Article

Assessment of gully erosion rates through interviews and measurements: A case study from northern Ethiopia

Earth Surface Processes and Landforms

February 2006
31(2):167 - 185

DOI:10.1002/esp.1317

Authors:

Jan Nyssen

Ghent University

J. Poesen

KU Leuven

Jan Moeyersons

Royal Museum for Central Africa

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Gullying has been widespread in the Ethiopian Highlands during the 20th century. It threatens the soil resource, lowers crop yields in intergully areas through enhanced drainage and desiccation, and aggravates flooding and reservoir siltation. Knowing the age and rates of gully development during the last few decades will help explain the reasons for current land degradation. In the absence of historical written or photographic documentation, the AGERTIM method (Assessment of Gully Erosion Rates Through Interviews and Measurements) has been developed. It comprises measurements of contemporary gully volumes, monitoring of gully evolution over several years and semi-structured interview techniques. Gully erosion rates in the Dogu'a Tembien District, Tigray, Ethiopia, were estimated in three representative case-study areas. In Dingilet, gullying started around 1965 after gradual environmental changes (removal of vegetation from cropland in the catchment and eucalyptus plantation in the valley bottom); rill-like incisions grew into a gully, which increased rapidly in the drier period between 1977 and 1990. The estimated evolution of the total gully volume in the other areas show patterns similar to those of the Dingilet gully. Average gully erosion rate over the last 50 years is 6·2 t ha−1 a−1. Since 1995, no new gullies have developed in the study area. Area-specific short-term gully erosion rates are now on average 1·1 t ha−1 a−1. The successful application of the AGERTIM method requires an understanding of the geomorphology of the study area and an integration of the researchers with the rural society. It reveals that rapid gully development in the study area is some 50 years old and is mainly caused by human-induced environmental degradation. Under the present-day conditions of ‘normal’ rain and catchment-wide soil and water conservation, gully erosion rates are decreasing. Copyright

ASTSN Gullies Ethiopia SC

Article

Full-text available

Mar 2025

Paolo Billi

P. Billi, Hydro-morphology of discontinuous gullies: an Ethi-opian example. Gully erosion is very common in Ehtiopia affecting large areas with different geomorphological, pedological and climatic characteristics. The amount of soil loss due to gullying has become a very serious problem in the recent decades leading to remarkable depletion of cultivated land. Field investigations on gully morphological development were carried out in two study areas of Ethiopia, the Lakes Region in the Main Ethiopian Rift Valley and the central highlands, representative of different geo-morphological and environmental conditions. Three main types of discontinuous gullies were identifies on the basis of their morphological characteristics. In order to investigate the main causes originating the different types of gullies, data on geomorphic parameters were collected in the field. From the analysis of field data hypotheses on the mechanisms responsible for gully development in the study areas were derived. The short-and mid-term gully expansion rate and the main processes involved are discussed as well. Riassunto-P. Billi, Idromorfologia dei solchi d'erosione discontinui: un esempio Etiopico. L'erosione per solchi è molto comune in Etiopia e colpisce vaste aree con diverse caratteristiche geomorfologiche, pedologiche e climatiche. La quantità di suolo perso a causa di questo fenomeno erosivo è dive-nuto, nei decenni recenti, un problema molto grave che ha portato ad un marcato degrado del territorio. Ricerche di campagna sullo svilup-po morfologico dei solchi d'erosione sono stati condotti in due aree dell'Etiopia, la Regione dei Grandi Laghi nella Rift Valley centrale e l'altopiano centrale, rappresentative di differenti condizioni geomor-fologiche ed ambientali. Sulla base delle loro caratteristiche morfolo-giche, sono stati identificati tre diversi tipi di solchi d'erosione. Allo scopo di identificare le principali cause che danno origine a questi differenti tipi di solchi d'erosione, dati dei loro parametri geomorfici sono stati misurati in campagna. L'analisi dei dati di campo ha permes-so di formulare delle ipotesi su processi fisici responsabili della loro formazione. Inoltre vengono discussi anche il loro tasso di espansione a breve e medio termine ed i fattori di controllo. Parole chiave-solchi d'erosione, idromorfologia, degradazione del suolo, zone aride, Etiopia

Historicizing Natural Hazards and Human-Induced Landscape Transformation in a Tropical Mountainous Environment in Africa: Narratives from Elderly Citizens

Article

Full-text available

Feb 2025

Studying natural hazards in the context of human-induced landscape transformation is complex, especially in regions with limited information. The narratives of the elderly can play a role in filling these knowledge gaps at the multi-decadal timescale. Here, we build upon a citizen-based elderly approach to understanding natural hazard patterns and landscape transformation in a tropical mountainous environment, the Kigezi Highlands (SW Uganda). We engaged 98 elderly citizens (>70 years old) living in eight small watersheds with different characteristics. Through interviews and focus group discussions, we reconstructed historical timelines and used participatory mapping to facilitate the interview process. We cross-checked the information of the elderly citizens with historical aerial photographs, archives, and field visits. Our results show that major land use/cover changes are associated with a high population increase over the last 80 years. We also evidence an increase in reported natural hazard events such as landslides and flash floods from the 1940s until the 1980s. Then, we notice a stabilization in the number of hazard events per decade, although the two most impacted decades (1980s and 2000s) stand out. Despite this new information, an increase in natural hazard frequency due to land use/cover change cannot yet be quantitatively validated, especially when the probable modulator effect of climate variability is considered. Nevertheless, the increase in the exposure of a vulnerable population to natural hazards is clear, and population growth together with poor landscape management practices are the key culprits that explain this evolution. This study demonstrates the added value of historical narratives in terms of understanding natural hazards in the context of environmental changes. This insight is essential for governments and non-governmental organizations for the development of policies and measures for disaster risk reduction that are grounded in the path dependence of local realities.

Historicizing Natural Hazards and Human-Induced Landscape Transformation in a Tropical Mountainous Environment in Africa: Narratives from Elderly Citizens

Preprint

Full-text available

Dec 2024

Studying natural hazards in the context of human-induced landscape transformation is complex, especially in regions with limited information. Elderly narratives can play a role in filling these knowledge gaps at the multi-decadal timescale. Here, we build upon a citizen-based elderly approach to understand natural hazard patterns and landscape transformation in a tropical mountainous environment, the Kigezi highlands (Uganda). We engaged 98 elderly citizens (70 years old and above) living in eight small watersheds with contrasting characteristics. Through interviews and focus group discussions, we reconstructed historical timelines and used participatory mapping to facilitate the interview process. We cross-checked the information of the elderly citizens with historical photographs, archives and field visits. Our results show that major land use/cover changes are associated with a high population increase over the last 80 years. We also evidence an increase in reported natural hazard events such as landslides and flash floods from the 1940’s until the 1980’s. Then, we notice a stabilization in the number of hazard events per decade, although the two most impacted decades (1980’s and 2000’s) stand out. Despite this new information, an increase of natural hazard frequency due to land use/cover change cannot yet be quantitatively validated, especially when the probable modulator effect of climate variability is considered. Nevertheless, the increase in exposure of vulnerable population to natural hazards is clear, and population growth together with poor landscape management practices are key culprits to explain this evolution. This study demonstrates the added value of historical narratives to understand natural hazards in the context of environmental changes.

Object-based image analysis (OBIA)-based gully erosion dynamics, sediment loading rate and sediment yield study in Lake Hawassa Sub-basin, Ethiopia

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Aug 2024

Object-based image analysis (OBIA)-based gully erosion dynamics, sediment loading rate and sediment yield study in Lake Hawassa Sub-basin, Ethiopia

Article

Full-text available

Jan 2023

Gully erosion is a serious environmental issue in Lake Hawassa Sub-basin. It has affected a large portion of the catchment, and a large amount of sediment has been transported into the lake. This condition needs to be addressed. However, before conservation techniques are implemented, the gully systems should be mapped, their extent and changes over time need to be measured, and their capacity to produce sediment from their catchments should be determined. The objective of this study were, therefore, to map and analyse the change in gully erosion and quantify the sediment loading rate and sediment yield from the active and connected gullies in Lake Hawassa Sub-basin using object-based image analysis (OBIA) with high-resolution SPOT 5 satellite image of the years 2011 and 2020. This method was integrated with field observation for mapping gully features of the study area, in comparison with automatic digitization carried out with the help of eCogenition Developer Version 9.1 and ArcGIS tools. Overall accuracy and Kappa coefficient were Natural Resource Modeling. 2023;e12368. wileyonlinelibrary.com/journal/nrm

Drivers of Gully Erosion and its Socio-economic and Environmental Effects in a Tropical Semi-arid Environment

Article

Full-text available

Mar 2024

Gully erosion is a form of severe land degradation, which is more pronounced in semi-arid and arid environments due to their vulnerable ecosystems. Establishing the causes and effects of gully erosion is therefore fundamental in policy formulation and resource allocation for up-scaling context-specific gully mitigation and rehabilitation measures. Thus, this study aimed at assessing the causes and effects of gully erosion in semi-arid region, in the North-West part of Kenya. A cross-sectional survey, field measurements, laboratory analysis, focus group discussions and key informants’ interviews were used to collect data on drivers and effects of gully erosion. Descriptive statistics and content analysis were used to analyze the data. From the findings, 60 % of the respondents reported deforestation as the main driver of gully erosion. Further, 37 and 34 % of the respondents reported surface runoff and steep slopes, respectively, as major drivers of gully erosion. Soils in the region had a high dispersion ratio, with values of between 0.3 and 0.9, making them highly erodible. About 66 and 55 % of the respondents reported that the major effects of gully erosion were reduction in arable land size and death of livestock due to fatal falls, respectively. Approximately 14 ha of arable land and 1,483,600 Mg of sediment have been lost to gully erosion at the rate of about 2,410 Mg ha-1 over a period of 45 years. The average growth rate and density of gullies in the study site stood at 154 Mg ha-1 yr-1 and 0.7 km km-2, respectively. Four people and about 100 cattle had died due to fatal falls into the deep gullies. Thus, there is an urgent need to rehabilitate existing gullies while mitigating occurrence of new gullies in the study area. This would convert existing badlands into hotspots of biodiversity.

