Automated Detection of Drainage Networks from Digital Elevation Models

COMPARAÇÃO DA TOPOGRAFIA E DA REDE DE DRENAGEM EXTRAÍDAS DE MODELOS DIGITAIS DE ELEVAÇÃO DO ALOS 3D E LIDAR (PE3D)

Conference Paper

Full-text available

Oct 2020

A crescente utilização de Modelos Digitais de Elevação (MDEs), para estudos hidrológicos, torna evidente a necessidade de verificação da qualidade dos diferentes produtos, hoje disponíveis, através do reconhecimento das suas limitações e dos impactos que estas podem causar nos produtos deles extraídos. Neste contexto, este trabalho objetiva analisar a topografia e as redes de drenagem extraídas para o munícipio de Jatobá-PE, a partir de dois produtos: o PE3D, resultado do levantamento LiDAR do projeto Pernambuco Tridimensional, com resolução espacial de 1 m; e o ALOS 3D, com dados globais disponibilizados gratuitamente para a resolução de 30 m. Foram analisadas também as variações topográficas existentes e consequentes perdas de informação para o modelo do PE3D, após a mudança da resolução de 1 a 10m. Para o estudo de caso, verificou-se que não há perda significativa de informações, para reduções até 10m. Já para as redes de drenagem, em comparação com o ALOS 3D, com resolução de 30m, as redes extraídas do PE3D, com resolução de 10m, apresentam, como esperado, um maior grau de precisão. Isso não descarta, entretanto, o uso dos modelos do ALOS 3D, uma vez que em determinados pontos, este apresentou semelhanças com as redes extraídas dos dados LiDAR. ABSTRACT-The increasing use of Digital Elevation Models (MDEs), for hydrological studies, makes evident the need to check the quality of the different products available today, through the recognition of their limitations and the impacts they can cause on the products extracted from them. In this context, this work aims to analyze the topography and the extracted drainage networks, for the municipality of Jatobá-PE; from two different products, PE3D, resulting froma Lidar survey of the Pernambuco Three-dimensional project, with a resolution of 1m; and ALOS 3D, a global data available free of charge for a resolution of 30m. There were also analyzed the existing topographic variations and consequent losses of information for the PE3D model, after changing its resolution from 1 to 10m. For the case study, it was found that there is no significant loss of information, for reductions up to 10m. The drainage networks derived from As for drainage networks; compared to ALOS 3D, with a resolution of 30m, extracted from PE3D, with a resolution of 10m; presented, as expected, a greater degree of precision. This does not rule out, however, the use of ALOS 3D models, since at certain points; this showed similarities with the networks extracted from the data with higher resolution. Palavras-Chave-Modelo Digital de Elevação, ALOS 3D, PE3D. INTRODUÇÃO A crescente utilização de Modelos Digitais de Elevação (MDEs), para estudos hidrológicos, torna evidente a necessidade de verificação da qualidade dos diferentes produtos, hoje disponíveis,

An integrated method for DEM simplification with terrain structural features and smooth morphology preserved

Article

Full-text available

May 2020

As a key focus of cartography and terrain analysis, the simplification of a digital elevation model (DEM) is used to preserve the pattern features of the terrain surface while suppressing its details over multiple scales. Statistical filtering and structural analysis methods are commonly used for this process. The structural analysis method performs well in identifying terrain structural edges, while it tends to discard the smooth morphology of a terrain surface. In addition, the filter that aims to reduce noise on a surface may over-smooth the terrain structural edges. Therefore, to preserve both the terrain structural edges and smooth morphology, we propose to combine the techniques of statistical filtering and structural analysis. Specifically, all the critical elevation points and structural edges are first detected from the DEM surface by using the structural analysis method. Then, the iterative guided normal filter is used to smooth the generalized DEM with the guidance of the structure of the original surface. After this process, the terrain structure is retained in the smooth surface of the DEM. The experimental results with a real-world dataset show that our method can inherit the merits of both structural analysis and statistical filter in preserving terrain features for multi-scale DEM representations. ARTICLE HISTORY

MNT à très haute résolution spatiale pour la représentation 3d de ravines d'érosion en montagne

Thesis

Jan 2009

A. Jacome

Le suivi et la compréhension de la dynamique spatio-temporelle de l'érosion par ravinement en zones de Badlands (montagnes marneuses à Draix, Alpes Françaises méridionales) ont besoin de méthodes de caractérisation détaillée, rapide et facilement reproductibles de ces phénomènes et de leurs manifestations sur le terrain. Nous avons testé deux approches d'observation spatiales afin de répondre à ces besoins : une approche aérienne à partir de la stéréophotogrammétrie d'images drone (en utilisant des appareils photos « grand public » et des méthodes de traitement informatique existant), et une approche terrestre à partir d'un scan LiDAR terrestre. L'analyse de résultats pour l'approche aérienne montre qu'il existe trois éléments clefs dans la chaîne de traitement stéréoscopique qui permettent de surmonter les contraintes d'une telle application : la préparation de terrain (nombre et distribution des mires) ; la compensation des erreurs systématiques issues de la géométrie d'acquisition d'images (par correction de déformation de lentilles et autocalibrage) ; et la stratégie de corrélation d'image (par algorithme multirésolution et normalisation du relief). Une combinaison adéquate de ces trois éléments nous a permis d'obtenir une précision, un détail et une cohérence hydrographique des MNT drone à la limite de la donnée (résolution d'image originale au sol autour de 3 cm, erreur moyenne en Z de 5 cm). Par rapport à l'approche terrestre, l'analyse du bruit de la mesure LiDAR sur tôles avec des formes géométriques connues nous montre une dispersion autour d'un centimètre pour une distance de mesure de 30 mètres. L'application d'une moyenne simple à un pas régulier d'un centimètre permet de réduire le bruit et aussi de récréer les formes de plus de 3 cm. Pour les formes géométriques plus petites, la dispersion des données est tellement importante qu'il n'est pas possible de les détecter. Le rapport « avantages-contraintes » entre ces deux approches est nivelé par les éléments « étendue-continuité » et « résolution-précision » des MNT résultants. L'approche aérienne produit des MNT avec une étendue et une continuité importante, tandis que l'approche terrestre produit des MNT plus précis et détaillé. Ces deux approches peuvent être considérées comme complémentaires à l'heure d'étudier les manifestations superficielles de l'érosion hydrique en montagnes marneuses. La qualité obtenue par le MNT drone sur les ravines étudiées, après application de toutes les corrections possibles, s'est révélée très proche de la qualité obtenue par les techniques LiDAR. Les résultats révèlent l'énorme potentiel du vecteur drone pour le développement des MNT peu coûteux, avec une très haute résolution spatiale, malgré de nombreuses contraintes. D'autre part, le LiDAR terrestre se révèle comme un système de lever de terrain permettant une rapidité et une répétitivité de mesure, ainsi qu'un niveau de détail intéressant pour le suivi des processus élémentaires d'érosion hydrique et ses manifestations sur le terrain.

Watershed prioritization for soil and water conservation aspect using GIS and remote sensing: PCA-based approach at northern elevated tract Bangladesh

Article

Full-text available

Apr 2020

The current study has been derived to understand morphometric parameters to pledge the reduction in the proclaimed drought influence for climate change. Watershed prioritization has been studied using the geographical information system and remote sensing techniques for soil erosion and water preservation measure at Plio–Pleistocene elevated tract in Bangladesh. Secondary data, i.e., SRTM DEM and the topographical sheets, have been used for the drainage network identification. Seventeen watersheds of fifth order and three watersheds of sixth order are selected for the whole study. Sixteen basic morphometric parameters that are categorized as areal, linear and relief aspects have been used for the study area. The study area comprises sixth stream order that has been obtained using a stream threshold value of 100-m length. Morphometric analysis is suitable for water and soil conservation practice where groundwater and relevant data sets are not available. For the categorization and correlation of the morphometric parameters, principal component analysis (PCA) has been used in the present study. PCA analysis is more suitable, well-known and widely used method for its simplicity to choose more influencing parameters (correlated parameters) that are responsible for watershed prioritization. Strongly correlated components (Dd, Rc, Re and Rb) are used for the compound parameter (Cp) and final priority (Rp) calculation. Low Cp value is suitable for water and soil conservation measure. Therefore, the corresponding low Cp has been taken as one for final priority ranking (Rp) purpose, then second lowest value as two, and so on.

Morphometric Analysis of Major Watersheds in Barind Tract, Bangladesh: A Remote Sensing and GIS-Based Approach for Water Resource Management

Article

Full-text available

Jan 2017

Watershed delineation from grid DEMs in GIS: effects of drainage lines and resolution

Conference Paper

Full-text available

Sep 2006

Watershed delineation is essential process in hydrological modelling and analysis since it allows evaluating the quality and quantity of water resources geographically. Most common approach that commercial GIS software offer is based on grid Digital Elevation Models (DEMs). Water flow direction and flow accumulation grids are required to extract drainage lines in this approach. Therefore, selected threshold value for flow accumulation is a distinctive input for watershed delineation. However, there is not a reliable method to define this value at different DEM resolutions. In this paper, an approach is proposed which is used to determine appropriate flow accumulation threshold value to extract drainage lines and their effect to the watershed delineation by comparing different approaches on this subject. Additionally, effects of the DEM resolution on watershed delineation are studied by using 10-metre and 30-metre DEMs in ArcGIS-ArcHydro and GeoMedia Grid software.

