Dissertations / Theses: '2D flood inundation modelling'

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Mousavi, Moghaddam Seyedali. "Inundation mapping of urban areas in case of severe rainfall events using HEC-RAS." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.

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The current study investigates the potential of HEC-RAS (2D) in simulating urban inundation patterns in case of sever rainfall scenarios expected in the Ferrara and Rimini cities in Italy. HEC-RAS is one to most known and used hydraulic model for river application, however, its rainfall module is relatively new and sparsely investigated. Comparison of different mesh sizes (10, 25 and 50m) indicated no significant difference in model performance. However, a significant difference was observed in simulation time. Inundation maps were obtained for 5, 20 and 100-year rainfall events. HEC-RAS model outputs are compared against ground evidence and detailed outputs obtained with other modelling scheme: filling-and-spilling algorithm and a two-dimensional (2D) hydraulic numerical model (jn Rimini). For both Ferrara and Rimini case studies, overall index of agreement between HEC-RAS and filling-and-spilling models is up to 88%, while the similarity (i.e., flood area index) between HEC-RAS and 2D hydraulic model simulation at Rimini is equal to 0.64. In general, this study provides addition insights concerning HEC-RAS potential and limitations for identifying pluvial flood-hazard spots across large urban environments.

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Chatzakis, Alexandros. "Calibration of a 2D hydrodynamic model for flood inundation extent using aerial photographs : A case study of the Hallsberg flood event in 5-9 September 2015." Thesis, KTH, Vattendragsteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-204901.

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Alteration of rainfall patterns is one major impact of climate change. Rainfall events with big precipitation volumes under short periods of time are predicted to become even more frequent in higher latitude regions, including Sweden. One characteristic example of such an intense rainfall occurred between the 5th and 6th of September 2015 in Hallsberg, a city in central Sweden, where approximately 105 mm of rain fell under 24 hours, causing severe flooding in the city. In order to be able to predict flood cases like the aforementioned one, hydrodynamic models are employed to simulate floods and investigate rainfall scenarios so that the competent authorities can take precaution measures. However, due to lack of calibration data most of flood models are not validated and are comprised of substantial uncertainty. This report aims to study the Hallsberg flood event in September 2015 by calibrating a hydrodynamic model using aerial photographs for the flood inundation extent. The utilized model is MIKE 21, which is a 2D overland flow model developed by DHI. Contrary to the common practice in flood studies where inclusion of the infiltration capacity is implemented with an arbitrary reduction of the rain volume, the infiltration module of MIKE 21, which is a new development in the model, was utilized. Apart from the inundation extent, the outputs were also evaluated for the water depth in two points based on a photograph captured from the streets of the affected area, the description of the course of events for the timing of flood’s culmination and the water volume on the pixels that were erroneously simulated as flooded. The results presented a high degree of agreement with the observations. The parameter of surface resistance, expressed as Manning’s “M”, was found to be of paramount importance with the suitable values for undeveloped areas being below 5. In addition, the culverts’ limited capacity played an important role in the flooding of the city and hence including them in the simulations is crucial. Finally, utilization of the infiltration module resulted in a higher accuracy of 8.3% although it can be considered more of an arbitrary deduction of water as some of the parameters used in it are not physically well justified.
Ändringar i nederbördsmönster är en tydlig konsekvens av klimatförändringen. Regnhändelser med stora volymer nederbörd under korta tidsperioder förutses bli alltmer frekventa i regioner vid högre breddgrader, däribland Sverige. Ett karaktäristiskt exempel av en sådan händelse skedde mellan den femte och sjätte september 2015 i Hallsberg. Ca 105 mm regn föll inom loppet av 24 timmar vilket orsakade stora översvämningar i staden. För att kunna förutse översvämningar så som den tidigare nämnd och möjliggöra vidtagning av förebyggande åtgärder används hydrodynamiska modeller för att simulera vattenflöden och undersöka möjliga scenarion av nederbörd. Emellertid, på grund av avsaknaden av data för kalibrering av modellerna medför användandet av dem en signifikant osäkerhet. Syftet med den här rapporten är att undersöka översvämningen i Hallsberg i september 2015 genom att kalibrera en hydrodynamisk modell med hjälp av flygbilder för översvämningens utbredning. Den använda modellen, MIKE 21, är en 2D modell över ytavrinningen utvecklad av DHI. Praxis vid studiet av översvämningar är att inkludera infiltrationsförmåga med ett godtyckligt avdrag av nederbörden. Här används istället infiltreringsmodulen för MIKE 21, vilket är en ny del som har utvecklats i modellen. Förutom översvämningens utbredning utvärderades även resultaten utifrån vattendjupet vid två punkter baseras på ett fotografi från gatorna i det drabbade området. Utvärdering av resultaten gjordes också mot tid av översvämnings kulm från beskrivning av händelses förlopp samt vattenvolym vid pixlarna som felaktigt simulerades som översvämmade. Resultatet visade på en hög grad av samstämmighet med gjorda observationer. Parametern ytans råhet, uttryckt som Mannings ”M”, visade sig vara av stor betydelse med lämpliga värden för underutvecklade områden under 5. Därtill spelade kulvertarnas begränsade kapacitet en viktig roll vid översvämmandet av staden. Att inkludera dessa i simuleringarna var därför avgörande. Slutligen, användandet av infiltreringsmodulen resulterade i en högre noggrannhet av 8.3 %, även om det kan anses vara ett godtyckligt vattenavdrag då vissa av de använda parametrarna inte är fysiskt välmotiverade.

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Schubert, Jochen Erik. "Landscape characterization for flood inundation modelling." Thesis, University of Nottingham, 2009. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.690049.

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Willis, Thomas D. M. "Systematic analysis of uncertainty in flood inundation modelling." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/7493/.

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Recent evaluations of 2D models have analysed uncertainty in data inputs into flood models, but have treated the model code as a black box. In this work, the influence of the numerical representation of the model on the results is evaluated. The purpose is not only to understand the significance of the physical scheme in the model on results, but also the importance of this in respect to other known sources of uncertainty, in particular boundary conditions, calibrated parameters such as Manning’s friction values, DEM accuracy and other more subjective forms of uncertainty associated with the choices used by modellers in constructing models, such as building representation. To further explore the impact that the level of physical representation has on model output, models were also analysed using risk and exposure based measures. The methods included vulnerability weighted measures and the use of damage curves from the Multi Coloured Manual. A series of Monte Carlo tests were undertaken for a range of parameters over 3 test cases using the LISFLOOD-FP code. The LISFLOOD-FP code was chosen as it has several formulations for solving 2D floodplain flow within its framework, each with different level of physical representation. The test cases included two urban events, a culvert overtopping event in Glasgow and canal embankment failure Coventry, and a river overtopping in Mexborough, Yorkshire a rural urban domain. The test cases provided a wider range of hydraulic conditions and are reflected events typically assessed with inundation models to ensure the effect of model bias was removed from the results. The results for the test cases indicated that the choice of physical representation was the most critical in affecting model results, particularly for the urban test case. However, the interaction between factors and parameters also indicated that for certain scenarios, this becomes less critical to model results. The use of risk based methods also identified areas of variations between parameters sets and numerical schemes that are not identified with traditional model evaluation techniques. Recent evaluations of 2D models have analysed uncertainty in data inputs into flood models, but have treated the model code as a black box. In this work, the influence of the numerical representation of the model on the results is evaluated. The purpose is not only to understand the significance of the physical scheme in the model on results, but also the importance of this in respect to other known sources of uncertainty, in particular boundary conditions, calibrated parameters such as Manning’s friction values, DEM accuracy and other more subjective forms of uncertainty associated with the choices used by modellers in constructing models, such as building representation. To further explore the impact that the level of physical representation has on model output, models were also analysed using risk and exposure based measures. The methods included vulnerability weighted measures and the use of damage curves from the Multi Coloured Manual. A series of Monte Carlo tests were undertaken for a range of parameters over 3 test cases using the LISFLOOD-FP code. The LISFLOOD-FP code was chosen as it has several formulations for solving 2D floodplain flow within its framework, each with different level of physical representation. The test cases included two urban events, a culvert overtopping event in Glasgow and canal embankment failure Coventry, and a river overtopping in Mexborough, Yorkshire a rural urban domain. The test cases provided a wider range of hydraulic conditions and are reflected events typically assessed with inundation models to ensure the effect of model bias was removed from the results. The results for the test cases indicated that the choice of physical representation was the most critical in affecting model results, particularly for the urban test case. However, the interaction between factors and parameters also indicated that for certain scenarios, this becomes less critical to model results. The use of risk based methods also identified areas of variations between parameters sets and numerical schemes that are not identified with traditional model evaluation techniques.

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Lewis, Matthew. "Uncertainties within future flood risk storm surge inundation modelling." Thesis, University of Bristol, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601160.

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Key uncertainties within inundation modelling of storm tide overflow were investigated for two regions. A northern Bay of Bengal LISFLOOD-FP inundation model was developed from freely available data sources, and forced with a storm surge model (IIDT) hind-cast of the 2007 cyclone Sidr flood event because no quality water-level records exist. Validation showed inundation prediction accuracy, with a Root Mean Squared Error (RMSE) on predicted water-level of...., 2 rn, which was similar in magnitude to the forcing water-level uncertainty. Indeed, when observed natural variability within five key cyclone parameters was propagated through the IID-T storm surge model, extreme water-level uncertainty was found to be very high in the Bay of Bengal, and should be considered in future work (and flood risk managers). Future flood hazard mapping uncertainty is much less in the data rich UK; however, when some key uncertainties were propagated through a North Somerset LISFLOOD•FP inundation model of the 1981 historic flood, storm tide spatial variability was found to significantly affect flood risk estimates, second only to sea level rise. A new method for prescribing the still peak water-level along a coastline was developed (Method C), which characteristics the spatial variability using a relatively short record of modelled extreme water-level events, relative to a tide gauge. Good agreement (RMSE 36 cm) was found between Method C predicted water-levels and tide gauge observations for two historic flood events in East Anglia (1953 and 2007). Furthermore, remotely sensed storm tide observations along the North Somerset coast indicated the accuracy of Method C between tide gauge observations; however, fine-scale wave and bathymetry effects need to be resolved for accurate coastal flood risk estimates in the UK. Indeed, the quantification of uncertainty, and the characterisation of natural variability, is necessary for a robust flood risk prediction.

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Yu, Dapeng. "Diffusion-based modelling of flood inundation over complex floodplains." Thesis, University of Leeds, 2005. http://etheses.whiterose.ac.uk/3360/.

