The natural movement of water is known as the hydrological cycle. Many different factors affect the hydrological cycle and the availability of freshwater. The availability of freshwater is essential for many human activities. Three of the UN SDG’s (Sustainable Development Goals), number 2, 6 and 7, directly or indirectly relate to freshwater supplies. SDG number 2, zero hunger; a part of fulfilling this goal is to have enough available freshwater to irrigate crops. SDG number 6 is about access to clean water and sanitation. It is possible to desalinate saline water, treat unclean water or transport water long distances, but these are often costly and energy demanding processes. Therefore, it is important to manage the freshwater supplies that are available wisely. Access to clean and affordable energy is SDG number 7. One source of clean and affordable energy is hydropower, in order to produce electricity in a hydropower plant, plenty of water and a change in potential energy is needed . To be able to fulfil all these goals, it is important to include all of the perspectives when making policies regarding agriculture, building hydropower plants or making big infrastructure changes. The complex relationships between the different areas of interest can make it complicated to analyse the effects of a change made in any area. The concept of connecting different perspectives is called Nexus. This aim of this thesis was to evaluate different computer-based hydrological modelling tools, and how they can be used for Nexus assessments. This was done by performing a market research, choosing two tools for further assessment, creating evaluation criteria and perform a case study on a watershed in Uganda. The case study results and the evaluation criteria were then compared to an existing model in WEAP. The two selected hydrological modelling tools were MIKE SHE and SWAT. These two modelling tools were evaluated based on specified evaluation criteria. In the case study they modelled the same area in Kamwenge, Uganda. The output of the models was compared and calibrated against observed flow in the river at the outlet of the watershed. The results of the case study were incomplete since the MIKE SHE model was not calibrated successfully. The different models have different strengths. The format of output data and flexibility of the program is superior in MIKE SHE, while SWAT is more intuitive and demands less computer power. Over all SWAT is easier to use and model in for a novice user, while MIKE SHE requires more expertise in order to run a successful model. SWAT is able to model more of the Nexus perspectives and are therefore the preferred model. / Många faktorer påverkar tillgängligheten av sötvatten som är väsentligt för många mänskliga aktiviteter. Tre av FN:s globala hållbarhets mål, nummer 2, 6 och 7 relaterar direkt eller indirekt till tillgång till sötvatten. Mål nummer 2, ingen hunger; en del av att uppfylla detta mål är att det måste finnas vatten för att bevattna grödor. Mål nummer 6, tillgång till rent vatten och sanitet; det är möjligt att rena vatten eller att transportera det längre distanser, men det är ofta energikrävande och kostsamt. Därför är det viktigt att förvalta tillgängliga sötvatten resurser klokt. Hållbar energi för alla är mål nummer 7. En källa till hållbar och ren energi är vattenkraft, för att producera vattenkraft behövs en skillnad i potentiell energi och mycket vatten. För att kunna uppfylla alla dessa mål är det viktigt att inkludera alla perspektiv när man bestämmer policys för jordbruk, bygger vattenkraftverk eller gör andra stora ändringar i infrastrukturen. De komplicerade förhållandena mellan dessa olika intresseområden för vatten kan göra det svårt att förutse hur en förändring i en av dem påverkar de andra. Konceptet att koppla ihop olika perspektiv kallas Nexus. Målet med denna uppsats var att utvärdera olika hydrologiska modelleringsverktyg och hur de kan användas för Nexus bedömning. Det gjordes genom att en marknadsundersökning genomfördes och två modelleringsverktyg valdes ut. De två utvalda modelleringsverktygen var MIKE SHE och SWAT. Dessa två verktyg utvärderades baserat på specificerade kriterier. I fallstudien modellerade båda modelleringsverktygen samma område i Kamwenge, Uganda. De båda modellerna kalibrerades mot observerade utflöden från avrinningsområdet. Resultaten jämfördes med en existerande modell i WEAP. Resultaten från fallstudien är ofullständiga då kalibreringen för MIKE SHE modellen inte lyckades.

