Locating potential flood areas in an urban environment using remote sensing and GIS, case study Lund, Sweden

Impervious surfaces, such as large parts of the urban area, reduce infiltration and increase above ground runoff (Chen et al. 2009) with risk of flooding as a result. Urban flooding has the potential to affect a large amount of people, and can cause great harm to economic interests. Therefore it is important to locate potential areas prone to flooding, and have storm water regimes in mind when planning expansions of built up areas (Barbosa et al. 2012). The focus of this paper was to develop and adapt methods to locate potential flood areas in built up areas using remote sensing and GIS analysis. The study area for this study was the city of Lund, located in southern Sweden. The methods included the use of high resolution (0.25 m) near-infrared ortho image and a high resolution (2 m) Digital Elevation Model (DEM). The ortho image was used in a land cover classification to locate and map impervious surfaces, while the DEM was used to map potential flow directions and catchment areas on the impervious surfaces. Precipitation data was used to simulate runoff volumes and was used together with the catchment areas to highlight those areas thought to be most prone to flooding. The resulting catchment areas Focus was initially put on the three catchment areas with the highest accumulated runoff volumes. These were areas with large homogenous surface cover (impervious surfaces) and continuous slope profile. In regard to accumulated runoff volume, these three areas were thought to be most prone to flooding. But in consideration to the method used to locate the areas, they could be said to simply represent the largest continuous surfaces and not necessarily the most flood prone areas. Therefore a runoff index (water level height) was introduced to filter out catchments based on runoff volume and catchment area. This procedure produced a different result with smaller catchments. The results based on the runoff index are thought to be a more accurate representation of the most flood prone areas, due the smaller size of the catchments that decrease the response time from precipitation to accumulation. Limitations of the model For the model to be more accurate, more information regarding drainage would be required as a parameter for infiltration. The land cover classification also introduced a certain amount of misclassification, e.g. in regards to bare soil and impervious surfaces (Lu and Weng 2004). To increase the accuracy, a more specific classification scheme could have been used for impervious surfaces (Han and Burian 2009). Another limiting factor is the flow direction algorithm; the use of a more advanced representation of flow direction could have produced a more realistic result (Zhou et al. 2011).Stadsmiljöer är ofta sårbara vid katastrofer eller extrema väderhändelser. En anledning till detta är att stora delar av de tätbebyggda områden som utgör en stadsmiljö består av ytor som inte tillåter vatteninfiltrering. Detta kan medföra att vissa områden i en stad är mer benägna än andra att drabbas av översvämning. Att lokalisera översvämningsbenägna ytor är en viktig del i en stads uppbyggnad och för att kunna förebygga översvämningar. Arbetet i denna rapport gick ut på skapa och anpassa befintliga metoder för att lokalisera områden som skulle kunna vara i farozonen för översvämning ifall ett kraftigt skyfall skulle inträffa över Lunds stad. För att genomföra undersökningen har detaljerade flygbilder används för att lokalisera så kallade hårdgjorda ytor, en yta som inte tillåter vatteninfiltrering. För dessa områden undersöktes möjliga färdvägar för flödande vatten. Med hjälp av vissa restriktioner lokaliserades ett antal områden som mer benägna att drabbas av översvämningar än andra. De översvämningsbenägna områdena Från undersökningen av flygbildstolkningen framgick det att 26,4% av det studerade området bestod av hårdgjorda ytor, vilka alltså inte tillåter vatteninfiltration. Inom detta urval lokaliserades ett antal områden som mer intressanta än andra, till största delen stora enhetliga ytor med en svacka. Dessa attribut möjliggör nämligen, förenklat, att vatten kan ansamlas i svackan utan att rinna undan. Självfallet förekommer det många sådana ytor inom Lunds stad, men ur resultatet valdes de tre ytor ut som kunde ansamla mest vatten. Men förenklat visar detta resultat egentligen bara vilka områden av de hårdgjorda ytorna som är störst. Istället riktades fokus på de ytor som kunde ansamla mest vatten beroende på ytans storlek, alltså en kvot av tillrunnet vatten genom ytans area. Resultat visade att många mycket mindre områden var mer intressanta än de tidigare beskriva stora enhetliga ytorna. Det kan också tolkas som att dessa mindre ytorna har en kortare tid mellan regn och översvämning än de större ytorna, eftersom sträckan vattnet måste rinna för att nå svackan är kortare än för de stora ytorna. Resultatet visar på att det finns fem olika ytor som beroende på nederbördsmängd och tid är de områden som är mest benägna att översvämmas på kortast tid. Vad betyder resultaten? De fem områden som pekas ut i arbetet är intressanta, men de är också beroende på begränsningar som finns i metoden. Tillvägagångssättet skulle kunna vara en användbar metod för undersökningar över områden där man inte har tillgång till all information. Med vissa ändringar i tillvägagångssättet kan resultatet peka ut de områden som är i störst behov av avrinningsbrunnar för att förhindra översvämningar