TAŞKIN RİSK YÖNETİMİNDE SAYISAL ARAZİ ALTYAPISI

Conference Paper

Full-text available

Apr 2013

Türkay Gökgöz

Ülkemizde yapılan taşkın çalışmaları incelendiğinde, gerekli çözünürlükte, doğrulukta ve duyarlıkta veriler kullanılmadığı; sayısal yükseklik, arazi ve yüzey modelleri üretiminde ticari yazılımların sunduğu kısıtlı yöntemler ile yetinildiği; bazı kritik aşamalarda deneme yanılma yoluyla öznel tercihler yapıldığı ve bu nedenlerle sayısal arazi altyapılarının yeterince sağlam olmadıkları görülmektedir. Bu durum, taşkın risk yönetimi sürecini başından sonuna olumsuz etkilemektedir. Bu yazıda, öncelikle, Sayısal Yükseklik Modeli (SYM) ile birlikte Sayısal Arazi Modeli ve Sayısal Yüzey Modeli oluşturmada kullanılabilecek global ve ülkemizde üretilen mevcut veriler ele alınmaktadır. SYM'lerden drenaj ağlarının türetilmesinde özel öneme sahip iki faktör (birikinti eşik değeri ve çözünürlük) bir diğer başlık altında incelenmektedir. Yükseklik eğrilerinden üçgen ağları elde edilirken karşılaşılan yatay üçgen sorununa değinilmektedir. Yalnız SYM verisi ile yüksek doğruluklu üçgen ağlarının elde edilmesi için geliştirilmiş bir yöntem tanıtılmaktadır. Son olarak, taşkın risk yönetiminde sayısal arazi altyapısı konusunda politika ve strateji anlamında bazı önerilerde bulunulmaktadır.

Study on feasibility of rainwater harvesting using MAR model in drought-prone Barind Tract, Bangladesh

Article

Full-text available

Oct 2023
Environ Dev Sustain

Bangladesh heavily relies on groundwater resource for all major uses and ranks sixth in the global league of large groundwater extracting countries. Its northwest part—the drought-prone Barind Tract faces challenges in rainfall scarcity and drought; constrain for runoff water conservation due to improper management; low infiltration capacity of thick top surface clay soil layer (Barind clay) to recharge aquifer insufficiently; loss of major portion of runoff water runs toward canals (Kharies), surrounding rivers, etc., immediately after rainfall; less potentiality of groundwater resource development results its depletion due to over-exploitation for domestic and agriculture sectors and eventually discharged into surrounding canals, rivers, etc., in both the dry and monsoon seasons. At the same time, unsustainable water management practice consequences are a rapid declination of groundwater level since the last few decades, the system leads to unbalance condition. Unfortunately, no such study for sustainable water source management has yet been conducted for the area. In this context, rainwater harvesting through artificial recharge of groundwater using managed aquifer recharge (MAR) has been considered as a viable solution to revert the ongoing depletion of this resource and to restore the water balance scenario as a terrific and challenging task. Here, the potentiality of MAR has been considered as an integrated approach of remote sensing and geographical information system using multi-criteria decision-making technique as time-consuming and cost-effective efforts. The potentiality of MAR application covers an area of 448 km² (20%) as ‘highly suitable’; that of 1456 km² (66%) as ‘moderately suitable’; and that of 312 km² (14%) as ‘unsuitable.’ Here, 35% of rainfall is lost as runoff and the remaining 14% as soil moisture. Again, groundwater resource used for irrigation equals 24% of the annual rainfall, whereas that of only 8.5% infiltrates to recharge aquifer naturally, and the rest 68% of runoff water has a scope to injection artificially to revert balanced condition. Using MAR, the cost of recharge per cubic meter of water is about US$ 0.18. Although this is little bit expensive, it can be a valuable gift for economically marginalized and unprivileged Barind communities facing hardship for drinking and agricultural water. Finally, the present study provides a guideline to water resource managers and decision makers to ascertain availability of water resource as lauded in the Bangladesh Water Act (BWA) (2013).

Hydrological, meteorological, and watershed controls on the water balance of thermokarst lakes between Inuvik and Tuktoyaktuk, Northwest Territories, Canada

Article

Full-text available

Jun 2023
HESS

Thermokarst lake water balances are becoming increasingly vulnerable to change in the Arctic as air temperature increases and precipitation patterns shift. In the tundra uplands east of the Mackenzie Delta in the Northwest Territories , Canada, previous research has found that lakes responded non-uniformly to year-to-year changes in precipitation , suggesting that lake and watershed properties mediate the response of lakes to climate change. To investigate how lake and watershed properties and meteorological conditions influence the water balance of thermokarst lakes in this region , we sampled 25 lakes for isotope analysis five times in 2018, beginning before snowmelt on 1 May and sampling throughout the remainder of the ice-free season. Water isotope data were used to calculate the average isotope composition of lake source water (δ I) and the ratio of evaporation to inflow (E/I). We identified four distinct water balance phases as lakes responded to seasonal shifts in meteorological conditions and hydrological processes. During the freshet phase from 1 May to 15 June, the median E/I ratio of lakes decreased from 0.20 to 0.13 in response to freshet runoff and limited evaporation due to lake ice presence that persisted for the duration of this phase. During the following warm, dry, and ice-free period from 15 June to 26 July, designated the evaporation phase, the median E/I ratio increased to 0.19. During the brief soil wetting phase, E/I ratios did not respond to rainfall between 26 July and 2 August, likely because watershed soils absorbed most of the precipitation which resulted in minimal runoff to lakes. The median E/I ratio decreased to 0.11 after a cool and rainy August, identified as the recharge phase. Throughout the sampling period, δ I remained relatively stable and most lakes contained a greater amount of rainfall-sourced water than snow-sourced water, even after the freshet phase, due to snowmelt bypass. The range of average E/I ratios that we observed at lakes (0.00-0.43) was relatively narrow and low compared with thermokarst lakes in other regions, likely owing to the large ratio of watershed area to lake area (WA/LA), efficient preferential flow pathways for runoff, and a shorter ice-free season. Lakes with smaller WA/LA tended to have higher E/I ratios (R 2 = 0.74). An empirical relationship between WA/LA and E/I was derived and used to predict the average E/I ratio of 7340 lakes in the region, which identified that these lakes are not vulnerable to desiccation, given that E/I ratios were < 0.33. If future permafrost thaw and warming cause less runoff to flow into lakes, we expect that lakes with a smaller WA/LA will be more influenced by increasing evaporation, while lakes with a larger WA/LA will be more resistant to lake-level drawdown. However under wetter conditions , lakes with a larger WA/LA will likely experience a greater increases in lake level and could be more susceptible to rapid drainage.

MORPHOMETRIC ANALYSIS OF LLAP RIVER WATERSHED (KOSOVO)

Article

Full-text available

Jun 2023

Hazir S. Çadraku

The Llap River is main tributary of Sitnica River, having a watershed of 780.23 km 2 which extends in northeast part of Republic of Kosovo. In this study, GIS and a high-resolution Digital Elevation Model have been utilized for estimation and analysis of the Llap River Watershed morphometric parameters. The drainage map generated from the ALOS-DEM was used for morphometric analysis of the watershed in terms of stream order, stream length, bifurcation ratio, drainage density, etc. This study identified the importance of watershed attributes for water resource management in line with the Water Framework Directive 2000/60 EC. Several morphometric parameters have been computed and analysed: linear aspects such as stream order, stream number, stream length, etc., areal aspects such as drainage density, drainage texture, form factor, etc. A total numbers of 1219 streams were identified. The number of streams belonging to the 1 st , 2 nd , 3 rd , 4 th , 5 th and 6 th order was found to be 959, 201, 48, 8, 2 and 1, respectively. The total length of the streams is 1240.85 km, while the mean bifurcation ratio is 3.92 and mean Gravelius coefficient is 1.77. The data and information presented in this study will be helpful for drafting the plan of the management of the Llap River Watershed within which is estimated to live about 100 thousand inhabitants.

A Rapid Water Region Reconstruction Scheme in 3D Watershed Scene Generated by UAV Oblique Photography

Article

Full-text available

Feb 2023

Oblique photography technology based on UAV (unmanned aerial vehicle) provides an effective means for the rapid, real-scene 3D reconstruction of geographical objects on a watershed scale. However, existing research cannot achieve the automatic and high-precision reconstruction of water regions due to the sensitivity of water surface patterns to wind and waves, reflections of objects on the shore, etc. To solve this problem, a novel rapid reconstruction scheme for water regions in 3D models of oblique photography is proposed in this paper. It extracts the boundaries of water regions firstly using a designed eight-neighborhood traversal algorithm, and then reconstructs the triangulated irregular network (TIN) of water regions. Afterwards, the corresponding texture images of water regions are intelligently selected and processed using a designed method based on coordinate matching, image stitching and clipping. Finally, the processed texture images are mapped to the obtained TIN, and the real information about water regions can be reconstructed, visualized and integrated into the original real-scene 3D environment. Experimental results have shown that the proposed scheme can rapidly and accurately reconstruct water regions in 3D models of oblique photography. The outcome of this work can refine the current technical system of 3D modeling by UAV oblique photography and expand its application in the construction of twin watershed, twin city, etc.

