The effect of interpolation methods on the quality of a digital terrain model for geomorphometric analyses

Danas su, bez obzira na rapidni razvoj tehnologije, većina prikupljenih (izmjerenih) podataka točkasti uzorci, dakle imaju točnu vrijednost odabrane varijable samo na izmjerenim x, y koordinatama. Da bi se dobile kontinuirane površine koje su neophodne za proučavanje, potrebno je procijeniti vrijednosti na neuzorkovanim područjima koristeći pritom različite metode interpolacije. Glavni cilj ovog istraživanja je vrednovanje dviju metoda interpolacije na kvalitetu digitalnih modela reljefa za potrebe geomorfometrijskih istraživanja. Za izradu modela i usporedbu metoda interpolacije korišten je skup visinskih podatka dobiven vektorizacijom izohipsi s HOK-a. Testirane su dvije metode interpolacije: triangulacijska nepravilna mreža (TIN) i ANUDEM (Topo to Raster). Za odabir prikladnije metode interpolacije korišteno je 8 statističkih parametara, grafički prikazi (dvodimenzionalni i trodimenzionalni), i geomorfometrijski parametar (nagib padina). Utvrđeno je da je ANUDEM bolja metoda za geomorfometrijska istraživanja od TIN-a. Analizom geomorfometrijskog parametra (nagib) zaključeno je da ne postoje značajnije razlike između DMR dobivenih iz različitih skupova visinskih podataka.Despite the modern technological advancements, contemporary methods of data gathering still rely on point samples, which means they feature a precise variable info only on specific x, y - coordinates. In order to get a continual representation of a surface necessary for research, it is necessary to approximate various data values on those surfaces which have not been sampled by using various methods of interpolation. The main aim of this research is to evaluate two different methods of interpolation based on the quality of digital terrain models used for geomorphometric analyses. For the purposes of developing and comparing these methods, a set of elevation data was attained by vectorization of contour lines from HOK. Two methods of interpolation were tested: triangulated irregular network (TIN) and ANUDEM (Topo to Raster). In order to get a more appropriate method, the research employed eight statistical parameters, various graphical representations (both two- and three-dimensional) and geomorphometric parameter of slope inclination. The research shows that ANUDEM is a better method for geomorphometric analyses than TIN is. After the analysis of geomorphometric parameters (slope), the conclusion is that there are no significant differences between the digital terrain models developed on the bases of different sets of elevation data

Analysis and visualisation of digital elevation data for catchment management

River catchments are an obvious scale for soil and water resources management, since their shape and characteristics control the pathways and fluxes of water and sediment. Digital Elevation Models (DEMs) are widely used to simulate overland water paths in hydrological models. However, all DEMs are approximations to some degree and it is widely recognised that their characteristics can vary according to attributes such as spatial resolution and data sources (e.g. contours, optical or radar imagery). As a consequence, it is important to assess the ‘fitness for purpose’ of different DEMs and evaluate how uncertainty in the terrain representation may propagate into hydrological derivatives. The overall aim of this research was to assess accuracies and uncertainties associated with seven different DEMs (ASTER GDEM1, SRTM, Landform Panorama (OS 50), Landform Profile (OS 10), LandMap, NEXTMap and Bluesky DTMs) and to explore the implications of their use in hydrological analysis and catchment management applications. The research focused on the Wensum catchment in Norfolk, UK. The research initially examined the accuracy of the seven DEMs and, subsequently, a subset of these (SRTM, OS 50, OS10, NEXTMap and Bluesky) were used to evaluate different techniques for determining an appropriate flow accumulation threshold to delineate channel networks in the study catchment. These results were then used to quantitatively compare the positional accuracy of drainage networks derived from different DEMs. The final part of the thesis conducted an assessment of soil erosion and diffuse pollution risk in the study catchment using NEXTMap and OS 50 data with SCIMAP and RUSLE modelling techniques. Findings from the research demonstrate that a number of nationally available DEMs in the UK are simply not ‘fit for purpose’ as far as local catchment management is concerned. Results indicate that DEM source and resolution have considerable influence on modelling of hydrological processes, suggesting that for a lowland catchment the availability of a high resolution DEM (5m or better) is a prerequisite for any reliable assessment of the consequences of implementing particular land management measures. Several conclusions can be made from the research. (1) From the collection of DEMs used in this study the NEXTMap 5m DTM was found to be the best for representing catchment topography and is likely to prove a superior product for similar applications in other lowland catchments across the UK. (2) It is important that error modelling techniques are more routinely employed by GIS users, particularly where the fitness for purpose of a data source is not well-established. (3) GIS modelling tools that can be used to test and trial alternative management options (e.g. for reducing soil erosion) are particularly helpful in simulating the effect of possible environmental improvement measures

