A Probabilistic Assessment of Soil Erosion Susceptibility in a Head Catchment of the Jemma Basin, Ethiopian Highlands

Soil erosion represents one of the most important global issues with serious effects on agriculture and water quality, especially in developing countries, such as Ethiopia, where rapid population growth and climatic changes affect widely mountainous areas. The Meskay catchment is a head catchment of the Jemma Basin draining into the Blue Nile (Central Ethiopia) and is characterized by high relief energy. Thus, it is exposed to high degradation dynamics, especially in the lower parts of the catchment. In this study, we aim at the geomorphological assessment of soil erosion susceptibilities. First, a geomorphological map was generated based on remote sensing observations. In particular, we mapped three categories of landforms related to (i) sheet erosion, (ii) gully erosion, and (iii) badlands using a high-resolution digital elevation model (DEM). The map was validated by a detailed field survey. Subsequently, we used the three categories as dependent variables in a probabilistic modelling approach to derive the spatial distribution of the specific process susceptibilities. In this study we applied the maximum entropy model (MaxEnt). The independent variables were derived from a set of spatial attributes describing the lithology, terrain, and land cover based on remote sensing data and DEMs. As a result, we produced three separate susceptibility maps for sheet and gully erosion as well as badlands. The resulting susceptibility maps showed good to excellent prediction performance. Moreover, to explore the mutual overlap of the three susceptibility maps, we generated a combined map as a color composite where each color represents one component of water erosion. The latter map yields useful information for land-use managers and planning purposes

Geomorphology of the upper Mkhomazi River basin, KwaZulu-Natal, South Africa, with emphasis on late Pleistocene colluvial deposits

We present a 1:50 000 scale geomorphological map of the upper Mkhomazi River basin, located in the foothills of the Drakensberg mountains in KwaZulu-Natal Province, South Africa. The sub-horizontal strata of the Permo-Triassic Beaufort Group forms plateau interfluves with a concave valley slope morphology. Locally, thick sequences of late Pleistocene colluvial deposits and associated buried paleosols (Masotcheni Formation) infill first-order tributary stream valleys and extend across the adjacent lower slopes. Surface runoff processes preferentially incise into the poorly consolidated, highly erodible sediments causing severe gully erosion that is responsible for widespread land degradation and desertification phenomena. The main purpose of this work is to derive a geomorphological map of the study area focussing on the erosional landforms to understand their spatial distribution and their relation to the colluvial deposits. Finally, a local and regional stratigraphic correlation of colluvial deposits and associated buried palaeosol profiles is proposed

Geomorphological processes, forms and features in the surroundings of the Melka Kunture Palaeolithic site, Ethiopia

The landscape of the surroundings of the Melka Kunture prehistoric site, Upper Awash Basin, Ethiopia, were studied intensively in the last decades. Nonetheless, the area was mainly characterized under a stratigraphic/geological and archaeological point of view. However, a detailed geomorphological map is still lacking. Hence, in this study, we identify, map and visualize geomorphological forms and processes. The morphology of the forms, as well as the related processes, were remotely sensed with available high-resolution airborne and satellite sources and calibrated and validated through extensive field work conducted in 2013 and 2014. Furthermore, we integrated multispectral satellite imagery to classify areas affected by intensive erosion processes and/or anthropic activities. The Main Map at 1:15,000 scale reveals structural landforms as well as intensive water-related degradation processes in the Upper Awash Basin. Moreover, the map is available as an interactive WebGIS application providing further information and detail (www.roceeh.net/ethiopia_geomorphological_map/)

Identification, characterisation and analysis of the Oltrepo Pavese calanchi in the Northern Apennines (Italy)