Object‐based image analysis (OBIA)‐based gully erosion dynamics, sediment loading rate and sediment yield study in Lake Hawassa Sub‐basin, Ethiopia

Article

Full-text available

Feb 2023
NAT RESOUR MODEL

Gully erosion is a serious environmental issue in Lake Hawassa Sub‐basin. It has affected a large portion of the catchment, and a large amount of sediment has been transported into the lake. This condition needs to be addressed. However, before conservation techniques are implemented, the gully systems should be mapped, their extent and changes over time need to be measured, and their capacity to produce sediment from their catchments should be determined. The objective of this study were, therefore, to map and analyse the change in gully erosion and quantify the sediment loading rate and sediment yield from the active and connected gullies in Lake Hawassa Sub‐basin using object‐based image analysis (OBIA) with high‐resolution SPOT 5 satellite image of the years 2011 and 2020. This method was integrated with field observation for mapping gully features of the study area, in comparison with automatic digitization carried out with the help of eCogenition Developer Version 9.1 and ArcGIS tools. Overall accuracy and Kappa coefficient were determined and were found to be 85.2% and 0.81, respectively, for the image of year 2020 and 81.1% and 0.76, respectively, for the image of year 2011. Based on the OBIA method, the extent of gullies (in area) were found to be 63.5 km2 in 2011 and 79.9 km2 showing a rapid increase between 2011 and 2020 (an increase of 16.4 km2 (24.4%) in the 10 years considered). The later result shows that 5.53% of the area of the Lake Hawassa Sub‐basin is affected by gully erosion. The maximum gully density in the study area was found to be 589 km/km2 in 2011 and this increased to 884 km/km2 in 2020. The sediment loading rate from the Lake's catchment was found to be in the range of 12.62 to 38.59 ton per hectare per year. The sediment yield from the Lake's catchment was 8.83 to 27.02 t/ha/year. The total annual volume‐based sediment yield at the Lake generated from the gully was 2.39 million cubic meter considering sediment delivery ratio of 70% for fully connected gullies. This result shows that 0.21% of the storage capacity of the Lake was being lost due to sedimentation from the gully system every year. From the result by dividing the total volume of the sediment by the surface area of the lake, one can see that a silt thickness of 2.51 cm was being deposited in the Lake every year. Gully erosion mapping and its dynamic activity over time is a critical step to monitor land degradation and to study its current and future local impacts. Quantifying gully erosion dynamics can help understand gully formation and is used for spatial and temporal evolution. Image‐based object analysis is a powerful technique used for such activities and the following are its core application of it: − Image‐based object analysis is the key function of feature extraction, change detection, and object identification having avoiding of errors made in manual digitization and taking much less time with the help of eCognition Developer excellent programming tool. − To protect and sustain the watershed and the Lake system from gully erosion and sedimentation, the natural resources managers to design sustainable planning strategies for the stabilization of gullies and the prevention of gully development in sensitive locations. − Effective application of OBIA technique might suggest a basis for increasing such type of technique in other future extraction can be an advantage. Image‐based object analysis is the key function of feature extraction, change detection, and object identification having avoiding of errors made in manual digitization and taking much less time with the help of eCognition Developer excellent programming tool. To protect and sustain the watershed and the Lake system from gully erosion and sedimentation, the natural resources managers to design sustainable planning strategies for the stabilization of gullies and the prevention of gully development in sensitive locations. Effective application of OBIA technique might suggest a basis for increasing such type of technique in other future extraction can be an advantage.

Understanding the process of valley bottom gully formation and development to reduce reservoir sedimentation in the highlands of North-western Ethiopia

Thesis

Jan 2022

Selamawit Damtew Amare

Life cycle of gullies: a susceptibility assessment in the Southern Main Ethiopian Rift

Article

Full-text available

Dec 2023
NAT HAZARDS

Gullies experience varying states of activity during their life cycle. For example, their highest growth rates are commonly observed in the period that follows their initiation, whereas they are less active when reaching stability. Understanding the environmental conditions under which gullies initiate, expand, and stabilize is therefore vital to mitigate their impacts. Data-driven susceptibility assessments are key approaches to understanding these conditions at the catchment scale. However, such assessments commonly focus, at best, only on one part of the problem (e.g., on the gully heads) and do not consider gully erosion processes. So far, no study has attempted to explicitly model the life cycle of gullies at regional scale using statistical approach. Here, we help bridging this research gap through modeling separately the location where new gullies initiate and where they stabilize using both gully initiation points and gully heads. More specifically, we study over 4400 active and inactive gullies in the Southern Main Ethiopian Rift. Using logistic regression models, we assess the susceptibility to gully initiation points derived from slope-drainage area (S–A) thresholds. This is then compared with the susceptibility of active or inactive gully heads at the level of four catchments considered together and separately. Highly susceptible areas for gully initiation are mainly located in rejuvenated landscapes downslope of rifting-associated knickpoints, where steep hillslopes are more recent than those of the surrounding relict landscapes and where landslides are present. Planform concave slopes with a higher surface runoff concentration favor initiation of gullies. In contrast, gullies stabilize in planform convex slopes with a more diffusive characteristic. The resulting susceptibility models can contribute to the decision-making process on the optimized locations of soil and water conservation measures during several stages of the life cycle of gullies.

Palaeoenvironmental research at Hawelti–Melazo (Tigray, northern Ethiopia) – insights from sedimentological and geomorphological analyses

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Jan 2023

The sites of Hawelti–Melazo in the Tigray region of the northern Ethiopian Highlands is an archaeological hotspot related to the D'mt kingdom (ca. 800–400 BCE). The existence of several monumental buildings, which have been excavated since the 1950s, underline the importance of this area in the Ethio-Sabaean period. We investigated the geomorphological and geological characteristics of the site and its surroundings and carried out sedimentological analyses, as well as direct (luminescence) and indirect (radiocarbon) sediment dating, to reconstruct the palaeoenvironmental conditions, which we integrated into the wider context of Tigray. Luminescence dating of feldspar grains from the May Agazin catchment indicate enhanced fluvial activity in the late Pleistocene, likely connected to the re-occurring monsoon after the Last Glacial Maximum (LGM). The abundance of trap basalt on the Melazo plateau, which provides the basis for the development of fertile soils, and the presumably higher groundwater level during the Ethio-Sabaean Period, provided favourable settlement conditions. The peninsula-like shape of the Melazo plateau was easily accessible only from the east and northeast, while relatively steep scarps enclose the other edges of the plateau. This adds a possible natural protective function to this site.

Implications of Land-Use and Land-Cover Changes for Geomorphic Processes in Selected Parts of Kebbi State, Nigeria

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Jun 2022

This paper examined the implications of land use and land cover changes for geomorphic processes in selected parts of Kebbi State. Specifically, the objectives of the study entailed a time series analysis of Landsat 5TM of 1991, Landsat 7 ETM of 2003 and 2020 Landsat 8 Operational land Imager (OLI) imageries of the study area to assess the rate and magnitude of LULC changes, identify the LULC change patterns and establish a relationship between changing land use/cover and geomorphic processes in the study area. Major land use classes used to determine changes in land use/ cover are built-up areas, water body, plantation, farmlands, scrubland and Badlands land uses. These were classified in the ArcGIS 10.5 environment. Descriptive statistics were used to summarize data obtained while the chi-square analysis was used to test for significant changes recorded over the examined period. The results showed that the land uses which recorded major changes are the built-up land use (increased from 18km2 to 334.73km2), scrubland (decreased from 2330.13 km2 to 1581.32km2) and water body (declined from 45 to 17.07) between 1991 and 2020. Chi-square analysis carried out to determine the level of significant changes in the land use and land cover categories for the periods studied shows statistical significance at p< 0.05. This result shows that significant changes occurred in the respective land use/land cover types over the examined period. Similarly, dominant geomorphic processes identified in the study area are erosion and flooding, triggered by land use and land cover changes. The study recommends improved technology in mapping and land suitability assessments, maintaining an up-to-date geo-information system and linking geomorphological information to infrastructural planning and development.

Gully erosion susceptibility mapping using four machine learning methods in Luzinzi watershed, eastern Democratic Republic of Congo

Article

Jan 2023

Soil erosion by gullying causes severe soil degradation, which in turn leads to severe socioeconomic and environmental damages in tropical and subtropical regions. To mitigate these negative effects and guarantee sustainable management of natural resources, gullies must be prevented. Gully management strategies start by devising adequate assessment tools and identification of driving factors and control measures. To achieve this, machine learning methods are essential tools to assist in the identification of driving factors to implement site-specific control measures. This study aimed at assessing the effectiveness of four machine learning methods (Random Forest (RF), Maximum of Entropy (MaxEnt), Artificial Neural Network (ANN), and Boosted Regression Tree (BRT)) to identify gully's driving factors, and predict gully erosion susceptibility in the Luzinzi watershed, in Walungu territory, eastern Democratic Republic of the Congo (DRC). In this study, gullies were first identified through multiple field surveys and then digitized using a very high-resolution image (CNI/airbus) from Google Earth. Overall, 270 gullies were identified, of which 70% (189) were randomly selected to train the four machine learning methods using topographical, hydrological, and environmental factors hypothesized to be gully-related conditioning factors. The remaining 30% (81 gullies) were used for testing studied methods using the threshold-independent area under the receiver operating characteristic (AUROC) and the true skill statistic (TSS) as performance measures. The results showed that RF and MaxEnt algorithms outperformed other methods; performance assessment results showed that the RF model with AUROC = 0.82 (82%) and MaxEnt (0.804: 80.4%) had higher prediction accuracies than BRT: 0.69 (69%) and ANN: 0.55 (55%). TSS results indicated that RF and MaxEnt are best methods in predicting gully susceptibility in Luzinzi watershed. On the other hand, the conditioning factors such as Digital Elevation Model (DEM), Normalized Difference Water Index (NDWI), Normalized Difference Vegetation Index (NDVI), slope, distance to roads, distance to rivers, and Stream Power Index (SPI) played key roles in the gully occurrence. Given the significance of these factors in gullies' occurrence, as shown in this study, policy-makers must adopt strategies that consider these factors to lower the risk of gully occurrence and related consequences at the watershed scale in eastern DRC.

Influência do Uso da Terra no Processo Erosivo de Voçorocamento em Cacequi, Rio Grande do Sul - Influence of Land Use on The Gully Erosion Process in Cacequi, Rio Grande do Sul

Article

Full-text available

Dec 2024

O estudo da erosão nas últimas décadas tem levado ao desenvolvimento de variadas técnicas de modelagem de dados para a compreensão deste fenômeno. Este trabalho objetiva mensurar o impacto do uso da terra em três voçorocas em Cacequi –RS. Foi aplicado o modelo empírico SCS-CN para a estimativa do escoamento superficial durante o período de 1975 a 2022 e o modelo EEFlux para a evapotranspiração dos cultivos atuais. O tipo de solo se mostrou a variável mais importante no escoamento superficial, apesar disso, as áreas de lavouras se mostraram mais propensas ao escoamento e as de silvicultura menos. Os dados de evapotranspiração evidenciam que os eucaliptos utilizam mais água do solo, podendo ter impacto na expansão das voçorocas, comoa diminuição dos movimentos de massa e rebaixamento do nível de base, permitindo maior desenvolvimento vertical das voçorocas, sendo que estes impactos necessitam de estudos mais detalhados na área.

Unveiling gully erosion susceptibility: A semi-quantitative modeling approach integrated with field data in contrasting landscapes and climate regions

Article

Full-text available

Oct 2024
GEOMORPHOLOGY

Morphological and Temporal Dynamics of Gully Erosion: a Case Study in Abelasta Watershed, Northwestern Ethiopia

Chapter

Jun 2024

In the Ethiopian highlands, gully erosion has many negative impacts on both cultivated and grazing lands. It also damages infrastructures and the socioeconomic situations of the society. Besides, sediment transport due to gully erosion fills reservoirs and reduces their lifetime. This study investigated the morphological and temporal dynamics of gully erosion in the Abelasta watershed using ground measurements and remote sensing products (Google Earth). In the 248-ha Abelasta watershed, the years 2005, 2013, 2016, and 2020 were used to assess the expansion of gullies. Gully dimensions (depth, width, and length) were measured from six gullies with a field survey in 2020 to determine soil loss due to gully erosion. The results showed that gullies were expanding by depth, width, and length from 2005 Morphological and Temporal Dynamics of Gully Erosion 591 to 2020. The productive land that was lost by the expansion of gullies was 6.3 ha (2005) and 13.3 ha (2020), respectively, indicating a doubled increment within 15 years. The soil loss analysis result of the six gullies with the measured data indicated that a 38.1 t ha-1 yr-1 of annual maximum soil loss was found from one of the six gullies (gully 6). The average annual soil loss from the entire Abelasta watershed was 22.3 t ha-1 yr-1. The result indicated that gully erosion needs much attention during catchment restoration to minimize its adverse effect on agricultural productivity and infrastructure failures.

Modeling onsite wastewater systems (OWSs) for nutrient fate and transport: The case of Lick Creek watershed, North Carolina.