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High-resolution data obtained from airborne remote sensing are increasing opportunities for representation of small-scale structural elements (e. g. walls, buildings) in complex floodplain systems using two-dimensional (2D) models of flood inundation. At the same time, 2D inundation models have been developed and shown to provide good predictions of flood inundation extent, with respect to both full solution of the depth-averaged Navier-Stokes equations and simplified diffusion wave models. However, these models have yet to be applied extensively to urban areas. This study applies a 2D raster-based diffusion wave model, either loosely-coupled or tightly-coupled to a ID river flow model, to determine patterns of fluvial flood inundation in urban areas using high-resolution topographic data. The aim of this study is to explore the interaction between spatial resolution and small-scale flow routing process, through model validation and verification. The model assumes that the prime source of the flood is fluvial: pluvial floods and floods associated with urban drainage systems are not addressed. The topographic data are based upon airborne laser altimetry (LiDAR) obtained for the City of York, U.K. Validation data were available in the form of inundation patterns obtained using aerial photography at a point on the failing limb of the flood event. Inflow data is provided either by a loosely-coupled or a tightly-coupled ID river flow model. The model was used to simulate a major flood event which occurred in the year 2000 in the City of York on the River Ouse at 4 different sites. Applications of the basic model showed that even relatively small changes in model resolution have considerable effects on the predicted inundation extent and timing of flood inundation. Timing sensitivity would be expected given the relatively poor representation of inertial processes in a diffusion wave model. Compared with previous work, sensitivity to inundation extent is more surprising and is associated with three connected effects: (i) the smoothing effect of mesh coarsening upon input topographical data; (ii) poorer representation of both cell blockage and surface routing processes as the mesh is coarsened, where the flow routing is especially complex; and (iii) the effects of (i) and (ii) upon water levels and velocities which in turn determine which parts of the floodplain the flow can actually travel to. The combined effects of wetting and roughness parameters can compensate in part for a coarser mesh resolution. However, the coarser the resolution, the poorer the ability to control the inundation process as these parameters not only affect the speed but also the direction of wetting. Thus, high resolution data will need to be coupled to more sophisticated representation of the inundation process in order to obtain effective predictions of flood inundation extent. A sub grid scale wetting and drying correction approach was developed and tested for use with 2D diffusion wave models of urban flood inundation. The method recognises explicitly that representations of sub grid scale topography using roughness parameters ill provide an inadequate representation of the effects of structural elements on the floodplain (e. g. buildings, walls) as such elements not only act as momentum sinks, but also have mass blockage effects. The latter may dominate, especially in structurally complex urban areas. The approach developed uses high resolution topographic data to develop explicit parameterization of sub grid scale topographic variability to represent both the volume of a grid cell that can be occupied by the flow and the effect of that variability upon the timing and direction of the lateral fluxes. This approach is found to give significantly better prediction of fluvial flood inundation in urban areas as compared with traditional calibration of sub grid-scale effects using Manning's n. In particular, it simultaneously reduces the need to use exceptionally high values of n to represent the effects of using coarser meshes, whilst simultaneously increasing the sensitivity of model predictions to variation in n. Finally, the model was coupled (tightly) to a one-dimensional solution of the Navier-Stokes equations. This showed that significantly better representation of urban inundation could be achieved in a tightly-coupled formulation as a result of better representation of boundary condition effects.

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Kvocka, Davor. "Modelling elevations, inundation extent and hazard risk for extreme flood events." Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/101761/.

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Climate change is expected to result in more frequent occurrences of extreme flood events, such as flash flooding and large scale river flooding. Therefore, there is a need for accurate flood risk assessment schemes in areas prone to extreme flooding. This research study investigates what flood risk assessment tools and procedures should be used for flood risk assessment in areas where the emergence of extreme flood events is possible. The first objective was to determine what type of flood inundation models should be used for predicting the flood elevations, velocities and inundation extent for extreme flood events. Therefore, there different flood inundation model structures were used to model a well-documented extreme flood event. The obtained results suggest that it is necessary to incorporate shock-capturing algorithms in the solution procedure when modelling extreme flood events, since these algorithms prevent the formation of spurious oscillations and provide a more realistic simulation of the flood levels. The second objective was to investigate the appropriateness of the “simplification strategy” (i.e. improving simulation results by increasing roughness parameter) when used as a flood risk assessment modelling tool for areas susceptible to extreme flooding. The obtained results suggest that applying such strategies can lead to significantly erroneous predictions of the peak water levels and the inundation extent, and thus to inadequate flood protection design. The third and final objective was to determine what type of flood hazard assessment methods should be used for assessing the flood hazard to people caused by extreme flooding. Therefore, two different flood hazard assessment criteria were modelled for three extreme flood events. The predicted results suggest that in areas prone to extreme flooding, the flood hazard indices should be predicted with physics-based formulae, as these methods consider all of the physical forces acting on a human body in floodwaters, take into account the rapid changes in the flow regime, which often occur for extreme events, and enable a rapid assessment of the degree of flood hazard to be made in a short time period.

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Schumann, Guy Jean-Pierre. "Water stages from remotely sensed imagery for improved flood inundation modelling." Thesis, University of Dundee, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.703286.

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Hunter, Neil Martin. "Development and assessment of dynamic storage cell codes for flood inundation modelling." Thesis, University of Bristol, 2005. http://hdl.handle.net/1983/c8858588-ee07-4810-aacc-4f1d74d7643a.

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Since 1962 storage cell codes have been developed to simulate flow on fluvial and coastal floodplains. These models treat the floodplain as a series of discrete storage cells, with the flow between cells calculated explicitly using some analytical flow formulae such as the Manning equation. Recently these codes have been reconfigured to use regular Cartesian grids to make full use of widely available high resolution data captured from remote sensing platforms and stored in a raster GIS format. Such raster-based storage cell codes have many of the advantages over full two-dimensional depth averaged schemes but without the computational cost, however their typical implementation results in a number of fundamental limitations. These include an inability to develop solutions that are independent of time step or grid size, and an unrealistic lack of sensitivity to floodplain friction. In this thesis, a new solution to these problems is proposed based on an optimal adaptive time step determined using a Courant-type condition for model stability. Comparison of this new adaptive time step scheme to analytical solutions of wave propagation/recession on flat and sloping planar surfaces and against field measurements acquired for four real flood scenarios demonstrates considerable improvement over a standard raster storage cell model. Moreover, the new scheme is shown to yield results that are independent of grid size or choice of initial time step and which show an intuitively correct sensitivity to floodplain friction over spatially-complex topography. It does, however, incur a prohibitive computation cost at model grid resolutions less than 50 m. This primary research is supplemented by an examination of the data and methods used to apply, and in particular calibrate, distributed flood inundation models in practice. Firstly, different objective functions for evaluating the overall similarity between binary predictions of flood extent and remotely sensed images of inundation patterns are examined. On the basis of the results presented, recommendations are provided regarding the use of various measures for hydrological problems. Secondly, the value of different observational data types typically available for calibrating/constraining model predictions is explored within an extended Generalised Likelihood Uncertainty Estimation (GLUE) framework. A quasi-Bayesian methodology for combining these individual evaluations that overcomes the limitations of calibration against any single measurement source/item is also presented.

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Wong, Jefferson See. "Exploring the impact of uncertainty of river morphology on flood inundation modelling." Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.701651.

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Our landscape is constantly evolving, and so to are our rivers. These changes can be perturbed due to many factors, including land use and climate change. But also changes in river morphology is a dynamic process that constantly evolves, particularly during extreme flood events. This can result in significant changes in channel morphology over short periods of time. Rivers, and the amount of flow they can convey within bank before their channel capacity is reached, is critical to predicting the extent of flood inundation in both rural and urban areas. An important research question is therefore to what extent are fluvial geomorphological changes critical to the prediction of flood inundation extents during and between events? Furthermore how uncertain are these processes and so can their effects be quantified within a risk based framework? This PhD tries to answer those questions using state-of-the-art flood simulation techniques that also comprehensively characterises the inherent uncertainties involved. Most flood modeling studies ignore the potential for morphological changes to alter channel conveyance and bed roughness, in and between large events. Furthermore the overall bedload and geomorphological catchment processes upstream are rarely considered, particularly within an uncertainty analyses framework. The research here within uses the following approaches to characterize this in 3 core results chapters: Chapter 4 uses simple approach to quantifying the potential changes in channel erosion that occur in flooding events to see the sensitivity to the resultant flood inundation extents predicted for the Cockermouth 2009 November flood event. Chapter 5 applies a catchment scale landscape evolution· model CAESAR-Lisflood to two catchments upstream of Cockermouth within an uncertainty analyses framework. This explored the use of uncertain data in• constraining the model simulations for the period of record available. Chapter 6 uses the constrained (behavioural) model simulations found in chapter 5 to simulate flood events at Cockermouth to see the impact of dynamic geomorphological changes during flood events to the predicted extent of flood inundation and flood depths. The results showed that by the inclusion of sediment transport this greatly changed flood dynamics both in terms of water depth and flow volume, with a wider bound of uncertainty quantified in the flood predictions generated. This has important implications for understanding and predicting flood risk across a range of catchments, particularly those that are more susceptible to ongoing geomorphological changes. Futhermore with the inclusion of sediment transport and the consideration of morphological changes, the uncertainties inherent in the observation data which were used to constrain the catchment behaviour had been accounted for and propagated to the downstream reach. This research showed that the prediction uncertainty bounds had been significantly widened in flood inundation extent, flood volume, and water depths. This reveals that the importance of connectivity between catchment dynamics and downstream behavior and flooding at reach scale cannot be examined in isolation from upstream. Hence, it is important and necessary for flood inundation modeling to consider the associated uncertainties from geomorphological impacts and incorporate both hydrodynamic and morphodynamic aspects for subsequent flood risk assessment.

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Åberg, Isabelle. "Flood Mapping: Assessing the uncertainty associated with flood inundation modelling. A case study of the Mora River, Sweden." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-315687.

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Expansion of cities and major infrastructure projects lead to changes in land use and river flows. The probability of flooding is expected to increase in the future as a result of these changes in combination with climate change. Hydraulic models can be used to obtain simulated water levels to investigate the risk of flooding and identify areas that might potentially be flooded due to climate change. Since a model is a simplification of the reality it is important to be aware of a model’s uncertainties. A part of this study is therefore aimed to perform a sensitivity analysis to determine which parameter has the largest impact on the model result and has to be treated more careful and accurately. In this study the 1-dimensional flow model Hydrologic Engineering Center-River Analysis System (HEC-RAS) were assed to simulate predicted water levels within the studied river. Topographic data was used to draw cross sections in Geographic Information Systems (GIS) with additional tools of HEC-GeoRAS, in order to get information about the streams geometry. The purpose of doing a sensitivity analysis was attained by investigating changes of the model results when changing different input parameters. This work is based on a reach along Mora river, in Södertälje, Sweden, as a case study. The sensitivity analysis indicate that the number of cross sections has a significant effect when simulating water levels of low flows and that the absolute error of simulated water levels increases as the average spacing between cross sections increases. The second part of the study aims to examine the effects of climate change and how it will affect water levels for the studied river. The results of the study showed that simulated water levels with flows of 100, 200 and 500 years return periods stay within the river channel and do not indicate flooded areas. The results also showed that a backwater effect due to sea level rise would affect the water levels in the stream up to a specific critical point along the studied reach. The lower reach indicated results to contain more uncertain region, where floodplain delineation changed easily as the number of cross section was changed. It is therefore important to identify the areas where uncertainties can be more critical for the results. Because of the uncertainties associated to the model used, it is important to notice that the results of this work correspond particularly to the case study in Mora River.
Studien genomförs inom Ostlänken, som är den första delsträckan av en ny höghastighetsjärnväg mellan Järna och Linköping. Bebyggelse och stora infrastrukturprojekt kommer förändra markanvändning och flöden i vattendrag. I följd av dessa förändringar, tillsammans med framtidens förändrade klimat, kommer risken för översvämningar kunna öka. För att undersöka riskerna för översvämningar och kartlägga områden som riskerar att översvämmas är en hydraulisk modell ett verktyg som kan användas. Då en modell endast är en förenkling av verkligheten och påverkas av flera olika parametrar är det viktigt att vara medveten om modellers osäkerheter. För att få modellen att efterlikna verkligheten så bra som möjligt kan det vara bra att veta vilka parametrar som har störst inverkan på modellens resultat och som bör bearbetas mer noggrant. Därmed är en del av studiens syfte att göra en känslighetsanalys för att utreda vilka modellparametrar och indata som påverkar modellresultaten, med fokus på att analysera simulerade vattennivåer. Känslighetsanalysen utförs genom en fallstudie över Moraån, där den endimensionella flödesmodellen HEC-RAS används för att beräkna vattendragets vattennivåer. Den andra delen av studiens syfte är att undersöka om hur framtidens klimatförändringar kommer kunna påverka det studerade området. En effekt av framtidens förändrade klimat är stigande havsnivåer som leder till ökad risk för översvämning vid kustnära områden. Till följd av dämningseffekter kommer de stigande havsnivåerna även ge ökade vattennivåer uppströms vattendragen, och beroende på vattendragens egenskaper och geometri kommer vattendrag längs med kusten att påverkas på olika sätt. För att undersöka riskerna för översvämningar i ett framtida klimat har modeller med olika klimatscenarios byggts upp där stigande havsnivåer kombinerats med flöden av varierande återkomsttider.