Pintavalunnan GIS-pohjainen mallintaminen:tapauksena topografialtaan tasainen metsäojitettu Jäälinjärven valuma-alue

Tiivistelmä. Tämän tutkielman aiheena on pintavalunnan mallintaminen paikkatietomenetelmillä. Tutkimuksen tavoitteena on luoda yhtenäinen virtausverkko, joka kuvaa tutkimusalueen päävirtausreittejä, ja alivaluma-aluejaottelu, joka jakaa tutkimusalueen pienempiin alueellisiin tarkasteluyksiköihin. Tutkimuksen kohteena on Oulussa sijaitseva Jäälinjärven valuma-alue, joka on tunnistettu haitallisen rautakuormituksen lähteeksi sen alapuolisissa vesistöissä. Pintavaluntamallin pohja-aineistona käytettiin 2 m x 2 m resoluution digitaalista korkeusmallirasteria ja mallin uomaoptimointiin maastotietokannan vesistö- ja tiestöaineistoja. Uomaoptimointi tarkoittaa virtauksen kohdistamista uomaverkostoon. Alueen uomaverkosto poltettiin korkeusmalliin stream burning -menetelmällä sekä madaltamalla tiepenkereet teiden alittavien tierumpujen kohdilta. Hydrologinen eheytys toteutettiin breaching-menetelmällä ja pintavalunnan mallinnus yksisuuntaisella D8-virtaussuunta-algoritmilla. Valunnan kumuloitumisen mallinnuksella määritettiin virtausverkko muodostumaan yhden hehtaarin kokoisilta valuma-alueilta alkaen. Virtausverkko luokiteltiin yläpuolisen valuma-alueen koon mukaan kuuteen luokkaan. Alivaluma-alueet määritettiin virtaussuunta- ja valunnan kumuloitumisen tulosrasterin pohjalta sekä 14 purkupisteen mukaisesti. Mallinnusalgoritmit suoritettiin ArcGIS Pro -paikkatieto-ohjelmiston ja avoimen lähdekoodin GIS Whitebox Geospatial Analysis Tools -ohjelmiston työkaluilla. Virtausverkon avulla tunnistettiin tutkimusalueen päävirtausreitit. Mallin paikkansapitävyyttä tarkistettiin maastossa tehtyjen havaintojen avulla, ja virtausverkko muodostui todellisten päävirtausreittien mukaisesti alivaluma-aluejaottelin mittakaavassa. Uomaoptimoidun mallin lisäksi tuotettiin vertailumalli yksinkertaisemmilla mallinnusmenetelmillä, ilman uomaoptimointia. Mallien vertailun pohjalta tunnistettiin tekijöitä, jotka vaikuttavat mallin lopputulokseen, ja arvioitiin uomaoptimoidun mallin sopivuutta tutkimuksen tavoitteisiin nähden. Työssä mallinnetuilla aineistoilla voidaan toteuttaa valuma-aluesuunnittelua: rautakuormituksen kannalta haitallisten hydrologisten yhteyksien vähentämistä, veden pidätystä, vesiensuojelurakenteiden tarpeen arviointia ja soveltuvan vesiensuojelurakenteen suunnittelua. Aineistojen avulla voidaan kohdentaa vesiensuojelutoimia ja resursseja alueille, joilla siitä on eniten hyötyä

Analyse von linearen Abflusswegen und ihr Einfluss auf die Effektivität von Gewässerrandstreifen