Economic development in an area attracts more people to live in it. This increment drives the necessity to improve available infrastructure, like roads for instance, to satisfy a higher demand. Bigger roads and higher number of vehicles have raised the concern about possible pollution coming from these sources In this thesis, copper coming from road runoff in a peri-urban catchment in Portugal was analyzed. The catchment is located in the Coimbra region, center of Portugal. In order to model copper pollution in road runoff, it is necessary to couple a hydrological model and a water quality Based on a previous study (Kalantari, Ferreira, Walsh, Ferreira, & Destouni, 2017) a physical based hydrological model  MIKE SHE  coupled with the hydraulic model MIKE 11was updated and further coupled with  ECO Lab to simulate water quality and ecological processes. The results show an improvement of the hydrological model compared with the original one, nash-sutcliffe efficiency was raised from 0.59 to 0.77 and the coefficient of determination varied from 0.64 to 0.79. For copper the model behavior for punctual and distributed sources was analyzed. For punctual sources, highest concentrations were present in the grid points where the incoming sources were located in the tributaries, and these concentrations are rapidly reduced downstream. On the other hand, distributed sources approach gives higher concentrations near the end of the river than in the tributaries upstream. Comparing time-averaged model results along the river, with fresh water quality criteria according to U.S. EPA (2004), for punctual sources an extension of 978 meters (7,6% of the river) presents a concentration above CCC or CMC, on the contrary, for distributed sources the extension is lower with 494 meters (3,8%). The organic carbon partitioning coefficient have bigger influence on the results than other factors, nevertheless this influence is not marked. Modeled copper values do not agree well with the mesured values specially for periods with higher discharge as the model simulates lower concentration with higher discharge and viceversa. Copper boundary values for the model represent a big challenge considering limited data available. This thesis gives good overview about the coupling process between MIKE 11 and ECO Lab, as well as analyzes the importance of some factors as well as model limitations and uncertainties.

Water is ubiquitous on our planet and constitutes a vital part of ecosystems. It supports the life of all beings on the earth while simultaneously evokes water-related issues such as water shortage, water contamination. As UN advocates, a globally shared blueprint for available clean water is depicted in Sustainable Development Goals (SDGs). However, there still exists a gap between current water management situations and our sustainable goals Modelling based on Hydro-Meteorological Data provides a way to understand regional hydrological processes and monitor environmental chemistry changes, especially for anthropogenic pollution. Furthermore, hydrological models make it possible to predict changes in water quantity and quality, under the context of climate change. The study area of this project is located in the Kringlan catchment, Norrström basins, occupying an area of 54.5 km2. The local discharges merge into Rastälven river and flow to the east, eventually discharging into the Baltic Sea. This project builds up a water balance model based on the meteorological data in the time frame from 2011 to 2012. The water balance model is calibrated to accurately simulate realistic hydrological components interactions, during each process, various parameters have been tested and adjusted to improve model robustness. Meanwhile, the project tries to strike a balance between the complexity of the model and amount of time it takes to run the model. The calibrated model is also validated to ensure model performance using statistical analysis. Additionally, a particle tracking model for the saturated zone is developed on the basis of the water balance model. Chloride is chosen as the trace element due to its feature of unreactive in ecological systems. The model results could also provide a value to groundwater age estimation. Suggested by previous researches targeting the area, leakage from vegetation and forest soil in this catchment have contributed to imbalances in local Cl- budgets. An internal source of chloride from soil leaching is specified in the model at the same time with an external source from stream discharge. The coupled modelling through the application of MIKE SHE software and calibration process help us to understand dynamic processes of hydrological modelling and chloride particle transport in the Kringlan catchment. A future improvement to consider is extending the current model boundary to a larger area and introducing more reference data. It is also possible to establish a fully integrated solute transport model to investigate Chloride transport in the catchment. / Vatten ersätter en viktig del av ekosystemet men det framkallar vattenrelaterade problem som vattenbrist och vattenförorening samtidigt. Emellertid finns det fortfarande ett gap mellan nuvarande vattenhanteringssituationer och våra hållbara mål. Modellering baserad på meteorologiska data erbjuder en möjlighet att förstå regionala hydrologiska processer och övervaka förändringar av miljömässiga kemikalier, särskilt för antropogena föroreningar. Dessutom finns det en hög potential för att förutse förändringar i vattenmängd och kvalitet med hydrologiska modeller, i samband med klimatförändringar. Studieområdet ligger i Kringlans upptagningsområde som ett av Norrström basins, med en yta på 54,5 km2. De lokala utsläppen sammanfogas i Rastälven och strömmar österut, så småningom mynnar