Huvudsyftet med den här studien var att undersöka vilka parametrar som har störst inverkan på trädens vattentillgång i BlåGrönGråa-system (BGG-system), utvecklat av Edge, och vilka förbättringar som kan göras för att vegetationen bättre ska klara av torka. Ett annat mål med denna studie var attundersöka hur väl det går att efterlikna och simulera BGG-system i modelleringsverktyget MIKESHE, utvecklad av Danish Hydraulic Institute (DHI). För att undersöka vilka parametrar som har störst inverkan på BGG-systems vattenhalt varierades; storleken på tillrinningsområdet, crop factor, växtsubstrat, djup på regnbäddarna, växtval, dräneringsdjup och dräneringshastigheten. Alla simuleringarna genomfördes med meteorologisk data för perioden 1991-2020 för att underöka hur årsvariationer påverkar vattenhalten i systemet. Resultaten visar att stadsträd som inte erhåller något tillskott av vatten via tillförsel av dagvatten kommer utsättas för extremt ogynnsamma förhållanden när det kommer till vattentillgång, och att den parameter som har störst inverkan på vattenhalten i BGG-system är storleken på tillrinningsområdet. För att ytterligare förbättra vattentillgången för träden i BGG-system kan växtsubstratet förbättras genom att öka mängden växttillgängligt vatten. Detta föreslås dock framförallt för större träd eller då tillrinningsområdet inte kan utökas ytterligare. Variationen av djupet på regnbäddarna har relativt liten effekt på resultatet, vilket delvis kan förklaras av andra val i satta parametrar. Växtvalet visar sig i denna studie har liten effekt på vattenhalten, vilket delvis beror på modellens utformning och valdaparametrar. Variationen av dräneringsdjupet och dräneringshastigheten visar sig inte ha någon effekt på de resultat som undersöks i denna studie. Modellen som har satts upp beskriver systemet på ett tillförlitligt sätt, och är ett bra första steg föratt ytterligare öka förståelsen för trädens förutsättningar i dagvattenhantering. Men för att kunna dramer långtgående slutsatser om hur träden klarar av torrperioder behöver ytterligare undersökningargenomföras på BGG-system. / The main purpose of this study was to investigate which parameters have the greatest impact on thetrees’ water supply in BlueGreenGray-systems (BGG-system), developed by Edge, and what improvements can be made to the system to make the vegetation able to withstand periods of droughts better. Another aim of this study was to investigate how well it is possible to imitate and simulate BGG-systems in the modeling tool MIKE SHE, developed by the Danish Hydraulic Institute (DHI). To investigate which parameters have the greatest impact on the water content in BGG-systems the following parameters was varied; the size of the catchment area, crop factor, plant substrate, depth of the rain beds, plant selection, drainage depth and drainage rate. All simulations were performed with meteorological data for the period 1991-2020 to investigate how annual variations affect the watercontent in the system. The results show that city trees that do not receive any addition of water via the supply of stormwater will be exposed to extremely unfavorable conditions when it comes to water supply, and that the parameter that has the greatest impact on the water content in BGG-systems is the size of the catchment area. To further improve the water supply for the trees in a BGG-system, the plant substrate can be improved by increasing the amount of plant available water. However, this is mainly proposed for larger sized trees or when the catchment area cannot be expanded further. The variation in the depth of the rain beds has a relatively small effect on the result, which can be partly explained by other choices in set parameters. The choice of plant in this study has little effect on the water content, which is partly due to the model’s design and selected parameters. The variation of the drainage depth and the drainage rate does not appear to have any effect on the results examined in this study. The model that has been set up describes the system in a reliable way, and is a good first step to furtherincrease the understanding of the trees conditions in stormwater management. However, in order tobe able to draw more far-reaching conclusions about how trees cope with dry periods, further studiesneed to be carried out on BGG-systems.