¿De dónde viene y a dónde va el agua de las ciudades? Base de datos integrada para 243 centros urbanos argentinos

Article

Full-text available

Dec 2022

Provisión y disposición de agua en 243 ciudades argentinas: Servicios ecosistémicos en el continuo territorio-ecosistema acuático-centro urbano

Article

Full-text available

Dec 2022

Las ciudades dependen de distintos ecosistemas que les proveen servicios. Para el caso de la provisión de agua potable y la disposición de aguas servidas en las ciudades argentinas, el reconocimiento de esto aún es incompleto y fragmentado. Aquí presentamos la primera base de datos que mapea y clasifica las fuentes de suministro de agua y destinos de los efluentes de todas las ciudades argentinas con más 20000 habitantes (en 2010). A partir de reportes existentes, noticias periodísticas e información satelital se registraron en 243 ciudades los puntos de toma y vertido de aguas, junto a otra infraestructura asociada. Se encontró que 30.5, 17.5 y 12.6% de la población se abastece sólo de grandes ríos transfronterizos, agua subterránea y ríos y arroyos internos, respectivamente, con 25.2% abastecido por fuentes mixtas. Las ciudades que están conectadas a las redes públicas de saneamiento recurren para su disposición sobre todo a ríos y arroyos internos (26.6%); sin embargo, de la población urbana que no está conectada a la red cloacal, una proporción elevada dispone sus vertidos en acuíferos libres. La mayoría de las ciudades argentinas no devuelven las aguas de saneamiento al mismo sistema que las provee, y predominan los trasvases desde fuentes subterráneas hacia ríos y arroyos internos. La base de datos evidencia la contrastante ‘presión efluente’ (relación población/caudal del sistema receptor) entre ciudades vinculadas a grandes ríos (e.g., la cuenca del Paraná, con 273 habitantes.m-3.s-1) y a cuencas internas (e.g., la cuenca de Mar Chiquita, con 16141 habitantes.m-3.s-1). Esta base de datos, abierta para la consulta y actualización, visibiliza la conexión espacial e hidrológica entre las ciudades y la red hidrográfica, y contribuye a mejorar la seguridad hídrica y a priorizar los esfuerzos de protección de los ecosistemas acuáticos que la garantizan desde todos los niveles de gestión.

Drainage reorganization induces deviations in the scaling between valley width and drainage area

Article

Full-text available

Sep 2022

The width of valleys and channels affects the hydrology, ecology, and geomorphic functionality of drainage networks. In many studies, the width of valleys and/or channels (W) is estimated as a power-law function of the drainage area (A), W=kcAd. However, in fluvial systems that experience drainage reorganization, abrupt changes in drainage area distribution can result in valley or channel widths that are disproportional to their drainage areas. Such disproportionality may be more distinguished in valleys than in channels due to a longer adjustment timescale for valleys. Therefore, the valley width–area scaling in reorganized drainages is expected to deviate from that of drainages that did not experience reorganization. To explore the effect of reorganization on valley width–drainage area scaling, we studied 12 valley sections in the Negev desert, Israel, categorized into undisturbed, beheaded, and reversed valleys. We found that the values of the drainage area exponents, d, are lower in the beheaded valleys relative to undisturbed valleys but remain positive. Reversed valleys, in contrast, are characterized by negative d exponents, indicating valley narrowing with increasing drainage area. In the reversed category, we also explored the independent effect of channel slope (S) through the equation W=kbAbSc, which yielded negative and overall similar values for b and c. A detailed study in one reversed valley section shows that the valley narrows downstream, whereas the channel widens, suggesting that, as hypothesized, the channel width adjusts faster to post-reorganization drainage area distribution. The adjusted narrow channel dictates the width of formative flows in the reversed valley, which contrasts with the meaningfully wider formative flows of the beheaded valley across the divide. This difference results in a step change in the unit stream power between the reversed and beheaded channels, potentially leading to a “width feedback” that promotes ongoing divide migration and reorganization. Our findings demonstrate that valley width–area scaling is a potential tool for identifying landscapes influenced by drainage reorganization. Accounting for reorganization-specific scaling can improve estimations of erosion rate distributions in reorganized landscapes.

Effectiveness of Digital Elevation Models in Morphometric analysis Using Remote sensing and GIS Approach for Smart Society

Chapter

Jun 2022

Geographical information systems (GIS) are proven to be extremely useful in a variety of natural resource applications in Smart Society, including topography hydrology modeling for water harvesting. The watershed is the basic object in such systems, which is either physically drawn on topographic map sheets or computationally generated from digital elevation model (DEM) data. This article describes a method for automatically defining drainage and watersheds using a terrain’s DEM. The efficacy of DEMs in morphometric analysis of Rapti sub-watershed in Gorakhpur District, Uttar Pradesh, was investigated in this study. The Rapti sub-watershed, which covers an area of 20.8 km2 in Gorakhpur, was selected and six different threshold levels of 0.05, 0.25, 0.50, 0.125, 1.0, and 2.0 km2 were applied during the automization process using ESRI ArcGIS, open-source QGIS software, and freely available DEMs and surface models of ASTER-GDEM, and ALOS-DSM displays streams with finer features than ASTER-GDEM at all stream thresholds. For ALOS-DSM, the correlation coefficient R2 between thresholds and stream length (Lu) is 0.8817, while for ASTER-GDEM, it is 0.9017. In the comparative assessment of ASTER-GDEM and ALOS-DSM, carried out has identified ALOS-DSM exhibits finer drainage networks in comparison with ASTER-GDEM proving ALOS-AW3D 30 DSM is the best alternate source available.KeywordsASTER-GDEMALOS-DSMMorphometryThresholds

Delimitação e análise da área de contribuição das barragens do rio Gavião na região Sudoeste da Bahia

Article

Full-text available

Aug 2022

O Rio Gavião nasce no município de Jacaraci, região sudoeste da Bahia, na Serra do Banho e banha o territórios de outros treze municípios dessa região até desaguar no rio de Contas, após percorrer mais de 300 km. A primeira grande barragem no leito deste rio foi construída no município de Anagé tendo em vista a perenização de um trecho do rio. Todavia, as localidades mais a montante desta barragem ainda sofrem com a carência hídrica. Neste sentido, duas regiões lutam, historicamente, pela construção de novos aproveitamentos hídricos: a região chamada de garganta do Espírito Santo, no município de Tremedal e a localidade de Morrinhos no município de Piripá. Diante desta problemática, este trabalho tratou da delimitação e cálculo das áreas, por meio de imagem de satélite, das bacias de contribuição das barragens existentes em Anagé e Tremedal, bem como das bacias de contribuição para as duas novas barragens. Além disso, foi feita a delimitação da área inundada pela barragem do Espírito Santo, uma vez que foi estimado um volume armazenado que consiga suprir a demanda local. Este estudo teve como principal objetivo a ampliação da discussão sobre a construção dessas obras tão importantes para a população da região.

The anatomy of a channel-fed ‘a‘ā lava flow system

Article

Full-text available

Jul 2022
B VOLCANOL

The stabilized channel is a crucial element of an ‘a‘ā flow system, delivering lava to forward extending zones of dispersed flow. However, the term stable implies that channel geometries, lava properties, and dynamics are invariable. However, just how stable are these in space and time? To answer this question, we constrain the degree of variation for an extremely well-exposed stabilized channel on Kīlauea (Hawai’i), carrying out mapping, facies analyses, and sampling down the entire 5.5-km length of the channel-levee unit. Though active for only 3 days, flow and emplacement dynamics were highly unstable, experiencing both temporal and spatial variation. This resulted in a complex construction history and solidified channel form, where construction comprised three emplacement phases: initial, free-flowing, and late-stage ponded. These three emplacement phases were coupled with variation in underlying substrate, slope, and volume flux. These temporally and spatially varying conditions combined to result in four channel types and geometries (tubed, stable, ponded, and braided); five lava facies (smooth pāhoehoe, rough/spiney, slabby, transitional, and ‘a‘ā); and four levee types (initial-rubble, surge-fed overflow, pond-fed overflow, and accretionary). Complexity in channel form was reflected in cooling rates that ranged from 6.6 °C km−1 for free-flowing conditions to 17.7 °C km−1 for ponded lava. Likewise, vesicularities ranged from gas-rich (as high as 74% vesicles) to outgassed (as low as 27%). Due to the high degree of variance at this system, we suggest that feeder channel is a better term for this component of a channel-fed ‘a‘ā lava flow field. This term stresses the role of the channel in feeding zones of dispersed flow and is not a term that implies channel form and flow dynamics are unchanging. Although flow conditions can be complex, flow for some periods can be stable. If depths, widths, temperatures, and crystallinities during phases of below-bank stability can be identified, then the system can be modelled. We show this by fitting down-channel variation in flow properties for stable periods to output of the FLOWGO thermorheological model. In doing this, we provide a dataset that can guide and benchmark models aimed at simulating the dynamics and properties of channel-fed systems.