i Östersjön. Detta projekt bygger upp en vattenbalansmodell baserad på meteorologiska data inom tidsramen från 2011 till 2012. Vattenbalansmodellen är kalibrerad för att exakt simulera realistiska hydrologiska komponentinteraktioner. För att förbättra modellens robusthet har olika parametrar testats och anpassats under varje process. Samtidigt försöker projektet att hitta en balans mellan modellens komplexitet och hur lång tid det tar att driva modellen. En partikelspårningsmodell för den mättade zonen har utvecklats med utgångspunkt i vattenbalansmodellen. Klorid används som spårämne eftersom det är inert i ekologiska system. Modellsresultaten kan också ge ett värde för grundvattenberäkningen. Tidigare undersökningar inriktade på området föreslår att läckage från vegetation och skogsmark i detta avrinningsområde har bidragit till obalanser i lokala Cl- budgetar. Med hjälp av MIKE SHE modellen har vi undersökt dynamisk process för hydrologisk modellering och kloridpartikelspårning i Kringlan avrinningsområde. Vad som kan gör i framtiden är att förlänga den nuvarande modellgränsen till ett större område med mer referensdata. Det är också möjligt att upprätta en fullständigt integrerad lösningsmodell för att undersöka kloridtransporter i ett avrinningsområde.

The increasing frequency of Cyanobacterial blooms in freshwater bodies raise concerns around the globe. The consequences of this phenomenon impact not only human health but the entire surrounding ecosystem. During the past decades, numerical modelling has been increasingly used to investigate and study aquatic systems. Hydrodynamic and Ecological models are developed in parallel to simulate processes, evaluate potential remedies, and investigate future scenarios. This project aimed at developing a 3D hydrodynamic and water quality (ecological) model to assess the eutrophication conditions of Lake Vomb under current and future scenarios. MIKE 3 FM software was used in the analysis with meteorological, hydrological, and water quality data. The hydrodynamic model performance was satisfactory in terms of water temperature simulation with root-mean-square-error (RMSE) ranging between 0.38-1.2 oC. In the ecological model, Chlorophyll-a (Chl-a) was simulated as a surrogate for Cyanobacteria. The model was adequate in simulating Chl-a concentrations with a Nash-Sutcliffe efficiency (NSE) of 0.94 during calibration and 0.84 after validation. The results showed that Lake Vomb’s nutrient concentrations are highly influenced by external nitrogen loading and internal phosphorus loading. The results also showed that Chl-a levels are correlated with the total phosphorus levels in the lake. Future water quality projections were attempted through two Representative Concentration Pathways (RCPs) for the year 2050. The projections utilized only changes in air temperatures and precipitations and suggested significant increase in Cyanobacteria biomass independence of changes in external nutrient loading.

Per and polyfluoroalkyl substances (PFAS) are found ubiquitously in the environment across the globe.These substances have high persistence due to the strong carbon and fluorine bond. In the aquaticenvironment, due to high persistence, these substances don’t decay easily and are detected on the surfaceas well as in groundwater sources. Human exposure to PFAS has been observed due to ingestion of PFAScontaminated food and water which has an adverse effect on the human health. High concentrations ofPerfluoroalkyl Octanoic Sulphonate (PFOS) and Perfluoroalkyl Hexanoic Sulphonate (PFHxS) wereobserved in Lake Ekoln. The main aim of this study was to analyze the spread of PFOS and PFHxS in thelake. Hydrodynamic modelling of flow and water quality modelling in the lake was performed usingMIKE 3 FM software for the evaluation of the spread pattern of PFOS and PFHxS in the lake. Twoscenarios with the different mass fluxes of PFOS and PFHxS for Fyrisån were assumed for investigatingthe uncertainties and influence of contribution from Fyrisån. Additionally, conductivity from differentinflows was modelled as a passive tracer for understanding the water quality and the circulation in thelake. The results of the simulation showed that Fyrisån and Kungsängsverket are major contributors of PFOSand PFHxS to the lake. Similarly, the analysis of the current spread of PFOS and PFHxS shows that theuncertainty in the model is high and is dependent mainly on the assumption of mass flux from theFyrisån. Due to the lack of sampling data on the concentration of PFOS and PFHxS, it was difficult to geta reliable assumption for the mass flux from the Fyrisån. From the study, it was identified that thesampled concentration of PFOS and PFHxS also had certain variations which might be due to theinfluence of concentration from different sources and processes. Likewise, the simulation result of PFOSand PFHxS was observed to have a similar pattern of spread. Although PFOS is a long-chain PFAS andPFHxS is a short-chain PFAS and they have different physio-chemical properties, the spread patternswere observed to be similar. As only the hydrodynamic processes were influencing the simulation for thespread of PFOS and PFHxS in the lake and other physiochemical processes such as sedimentation andbioaccumulation were not included in the model, the simulated PFAS results were found similar. To conclude, the study shows that the spread of PFOS and PFHxS is mainly influenced by the flow andconcentration in Fyrisån. Also, higher uncertainty in the model performance was observed due to theissue of reliable mass flux estimation from Fyrisån. Similarly, the influence of processes such assedimentation and bio accumulation are necessary to be included in the model for analysis of spread ofPFAS with different physio-chemical properties.