Chapter

Jun 2024

Failing onsite wastewater systems, OWSs, can potentially contribute significant nutrient (Nitrogen and Phosphorus) loadings to surface and groundwater. While the impact could be monitored on a specific site, it is very complex to quantify the impacts on a watershed scale. In this study, a physically based watershed scale model, Soil and Water Assessment Tool, SWAT, which is capable of simulating OWSs through biozone processes, was adopted to quantify and analyze the impacts of failing OWSs in the Lick Creek Watershed, North Carolina, USA, at various spatial scales. OWSs were identified by combining the sewer line system and parcel map, which resulted in 1,270 OWSs within the watershed. OWSs were then integrated with the land use map to facilitate the development of septic hydrologic response units, HRUs, for SWAT simulation of OSWs. A total of 53 septic HRUs were created which were aggregated within each subbasin for the same soil types. Due to the limited availability of monitoring data in and around the watershed, the SWAT model was pseudo-calibrated for hydrological simulation using data from literature and expert opinion. The test result shows that, at a 95% confidence level, there is enough evidence to conclude that OWSs status has a significant effect on water quantity and quality parameters at the HRU level. The largest impact on water quality was observed in the case of the White Store soil type, hydrologic group D, which was found to be the dominant soil group in the Lick Creek Watershed. The simulation results at the watershed outlet show an increase in total nitrogen and total phosphorus loadings due to failing OSWs on an average annual basis; however, the impact was not found to be statistically significant. It is recommended to pay attention to OWSs in White Store soil for new installations or design and implementations of OWSs nutrient management strategies.

Spatial variation in gully expansion rate in a loess-covered tableland region based on systematic sampling and high-resolution image interpretation

Article

Dec 2023
CATENA

Soil erosion is a major soil degradation threat to land worldwide, and gully erosion is an important soil erosion process. The lack of research on the spatial variation in gully erosion has constrained planning for gully control at a large scale. In this study, high-resolution historical and present remote sensing images were used to investigate the areal gully growth rate (RA) with systematic sampling methods on loess-covered tablelands at a regional scale. Gully growth (not disturbed by human excavation or landfill) was identified in 74 of 98 sampling watersheds in the 10,000-km2 study area, and the average ratio of gully growth area to the gully area was 0.159 % (1969 ∼ 2021), with a coefficient of variation of 0.006. Moran's I index showed a significant spatial autocorrelation with RA in the study area. Runoff depth, drainage area, and soil bulk density were significantly correlated with RA in the sampling watersheds. GeogDetector revealed that the spatial variation in RA was significantly influenced by runoff depth, precipitation, soil bulk density at the regional scale. The spatial pattern of runoff depth had the largest effect on the spatial variation in RA when comparing the individual effect of each factor, while the precipitation and soil bulk density best explained the spatial patterns of areal gully growth at the regional scale. A random forest regression model performed well for simulating watershed RA, with R2 = 0.829. These results improve our understanding of the mechanisms of gully erosion in loess-covered regions.

Prioritising interventions for the reduction of erosion in classical gullies: a modelling study

Article

Full-text available

Dec 2023

Context Gully erosion is a significant socioeconomic and environmental issue that affects agricultural productivity, infrastructure, and water quality of receiving waters. Despite a variety of interventions to prevent gully formation and rehabilitate existing gullies, cost-effective interventions are specific to individual gullies. Aims The aim of this study was to assess the performance of a suite of gully management interventions across three different classical gullies. Methods A one-dimensional process-based model, MERGE (modelling erosion resistance for gully erosion), was used to quantify the sediment yield exiting the gullies, in response to various management interventions. Key results The net decrease in sediment yield was 2.5–57.4% for each of four interventions applied in isolation and 51.2–78.7% in combination. Reductions in sediment yield for each intervention varied markedly among sites, by a factor of 2.6–78.3 in absolute terms. This resulted in a unique ranking of the interventions by their effectiveness for a given site. Overall, interventions applied in combination were most effective, outperforming those applied in isolation by a factor of 1.24–1.37, but the effect of applying interventions in combination was not additive. Conclusions This study demonstrates the ability of the gully erosion model MERGE to be a useful tool to identify and tailor effective intervention strategies for individual gullies, and be a useful guide for decision making for erosion management. Implications Analysis of expected benefits of gully remediation using tools such as MERGE is important for assessing options at gully sites due to their widely varying response.

Examining the Impacts of Plantation Forests on Human and Plant Communities in the Ethiopian Highlands

Article

Full-text available

Oct 2023

A critical analysis of soil (and water) conservation practices in the Ethiopian Highlands: Implications for future research and modeling

Article

Full-text available

Oct 2023

Soil and water conservation have been traditionally part of farming practices for thousands of years. Despite massive efforts to implement modern soil and water conservation practices (SWCPs) in the Ethiopian Highlands, soil erosion increased after the 1970s when social and political events led to a remarkable change in land use. This review aims to critically analyze the impact of conservation practices on soil loss and crop yield and highlight research and modeling gaps. In doing so, 120 published articles on experimental and simulated soil losses in the Ethiopian Highlands were retrieved from the refereed literature. We found that most published experimental studies evaluating SWCPs lasted less than five years in areas of less than 100 ha. Most modeling studies were over short periods, too; some models simulated soil loss over large areas. The literature analysis for these short-term experimental studies showed that SWCP decreased soil loss on individual sites and increased crop yield in semi-arid regions. Simulated sediment concentration increased as a function of watershed size, while observed soil losses did not follow this trend. Moreover, the decrease in soil loss due to the soil and water conservation practices on small plots was also greatly overestimated. Consequently, past research and current modeling techniques are inconclusive on the effectiveness of SWCPs in large catchments over periods exceeding five years and those with active gullies. Additional long-term experimental studies in catchments are required to evaluate whether SWCPs can decrease sediment loads.

A critical analysis of soil (and water) conservation practices in the Ethiopian Highlands: Implications for future research and modeling

Article

Oct 2023
CATENA

A modest Tigray botanical garden in Belgium - illustration of the Afromontane vegetation

Technical Report

Full-text available

May 2024

Jan Nyssen

The Afromontane biogeographic region includes plant species found in Africa's highlands. Temperatures in these regions are comparable to those encountered in temperate climates, with the major temperature contrast being between day and night. The Dogu'a Tembien massif in Tigray is a ‘sky island’, that served as model for the establishment of a modest Afromontane floral park. The garden, dedicated to the slain Tigray people, was established in 2023 and holds thirteen woody, seven herbaceous, one palm and one succulent species. The garden is managed organically, with compost used as fertilizer, no herbicides, and only a metaldehyde-based molluscicide. Geomembrane sheets are used to limit the abundant local vegetation, and plant labels are prepared in French with scientific and Tigrinya names in small lettering.

Evaluation of Spatial-Temporal Variation of Soil Loss and Best Conservation Measures in an East Africa Catchment

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Full-text available

May 2023

Soil conservation (SC) is essential to maintain the reservoir service life and increase the yield since soil erosion is a major global concern that adversely affects not only the storage capacity but also the land fertility. This study evaluates the spatio-temporal variation of soil erosion using the popular SWAT model and identifies the best SC practice for Tekeze watershed located in the Northern part of Ethiopia. To accomplish this, four soil conservation management scenarios involving baseline, terracing, contouring, and grassed waterway scenarios are selected for soil loss evaluation. The SWAT model was calibrated and validated with R² values of 0.7 and 0.9 and NSE values of 0.8 and 0.7, respectively, indicating satisfactory model performance. Five sub-basins of the catchment were found to be more susceptible to erosion with an average annual soil loss of 25.15 tons/ha/yr. Employment of the proposed SC measures in the sub-watershed erosion was reduced by 35.18%, 27.11%, and 18.76%, respectively, which is significant when compared with the baseline scenario. Since the investment cost of execution of an SC measure in a large watershed is very high, priority areas are also identified for cost savings as well as improved work efficiency.

Gullies and badlands of India: Genesis, geomorphology and land management

Article

Full-text available

Apr 2023
EARTH SURF PROC LAND

Gully erosion is a formidable land degradation process globally. It is omnipresent across India, wherein two of the largest badlands regions in the world also exist. However, despite being affected by widespread gullying, gully erosion research in India has been rather limited, with key aspects of gully formation, morphologies and dynamics remaining unknown. Through this comprehensive systematic review, we synthesise previous studies on gully erosion in India and in turn highlight pivotal knowledge gaps. The review starts with a discussion of the causal factors of gullying in India, which underlines how gully initiation in several regions was an aftermath of deforestation and overgrazing. Contrastingly, the badlands of Central and Western India have mainly developed in response to natural triggers like neotectonics and Holocene climate change. The section on mapping highlights how mapping methodologies have not only been dictated by the availability of imagery and/or means of data processing, but also the mapping purpose—that is, individual gully channels or entire badlands. Although a few studies applying concepts of fractal geometry to characterise badlands’ geomorphology are innovative and unique, the most striking research gaps we have identified also pertain to understanding and quantification of gully geomorphology and erosion dynamics in different regions of India. Our review reveals that gullies of peninsular India have been the least studied, followed by those of the Himalayan and Sub‐Himalayan region. Although the literature provides interesting examples of linkages between badlands development and the wider geomorphic evolution of the landscape, better chronological understanding is required to disentangle the relative importance of natural and anthropogenic drivers of landscape change in India's badlands. Large‐scale mapping of gully characteristics, quantification of gully morphologies, gully erosion rates and its share in catchment sediment budget across various physiographic regions or river basins of the country also constitute important areas for future research.

Recent gully erosion intensity in an agricultural landscape underlain by fluvioglacial sediments (NE Czechia)

Article

Full-text available

Apr 2023
LAND DEGRAD DEV

Inappropriate agricultural management practices combined with intense rainfall often lead to gully erosion. Knowledge of the causes and consequences of past erosion pulses is essential not only for farmers to improve land management, but also for municipalities to define infrastructure threats associated with material transport. This study comprehensively evaluates accelerated gully erosion and estimates gully transport capacity in fluvioglacial sediments left by a Pleistocene ice sheet in northeastern Czechia. Geomorphic mapping of an area of approximately 2 km² revealed gullies up to 3.5 m wide and deep, with their heads starting at the boundaries of fields and pastures. The ground‐penetrating radar survey confirmed the presence of soil pipes contributing to gully formation due to unmaintained field drainage combined with the natural occurrence of soil pipes. Microscopic analysis and dendrogeomorphic dating of 102 cross‐sections from 28 exposed tree roots revealed 18 years of gully incision since 1985, with increased activity from 2007 to 2014. The mean incision rates ranged between 1–20 cm/year, but could reach 1 m during individual events. More intensive incisions were typical for soils with higher smectite content. The last severe erosion event in 2014 caused clogging of culverts and damage to infrastructure by transporting boulders up to 34 cm in diameter at critical flow velocities of 2.4–2.8 ms⁻¹. Considering the predominance of human‐induced factors (e.g., current soil compaction due to grazing and failure to maintain the drainage pipe outlets), ongoing gully erosion can be expected during intense rainfall events unless appropriate agricultural or stabilization measures are addressed.