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Edwards, Christopher Hyde. "Forecasting Inundation Extents in the Amazon Basin Using SRH-2D and HAND Based on the GEOGloWS ECMWF Streamflow Services." BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/9255.

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Floods are the most impactful natural disasters on earth, and reliable flood warning systems are critical for disaster preparation, mitigation, and response. The GEOGloWS ECMWF Streamflow Services (GESS) provide forecasted streamflow throughout the world. While forecasted discharge is essential to flood warning, forecasted inundation extents are required to understand and predict flood impact. In this research, I sought to expand GESS flood warning potential by generating inundation extents from streamflow forecasts. I compared Height Above Nearest Drainage (HAND), a method beneficial for flood mapping on a watershed scale, to a 2D hydrodynamic model, specifically Sedimentation and River Hydraulics â€“ Two Dimension (SRH-2D), a method localized to specific areas of high importance. In three study areas in the Amazon basin, I validated HAND and SRH-2D flood maps against water maps derived from satellite SAR imagery. Specifically, I analyzed what features of an SRH-2D model were required to generate more accurate flood extents than HAND. I also analyzed the practicality of using SRH-2D for forecasting by comparing flood extents generated from simulating a complete forecast hydrograph to flood extents precomputed at predetermined, incremental flowrates. The SRH-2D models outperformed HAND, but their accuracy decreased at flowrates different than those used for calibration, limiting their reliability for forecasting and impact analysis. Based on this study, the key features necessary for a reliable SRH-2D model for forecasting include (1) a high-resolution DEM for an accurate representation of the floodplain, (2) correct representation of channel flow control, and (3) a channel bathymetry approximation and exit boundary rating curve that correctly predict water levels at a range of input flowrates. For forecasting practicality, the precomputed flood extents had accuracies comparable to the complete hydrograph simulations, showing their potential for estimating forecasted inundation extents. Future research should include (1) a more comprehensive analysis using existing SRH-2D models in areas with more bathymetry information and calibration data, (2) further assessment of the reliability of precomputed flood maps for forecasting applications, and (3) quantifying the effect of error in the streamflow forecasts on the accuracy of the resulting flood extents.

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Lim, Nancy Joy. "Performance and uncertainty estimation of 1- and 2-dimensional flood models." Thesis, Högskolan i Gävle, Avdelningen för Industriell utveckling, IT och Samhällsbyggnad, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-9642.

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Performance-based measures are used to validate and quantify how likely the system’s results resemble that of the actual data. Its application in inundation studies is performed by comparing the extents of the predicted flood to the real event by measuring their overlap size and getting the percentage of this size to the union of both data. In this study, performances of 1- and 2-dimensional flow models were assessed when used with different topographic data sources, rasterisation cell sizes, mesh resolution and Manning’s values with the help of Geographic Information Systems (GIS). The Generalised Likelihood Uncertainty Estimation (GLUE) was also implemented to evaluate the behaviour and the uncertainties of the Hydrologic Engineering Center-River Analysis System (HEC-RAS) steady-flow model in delineating the inundation extents when various sets of friction coefficients for floodplain and channel were utilised as inputs. Although it was not possible to perform the GLUE procedure with Telemac-2D due to the simulation time, Manning’s n performances’ effects were evaluated using ten randomly selected sets of friction for the channel and floodplain. The LiDAR data, which had the highest resolution, performed well in all simulations, followed by Lantmäteriet data at 50 m resolution. The lowest resolution Digital Terrain Elevation Data (DTED) showed poor resemblance to the actual event and big misrepresentations of flooded areas. Rasterisation cell sizes in HEC-RAS showed minimal effect to the inundation limits when used between 1 m and 5 m, but performance started to deteriorate at 10 m (Lantmäteriet) and 20 m (LiDAR). The 10 m mesh resolution used for LiDAR behaved poorer than the 20 m mesh, which performed well in the different 2D simulations. For HEC-RAS, =0.033 to 0.05 performed well when paired with =0.02 to 0.10. It was apparent, therefore, that the channel’s Manning’s n affected the performances of the floodplain’s . Furthermore, the study also showed that using heterogeneous roughness values corresponding to the different land use classes is not as effective as using single channel and floodplain’s Manning. The dependence of the floodplain’s roughness to the channel’s friction values had also been manifested by Telemac, even though it required lower values than the 1D simulator. = 0.007 to 0.019 and =0.01 to 0.04 gave good performance to the 2D system. In terms of the overall model performance, HEC-RAS 1D exhibited good results for Testeboån. Even when the average distances to the actual data were estimated, the breadths were shorter compared to the most optimal output of the two-dimensional simulator, which showed more overestimated areas, despite the fact that the overlap size with the 1977 actual event was better than HEC-RAS. It could be because the measures-of-fit took into consideration the areal sizes that were over- and under-predicted aside from the overlap sizes between the observed and modelled results. This could be the same reason with the mean distances produced, wherein higher values were computed for Telemac-2D due to its bigger gap from the actual flood as brought by the enlargement in the flood extents. But it was also made known in the study that such ambiguities in the model performance were further contributed by the characteristics of the floodplain’s topography of being flat. Testeboån’s inclination to the banks was averaged at 0.027 m/m, with the central portion at 0.002 m/m. The middle portion of the floodplain was illustrated to contain more uncertain regions, where water extents changed easily as the parameters were altered. Distances greater than 200 m were also mostly located within these inclination values or within 0.005 to 0.006 m/m. The response of distance to the floodplain’s gradient improved when the slope value became higher, and this had been particularly noticed between 0 to 50 m.

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14

Horgby, Åsa. "The Usability of Remote Sensing Data for Flood Inundation Modelling: a Case Study of the Mississippi River." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-255595.

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The probability and impact of flooding is projected to increase in the future. This is due to climate and land-use changes (e.g. urbanization) in addition to the ongoing socioeconomic development of many floodplain areas. Exploiting the increasing availability of satellite data for flood inundation modelling will allow mapping floods in remote, data-poor areas to lower costs, and thereby make it possible to estimate flood risks in areas that today lack the economic resources needed for supporting risk assessment. In this context, this study has investigated the potentials and limitations of using low-cost, global remote sensing data (i.e. SRTM) to support flood inundation modelling. To this end, a case study of a river reach along the Mississippi was exploited. In particular, two flood inundation models were built by using the same 2D hydraulic model code (LISFLOOD-FP), but with two different topographical inputs, i.e. high quality/accuracy LiDAR topography data and the freely available SRTM topography data. The LiDAR data was lowered to the same resolution as the SRTM data and the two models were run with the resolution of 83x83 m2 . Thereafter, the models were compared by simulating two historical flood events of different magnitude. The comparison of the two models showed that flood inundation modelling with satellite data is more accurate (closer to the reference model, i.e. LiDAR-based model) for the higher magnitude flood event than for the lower magnitude flood event. This was attributed to the relatively reduced importance of micro topography during bigger flood events. An area-based performance measure gave a value of the correspondence (i.e. the fit) between the predicted flood extents for the two models. The areas/pixels were reclassified in ARC GIS to flooded or dry. Thereafter, areas flooded in both the LiDAR and the SRTM simulations were divided by the sum of the areas flooded in both or in one of the simulations (LiDAR or SRTM). From this procedure the fit could be determined, where a fit of 100 % would mean that the simulations had predicted the same flood extents. For the high magnitude flood event simulated in this study, the fit in terms of flood extent between the LiDAR-based and the SRTM-based model was 72 %, while the fit for the smaller flood was only 38 %. In this study, model calibration was preformed manually because of limited availability of time and computational power. However, this is not considered a major limitation as the work does not aim to make a faultless model of this river reach of the Mississippi, but rather to determine the potentials and limitations of SRTM topography data in supporting flood inundation modelling. Additional studies of rivers systems with different properties, flood magnitudes, vegetation covers and river scales should be conducted, to further validate the usability of remote sensing data for flood inundation modelling.
Stora områden runt om i världen har problem med översvämningar, som står för 40 % av alla dödsfall orsakade av naturkatastrofer. Det är troligt att risken för översvämningar kommer att öka i framtiden på grund av klimatförändringar och ändrad landanvändning, som till exempel urbanisering. Ett problem är att det ofta är dyrt att göra kartor som beskriver översvämningsrisker och därför finns det många områden där kunskap om riskerna saknas. I denna studie har det undersökts huruvida det är möjligt att använda globala fjärranalysdata (data från satelliter) för översvämningsmodellering. Detta skulle möjliggöra framställandet av kartor över översvämningsrisker till en låg kostnad, och därmed nå ut till områden där idag inte finns ekonomiska resurser nog för detta. En fallstudie har gjorts av en sträcka utmed Mississippifloden (USA) och två översvämningsmodeller har byggts genom att använda samma hydrauliska modelleringskod (LISFLOOD-FP). Skillnaden mellan modellerna var att den ena modellen byggdes med hjälp av LiDAR-topografidata, medan den andra modellen baserades på gratis SRTMtopografidata. LiDAR-data är högkvalitativt och högupplöst data (1 meter upplösning) insamlat från flygplan med hjälp av laser. SRTM-data har endast 30-90 meters upplösning (83 meter inom fallstudieområdet) och är insamlat av satelliter. Upplösningen av LiDAR-datat ändades till samma upplösning som för SRTM-datat och båda modellerna kördes med en upplösning av 83x83 m2 . De två modellerna jämfördes genom att två historiska översvämningar, en liten år 2008 och en mycket stor år 1993, simulerades. Jämförelsen av de två modellerna visade på att modellering med hjälp av satellitdata är mer precist och närmare referensmodellen, det vill säga den LiDAR-baserade modellen, för större översvämningar än för mindre översvämningar. Förklaringen till detta tillskrevs den relativt reducerade betydelsen av mikrotopografi för större översvämningar. Överrensstämmelsen mellan modellresultaten räknades ut genom att områdena/pixlarna först blev omklassificerade i ARC GIS som översvämmande eller icke översvämmade. Därefter delades antalet områden som svämmades över i båda simuleringarna med antalet områden som svämmades över i båda simuleringarna eller i den ena av simuleringarna. På detta sett kunde en faktor för överensstämmande bestämmas, där en faktor på 100 % innebar att modellerna förutspådde lika stora översvämningar. För den större översvämningen som simulerades överensstämde, i fråga om utbredning, de två modellerna (LiDAR och SRTM) till 72 %, medan modellerna för den mindre översvämningen endast överensstämde till 38 %. I denna studie gjordes kalibreringen manuellt då den tillgängliga tiden och datorkapaciteten var begränsad. Dock så anses inte detta vara en stor begränsning eftersom studien inte syftade till att göra en felfri modell av översvämningsriskerna utmed en sträcka av Mississippifloden, utan till att undersöka användbarheten och begränsningarna av satellitdata för översvämningsmodellering. Denna studie stödjer tidigare teorier om att globala satellitdata har stort användningsområde för att simulera översvämningsrisker. Dock behövs fler studier av flodsystem med olika egenskaper, storlek på översvämningar och vegetation göras för att ytterligare validera detta.

