Integrated Assessment of Gully Erosion Processes, Using Multispectral Remote Sensing, Stochastic Modelling, and GIS-based Morphotectonic Analysis; A Case Study in the Southwest of Iran

Bodenerosion und besonders Gully-Erosion sind zwei der hauptverantwortlichen Erscheinungen auf der Erde, die zu einer Abnahme der Produktivität von Böden und zur Verunreinigung von Wasserressourcen führen. Gully-Erosion gehört zu den intensivsten Prozessen der Land-Degradation, besonders in großen Teilen Irans, die ackerbauliche Nutzung und Weideland bedrohen. Vorangegangenen Studien zufolge zählen das anstehende Gestein, die Vegetationsdichte, die Topographie und die Landnutzung und ihre Veränderung zu den Hauptursachen für Bodenerosion und Gully-Erosion im Speziellen. Im ersten Teil der Arbeit wird die Anfälligkeit des Mazayjan-Beckens (MZJ) im Südwesten Irans hinsichtlich der Gully-Erosion ermittelt. Hierfür wurden eine detaillierte digitale Geländeanalyse sowie eine stochastische Modellierung basierend auf den Prinzipien der mechanischen Statistik durchgeführt. Zu den Geländeparametern mit dem größten Einfluss zählen der Konvergenz Index, die Horizontalwölbung sowie die Hangneigung. Gully-Erosion ist die einflussreichste Form der Wasser-Erosion und trägt signifikant zur Sedimentdynamik im Einzugsgebiet bei. Aus diesem Grund wurden im zweiten Teil dieser Arbeit Geographische Informationssysteme und Fernerkundungsdaten eingesetzt, um Eingabedaten für die numerischen Modelle zu generieren, welche Erosions- und Ablagerungsraten im MJZ-Becken ermitteln. Da verschiedene Mechanismen wie Graben-, Sheet- und Gully-Erosion im Untersuchungsgebiet vorkommen, wurde das Unit Stream Power-based Erosion Deposition-Modell (USPED) in Kombination mit dem Stream Power Index (SPI) und der Flow Accumulation (FA) ausgewählt. Den Berechnungen zufolge, bei welchen die USPED angewandt und Gully- Erosion durch den SPI ermittelt wurde, sind rund 17,5 % der Flächen im Untersuchungsgebiet stabil oder von sehr geringen Erosions- und Ablagerungsraten betroffen. 28,2 % hingegen unterliegen sehr hoher Erosion und 19,2 % sind von Ablagerungsprozessen betroffen. Tektonische Aktivität im Untersuchungsgebiet, welches Teil der Zargos-Berge (ZM) ist, trug in der Vergangenheit signifikant zur Ausbildung der Abflussbedingungen bei und dadurch zur Entwicklung der Landschaft. Jüngere tektonische Prozesse (Oberes Quartär) in Form von Erdbeben und damit verbundenen Hebungsprozessen, Brüchen und Verwerfungen sind in großen Teilen des Untersuchungsgebiets noch aktiv. Im dritten Teil dieser Arbeit liegt der Schwerpunkt auf der Ermittlung der Anfälligkeit geologischer Formationen hinsichtlich der Gully-Erosion, welche auch durch die jüngeren tektonischen Aktivitäten verursacht wurden Dies erfolgte anhand von Digitalen Oberflächenmodellen (DEMs) unterschiedlicher Herkunft (ASTER-Daten, Topographische Karten und Luftbilder) und räumlicher Auflösung (30 m, 10 m und 5 m). Weitere Untersuchungen zum Vorkommen von Gullysystemen und tektonischen Aktivitäten, wie beispielsweise die Analyse von Flußeinzugsgebietsmorphologien sowie der Analyse der Longitudinalprofile der Vorfluter, zeigen dass die Gebiete, welche besonders anfällig gegenüber Gully-Erosion sind, durch Hebungen und Verwerfungen geprägt sind. Die Software TecDEM wurde verwendet, um abrupte Veränderungen im Flussprofil im mittleren Bereich des Einzugsgebiets (alluviale Ablagerungen) zu ermitteln. Folglich deutet das Vorhandensein von “Knickpoints“ tektonische Aktivitäten an, welche wiederum die Erosionsprozesse entlang des Flussprofils verändern. Die Ergebnisse zeigen, dass starke Gully-Erosion in Zusammenhang mit diesen tektonischen Aktivitäten steht, insbesondere im Südwesten des MZJ-Beckens.Im letzten Teil dieser Arbeit wurde die Anfälligkeit für Gully-Erosion in einem GIS-basierten stochastischen Modell, dem “Maximum Entropy Modell“ regionalisiert. Dies erfolgte unter der Verwendung von multispektralen ASTER-Daten, aus welchen die geologischen Faktoren, welche hauptverantwortlich für die räumliche Verteilung von Gully-Erosion sind, durch Band-Ratios abgeleitet wurden. Eine multispektrale Analyse von ASTER-Daten liefert wertvolle Ergebnisse über die mineralische Ausdifferenzierung im ZM-Gebiet, welche räumlich höher aufgelöste Informationen liefert als die herkömmlichen geologischen Karten des Gebiets. In dieser Studie wurde das Verhältnis zwischen vorhandener Gully-Erosion und der Kombination von Predictor-Variablen, bestehend aus topographischen Indizes und ASTERBand- Ratios, untersucht. Die räumliche Vorhersage zeigt, dass Gully-Erosion überwiegend in colluvialen/ alluvionalen Gebieten mit hohen Anteilen von Salz, Gips und/ oder schluffiger Textur auftritt und besonders in den Ebenen im südlichen Untersuchungsgebiet vorkommen. Die vorgestellte Methode ermöglicht eine wirkungsvolle Abschätzung der Gully-Erosion, welchen den Bodenschutz und das Land-Management im Südwesten Irans unterstützen kann