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.

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.

Aujourd’hui, les zones côtières concentrent souvent des villes densément peuplées où le développement économique est associé à une rapide urbanisation. Dans de nombreux endroits, les cours d’eau sont intégrés en zone urbaine présentant à la fois des ressources et des risques potentiels. La concurrence croissante entre les activités économiques et l'espace essentiel aux rivières et aux milieux naturels nécessite une gestion intégrée basée sur des outils fiables capables de fournir des informations hydrologiques. La basse vallée du Var, dans le sud de la France, est spécifiquement exposée à une augmentation de l’activité humaine, et les impacts sociaux sur l’environnement deviennent de plus en plus intenses. Par conséquent, le cycle de l’eau est déséquilibré et induit des problèmes liés à l’eau. Pour traiter ces problèmes, les collectivités territoriales ont besoin d’outils d’aide à la décision qui simulent le comportement du bassin versant. Tel est l’objectif du projet AquaVar qui repose sur trois modèles numériques : Mike SHE pour le bassin versant du Var, Mike 21FM pour la rivière, et Feflow pour l’aquifère. Ces travaux de recherches se concentrent sur le modèle des écoulements à surface libre et son intégration au sein de l’outil d’aide à la décision.Les modèles hydrauliques 2D sont fréquemment utilisés car ils fournissent une vision précise des phénomènes physiques en rivière et de l’hydrodynamique durant des événements extrêmes (inondation, sécheresse et pollution accidentelle). Le modèle des écoulements à surface libre 2D est conçu avec le logiciel Mike 21FM en utilisant la méthodologie classique. Il est calibré et validé pour des conditions spécifiques de la basse vallée du Var : hautes eaux au mois de novembre, hautes eaux au printemps dues à la fonte des neiges et basses eaux en été. Le modèle hydraulique peut non seulement être utilisé pour simuler des scénarios d’événements extrêmes, mais il est également capable d’interagir avec le modèle des écoulements souterrains développé avec Feflow. Une interface spécifique est développée pour connecter le Var et son aquifère dans la basse vallée. Elle nécessite cependant une phase de validation afin de précisément simuler les échanges nappe-rivière.De toute évidence, le modèle Mike 21FM est le cœur de l’outil d’aide à la décision. L'hydrodynamique du fleuve dépend de la transformation des précipitations en débit (modélisée par Mike SHE) et du volume d'eau échangé avec l'aquifère (modélisé par Feflow). La dernière partie est consacrée à la construction de l'outil d’aide à la décision avec l'intégration du modèle hydraulique 2D. Ce système de modèles est implémenté dans une interface web et accessible par différents utilisateurs. Cet outil peut être facilement mis à jour en partageant les données de chaque partenaire. Dans le futur, cet outil pourrait intégrer le petit cycle de l'eau (réseaux d’assainissement et d’alimentation en eau potable). Les autorités locales pourraient donc prévoir et contrôler leurs ressources en eau et les risques potentiels. / Nowadays, the coastal areas concentrate frequently densely populated cities where economic development is associated to a fast urbanization. In many locations rivers are integrated within the urban areas and present both resources and potential risks. The growing competition between the economic activities and the essential space for the rivers requests an efficient management based on reliable tools able to provide hydrological information. Typically, the Lower Var valley, in south of France, faces to an increase of human activities, and the social impacts on the natural environment have become more and more intensive. Therefore, the water cycle is unbalanced implying water problems. To deal with this issue, local authorities needs a Decision Support System (DSS) tool to simulate the behaviour of water system. This is the objective of the AquaVar research which includes three numerical models: Mike SHE