Resident's Perception of the Effects of Erosion on Streets and Roads in Jalingo Metropolis, Taraba State, Nigeria BY

Article

Full-text available

Oct 2022

Vertical distribution of vegetation roots and its influence on soil erosion resistance along gully headwalls in the gullied Loess Plateau

Article

Full-text available

Nov 2022
J SOIL SEDIMENT

Purpose On-wall flow on gully headwalls plays a critical role in gully headcut erosion, and the erosion morphology of gully headwalls caused by on-wall flow scouring varies under different land uses/covers due to variations in soil resistance. However, it is unclear how vegetation roots affect the soil resistance of gully headwalls to on-wall flow scouring. Materials and methods Taking bare land as the control, this study analysed the vertical distribution of vegetation roots and its influence on the soil properties and antiscourability (ANS) of gully headwalls under three land uses (forestland, grassland, and farmland). Results and discussion The results showed that root mass density (RMD), root length density (RLD), root surface area density (RAD), and root volume density (RVD) decreased overall with increasing soil vertical depth at the gully headwall under the three land use types. The soil ANS ranked highest to lowest in forestland, grassland, farmland, and bare land. Compared with that of bare land, the ANS of each soil layer (0–20, 20–40, 40–60, 60–80, and 80–100 cm) under the three land use types increased by 3.0–9.1, 6.7–8.6, 2.6–10.5, 3.9–5.6, and 0.2–1.9 times, respectively. The ANS of the gully headwalls had a logarithmic relationship with RLD, RAD, and RVD (R² = 0.45–0.56, P < 0.01). In particular, the most significant correlation was found between the ANS and RVD of fine roots (diameters of 0–0.5 mm). The ANS decreased with the decrease in root density with vertical depth. Conclusions Our results reveal that vertically distributed roots determine the vertical variations in soil ANS on gully headwalls in the gullied Loess Plateau.

Gully erosion susceptibility mapping using four machine learning methods in Luzinzi watershed, eastern Democratic Republic of Congo

Article

Nov 2022
PHYS CHEM EARTH

Soil erosion by gullying causes severe soil degradation, which in turn leads to severe socio-economic and environmental damages in tropical and subtropical regions. To mitigate these negative effects and guarantee sustainable management of natural resources, gullies must be prevented. Gully management strategies start by devising adequate assessment tools and identification of driving factors and control measures. To achieve this, machine learning methods are essential tools to assist in the identification of driving factors to implement site-specific control measures. This study aimed at assessing the effectiveness of four machine learning methods (Random Forest (RF), Maximum of Entropy (MaxEnt), Artificial Neural Network (ANN), and Boosted Regression Tree (BRT)) to identify gully's driving factors, and predict gully erosion susceptibility in the Luzinzi watershed, in Walungu territory, eastern Democratic Republic of Congo (DRC). In this study, gullies were first identified through multiple field surveys and then digitized using a very high-resolution image (CNI/airbus) from Google Earth. Overall, 270 gullies were identified, of which 70% (189) were randomly selected to train the four machine learning methods using topographical, hydrological, and environmental factors hypothesized to be gully-related conditioning factors. The remaining 30% (81 gullies) were used for testing studied methods using the threshold-independent area under the receiver operating characteristic (AUROC) and the true skill statistic (TSS) as performance measures. The results showed that RF and MaxEnt algorithms outperformed other methods; performance assessment results showed that the RF model with AUROC = 0.82 (82%) and MaxEtent (0.804: 80.4%) had higher prediction accuracies than BRT: 0.69 (69%) and ANN: 0.55 (55%). TSS results indicated that RF and MaxEnt are best methods in predicting gully susceptibility in Luzinzi watershed. On the other hand, the conditioning factors such as Digital Elevation Model (DEM), Normalized Difference Wetness Difference Index (NDWI), Normalized Difference Vegetation Index (NDVI), slope, distance to roads, distance to rivers, and Stream Power Index (SPI) played key roles in the gully occurrence. Given the significance of these factors in gullies' occurrence, as shown in this study, policy-makers must adopt strategies that consider these factors to lower the risk of gully occurrence and related consequences at the watershed scale in eastern DRC.

Effectiveness of measures aiming to stabilize urban gullies in tropical cities: Results from field surveys across D.R. Congo

Article

Oct 2022

Urban gullies are a rapidly growing concern in many tropical cities of the Global South. Various measures are already implemented for their stabilization. However, an overview of these measures and their overall effectiveness is currently lacking. We aim at addressing this gap by documenting existing initiatives to stabilize urban gullies in D.R. Congo and assessing their overall effectiveness. To this end we conducted extensive field campaigns in Kinshasa, Kikwit and Bukavu and combined our terrain observations with data on gully expansion rates (derived from series of satellite imagery). In total, we characterized present and past stabilization initiatives for 398 urban gullies. For 69 of these gullies, the effect of a specific measure on gully expansion rates could be estimated. Results show that for the large majority of gullies, various measures have been implemented. Yet, these are mainly ad-hoc measures installed by the affected population. More structural measures based on larger engineering works were observed for only 20–30% of gullies. The huge efforts invested in the installation of measures strongly contrast with their overall low impact. Among all strategies, only the deviation of runoff resulted in significantly lower expansion rates after installation. The numerous initiatives that rely on the sparse means available seem to have limited effects. This does not imply, however, that they are completely ineffective and should be abandoned. Based on our findings, we formulate recommendations for further research on how to effectively prevent and stabilize urban gullies, taking into account the difficult environmental and socio-economic context.

Comparison of gully initiation thresholds estimation techniques: a case study from India

Conference Paper

Sep 2022

Theory and praxis of integrating indigenous knowledge and science for Disaster Risk Reduction A socio-epistemic case study of floods in the Rwenzori (Uganda)

Book

Full-text available

Dec 2021

Bosco Bwambale

Scholarly debates on disaster risk reduction have widely highlighted the interest in integrating indigenous knowledge with science to produce hybrid context-specific knowledge to suitably tackle disaster risk. Yet, an epistemological framework to enable hybridization remains a challenge. Focused on the case of floods, this dissertation investigated the (socio-)epistemic nature of indigenous knowledge and developed a framework to guide the best way to integrate it with science. Two key research techniques were used throughout: critical review of scientific literature and policy documents, and empirical analysis through participatory ethnography. Starting with questioning existing literature, the lack of an epistemological framework for knowledge integration is evidenced. The hylomorphic framework is proposed as a suited theoretical framework for integrative science in understanding and tackling disaster risk. This framework is standpoint in nature; it stresses the primacy of two intrinsic elements: the indigenous lived experience of a specific hazard-prone context (i.e., the hyle) and the context-specific risk science (i.e., the morphe). Based on this theoretical framework, three empirical case studies were conducted to structure the processes through which indigenous knowledge on understanding and tackling disasters is produced. The first empirical case study, exemplifying the empiricist constructive approach to understanding natural hazards, shows that locality and weaving into culture hardly stand in the way of indigenous systematization and/or objectivity. The other two add evidence that indigenous knowledge can be trans-local and adapting while being based on lived experiences and open sociocultural deliberations. Then the praxis of incorporating indigenous knowledge was evaluated from the viewpoint of the dominant discourse(s) that inform interventions on disasters. It evidenced that the discourse followed by key stakeholders (e.g., policymakers and scientists) determines whether indigenous knowledge is incorporated. This was further evidenced in the field testing of the hylomorphic framework: skewing the evaluation criteria to the vantage point of communities-at-risk enabled coalescing epistemologies, ontologies, values, and re-politicization. These attributes thus constitute the core epistemic processes of coalescing science and indigenous know-how into a hybrid epistemology of knowledge integration on disaster risk reduction. Based on these attributes, recommendations are made. They encompass science, society, and practice in the context of suitably understanding and reducing disaster risk.

A drone- and field-based investigation of the land degradation and soil erosion at an opencast coal mine dump after 5 years’ evolution of natural processes

Article

Full-text available

Dec 2022

Opencast coal mining has a large impact on the land surface, both at the mining pits themselves and at waste sites. After artificial management is stopped, a reclaimed opencast coal mine dump is affected by wind and water erosion from natural processes, resulting in land degradation and even safety incidents. In this paper, the soil erosion and land degradation after 5 years of such natural processes, at the Xilinhot opencast coal mine dump in Inner Mongolia, were investigated. A multi-source data acquisition method was applied: the vegetation fraction coverage (VFC) was extracted from GF-1 satellite imagery, high-precision terrain characteristics and the location and degree of soil erosion were obtained using a drone, and the physical properties of the topsoil were obtained by field sampling. On this basis, the degree and spatial distribution of erosion cracks were identified, and the causes of soil erosion and land degradation were analyzed using the geographical detector. The results show that (1) multi-source data acquisition method can provide effective basic data for the quantitative evaluation of the ecological environment at dumps, and (2) slope aspect and VFC are the main factors affecting the degree of degradation and soil erosion. Based on above analysis, several countermeasures are proposed to mitigate land degradation: (1) The windward slope be designed to imitate the natural landform. (2) Reasonable engineering measures should be applied at the slope to restrain soil erosion. (3) The Pioneer plants should be widely planted on the platform at the early stage of reclamation.

Gully erosion in southeast Nigeria: influence of land-use changes on gully catchment hydrology

Preprint

May 2022

Gully erosion leads to soil loss and poses significant threats to availability of land for cultivation, food security and development of infrastructure. Hydrological changes driven by land-use changes are often identified as drivers of gully erosion. The aims of this paper are to assess the influence of changes in land use on gully catchment hydrology and relate these changes to gully erosion. To achieve these aims, we used The Soil Water and Assessment Tool (SWAT, 2012 version) to assess hydrological changes driven by land-use changes in 22 gully catchments in the Orlu region of southeast Nigeria between 2009 and 2018. In the absence of measured hydrological data, we used a mixed-method approach to validate modelling results: literature review, field observations and focus group meetings. Increase in surface runoff estimates was observed in 21 catchments where reductions in fallow cover were observed. In one catchment where increased fallow was observed, we identified reduction in surface runoff. Surface runoff erosion was identified as a dominant process of gully expansion in the study area, but there was no significant relationship between changes in gullied area and changes in runoff volumes (r = 0.15, p = 0.08). Within-catchment variations in land-use configuration influences surface runoff volumes and pathways, and by extension, gully erosion. This was evident in the slow gully expansion rate/gully reduction identified at gullies with vegetated adjacent lands as opposed to active runoff incision observed in gullies with bare adjacent lands. Therefore, the key finding of this study is that it is important to identify and incorporate the uniqueness of gully catchments in gully management as a successful management technique in a particular catchment may not work in another.

The socio-epistemic process of indigenous disaster risk reduction: Evidence of adapting yet endangered indigenous strategies

Article

Apr 2022

The added value of indigenous practices for Disaster Risk Reduction (DRR) is increasingly stressed by scholars. Yet this fails to translate into practical application as these scholars miss a clear understanding of the processes that shape indigenous DRR. Based on a case of floods in the Rwenzori (Uganda), in this study, the aimed is to conceptualize the socio-epistemic processes through which Indigenous people question their practices and develop adapted DRR strategies. By trying out various practices over several floods, Indigenous people developed a toolbox of criteria to address the changing disaster risk. The capacity to learn from each event is illustrated by crafting practices that enhance ecological integrity, livelihoods, and sociocultural well-being across the watershed. This skill is largely attributed to the community structures organized around the cultural stewardship which favor a holistic approach to produce best practices. Yet, through history, adapted indigenous DRR strategies remain hampered by external pressures that are sociopolitical and capitalistic in nature. It is thus argued that cultural stewardship is crucial in enabling development of adapted indigenous DRR insofar as external sociopolitical and/or capitalistic situations permit.