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15

Schück, Fredrik. "Implementation of Citizens’ Observations in Urban Pluvial Flood Modelling." Thesis, KTH, Hållbar utveckling, miljövetenskap och teknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-297552.

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Damages caused by urban pluvial floods are believed to increase due to climate change and urbanization as more citizens are impacted in densely populated cities and extreme rainfalls occur more frequently with higher intensities. To prepare cities for these calamities, urban pluvial flood models are created to provide knowledge about how an extreme rainfall event could inundate the studied city. However, due to the scarcity of observation data from these rainfall events, flood models are seldom calibrated which is necessary to ensure their accuracy. To improve the feasibility of calibrations an emerging data source was tested, crowdsourced images from citizens. Citizens’ observations have become increasingly available due to the increase of mobile phones and the development of social media enabling citizens to document and upload their observations to the public. Researchers could use these observations as an unconventional data source to calibrate models and reduce the knowledge gap regarding urban floods. The aim of this study was to explore and increase our understanding of how citizen’s observations can be used to calibrate an urban pluvial flood model. A case study about the cloudburst event in Malmö was conducted to study this topic. During that event, more than 100 mm of rain fell over a period of 6 hours in the city and caused 60 million euros of damages. A total of 297 images depicting the flood caused by the cloudburst event were gathered from social media platforms, newspapers archives, and by inquiring citizens. Images were screened and analysed: water levels were estimated in 66 images and were then used to calibrate a 2D flood model. Furthermore, a sensitivity analysis of the calibrated results was conducted by calculating the RMSE for different subsets and compare it with the RMSE for the full dataset of citizens’ observations. This was done to study how different characteristics, such as timestamp and source as well as sample size and location of the images influences the calibration procedure. After the model was calibrated, the importance of spatial variability in the rainfall input was tested by comparing the flood model output between the spatially varied observed rainfall and a Chicago Design Storm rainfall, which lacks spatial variability. It was concluded that images from citizens can be used to calibrate an urban pluvial flood model, but the procedure is time-consuming. However, it was also evident that images directly inquired from citizens reduced the time needed as their local knowledge could be integrated. The calibration procedure was also sensitive to the quality of the observations, especially when the images were photographed in relation to the rainfall event. Even though the study had limitations it demonstrates new possibilities to calibrate urban pluvial flood models.
Konsekvenserna av översvämningar från skyfall i städer, så kallade pluviala översvämningar, förväntas öka på grund av urbanisering och klimatförändringar. Det är för att fler påverkas av översvämningar i tätbyggda städer samt att skyfall förväntas öka, både i intensitet och frekvens. Med hjälp av skyfallsmodeller kan dock förståelsen för hur extrema regn översvämmar städer öka. Med denna kunskap kan åtgärder för att minimera konsekvenserna implementeras, såsom blågrön infrastruktur. Däremot finns det en brist av observationsdata från pluviala översvämningar och vilket medför att dessa modeller ytterst sällan kalibreras. Kalibrering är viktig för att säkerställa tillförlitliga modeller. För att öka möjligheten att kalibrera dessa modeller undersöktes hur observationer från medborgare kan implementeras. Dessa observationer är en relativ oprövad metod men har blivit alltmer tillgängliga tack vare allt bättre mobiltelefonkameror och utvecklingen av sociala medier, vilket gör det enkelt för medborgare att dokumentera och ladda upp sina observationer till allmänheten. Syftet med denna studie är därför att öka förståelsen för hur bilder från medborgare kan användas för att möjliggöra kalibreringen av översvämningsmodeller. En fallstudie över ett skyfall i Malmö 2014 används för att utvärdera denna metod. Under detta skyfall regnade det mer än 100 mm vilket orsakade skador för cirka 600 miljoner kronor. Totalt samlades 297 bilder som föreställde översvämningen som orsakades av skyfallet. Bilderna samlades ifrån sociala media, tidningsbildarkiv och genom att fråga medborgare efter bilder. Vattennivåerna uppskattades i 66 bilder och de användes sedan för att kalibrera en 2D- skyfallsmodell. Utöver kalibreringen genomfördes en känslighetsanalys av de kalibrerade resultaten genom att jämföra medelfelet för olika subgrupper av bilderna mot medelfelet för alla bilder. Detta gjordes för att studera hur olika egenskaper, såsom när bilden togs och deras ursprung samt bildernas urvalsstorlek och placering påverkar kalibreringsprocessen. Efter att modellen kalibrerats testades också betydelsen av spatial variation i nederbörden genom att jämföra de simulerade vattennivåerna mellan den spatialt varierade historiska regnet och ett syntetiskt CDS-regn som saknar variation. Utifrån det drogs slutsatsen att bilder från medborgare kan användas för att kalibrera en skyfallsmodell, men metoden är tidskrävande. Dock var det tydligt att bilder som direkt efterfrågades från medborgarna minskade arbetsbördan då deras lokalkännedom kunde inkluderas. Kalibreringen var också känslig för observationerna datakvalitet, särskilt när bilderna fotograferades i förhållande till regnet. Även om studien hade begränsningar visar den att det finns stora möjligheter att kalibrera skyfallsmodeller med observationer från medborgare.

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16

Leandro, Jorge. "Advanced modelling of flooding in urban areas : integrated 1D/1D and 1D/2D models." Thesis, University of Exeter, 2008. http://hdl.handle.net/10036/41949.

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The research presented in this Thesis aims at defining the strengths and weaknesses of an Improved 1D/1D model when compared with a more accurate 1D/2D model. Although both coupled-models (sewer/surface) solve the St.\ Venant equations in both layers, the latter uses a higher approximation (2D two-dimensional) on the surface layer. Consequently, the 1D/1D model is computationally more efficient when compared to the 1D/2D model, however there is some compromise with the overall accuracy. The hypothesis is that "The inundation extent of urban flooding can be reproduced by 1D/1D models in good agreement with the 1D/2D models if the results are kept within certain limits of resolution and under certain conditions". The Thesis starts by investigating ways of improving an existing 1D/1D model to rival the more accurate 1D/2D model. Parts of the 1D/1D model code are changed and new algorithms and routines implemented. An innovative GIS tool translates the 1D output-results into 2D flood-inundation-maps enabling a thorough comparison between the two models. The methodology assures the set-up of two equivalent models, which includes a novel algorithm for calibrating the 1D/1D model vs.\ the 1D/2D model results. Developments are tested in two distinctly different case studies of areas prone to flooding. The conclusion is that the 1D/1D model is able to simulate flooding in good agreement with the 1D/2D model; however, it is found that features such as topography, density of the urbanised areas and rainfall distribution may affect the agreement between both models. The work presented herein is a step forward in understanding the modelling capabilities of the analysed coupled-models, and to some extent may be extrapolated to other models. Research is growing in urban flooding and this work may well prove to be a strong foundation basis for future research.

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17

Andersson, Evelina. "Flood modelling in urban areas : A comparative study of MIKE 21 and SCALGO Live." Thesis, KTH, Hållbar utveckling, miljövetenskap och teknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-300466.

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Pluvial flooding originating from extreme rainfall is problematic and an increasing issue in Sweden. Higher requirements on adapting cities in urban areas to these challenges have been placed on both municipalities and the county administration. Thus, an increased need for water modelling, both in existing and planned areas have emerged. The Danish Hydrological Institute (DHI) has developed several models and tools to simulate floods and heavy rains, of which MIKE 21 is one. MIKE 21 is a dynamic model consisting of hydrological calculations in each cell, requiring modelling skills and long simulation time, but is proven to be a good and credible model. SCALGO Live, on the other hand, is a static tool simulated by raster-based algorithms and capable of giving fast results directly on the platform. However, compared to MIKE 21, SCALGO Live is not as evaluated nor is its use as widespread for simulating floods and heavy rain events. This study aims to investigate how inundation in twenty urban areas caused by cloudbursts is simulated in both programs to examine how well the result coming from SCALGO Live, is equivalent to the result from the MIKE 21-model. The comparison is made in both depth and spread using three comparative indexes, two statistical equations and one map, showing the extension of the inundation in both models. To make the models comparable, the model in MIKE 21 is made as equivalent as possible with SCALGO Live before simulation and the purpose is to investigate whether there is any type of area where the two different models are equivalent. The result shows that the flooded areas from SCALGO Live are in good agreement in most areas with the MIKE 21-model, but that the depth in the depression zones is somewhat overestimated, compared with the highest value in MIKE 21. The MIKE 21-model has a greater spread upstream, showing flowpaths if compared directly with the flooded areas from SCALGO Live, but if activating the flow accumulation tool in SCALGO Live, the differences are reduced but cannot be quantified in this study. The differences between the models increase with a higher resolution, longer flowpaths and a larger catchment, at least for the confined catchments. To conclude, SCALGO Live is best suited for smaller confined catchments where there are no long or complex flowpaths. SCALGO Live also works well at an early stage in the planning process and as a platform for combining detailed data and results. However, for the more complex areas, MIKE 21 is better suited, since various parameters can be considered.

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18

Van, Tri Pham Dang. "Hydraulic modelling and flood inundation mapping in a bedrock-confined anabranching network : the Mekong River in the Siphandone Wetlands, Laos." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/160907/.

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Anabranching fluvial networks recently have become the focus of attention from environmental specialists, especially in the hydraulic field. Anabranching networks can be found in different physical environments; however, the hydraulic and geomorphological natures of such river networks are still not well known leading to on-going discussions on the definition and nature of the networks. Even though, alluvial anabranching networks generally have common features like vegetated islands, low water surface slope and stable channel planform, bedrock-confined anabranching networks also have their own characteristics inherited from the geological and structural controls imposed on the single channels that compose the network complex. This thesis focuses on the provision of a benchmark describing the bulk hydraulic characteristics of a large bedrock-confined, anabranching river network, located within southern Laos. The network can be separated into: (i) the upper river network constituted by two bifurcations and one confluence with an interpolated bathymetry based on soundings of cross-sections along the navigation channels; and, (ii) the downstream river network characterised by a complex anabranching network with five bifurcations and five confluences for which there is no bathymetric survey. The river network as whole is a ‘composite’ – partly bedrock (especially the channel-bed) and partly alluvial-filled and as such it does not accord fully with any prior description or classification of anabranching channel networks (e.g. Huang and Nanson, 1996). To understand the hydraulic nature of the river network, the energy approach in a onedimensional (1D) steady-flow hydraulic model (HEC-RAS) was applied to the network. Significant challenges arose due to the lack of boundary conditions throughout the model, namely: (i) unknown splitting discharge ratios at each bifurcation; (ii) partly non-survey bathymetry; and, (iii) ungauged downstream boundary condition of one of the channel outlets. To determine the discharge entering each channel, the splitting discharge ratio at each bifurcation was defined originally by the ratio of the cross-sectional area of the first crosssection of each downstream channel and then adjusted based on the Flow Optimization function in HEC-RAS to minimize any rise or drop of the modelled water surface around a junction. For the channels with non-surveyed bathymetry, a SPOT satellite image was processed to construct a pseudo-bathymetry showing a range of elevations, including shallow and deep portions of channels, rather than detailed bed elevations as would be obtained from a measured bathymetry. To define the boundary condition of the ungauged channel outlet, the water surface elevation was interpolated and validated according to predefined assumptions (i.e. the water surface slope along the ungauged channel was interpolated according to the available DEM and cross-sectional width extracted from a SPOT image for low discharge conditions was assumed to be similar to the gauged channels for flooding discharges). In general, the study has helped to develop methods to model the complex river network with data constraints (i.e. the boundary conditions). The findings include: (i) the developed pseudo-bathymetry based on a SPOT image is useful to model a large river network using the energy approach in a 1D hydraulic model in which the cross-sectional area is important in modelling the bulk hydraulic parameters but the influence of the cross-sectional shape is subordinate; (ii) the in-channel hydraulic roughness coefficient at each cross-section may be significantly different from neighbouring values due to the variation in the local bedrock roughness and the roughness of intervening alluvial reaches; and, (iii) the hydraulic roughness of the riparian land cover along the floodplains does not contribute noticeably to the modelled stage along the river network nor to the planform extent of flooding for overbank flooding discharges. Rather, changes in land-cover, and hence the riparian roughness, are registered as small, but measureable, changes in the local velocity over the riparian floodplain and in the average in-channel velocity. Citations: Van, P.D.T., 2009. Hydraulic modelling and flood inundation mapping in a bedrockconfined anabranching network: The Mekong River in the Siphandone wetlands, Laos. Unpublished PhD thesis submitted to the Faculty of Engineering, Science and Mathematics, University of Southampton, England.