The application of GIS-based binary logistic regression for slope failure susceptibility mapping in the Western Grampian Mountains, Scotland

Slope failure has resulted in significant disruption to the Scottish road network in recent years and failure processes are widely considered to pose a very real risk to both infrastructure and road users. The manifestation of proposed regional climate variations could increase the hazard posed by landslide and debris flow activity within upland environments. It is therefore in the interests of decision makers and land managers to delineate the susceptibility of these areas to failure activity. The availability of accurate and high resolution geophysical data presents an opportunity to conduct a susceptibility analysis of proposed risk areas based on existing sites of failure. It is considered that failure sites are identifiable prior to activity and that events are triggered by external forcing in the form of excessive antecedent precipitation conditions. Binary logistic regression analysis is utilized to identify independent geophysical parameters that have been most associated with instances of past failure events. This technique facilitates the delineation of locations characterized by key parameter conditions most inductive to failure given the occurrence of an external trigger. It is proposed that when exposed to external forcing these locations are most susceptible to failure. To identify these locations is paramount to the successful application of any monitoring and/or preventative strategy. A Geographical Information System (GIS) is the ideal platform from which to undertake such a susceptibility analysis as it facilitates the precise identification of key independent parameter data associated with recorded instances of existing failure locations. The preparation, storage, extraction and analysis of intrinsic geophysical parameters promotes the development of a consistent modelling approach which can be applied to additional regions in the future

Methane exchange in a boreal forest: : the role of soils vegetation and forest management

Popular Abstract in English Forests have a positive impact on the level of greenhouse gases in the atmosphere because they absorb carbon dioxide through photosynthesis and store carbon in the soil. Moreover, many forests function as a sink for the greenhouse gas methane (CH4). The uptake of CH4 takes place in well-aerated soils through oxidation by methanotrophic bacteria. However, there is a net production of CH4 in anaerobic soils, such as submerged soils, by microorganisms, archaeans. CH4 dissolved in ground water can be taken up by trees and discharged through stems or foliage. CH4 can also be formed in green plants and emitted, which mainly occurs when plants are exposed to high UV radiation, high temperature, or if the foliage is damaged. The work in this thesis focus on the CH4 exchange in a boreal forest, at the research station Norunda, in central Sweden. The aim is to quantify the net CH4 exchange at the site and investigate what factors constitute the main control of the exchange in soil and vegetation. The impact of clear-cutting, stump harvesting and thinning on the CH4 exchange was also studied. Chamber measurements in undisturbed and thinned forest show that the soil is a sink of CH4. The uptake generally benefits from a large groundwater depth, low soil moisture and high temperatures. Chamber measurements on clear-cut and stump harvested plots show net emissions, which is associated with increased groundwater levels and increased soil moisture as a result of harvesting. Branch chamber measurements on shoots of spruce, pine, birch and rowan also show an uptake of CH4, which is in contrast to previous studies, mostly done in laboratories, which found net emissions from plants. Uptake by vegetation correlated with photosynthetically active radiation, which indicates a coupling to photosynthesis. Unlike our measurements on soil and vegetation, results from our micrometeorological measurements above the canopy showed net emissions from the forests to the atmosphere. These measurements represented a larger area than the chambers and differences could therefore be explained by large CH4 production in small wet areas, which exceeds the uptake in the rest of the soil. However, scaling of soil chamber measurements based on elevation data, indicate that the soil in the main study area was a sink of CH4 regardless of some minor areas with CH4 production. CH4 emissions from vegetation or transport of CH4 from surrounding source areas are other possible explanations for this discrepancy

Factors affecting the invasion of Pteronia incana (Blue bush) onto hillslopes in Ngqushwa (formerly Peddie) District, Eastern Cape