Österreich fördert im Agrar-Umweltprogramm ÖPUL 2007 erstmal die Anlage von Gewässerrandstreifen zum Schutz von Fließ- und Oberflä-chengewässer durch Sediment- und Nährstoffeinträge aus landwirt-schaftlich genutzten Flächen. Die vorliegende Diplomarbeit befasst sich mit der Analyse von linearen Abflusswegen in der Landschaft und ihre Auswirkungen auf die Effek-tivität von Gewässerrandstreifen. Oberflächenabfluss und darin ent-haltene Sediment- und Schadstoffe, können durch anthropogen beding-te, lineare Strukturen wie Straßengräben, konzentriert werden und so an Filterstreifen vorbei, direkt in Fließgewässer münden. Im gesamten Bundesgebiet wurden drei Fördergebiete ausgewiesen. Die Analyseergebnisse dieser Arbeit beziehen sich ausschließlich auf das Fördergebiet im südlichen Weinviertel, in Niederösterreich. Dort wurden fünf, für das gesamte Gebiet repräsentative, Testgebiete aus-gewählt. Anhand von Kartierungen im Gelände, wurden lineare Abflusswege erhoben und anschließend mittels GIS (Geographisches Informations-system) in Höhenmodelle integriert. Die Analysen wurden mittels drei Höhenmodellen mit unterschiedlicher Auflösung durchgeführt. Auf diese Weise wurde der Einfluss der Rasterweite auf die Ergebnisse ge-prüft. Auf Basis dieser Höhenmodelle wurden alle weiteren Berech-nungen durchgeführt. Für die Modellierung des Oberflächenabflusses wurden zwei unter-schiedliche Algorithmen (D8 und D-Infinity) verwendet. Dies wurde durchgeführt, um den Einfluss der verwendeten Algorithmen auf die Ergebnisse gering zu halten. Ziel dieser Berechnungen war es, die Testgebiete in Teileinzugsgebiete zu untergliedern. Es wurden einerseits Gebiete ausgewiesen, die durch potentielle Gewässerrandstreifen geschützt in den Vorfluter entwäs-sern. Zum anderen wurden Gebiete ausgewiesen, die in lineare Struk-turen wie Straßengräben oder Kanäle entwässern und deren Oberflä-chenabfluss ungeschützt durch Filterstreifen, in den Vorfluter mün-den. Aus diesen Teileinzugsgebietsflächen wurde ein Flächenverhält-nis erstellt. Die Bodenerosionswerte für die Testgebiete standen ebenfalls zur Ver-fügung. Diese wurden anschließend mit den ermittelten Teileinzugsge-bieten verschnitten, um festzustellen, wie vulnerabel die Testgebiete in Bezug auf Bodenabtrag durch Wasser sind. Es ergaben sich Bodenab-tragswerte von minimal 1,8 t/ha/y und maximal 4,0 t/ha/y. Im Bezug auf die erstellten Flächenverhältnisse war das Ergebnis im besten Fall, dass das gesamte Testgebiet geschützt durch potentielle Gewässerrandstreifen in den Vorfluter entwässert. Im schlechtesten Fall war das Testgebiet lediglich zu rund 60 % geschützt, die restlichen 40 % des Einzugsgebietes entwässerten ungeschützt in den Vorfluter. Bezüglich des Einflusses der Rasterweite der Höhenmodelle, kann zwar gesagt werden, dass das Höhenmodell, das auf Basis des hochauf-lösenden Laserscans (1 m Rasterweite) erstellt wurde, die besten Er-gebnisse lieferte, eine eindeutige Aussage konnte allerdings nicht ge-troffen werden. Wesentliches Ergebnis dieser Arbeit ist, dass anthropogen bedingte, li-neare Abflusswege in der Landschaft Einfluss auf die Effektivität von Filterstreifen haben. Durch sie wird Oberflächenabfluss vielfach an Gewässerrandstreifen vorbei geleitet und vermindert so ihre Effektivität. Bei der Anlage von Gewässerrandstreifen sind gute Kenntnisse über die Abflusssituation im Gelände entscheidend. Um Gewässer vor Sediment- und Nährstoffeinträgen besser schützen zu können, sind weiters Maßnahmen sinnvoll, die bereits im Vorfeld eines Gewässerrandstreifens wirken, wie beispielsweise konservieren-de Bodenbearbeitungsmaßnahmen.The main objective of this thesis is an analysis of convergent surface runoff in landscape and its impact on the efficiency of vegetated filter strips. In highly agriculturally used regions, surface runoff often contains sediments, pollutants and nutrients which badly influence the stream water quality. Flow convergence often takes place in ditches or chan-nels. Hence, surface runoff is not buffered through vegetated filter strips before entering surface water. On the basis of field mapping, ditches, channels and comparable linear structures were mapped in five test areas. These linear structures were integrated into digital elevation models (DEM). To analyse the impact of grid resolution, three different DEM’s were used. To model surface runoff two different algorithms were used. In this way the catchment area from which surface runoff was routed through vegetated filter strips was compared to the catchment area which drained directly into ditches or channels and therefore bypasses the filter strips. By using these algorithms, which were implemented in a GIS (Geographic Information System), surface ratios of protected against unprotected areas were computed. The catchment areas obtained were related to soil erosion data to prove the vulnerability of these areas. The main conclusion of this thesis is that linear flow paths may con-centrate water flow before surface runoff enters the aquatic ecosystem. Because of these flow paths, convergent runoff takes place and by-passes vegetated filter strips, thus reducing their effectiveness