This dissertation argues that stormwater management is fragmented both at that vertical fragmentation (at the level of intergovernmental relations) and horizontal fragmentation (within the level of governments). The first essay focuses on the institutional arrangements used by states to implement stormwater management policies. Building on the race to the bottom literature, I examine the impact of the institutional arrangement centralization on state water quality in California, Texas, Virginia, and Minnesota. A five-year (2013-2018) permitting cycle was used to analyze five dimensions: formalism, coercion, education, prioritization, and accommodation.There is an inverse relationship between the quality of stormwater and the degree of centralization in the institutional arrangements adopted by state governments to implement their stormwater management policies. The second essay focuses on a local government's decision to join an inter-local agreement to comply with federal/state stormwater management policies. Building on the transaction cost framework, the study used a cross-sectional design to analyze a case study. The case study consists of 119 cities subjected to stormwater regulation requirements in northern Texas during 2017. The dependent variable is the membership of the regional inter-local agreement, and the independent variables are the number of neighboring cities and population density. Community wealth, public works spending, stormwater fees, government type, and the percent of the population over 65 were used as control variables. Logistic regression was used for data analysis. This study concludes that the increase in the number of neighboring regulated local governments is associated with an increase in the likelihood of a decision by the regulated local government to join an interlocal agreement (ILA), as well as finding that an increase in the population density is associated with an increase in the likelihood of a decision by the regulated local government to join the ILA. In addition, the study found that the type of government also affects a decision to enter into a cooperative relationship to meet the regulative burdens associated with implementing the stormwater management policies imposed by state/federal governments. The results found in this dissertation contribute to bridging the gap in our knowledge on the impact of the institutional framework adopted by the states to implement environmental policy through empirically evaluating the effect of institutional arrangements (as represented in the States general MS4 permits) on the policy output (reducing the level of stormwater pollution).

Much like other cities Stockholm has traditionally used a technical system for managing stormwater. With time this system has become overburdened and has led to large environmental concerns. To reach water quality goals set by the EU Stockholm needs to decrease pollution released to recipients by 70-80%.  Green infrastructure (GI) has increasingly been used as an alternative and addition to technical stormwater systems. Many studies have been conducted on different solutions and their stormwater management performance. The City of Stockholm have done research on numerous solutions to evaluate their performance in the context of Stockholm as well. However, implementation in the inner city is slow, thus this study explores why this is the case, and how Stockholm’s stormwater management goals can be reached. Stockholm predominately uses trees planted in plant beds using structural soil, and a combination of constructed wetlands and wet ponds for stormwater management. In new developments there is no real concern, as the GI can be included in planning at an early stage. Including these solutions in existing environments causes issues related to space, both above and below ground, and costs. Therefore, other solutions need to be found. This study explored green roofs, green walls and permeable pavements as possible options. Additionally, it found that finding new space that has previously not been used for GI could be an option. To mitigate financing issues new ways of promoting investment into GI from private property owners could be utilized, but that there also is a mismatch between supposed support for sustainable stormwater management on the political side and funds allocated. Finally, the study recommends that Stockholm takes the technical systems into account and explores what GI measures best work together with it to more effectively decrease pollution.

Increased urbanisation and climate change are negatively affecting the water cycle and are increasing floods and creating concerns for the built environment and human wellbeing. This has created a need to research sustainable water management in cities. Nature-based solutions (NBS) can offer more sustainable ways of water management, but conventional systems are still favoured in governance. Hence, the aim of this thesis is to identify opportunities and challenges of implementing NBS at Årstafältet in Stockholm and the related governance processes from a Socio-Ecological-Technical system perspective in order to bring a holistic view on sustainable urban stormwater management. The methods used in triangulation for this case study are interviews, a site visit, and desktop study of associated planning documents. The collected data is analysed with an analytical framework that investigates the Social-Ecological-Technical System (SETS) dimensions, in relation to governance. The results show that the implementation of NBS at Årstafältet has been largely successful, due to contextual factors, as well as an adaptive and reflexive governance approach. However, identified system dynamics, interrelations and tensions have shown that there is room for improvements. By increasing transdisciplinarity in early stages of the process to overcome rigid governance structures and techno-centricity. The application of the SETS framework has proved to be successful in identifying dynamics, interrelations, and tensions but there are issues related to uncertainties in how to categorise system components. Nevertheless, the SETS perspective has been useful for identifying challenges and opportunities related to governance and planning processes of implementing NBS.