Assessment of soil erosion extent using RUSLE model integrated with GIS and RS: the case of Megech-Dirma watershed, Northwest Ethiopia

Article

Full-text available

May 2022
ENVIRON MONIT ASSESS

Soil erosion valuation at a spatial scale is crucial for assessing natural resource quality in a farming country like Ethiopia. The study’s goal was to determine the rate of soil erosion in the Megech-Dirma catchment in Northwest Ethiopia using the Revised Universal Soil Loss Equation model aggregation with Geographic Information System and Remote Sensing. Sediment yield and transport were also estimated using sediment delivery ratio. Revised Universal Soil Loss Equation model data inputs included precipitation data for the R value, soil data for the K value, land cover data from satellite images for the C and P value, and topographical data from a Digital Elevation Model for the LS component. It was completed using the ArcGIS 10.4 software. The mean annual soil loss is 110.60 t ha−1 yr−1. Each year, a total of 8499.74 t ha−1 yr−1 of soil eroded and on average resulting in 1605.30 t/km2/yr, sediment material has been transported to the stream channels and deposited with a sediment delivery ratio of 1.87. The strength of soil erosion in the area is divided into six categories. The erosion rate classes were 46.38 percent (0–12 t ha−1 yr−1) low, 13.63 percent (12–20 ha−1 yr−1) moderate, 9.22 percent (20–35 ha−1 yr−1) high, 12.30 percent (35–50 ha−1 yr−1) very high, 7.20 percent (50 up to 100 ha−1 yr−1) severe, and 11.27 percent (>100 ha−1 yr−1) very severe erosion. According to erosion severity, 46.38 percent of the watershed is at risk of low erosion, while 11.27 percent is at risk of extremely severe erosion. The north and northeastern sections of the watershed have a moderate to extremely severe erosion risk due to steep slopes, high rainfall, and weak conservation measures. The severely eroded parts of the plateau and steep portions are proposed to be covered by plantation, stone bund, and check dam constructions.

A multi‐method approach to analyse changes in gully characteristics between 2009 and 2018 in southeast Nigeria

Article

Full-text available

Mar 2022
LAND DEGRAD DEV

Gully erosion is the dominant environmental problem in southeast Nigeria and has led to loss of human and material resources. In this study, we evaluated changes in gully characteristics in southeast Nigeria and their potential drivers between 2009 and 2018 using a multi‐method approach: analysis of high‐resolution satellite imagery (2–5 m) and focus group discussions. Gully numbers increased from 26 to 39 and mean gully length increased from 0.39 to 0.43 km. We found that land adjacent to rivers had the highest concentration of gullies which is associated with an increase in slope angle from 10 to 58% up to 500 m from rivers. Regarding potential gully‐drivers, land‐use changes were observed. Non‐vegetated lands increased from 58.6 to 144.7 km² between 2009 and 2018, while reductions in fallow lands from 281.2 to 57.8 km² were observed. Results from focus group meetings indicate there was no gullying in the area before the Nigerian civil war (1967–1970). War‐time activities such as digging trenches and increased population density were said to have led to the formation of the oldest gullies in the area. Although war‐time activities have ceased, meeting attendees believed that present land‐use changes have increased the volume of surface runoff and thus enhancing gully erosion. Incorporating local knowledge in this study has therefore provided a valuable understanding on the key drivers of gullying that pre‐dates the availability of freely available high‐resolution satellite data.

Runoff and suspended sediment yield and implications for watershed management

Article

Full-text available

Jun 2022

Improper implementation of conservation structures in the Ethiopian highlands in general and in the Yewoll watershed, in particular, enabled the existence of soil erosion at an aggressive rate. This research aimed to enable a better understanding of the hydrological processes of the Yewoll watershed in the upper Blue Nile basin, Ethiopia. Rainfall, runoff, and suspended sediment load data were collected for 2 years, and stage-discharge curves were developed. Suspended sediment load from runoff samples, soil infiltration rate, and shallow groundwater level were measured using a Whatman filter paper, double-ring infiltrometer, and piezometers, respectively. A high rate of soil water infiltration (greater than 250 mm/h) was observed at upland steep slope areas. The shallow groundwater level was closer to the surface for most of the rainy season in the valleys and bottoms of the hillslope areas. At the outlet of the watershed, it takes a longer time to drain the runoff after a rainstorm than the gentle slope and hillslope areas of the upstream area. The upstream watershed (a drainage area of 52.5 km²) received a maximum annual rainfall of 689 mm, while it was 647 mm for the whole watershed (a drainage area of 68.7 km²). The presence of an abundance of gullies in the sub-watershed located between the two gauging sites as opposed to the upstream steep sloppy area is the main source of annual runoff and generation of sediment loads representing hot spots areas for soil erosion, hence require priority investment in managing Yewoll watershed.

The Nexus between Land Use Land Cover Dynamics and Soil Erosion Hotspot Area of Girana Watershed, Awash Basin, Ethiopia

Article

Full-text available

Feb 2022

Belachew Beyene Alem

Maintaining hilly agriculture and food security remains challenging due to the ongoing degradation of the land caused by soil erosion on Ethiopia's highlands. . Soil erosion is one of the major problems affecting land and water resources. With the increase of land-use change, erosion and soil degradation increase significantly, leading to a loss of fertile soil every year. This study was therefore designed to identify erosion hotspot areas and their spatial and temporal alteration with land use land cover (LU/LC) change in the Girana watershed to give an option to local government decisions makers towards watershed management strategies. An attempt was made to combine a set of factors such as topographic wetness index (TWI), soil type, land use (1989 and 2019), slope, rainfall, and gully locations using geographic information system (GIS) based multi-criteria decision analysis (MCDA) to achieve the stated objective. Criterion maps of each factor have been processed and the factors were weighted using analytical hierarchy process(AHP) based pair-wise comparison methods, and weights have been combined using weighted overlay analysis to obtain the final erosion hotspots areas of the two-time references (1989 and 2019). The result found that 0.01%, 8.01%, 84.06%, and 7.92% of the total area fall under highly sensitive, moderately sensitive, marginally sensitive, and currently not sensitive erosion risk zone respectively for the year 1989 and 0.06%, 17.42%, 80.88% and 1.63% of the total area fall under highly sensitive, moderately sensitive, marginally sensitive, and not sensitive erosion risk zone respectively for the year 2019. Parts of the area that are highly sensitive, and moderately sensitive to Soil erosion classes increased markedly for the last thirty years in the Girana watershed, as a result of the conversion of thousands of forest areas to cultivated land and residential area. Therefore an urgent soil conservation intervention in hotspot areas is compulsory in the Girana watershed.

2021 Book NileAndGrandEthiopianRenaissan 2

Chapter

Jan 2022

Arega Mulu

Abstract Tana sub-basin receives rainfall during summer as a primary source of stream flow. This research aimed to relate the catchment characteristics with hydrology of headwater catchments. Rainfall-runoff and sediment yield modeling in relation to catchment characteristics was conducted. Land use, soil, digital elevation model (DEM), precipitation, water quality and quantity were used in the analysis. ERDAS, GIS and HYDATA software were used to evaluate the physical catchment characteristics and meteorological data. Model parameters were calibrated using observed data of 2009–2011 and validated over the period of 2012. Particle swarm optimization was used to determine optimal model parameters. The model parameters were related to catchment characteristics using linear regression in a statistical software. Normalized difference vegetation index (NDVI) and hypso�metric integral are directly proportional to direct runoff parameter C. Likewise, the baseflow model parameter b is positively affected by elongation ratio and average slope, and NDVI shows negative effect. Finally, regional model for the hydrology of the headwater catchments was developed.

Management Implication of Understanding Flood Variabilities in Transboundary Rivers for Future: A Case of Wabi Shebele River Basin, Ethiopia

Chapter

Sep 2021

Floods are among the most severe hydrological extremes, in terms of social impact and potential economic damage. In this study, flood variability and associated impacts and managements are investigated in the Wabi Shebele RiverWabi Shebele River Basin. In early twenty-first century, floods indicate increasing trend in magnitude and frequency in the entire basin. For longest period, 1981–2010, the annual maximum flood discharge shows upward trends in upper and middle catchments while downward trends are in eastern and lower catchments of Wabi Shebele Basin. Among these, annual maximum discharge shows a significant increasing trend in middle catchments (i.e. Erer at Hamaro and Gololcha at Wabi junction) and significant decreasing trend in Fafen watersheds at Jijiga and Kebridehar gauging stations. Flood variability and socio-economic damages follow similar trend tendency in the basin. Like variability analysis result in early twenty-first century, the number of peoples affected indicates increasing trend in study area. In such case, one must shift from defensive action against hazards to management of the risk considering the evolution and trends of floods. Due to its nature, floods in transboundary riverTransboundary rivers basin have transboundary consequence which indicates need of cooperation in between riparian countries for Integrated Flood ManagementIntegrated flood management (IMF). IMF is approach which adopts the best mix of both structural and non-structural strategies by ensuring a participatory approach and adopting integrated hazard management approaches.

Soil erosion modelling of degraded semi-arid highlands in Northern Ethiopia

Article

Nov 2024
HYDROLOG SCI J

Characteristics and development of steepland gullies in the dry valleys of Southwest China

Article

Full-text available

Nov 2024

In semi-arid and arid areas, gully erosion is one of the most destructive forms of erosion and causes serious land degradation and resource destruction. Steepland gullies are widely distributed in the dry valleys of southwest China, and their formation is one of the main causes of soil erosion and the destruction of sloping farmland in the region. Previous research on the development of steepland gullies is limited, and further study is needed. In this study, 11 steepland gullies at various stages of development located in Guobu Village, Xide County, Liangshan, Sichuan Province, were selected for investigation using a digital elevation model (DEM) derived from unmanned aerial vehicle data as the primary data source. These data had a spatial resolution of 0.1 m. Fundamental parameters such as the gully length, width, depth, area, and volume were extracted from the remote sensing data. Other characteristic parameters, including the coefficient of main and tributary gullies, vertical gradient, gully elongation, and gully openness, were also investigated. The results indicate a significant linear positive correlation between the gully’s degree of openness and elongation as the gully’s length, width, and depth increase. Furthermore, the vertical gradient and coefficient of main and tributary gullies exhibit power-law relationships with these gully dimensions. The development of steepland gullies was divided into infancy, youth, maturity, and old age based on the use of the gully length as an ergodic indicator in space-for-time substitution. The morphological characteristics of these different stages were quantitatively analyzed, and a proposed mechanism for how the evolution of the gullies proceeds was developed. An empirical model of volume–length erosion was established to investigate the development process of steepland gullies in the dry valleys. It has been observed that the development law of steepland gullies is essentially consistent with the very active stage of typical gully formation, suggesting that steepland gully may represent the initial stage of gully development. The results show that these steepland gullies have their origin in high-intensity rainfall events that are accompanied by the formation of steps and drop water. The effects of gravity erosion and hydraulic erosion then cause the gullies to expand rapidly, forming gullies with a large head and a small tail before they gradually stabilize. The results of this study will help with the understanding of the formation and evolution of steepland gullies and will be of practical significance for the prevention of gully erosion and the protection of sloping farmland in the dry valley region of southwest China.

Gully rehabilitation in Southern Ethiopia – value and impacts for farmers

Preprint

Full-text available

Apr 2024

Gully erosion can be combatted in severely affected regions like sub-Saharan Africa by a range of low-cost interventions that are accessible to affected farmers. However, for successful implementation, biophysical evidence of the effectiveness of interventions needs to be combined with buy-in and input from local communities. Working with farmers in a watershed in Southern Ethiopia, we investigated (a) the effectiveness of low-cost gully rehabilitation measures to reduce soil loss and upward expansion of gully heads, (b) how farmers and communities view gully interventions, and (c) whether demonstrating gully interventions in-context changes farmers’ knowledge and perceptions of their capacity to act. On-farm field experiments, key informant interviews, focus group discussions and household surveys were used to collect and analyze data. Three gully treatments were explored, all with riprap, one also with grass planting, and one with grass planting and check-dam integration. Over a period of 26 months these low-cost practices ceased measurable gully head expansion, whereas untreated gullies had a mean upward expansion of 671 cm resulting in a calculated soil loss of 11.0 tonnes. Farmers viewed these gully rehabilitation measures positively, apart from the high cost of input materials and technical requirements of gabion check-dams. Ongoing rehabilitation activities and on-farm trials influenced knowledge and understanding of similar gully treatments among survey respondents. On-farm experiments and field day demonstrations empowered farmers to act, addressing pessimism from some respondents about their capacity to do so.