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19

Rajnoch, Dalibor. "Návrh PPO na zvolené části toku." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227481.

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The diploma thesis copes with the evaluation of status quo and further proposal for a flood control arrangements for the river Dřevnice (Zlín district). The evaluation as such has been made by the hydraulic calculation of flow alongside 2D numeric model - SMS-TUFLOW software was used for these calculations and sub-calculations. Based on the results as evaluated by numerical model, the proposal for a flood control arrangements has been made and is further available within the document. Last not least, the utilization of the aforementioned arrangements was measured and described.

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20

Negretto, Giacomo. "The impact of spatial representation on flood hazard assessment: a comparison between 1D, quasi-2D and fully 2D hydrodynamic models of Rio Marano (Rimini)." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/17600/.

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Four hydrodynamic numerical models were constructed and compared for a case study along the Marano stream (Rimini) using the software HEC-RAS . The models include a 1D model, with extended cross-sections to represent the floodplain flow; a 1D model, with floodplain represented as hydrostatic Storage Areas; a coupled 1D/2D model, with a 1D representation of the main channel and a 2D representation of the floodplain inundation, and a fully 2D model, with both main channel and floodplains represented through a two-dimensional hydrodynamic numerical scheme. First, 1D steady flow simulations were performed to get a conservative estimate of the maximum water levels along the stream. Second, unsteady flow simulations were performed with all four hydraulic models in order to assess flood attenuation associated with the routing. Third, the floodplain inundation dynamics resulting from each model were compared. The results of the steady flow simulations showed that six bridges are inadequate and most of the natural floodplains of the stream are inundated proportionally to the flood discharge considered. Concerning the unsteady flow simulations, each model returned different results in terms of flood attenuation and floodplain inundation dynamics. The 1D model resulted inadequate for modeling channel-floodplain interactions and floodplain inundation dynamics. The 1D model with Storage Areas resulted to be suitable for assessing the flood attenuation induced by the introduction of levees separating the floodplain from the main channel. Regarding the coupled 1D/2D model, the results showed that the elevation profile of the structure coupling 1D and 2D flow areas has a significant impact on modelling results. The 2D model returned the most detailed information regarding flood propagation in both main channel and floodplains.

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21

Lopes, Carina de Lurdes Bastos. "Flood risk assessment in Ria de Aveiro under present and future scenarios." Doctoral thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/16277.

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Doutoramento em Física
Floods are a major threat to coastal regions, affecting millions of people, socioeconomic activities and natural ecosystems. Ria de Aveiro is a coastal lagoon, particularly threatened by floods, facing permanent changes motivated by both natural and anthropogenic factors. Consequently, the main aim of this study is to assess flood risk for floods of oceanic, fluvial and combined origin in Ria de Aveiro under present and future scenarios. This study also aims to propose and evaluate the effectiveness of structural measures on flood risk mitigation. These goals were achieved by applying the methodology Source - Pathway - Receptor, which is a multidisciplinary approach that comprised the following steps: 1) characterization of flooding drivers (oceanic and fluvial) through statistical analysis; 2) implementation, calibration and application of hydro/morphodynamic models to identify the flooding pathway and the flood extent; 3) assessment of flood damage by identifying the socio-economic and ecological assets exposed to flood hazard and determining flood risk by combining the probability and the adverse effects of flood events on assets. In addition, the effectiveness of flood barriers and changes in the lagoon central area geometry on flood risk mitigation was assessed. Results highlight that oceanic floods are consequence of signifcant sea levels induced by storm surge events (>0.4 m) and high tidal levels (>3.3 m), which increased in the last decades due to the general lagoon deepening motivated by dredging activities. These morphological changes increased the tidal prism, the tidal currents and the flood extent, increasing the threat to floods of oceanic origin. These endanger settlements and economic activities (mainly, agriculture, industry and commerce) located along the lagoon main channels margins as well as habitats in the lagoon central area. Floods of fluvial origin occur during adverse weather conditions, and endanger the rivers mouth adjacent regions causing damage in restricted settlements, economic activities (almost only agriculture) and farmland habitats. Besides the areas dominated by oceanic and fluvial forcing, the events of combined origin also affect the margins adjacent to the transition zones, once the flood water drainage is hindered by high sea levels. Although the uncertainties associated to the influence of anthropogenic actions on the lagoon geomorphology, it is predicted an/a increase/decrease of flood risk for events of oceanic/fluvial origin under future scenarios, as consequence of mean sea level rise/river discharges reduction predicted for the region. Finally, this work demonstrated the potential of hydrodynamic modelling for simulate the effectiveness of structural measures on flood risk mitigation, and consequently in supporting the decision making process underlying the flood risk management.
As inundações são uma das maiores ameaças às regiões costeiras, afetando milhões de pessoas, atividades socioeconómicas e ecossistemas. As lagunas costeiras, como a Ria de Aveiro, são sistemas de baixo relevo marginal, particularmente ameaçados por inundações, que enfrentam permanentes mudanças motivadas por fatores naturais e antropogénicos. Consequentemente, o presente estudo tem como objetivo principal avaliar o risco de inundação para eventos de origem oceânica, fluvial e combinada na Ria de Aveiro em cenários presentes e futuros. É também objetivo deste trabalho propor e avaliar a eficiência de medidas estruturais na mitigação do risco de inundação. Para alcançar estes objetivos foi aplicada a metodologia Fonte - Percurso - Recetor, uma abordagem multidisciplinar que compreendeu a realização dos seguintes passos: 1) caracterização dos agentes forçadores de cheias (oceânicos e fluviais) através de análises estatísticas; 2) implementação, calibração e aplicação de modelos hidro/morfodinâmicos para identificação do percurso e extensão de inundação; 3) avaliação dos danos causados pelas inundações, através da identificação dos elementos socioeconómicos e ecológicos expostos ao perigo de inundação e do cálculo do risco combinando a probabilidade com os efeitos adversos das inundações nos elementos expostos. Adicionalmente avaliou-se a eficiência de barreiras de inundação e de alterações na geometria da área central da laguna na mitigação do risco de inundação. Os resultados evidenciam que as inundações de origem oceânica são consequência de elevações significativas no nível do mar induzidas por sobre-elevações de origem meteorológica (>0.4 m) e níveis de maré elevados (>3.3 m), os quais aumentaram na Ria de Aveiro nas últimas décadas em resposta ao aprofundamento generalizado da laguna motivado por dragagens nos canais principais. Estas alterações morfológicas aumentaram o prisma de maré, as correntes de maré e a extensão de inundação, aumentando a ameaça de inundações de origem oceânica. Estas ameaçam aglomerados populacionais e atividades económicas (principalmente agricultura, indústria e comércio) localizadas ao longo das margens dos canais principais e ainda habitats localizados na área central da laguna. As inundações de origem fluvial ocorrem em condições atmosféricas adversas e ameaçam as regiões adjacentes à foz dos rios, causando danos em pequenos aglomerados populacionais e atividades económicas (quase exclusivamente agricultura). Além das regiões de influência oceânica e fluvial, os eventos de origem combinada afetam particularmente as áreas adjacentes às zonas de transição, uma vez que aí a drenagem é dificultada pela sobre-elevação do nível do mar. Apesar das incertezas relacionadas com a infuência de atividades antropogénicas na geomorfologia da laguna, prevê-se uma intensificação/redução do risco de inundação de origem oceânica/fluvial em cenários futuros, como consequência do aumento do nível do mar/diminuição das descargas fluviais previstas para a região. Finalmente, este trabalho demonstrou o potencial da modelação hidrodinâmica para simular a eficiência de medidas estruturais na mitigação do risco de inundação, e consequentemente no suporte ao processo de tomada de decisão subjacente à gestão do risco de inundação.

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22

Andersson, Sara. "Mapping Uncertainties – A case study on a hydraulic model of the river Voxnan." Thesis, KTH, Mark- och vattenteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-173848.

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This master thesis gives an account for the numerous uncertainties that prevail one-dimensional hydraulic models and flood inundation maps, as well as suitable assessment methods for different types of uncertainties. A conducted uncertainty assessment on the river Voxnan in Sweden has been performed. The case study included the calibra-tion uncertainty in the spatially varying roughness coefficient and the boundary condi-tion uncertainty in the magnitude of a 100-year flood, in present and future climate conditions. By combining a scenario analysis, GLUE calibration method and Monte Carlo analysis, the included uncertainties with different natures could be assessed. Significant uncer-tainties regarding the magnitude of a 100-year flood from frequency analysis was found. The largest contribution to the overall uncertainty was given by the variance between the nine global climate models, emphasizing the importance of including projections from an ensemble of models in climate change studies. Furthermore, the study gives a methodological example on how to present uncertainty estimates visually in probabilistic flood inundation maps. The conducted method of how the climate change uncertainties, scenarios and models, were handled in frequency analysis is also suggested to be a relevant result of the study.

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23

Pumchawsaun, Phat. "Integrated hydrodynamic and socio-economic damage modelling for assessment of flood risk in large-scale basin : The case study of Lower Chao Phraya River Basin in Thailand." Thesis, Stockholms universitet, Institutionen för naturgeografi, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-157381.