Evidence of geoelectrical resistivity values on groundwater conditions in Wadi El Natrun and its vicinities, West Delta, Egypt (cases studies)

Article

Full-text available

Jun 2022

Recently, Wadi El Natrun and its surroundings have witnessed intensive investments in land reclamation, including the arbitrary drilling of hundreds of groundwater wells. Currently, serious hydrogeological and environmental problems have been addressed, such as groundwater quality degradation and water head drop. Electrical resistivity measurements were performed at six locations across the study area to assess its ability to reveal the heterogeneous subsurface stratigraphic and hydrogeological setting of groundwater aquifer(s). The geoelectrical results successfully reflect the current vulnerable hydrogeological setting of the study sites. The current study highlights the current practice in which farmers rely on isolated 1-dimensional vertical electrical sounding (1D VES), which is not the only exploration tool for such electrically conductive stratigraphic succession. One of the main findings is addressing the advantage of applying 2-dimensional electrical resistivity imaging (2D ERI), where it offers a more robust view of both vertical and lateral variation of the investigated subsurface section (Case 3). On the other hand, the Geographic Information System (GIS) could mirror the present groundwater potentiality status, where both GIS analysis and resistivity results coincide, and where the good potentiality zone is restricted to the west and southwest directions of the study area (area of interest (aoi)), where the resistivity values of water bearing are relatively high and lie on the main drainage (Cases 2, 5, and 6). On the contrary, poor potentiality zones are deemed because of their proximity to tiny attributers, and are characterized by low resistivity values (Cases 1, 3 & 4), Finally, the current research study demonstrates the significance of combining morphometrical analysis with geophysics techniques for such environmental problems, where groundwater is primarily controlled by geomorphological features and geological conditions, including lithology and geological structures.

Terrain feature-aware deep learning network for digital elevation model superresolution

Article

Jul 2022
ISPRS J PHOTOGRAMM

Neural networks (NNs) have demonstrated the potential to recover finer textural details from lower-resolution images by superresolution (SR). Given similar grid-based data structures, some researchers have transferred image SR methods to digital elevation models (DEMs). These efforts have yielded better results than traditional spatial interpolation methods. However, terrain data present inherently different characteristics and practical meanings compared with natural images. This makes it unsuitable for existing SR methods on perceptually visual features of images to be directly adopted for extracting terrain features. In this paper, we argue that the problem lies in the lack of explicit terrain feature modeling and thus propose a terrain feature-aware superresolution model (TfaSR) to guide DEM SR towards the extraction and optimization of terrain features. Specifically, a deep residual module and a deformable convolution module are integrated to extract deep and adaptive terrain features, respectively. In addition, explicit terrain feature-aware optimization is proposed to focus on local terrain feature refinement during training. Extensive experiments show that TfaSR achieves state-of-the-art performance in terrain feature preservation during DEM SR. Specifically, compared with the traditional bicubic interpolation method and existing neural network methods (SRGAN, SRResNet, and SRCNN), the RMSE of our results is improved by 1.1% to 23.8% when recovering the DEM from 120 m to 30 m, by 4.9% to 22.7% when recovering the DEM from 60 m to 30 m, and by 7.8% to 53.7% when recovering the DEM from 30 m to 10 m. The source code that has been developed is shared on Figshare (https://doi.org/10.6084/m9.figshare.19597201).

Multi-criterion methods to extract topographic feature lines from contours on different topographic gradients

Article

Mar 2022

The existing methods of the automatic extraction of topographic feature lines from terrain representation either have too high sensitivity to terrain noise or lose significant branches. In this study, we present new multi-criterion methods to extract topographic feature lines from contours on different topographic gradients according to the negative or positive signs of the curvature and neighboring feature points on the contours, the hierarchical structure of these feature points, and the spatial relationships between topographic feature lines and contours. First, the digitization directions of source contours were automatically detected and adjusted (when necessary) to establish the spatial relationships among the contours before we extract and group the feature points in the terrain. Second, we determine the ‘mainstreams’ and ‘tributaries’ of the topological structure trees according to the relationships among the previously identified feature point groups. Finally, a key aspect of our paper is the proposition of multi-criterion methods to extract topographic feature lines. Compared with the regular square grids (RSG)-based and Voronoi skeleton-based methods, the proposed methods can extract topographic feature lines with higher accuracy, better continuity, lower spatial logical conflicts between topographic feature lines and contours.

Granularity of Digital Elevation Model and Optimal Level of Detail in Small-Scale Cartographic Relief Presentation

Article

Full-text available

Mar 2022

Timofey Samsonov

One of the key applications of digital elevation models (DEMs) is cartographic relief presentation. DEMs are widely used in mapping, most commonly in the form of contours, hypsometric tints, and hill shading. Recent advancements in the coverage, quality, and resolution of global DEMs facilitate the overall improvement of the detail and reliability of terrain-related research. At the same time, geographic problem solving is conducted in a wide variety of scales, and the data used for mapping should have the corresponding level of detail. Specifically, at small scales, intensive generalization is needed, which is also true for elevation data. With the widespread accessibility of detailed DEMs, this principle is often violated, and the data are used for mapping at scales far smaller than what is appropriate. Small-scale relief shading obtained from fine-resolution DEMs is excessively detailed and brings an unclear representation of the Earth’s surface instead of emphasizing what is important at the scale of visualization. Existing coarse-resolution global DEMs do not resolve the issue, since they accumulate the maximum possible information in every pixel, and therefore also require reduction in detail to obtain a high-quality cartographic image. It is clear that guidelines and effective principles for DEM generalization at small scales are needed. Numerous algorithms have been developed for the generalization of elevation data represented either in gridded, contoured, or pointwise form. However, the answer to the most important question—When should we stop surface simplification?—remains unclear. Primitive error-based measures such as vertical distance are not effective for cartography, since they do not account for the landform structure of the surface perceived by the map reader. The current paper approached the problem by elaborating the granularity—a newly developed property of DEMs, which characterizes the typical size of a landform represented on the DEM surface. A methodology of estimating the granularity through a landform width measure was conceptualized and implemented as software. Using the developed program tools, the optimal granularity was statistically learned from DEMs reconstructed for multiple fragments of manually drawn 1:200,000, 1:500,000, and 1:1,000,000 topographic maps covering different relief types. It was shown that the relative granularity should be 5–6 mm at the mapping scale to achieve the clearness of relief presentation typical for manually drawn maps. We then demonstrate how the granularity measure can be used effectively as a constraint during DEM generalization. Experimental results on a combination of contours, hypsometric tints, and hill shading indicated clearly that the optimal level of detail in small-scale cartographic relief presentation can be achieved by DEM generalization constrained by granularity in combination with fine DEM resolution, which facilitates high-quality rendering.

Design and development of a web‐based interactive twin platform for watershed management

Article

Full-text available

Jan 2022

There are limitations to traditional digital watershed platforms in terms of realistic visualization of geospatial elements and powerful decision support for watershed management. To advance the status quo, a web‐based digital twin is designed and implemented in this article that can: (1) realize virtual simulation of geographic elements on the browser side; (2) present the current situation and excessive information of the watershed water environment; and (3) provide decision support for integrated watershed management. Multiple 3D modeling methods are adopted cooperatively for total‐factor virtual simulation of geographic elements, and a browser‐side data loading scheme is designed for dynamic loading and cull rendering of 3D models. Additionally, schemes for spatiotemporal modeling of multisource data, analysis of multitype data, and scientific computation of mathematical models are proposed to support precise watershed management, making the platform practical. The implemented digital twin is applied in the Chaohu Lake Watershed, demonstrating that it can realize both stunning visual effects and practical decision‐support functions.

Potential of X-band polarimetric SAR co-polar phase difference for Arctic snow depth estimation

Preprint

Full-text available

Oct 2021

Changes in snowpack associated with climatic warming has drastic impacts on surface energy balance in the cryosphere. Yet, traditional monitoring techniques, such as punctual measurements in the field, do not cover the full snowpack spatial and temporal variability, which hampers efforts to upscale measurements to the global scale. This variability is one of the primary constraints in model development. In terms of spatial resolution, active microwaves (synthetic aperture radar—SAR) can address the issue and outperform methods based on passive microwaves. Thus, high spatial resolution monitoring of snow depth (SD) would allow for better parameterization of local processes that drive the spatial variability of snow. The overall objective of this study is to evaluate the potential of the TerraSAR-X (TSX) SAR sensor and the wave co-polar phase difference (CPD) method for characterizing snow cover at high spatial resolution. Consequently, we first (1) quantified the spatio-temporal variability of the geophysical properties of the snowpack in an Arctic catchment, we then (2) studied the links between snow properties and CPD, considering ground vegetation. Snow depth (SD) could be extracted using the CPD when certain conditions are met. A high incidence angle (> 30°) with a high Topographic Wetness Index (TWI) (> 7.0) showed correlation between SD and CPD (R-squared up to 0.72). Further, future work should address a threshold of sensitivity to TWI and incidence angle to map snow depth in such environments and assess the potential of using interpolation tools to fill in gaps in SD information on drier vegetation types.

Évaluation du potentiel de la méthode par différence de phase copolaire de l’onde radar (CPD) en bande-X pour l’extraction de l’épaisseur du couvert nival arctique.

