shedding as well as the implications to across-wind force generation mechanism; (iii) the effects of geometry parameters (aspect ratio and side ratio) on the characteristics of the three-dimensional building wake structures and coherent flow motions; (iv) the comparative study of these coherent motions obtained from experimental and CFD data and the possibility of investigation on other physical phenomena, such as the regular arch-type vortex shedding and its connection with tip vortex system, from the three-dimensional CFD data. Meanwhile, the characteristics of time-averaged mean wake patterns are also summarized and documented.
In terms of findings, this study reveals the coexistence of antisymmetric and symmetric coherent structures with different occurrence probabilities, representing Karman-type and arch-type vortex shedding, respectively. These energetic low-order coherent structures are found to govern grossly the dominant features of extreme wake patterns producing peak flow events such as strongest and weakest air ventilation and pollutant transport. In wind loadings, the large-scale antisymmetric coherent motions are demonstrated to be closely associated with the generation of peak across-wind forces. Ascribe to the downwash flow, the flow unsteadiness at the free end is observed to modulate the spanwise in-phase vortex activities with a low-frequency oscillation.published_or_final_versionCivil EngineeringDoctoralDoctor of Philosoph
Hyporheic zone performances : influential factors and applications in hyporheic restoration
No full textHyporheic zone (HZ), the interstitial region beneath or alongside a streambed with active groundwater and surface water mixing, is important to stream ecosystem. To better understand the uncertainties of the HZ performance and its important applications in hyporheic restoration, this thesis investigated the major influential factors such as streambed hydraulic conductivity (K) and a storm event, developed numerical models for biogeochemical reaction simulation in the HZ, and proposed a method to optimize the design of in-stream structure for hyporheic restoration.
The spatial uncertainties of the HZ performance induced by the K were analyzed. Residence time (RT), which represents the duration of a water molecule or a solute remaining within the HZ, was employed as the indicator. From the simulation results with different K distributions at the streambed, both heterogeneity and anisotropy could shorten the mean and median RTs while increasing the range of the RTs. Moreover, K fields arranged in a more orderly pattern had longer RTs than those with random K distributions. These results could facilitate the selectiondesign of the K values and distributions to achieve the desired RT during hyporheic restoration.
The spatial and temporal uncertainties of the HZ performance induced by a storm event were analyzed. The impacts of rainfall intensity (RI) and rainfall duration (RD) were investigated, and two indicators, i.e., the influential time (IT) and the influential depth (ID) were proposed. The results revealed that the RI and RD both display logarithmic relationships with the IT and ID, but only between certain thresholds of the RI and RD. In addition, the IT had a linear negative correlation with the groundwater response while the ID was not affected. These results could facilitate the future predictions of the IT and ID during transient events.
More accurate numerical models for simulating biogeochemical reactions (i.e., denitrification and nitrification) were developed to evaluate the nitrogen removal in the HZ. Three models were proposed, and the results showed that the third model using pre-determined reaction zones for the biogeochemical reactions and coupling genetic programming had the best performance. Moreover, case studies revealed that the HZ would be more effective in removing nitrogen when the water quality was at a certain level. These results could potentially benefit the HZ management in face of the continual degradation caused by human activities.
Finally, a method for optimizing the design of in-stream structures (e.g., weir) was proposed. The objective function for calculating the optimal height of the weir was formulated as the product of variables related to both nitrogen removal amount and ratio in the HZ. The results demonstrated the method’s generally good performance and could enhance the understanding towards the optimal design of in-stream structures for hyporheic restoration.
This thesis presents the state of knowledge on the HZ performance including influential factors and applications in hyporheic restoration. It provides improved numerical models for biogeochemical reaction simulation, and offers new insights into the methods for the optimal design of in-stream structure. The present study not only has theoretical significance but also has practical engineering implications.published_or_final_versionCivil EngineeringDoctoralDoctor of Philosoph
Energy balance across the eddy covariance sites
No full textEddy covariance technique has become one of the most reliable approaches to study the interactions between atmosphere and earth’s surface. However, observations from single or multiple eddy covariance systems always lack energy balance closure (EBC) across all the FLUXNET research sites. Particularly, the measurements over the heterogeneous surface are questionable and the heterogeneity is closely related to the energy imbalance issue. This dissertation is broadly divided into three parts: the first part investigates the temporal and spatial variations of EBC across 150 FLUXNET research sites, the other two parts performs field measurements respectively over the wetland heterogeneous surface and the urban heterogeneous surface.
Chapter 2 investigates the temporal and spatial variations of EBC across 150 FLUXNET research sites covering nine landscapes and five climate zones. Overall, the best EBC is observed over the sites covering with savannahs and grass, and the worst EBC is found in the wetland sites. And EBC generally decreases from Köppen climate zone A to E. The results from this part of study could be used to correct eddy covariance data and EBC related models; they also connect the cross-influenced relationships between various environmental variables and EBC to the stomata aperture and metabolism of the vegetation, which enhances our understanding of the potential link between EBC and vegetation physiology.