Badlands are characteristic erosional forms distributed along the entire Apennines. In the Italian context badland areas are called “calanchi”, the plural of the word “calanco”. In this paper we present the first calanchi inventory map of the Oltrepo Pavese area, Northern Apennines (Italy). In total 263 calanchi were mapped using remote sensing techniques like Orthophotos, Google Earth images, as well as field recognition. Moreover, calanchi were characterised from a geomorphologic, geologic and a morphometric point of view. The calanchi of the Oltrepo Pavese have been categorised in two geomorphological classes based on process related morphologies. In the study area calanchi mainly occur in soft sedimentary bedrock materials such as melanges, marls, claystones, and interstratified rocks. The results show that calanchi formations are often related to faults and tectonic lineaments present in the study area. Moreover, we analyse a 5 m cell size Digital Terrain Model to detect correlations between calanchi and morphometric indices. The calanchi, defined and categorised for the first time in the study area, show typical morphometric characteristics of Apennine calanchi forms and features. In particular, they occur on concave south-facing slopes on soft bedrock formations. Finally, a multitemporal air photo interpretation over a 40 years period indicated a general decrease in calanchi areas. The area reduction is mainly correlated to intensive land use changes combined with variations of precipitation pattern. The revegetation trend was also confirmed by NDVI analysis based on Landsat satellites images. The calanchi were digitized and stored in a GIS database providing the information for future quantitative modelling assessments

Assessment of calanchi and rill–interrill erosion susceptibilities using terrain analysis and geostochastics: A case study in the Oltrepo Pavese, Northern Apennines, Italy

Soil erosion is one of the most important environmental problems distributed worldwide. In the last decades, numerous studies have been published on the assessment of soil erosion and the related processes and forms using empirical, conceptual and physically based models. For the prediction of the spatial distribution, more and more sophisticated stochastic modelling approaches have been proposed – especially on smaller spatial scales such as river basins. In this work, we apply a maximum entropy model (MaxEnt) to evaluate badlands (calanchi) and rill–interrill (sheet erosion) areas in the Oltrepo Pavese (Northern Apennines, Italy). The aim of the work is to assess the important environmental predictors that influence calanchi and rill–interrill erosion at the regional scale. We used 13 topographic parameters derived from a 12 m digital elevation model (TanDEM-X) and data on the lithology and land use. Additional information about the vegetation is introduced through the normalized difference vegetation index based on remotely sensed data (ASTER images). The results are presented in the form of susceptibility maps showing the spatial distribution of the occurrence probability for calanchi and rill–interrill erosion. For the validation of the MaxEnt model results, a support vector machine approach was applied. The models show reliable results and highlight several locations of the study area that are potentially prone to future soil erosion. Thus, coping and mitigation strategies may be developed to prevent or fight the soil erosion phenomenon under consideration. © 2020 John Wiley & Sons, Ltd

Evaluation of Gully Erosion Susceptibility Using a Maximum Entropy Model in the Upper Mkhomazi River Basin in South Africa

Soil erosion is one of the most challenging environmental issues in the world, causing unsustainable soil loss every year. In South Africa, several episodes of gully erosion have been documented and clearly linked to the presence of Quaternary colluvial deposits on the Drakensberg Mountain footslopes. The aim of this study was to identify and assess the triggering factors of gully erosion in the upper Mkhomazi River basin in KwaZulu-Natal, South Africa. We compiled a gully inventory map and applied remote sensing techniques as well as field surveys to validate the gully inventory. The gullies were subdivided into slope gullies and fluvial gullies. We derived susceptibility maps based on the spatial distribution of gully types to assess the most important driving factors. A stochastic modeling approach (MaxEnt) was applied, and the results showed two susceptibility maps within the spatial distribution of the gully erosion probability. To validate the MaxEnt model results, a subset of the existing inventory map was used. Additionally, by using areas with high susceptibilities, we were able to delineate previously unmapped colluvial deposits in the region. This predictive mapping tool can be applied to provide a theoretical basis for highlighting erosion-sensitive substrates to reduce the risk of expanding gully erosion

Evaluation of Gully Erosion Susceptibility Using a Maximum Entropy Model in the Upper Mkhomazi River Basin in South Africa

Soil erosion is one of the most challenging environmental issues in the world, causing unsustainable soil loss every year. In South Africa, several episodes of gully erosion have been documented and clearly linked to the presence of Quaternary colluvial deposits on the Drakensberg Mountain footslopes. The aim of this study was to identify and assess the triggering factors of gully erosion in the upper Mkhomazi River basin in KwaZulu-Natal, South Africa. We compiled a gully inventory map and applied remote sensing techniques as well as field surveys to validate the gully inventory. The gullies were subdivided into slope gullies and fluvial gullies. We derived susceptibility maps based on the spatial distribution of gully types to assess the most important driving factors. A stochastic modeling approach (MaxEnt) was applied, and the results showed two susceptibility maps within the spatial distribution of the gully erosion probability. To validate the MaxEnt model results, a subset of the existing inventory map was used. Additionally, by using areas with high susceptibilities, we were able to delineate previously unmapped colluvial deposits in the region. This predictive mapping tool can be applied to provide a theoretical basis for highlighting erosion-sensitive substrates to reduce the risk of expanding gully erosion