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Thailand has been often affected by severe flood events over the past century. The 2011’s Thailand Flood Catastrophe was the costliest in country’s history, and it was ranked to be the second most damaging natural hazard in the world in terms of economic losses. The Chao Phraya River Basin was noted to be the most vulnerable area prone to flooding in Thailand. The dynamics of flood risk in the river basin have changed drastically over the past fifty years. In particular, flood exposure increased due to rapid urbanization and population growth. Since 2012, integrated flood risk management has been addressed to be the major framework of water-related disasters with the goal of losses and damage reductions. However, there is currently little research in Thailand on how to quantify flood risks and mitigate flood inundation damage on the relation between the occurrence of flood events and their consequential socio-economic implications. In this study, a tradition method in flood risk assessment is implemented by integrating 2D hydrodynamic modelling and the assessment of socio-economic impact of floods into the Chao Phraya River Basin. More specifically, the fully 2D version of the LISFLOOD-FP model code was used to model flood inundation processes. The output of the model was then used to map inundation depth and assess the levels of physical/environmental risk associated to flood hazards on multiple receptors/elements at risk. The European Flood Directive and the KULTURisk methodology were applied to quantify flood risks in monetary terms for residential, industrial, and agricultural sectors. The 2011 flood event was used for model calibration, while a hypothetical flood event with a return period of 100 years was simulated to identify the potential flood losses. Depth-damage functions comprising of JRC-ASIA, the Flemish, and JICA models were used to estimate potential damage for residential and industrial structures. The results showed that LISFLOOD-FP could satisfactorily reproduce the flood inundation extent obtained from satellite imagery in 2011. The model performance (Critical Success Index or F1) was of 56%, with a Bias of 112%. The latter meant the total inundated area was 12% larger than flood extent’s observation. Moreover, the model could simulate flood levels with overall Root Mean Square Error (RMSE) and Mean Absolute Error (MAE) of 2.03 m a.s.l. and 1.78 m a.s.l., respectively. For the estimation of flood damage and losses, the Flemish model showed the strongest agreement with the reported flood damage in the residential sector, while JICA-ASIA model underestimated flood damage for industrial sector by just 1%. The KULTURisk methodology also well-estimated crop losses in the 2011 event which an overestimation about 21% from the reported value. Apart from that, fully 2D numerical method could not perfectly represent 1-in-100 year flood inundation due to non-consideration of important features such as the precise river channel topography, hydraulic infrastructures, and flood protection schemes in the river basin. Lack of such features results in an overestimation of flood damage and losses for 1-in-100 year flood comparing to the national flood hazard map and damage assessment which are simulated and estimated by JICA’s study. Such features can be better handled by using a coupled 1D/2D numerical method in order to simulate flood inundation extent more realistically and estimate flood losses. This could help the Thai government to better prepare a budget for flood risk prevention. In addition, even if the Flemish model indicates a good representation of relative flood damage to housing structures, the government should establish depth-damage curves specific for Thailand.

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Annis, Antonio Verfasser], and Wolfgang [Akademischer Betreuer] [Niemeier. "Large scale 2D hydraulic modelling : improving the analysis of flood dynamics with remote sensing and voluntary geographic information / Antonio Annis ; Betreuer: Wolfgang Niemeier." Braunschweig : Technische Universität Braunschweig, 2019. http://d-nb.info/1179355431/34.

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Olsson, Jimmy. "The influence of storm movement and temporal variability of rainfall on urban pluvial flooding : 1D-2D modelling with empirical hyetographs and CDS-rain." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-387898.

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Pluvial floods are formed directly from surface runoff after extreme rain events. Urban areas are prone to suffer from these floods due to large portions of hardened surfaces and limited capacity in the stormwater infrastructure. Previous research has shown that catchment response is influenced by the spatio-temporal behaviour of the rainstorm. A rainstorm moving in the same direction as the surface flow can amplify the runoff peak and temporal variability of rainfall intensity generally results in greater peak discharge compared to constant rainfall. This research attempted to relate the effect of storm movement on flood propagation in urban pluvial flooding to the effect from different distributions of rainfall intensity. An additional objective was to investigate the flood response from recent findings on the temporal variability in Swedish rain events and compare it to the flood depths produced by a CDS-rain (Chicago Design Storm), where the latter is the design practice in flood modelling today. A 2D surface model of an urban catchment was coupled with a 1D model of the drainage network and forced by six different hyetographs. Among them were five empirical hyetographs developed by Olsson et al. (2017) and one a CDS-rain. The rainstorms were simulated to move in different directions: along and against the surface flow direction, perpendicular to it and with no movement. Maximum flood depth was evaluated at ten locations and the model results show that storm movement had negligible effect on the flood depths. The impact from the movement was likely limited by the big difference in speed between the rainstorm and the surface flow. All evaluated locations showed a considerable sensitivity to changes in the hyetograph. The maximum flood depth increased at most with a factor of 1.9 depending on the hyetograph that was used as model input. The CDS-rain produced higher flood depths compared to the empirical hyetographs, although one of the empirical hyetographs produced a similar result. Based on the results from this case study, it was concluded that storm movement was not as critical as the temporal variability of rainfall when evaluating maximum flood depth.
Pluviala översvämningar skapas från ytavrinning vid intensiva nederbördstillfällen. De uppstår ofta i urbana miljöer till följd av den höga andelen hårdgjorda ytor och ledningsnätets begränsade kapacitet. Forskning har visat att ett regnmolns rörelseriktning och hastighet påverkar avrinningsförloppet. Om molnet rör sig längs med flödesriktningen i terrängen kan en ökning i vattenlödet nedströms ett avrinningsområde uppstå. Denna effekt har visat sig vara störst om hastigheten hos regnmolnet och vattenflödet är likvärdiga. Ytterliggare en faktor som påverkar avrinningsförloppet är hur regnintensiteten är fördelad över tid. Olsson et al. (2017) har tagit fram fem empiriska regntyper som speglar tidsfördelning inom ett Svenskt regntillfälle. Inom översvämningsmodellering är det vanligt att använda ett så kallat CDS-regn (Chicago Design Storm), vilken har en given tidsfördelning. Med anledning av detta är det intressant att jämföra översvämningar genererade av ett CDS-regn och av de empiriska regntyperna. Syftet med denna studie var att utreda hur regnmolns rörelse påverkar urbana pluviala översvämningar med avseende på vattendjup, samt att jämföra denna påverkan med effekten från olika tidsfördelningar av regnintensiteter. En kombinerad dagvattenmodell (1D) och markavrinningsmodell (2D) av en mindre svensk tätort användes för att simulera olika regnscenarier. De fem empiriska regntyperna och ett CDS-regn simulerades med en rörelseriktning längs med, emot och vinkelrätt i förhållande till flödesriktningen. Även scenarier med stationära regnmoln simulerades. Maximala översvämningsdjup utvärderades i tio punkter spridda över hela modellområdet. Resultatet från simuleringarna visade att regnmolnets rörelse hade försumbar påverkan på översvämningsdjupen. De olika tidsfördelningarna av regnintensitet hade däremot betydande påverkan på de maximala översvämningsdjupen. Som mest var det det maximala översvämningsdjupet 1.9 gånger större beroende vilken regntyp som användes som indata. CDS-regnet genererade i regel de största översvämningsdjupen, även om utfallet från en av de fem empiriska regntyperna var förhållandevis likvärdigt. Regnintensitetens tidsfördelning var därmed en kritisk parameter vid den hydrauliska modelleringen av urbana pluviala översävmningar, till skillnad från molnrörelse som hade försumbar påverkan.

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Friman, Jacob. "Skyfallskartering i Kumla : 2D-hydraulisk modellering och känslighetsanalys." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-325123.

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Översvämningar till följd av intensiva nederbördstillfällen har de senaste åren ökat i antal och omfattning. Dessa händelser förväntas bli vanligare i framtiden och skapa fler översvämningar. Med anledning av detta är det intressant att undersöka hur översvämningar i framtiden breder ut sig och vilka vattennivåer som bildas med förväntad nederbörd. Att modellera översvämningar kräver data som i vissa fall kan vara både tidskrävande och omständig att införskaffa. Möjliga avgräsningar och antaganden i modellparametrar kan då vara intressanta att göra som fortfarande ger användbara resultat. En skyfallskartering har genomförts med 2D-hydraulisk modellering i Kumla med programvaran MIKE 21 Flow Model FM. De översvämningskartor som skapades användes för att identifiera områden i Kumla som riskerar att drabbas av höga vattennivåer till följd av skyfall motsvarande 100- och 200-årsregn. En stor osäkerhet vid modellering av översvämningar är att validera resultaten som fås fram. Ofta saknas information om tidigare översvämningar. De nederbördstillfällen som används är ofta så stora att det saknas data om liknande händelser tidigare. Vid översvämningsmodellering anväds data som beskriver olika typer av modellparametrar. Dessa kommer med ytterligare osäkerheter som kan göra valideringen problematisk. För att undersöka hur stor effekt olika modellparametrar har på resultatet genomfördes en känslighetsanalys där differenskartor skapades mellan undersökta scenarion och referenskartor. Skyfallskarteringen visade att stora delar i Kumla drabbas av översvämningar för både ett 100- och 200-årsregn. Området Kumlaby identifierades som känsligt och får höga vattennivåer. Detta beror mest troligt på omgivningens topografi och att Kumlaby underlagras av leror med låg infiltrationskapacitet. I känslighetsanalysen identifierades markens råhet och infiltrationskapacitet vara styrande parametrar för översvämningens utbredning och vattennivåer. Dessa påverkar främst hur höga vattenflöden som uppstår och översvämningens utbredningen och vattennivåer. Kunskap om dessa parametrar är viktigt för att undvika över- eller underskattning av en översvämning. Användningen av avrinningskoefficienter istället för markens råhet, infiltrationskapacitet och evaporation undersöktes. Differensen i översvämningens utbredning och vattennivåer blev stor i och utanför Kumla tätort. På mindre områden kan det vara mer lämpligt att använda en avrinningskoefficient när en mer detaljerad klassning kan göras av de markytor som finns. Ett scenario som undersöktes i känslighetsanalysen var installation av gröna tak på alla byggnader i Kumla. Simuleringarna som genomfördes visade att både utbredningen och vattennivåer minskade. Detta till följd av större lagringskapacitet och motstånd mot vattenflöden som kommer med gröna tak.
Urban floods caused by intense rainfall have occurred more frequently the last couple of years. These rainfall events are expected to become more common in the future and create more floods in urban areas. This makes it important to investigate the extent and water levels from urban floods in the future. In order to simulate floods, different types of data is needed. This data can be both time consuming and difficult to obtain. With this in mind, it is interesting to investigate possible simplifications and assumptions of model parameters. A cloud burst mapping was made with 2D hydraulic modelling in Kumla with the software MIKE 21 Flow Model FM. The flood maps created were used to identify areas in Kumla which have a higher risk of being subject to high water levels. One uncertainty while modelling urban floods is the process of validating the results. There is often a lack of data for the used rainfall events or information from previous floods in the area. In flood modelling data is used which describes different model parameters, these comes with additional uncertainties and can make the validation more difficult. A sensitivity analysis was made to be able to examine effects on the results from variations in model parameters. The cloud burst mapping showed that large parts of Kumla will be affected by water levels which goes up to 1 m. The area Kumlaby was identified as being sensitive for high water levels. This is due to placement of Kumlaby below higher ground which causes water to flow toward Kumlaby. The ground below is mostly made up of clay which has low infiltration capacity. In the sensitivity analysis the bed resistance and infiltration capacity were identified as governing parameters regarding the extent and water levels of urban floods. In order to avoid over- or underestimation of floods it is important to have knowledge about these parameters in the model area. The use of a runoff coefficient instead of bed resistance, infiltration and evaporation were examined. The difference of the resulting flood were large in the whole model area. In smaller areas a runoff coefficient could be used with better results when a more detailed description can be made of the surfaces in the area. A scenario where green roofs were assumed to have been installed on all buildings in Kumla were examined. The simulations showed that both the extent and water levels decreased. This due to the fact that green roofs have a capacity to store water and delay flows of water.