Given that the worst EBC is observed over the wetland sites in Chapter 2, field measurements are firstly conducted in a sub-tropical wetland of Hong Kong in Chapter 3, to explore the overlooked influence of lateral energy fluxes in the subsurface (Q_Sub) on EBC. The results show that Q_Sub could not account for the energy imbalance here because their magnitudes are relatively small and fluctuate in out of phase with the energy budget residuals. This part of study enhances our understanding of energy exchanges between a terrestrial biotope and the surrounding water, which might further generate insights into the biochemical processes in wetlands.
In Chapter 4, the eddy covariance tower is installed on a building roof in a highly-dense and compact urban area of Hong Kong to assess the surface energy fluxes and EBC over such complex urban surface. With a high density of high-rise buildings, as well as small fraction of vegetation, the measured energy fluxes are featured with smaller latent heat fluxes, larger sensible heat fluxes and the extremely higher anthropogenic heat fluxes comparing with other urban sites but with low and sparse buildings. EBC displays a significant difference among various wind directions, and generally shows a negative relationship with surface heterogeneity. This part of the study helps to fill a gap in our understanding of surface energy fluxes and EBC in highly-dense cities, and sheds insights into the future installation of eddy covariance tower in similar areas.
Overall, the results of this dissertation improve our understanding of the interaction of energy and gas fluxes between the heterogeneous land surface and atmosphere, as well as facilitate the application of an eddy covariance system over the heterogeneous surface. They also benefit the optimization of models related to EBC and enhance the understanding of the relationship between EBC and different environmental variables.published_or_final_versionCivil EngineeringDoctoralDoctor of Philosoph
Effects of climate and hydrology on subtropical mangrove growth and community composition
No full textMangroves are of great significance in sequestrating carbon, resisting storm surges and supporting coastal species. However, mangroves face many threats from both humans and nature. Despite many studies on the anthropogenic threats such as deforestation and urbanization, there is still a lack of study that integrates natural effects at both regional and local scales. Unlike tropical mangroves, subtropical mangroves live in environments with highly variable climatic and hydrological conditions. Understanding the climatic and hydrological effects on mangroves is therefore crucial. The first two parts of this thesis identified the key climatic and hydrological factors affecting subtropical mangroves, and the third part of the thesis built a numerical model to investigate the response of mangroves to these identified climatic and hydrological factors and to explore the mangrove composition changes under future sea-level rise scenarios.
In Chapter 2, the regional effects of macro- climatic and hydrological factors such as temperature, precipitation, solar radiation and evapotranspiration on mangrove cover were investigated through statistical analysis for one tropical and six subtropical mangrove stands in southern China. The results indicate that subtropical regions are more influenced than tropical regions by macro- climatic and hydrological factors. Precipitation and temperature are the governing macro- climatic and hydrological factors associated with mangrove area variations. Moreover, the relationship between precipitation and mangrove cover is not necessarily positive at finer temporal resolutions, which may be due to the local groundwater salinity and the salt tolerance of dominant species.
Considering groundwater salinity is an important factor that affects mangrove growth and possibly affects the response of mangroves to external climatic and hydrological changes as proposed in Chapter 2, Chapter 3 performed field measurements to investigate the variations of groundwater piezometric head and salinity at a local subtropical mangrove swamp and analyzed the driving factor. The results indicate that tide is the driving factor that leads the fluctuations in mangrove groundwater, and tidal effects differ horizontally and vertically. The active root zone showed high dependence on the tidal variations due to the presence of macropores, and the groundwater fluctuations, especially the salinity fluctuations, were highly attenuated owing to capillary effects underneath the active root zone.
In Chapter 4 and 5, a three-dimensional (3D) coupled hydro-vegetation model was first developed to simultaneously simulate the mangrove and groundwater variation in temporally varying climatic and hydrological conditions, and was then employed to simulate the spatial and temporal distribution of native and exotic mangroves in a subtropical mangrove forest with and without sea-level rise for 120 years. The results indicate that salinity increase resulted from future sea-level rise is likely to benefit the native mangrove growth and inhibit the exotic mangrove growth.
In general, this thesis systematically evaluated the effects of climate and hydrology on subtropical mangroves. The regional and local study facilitated the monitoring and understanding of the mangrove ecosystem variations in response to climatic and hydrological changes. The developed numerical model advanced the understanding of mangrove composition changes in varying climatic and hydrological conditions, which could further facilitate future research works in this area.published_or_final_versionCivil EngineeringDoctoralDoctor of Philosoph
Assessing and optimizing green infrastructure designs for stormwater management using relative performance evaluation framework and data-driven approach
No full textGreen infrastructures (GIs) are considered as environmentally-friendly alternatives to the conventional stormwater drainage infrastructures. Their hydro-environmental impacts and design optimization have been investigated in various previous studies. However, there exist a few common challenges confronting the modeling, assessment, and optimization of GIs.