Thesis

Full-text available

Oct 2021

Joëlle Voglimacci

Changes in the state of the snowpack in the context of observed global warming must be considered to improve our empirical understanding of the processes governing thermal and radiative interactions within the cryosphere. The spatiotemporal variability of the snowpack means that the data acquisition approach using traditional techniques, such as point measurements in the field, cannot fully address global-scale research questions (Bokhorst et al., 2016). This variability is one of the primary constraints in model development that active microwaves (synthetic aperture radar - SAR) can address by outperforming methods using passive microwaves in terms of spatial resolution. High spatial resolution monitoring of snow depth (SD) would allow for better parameterization of local processes that drive the spatial variability of snow, which is a known limitation for model development in these regions (Domine et al., 2018; King et al., 2018; Meloche et al., 2020). The overall objective of the study is therefore to evaluate the potential of the TerraSAR-X (TSX) sensor with the wave copolar phase difference (CPD) method for characterizing snow cover at high spatial resolution. To achieve this objective, the following steps were performed: (i) Quantify the spatio-temporal variability of geophysical properties and snowpack depth in an Arctic watershed; (ii) Quantify the evolution of snow as a function of land cover; and (iii) Correlate the TSX satellite signal to snow depth based on information from snow properties measured in (i) and the links to land cover quantified in (ii). This study was the first to perform a complete characterization of the snow covering Herschel Island, combined with SAR data. Using a high spatial resolution vegetation classification available to the project, we were able to quantify the variability of snow depth as well as the topographic soil wetness index (TWI). The TWI provided a better understanding of the electromagnetic wave-ground interaction where a high incidence angle with a high TWI (>7.0) allows us to extract a correlation between snow depth and CPD. Future work should focus on developing a threshold for the sensitivity of CPD to TWI and incidence angle to map snow depth in such environments and to evaluate the potential of using interpolation tools to supplement snow depth maps where the CPD approach is not possible.

Network representation in hydrological modelling on urban catchments in data-scarce contexts: A case study on the Oued Fez catchment (Morocco)

Article

Mar 2021

Urban catchments are heterogeneous in terms of land use and have both natural and artificial drainage networks. Modelling them is not a straightforward task especially in data-scarce settings. This study investigates network representation in hydrological modelling using field data collected between 2008 and 2018 on the Oued Fez catchment. The road network is used as a proxy for the stormwater network. Two production functions, SCS (1972) and a linear reservoir, are coupled to the lag and route transfer function. Three types of land use classes are used. Tests are carried out at hourly and 5-minute time steps using both the natural and modified drainage Fifty-three rainfall–runoff events are monitored on the urban part of the catchment over the 2008–2018 period. The highest rainfall values are recorded in 2008/2009, while the highest peak flow values are recorded in 2017/2018. This is due to stream channelisation and increased stormwater network coverage. Using the road network with minimal land use classes improves the model performance at both the hourly and 5-minute time steps.

Incorporation of Slope and Rainfall Variability in Channel Network Extraction from DEM Data at Basin Scale

Article

Full-text available

Feb 2021

This work presents an analytical framework that includes slope and rainfall variability with value of the critical area in defining a threshold for channel initiation processes for the whole river basin. The study overcomes the existing limitation of application of constant threshold for extracting channels throughout the basin by proposing slope and rainfall dependent variable threshold. The proposed algorithm successfully captures the spatial variability in drainage patterns at basin-scale characterized by different topographic characteristics. As basin-scale studies are mostly carried out using coarse-resolution Digital Elevation Model (DEM), this methodology has been developed using SRTM data of 30 m spatial resolution. The resultant drainage pattern was compared with the published map based on field observations, which shows a closer match with field conditions. A front-end application was developed to implement the methods as an end to end process to make user interaction simpler.

AERIAL LiDAR TECHNOLOGY IN SUPPORT TO AVALANCHES PREVENTION AND RISK MITIGATION: AN OPERATIVE APPLICATION AT “COLLE DELLA MADDALENA” (ITALY)

Article

Full-text available

Nov 2020

Snow avalanches are the result of unstable snow masses that detach from steep slopes as consequence of changes in snowpack structure. Nowadays, remote sensing technologies can improve the knowledge of avalanches phenomenon. This work focuses on the use of high point density aerial LiDAR (Light Detection And Ranging) technology as support to avalanche events prevention and risk mitigation, by presenting an operative application at Colle della Maddalena (Italy), along the road SS n. 21, nearby the French state border. The area is often involved in intense avalanche events that adversely impact on traffic and freight transport. For this reason, regional administrations will activate the Avalanche Artificial Detachment Intervention Plan (PIDAV, 2012) in order to prevent and manage the avalanche risk in the study area, also adopting artificial detachment systems. Main aim of the present work was to generate high resolution information related to geomorphological characterization (i.e. digital elevation models, slope and aspect) of avalanche sites derived from LiDAR data processing, that will help involved authorities in the management of the avalanche control plan. Digital elevation models at 0.5 m of spatial resolution were generated together with relative tridimensional models. Secondly, a preliminary investigation about capabilities and limits of LiDAR technology was done in the identification of avalanche sites only relying on geomorphological information directly derived by LiDAR data processing. Results showed that position of avalanche sites were correctly identified while no information could be obtained about the extension of the sliding area and identification of detachment areas.

AERIAL LiDAR TECHNOLOGY IN SUPPORT TO AVALANCHES PREVENTION AND RISK MITIGATION: AN OPERATIVE APPLICATION AT "COLLE DELLA MADDALENA" (ITALY)

Conference Paper

Full-text available

Oct 2020

Snow avalanches are the result of unstable snow masses that detach from steep slopes as consequence of changes in snowpack structure. Nowadays, remote sensing technologies can improve the knowledge of avalanches phenomenon. This work focuses on the use of high point density aerial LiDAR (Light Detection And Ranging) technology as support to avalanche events prevention and risk mitigation, by presenting an operative application at Colle della Maddalena (Italy), along the road SS n. 21, nearby the French state border. The area is often involved in intense avalanche events that adversely impact on traffic and freight transport. For this reason, regional administrations will activate the Avalanche Artificial Detachment Intervention Plan (PIDAV, 2012) in order to prevent and manage the avalanche risk in the study area, also adopting artificial detachment systems. Main aim of the present work was to generate high resolution information related to geomorphological characterization (i.e. digital elevation models, slope and aspect) of avalanche sites derived from LiDAR data processing, that will help involved authorities in the management of the avalanche control plan. Digital elevation models at 0.5 m of spatial resolution were generated together with relative tridimensional models. Secondly, a preliminary investigation about capabilities and limits of LiDAR technology was done in the identification of avalanche sites only relying on geomorphological information directly derived by LiDAR data processing. Results showed that position of avalanche sites were correctly identified while no information could be obtained about the extension of the sliding area and identification of detachment areas.

A methodological framework towards the formulation of flood runoff generation models suitable in alpine and prealpine regions

Thesis

Full-text available

Jan 2002

Richard Kuntner

Severe floods regularly occur at different places all over the world including the European Alps and Prealps. They are responsible for important damages and a large number of fatalities. Consequently, research activities in physical and engineering sciences have long focused on understanding the underlying physical processes and on developing methods to reproduce and predict floods. Despite considerable progress in both fields over the last few years, a number of questions still remain open. The frequent over- or underestimation of both structural and non-structural measures for flood mitigation are, however, only partially caused by this fact. Recent and more sophisticated methods of flood estimation do not often penetrate to everyday hydrological practice in engineering companies and federal agencies. These methods are abandoned in favour of simple empirical methods, mainly due to their extended demand in input data. The reliability of the results obtained by these simple methods is, however, often unsatisfactory and there is a strong demand for better performing practice-oriented methods. This work intends to add a step towards the solution of this problem. The overall goal consists in developing / adapting a methodology for the estimation of overland flow suited to the Swiss alpine and prealpine context. The methodology should further exclusively rely on widely available geographic information. It was decided in this respect to work with the geographic database GEOSTAT. GEOSTAT is operated by the Swiss Federal Statistical Office (Bundesamt für Statistik) and covers the whole country. The highest spatial resolution of the maps is 1 hectare. For overland flow estimation the Curve Number method is used. The Curve Number method was developed by the US Natural Resources Conservation Service (formerly known as Soil Conservation Service) and allows for the estimation of direct runoff for a given rainfall input based only on qualitative information on soil type and land use. The goal then consists in adapting the Curve Number method in order to allow for a correct reproduction of overland flow for all types of hydrological different reacting areas which can be differentiated based on information from the GEOSTAT maps. This goal is addressed by reproducing hydrographs of annual flood events observed in four alpine and prealpine catchments by means of a spatially distributed Rainfall-Runoff model. The spatial resolution of the model corresponds to the spatial resolution of the information from the GEOSTAT maps (1ha). For each single grid cell, the overland flow is further calculated separately by the Curve Number equation. The simulations then allow for indications on the performance and the parameterisation of the Curve Number equation for single hydrological different reacting areas. These indications are however exposed to larger uncertainties. The simulated hydrograph is influenced by different hydrological areas which react similarly and different modules of the model (e.g. subsurface flow module). Therefore the single hydrological different reacting areas cannot be analysed independently. In order to reduce the uncertainty, the performance of the Curve Number equation was also analysed based on data from a number of small scale 6800$5< rainfall experiments. These experiments are of interest in the context of the present study, as the runoff processes and the soil characteristics at the plot sites were observed and measured in detail. Consequently, the performance of the Curve Number equation can be investigated separately for single soil types. The results from the analysis at this plot scale show that the equation mainly performs well for rainfall plots in which Hortonian runoff processes dominate and which are located on Cambisols and Gleysols. The equation shows a lower performance for plots on soils such as Rendzina, Ranker and Podsol. In terms of reparameterisation, only preliminary indications are gained from the analysis mainly due to the limited number of experiments. For a number of plot sites the runoff behaviour is furthermore dominated by local structures such as macropores. At basin scale the Rainfall-Runoff model in general and the Curve Number equation in particular show a satisfactory performance in reproducing the flood runoff observed in the prealpine catchments. In the alpine catchment considered a reproduction of the flood events was however not successful due to the large uncertainty of the spatial rainfall distribution and the influence of snow on the flood events. The simulations generally result in rough indications on the performance and the parameterisation of the Curve Number equation for a number of hydrological different reacting areas. For storm events characterised by rainfall peaks interrupted by periods of rainfall of low intensity, modification of the Curve Number method is further required and proposed. A comparison of the resulting parameterisation with event characteristics then shows that the relation of parameterisation and antecedent wetness conditions presented in the original Curve Number method are not valid in the alpine and prealpine context. The found Curve Number values further decline with increasing storm rainfall volume. The indications on the parameterisation of the Curve Number equation are however exposed to larger uncertainties. The findings from the analysis at plot scale are partially helpful in reducing these uncertainties. This study represents a first important step towards the modification of the Curve Number method to a method for the estimation of the overland flow in the Swiss alpine and prealpine environment. Further steps mainly consist in extending the analysis / adaptation of the Curve Number method to a large number of additional mesoscale catchments of the Swiss Plateau and the Prealps. When selecting the catchments, similar hydrological different reacting areas should be present in several catchments. This permits a more precise idea on the performance of the Curve Number equation for single hydrological different reacting areas. The simulations of flood events from additional catchments may also serve to refine the proposed modification of the Curve Number equation and gain insight into how the parameterisation relates with the antecedent wetness conditions.