As rain events are likely to intensify and the proportion of impervious areas in cities increases, greater demands are put on stormwater management. Nature-Based Solutions (NBS) have become more popular over the past decades to be integrated into the stormwater strategy in order to reduce the volume of runoff in cities. For NBS to be effective over long term, maintenance must be prioritized. This study addressed two questions, what are the difficulties in modeling (lack of) maintenance over time and what are the consequences in terms of water quantity with inadequate maintenance on the long- term efficiency of NBS?. This was found by developing a hydrodynamic model in SWMM, where three NBS types were modeled, rain garden, permeable pavement, and infiltration trench. The efficiency of maintenance was investigated by creating several scenarios where different parameters were identified to represent maintenance. The parameters were varied for different precipitation events, as the effect of maintenance depends on the type of precipitation used. In general, inadequate maintenance has been proven to have little impact on rain events with a return period of 2-years, while a large difference could be seen for intense rains. Two consequences as a result of an absence of maintenance are overgrown vegetation and clogging of the media. Clogging was investigated for all three NBS types, and was found to have a large impact on its efficiency over time. The result also shows that despite the inadequate management, NBS can still contribute to manage stormwater, but with lower efficiency. / I takt med att regnen kommer att intensifieras och andelen hårdgjorda ytor i städer ökar, så ställs allt högre krav på dagvattenhantering. Naturbaserade lösningar (NBS) har under senaste decenniet blivit alltmer populära att integrera i dagvattenstrategin för att minska mängden dagvatten i städer. För att NBS ska vara effektiv över tid behöver skötseln prioriteras. Den här studien adresserar två frågor, vilka är svårigheterna med att modellera (bristfällig) underhåll över tid och vad är konsekvenserna av bristfälligt underhåll på NBS effektivitet över tid. Detta besvarades genom att skapa en modell i SWMM där tre NBS typer modellerades, regnbädd, genomsläpplig yta och infiltrationsdike. Effekten av underhåll undersöktes genom att skapa flera scenarion där olika parametrar som identifieras för att representera underhåll. Parametrarna förändrades sedan för olika nederbördstyper, då effekten av underhåll beror på vilken nederbördstyp som studeras. Bristfälligt underhåll sågs generellt inte ha någon större påverkan på 2-års regn, medan en stor differens kunde ses för de intensiva regnen. Igenvuxen vegetation på ytan och igentäppning av media, som konsekvens av undermåttligt underhåll, undersöktes bland annat för de tre NBS typerna, och resultatet visade att det har stor påverkar på dess effektivitet över tid. Resultatet visar också, trots otillräckligt underhåll, att kan NBS ändå bidra till att hantera dagvatten, men med betydligt lägre effektivitet.

The city of Falun has a rich history of mining with the open mine, Stora Stöten, centrally located in the city and nowadays a well-known world heritage tourist attraction. The mine is the main reason that Falun even exists. During its glory days, Falun was one of Sweden’s largest cities, at that time considered to be world-leading in mine engineering and Europe’s main supplier of copper.  A less flattering effect of the mining era was that the city became poisonous and almost unhabitable. Both waters from the mine and from piles of mining waste ended up in rivers and lakes around Falun. Over the years several successful actions have been taken to improve and restore the environment which has decreased the amount of heavy metals leaked into Faluån and lake Tisken. Though, the water is still polluted, and Tisken has in practice for a long period of time worked as a deposit with an increasing amount of poisonous sediments.  This has unfortunately made Falun central waterbodies disabled for human use and made humans no longer have a relationship to the water despite its central location, importance, and potential for the city.  This thesis project seeks to unlock the lost potential of water in Falun by reviving it as a living and interweaved spine in the city in a systematic and schematic approach. The project aims to address the polluted water and sediment challenges while promoting sustainable stormwater and flooding management. A connected green structure linked with a movement network for pedestrians and bicyclists promotes sustainable transport to the spine and existing nodes in the city. The different layers in the project enable new nodes with new potentials for Falun

This study addresses flood risk assessment in the Catalpa Creek watershed, located in northeast Mississippi, USA. Employing the Hydrological Modeling System (HEC-HMS) and the River Analysis System (HEC-RAS), integrated models were developed and calibrated, to predict flood behavior within the watershed. The study conducted flood frequency analyses for return periods ranging from 2 to 100 years and generated flood inundation maps, pinpointing flood-prone areas. Mitigation measures for flood risk management were recommended. The results underscore the effectiveness of the integrated modeling approach for simulating and understanding the complex dynamics of flood events. The research identified critical flood-prone zones, emphasizing the importance of proactive flood risk management. The calibrated hydrological model serves as a valuable tool for stormwater management, water resource planning, and watershed assessment. The study provides insights into flood risk in the Catalpa Creek watershed, offering valuable guidance to regional decision-makers. This study lays the foundation for future investigations in floodplain encroachment, sediment transport, stream restoration, and flood inundation hazard mapping.

Cities worldwide are facing problems to mitigate the impact of urban stormwater runoff caused by the increasing occurrence of heavy rainfall events and urban re-densification. This study presents a new approach for estimating the potential of the Management of Urban STormwater at Block-level (MUST-B) by decentralized blue-green infrastructures here called low-impact developments (LIDs) for already existing urban environments. The MUST-B method was applied to a study area in the northern part of the City of Leipzig, Germany. The Study areas was divided into blocks smallest functional units and considering two different soil permeability and three different rainfall events, seven scenarios have been developed: current situation, surface infiltration, swale infiltration, trench infiltration, trough-trench infiltration, and three different combinations of extensive roof greening, trough-trench infiltration, and shaft infiltration. The LIDs have been simulated and their maximum retention/infiltration potential and the required area have been estimated together with a cost calculation. The results showed that even stormwater of a 100 year rainfall event can be fully retained and infiltrated within the blocks on a soil with low permeability (kf = 10−6 m/s). The cost and the required area for the LIDs differed depending on the scenario and responded to the soil permeability and rainfall events. It is shown that the MUST-B method allows a simple down- and up-scaling process for different urban settings and facilitates decision making for implementing decentralized blue-green-infrastructure that retain, store, and infiltrate stormwater at block level.

