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I världen idag pågår en urbanisering, vilket innebär att fler människor flyttar in till städerna. Det innebär att fler bostäder måste byggas för att uppfylla de nya behoven, och detta görs ofta genom förtätning av redan exploaterade områden. Vid förtätning av bostadsområden ökar ofta andelen hårdgjorda ytor. En hårdgjord yta är en icke permeabel yta där dagvatten inte kan infiltrera ner i marken utan istället bildar ytavrinning. Vattnet som avrinner färdas mot lågpunkter i terrängen vilka riskerar att översvämmas. Klimatförändringar väntas leda till häftigare väder, bland annat i form av skyfall. Kraftigare regn i kombination med större andel hårdgjorda ytor väntas öka risken för pluviala översvämningar. För att undvika pluviala översvämningar krävs strategier för att hantera städers dagvatten. Det existerande ledningsnätet är högt belastat och kombineras med hållbara dagvattenlösningar för att minska avrinningen. Grönytor ses ofta som goda infiltrationsytor, men en osäkerhet råder kring hur effektiva olika typer av grönytor är. Det är därför av intresse att undersöka hur goda infiltrationsytor urbana grönområden är och hur stor betydelse de har vid skyfall för att minimera pluviala översvämningar. Syftet med examensarbetet är att undersöka infiltrationskapaciteten för grönytor på ett antal olika platser i Stockholm. Syftet är vidare att undersöka hur resultaten från fältförsöken kan användas i det hydrauliska modelleringsprogrammet MIKE 21 för att återspegla det verkliga infiltrationsförloppet och därmed få en god bild av hur stora översvämningsriskerna är för olika områden. Totalt utfördes 13 separata mätningar i två grönområden i Stockholm. Vid 11 av mätningarna användes en dubbelringsinfiltrometer och vid två av mätningarna användes en enkelringsinfiltrometer. Mätningarna utfördes under 0,5-2 timmar beroende på vattentillgång. Infiltrationsförsöken visade att det finns en stor variation i infiltrationskapacitet, även inom mycket små områden. De visade också att det finns en tendens till högre infiltrationskapacitet för mindre kompakterade grönytor. Kornstorleksfördelningen och vattenhalten skiljde sig inte nämnvärt mellan de två områdena och dessa två parametrar kunde inte kopplas till någon skillnad i infiltrationskapacitet för de två undersökta områdena. Resultaten från simuleringarna i MIKE 21 visade att vilka värden som anges för infiltrationskapaciteten är av större betydelse än på vilket sätt dessa anges. Resultaten visade också att parametrar såsom vattenhalt och porositet hade en inverkan på infiltrationsförloppet men infiltrationszonens mäktighet hade liten inverkan på resultaten. Sammanfattningsvis kan sägas att det finns en stor variation i infiltrationskapacitet för grönytor och den osäkerheten påverkar resultaten vid modellering av översvämningsrisker i MIKE 21. / The ongoing urbanization in the world today means that more people are moving into the cities and therefore more housing is required. When building in cities there is a tendency for an increase in impermeable surfaces. An impermeable surface is defined as a surface where no water can infiltrate into the subsurface soil and instead there is an increase in surface runoff. The water flows through the terrain towards low-lying areas, which are at risk for flooding. Climate changes are expected to result in more extreme weather such as extreme rain. An increase in extreme rain in combination with more impermeable surfaces will increase the risk for pluvial flooding. To avoid pluvial flooding different strategies is required to cope with the urban stormwater. The traditional stormwater systems are usually put under high stress and sustainable stormwater management needs to be implemented to decrease the surface runoff in urban areas. Green areas are often thought to be good infiltration surfaces but there is a big uncertainty in regards to exactly how effective different green areas is for infiltration purposes. There is an interest to investigate how good the infiltration capacity is for urban green areas to map and to mitigate pluvial flooding. The aim for this master thesis is to investigate the infiltration capacity through field measurements for two different green areas in the city of Stockholm, Sweden. Furthermore, the aim is to investigate how the results from the field measurements can be implemented in the hydraulic modelling software MIKE 21 to represent the real infiltration pattern in order to map the risk for pluvial flooding for different areas. A total of 13 measurements were conducted in two green areas around Stockholm, using a double ring infiltrometer. For two of the measurements a single ring infiltrometer was used. The measurements were conducted during 0.5-2 h depending on the water accessibility. The field measurements showed that there is a large variability in infiltration capacity, even within very small areas. The measurement showed that there was a tendency for higher infiltration rates for less compacted soil. The grain size distribution showed little impact on the infiltration rate, and so did the water content. The simulations in MIKE 21 showed that the magnitude of the infiltration rate is of greater importance than the way it is implemented in MIKE 21. The results also showed that parameters such as water content and porosity had an effect on the infiltrated volume, but the depth of the infiltration zone had little impact on the results. In conclusion, there is a large variability in infiltration capacity for green areas and this uncertainty does affect the results when modelling the risk for pluvial flooding in MIKE 21.