for the Var catchment, Mike 21FM for the Lower Var River, and Feflow for the aquifer. Here, the research is focused on the 2D free surface flow model and its integration in the DSS tool.The 2D hydraulic models represent a meaningful approach that can provide an accurate view on the physical processes within the river and on the hydrodynamics during the extreme events (inundation, drought and accidental pollution). The 2D free surface flow model is designed with Mike 21FM software using common methodology. It is calibrated and validated for the three specific weather conditions in the Lower Var valley: floods which occur in November, spring floods due to snow melting and droughts in summer. Not only the 2D hydraulic model allows to simulate scenarios of inundation and accidental pollutions, but it is also able to exchange water volume with the groundwater model developed with Feflow. A specific interface is developed to connect river and aquifer in the Lower Var valley. It required validation cases to accurately simulate the river-aquifer exchanges.Obviously, Mike 21FM is finally the core of the DSS tool because it is the centre of the modelling system. The hydrodynamics of the river depends on precipitations converted in flow by Mike SHE model, and exchanges water volume with the aquifer modelled by Feflow. The last part of this research is dedicated to the construction of the DSS tool and the integration of the 2D hydraulic model. The modelling system is implemented in a web interface adapted for different types of users. This DSS tool can be easily updated by sharing data from all the stakeholders. In the future, this tool could integrate sewage network and drinking water supply system to consider all the water cycle. Hence, local authorities could forecast and control the water resources and the potential risks.

Societies are facing great challenges with obtaining a good quality and quantity of drinking water in the context of climate change. Increases in natural organic matter (NOM) and per- and polyfluoroalkyl substances (PFAS) have been observed in lakes and drinking water the past years, which is of great concern for water treatment plants in Sweden. It is therefore vital to increase the knowledge regarding the distribution of these substances in the environment. The main objective of this project was therefore to further develop a hydrodynamic model for lake Ekoln by including transportation and degradation of NOM. This was to be done by calibrating the model in terms of total organic carbon (TOC) and Water colour (Colour). A second objective was to investigate the requirements to successfully model PFAS in Ekoln for future studies. The study was done using the model MIKE 3 FM, developed by the Danish Hydraulic Institute (DHI) The two variables TOC and Colour, were calibrated separately for the period of February 2017 to September 2018. For TOC the within-lake processes were decay and sedimentation. These were described using a reference decay constant for 20 °C (k0), that was scaled using the Arrhenius temperature coefficient (θ), and sedimentation was represented by a settling velocity (vsm). For Colour the included process was photooxidation. This process was described using a maximum photooxidation rate (kphoto) that was scaled using the Monod relation including parameters for minimum photosynthetically active radiation (PAR) necessary for photooxidation to occur (Imin) and a PAR half saturation constant (I1/2). The calibration of TOC resulted in the following best fit parameters for k0  of 0.001 d-1, θ of 1.07 and vsm of 0.001 md-1. The calibration of Colour resulted in the following best fit parameters for kphoto of 0.0125 d-1, Imin of 0 µmol photons m-2s-1 and I1/2 of 4 µmol photons m-2s-1. Overall it can be concluded that the chosen processes managed to capture the seasonal variations of TOC and Colour, and the calibrated parameter values are in line with similar studies. The assumption of not including autochthonous input proved to be the biggest source of error in the calibration of TOC but