Assessment of piping-sinkhole development in a fluvial-terrace scarp retreat environment: A multi-temporal analysis on the lower Ticino River (Italy)

This paper investigates, from a geomorphological and hydrogeological point of view, the development of piping-sinkhole phenomena at a retreating fluvial-terrace scarp along the lower Ticino River, near Casottole, northern Italy. Piping forms and features are well documented in the literature as complex soil erosion phenomena, usually associated with clayey or carbonate substrata, or to specific fluvial deposits. Such phenomena appear to have never been mapped in the lower Ticino area, and up to now, no evidence of piping-sinkhole occurrence in terraced alluvial plains strictly associated with terrace scarp erosion processes have been observed and reported in the literature. The geomorphological peculiarities of the area were assessed through field surveys, photographic and drone imaging, photointerpretation, and GIS analysis. Moreover, the riverbed morphological evolution was evaluated since the 1950s, and the hydrogeological conditions were analysed. Finally, a large piping-sinkhole database composed by 35 landforms was assembled in a WebGIS system. The piping-sinkhole phenomena were associated with the presence of perched water tables with flows towards the Ticino River, whose origin can be associated with site conditions, the large up dip network of surface water, and local irrigation practices. The research presented here provides a new contribution to the understanding of sinkhole occurrence and formation in previously unstudied terrace-scarp settings, and new insights for fluvial-terrace scarp modelling. Furthermore, it represents an important knowledge base to inform sustainable and effective measures for environmental management and hydrogeomorphic risk mitigation with reference to terrace scarp erosion and sinkholes

A probabilistic assessment of soil erosion susceptibility in a head catchment of the jemma basin, ethiopian highlands

Soil erosion represents one of the most important global issues with serious effects on agriculture and water quality, especially in developing countries, such as Ethiopia, where rapid population growth and climatic changes affect widely mountainous areas. The Meskay catchment is a head catchment of the Jemma Basin draining into the Blue Nile (Central Ethiopia) and is characterized by high relief energy. Thus, it is exposed to high degradation dynamics, especially in the lower parts of the catchment. In this study, we aim at the geomorphological assessment of soil erosion susceptibilities. First, a geomorphological map was generated based on remote sensing observations. In particular, we mapped three categories of landforms related to (i) sheet erosion, (ii) gully erosion, and (iii) badlands using a high-resolution digital elevation model (DEM). The map was validated by a detailed field survey. Subsequently, we used the three categories as dependent variables in a probabilistic modelling approach to derive the spatial distribution of the specific process susceptibilities. In this study we applied the maximum entropy model (MaxEnt). The independent variables were derived from a set of spatial attributes describing the lithology, terrain, and land cover based on remote sensing data and DEMs. As a result, we produced three separate susceptibility maps for sheet and gully erosion as well as badlands. The resulting susceptibility maps showed good to excellent prediction performance. Moreover, to explore the mutual overlap of the three susceptibility maps, we generated a combined map as a color composite where each color represents one component of water erosion. The latter map yields useful information for land-use managers and planning purposes

Litho-structure of the Oltrepo Pavese, Northern Apennines (Italy)

In this article we present a detailed litho-structural map of the Oltrepo Pavese, a sector of the Northern Apennines, Southern Lombardy, Italy. Lithology and geological structures are an important basis for different disciplines of Earth Sciences. In particular, for the assessment of earth surface processes such as soil erosion, mass movements, flooding, etc. The Oltrepo Pavese is characterised by a complex geology and related tectonic settings. In this study, we conducted a comprehensive lithological mapping approach considering existing geological maps, and detailed field surveys. The lithotypes have been subdivided into 11 classes based on the dominant outcropping lithologies. Integrating bibliographic data and a detailed Digital Terrain Analysis of a high-resolution DTM (5 m) we detected faults, folds and tectonic lineaments in the study area. The final result is represented by a litho-structural map of the Oltrepo Pavese-area, consisting in two shape files elaborated in an open source GIS environment