Our planet stands before many great challenges, where climate change and urbanization are two of the major challenges. One of the challenges due to climate change is the increased amount of precipitation and of extreme rainfall, which creates a higher amount of stormwater within the urban areas and an increased risk of urban flooding. Urbanization and an increasing global population put pressure on the environment as more land is exploited and existing urban areas are further developed and densified. Urban areas are already under high pressure to handle the risks of climate change, therefore is climate change adaptation prominent to create more resilient and sustainable urban areas, where stormwater management is one of the challenges that need to be tackled. The aim of this study is to answers one main research question and three sub research question about enablers, barriers, and key factors regarding planning, designing, and implementing sustainable urban drainage systems in the built environment. The used methods are literature study research and multiple case study research. Five case study areas where studied to gather knowledge about areas that have implemented sustainable urban drainage systems. Lessons learned for each of the case study areas where gathered and connected to the literature and used to answer the research questions. The gathered knowledge from the literature and case studies where used to compile recommendations of how a sustainable urban drainage system could be planned and implemented at a pilot study area, which is Välsviken in Karlstad, Sweden. To be able to achieve a sustainable and resilient urban drainage system, that can handle the challenges of climate change and urbanization, it is important that the stormwater planning process is changing. It is crucial to implement facilities and systems that are sustainable, multifunctional, and flexible. The planning process needs to use planning and costing approaches that include flood mitigation and co-benefits, in the long-term and short-term simultaneously. Implementation of sustainable urban drainage systems also needs to be enabled in new areas or being retrofitted into already exploited areas. This could make it possible to create urban areas that are able to tackle the challenges of climate change and urbanization, and create multifunctional, sustainable, and flood mitigated urban areas. / Vår planet står inför många stora utmaningar, där klimatförändringar och urbanisering är två av dessa. En av utmaningarna med avseende på klimatförändringarna är den ökade mängden av nederbörd och extrema regntillfällen, vilka bidrar till större mängder dagvatten i urbana områden och en ökad risk för översvämningar. Urbaniseringen och det ökande antalet invånare globalt sätter press på miljön eftersom mer landyta exploateras och nuvarande urbana områden fortsätter att bebyggas och förtätas. De urbana områdena har redan stora utmaningar med att hantera riskerna med klimatförändringarna. Klimatanpassning är därför viktigt för att skapa mer resilienta och hållbara urbana områden, där dagvattenhanteringen är en av utmaningarna som behöver hanteras. Målet med denna studie är att besvara en övergripande forskningsfråga och tre underliggande forskningsfrågor om möjliggörare, barriärer och nyckelfaktorer gällande planering, design och implementering av hållbara urbana dagvattensystem i den bebyggda miljön.  Metoderna som användes var litteraturstudie och multipel fallstudie. Arbetet började med litteraturstudien och sedan genomfördes en fallstudie där fem områden som implementerat hållbara urbana dagvattensystem undersöktes. Lärdomar från varje område sammanställdes och kopplades samman med den andra litteraturen för att besvara forskningsfrågorna.  Utifrån litteraturen och fallstudierna sammanställdes rekommendationer för hur ett hållbart urbant dagvattensystem kan planeras och implementeras inom ett utvalt studieområde, vilket är Välsviken i Karlstad, Sverige.   För att åstadkomma ett hållbart och resilient urbant dagvattensystem, som kan hantera utmaningarna gällande klimatförändringar och urbanisering, är det viktigt att planeringsprocessen för dagvatten ändras. Det är viktigt att implementera anläggningar och system som är hållbara, multifunktionella och flexibla. Planeringsprocessen behöver använda planerings- och kostandsmetoder som inkluderar översvämningsanpassning och sidofördelar, både långsiktigt och kortsiktigt samtidigt. Man behöver också möjliggöra implementering av hållbara urbana dagvattensystem i nya områden eller anpassa områden som redan är bebyggda. Detta kan bidra till att skapa urbana områden som kan hantera klimatförändringarnas och urbaniseringens utmaningar, och skapa multifunktionella, hållbara och översvämningssäkrade områden.

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