A TOOLBOX FOR SEDIMENT BUDGET RESEARCH IN SMALL CATCHMENTS

© 2017, Lomonosov Moscow State University. All rights reserved. Sediment monitoring and assessment remain one of the most challenging tasks in fluvial geomorphology and water quality studies. As a response to various environmental and human disturbance effects, the main sources and pathways of the sediments transported within catchments, especially most pristine small one, may change. The paper discusses state-of-the-art in the sediment budget research for small catchments. We identified nine independent approaches in the sediment transport assessment and applied them in 11 catchments across Eurasia in the framework of an FP-7 Marie Curie-International Research Staff Exchange Scheme in 2012-2016. These methods were classified as: i) Field-based methods (In-situ monitoring of sediment transport;-Soil morphological methods and dating techniques; Sediment source fingerprinting; Sediment-water discharge relationships), ii) GIS and remote sensing approaches (Riverbed monitoring based on remote sensing/historical maps; parametrization of the channel sediment connectivity; Sediment transport remote sensing modeling), and iii) Numerical approaches (Soil erosion modeling and gully erosion (stochastic and empirical models); channel hydrodynamic modeling). We present the background theory and application examples of all selected methods. Linking fieldbased methods and datasets with numerical approaches, process measurements as well as monitoring can provide enhanced insights into sediment transfer and related water quality impacts. Adopting such integrated and multi-scale approaches in a sediment budget framework might contribute to improved understanding of hydrological and geomorphological responses

A toolbox for sediment budget research in small catchments

© 2017, Lomonosov Moscow State University. All rights reserved. Sediment monitoring and assessment remain one of the most challenging tasks in fluvial geomorphology and water quality studies. As a response to various environmental and human disturbance effects, the main sources and pathways of the sediments transported within catchments, especially most pristine small one, may change. The paper discusses state-of-the-art in the sediment budget research for small catchments. We identified nine independent approaches in the sediment transport assessment and applied them in 11 catchments across Eurasia in the framework of an FP-7 Marie Curie-International Research Staff Exchange Scheme in 2012-2016. These methods were classified as: i) Field-based methods (In-situ monitoring of sediment transport;-Soil morphological methods and dating techniques; Sediment source fingerprinting; Sediment-water discharge relationships), ii) GIS and remote sensing approaches (Riverbed monitoring based on remote sensing/historical maps; parametrization of the channel sediment connectivity; Sediment transport remote sensing modeling), and iii) Numerical approaches (Soil erosion modeling and gully erosion (stochastic and empirical models); channel hydrodynamic modeling). We present the background theory and application examples of all selected methods. Linking fieldbased methods and datasets with numerical approaches, process measurements as well as monitoring can provide enhanced insights into sediment transfer and related water quality impacts. Adopting such integrated and multi-scale approaches in a sediment budget framework might contribute to improved understanding of hydrological and geomorphological responses

Quantitative mapping of desertification risk using the modified MEDALUS model :a case study in the Mazayejan Plain, Southwest Iran

This paper presents the Modified MEDALUS (MMEDALUS) approach, a quantitative assessment of desertification, in the case study area located in the Southern part of Iran. Six main factors of desertification including: soil, climate, plant cover, management, erosion state and ground water situation were considered for the model approach. Then several sub-factors determining the quality of each main factor were quantified according to their quality and weighted on a scale between 1.0 and 2.0. We used a Geographic Information System (GIS) software to analyze and prepare the spatial distribution of the factor layers. Subsequently, the final desertification hazard map was prepared by combining the different MEDALUS factors in Arc GIS 10.3 in order to define the final hazard classes on the basis of hazard scores based on the geometric mean of the main factors. The MEDALUS and MMEDALUS models show the “Desertification Potential” that in turn was validated with the current state of desertification observed in the field. The results show that the applied MMEDALUS approach yield significantly better results than the MEDALUS model in the study area. The results also show that the areas under severe and very severe hazard are the most extensive classes in the desertification map. Thus, we illustrate that most of the study area is sensitive to desertification. However, we highlight that management, climate and water table qualities were the most important indicators affecting the desertification processes, while soil quality seems to play a minor role in our study area.23223