Contribution of changing precipitation and climatic oscillations in explaining variability of water extents of large reservoirs in Pakistan

Article

Full-text available

Dec 2019

Major threat that Pakistan faces today is water scarcity and any significant change in water availability from storage reservoirs coupled with below normal precipitation threatens food security of more than 207 million people. Two major reservoirs of Tarbela and Mangla on Indus and Jhelum rivers are studied. Landsat satellite’s data are used to estimate the water extents of these reservoirs during 1981–2017. A long-term significant decrease of 15–25% decade−1 in water extent is found for Tarbela as compared to 37–70% decade−1 for Mangla, mainly during March to June. Significant water extents reductions are observed in the range of −23.9 to −53.4 km2 (1991–2017) and −63.1 to −52.3 km2 (2001–2010 and 2011–2017) for Tarbela and Mangla, respectively. The precipitation amount and areas receiving this precipitation show a significant decreasing trend of −4.68 to −8.40 mm year−1 and −358.1 to −309.9 km2 year−1 for basins of Mangla and Tarbela, respectively. The precipitation and climatic oscillations are playing roles in variability of water extents. The ensuing multiple linear regression models predict water extents with an average error of 13% and 16% for Tarbela and Mangla, respectively.

Morphometric analysis and hydrological inference for water resource management in Atrai-Sib river basin, NW Bangladesh using remote sensing and GIS technique. Journal of the Geological Society of India Springer link.vol.91p: 613-620

Article

May 2018

Delineation of Groundwater Potential Zones of Atrai-Sib River Basin in North-West Bangladesh using Remote Sensing and GIS Techniques. Sustainable Water Resources Management, Springer Doi.org/10.1007/s40899-018-0240-x

Article

May 2019

DELIMITAÇÃO AUTOMÁTICA DE BACIAS HIDROGRÁFICAS: APLICAÇÃO E ANÁLISE EM DIFERENTES PAISAGENS NO BRASIL

Article

Full-text available

May 2023

A bacia hidrográfica representa uma unidade ideal de planejamento e sua delimitação pode ocorrer por métodos manuais ou computacionais, sendo que estes últimos, quando apoiados em ambiente de Sistemas de Informações Geográficas (SIG), proporcionam eficiência e agilidade ao processo. O presente estudo tem por objetivo a aplicação e análise da metodologia de delimitação automática de três bacias hidrográficas em diferentes paisagens do Brasil (biomas Mata Atlântica, Amazônia e Pantanal), empregando softwares SIG. Pela análise de discrepâncias entre as delimitações automáticas realizadas, foram obtidas variações de área menores que 1% para a bacia presente na Mata Atlântica e menor divergência entre os limites resultantes da bacia. Já para bacia localizada na Amazônia, os valores totais de área foram próximos. Para a bacia delimitada no Bioma Pantanal, de relevo predominantemente plano, os valores de área foram 50% menores em relação à delimitação manual (utilizada como referência), em média, com divergências significativas entre os limites das bacias. Os resultados alcançados reforçam a necessidade do usuário se atentar às limitações existentes em processos de delimitação automatizados, em paisagens distintas do país, visto os potenciais impactos nos processos de tomada de decisão, apoiados neste tipo de dado, mesmo que obtidos em diferentes ferramentas de SIG.

A Review on the Relationship between LULC and LST using Geospatial Technologies

Conference Paper

Dec 2022

Human actions involved in the development activities have put a pressure on natural and existing landscape. Changes in the Land Use Land Cover (LULC) were the most significant disturbances which are being induced by human beings. Such Land Use Land Cover Changes (LULCC) can be linked with the environmental and climate changes taking place at local, regional and global levels with the increasing growth of impermeable surfaces like built-up areas or highways which has direct impact on Land Surface Temperature (LST). The effects of LULC on LST have been the subject of numerous researches. This article represents the linkage between LULC and LST by using satellite data. After reviewing the current scope of the study, it can be concluded that in the various LULC types, built-up experienced more LST as compared to other Land types and vegetation land experienced the lowest LST. Keywords: Remote Sensing, LULC, LULCC, LST

Comparative analysis of performance and mechanisms of flood inundation map generation using Height Above Nearest Drainage

Article

Nov 2022
ENVIRON MODELL SOFTW

The National Water Center (NWC) implemented Height Above Nearest Drainage (HAND) for nationwide flood mapping in the continental United States. Although having a large coverage and high accuracy, the implementation (NWCH) relies heavily on the NHDPlus dataset which limits its potential to handle user defined datasets. Comparison of the NWCH model accuracy and computational performance against the original HAND is missing in the literature. This study evaluated the flood maps generated using NWCH and a web-based implementation of the original HAND (WBH). An in-depth sensitivity analysis was conducted for WBH. Results suggest that WBH can generate comparable inundation extent with few inputs in regions where the water depths from the synthetic and catchment rating curves are consistent. Multi-depth approaches help resolve underestimations of WBH. This study demonstrated the original HAND's efficacy in flood mapping and its potential for applications for fast predictions with acceptable accuracy with limited computational resources.

Integration of Volunteered Geographic Information in Global Digital Elevation Models in the representation of water lines

Thesis

Full-text available

Jul 2019

Elisabete Monteiro

The Digital Elevation Models (DEMs) allow the extraction of topographic parameters used in hydrological modelling. The altimetric definition of the river basin allows to delineate its boundary, the extraction of the drainage network as well as other topographic parameters such as the network ramification, the watercourse length, the total length of the network and the slope. The accuracy of all these parameters is dependent on the accuracy of the DEM. The present thesis presents a methodology that allows to improve the accuracy of the Global Digital Elevation Models (GDEMs), as well as the accuracy of the topographic parameters extracted from them, using data from the OpenStreetMap (OSM) collaborative project, namely the water lines. New DEMs are created from the elevation points extracted from the original GDEMs Advanced Spaceborn Thermal Emission and Reflection Radiometer (ASTER) and Shuttle Radar Topography Mission (SRTM) that are interpolated with the water lines available in OSM. The drainage networks were extracted from the original and the rebuilt DEMs. The accuracy of the new DEMs and derived topographic parameters, namely the drainage networks, was evaluated. Reference data were used to compare them with the data under analysis. The methodology was applied in a phased way to three case studies.

A comprehensive web-based system for flood inundation map generation and comparative analysis based on height above nearest drainage

Article

Mar 2022
SCI TOTAL ENVIRON

It is critical to obtain accurate flood extent predictions in a timely manner in order to reduce flood-related casualties and economic losses from floods with greater magnitudes and fall outside the handling capacity of our existing mitigation systems. Running a real-time flood inundation mapping model is helpful in supporting quick response decisions for unplanned floods, such as how to distribute limited resources and labor so that the most flood-prone areas receive adequate mitigation efforts and how to execute evacuations that keep people safe while causing the least amount of unneeded disruption. Most inundation systems, on the other hand, are either overly demanding in terms of data and computing power or have limited interaction and customization with various input and model configurations. This paper describes a client-side web-based real-time inundation mapping system based on the Height Above the Nearest Drainage (HAND) model. The system includes tools for hydro-conditioning terrain data, modifying terrain data, custom inundation mapping, online model performance evaluation, and hydro-spatial analyses. Instead of only being able to work on a few preprocessed datasets, the system is ready to run in any region of the world with limited data needs (i.e., elevation). With the system's multi-depth inundation mapping approach, we can use water depth measurements (sensor-based or crowdsourced) or model predictions to generate more accurate flood inundation maps based on current or future conditions. All of the system's functions can be performed entirely through a client-side web browser, without the need for GIS software or server-side computing. For decision-makers and the general public with limited technical backgrounds, the system provides a one-stop, easy-to-use flood inundation modeling and analysis tool.