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Bastviken, Paulina. "Flood Risk Mapping in Africa: Exploring the Potentials and Limitations of SRTM Data in the Lower Limpopo, Mozambique." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303910.

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Many regions in Africa are presently faced with an increasing flood risk due to impending climate change and population growth. One useful mitigation strategy to decrease this risk would be to map it, so that urban planning, warnings systems and emergency response subsequently could be designed to reduce societal vulnerability. This is, however, not widely feasible on the African continent, as developing countries often lack access to the topography and discharge data required to produce high- quality flood risk maps. To seek a way around this problem, on-going research is investigating the possibility of obtaining alternative model inputs, by using global datasets of elevation, derived from remote sensing, and methods to estimate flood flows. This thesis presents a case study within this context where the aim was to determine the accuracy of an African catchment-scale flood map, produced with the satellite product SRTM (Shuttle Radar Topography Mission) as topography input, and to explore the potentials and limitations of such a model scheme. Two high-magnitude floods, occurring in year 2000 and 2013 in the Lower Limpopo Basin (Mozambique), were modelled for inundation extent, using a no-channel 2D model built for the LISFLOOD-FP flood modelling software. Flood water levels were also simulated to assess the models vertical performance. Model outcomes were evaluated against satellite imagery and recordings of high watermarks, adjusting the value representing the roughness of the floodplain to optimize flood extent correspondence. Due to different hydrograph dynamics, simulations of the two floods required different values of roughness (0.02 and 0.09 s m-1/3) to reach maximum accuracy (F = 0.59 and 0.64, respectively). However, the results also indicated that a model calibrated with a flood of relatively low return period potentially could be used to map rare flood events. Simulation inaccuracies were mainly attributed to (1) reservoirs and streams, temporarily connecting to the river system during high flow conditions, (2) limitations of the topography data, in terms of recognizing riverbed geometry and floodplain micro-topography, and (3) cloud cover, reducing the accuracy of flood extent reference data. The vertical simulation accuracy, with an average error of ± 2 m, was well within the uncertainty bounds of input data. Errors were in this case ascribed the SRTM’s representation of high slope terrain and possible radar speckles in urban areas. The findings of this study indicate that there is high potential in using SRTM data for mapping of high-magnitude flood risk in Africa, but also that consideration to river system complexity is crucial.
Många områden i Afrika står för närvarande inför en ökad översvämningsrisk på grund avklimatförändringar och befolkningstillväxt. En användbar strategi att minska denna risk skulle vara att kartlägga den, så att stadsplanering, varningssystem och respons vid nödsituationer därefter skulle kunna utformas till att begränsa samhällets sårbarhet. Detta är dock inte möjligt på bred front över Afrikas kontinent, då utvecklingsländer ofta saknar det data av topografi och vattenflöde som behövs för producera högkvalitativa översvämningsriskkartor. För att försöka hitta ett sätt att kringgå detta problem undersöker pågående forskning möjligheten att generera alternativ modelleringsinput, från globalt tillgängligt höjddata, insamlat av satelliter, och metoder att uppskatta översvämningsflöden. Denna uppsats presenterar en fallstudie inom denna kontext där syftet var att bestämma kvalitén hos en översvämningskarta över ett Afrikanskt avrinningsområde, producerad med satellitprodukten SRTM (Shuttle Radar Topography Mission) som topografiinput, och att utforska möjligheterna och begränsningarna med en sådan karteringsmodell. Två stora översvämningar, vilka inträffade år 2000 och 2013 i Nedre Limpopobassängen (Mocambique), simulerades för utbredning med hjälp av en 2D- model utan flodfåra byggd för modelleringsprogrammet LISFLOOD-FP. Vattennivåer simulerade också för att kunna bedöma modellens vertikala prestation. Resultaten jämfördes med satellitbilder och dokumenterade höga vattenmärken (observerade på t ex. husfasader), samtidigt som flodplanets flödesmotstånd justerades för att optimera överensstämmelsen. Då översvämningarna var av olika karaktär behövdes olika flödesmotstånd (0.02 and 0.09 s m-1/3) för att maximal kvalité på respektive översvämningskarta skulle uppnås. Denna kvalité beräknades till 0.59 och 0.64, på en index-skala (F) där 1.00 motsvarar en perfekt simulering. Trots olika optimala flödesmotstånd antydde resultaten även att en modell kalibrerad med en relativt frekvent återkommande översvämning möjligtvis kan användas till att kartlägga sällsynta översvämningar. Avvikelserna mellan dokumenterad och simulerad översvämningsutbredning tillskrevs i huvudsak: (1) sjöar och vattendrag som temporärt ansluter till flodsystemet under höga flöden, (2) begränsningar i topografidatat gällande att fånga flodens geometri och flodplanets mikro-topografi samt (3) moln som skymmer översvämningarna i referensdatat och minskar dess sanningshalt. Vattennivåer simulerades med ett genomsnittligt fel av±2 m, vilket med marginal ligger inom inputdatats totala osäkerhetsram. Avvikelserna troddes i detta fall bero på SRTM-datats representation av sluttande terräng och möjliga radarfläckar (reflektioner) i urbana områden. Resultaten i denna studie indikerar att det ligger stor potential i att använda SRTM- data för att kartlägga risken för stora översvämningar i Afrika, men belyser också vikten av attuppmärksamhet ges till flodsystems komplexitet.

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Kreiselmeier, Janis. "Development of a Flood Model Based on Globally-Available Satellite Data for the Papaloapan River, Mexico." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-256399.

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Flood inundation modelling is highly dependent on an accurate representation of floodplain topography. These remotely sensed accurate data are often not available or expensive, especially in developing countries. As an alternative, freely available Digital Elevation Models (DEMs), such as the near-global Shuttle Radar Topography Mission (SRTM) data, have come into the focus of flood modellers. To what extent these low-resolution data can be exploited for hydraulic modelling is still an open research question. This benchmarking study investigated the potentials and limitations of the SRTM data set for flood inundation modelling on the example of the Papaloapan River, Mexico. Furthermore the effects of vegetation signal removal from the SRTM DEM as in Baugh et al. (2010) were tested. A reference model based on a light detection and ranging (LiDAR) DEM was set up with the model code LISFLOOD-FP and run for two flood events. Test models based on SRTM DEMs were run and output flood extents compared to the reference model by applying a measure of fit. This measure of fit, which was based on binary wet/dry maps of both model outputs, gave information on how well the test models simulated the flood inundation extents compared to the reference model by giving a percentage of the model performance from theoretically 0 to 100 %. SRTM-based models could not reproduce the promising results of previous studies. Flood extents were mostly underestimated and commonly flooded areas were almost exclusively made up out of the main channel surface. One of the reasons for this likely was the much steeper slope of the SRTM DEM as opposed to the LiDAR DEM where water probably was conducted much faster though the main channel. Too high bank cells as well as generally more pronounced elevation differences of the SRTM DEM throughout the whole floodplain were another problem of the SRTM DEM preventing accurate flood inundation simulations. Vegetation signal removal was successful to a certain degree improving the fit by about 10 %. However, a realistic shape of flood extent could not be simulated due to too big pixel sizes of the used canopy height data set. Also, the conditioned models overestimated flooded areas with increasing vegetation signal removal, rendering some of the models useless for comparison, as water leaving the model domain could not be accounted for in the measure of fit. This study showed the limitations of SRTM data for flood inundation modeling where an accurate approximation of the river slope as well as accurately captured bank cells and floodplain topography are crucial for the simulated outcome. Vegetation signal removal has been shown to be potentially useful but should rather be applied on more densely covered catchments.
Översvämningar skapar stora problem världen över och fler och fler människor lever i områden som är utsatta för risk för att svämmas över. Dessutom förväntas översvämningar förekomma mer frekvent i många delar av världen i framtiden på grund av klimatförändringar. Skada orsakad av översvämningar kan överstiga flera miljarder US$. Men översvämningar orsakar också andra problem, förutom ekonomiska förluster. De senaste 10 åren har mer än 60 000 människor dött på grund av översvämningar. Ytterligare 900 000 000 människor har drabbats på något sätt. Därför är det viktigt att man vet vilka områden som är utsatta för hög risk. Ett av de verktyg för att avgöra översvämningsrisker är hydrauliska datormodeller som försöker förutse hur en bestämd översvämning breder ut sig. Modellerna är baserade på fysiska principer och topografisk information. Helst vill man ha topografisk information med hög kvalitet och upplösning. Ofta har man data från fjärranalyser, insamlade från flygplan. Ett exempel på det är LiDAR-data som är baserad på laser. Dock är det ofta dyrt eller inte tillgängligt med LiDAR i avlägsna områden och utvecklingsländer, där man behöver sådan data som mest. Därför har forskare försökt att använda globalt tillgängliga topografiska data av låg kvalitet för hydrauliska modeller. En sådan datauppsättning är det så kallade SRTM-datat från amerikanska NASA. SRTM samlas in med hjälp av radarstrålar från satelliter. I flera studier har man fått goda resultat inom översvämningsmodellering med SRTM. Dock måste man testa det vidare för fler avrinningsområden. I den här studien har man försökt att använda SRTM i en hydraulisk modell för den mexikanska floden Papaloapan. För att se hur bra (eller dålig) SRTM-modellen är för att simulera hur en översvämning sprids har man jämfört den med en modell baserad på högkvalitativ LiDAR-data. Båda modellerna simulerade samma översvämningar. Topografiska information från SRTM-data är oftast inkorrekt där det finns väldigt tät och hög vegetation, eftersom radarsignalen då inte räcker till marken och den uppskattade höjden är därför för hög i sådana områden. Av denna anledning ville man därför i denna studie även testa hur resultatet av SRTM-modellen skulle förbättras om man tog bort viss vegetation. Dessvärre var den utformade SRTM-modellen inte så bra för det här fallstudieområdet och SRTM-modellen förutspådde mycket mindre översvämningar än den förmodade mer korrekta LiDAR-modellen. Då vegetation avlägsnandes kunde man förbättra SRTM-modellen till viss mån, men det var fortfarande inte tillräckligt för det här området. Denna studie visar att det är viktigt att fortsätta undersöka hur passande och användbart SRTM är, eftersom det har visat sig att SRTM inte är lämpligt för att förutspå översvämningar i alla delar av världen.

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Oukacine, Marina. "Étude expérimentale et numérique des écoulements à surface libre en présence d'obstacles émergés et faiblement submergés." Thesis, Paris Est, 2019. http://www.theses.fr/2019PESC1019.