Traditional gold mining in the highlands of Ethiopia: Its effect on soil loss and possible reclamation measures

Article

Full-text available

Apr 2024

Traditional gold mining (TGM) is among the off-farm income sources of smallholder communities in the highlands of Ethiopia. However, information on their impact on land degradation, taking soil loss as a key indicator, was scant. Hence, this study aimed at i) analyzing local communities’ attitudes toward TGM practice, ii) TGM impact on soil loss, and iii) possible restoration measures for the degraded gold-mined landscapes. For the evaluation of community perceptions, 96 beneficiaries were selected from three gold mining sites following stratified random sampling techniques. Soil loss measurement was done through measurement of i) the mass of soil excavated and transported to the river (TR) from 96 individuals and ii) soil volume excavated in 45 excavated soil pits (EP). Descriptive statistics and one-way ANOVA were used to analyze soil loss data, while community perception was analyzed qualitatively. The survey results indicated that the average soil loss from TR and EP were 6,075.97±8.9 t ha-1 yr-1 and 32,549.99±753.68 t ha-1, respectively. The magnitude of soil loss also showed a significant (p<0.001) difference among the three sites. Due to a lack of awareness and hiding the reality, most of the gold miners believe that TGM practice has no negative impact on the soil resource, and no post-mined reclamation strategy is implemented. It can be concluded that the existing TGM practices are not done in an environmentally friendly approach and result in adverse soil loss. Hence, stabilizing the topography of the mined sites via backfilling of mined pits and topsoil conservation and amendment measures can be suggested.

Life cycle of gullies: A susceptibility assessment in the Southern Main Ethiopian Rift

Preprint

Full-text available

May 2023

Gullies experience varying states of activity during their life cycle. For example, their highest growth rates are commonly observed in the period that follows their initiation, whereas they are less active when reaching stability. Understanding the environmental conditions under which gullies initiate, expand, and stabilize is therefore vital to mitigate their impacts. Data-driven susceptibility assessments are key approaches to understanding these conditions at the catchment scale. However, such assessments commonly focus, at best, only on one part of the problem (e.g., on the gully heads) and do not cast a critical eye on the significance of the processes they would highlight. So far, no study has attempted to explicitly model the life cycle of gullies. Here we address this research gap through modelling separately the location where new gullies initiate and where they stabilize using both gully initiation points and gully heads. More specifically, we study over 4400 active and inactive gullies in the Southern Main Ethiopian Rift. Using logistic regression models, we assess the susceptibility to gully initiation points derived from slope-drainage area (S-A) thresholds. This is then compared with the susceptibility of active or inactive gully heads at the level of four catchments considered together and separately. Highly susceptible areas for gully initiation are mainly located in rejuvenated landscapes downslope of rifting-associated knickpoints, where steep hillslopes are more recent than those of the surrounding relict landscapes. Concave slopes with a higher surface runoff concentration favour initiation of gullies. In contrast, gullies stabilize in convex slopes with a more diffusive characteristic. The resulting susceptibility models are a step towards contributing to the decisionmaking process on the optimized locations of soil and water conservation measures during several stages of the life cycle of gullies.

ANÁLISE ESPAÇO-TEMPORAL DE BOÇOROCA PERIURBANA NA MICROBACIA DO RIBEIRÃO ALEGRETE EM MARTINÓPOLIS-SP

Technical Report

Dec 2019

Alyson Bueno Francisco

Relatório de pós-doutorado

Estimation of Reservoir Sedimentation Using Bathymetry Survey at Shumburit Earth Dam, East Gojjam Zone Amhara Region, Ethiopia

Article

Full-text available

Dec 2022

Sediment accumulation is a major factor in reducing the useful life of irrigation reservoirs. As a result, information on any changes in storage capacity is required to reduce the reservoir's risk. Therefore, the goal of this research was to identify the amount of sediment accumulated in the reservoir using a bathymetric survey. The bathymetric survey method involves subtracting the two-period capacities (before dam construction and after dam construction). The bathymetric survey of the reservoir was carried out by analyzing volume and surface area using ArcGIS 10.8, and developing the Triangulated Irregular Network (TIN) surface from topo-sheet data. The bathymetric survey showed that 297,000 m³ (362,340 tons) of sediment had accumulated in the reservoir over six years of operation. This means the reservoir's total capacity has been reduced by 7.52% over the last six years. The average rate of sedimentation was assessed to be 49,500 m³/y (60,390 tons/year) and the annual capacity reduction of the reservoir was 1.25 percent. The proportion of dead storage capacity to sediment deposition level was used to calculate the reservoir's useful life. Hence; the sedimentation rates of the dead storage and live storage regions were 31,666.67m³/year and 48,333.33m³/year, respectively. Finally, this indicates that the reservoir will not be functional for more than 15 years if the sediment deposition rate remains the same as the previous six years throughout the operation periods.

Comparison of the Sediment Yield Estimation Using Bathymetric Survey and Modified Universal Soil Loss Equation at Shumburit Reservoir, East Gojjam Zone Amhara Region, Ethiopia

Preprint

Full-text available

Sep 2022

Sediment accumulation is a major factor in reducing irrigation reservoir useful life as well as reducing the reservoir capacity. Therefore, the goal of this study was to estimate the volume of sediment accumulated in the reservoir using a bathymetric survey and to assess the watershed sediment yield to reservoirs using the Modified Universal Soil Loss Equation (MUSLE) model. The bathymetric survey method involves subtracting the two-period capacities, one before dam construction and one after dam construction. On the other hand, the sediment deposition calculated by the MUSLE model over the last six years is estimated after determining the physical parameters (K, LS, C, and P factors) and runoff index (VQ and QP) from the watershed using ArcGIS 10.8 and Excel software. The bathymetric survey showed that 297,000m3 (362,340 tons) of sediment had accumulated in the reservoir over six years of operation, whereas the Modified Universal Soil Loss Equation estimated 256,262.86 tons of sediment yield at the outlet of the watershed (inflow to the reservoir). This means the reservoir's total capacity has been reduced by 7.52 percent and 5.4 percent, respectively, over the last six years of operation, using a bathymetric survey and the Modified Universal Soil Loss Equation. According to the bathymetric survey results, the reservoir will not be functional for more than 15 years if the sediment rate remains the same as in the previous six years. Using the bathymetry method, the sedimentation rates of the dead storage and live storage zones were 31,666.67 m3/year and 48,333.33 m3/year, respectively. The watershed's sediment yield and specific sediment yield were determined using bathymetry survey results to be 61,371.95 tons/year and 45.46 tons/ha/year, respectively; whereas the sediment yield using the MUSLE model was 31.64 tons/ha/year.

Spatiotemporal Dynamic Complexity of Gully Erosion in an Antarctic Periglacial Shore Environment: Foster Bay, Deception Island (South Shetlands)

Article

Jan 2022

SOCIAL-ECONOMIC THRESHOLD FACTORS FOR GULLY EROSION STABILIZATION IN SEMI-ARID ENVIRONMENT OF WANJOGA RIVER CATCHMENT, UPPER TANA BASIN, KENYA

Article

Full-text available

Jan 2021

Gullies are a major environmental challenge in semi-arid areas, leading to expansion of semi-arid regions, triggering landslides, causing pollution, limiting agricultural activities and damaging infrastructure, which pose a threat to livelihoods. Despite massive threat posed by gully erosion, farmers lack capacity for designing appropriate rehabilitation structures. Thus, understanding conservation techniques adoptable by locals for conserving degraded ecosystem in semi-arid environments is necessary. The study examined social-economic threshold factors for gully stabilization in the semi-arid environment of Wanjoga Catchment. Objectives of study included; to evaluate perception of farmers on gully stabilization and conservation, and establish success levels of gully stabilization methods used by farmers. Landsat images were generated to predict gully venerability. Field surveys revealed total of 98 respondents whose farmlands had gullies of width and depth ≥ 0.5meters and interviewed. Paired t-test and chi-square, data revealed a positive significant relationship (p = 0.001 < 0.05), between preferred rehabilitation structures and topographical differentiation, with gabions indicating low levels of effectiveness; 12.1% of structures diverting threat or accelerating erosion down slope. Paired sample t-test p=0.000, revealed, gulley rehabilitation measures used by farmers have not healed a significant number of gullies. Keywords: Gullies, Rehabilitation structures, Overland flow, Farmers.

Phases of soil erosion during the Holocene in the Highlands of Western Tigray (Northern Ethiopia): A preliminary report

Article

Full-text available

Jan 1997

Contribution of Gully Erosion to Sediment Production in Cultivated Lands and Rangelands

Article

Full-text available

Jan 1996

Sediment production by gully erosion and by interrill and rill erosion in three study areas, representing contrasting agricultural environments (i.e. central Belgium, southeast Portugal and southeast Spain), is assessed through soil erosion mapping and analysis of aerial photos. The data indicate that mean annual soil losses due to ephemeral gullying are far from negligible in the studied environments: i.e. 3.6 m3 ha-1 year-1 in central Belgium, 3.2 m3 ha-1 year-1 in southeast Portugal and 9.7 m3 ha-1 year-1 in southeast Spain. Mean sediment production by ephemeral gully erosion represents 44% of total sediment produced in intensively cultivated small catchments with loess-derived soils, but 80% or more in Mediterranean areas with stony soils. These figures are not constant for the studied environments but vary over time with rainfall intensity and land-use. The limited data available indicate that sediment production due to bank gully erosion is about one order of magnitude smaller than sediment produced by ephemeral gully erosion in central Belgium. The results obtained indicate that more attention should be given to the rate of ephemeral gully erosion when assessing and modelling the impact of environmental change on sediment production.

Some aspects of climate variability in the North East Ethiopian Highlands – Wollo and Tigray

Article

Full-text available

Feb 2000

Declan Conway

This paper presents a review of climate variability in the northeast Ethiopian Highlands, particularly Wollo and Tigray, during the last 10000 years (the Holocene) and an analysis of rainfall variability during the historical period. To date little work has been done on climate reconstruction in Tigray and Wollo, however, a number of ongoing studies in the area using palaeosoil analysis, archaeological techniques and lake level reconstruction will help reveal the magnitude of past climate variability in the region. On recent time scales, rainfall over Wollo is characterised by a distinctive bi-modal pattern with Belg rains in April-May preceding the main wet season Krempt, July to September, which is typical of the study region along much of the eastern escarpment. Further north over Tigray the Belg rains are less marked and the main Krempt rains dominate the seasonal pattern. Only three stations in the region, Dessie, Combolcha and Mekele, possess relatively unbroken records back to the 1950s. In all three, 1984 stands out as the driest year on record due to very low rainfall during the Krempt season, whilst 1999's Belg season was the driest on record. Although the succession of dry years between the late 1970s and late 1980s produced the driest decade in the Ethiopian Highlands this century there is no evidence for a long-term trend or change in the region's annual rainfall regime. Rainfall during the 1990s has seen a return to more humid conditions since the dry 1980s. The paper ends with a discussion of the major influences on rainfall variability over the Ethiopian Highlands: the El Niño-Southern Oscillation - El Niño events tend to be associated with lower than average rainfall; Atlantic, Indian and Pacific Ocean sea surface temperatures play a varying role in different seasons; the strength of the Indian Summer Monsoon; and the frequency of several tropical depressions over the Southwest Indian Ocean. SINET: Ethiopian Journal of Science Vol. 23, No. 2 (December 2000), pp. 139-161

The Rate Law in Fluvial Geomorphology

Article

Full-text available

Feb 1977

William L. Graf

The impact of human activities on geomorphic systems consists primarily of the disruptions of natural processes and the disturbances of steady states. The times required for the systems to achieve new steady states after disruptions (relaxation times) are significant factors in the assessment of man's impact on landform processes. Spatial and dimensional characteristics of fluvial systems can be used as indicators of equilibrium. Dendrochronologic, photographic, and field evidence from gully networks in the Colorado Piedmont indicate that a rate law in the form of a negative exponential function similar to that used for describing relaxation times of radioactive materials and chemical mixtures provides a useful model for relaxation times in geomorphic systems.