“Global floods and extreme rainfall events have surged by more than 50% in the past decade and recent studies show that they are occurring four times higher than in 1980” (Neslen, 2018). At the same time, the urban population is rising. Today, 55% of the world’s population lives in urban areas and it is estimated to increase to 70% by 2050 (United Nations, 2018). This expansion of urbanized areas is correlated with the increase of impermeable surfaces that, in case of extreme weather events, are not able to drain the water efficiently. The rainfall-runoff is channelled from roads, parking lots, buildings, and other impervious surfaces to storm drains and sewers that cannot handle the volume. The high ratio of impermeable surfaces and the increased extreme rainfall events cause severe environmental, social, economical problems in urban areas. Merely technical and engineering solutions are no sufficient, therefore a new approach that can maintain and adapt the natural water cycle inside the urban areas is needed. Ecosystem services and resilience thinking have become key principles in adaptation strategies at different levels, from international policies (e.g. Sustainable Development Goals) to local actions (e.g. Copenhagen adaptation plan 2015) and design (e.g. climate resilient San Kjeld in Copenhagen). In this scenario, the design approach of Water Sensitive Urban Design (WSUD) aims to promote resilience at the local level by managing stormwater, encouraging the defence of the aesthetic value of green and blue areas. WSUD is a multidisciplinary approach that involves water management, urban planning, architecture, and landscape design. The main idea of WSUD is that sustainable stormwater systems should be beautiful, meaningful, and educational (Echols, 2007). This master thesis explores the concept of Water Sensitive Urban Design and its application in the cities of Copenhagen, Malmö and Rotterdam. The case study of PHVision in Heidelberg, Germany, is analysed from the concept of WSUD. Design improvements are suggested stemming from the analysed European examples and the theoretical background.

Utilizing survey data gathered from local local level floodplain administrators (FPAs) operating within Federal Emergency Management Agency Region 6, this study provides a more nuanced understanding of perceived competency among FPAs across key floodplain management topics through the use of a principal component analysis (PCA). PCA identified six distinct components related to perceived competency among FPAs including; Modification and Update Process, General Knowledge, Grants and Programs, Analysis, Development and Real Estate, and Administration and Outreach. The study then employed regression analyses to identify organizational and individual level characteristics that predict perceived competency. Data analyses identified several organizational variables as significant positive predictors of perceived competency including working within an urban community, full-time job status and overall workload percentage dedicated to floodplain management. Additionally, several individual characteristics such as educational attainment, professional certification, previous disaster experience, and years of experience working as an FPA were also identified as significant positive predictors of perceived competency. Based on these findings the study makes several recommendations about improvements to training and educational materials for practitioners and students.

No description available.

Flooding is and remains to be a serious hazard to human society, with about one in five people globally living within 1 in 100 year flood risk areas. Previous research shows that there are social and economic inequalities in flood exposure, with deprived groups often being more at risk. Exposure studies investi- gated a variety of socioeconomic characteristics over the years by overlaying social data with modelled flood hazard areas. New studies reveal, however, that there can be significant socioeconomic differences between populations in theoretical hazard zones, as predicted by flood models, and flooded areas during extreme events. Despite this, case studies are still rare and are mainly limited to the United States. This thesis explores how material deprivation differs between modelled and flooded areas during the 2007 floods in Gloucester and Kingston upon Hull in the United Kingdom. During this extreme event, more advantaged areas experienced more flooding, both inside and outside the modelled flood hazard zones. In Gloucester, more deprived areas were covered by the modelled hazard map but were not flooded during this event. This work sheds light on the importance of using both hazard models and maps of real events when studying flood exposure. Without considering how social and economic factors can interplay with exposure to natural hazards, disaster management strategies will not be able to protect all vulnerable groups.