Accounting for uncertainty in real-time flood inundation mapping using HAND model: Iowa case study

Article

Full-text available

May 2022
NAT HAZARDS

This study examines the uncertainties associated with a rapid flood inundation mapping approach based on height above the nearest drainage (HAND) model's parameters, inputs, reference, and computing procedure. The effects of changing the drainage threshold, water depth, and horizontal resolution were studied in two Iowan regions of around 100 km². To assess the uncertainty from rasterized inundation extent maps used as the reference, a regional and community-level evaluation with three distinct water depth estimates was performed for a five-county region in Iowa. An inner zone approach was utilized to demonstrate the uncertainties around the computational boundary of regions. The results reveal that the HAND model's performance depends on the research area's morphological characteristics, even though they are not directly input into the calculation. A good parameter set for one site does not ensure good performance for another. Moreover, the findings suggest that the DEM's resolution should be carefully chosen, as overgeneralization reduces the reliability of forecasts. Finally, the HAND model relies on drainage accumulation to build the simulation network; therefore, the calculation around the region border can introduce uncertainty. The findings of this study provide guidelines for effective model setup, adjustments, and performance improvement for non-rating-curve-based HAND.

Estimates of soil erosion rates in a principal watershed in Gozo, Malta under current and future climatic conditions

Article

Mar 2022
CATENA

The aim of the study was to estimate the current and future annual soil erosion rate in the Ramla watershed situated in Gozo, Malta. The RUSLE-GIS was applied using innovative approaches, such as the inclusion of the highest possible DEM data as well as reflecting climatic changes to the R Factor based on the latest climate projections for Gozo derived from a total of eight CMIP6 climate change models. A climate change impact analysis was carried to estimate the likely future risk of soil erosion in this local watershed for the first time. The estimated annual soil loss, as a percentage of the total area of study varies from low (85.1%), to moderate (13.3%) and high (1.6%). Within a climate change context, a reduction in the annual soil erosion rate has been estimated for the period 2080–2100, ranging from −5 ton ha⁻¹ yr⁻¹ under SSP126 to −6 ton ha⁻¹ hr⁻¹ under SSP585. The estimated decrease of annual soil loss within the high soil erosion risk category is attributed to an increased aridity of the local climate as projected by eight CMIP6 climate models. Specific hydrological sub-watersheds were identified within the study area that warrant urgent considerations. The outcomes of this study are based on the inclusion of micro-topographical information derived from high resolution 1 m LiDAR DEM. This modelling work is seen as the first study which can be used to provide some objective guidance on the minimization of potential soil losses within the Ramla watershed. Our estimated soil loss and its spatial distribution can assist in a fuller management plan for the sustainability of this watershed. These results should not be interpreted in absolute terms but as an understanding of the underlying controlling processes, the relative spatial and temporal variations, and of possible future scenarios.

Model Builder and ArcHydro Tools of Geospatial Technology to Extract Drainage Network and Watershed Delineation using Digital Elevation Model

Article

Full-text available

Dec 2019

For any hydrological modeling, delineation of watershed details like drainage network and catchment area extraction are very important. It is of great need to delineate the catchment area in the form of sub watershed areas to find out the characteristics easily. It is possible to develop using geospatial technologies due to temporal and spatial variations. Automatic delineation of watershed is time consuming when compare to manual method. With the development of Geospatial technology, automatic extraction of watershed details became very popular. Digital Elevation Model (DEM) data can be considered as input data to delineate catchment area and drainage network using GIS. ArcHydro is an add-on tool in ArcGIS software, which plays a vital role in building any hydrological information system for the support of hydrologic modeling in water resources development. In ArcHydro model, there are many sequential dropdown tools available, which are to be properly followed in order to delineate watershed for the management of water resources. Hence, a comprehensive geospatial model has been developed in Model Builder of ArcGIS software to run the model at a time to complete the process to extract the features like drainage network and catchment area from ArcHydro tool. In the present research, Nandyal area is selected to delineate catchment area and drainage network. 30m DEM data was used for delineation of watershed as input data. The major functions of ArcHydro tool are Flow Direction, Flow Accumulation and determining watershed and extraction of drainage lines.

GEOGRAPHIC INFORMATION SYSTEMS BASED URBAN DRAINAGE EFFICIENCY FACTORS

Conference Paper

Full-text available

May 2015

Urban areas in the developing world are experiencing increasingly dangerous flood events due to urban constructions and climate change. Urban flooding has become a major global concern, and for obvious reasons it is mostly an urban phenomenon. Urbanization creates impervious ground surfaces, inhibiting infiltration. Ill-advised urbanization practices lead to the blockage of natural flow routes. Urban centres are growing very fast in Africa. Where drainages are constructed they are mostly road edge drainages constructed to protect the roads instead of landscape drainages. Urban flooding can only be taken care of by efficient landscape drainages. The research work reported here determined efficiency factors of drainages which include the locations, alignments, slopes and sizes of drainages on a Geographic Information Systems (GIS) platform. The aim of the drainage efficiency factors guidelines is to ensure that the drainages will serve to convey runoff in ways that eliminate the danger of either erosion or flooding to the environment. The research effort created a Digital Elevation Model (DEM) of Owerri in Southeast Nigeria, using data from topographical maps of the city. The data was authenticated using three dimensional (3D) coordinates of sample points derived from Global Navigational Satellite Systems (GNSS) surveys. The DEM was processed by the ArcHydro software to determine primary natural flow routes and the sub-catchments that flood them. The primary landscape unit for drainage design is the subcatchment. The size of each sub-catchment useful for computing volumes of runoff that would have to be conveyed by the constructed urban drainages were determined using GIS. A scheme of urban drainage network as a runoff collector system that conveys runoff from the entire landscape to the primary drainage routes is suggested. The efficiency factors determined for Owerri were used to test the existing drainage systems. The failure of the existing drainages to conform with the guidelines explains why the study area would flood at every rain storm event.

From Spot Heights to Cell Heights - the Data Structure and the Dynamics of the Digital Elevation Model

Conference Paper

Full-text available

Jun 2014

This paper notes the increasing growth of the use of the Digital Elevation Model (DEM) in Digital Terrain Analysis (DTA) and terrain characterizing and phenomenon modelling. It explores ongoing researches in the data structures and applications of the Digital Elevation Model. The different data structures of the Triangulated Irregular Network (TIN) and the grid Digital Elevation Model are presented. Sources of DEM data and their possible sources of errors and their accuracies are discussed. One notable area where the DEM has been very successful in Digital Terrain Analysis (DTA) is in the area of delineating drainage routes and marking out sub-catchments. The scheme of this analysis is discussed. Processing the DEM produces the Flow Direction Grid, this is processed to determine the number of cells that their runoff will flow into a given cell, producing the Flow Accumulation Grid, and then the stream link grid is produced. The paper points out that obviously the topographic content represented by the DEM is the most important factor in the terrain characterization and terrain phenomenon modelling such as stream and drainage route and ridge delineation, erosion modelling, flood risk potential simulation, etc. It is the DEM that is used in various Digital Terrain Analysis (DTA) of all branches of the geosciences. The paper then calls for the training of surveyors with the skills for developing the Digital Elevation Models and to apply the same.

Applying Continuous Surface Argument in Refining SRTM DEM and ASTER DEM

Conference Paper

Full-text available

May 2016

Use of HAND terrain descriptor for estimating flood-prone areas in river basins

Article

Full-text available

Aug 2021

The flood hazard mapping in a river basin is crucial for flooding risk management, mitigation strategies, and flood forecasting and warning systems, among other benefits. One approach for this mapping is based on the HAND (Height Above Nearest Drainage) terrain descriptor, directly derived from the Digital Elevation Model (DEM), in which each pixel represents the elevation difference of this point in relation to the river drainage network to which it is connected. Considering the Mamanguape river basin (3,522.7 km²; state of Paraíba, Brazil) as the study location, the present research applied this method and verified it as for five aspects: consideration of a spatially variable minimum drainage area for denoting the river drainage initiation; the impact of considering a depressionless DEM; evaluation of hydrostatic condition; effect of incorporating an existing river vector network; and comparative analysis of basin morphology regarding longitudinal river profiles. According to the results, adopting a uniform minimum drainage area for the river network initiation is a simplification that should be avoided, using a spatially variable approach, which influences the amount and spatial distribution of flooded areas. Additionally, considering the depressionless DEM leads to higher values of HAND and to a smaller flooded area (difference ranging between 3% and 99%), when compared with the use of DEM with depression, despite 3.1% of the pixels representing depressions. The use of the depressionless DEM is recommended, whereas the DEM pre-processing by incorporating a vector network (stream burning) generates dubious results regarding the relation between HAND and the morphological pattern presented in the DEM. Moreover, the estimation of flooded areas based on HAND does not guarantee the hydrostatic condition, but this disagreement comprises a negligible area for practical purposes.