Soil erosion under global change

Article

Full-text available

Jan 1996

Christian Valentin

Some reflections on the origin and land use of pediments on Ethiopian highlands

Article

Jan 1993

Pediments seem to be widespread on the Ethiopian highlands. They form a smooth transition between the steeper mountain or hill front and the flat surfaces downslope. The piedmont angle, characteristic of pediments elswhere is absent here. This form is not due to the original structural surface formed by the aggradation of the pyroclastic materials at the foot of the volcanic hills or mountains, since pediments also occur at the base of horizontally bedded remanent hills of Trap series lavas and sedimentary rocks. Where they are formed at the foot of volcanic hills, they do not correspond to the much steeper original bedding of the pyroclastic deposits. They are cut in rock (lava, pyroclastic, sedimentary) and are covered by a thin veneer of soil and colluvium. The relative absence of linear erosion and the smooth, grading of the slope (both upward and down to the present day valley bottoms or flat plains) suggest that the modelling of many of these pediments is either very recent or belongs to the present-day processes (mainly sheet flow). These surfaces mainly act as transport slope for the finer particles (soil and pyroclastics) brought from upslope. The sheet flow along the pediments is frequently changed into channelled flow because of the presence of roads collecting water of the slope. Gullies are forming in the basal part of pediments, whose maximum depth is close to the base of the bridge, where discharge is concentrated. Downslope, the depth decreases, until finally the gullies disappear. -from Authors

Ravijnontwikkeling en -erosiecontrolemaatregelen in een tropisch bergrivierbekken, Tigray, Ethiopië

Article

Jan 2001

Vertic movements and the development of stone covers and gullies, Tigray Highlands, Ethiopia

Article

Jun 2000
Z GEOMORPHOL

Apart from general management problems, typical for Vertisols, the valley Vertisols in the Tigray Highlands, Ethiopia, raise the problems of physical and chemical destabilisation by increased gullying and of stone mantle formation. This study indicates that gully head development depends in some cases on activity of polygonal bow structures in the Vertisols. Evidence is provided that the stone mantle, resting on the valley Vertisols, is coarse material from below, pushed up along the edges of active polygons. A preliminary estimation of the rate of upsqueezing is given. Solutions for the reduction of gully head development and stone cover formation comprise inactivation of valley Vertisols.

Soil Erosion in the Kingdom of Lesotho and Development of Historical Environmental Impact Assessment

Article

May 1996

Kate B. Showers

Solutions to past environmental problems affect the landscape. Their evaluation is often limited by a lack of scientific data. Yet valid scientific questions remain for which alternative research methods must be found. Soil erosion and the effects of conservation methods in the Kingdom of Lesotho, southern Africa, posed such problems. Three separate but complementary studies used field observations, archival research, and interviews with rural people to obtain information about past conditions of the landscape and the effects of soil conservation programs. At the time of the first conservation program in the 1930s, soil erosion was not widespread. The primary cause of gully erosion was roads and paths. A structure-based conservation program to protect the landscape actually caused gully initiation in some fields. While official documents provided general descriptions, older people gave detailed descriptions of erosion processes. They also described their own monitoring of the structures and efforts to mitigate their ill effects. The removal or modification of structures was an act of conservation, not of destruction. These studies led to the formulation of an historical environmental impact assessment (HEIA) to reconstruct the effects of past interventions in landscapes. The steps of conventional impact assessments were modified for work in the past, HEIAs could provide information about undocumented environments, extend baselines of modern EIAs, and identify past failures and successes to guide modern programs.

The environmental significance of the remobilisation of ancient mass movements in the Atbara–Tekeze headwaters, Northern Ethiopia

Article

Jan 2003
GEOMORPHOLOGY

Old landslides are prominent features in the landscape around Hagere Selam, Tigray Highlands, Ethiopia. The available evidence suggests their Late Pleistocene to Middle Holocene age and conditions of soil humidity. The affected geological layers, often silicified lacustrine deposits prone to sliding, rest upon or above the water holding Amba Aradam sandstone aquifer.Three examples of present-day (remobilisation of old) mass movements are illustrated and discussed. The aims of the study were to unravel the environmental conditions of the present-day remobilisation of ancient flows, as well as those of first-time landslides. The first two mass movements discussed are slumps, located in areas with vigorous regeneration of (grassy) vegetation. Their activation is thought to be the consequence of an increase in infiltration capacity of the soils under regenerating vegetation. One of these slumps had a horizontal movement of the order of 10–20 m in 1 day.The other case is the remobilisation of the May Ntebteb debris flow below the Amba Aradam sandstone cliff. The debris flow presently creeps downslope at a rate of 3–6 cm year−1. Palynological evidence from tufa shows that the reactivation of the flow started 70 years ago. Shear resistance measurements indicate the danger for continuous or prefailure creep. From the soil mechanics point of view, the reactivation of the debris flow is due to the combination of two factors: (1) the reduction of flow confining pressures as a result of gully incision over the last hundred years, and (2) the increase of seepage pressure as a consequence of the cumulative effect of this incision and the increase in infiltration rates on the lobe since grazing and woodcutting have been prohibited 8 years ago. The role of such exclosures as possible landslide triggers is discussed.From the geomorphological point of view, the ancient movements and their present-day reactivation cannot be compared: the ancient movements led to the development of debris flows, whereas the reactivations relate to the dissection of these mass movement deposits.

Differences in annual evaporation between grazed pasture and Eucalyptus species in plantations on a saline farm catchment

Article

Jun 1985
J HYDROL

Daily evaporation (including evaporation from the ground surface) from grazed annual pastures and from five species of Eucalyptus in two farm plantations was measured at regular intervals for a year. Leaf area of trees and pasture, and rainfall interception and stem flow by trees, were also measured. The trees were in their seventh year after germination. The site was a first-order catchment that had developed a saline seep midslope after the felling of the prior forest. One plantation was upslope, the other was immediately above the seep. The work is part of a salinity reclamation study based on increased evaporation through the strategic use of trees.Annual evaporation from pastures was 390 mm regardless of position in the landscape. Annual evaporation from trees upslope was 2300 mm for Eucalyptus maculata and 2700 mm each for E. globulus and E. cladocalyx. Values at midslope were 1600 mm for E. wandoo, 1800 mm for E. leucoxylon and 2200 mm for E. globulus. Expressed as a proportion of annual rainfall (680 mm), annual evaporation was 0.6 for pasture and ranged from 2.4 to 4.0 for trees while interception by trees ranged from 0.16 to 0.36, and stem flow was less than 0.02. Annual evaporation, but not interception, was correlated with leaf area. The application of these findings is discussed.We conclude that the planting of discrete areas of trees has the evaporation potential to assist in reclamation of saline farm land in the southwest region of Australia and that some species are much more effective than others.

Tillage erosion on slopes with soil conservation structures in the Ethiopian Highlands

Article

Nov 2000
SOIL TILL RES

Soil translocation due to tillage by the ox-drawn ard plough appears to be an important source of colluviation behind stone bunds and lynchets in the Ethiopian highlands. To quantify erosion rates caused by this plough in Ethiopia, painted and numbered rock fragments, 3–5cm in intermediate diameter, were used as tracers to monitor soil movement on 16 sites, each having a different slope gradient, in the district of Dogu’a Tembien, Tigray Region, Ethiopia. Average tillage depth was 8.1cm and the net mean downslope displacement distance per tillage operation ranged from 4.7cm for a 0.03mm−1 slope to 34.4cm for a field with a gradient of 0.48mm−1. There was a strong correlation (R2=0.84, P15cm intermediate diameter) are obstacles to the downslope movement of tilled soil. The unit soil transport rate (Qs) per tillage operation ranged from 4.8kgm−1 on the 0.03mm−1 slope to 38.7kgm−1 on the 0.48mm−1 slope. These values represent the mass of soil deposited by tillage behind 1m of lynchet or stone bund. During each tillage operation the same mass of soil is also removed from the foot of the upper stone bund or lynchet. For the first tillage operation, before the onset of the rainy season, the tillage transport coefficient (K) was 68kgm−1. As farmers till 1–4 times per year, annual K values can be assessed to range from 68 to 272kgm−1. These values are less than those observed for mechanised tillage, which however, is usually conducted on less steep slopes. On average, tillage erosion can be held responsible for half of the sediment deposited behind newly constructed stone bunds in the Tigray highlands.

Soil and erosion features of the Central Plateau Region of Tigrai, Ethiopia

Article

May 1978

The results of reconnaissance soil surveys covering 6,000 km2 are used to describe the Central Plateau region, which lies at elevations of 2,000 to 2,800 m in northern Ethiopia. Landform and soil sequences on calcareous shales, dolerites and sandstones are described, in which the principal soil units are Lithosols, Luvisols, Cambisols, Arenosols and Vertisols. Detailed morphological and analytical data are presented for a profile representative of arable soils in each sequence.Small-scale subsistence cultivation of cereals is the dominant land use; all land which is physically cultivable is at present cultivated. Settlement patterns are closely related to soil type, nucleated settlement occurring on fine textured soils but dispersed settlement on coarser textured and more freely draining soils.Erosion and soil moisture features of the three landforms described were investigated and compared. Empirical methods and suspended sediment measurements indicate high rates of regional soil loss (17–33 t ha−1 yr−1), accounted for by seasonally high rates of rainfall erosivity, steep terrain and poor land use. The recent development of gully erosion is seen to be linked to the disintegration of waterfall tufas. Application of the universal soil loss equation to arable lands indicates potential annual soil losses in the range of 400 t ha−1 on Vertisols to 200 t ha−1 on Cambisols: differences in rates are ascribed principally to differences in crop planting dates, which affect the degree of vegetative protection during periods of high rainfall erosivity.Soil moisture is shown to be in the available range for less than three months in the year. The time at which moisture in the profile enters the available range differed between the three soils monitored and was found to be closely related to the crop planting date, thus indirectly affecting the erosion hazard.

Effectiveness of stone bunds in controlling soil erosion on cropland in the Tigray Highlands, northern Ethiopia

Article

Mar 2006
SOIL USE MANAGE

Abstract Use of stone bunds to enhance soil and water conservation was first introduced to Tigray, northern Ethiopia in 1981. This study was designed to examine the factors that control the effectiveness of bunds installed on cropland. Qualitative and quantitative assessments of soil loss and sediment accumulation were conducted on 202 plots at 12 representative sites in Dogu'a Tembien district. Mean annual soil loss from the foot of the bunds due to tillage erosion was estimated at 39kgm−1yr−1 or 20tha−1yr−1, a rate which decreased with increasing age of bund. The assessed mean annual soil loss rate by sheet and rill erosion in the absence of stone bunds is 57tha−1yr−1. The mean measured annual rate of sediment accumulation behind the stone bunds is 119kgm−1yr−1/sp or 59tha−1yr−1. The measurements show that the introduction of stone bunds to the region has led to a 68% reduction in annual soil loss due to water erosion. This reduction is due to the accumulation of sediment behind the stone bunds, which occurs faster in the early years after construction and decreases as the depression behind the bunds becomes filled with sediment. New stone bunds are particularly effective in trapping sediment in transport, but regular maintenance and increase in height of the bunds is necessary to maintain their effectiveness. The average USLE P factor for stone bunds in the study area is estimated to be 0.32.