The sheer volume as well as the schema complexity of today’s graph databases impede the users in formulating queries against these databases and often cause queries to “fail” by delivering empty answers. To support users in such situations, the concept of differential queries can be used to bridge the gap between an unexpected result (e.g. an empty result set) and the query intention of users. These queries deliver missing parts of a query graph and, therefore, work with such scenarios that require users to specify a query graph. Based on the discovered information about a missing query subgraph, users may understand which vertices and edges are the reasons for queries that unexpectedly return empty answers, and thus can reformulate the queries if needed. A study showed that the result sets of differential queries are often too large to be manually introspected by users and thus a reduction of the number of results and their ranking is required. To address these issues, we extend the concept of differential queries and introduce top-k differential queries that calculate the ranking based on users’ preferences and therefore significantly support the users’ understanding of query database management systems. The idea consists of assigning relevance weights to vertices or edges of a query graph by users that steer the graph search and are used in the scoring function for top-k differential results. Along with the novel concept of the top-k differential queries, we further propose a strategy for propagating relevance weights and we model the search along the most relevant paths.

Climate change is predicted to cause an increase in cloudbursts and heavy precipitation, which makes urban flooding an issue that needs to be dealt with. The term Sponge city is a theory that intends to deal with urban flooding and worsening water quality in urban areas with absorption. The study area Hemlingby is an area that has been prone to flooding before, for instance on the 17–18 of August 2021. The area is located about 3 km from the city center Gävle with Hemlingbybäcken running north through the study area. The study was performed in several parts, the first was to use the GIS tool ArcMap 10.8 and hydraulic software CAESAR-lisflood 1.8 to investigate which areas are considered sensitive. In ArcMap 10.8, a bluespot map was created to estimate how much water is needed to fill different areas of Hemlingby, and in CAESAR-lisflood 1.8, the flood inundation area was mapped based on different water flow scenarios. Subsequently, two site visits were made to the study area to photograph and validate the results from the GIS analyses. Based on the GIS analyses, an interview with the municipality of Gävle and an extensive literature analysis, measures were identified that suited both the concept and the study area. The results show what affects the drainage in Hemlingby and how it could be improved through the use of Sponge city. Hemlingbybäcken, which is easily flooded by large water flows, and the topography of the area are factors that have been identified as particularly problematic for the study area's drainage. To show how the area could be planned after the Sponge city concept, proposals for both types of measure and location have been presented, also restrictions and how similar concepts can be applied in other areas are presented. Given that the frequency and intensity of future cloud bursts are not known, there is no answer as to whether the measures presented in the study would stop the study area from being flooded in the future. Especially when data and statistics from previous rainfall were missing, the area's exact reaction to a cloud burst could not be analyzed. On the other hand, it is possible to determine from the analyzes in the method that the study area was not adapted to the type of downpour it was affected by. Therefore, measures aimed at Hemlingbybäcken become significant as the topography or soil type of the area is much more difficult to influence. In order to investigate exactly what impact the proposed measures would have on Hemlingby, further studies need to be carried out to map both the collection capacity and the impact on Hemlingbybäcken the proposal has. / Klimatförändringar förutspås i framtiden leda till en ökning av antalet skyfall och kraftig nederbörd generellt, vilket gör översvämningsproblematiken i urbana områden till ett allt större problem som måste hanteras. Konceptet Sponge city syftar på en teori vars huvuduppgift är att hantera urbana översvämningar och försämrad vattenkvalitet i städer med hjälp av absorberande ytor. Studieområdet Hemlingby i Gävle är ett område som tidigare drabbats av kostsamma översvämningar vid skyfall, bland annat 17–18 augusti 2021. Studieområdet ligger cirka 3 kilometer från Gävle stadskärna och har Hemlingbybäcken rinnandes norrut genom området. Studien utfördes i flera delar, där den första var att med hjälp av GIS-verktyget ArcMap 10.8 och den hydrologiska programvaran CAESAR-lisflood 1.8 utreda vilka områden som bedöms känsliga för översvämning. I ArcMap 10.8 skapades en bluespot-karta för att uppskatta hur mycket vatten som krävs för att fylla olika områden av Hemlingby och i CAESAR-lisflood 1.8 karterades översvämningsutbredningen utifrån olika vattenföringsscenarion. Därefter utfördes ett platsbesök i studieområdet för att fotografera och validera resultatet från GIS-analyserna. Utifrån GIS-analyserna, intervju med Gävle kommun samt omfattande litteraturanalys identifierades åtgärder som både passade konceptet och studieområdet. Resultatet visade vad som påverkar dräneringen i Hemlingby och hur den skulle kunna förbättras genom implementering av konceptet Sponge city. Hemlingbybäcken, som lätt översvämmas vid stora vattenflöden, samt områdets topografi är egenskaper som identifierats som särskilt problematiska för studieområdets dränering. För att visa hur området skulle kunna planeras efter Sponge city har förslag på både åtgärdstyp och placering presenterats, men även begränsningar och hur liknande koncept kan appliceras i andra områden presenteras. Med tanke på att frekvensen och intensiteten på framtida skyfall inte går att veta exakt, finns inget svar på om åtgärderna presenterade i studien skulle stoppa studieområdet från att översvämmas i framtiden. Eftersom data och statistik från tidigare skyfall till viss del saknats har områdets exakta reaktion på ett skyfall inte kunnat analyseras. Däremot går det att utifrån analyserna i metoden fastställa att studieområdet inte var anpassat för den typen av skyfall det drabbats av. Därför blir åtgärder riktade mot Hemlingbybäcken av mycket stor vikt, eftersom områdets topografi eller jordarter är betydligt svårare att förändra. För att undersöka exakt vilken påverkan föreslagna åtgärder skulle ha på Hemlingby behöver ytterligare studier genomföras för att kartlägga både uppsamlingsförmågan och påverkan på Hemlingbybäcken förslaget har.