proved to have a minor influence on the calibration of Colour. To achieve a more realistic representation of photooxidation in the vertical profile, for the simulation of Colour, more processes should be considered to be added in the model in future studies. The results presented in this study contributes with increased knowledge of carbon budgets in lakes and can be used to predict water quality hazards connected to climate change and extreme events. The limited access to PFAS data for Ekoln, constrained the study of PFAS and only two sources could therefore be studied: The sewage treatment plant Kungsängsverket and precipitation. The results showed that the simulated concentrations of PFAS in Ekoln only accounted for 40 % of the observed concentrations. It could further be concluded that the contribution from precipitation is negligible. For future studies it is judged to be vital to include Fyrisån as a PFAS source, and to look into processes that influence PFAS distribution, such as sedimentation and adsorption to organic matter. / Samhällen står idag inför stora utmaningar vad gäller att tillhandahålla god kvalitet och kvantitet av dricksvatten under rådande klimatförändringar. De senaste åren har det observerats ökande halter av naturligt organiskt material (NOM) och per- och polyfluorerade alkylsubstanser (PFAS) i sjöar och dricksvatten, vilket är bekymmersamt för Sveriges vattenreningsverk. Det är därför av största vikt att öka kunskapen om dessa ämnens distribution i miljön. Huvudsyftet med denna studie var därför att vidareutveckla en hydrodynamisk modell för sjön Ekoln så att den även inkluderar transporten och nedbrytningen av NOM. Detta utfördes genom att kalibrera modellen för totalt organisk kol (TOC) och Vattenfärg (Färg). Ett andra syfte var att undersöka vilka förutsättningar som krävs för att kunna modellera PFAS på ett korrekt sätt i Ekoln. Studien utfördes i modellverktyget MIKE 3 FM, utvecklat av DHI.  De två variablerna TOC och Färg kalibrerades separat för perioden februari 2017 – september 2018. Processerna som valdes att påverka TOC var nedbrytning och sedimentation. Dessa processer beskrevs med hjälp av en referens-nedbrytningskonstant för 20 °C (k0), vilken anpassades med hjälp av Arrhenius temperaturkoefficient (θ) och sedimentation beskrevs med hjälp av en sedimentationshastighet (vsm). Färg påverkades endast av processen fotooxidation vilken beskrevs med en maximal hastighet för fotooxidation  (kphoto) som anpassades med hjälp av Monods relation. Anpassningen skedde med hjälp av parametern för minimal fotosyntetiskt aktivt ljus (PAR) för att fotooxidation ska ske (Imin) samt en PAR halv mättnads konstant (I1/2) .  Kalibreringen resulterade i värden för k0 av 0.001 d-1, θ av 1.07 och vsm av 0.001 md-1. Kalibreringen för Färg resulterade i värden för kphoto av 0.0125 d-1, Imin av 0 µmol fotoner m-2s-1 och I1/2 av 4 µmol fotoner m-2s-1. Det kan konstateras att de valda processerna lyckas med att beskriva säsongsvariationerna av både TOC och Färg och att de kalibrerade parametervärdena stämmer överens med litteraturen. Antagandet om att inte inkludera autoktont tillförsel av organiskt material (NOM från ytvatten), visade sig vara den största felkällan i simulering av TOC, men visade sig ha en mycket liten påverkan på simuleringen av Färg. För en mer realistisk bild av fotooxidations spridning i djupled, för simuleringen av Färg, bör fler processer övervägas att inkluderas i modellen för framtida studier.  Studien av PFAS var begränsad av tillgången till data, vilket medförde att endast två källor av PFAS till Ekoln analyserades: reningsverket Kungsängsverket och nederbörd. Resultaten visade att den simulerade koncentrationen av PFAS endast motsvarade 40 % av den observerade. Vidare kunde det konstateras att tillförsel av PFAS från regn kan antas vara försumbar. För framtida studier av PFAS i Ekoln bedöms det vara avgörande att inkludera Fyrisån som en källa, samt att vidare undersöka processer som påverkar transporten av PFAS så som sedimentation och adsorption till organiskt material.