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Selon le Ministère de la Transition Écologique et Solidaire, les inondations sont le principal risque naturel en France. Du fait du dérèglement climatique, les inondations extrêmes deviendront plus fréquentes. Les personnes et les biens, i.e. habitations, installations industrielles, doivent donc être protégés contre ces crues pour lesquelles les données sont très rares voire inexistantes. Lorsque l’on passe d’une crue faible à une crue extrême, l’extension spatiale de l’inondation en lit majeur varie fortement. La nature des obstacles rencontrés varie : végétation basse, arbres, habitations... Ces obstacles ou macro-rugosités hydrauliques peuvent être émergés, ou faiblement immergés.Le but de ce travail de thèse est d’analyser les processus physiques dominants associés à des écoulements de crues extrêmes en présence d’obstacles émergés ou faiblement submergés. Cette thèse s’organise en deux parties : une partie expérimentale et une partie numérique.La partie expérimentale porte sur l’exploration, dans un canal de laboratoire, de la structure verticale du profil de vitesse et des effets géométriques liés à la configuration étudiée représentant une plaine d’inondation urbanisée avec des taux d’immersion de (symbole dollar) D/h = à 0,42 ; 0,93 ; 0,98(symbole dollar) et (symbole dollar)1,48(symbole dollar) ((symbole dollar) D(symbole dollar) étant la hauteur d’eau et (symbole dollar) h(symbole dollar) la hauteur de l’obstacle). Des mesures ADV et PIV des vitesses moyennes et des fluctuations turbulentes ont montré que les propriétés de l’écoulement changent notablement selon que les écoulements sont émergés ou faiblement submergés. Les interactions entre le détachement tourbillonnaire, la surface libre, les obstacles et la rugosité de fond sont étudiées.La partie numérique analyse différents types de modélisation classiquement utilisés pour simuler des événements de crue. Le cas expérimental de la première partie de thèse sert de référence.D'abord, un modèle analytique basé sur l’écriture du bilan de quantité de mouvement au niveau d’un volume hydraulique élémentaire permet de considérer différentes modélisations de la résistance globale à l’écoulement d'obstacles en régime uniforme. Un premier modèle simple intègre la résistance à l’écoulement du au frottement de fond et aux obstacles dans un même terme de type « frottement~». Un second modèle décompose en deux parties la résistance à l’écoulement~: un frottement de fond et une résistance due aux obstacles représentée par un terme de traînée. L’obstruction à l’écoulement sera alors représentée par un terme de porosité.L’analyse porte sur la pertinence d’utiliser les coefficients de frottement ou de traînée calibrés pour l’écoulement avec le plus faible débit pour simuler des écoulements à fort débit et en particulier la transition de l’émergence à la submergence des obstacles.Ensuite, les obstacles seront représentés explicitement dans le cadre d’un modèle « Saint-Venant » bidimensionnel. La convergence en maillage est étudiée et une analyse comparative des résultats expérimentaux et simulés est menée. De plus,L’influence de la répartition géométrique des obstacles sur le profil vertical de la vitesse moyenne longitudinale est étudiée avec une modélisation 3D-LES utilisant Code_Saturne. Les résultats expérimentaux serviront de cas de référence pour la validation.Au terme de cette seconde partie de thèse, des recommandations seront émises pour modéliser de façon pertinente ces écoulements au regard d’objectifs opérationnels
According to the Ministry of Ecological and Solidarity Transition, floods are the main natural risk in France. As a result of climate change, extreme floods will become more frequent. People and property, such as housing and industrial installations, must therefore be protected against these floods for which data are very scarce or even non-existent. When moving from low to extreme flooding, the spatial extent of flooding in the floodplain varies greatly. The nature of the obstacles encountered varies: low vegetation, trees, houses... These hydraulic obstacles or macro-roughnesses can be emerged, or slightly submerged.The purpose of this thesis work is to analyze the dominant physical processes associated with extreme flood flows in the presence of emerged or slightly submerged obstacles. This thesis is organized in two parts: an experimental part and a numerical part.The experimental part concerns the exploration, in a laboratory channel, of the vertical structure of the velocity profile and the geometric effects related to the studied configuration representing an urbanized floodplain with immersion rates of (dollar symbol) D/h = 0.42, 0.93, 0.98(dollar symbol) and (dollar symbol)1.48(dollar symbol) ((dollar symbol) D(dollar symbol) being the water depth and (dollar symbol)h(dollar symbol) the obstacle height). ADV and PIV measurements of mean velocities and turbulent fluctuations have shown that flow properties change significantly depending on whether the obstacles are emerged or slightly submerged. The interactions between vortex detachment, the free surface, obstacles, and bottom roughness are studied.The numerical part analyses different types of modelling conventionally used to simulate flood events. The experimental case of the thesis serves as a reference.First, an analytical model based on the conservation of momentum of an elementary hydraulic volume allows considering different models of the overall flow resistance to obstacles in a uniform regime. The first simple model integrates the resistance to flow due to bottom friction and obstacles in a single "friction" type term. A second model divides the flow resistance into two parts: a bottom friction term and an obstacle resistance, represented by a drag coefficient. The obstruction to the flow is then represented by a porosity coefficient.The analysis focuses on the ability to use friction or drag coefficients calibrated for the lowest flow rates to simulate high flow rates, and in particular, the transition from emergent to submergent obstacle flows.Then, the obstacles are explicitly represented in a two-dimensional Shallow-Water model. Mesh convergence is studied and a comparative analysis of experimental and simulated results is conducted.Furthermore, the ingluence of the geometric distribution of obstacles on the vertical profile of the average longitudinal velocity is studied with 3D-LES model using Code_Saturne. The experimental results serve as a reference case for validation.Recommendations are made for how to model these flows for operational applications

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30

Novák, Radomír. "Návrh malé víceúčelové nádrže v k.ú Velké Albrechtice." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226858.

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The first section of this diploma thesis pursues an algorithm design of flood wave transformation in Excel software and its application afterwards. The software is used to design a small multipurpose reservoir. The algorithm covers consumption calculations of typical dam structures such as discharge structures, sluice planks, narrowed section of discharge pipes and safety spillways. The thesis also includes a mathematical model of water infiltration into the bottom of the inundation area and through the dam body. The last section of the thesis is dealing with an aesthetic integration of the whole structure into the local environment.

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Mkwananzi, Nokuphumula. "Modelling flood inundation in the Mlazi river under uncertainty." Thesis, 2003. http://hdl.handle.net/10413/3767.

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The research project described in this dissertation studies the modelling techniques employed for the Mlazi River in the context of flood analysis and flood forecasting in order to model flood inundation. These techniques are applicable to an environment where there is uncertainty due to a lack of historical input data for calibration and validation purposes. This uncertainty is best explained by understanding the process and data required to model flood inundation. In order to model flood inundation in real time, forecasted flood flows would be required as input to a hydraulic river model used for simulating flood inundation levels. During this process, forecasted flood flows would be obtained from a flood-forecasting model that would need to be calibrated and validated. The calibration process would require historical rainfall data correlating with streamflow data and subsequently, the validation process would require real time streamflow data. In the context of the Mlazi Catchment, there are only two stream gauges located in the upper subcatchments. Although these stream gauges have recorded data for 20 years, the streamflow data does not correlate with disaggregated daily rainfall data, of which there are records for at least 40 years. Therefore it would be difficult to develop the forecasting model based on the rainfall and streamflow data available. In this instance, a more realistic approach to modelling flood inundation involved the integration of GIS technology, a physically based hydrological model for flood analysis, a conceptual forecasting model for real time forecasting and a hydraulic model for computation of inundation levels. The integration of modelling techniques are better explained by categorising the process into three phases: Phase 1 Desktop catchment modelling: A continuous, physically based simulation model (HEC-HMS Model) was set up using GIS technology. The model applied the SCS-UH method for the estimation of peak discharges. Synthetic hyetographs for various recurrence intervals were used as input to the model. A sensitivity analysis was implemented and subsequently the HEC-HMS model was calibrated against output SCS-UH method and peak discharges simulated. The synthetic hyetographs together with results from the HEC-HMS model were used for validation of the Mlazi Meta Model (MMM) used for real time flood forecasting. Phase 2 Implementation of the Inundation Model: The hydraulic model (HEC-RAS) was created using a Digital Elevation Model (DEM). A field survey was conducted for the purpose of capturing the roughness coefficients and hydraulic structures, which were incorporated into the model and also for the confirmation of the terrain cross sections from the DEM. Flow data for the computation of levels of inundation were obtained from the HEC-HMS model. The levels of inundation for the natural channel of Mlazi River were simulated using the one dimensional steady state analysis, whereas for the canal overbank areas, simulation was conducted for unsteady state conditions. Phase 3 Creation of the Mlazi Meta Model (MMM): The MMM used for real time flood forecasting is a linear catchment model which consists of a semi-distributed three reservoir cell model (Pegram and Sinclair, 2002). The MMM parameters were initially adjusted using the HEC-HMS model so that it became representative of the Mlazi catchment. This approach sounds unreasonable because a model is being validated by another model but it gave the best initial estimate of the parameters rather than using trial and error. The MMM will be further updated using record radar data and streamflow data once all structures have been put in place. The confidence in the applicability of the HEC-HMS model is based on the intensive efforts applied in setting it up. Furthermore, the output results from the calibrated HEC-HMS model were compared with other reliable methods of computing design peak discharges and also validated with frequency analysis conducted on one of the subcatchments.
Thesis (M.Sc.)-University of Natal, Durban,2003.

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32

Koh, Yen Hui, and 高延輝. "Development of BEEMD Based Smoothing Algorithm for Topography and a 2D Storage Cell Based Flood Inundation Model." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/63789228099642936728.

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碩士
國立臺灣大學
土木工程學研究所
103
As rapid population growth and land-use changes increasingly exposed human beings to a greater degree of flood hazards, disaster prevention and mitigation projects have heavily applied numerical modelling methods to assess the risks and impacts at different temporal and spatial scales. Among the wide range of models available, 2D hydrodynamic models are probably the most common tools applied in investigating flood events, owing to its rigorous physical basis and mathematics foundation. However, the presence of highly nonlinear derivatives in the momentum equations have often found triggering numerical instabilities when the model is applied over a complex topography of high curvature variation. In this study, two different strategies are proposed to approach the difficulty. The first method applied is to reduce the local scale curvature through topography smoothing. Here a bi-dimensional ensemble empirical mode decomposition (BEEMD) based smoothing algorithm, namely the Fast and Adaptive Bi-dimensional Ensemble Empirical Mode Decomposition (FABEEMD), is introduced. This new technique is an improvement of Bhuiyan’s work in which pairs of positive and negative signed white noise sets are added into the signal during each iteration of FABEEMD. The introduction of white noise conjugate pairs has resolved the difficulties of mode-mixing and extrema lacking as encountered in the original framework while preserving the extracted bi-dimensional intrinsic mode function (BIMFs) noise-free. As a result, only a small ensemble is required in FABEEMD, enabling the algorithm to decompose any size economically without sacrificing the fidelity. The required smoothed topography is then constructed by reassembling the low frequency components upon the model toleration on surface roughness. The decomposition shows that the proposed method consistently performed much better than the original framework in distinguishing and extracting the local features of different surface roughness. As the noise amplitude increased, macro topographical variation is observed gradually shifting from high to low frequency components, giving the latter a more detailed depiction of the surface. This enables the smoothing to adapt to the surface roughness requirement of the flood simulation model. The second strategy adopted in this work is to develop a simplified flood inundation model by replacing the shallow water equations with Manning’s formula to omit the nonlinear derivatives from momentum computation. The computational domain are spatially discretized into a Triangulated Irregular Network (TIN) with each element being treated as a storage tank. To spatially distribute the runoff with 1D uniform flow formula, we incorporate the Manning’s formula with a multiple flow direction (MFD) framework to form a two steps algorithm in which the total outflow of an element is first computed through weighted averaging the variables required in Manning’s formula, then partitioned into directional components according to their corresponding hydraulic gradients. For urban flooding, underground sewer system and rainwater harvesting are incorporated with the model to provide more reliable simulation. The model was applied to Linbian River watershed during Typhoon Morakot of August 2009 and an idealized urban terrain inundated by a designed rainstorm. In the former, the model has shown satisfactory results in terms of inundation extent and depth by verifying against in-situ observation and the simulation of a 2D hydrodynamic model. For urban flood modeling, the simulation is shown reasonable and stable. In both cases, 0% of mass loss was achieved.

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Dissertations / Theses on the topic '2D flood inundation modelling'

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