The factors that influence the invasion of hillslopes by the shrub Pteronia incana in the communal rangelands of Ngqushwa (formerly Peddie) district were investigated. Mgwalana, one of the catchments in the district where encroachment by the species is widespread, was chosen. The study combined field observations with image analysis based on high resolution infrared imagery. The catchment was flown and high resolution infrared images (1mx1m) were taken using a Kodak DCS420 digital, colour-infrared camera. The images were analysed using Idrisi32 and Kilimanjaro GIS versions. The ability of different vegetation indices to separate P. incana from the other cover types was investigated. Field observations of the degree of P. incana invasion in relation to, inter alia, soil surface conditions, slope angle and visible forms of erosion were made. A Digital Elevation Model (DEM) of 20m spatial resolution was used to derive terrain parameters. The presence and absence of P. incana in relation to slope gradient and aspect were determined. The combined influence of the two terrain parameters and land use on the invasion was also investigated. The Topographic Wetness Index (WI), a component of the TOPMODEL was derived from the DEM and its relationship with the spatial distribution of P. incana was explored. Soil moisture dependencies for P. incana and grass species as well as surrogates for runoff under the shrub and adjacent bare areas were determined in the field. A high level of classification accuracy confirmed the reliability of digital camera imagery for spatial analyses. Distinct spectral separability for the surface vegetation cover types was achieved by means of the Perpendicular Vegetation Index (PVI) as opposed to the ratio based vegetation indices (NDVI, SAVI and MSAVI). The absence/presence of P. incana was noted to be strongly influenced by slope angle and aspect. The probability for P. incana occurrence increased with slope steepness and southerly slope orientation. Abandoned and grazing lands were identified as the main invasion hotspots. Blanket invasion of the former signified the high susceptibility of abandoned land to P. incana invasion. The combined influence of land use, slope gradient and aspect was also noted to have promoted the invasion. This is borne out by the concentration of the invasion on abandoned steep slopes with a southerly orientation. Local topographic variations were identified as having a strong bearing on P. incana spatial distribution. The topographically driven WI confirmed this relationship, such that P. incana was associated with the low WI values of convexities. Differences in the moisture dependencies between P. incana and grass species were demonstrated by the greater rooting depth of the former. During field surveys, soil surface crusting was noted as inherent to P. incana patchiness. The coupling between local topography and soil surface crusting underpins soil moisture variability at hillslope and patch scales respectively. This in turn determines the competition between P. incana and grass species and the eventual replacement of the latter by the former. A close spatial correlation between fully established P. incana and severe forms of soil erosion was observed. Loss of patchiness and expansion of inter-patch bare areas promote runoff connectivity erosion. As most of the runoff becomes run out, hillslopes tend towards dysfunctional systems. Greater soil moisture storage after rainstorms under P. incana tussocks than the adjacent bare areas signifies the shrub’s water harvesting capabilities. The tussocks could thus serve as a starting-pointbuilding- block for the rehabilitation of dysfunctional hillslope systems

Desertification in Europe: mitigation strategies, land use planning: Proceedings of the advanced study course held in Alghero, Sardinia, Italy from 31 May to 10 June 1999

The present volume is based on lectures given at the course held in Alghero, Sardinia, Italy, from 31 May to 10 June 1999 on ‘Desertification in Europe: Mitigation Strategies, Land Use Planning’. It also contains presentations, given by the participating students, on their own research activities and interests. With the adoption of the International Convention to Combat Desertification, which represents a follow up of the Rio recommendations, this publication is timely. It highlights the specific situation of the Southern European regions and provides a comprehensive and state-of-the-art review of this complex issue

Developing a spatial approach to support local flood-risk-based land use planning

Flood-risk-based land use planning is largely a local government responsibility in Australia. In my research I sought to develop a new spatial approach to improve the implementation of flood-risk-based land use planning that can be used by local governments. In Australia, strategies for floodplain management to reduce and control flooding are best implemented at the land use planning stage. Flood-risk-based land use planning results in sustainable land management activities, including floodplain management. Flood-risk-based land use planning is largely dependent on flood behaviour across the land development areas, which can be documented in the form of planning zones that warn land use planners about the flood-threatened area. However, these are often out-dated so do not reflect the influence of recent land use changes. This is particularly for peri-urban areas (largely focus on riverine floods) and expensive to update. Developing a new approach based on geospatial science facilitates the implementation of flood-risk-based land use planning process and can provide a better approach for local governments in terms of cost, accuracy and ease of updating. To develop a new approach, a clear understanding of responsibility for flood-risk-based land use planning, the workflow processes in the authority responsible for such planning, the quality of existing database and how new data sources and the technology (e.g., LiDAR data and crowd source data) that can be used for flood-risk-based land use planning, is essential. The research involved a case study to document the process of flood-risk-based land use planning processes used by a Victorian council, an assessment of flood-relevant database completeness and accuracy, determination of missing datasets and information in the council’s flood-relevant GIS database, and development of methods based on GIS-embedded hydrological models to generate those datasets