With an intensification of heavy rain events in a changing climate and a rapid urbanization the risk for pluvial flooding is increasing in our societies. Pluvial flooding, which is formed when the rainfall rate exceeds the infiltration or drainage rate, can occur rapidly and cause great damages, large economic losses and possibly risk human lives. This kind of flooding is difficult to predict since it is caused by short-term and often local processes, but preventive measures and more robust infrastructure developed over the last decades have decreased the risk of the most severe damages. One way to prevent damage is to map risk areas and take measures by performing a cloudburst modelling, which can be done as a 2D hydraulic modelling. Common practice in cloudburst modelling today is to use a uniform design storm, often the Chicago Design Storm (CDS), with the same hyetograph applied evenly over the whole model area. Even though rain is not spatially uniform this assumption might be valid for more stratiform frontal rain. Intense rain events however have a higher spatial variation in rain intensity, and an assumption like this might significantly affect the results. This study aimed to investigate the effect of the spatial variation in rain intensity on the modelled hydraulic response from an intense rain event. It was performed through a case study of the cloudburst in Gävle, Sweden, in August 2021. A 2D hydraulic model of the city was prepared in the software MIKE 21 Flow Model FM and the cloudburst event was simulated with a spatially varied rainfall input, based on radar data from the event with a 2x2 km resolution, and with spatially uniform rainfall input both with the temporal variation in rain intensity from the event and with a Chicago Design Storm, all with the same total volume. The scenarios were evaluated in terms of proportion of the model area being flooded, the average maximum flooding depth and by mapping the difference in flooding depth over the whole area. The results showed that the spatial variation of rainfall input had a significant effect on the hydraulic response in the city and that assuming a uniform rainfall might lead to an underestimation of the flooding depths in parts of the model area compared to a varied one. The average flooding depth was only a few percent higher for the spatially varied rain compared to the uniform rain with a similar time variation, but in large central areas of the city the model with the uniform rain underestimated the maximum flooding depth by 5-35%. The uniform CDS rain was seen to both over- and underestimate the flooding depth, but in the central and flooded parts of the city underestimation dominated. This points out a risk of using uniform design storms in cloudburst modelling, since a spatially varied rain of the same volume could give more severe effects than the simulated response and that using a uniform design storm potentially introduces an uncertainty in the modelled results that could be important to point out and further quantify. / Med en intensifiering av häftiga regnväder i ett förändrat klimat och en allt snabbare urbanisering ökar risken för pluviala översvämningar i våra samhällen. Pluviala översvämningar, som skapas av att regnintensiteten är högre än infiltrations- eller dräneringshastigheten, kan uppstå plötsligt och orsaka stora skador, ekonomiska förluster och även i värsta fall riskera människoliv. Denna typ av översvämning är svår att förutse eftersom den orsakas av snabba och ofta lokala processer, men förebyggande åtgärder och mer robust infrastruktur som har utvecklats de senaste decennierna har minskat risken för de allvarligaste skadorna. Ett sätt att förebygga skador är att kartera riskområden genom skyfallsmodellering, till exempel med en tvådimensionell hydraulisk modell. Praxis idag är att använda spatialt uniforma typregn vid skyfallsmodellering, där samma hyetograf appliceras jämnt över hela modellområdet. Detta antagande kan ge giltiga resultat för mer stratiforma frontregn, men intensiva regn, skyfall, har generellt sett en hög spatial variation i intensiteten vilket gör att antagandet skulle kunna påverka resultatet signifikant. Denna studie syftade till att undersöka effekten av den spatiala variationen i regnintensitet på den simulerade hydrauliska responsen från ett intensivt regn och den utfördes som en fallstudie av skyfallet i Gävle 17-18 augusti 2021. En 2D hydraulisk modell av Gävle förbereddes i programmet MIKE 21 Flow Model FM och simuleringar utfördes med en spatialt varierad regnindata, baserad på radardata från tillfället med en 2x2 km upplösning, och med spatialt uniforma regnindata både med den verkliga tidsvariationen och med en Chicago Design Storm (CDS), alla med samma totala volym. Skillnaden mellan scenarierna utvärderades genom att jämföra andel översvämmat modellområde, medel av maximala översvämningsdjupet och en kartering av skillnaden i översvämningsdjup över hela modellområdet. Resultaten visade att den spatiala variationen i regnindatan hade en signifikant effekt på den simulerade hydrauliska responsen i staden och att antagande om uniform regnintensitet kan leda till en underskattning av översvämningsdjupen i modellområdet jämfört med ett varierat regn. Medelvärdet av översvämningsdjupet var endast några procent högre  för det spatialt varierade regnet, men i stora centrala områden underskattade modellen med det uniforma regnet det maximala översvämningsdjupet med 5-35 %. Det uniforma CDS-regnet både under- och överskattade översvämningsdjupet, men i centrala och översvämmade områden var det större delar som underskattades. Detta visar på en risk med att använda uniforma typregn i skyfallsmodellering, då ett spatialt varierat regn med samma volym skulle kunna ge betydligt allvarligare effekter än de som modellen har visat och att användandet av uniforma testregn potentiellt inför en osäkerhet i resultaten som är viktig att poängtera och även att vidare undersöka och kvantifiera.