Prediction of gully erosion susceptibilities using detailed terrain analysis and maximum entropy modeling: A case study in the Mazayejan plain, southwest Iran

Gully erosion is one of the most severe environmental problems in large areas of Iran. Land degradation and accelerated desertification are the consequence in susceptible areas. Gully erosion normally takes place when surface runoff is concentrated and thus, detach and transfer soil particles down the slopes into the drainage network. In traditional soil erosion studies these processes often have been neglected. In this study we investigate the spatial distribution of gully erosion processes with a quantitative method since in many national assessment approaches just qualitative models were applied. For this study we utilized a detailed terrain analysis and a stochastic modeling approach using mechanical statistics. Moreover we predict the potential spatial distribution of gullies in the Mazayejan plain of Fars province in southwestern Iran where gully erosion is the main environmental threat. Our methodological approach consists in the following steps: i) mapping of gully erosion phenomena in a test area based on Google Earth images; ii) development of a digital elevation model (DEM) with 10 meter resolution, iii) detailed terrain analysis deriving more than 20 terrain indices, iv) application of the Maxent model for the test area using the gully erosion forms as dependent variable and topographic indices as predictor variable and finally v) prediction of the spatial distribution of gully erosion potential for the entire study area. Model performance was evaluated by the Receiver Operating Characteristic (ROC). The results obtained show that the Maxent model perform very well and thus, it is suitable for the prediction of the gully erosion potential in the area. Among the terrain indices utilized in the prediction the most important ones are: convergence index, plan curvature, and slope. The proposed methodology allows conducting a proper gully erosion assessment in order to identify the priority areas for soil conservation and land use management

Prediction of gully erosion susceptibilities using detailed terrain analysis and maximum entropy modeling: A case study in the Mazayejan plain, southwest Iran

Gully erosion is one of the most severe environmental problems in large areas of Iran. Land degradation and accelerated desertification are the consequence in susceptible areas. Gully erosion normally takes place when surface runoff is concentrated and thus, detach and transfer soil particles down the slopes into the drainage network. In traditional soil erosion studies these processes often have been neglected. In this study we investigate the spatial distribution of gully erosion processes with a quantitative method since in many national assessment approaches just qualitative models were applied. For this study we utilized a detailed terrain analysis and a stochastic modeling approach using mechanical statistics. Moreover we predict the potential spatial distribution of gullies in the Mazayejan plain of Fars province in southwestern Iran where gully erosion is the main environmental threat. Our methodological approach consists in the following steps: i) mapping of gully erosion phenomena in a test area based on Google Earth images; ii) development of a digital elevation model (DEM) with 10 meter resolution, iii) detailed terrain analysis deriving more than 20 terrain indices, iv) application of the Maxent model for the test area using the gully erosion forms as dependent variable and topographic indices as predictor variable and finally v) prediction of the spatial distribution of gully erosion potential for the entire study area. Model performance was evaluated by the Receiver Operating Characteristic (ROC). The results obtained show that the Maxent model perform very well and thus, it is suitable for the prediction of the gully erosion potential in the area. Among the terrain indices utilized in the prediction the most important ones are: convergence index, plan curvature, and slope. The proposed methodology allows conducting a proper gully erosion assessment in order to identify the priority areas for soil conservation and land use management

A TOOLBOX FOR SEDIMENT BUDGET RESEARCH IN SMALL CATCHMENTS

Sediment monitoring and assessment remain one of the most challenging tasks in fluvial geomorphology and water quality studies. As a response to various environmental and human disturbance effects, the main sources and pathways of the sediments transported within catchments, especially most pristine small one, may change. The paper discusses state-of-the-art in the sediment budget research for small catchments. We identified nine independent approaches in the sediment transport assessment and applied them in 11 catchments across Eurasia in the framework of an FP – 7 Marie Curie – International Research Staff Exchange Scheme in 2012-2016. These methods were classified as: i) Field-based methods (In-situ monitoring of sediment transport;– Soil morphological methods and dating techniques; Sediment source fingerprinting; Sediment-water discharge relationships), ii) GIS and remote sensing approaches (Riverbed monitoring based on remote sensing/historical maps; parametrization of the channel sediment connectivity; Sediment transport remote sensing modeling), and iii) Numerical approaches (Soil erosion modeling and gully erosion (stochastic and empirical models); channel hydrodynamic modeling). We present the background theory and application examples of all selected methods. Linking fieldbased methods and datasets with numerical approaches, process measurements as well as monitoring can provide enhanced insights into sediment transfer and related water quality impacts. Adopting such integrated and multi-scale approaches in a sediment budget framework might contribute to improved understanding of hydrological and geomorphological responses