Geomorphometrische Struktur eines mesoskaligen alpinen Geosystems

Im Zentrum dieser Arbeit steht die Analyse der geomorphometrischen Struktur eines mesoskaligen alpinen Geosystems am Beispiel des Turtmanntals, Wallis, Schweiz. Diese Arbeit ist als Teilprojekt B1 `Semantische geomorphometrische Strukturdefinition' in das Graduiertenkolleg 437 `Das Relief - eine strukturierte und veränderliche Grenzfläche' eingebunden. Zur Einordnung des Reliefcharakters des Untersuchungsgebietes erfolgte zunächst die Definition und Abgrenzung von Bergen, Gebirgen und Hochgebirgen zu anderen Relieftypen. Eine rein auf geomorphometrischen Kriterien basierende Hochgebirgsdefinition erfasst jedoch nicht alle für eine geomorphometrische Analyse wesentlichen Aspekte der Hochgebirgsnatur. Auf eine universelle Anwendbarkeit zielt die landschaftsökologisch beeinflusste Hochgebirgsdefinition von Carl Troll. Doch auch sie greift letztendlich auf die europäischen Alpen und die dort auftretenden Formen als Typlokalität für das Hochgebirge zurück. Die Sicht auf das skulpturelle Kontinuum des Georeliefs als verschachtelte Hierarchie unterschiedlich großer und unterschiedlich alter Reliefformenassoziationen bildet das theoretische Fundament dieser Arbeit. Da die weiteren Ausführungen auf dieser Reliefsicht basieren, werden die grundlegenden Konzepte der Geomorphometrie und der Reliefgliederung systematisch erläutert. Sie umfasst Eigenschaften des Georeliefs wie die Dimensionsorientierung und die Bildung von räumlichen Strukturen. Darauf folgt eine systematische Darstellung wichtiger Konzepte zur Gliederung des Reliefs unter geomorphologisch/geomorphometrischen Gesichtspunkten. Die Auffassung des Reliefs als Palimpsest von Reliefformen findet auch ihren Niederschlag im anschließend vorgestellten Katalog von Reliefformen des Hochgebirges. Gleichsam als Konkretisierung der eingangs gegebenen Hochgebirgsdefinitionen werden hier die typischerweise in einem Hochgebirgstal auftretenden Reliefformen unter Berücksichtigung geomorphometrischer und topologischer Aspekte erläutert und durch zahlreiche Photographien illustriert. Die Fachliteratur bietet eine Vielzahl geomorphometrischer Methoden und Techniken zur quantitativen Beschreibung des Reliefs im Allgemeinen und des Hochgebirgsreliefs im Speziellen. Einem Überblick über diese Methodenvielfalt ist ein eigenes Kapitel gewidmet. Der Überblick umfasst sowohl Methoden zur Beschreibung spezifischer Reliefformen und der Verteilung von Reliefformen im Raum als auch Methoden der Berechnung geomorphometrischer Parameter und der Ableitung von Objekten aus dem Kontinuum des Georeliefs respektive dem digitalen Höhenmodell. Eine Auswahl der zuvor beschriebenen Methoden und Techniken zur geomorphometrischen Analyse wurde auf zum Teil selbst erstellte digitale Höhenmodelle des Turtmanntals angewandt. Die Auswahl erfolgte nach den Kriterien der Eignung für die Analyse des Hochgebirgsreliefs, den Möglichkeiten zur Beschreibung geomorphometrischer Struktur und der Anwendbarkeit auf die vorhandenen Daten. Die Eignung geomorphometrischer Parameter und Methoden zur Analyse der geomorphometrischen Struktur des Georeliefs ist von der betrachteten Raumskale abhängig. Geomorphometrische Analysen wurden deshalb auf verschiedenen Raumskalen des Reliefs durchgeführt. Untersucht wurden das Gesamttal, drei ausgewählte Hängetäler und drei Blockgletscher unterschiedlichen Aktivitätsgrades Die geomorphometrische Analyse des Hochgebirgsreliefs erfordert aufgrund des Reliefcharakters neue Methoden und Parameter. Der seit langem beklagte Mangel der Parametrisierung komplexer Reliefformen gilt besonders für die Formen des Hochgebirges. Durch die die Entwicklung und Modifiation geomorphometrischer Parameter und Methoden sowie geomorphometrische Analyse eines alpinen Tales auf unterschiedlichen räumlichen Skalen wurde hierzu ein Beitrag geleistet