The first challenge is that most of the current performance assessment frameworks of GIs do not explicitly account for the preferences of stakeholders and commonly involve a tedious parametrization process for valuing the intangible hydro-environmental impacts of GIs. This thesis thus proposes an integrated assessment framework that uses relative performance evaluation (RPE) methods to tackle this challenge. In this framework, the performance of a GI design alternative for each impact of interest is measured by its relative effectiveness as compared to the other considered alternatives. The relative effectiveness obtained for different impacts can be then aggregated to derive the overall effectiveness of an alternative. During aggregation, specific weights can be assigned to the different impacts to reflect the preferences of stakeholders. This assessment framework can be useful for comparing and selecting GI design alternatives when multiple performance indicators and various stormwater management interests are considered.
Second, in GI-related studies, the accuracy of the commonly-used process-based hydrological models is sometimes affected by their model structure and the availability of field measurements. Data-driven modeling approaches can potentially avoid these issues by directly modeling the correlation between the input (e.g., rainfall time series) and the response (e.g., outflow hydrograph) of a system. Deep learning is a specific type of data-driven modeling that is capable of modeling high-dimensional data. Deep learning is used in this thesis to solve various problems in several GI sites, e.g., high-resolution rainfall-runoff modeling in a complex urban catchment with multiple GIs, and overflow occurrence prediction in a bioretention cell with censored field observations. This thesis shows that deep learning models can achieve comparable or better prediction accuracies when compared to calibrated process-based models and conventional machine learning models. Deep learning models and calibrated process-based model are found to have similar responses when tested under various rainfall conditions. This thesis also shows that knowledge in runoff generation processes can improve the design of deep learning models, and a model’s hidden states can be useful for confirming its credibility and generating hydrological insights.
Third, researches on the optimal design of GIs for multi-objective stormwater management are limited. This thesis thus applies the RPE method to identify suitable implementation levels of GIs to concurrently achieve multiple stormwater quality and quantity management targets. This study also proposes a method to summarize and generalize simulation results for rapid assessment and selection of GI alternatives considering multiple targets.
In conclusion, this thesis evaluates the effectiveness of various potential solutions to several common challenges in GI-related studies to generate insights to inform decision making in stormwater management. The frameworks, methods, and tools developed for solving individual challenges, in the end, form a comprehensive simulation-optimization framework which improves the current practices of identifying and deriving optimal GI designs.published_or_final_versionCivil EngineeringDoctoralDoctor of Philosoph
Enhancing urban flood management : the issues of data availability, model configuration, and robustness
No full textUrban areas are highly susceptible to flooding, necessitating effective strategies for urban flood management. This thesis centers on enhancing urban flood management through three principal avenues: data accessibility, model configuration, and model robustness.
For data availability, one major obstacle is the limited availability of timely and reliable information regarding the flood event and its consequences. However, the growing volume of social media data offers an invaluable and rapidly accessible untraditional source. This thesis thus developed a standardized and optimized workflow to assess the impacts of urban flooding by extracting and analysing social media data, as well as identifying the intensive public response areas. Using the 2020 Chengdu rainstorm-induced flooding in China, social media data provide spatial flood information and 232 flood sites with geological locations. The spatiotemporal analysis of social media revealed the process of flooding and enables quick determination of severely affected areas, demonstrating the potential of social media to support urban flooding impact assessment and storm-flooding numerical modelling by obtaining extra valuable flood data.
For model configuration, the complexity of urban surfaces and limited subsurface drainage information pose great challenges to modelling urban rainfall-runoff and flood hydraulics. This thesis developed an integrated hydrodynamic model framework incorporating both surface and subsurface drainage processes. To properly involve drainage flow effects, we presented three methods to quantify the drainage flow process with limited pipe data. The model framework was verified against six benchmark cases, showing that both hydrological and hydraulic processes can be well reproduced by the model with NSE all larger than 0.5. The model was also successfully applied to simulate rainstorm-induced flood events in a rural-urban catchment, the upper Shenzhen River catchment. Results further demonstrated the robust capability of the model in the quantification of flow exchange between surface and subsurface systems to some extent even in the absence of drainage information.
For model robustness, the scarcity of high-precision data, such as topographic data, rainfall data, and validation data, intensifies the uncertainty associated with models. This thesis developed a bottom-up approach for urban flood hazard mapping at multiple levels (grid-kilometer-district), built upon the integration of the developed flood modelling with data acquisition from open sources. The developed model was applied to flooding in Chengdu in August 2020 with the support of the identified social media flood data. The multilevel hazard mapping approach developed here shows less sensitivity to the data input quality and model uncertainty, indicating relatively higher reliability.
Overall, this thesis confirmed the capacity of social media data to support urban flood management; optimized modelling configuration to achieve robust and accurate simulations even with limited availability of detailed sewer data; proposed a multilevel urban flood hazard mapping method to mitigate the negative impact of data scarcity and quality on hazard modelling. These findings and methodologies have the potential to strengthen overall resilience and minimize the negative impacts of flooding in urban areas.published_or_final_versionCivil EngineeringDoctoralDoctor of Philosoph
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