Photogrammetrical UAV-based investigation of torrents

Debris flows are a major hazard in mountainous regions. Cost-effective, long-term studies of debris flow torrents, however, are rare, leading to considerable uncertainties in hazard mitigation methods. Here, we address the question if cost effective remote sensing techniques can be applied along the hazard assessment of mountain torrents and further to gather accurate, long-term information on the evolution of the catchment. Active torrents prone to debris flows are often devoid of vegetation and hence can be well captured with photogrammetrically derived methods based on uncrewed aerial vehicle (UAV) surveys. The possibility of automatic extraction of torrent parameters from high resolution terrain models, such as cross-section area, gradient, etc., is investigated. The presented methodology yields continuous and automatically derived parameters along the torrent, which is a major advantage compared to discretized field surveys. Cross-validation thereof with field measurements show strong congruence. Those parameters are highly accurate along sharply incised sections with strong limitations along sections with steep adjacent slopes and/or dense vegetation. A further important result of this work is that multiple UAV acquisitions enable a highly accurate mass-balance characterization of watersheds. After a successful co-registration, the M3C2 algorithm provides valuable results, from which debris flow events can be back-calculated and thus support the determination of site-specific model input parameters. A complete debris flow hazard assessment procedure - missing in current guidelines - is presented. We show that such assessments strongly benefit from UAV data and a subsequent automated parameter extraction: The original point clouds allow to obtain a first overview of the torrent. Derived parameters provide further insights such that key sections and weak spots can be identified and precisely evaluated in the field. The study highlights that the extraction of the true location of the ground poses the key challenge. We show that photogrammetric routines are severely limited by dense vegetation. We find that UAV data can contribute to a comprehensive, reproducible, and objective assessment of torrent processes and predispositions. However, ground-truthing fieldwork remains essential and further research on remote sensing supported hazard assessment of debris flow prone torrents is highly indispensable

Supraglacial lake evolution on the Greenland Ice Sheet

Abstract. Supraglacial lakes form annually on the surface of the Greenland Ice Sheet around Paakitsoq, north of the Jakobshavn Isbrae outlet glacier. The lakes are ephemeral, drain through moulins or crevasses at their bed throughout the melt season, and deliver large volumes of water to the subglacial hydrological system. Such inputs of water can cause spatially and temporally constrained speed-up events affecting the normally slow, marginally-terminating inland ice flow regimes. This dynamic response of the Greenland Ice Sheet to increased basal lubrication is likely to be influenced under global warming scenarios as more meltwater will be produced with increased temperatures. An understanding of the evolution of supraglacial lakes is helpful to understanding the volumes of water delivered to the subglacial hydrological system, and the present study focusing on Paakitsoq investigates lake volume evolution as observed in satellite imagery collected through the melt season in 2008, and through the use of a numerical model to predict lake inputs. The surface energy balance model used is a more advanced numerical model than has been used in previous study and model results are mixed. Conclusions are drawn from model and observed results, and suggest that with further investigation and manipulation, the model may provide accurate results that represent true melt water volumes, and the patterns of observed supraglacial lake evolution on the surface of the Greenland Ice Sheet. It is suggested that the present and future studies on surface lake evolution on the ice sheet would benefit from the collection of data from the Paakitsoq ice surface and from a higher resolution digital elevation model