适用于大尺度水文气候模式的DEM洼地填充和平坦区处理的新方法

Article

Full-text available

Dec 2007

Abstract :The new method is composed of two algorithms for processing the depressions and plain areas in DEM .The first one is quantile classification algorithm which utilizes the statistics characteristics to compute the quantile and carries out the classification .Since its time complexity is O( N) , the working speed is much faster than the traditional method .The other algorithm further processes the quantilized depressions and flat areas initiated from the lowest elevation until the end .The assessments by using various method based on DEM with 90 ×90 grids show that the new method has very high processing speed .In average, this method is faster than the Jenson &Domingue method by thousands times . Key words: DEM ; depression filling ; flat area; algorithm ; quantile classification

Geomorphological Evaluation of Using the Digital Elevation Model (DEM) for Identifying the Morphmetrical Characteristics of Basins Case study: Wadi Abu Had, Eastern desert, Egypt

Article

Full-text available

May 2015

Ahmed Abou raiah

ABSTRACT. Water erosion is defined as soil erosion and physical degradation of the landscape over time. The process begins when soil particles are separated from their original configuration by the forces of erosion of rainfall by splash, sheet, rill or gully. Can then be transported soil particles by overland flow in rivers by has networks. The Daihachiga basin is considered to be most important water resource of Takayama city, the basin contains many natural resources which enable substantial agricultural development. The researcher depends on Gavrilovic's model; Potential Method Erosion (EPM), which was designed for mountainous areas, to determine the surface water erosion hazards in the basin. This model has been applied using remote sensing (RS) techniques and geographic information system (GIS). It was possible to calculate the credibility of the basin as well as the annual erosion rate for the whole basin and sub-basins, based on pixel unit calculations. According to digital elevation model (DEM), gradient model of the watershed was prepared too, and it used for some Morphometric parameters. It was clear the foothill and towards the outlet basin areas subject to flooding affecting as the result of the geological structure of the basin, and the steep slopes, vegetation caver, which is an important factor in slowing the runoff, and the weak of the management for retarding floods effect on soil erosion. Key words: Gifu prefecture; Water Erosion; RS; GIS; DEM; EPM

Reproducible topographic analysis

Chapter

Jan 2020

The ability to reproduce the results of an experiment is a fundamental component of the scientific method. However, precisely what is meant by the terms replicable and reproducible often varies between and within disciplines. Here, we present clear definitions of these two terms for geomorphic research and communicate the importance of performing reproducible analysis of remotely sensed topographic data. We argue that the reproducibility of an analysis is not a static, binary state but rather that there is a continuum from irreproducibility to replicability, with reproducibility falling between the two and that the aim of a researcher should be to get as close to reproducibility as possible, favoring a pragmatic rather than dogmatic approach. A brief review of the development of topographic analysis as a discipline is used to highlight the progress made in making topographic analysis more reproducible, and the challenges inherent within common working patterns. The chapter concludes with a series of recommendations on how best to achieve reproducible topographic analysis.

Extração Automática de Drenagem: uma Análise Comparativa a Partir de Diferentes Ferramentas e Bases de Dados (Draining automatic extraction: a comparative analysis of different from the tools and databases )

Article

Full-text available

Oct 2016

A necessidade de planejamento e gerenciamento de bacias hidrográficas tem incitado pesquisa que buscam compreender sua dinâmica hidrológica. Em regiões que apresentam carência de mapeamento topográfico em grande escala, é comum o uso de modelos digitais de elevação (MDE) para extração automática da rede de drenagem, delimitação de bacias hidrográficas e obtenção de parâmetros hidrográficos e morfométricos. Diante deste cenário o presente trabalho teve como objetivo avaliar a eficiência de duas ferramentas computacionais (Hydrology e TauDEM) e três bases de dados (SRTM, AGEDM e AW3D) para a extração de rede de drenagem e cálculo de parâmetros hidrográficos. Concluiu-se que o software TauDEM representa a melhor solução da extração de drenagem, pois minimiza a geração de drenagem retilínea e paralela em áreas de relevo plano. Dentre as bases de dados, a drenagem extraída dos dados AW3D apresentaram maior correspondência com drenagem de referência do IBGE. De modo geral, os parâmetros morfométricos calculados para a Bacia Hidrográfica do Alto Gurguéia (BHAG), a partir das três bases de dados selecionadas, não apresentaram diferenças significativas, indicando o potencial das ferramentas e bases de dados para análises hidrográficas de médias e grandes bacias. Em todo caso, recomenda-se a inspeção e correção manual da rede de drenagem ao aplicar qualquer método de extração automática, com o intuito de reduzir os erros decorrentes das limitações dos softwares. A B S T R A C T The need for planning and management of river basins has prompted research that seek to understand their hydrological dynamics. In regions with lack of topographic mapping on a large scale, it is common to use digital elevation models (DEM) for automatic drainage network extraction, delineation of watersheds and obtain hydrographic and morphometric parameters. Against this background the present study aimed to evaluate the efficiency of two computational tools (Hydrology and TauDEM) and three databases (SRTM, AGEDM and AW3D) for drainage network extraction and calculation of hydrographic parameters. It was concluded that the TauDEM software is the best solution drain extraction, because it minimizes the generation of rectilinear and parallel drainage in flat terrain areas. Among those databases, the drainage extracted of the AW3D data had higher correlation with the IBGE reference drainage. Overall, the morphometric parameters calculated for the basin of the Upper Gurguéia (BHAG), from the three selected databases, no show significant differences, indicating the potential of tools and databases for hydrographic analysis of averages and large basins. In any case, it is recommended to inspection and manual correction of the drainage network when applying any automatic extracting method, in order to reduce errors due to limitations of the software. Keywords: Drainage Neytwork. Digital Elevation Model. Geoprocessing.

Assessing the influence of DEM source on derived streamline and catchment boundary accuracy

Article

Full-text available

Oct 2019

Accurate DEM-derived streamlines and catchment boundaries are essential for hydrological modelling. Due to the popularity of hydrological parameters derived mainly from free DEMs, it is essential to investigate the accuracy of these parameters. This study compared the spatial accuracy of streamlines and catchment boundaries derived from available digital elevation models in South Africa. Two versions of Stellenbosch University DEMs (SUDEM5 and DEMSA2), the second version of the 30 m advanced spaceborne thermal emission and reflection radiometer global digital elevation model (ASTER GDEM2), the 30 and 90 m shuttle radar topography mission (SRTM30 and SRTM90 DEM), and the 90 m Water Research Commission DEM (WRC DEM) were considered. As a reference, a 1 m GEOEYE DEM was generated from GeoEye stereo images. Catchment boundaries and streamlines were extracted from the DEMs using the Arc Hydro module. A reference catchment boundary was generated from the GEOEYE DEM and verified during field visits. Reference streamlines were digitised at a scale of 1:10 000 from the 1 m orthorectified GeoEye images. Visual inspection, as well as quantitative measures such as correctness index, mean absolute error, root mean squares error and figure of merit index were used to validate the results. The study affirmed that high resolution (<30 m) DEMs produce more accurate parameters and that DEM source and resampling techniques also play a role. However, if high resolution DEMs are not available, the 30 m SRTM DEM is recommended as its vertical accuracy was relatively high and the quality of the streamlines and catchment boundary was good. In addition, it was found that the novel Euclidean distance-based MAE and RMSE proposed in this study to compare reference and DEM-extracted raster datasets of different resolutions is a more reliable indicator of geometrical accuracy than the correctness and figure of merit indices.

Comparative Study of Different Types of Digital Elevation Models on the Basis of Drainage Morphometric Parameters (Case Study of Wadi Fatimah Basin, KSA)

Article

Full-text available

Aug 2019

Nowadays there are a lot of geospatial datasets available in the form of different types of Digital Elevation Models (DEMs) which were launched with different resolutions. These datasets are used for studying the physiographical features of the hydrographic basins through the tracing and extracting the elevation points, watershed boundaries, streamlines, flow directions and morphometric parameters assessment. Many researchers have used these datasets to study and evaluate the hydrologic behavior of the basins which is considered as the reflection of physiographic features of the hydrographic basins. In the Middle East especially in Saudi Arabia, the trend of using DEMs increased for hydrographic basin analysis and assessment of hydrologic behavior. So, there is an important question about the accuracy and sensitivity of these datasets which are acquired from different DEMs. This study deals with four types of DEMs, first is derivative from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER 30 m resolution), second is Shuttle Radar Topographic Mission (SRTM 90 m resolution), third is SRTM 30 m resolution and the fourth is the Advanced Land Observing STLT (ALOS 30 resolution). More than 35 morphometric parameters including drainage network, basin geometry, basin texture and basin relief characteristics were measured and calculated using these four types of DEMs and calibrated with topographic maps of 1:250 K and 1:50 K scale and also google earth maps. Results show that the SRTM 30 m is characterized by high accuracy and has a very good matching with google earth maps and topographic map of scale1:50,000. This research is dealing with the comparison of the morphometric parameters of the hydrographic basin based on the type of DEM. It is clear to conclude that the SRTM 30 resolution is the best type for hydrology and water resources study.

Automated Detection of Drainage Networks from Digital Elevation Models

Abstract

No full-text available

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