This thesis uses flooding driven by Hurricane Harvey in 2017 and a history of inundation in Houston, Texas to critique the systems of floodplain mapping through the National Flood Insurance Program (NFIP). The role of Geographic Information Systems becomes a subject of interest in the context of U.S governance and the role of property as a driving force in urban development. The shortcomings of existing systems of mitigation are examined through mappings that bring measures of risk, damage, and recovery into contrast with each other. Racial and economic inequality are integrated into the analysis through a deeper consideration of the NFIP as the main form of federal protection against losses. Seeing that the NFIP has not protected the true status quo of urban life, it is argued that public perceptions of risk are formed contrary to the logic of home insurance, leading to observable inequalities in preparation and recovery

Extrema skyfall till följd av klimatförändringar blir att vanligare och när de inträffar riskerar de att leda till urbana översvämningar. Den ökade frekvensen av skyfall är anledningen till att urbana översvämningar har lyfts som ett problem i svensk lagstiftning. Enansvarsproblematik har identifierats i relation till detta, då fastighetsägare inte är medvetna om sitt eget ansvar och därför inte anpassar sina bostäder. En kunskapsbrist bland fastighetsägare samt uppfattningen om deras exponering och utsatthet har identifierats som grunden bakom denna problematik. Sommaren 2021 inträffade ett skyfall i Gävle vilket ledde till omfattande översvämningar. Många fastighetsägare drabbades, däribland bostadsrättsföreningar. Hur bostadsrättsföreningar påverkas och resonerar kring översvämningar är ett relativt outforskat forskningsområde i svensk kontext. Av den anledningen blev därför syftet med denna studie att undersöka föreningarnas uppfattning om risk och anpassning. Detta genom att studera ordföranden inom föreningarnas uppfattning om utsatthet, sårbarhet samt möjlighet till hantering i relation till översvämningen. För att ta reda på detta genomfördes semistrukturerade intervjuer. Resultaten visar på att föreningarna har fått en något högre riskuppfattning kopplat till översvämning. I kontrast till tidigare studier kan respondenterna även identifiera ett samband till klimatförändringar. Den faktor som främst påverkade föreningarnas anpassningsförmåga negativt var att det rådde en utbredd kunskapsbrist inom föreningarna. Det finns därmed ett fortsatt stort behov av en ökad kunskap och vägledning från externa aktörer. / Extreme cloudbursts due to climate change are increasing and when these events occur urban flooding is a potential consequence. This is the reason urban flooding has been addressed in the Swedish legislation, at a national level. However, liability issues have been identified, as property owners are not fully aware of their responsibility and therefore neglect adaptation. A lack of knowledge has been identified as the main reason, as well as perception of risk. In the summer of 2021, cloud bursts struck Gävle and caused substantial urban flooding. Many housing co-operatives were affected. Housing co-operatives and how they are affected by flooding is a relatively unexplored research area in a Swedish context and therefore the purpose of this study became to: analyze how experiences of flooding has affected housing co-operatives' perception of risk and adaptation by exploring chairmans perceptions of exposure, vulnerability and flood risk management. Semi structured interviews were performed with chairmans within the boards of the housing co-operatives. The results proved there had been a slight increase in flood risk awareness. The respondents were also able to connect the flood with climate change. However, a large lack of knowledge negatively affects the adaptive capacity of the housing co-operatives. The need for further knowledge and guidance from external actors is therefore large. / Stöd för aktörssamverkan och mångfunktionell anpassning av bostadsområden