Exploring the potential impacts of waste disposal sites on ocean ecosystem contamination in Newfoundland: a geospatial analysis and public perception study

This study endeavors to identify historical (closed) and currently operational landfill/waste disposal sites in Newfoundland that might be environmentally sensitive. The primary focus is to understand the potential impacts of these sites on neighboring water bodies and ocean ecosystems. Through the utilization of geospatial analysis, this study examines how waste disposal sites in Newfoundland could possibly contaminate water bodies and ocean ecosystems. Additionally, the study assesses public perceptions concerning the ecological and human health implications of waste disposal sites on the surrounding environment. Employing a geographic information system and the multiple criteria decision-making model, this study assesses the influence of waste disposal sites on nearby water bodies and the ocean. By implementing an analytical hierarchical process, a variety of environmental factors such as soil composition, topography, groundwater vulnerability index, hydrogeology, land use, and land cover are systematically ranked to determine the environmental vulnerability of each waste disposal site. The outcome is presented through a vulnerability assessment map, which categorizes dumpsites based on their level of vulnerability—high, moderate, or low. Recognizing the potential of public engagement to bolster social justice and draw attention to pertinent issues, this study integrates a diverse group of stakeholders such as community members, town councilors, mayors, landfill managers, public health experts, environmental scientists and engineers, provincial government officials, recyclers, and waste disposal service providers. Interviews were conducted with these stakeholders to gain their perspectives on the potential impacts of waste disposal sites on ocean contamination in Newfoundland. From the transcribed interview data, multiple thematic areas pertaining to present waste management practices and the environmental and health ramifications of waste disposal sites were comprehensively identified

Factors influencing thermal variability and fish distribution in small boreal steams / by Lisa McKee.

The spatial variability of stream temperature is an important component of habitat within streams providing optimal temperatures for foraging and thermal refugia for sensitive species such as brook trout. Riparian shading and lateral contributions of groundwater through the hyporheic zone are the main contributors to spatial variability in stream temperature. The first two objectives of this study were to quantify thermal variability in stream systems through extensive mapping of streambed temperatures and to evaluate the influence of thermal variability on the stream fish distribution and community structure. The third objective was to examine associations between thermal variability and environmental variables at reach, riparian and catchment scales to identify features that may be used to characterize thermally important stream reaches. A total of 55 sample sites were surveyed during the warmest and driest season for Northwestern Ontario (mid-July - September) in streams from 4 catchments size classes; 1, 3, 5 and 10 km [squared]. Streambed thermal variability occurred on a sub-metre scale with temperature fluctuating up to 5.8 °C across a transect perpendicular to stream flow. The maximum variability found was 10.1 °C within a 50 m reach and 12.0 °C within a 300 m survey. Thermal variability was driven by cold streambed temperatures; 44 of 55 reaches had larger deviations below the mean streambed temperature than above the mean, which is an indication of cool groundwater entering the streambed. Fish species diversity and brook trout abundance was significantly higher in reaches with high thermal variability, while rainbow trout abundance was significantly lower. Fish species richness within a reach could be predicted as low (5), with thermal variability as an independent variable using logistic regression. High (>0.10) or low (<0.10) rainbow trout abundance (fish/m[squared]) could also be predicted using thermal variability. Fish size was not found to be associated to thermal variability. Furthermore, thermal variability was correlated with terrestrial variables associated with groundwater movement, including the amount of adjacent land contributing surface and subsurface runoff to the stream, also known as reach contributing area (RCA). Reaches with large RCAs had significantly higher levels of thermal variability compared to reaches with small RCAs. However, the relationship between thermal variability and RCA was only found for reaches in the two largest stream catchment size classes (5 and 10 km[squared]) due to the dominance of groundwater during base flow of the two smallest catchments (1 and 3 km[squared]). Areas of low and high thermal variability differed in landscape topography, terrestrial surface roughness, landform geology and streambed permeability, which are all related to groundwater flow. In regions such as Northwestern Ontario, where hydrologic pathways are related to topographic features it is possible to use environmental features, such as RCA, to locate lateral groundwater inputs into streams. This predictive ability allows for identification, management and protection of valued ecosystem components important for the maintenance of ecological integrity of streams. Study area : Nipigon Bay Basin, Northwestern Ontario