The effectiveness of loose rock check dams for gully control in Tigray, Northern Ethiopia

Article

Jan 2006
SOIL USE MANAGE

Over the last two decades, large gully control programmes have been established in Ethiopia. Based on detailed observations and measurements of 400 check dams in the highlands near Hagere Selam (Tigray, northern Ethiopian Highlands), the effectiveness of the check dam technique was assessed. In this study, catchment area, slope gradient, technical characteristics and the presence of smectite clays are the main factors controlling dam stability. Simple and logistic regression techniques were used to analyse the data. The frequent collapse of dams (39% after two years) is strongly associated with drainage area (A) and slope gradient of the soil surface near the gully (S), the product of these factors (S×A) being a proxy for runoff energy. Good functioning dams have a spillway, apron, concave plan form (when looking downslope) and are built at vertical intervals and with heights that result in a negative slope gradient of the line connecting the spillway and the foot of the upstream dam. Therefore, a reverse slope of this line is recommended. Furthermore, if large cracks are present in smectite-rich soils, the construction of check dams can lead to piping and concentrated flow bypassing the dam. Given that the collapse of some check dams seems inevitable where catchment areas are large or there are steep slopes, it is necessary to repair dams as soon as partial collapse starts and to complement this gully control technique with biological control measures.

Specific sediment yield in Tigray-Northem Ethiopia: Assessment and semi-quantitative modelling

Article

Jul 2005
GEOMORPHOLOGY

Sediment deposition in reservoirs is a serious off-site consequence of soil erosion in Tigray (Northern Ethiopia). So far insufficient and less reliable sediment yield data have been collected for Northern Ethiopia. Nor are there any adaptable methodologies for sediment yield assessment in the country as a whole, which could be used when designing new reservoirs. This study addresses those problems by (1) undertaking reservoir sediment deposition measurements and (2) by calibrating and adapting the Pacific Southwest Inter Agency Committee (PSIAC) and the Factorial Scoring Model (FSM) sediment yield assessment models to Ethiopian conditions. Field rating of catchment characteristics and the sediment yield data from the reservoir survey were used for calibration and validation of the models. Our reservoir survey indicates that specific sediment yield (SSY) varies significantly between catchments: i.e. 487 t km−2 year−1 to 1817 t km−2 year−1 with an average of 1054 (± 446) t km−2 year−1. Since the variability of SSY is high between the studied reservoirs, care should be taken in the study area to adopt representative SSY values during reservoir and soil water conservation planning. The PSIAC SSY prediction is found to fit well with observed SSY without adjustment. While the FSM was found to have, after modifying the description of factors and incorporating new controlling factors, a good fit between the predicted and observed SSY. Studies of the relationship between the known sediment yield rates and the catchment conditions using semi-quantitative approaches such as PSIAC and FSM can be of substantial benefit in extrapolating data for areas where no detailed information is available in a cheap and quick way. However, calibration and modification of such models may be necessary if they are to be used beyond the region where they were developed.

Impact of Road Building on Gully Erosion Risk: A Case Study from the Northern Ethiopian Highlands

Article

Nov 2002
EARTH SURF PROC LAND

Although obvious in the field, the impact of road building on hydrology and gullying in Ethiopia has rarely been analysed. This study investigates how road building in the Ethiopian Highlands affects the gully erosion risk. The road between Makalle and Adwa in the highlands of Tigray (northern Ethiopia), built in 1993–1994, caused gullying at most of the culverts and other road drains. While damage by runoff to the road itself remains limited, off-site effects are very important. Since the building of the road, nine new gullies were created immediately downslope of the studied road segment (6·5 km long) and seven other gullies at a distance between 100 and 500 m more downslope. The road induces a concentration of surface runoff, a diversion of concentrated runoff to other catchments, and an increase in catchment size, which are the main causes for gully development after road building. Topographic thresholds for gully formation are determined in terms of slope gradient of the soil surface at the gully head and catchment area. The influence of road building on both the variation of these thresholds and the modification of the drainage pattern is analysed. The slope gradient of the soil surface at the gully heads which were induced by the road varies between 0·06 and 0·42 m m−1 (average 0·15 m m−1), whereas gully heads without influence of the road have slope gradients between 0·09 and 0·52 m m−1 (average 0·25 m m−1). Road building disturbed the equilibrium in the study area but the lowering of topographic threshold values for gullying is not statistically significant. Increased gully erosion after road building has caused the loss of fertile soil and crop yield, a decrease of land holding size, and the creation of obstacles for tillage operations. Hence roads should be designed in a way that keeps runoff interception, concentration and deviation minimal. Techniques must be used to spread concentrated runoff in space and time and to increase its infiltration instead of directing it straight onto unprotected slopes. Copyright © 2002 John Wiley & Sons, Ltd.

Discontinuous Ephemeral Streams

Article

Jul 1997
GEOMORPHOLOGY

William B. Bull

Many ephemeral streams in western North America flowed over smooth valley floors before transformation from shallow discontinuous channels into deep arroyos. These inherently unstable streams of semiarid regions are sensitive to short-term climatic changes, and to human impacts, because hillslopes supply abundant sediment to infrequent large streamflow events. Discontinuous ephemeral streams appear to be constantly changing as they alternate between two primary modes of operation; either aggradation or degradation may become dominant. Attainment of equilibrium conditions is brief. Disequilibrium is promoted by channel entrenchment that causes the fall of local base level, and by deposition of channel fans that causes the rise of local base level. These opposing base-level processes in adjacent reaches are maintained by self-enhancing feedback mechanisms.

Soil wettability in forested catchments in South Africa; as measured by different methods and as affected by vegetation cover and soil characteristics

Article

May 2000
J HYDROL

David Findlay Scott

Earlier studies in South Africa had shown that water repellency in the soils of timber plantations was associated with a greater risk of overland flow and soil erosion on mountain slopes. This paper reports on a follow-up study to determine how prevalent water repellent soils are in the forestry areas of South Africa, and to what extent this phenomenon is associated with specific vegetation types. Soils from a representative series of forestry sites around South Africa were sampled from beneath each genus or plantation type and the range of local vegetation types. These soils were dried at low oven temperatures and then subjected to a series of tests of soil wettability, namely, water drop penetration time, infiltration rate, critical surface tension and apparent advancing contact angle as determined by the equilibrium capillary rise test.Water repellency is common in dried soils from timber plantations. The dominant variation in repellency is explained by the different vegetation types: soils beneath eucalypts are most repellent, followed by those beneath wattle (Acacia species), indigenous forest and pine. Soils beneath grassland and fynbos scrub were least likely to show repellency, perhaps because regular fires remove plant litter and thus the potential for hydrophobic substances to develop. Soil characteristics explained very little of the variation in repellency. Organic carbon content was weakly correlated with higher repellency, but organic carbon content and soil texture added little explanation to models that first accounted for variation in vegetation type and point of origin. These results are broadly the same regardless of which method of measuring repellency was used. However, the critical surface tension test was far superior to the others in terms of information gained, speed, efficiency and statistical utility of the resultant scores.

Rainfall erosivity and variability in the Northern Ethiopia Highlands

Article

Sep 2005
J HYDROL

The Ethiopian Highlands are subjected to important land degradation. Though spatial variability of rain depth is important, even at the catchment scale, this variability has never been studied. In addition, little is known on rain erosivity for this part of the world. The objectives of this study are (a) to assess the spatial variation of rain in a 80 km² mountain area (2100–2800 m a.s.l.) in the Northern Tigray region, and how this variation is influenced by topography, geographical position and lithology, (b) to analyse the temporal variations and (c) to quantify rain erosivity and the different factors determining it, such as rain intensity, drop size and kinetic energy.

Stone bunds for soil conservation in the northern Ethiopian highlands: Impacts on soil fertility and crop yield

Article

Nov 2006
SOIL TILL RES

In the Ethiopian highlands, large-scale stone bund building programs are implemented to curb severe soil erosion. Development of soil fertility gradients is often mentioned as the major drawback of stone bund implementation, as it would result in a dramatic lowering of crop yield. Therefore, the objectives of this study are to assess soil fertility gradients on progressive terraces and their influence on crop yield, in order to evaluate the long-term sustainability of stone bunds in the Ethiopian Highlands.

Paleoenvironmental Changes during the Last 4000 yr in the Tigray, Northern Ethiopia

Article

May 1998

In the Tigray region at the northern Ethiopian Highlands, paleoenvironmental reconstruction based on several infilled valley deposit sequences suggests that the past 4000 yr comprised three major wetter periods (ca. 4000–3500 yr B.P., 2500–1500 yr B.P., and 1000–960 yr B.P.), during which soils were formed, and two degradation episodes (ca. 3500–2500 yr B.P. and 1500–1000 yr B.P.), during which there was an increase of sediment yield from the slopes into the valleys. For the past 1000 yr, and in particular since the early 17th century, stratigraphic records together with historic chronicles suggest increasing aridity. Although difficulties arise in distinguishing between natural and human impacts, particularly in a region with a long established agricultural background, stratigraphical and proxy paleoclimatic data have indicated climate as the main controlling factor responsible for the environmental changes in the Tigray.

Medium-term evolution of a gully developed in loess-derived soil

Article

Aug 2002
GEOMORPHOLOGY

Field surveys in the Belgian loess belt revealed the presence in many forested areas of large, permanent gully systems, most of which are currently inactive. In cultivated areas, such gullies can only be observed in cross-sectional soil profiles through hollows, as virtually all such large gullies are currently infilled with colluvium. Little is known about the spatial distribution, initiation and temporal evolution of these large, permanent gully systems on loess-derived soils. Therefore, the medium-term evolution of a gully initiated in a cultivated area on loess-derived soils southwest of Leuven (Belgium) in May–June 1986, was studied over 13 years. Two intense rainfall events created this (ephemeral) gully, which was not erased by subsequent tillage. Between June 1986 and the December 1999, eight field surveys were conducted to measure gully dimensions. During two surveys, topographic indices (e.g., slope and drainage area) were also measured. Daily rainfall for the measuring period were obtained from a rainfall station located some 10 km southwest of the gully. Analysis of rainfall data showed that no extreme rainfall event was required to initiate such large (permanent) gullies, as observed in forested areas and through cross-sectional profiles in cultivated fields in the Belgian loess belt. Return periods of the event that caused the gully varied between <1 year and 25 years, depending on the assumptions used for defining event rain intensity. Once established, length, surface area and volume of the studied gully evolved with time, cumulative rainfall or cumulative runoff, following a negative exponential relation. This accords with observations reported for gullies in Australia and the USA. This study shows that a degressive increase of gully extension, can be largely explained by the evolution of a “slope–drainage area” factor (S×A, which is proportional to stream power) with time. While gully length and gully surface area asymptotically evolve towards a final value, gully volume decreased at a given point in time. From this, it is inferred that sediment deposition will potentially infill the gully to such an extent that the farmer can drive across it. From this moment on, the combined effect of water and tillage erosion in the gully drainage area, will lead towards rapid infilling. This expected evolution of a gully in cultivated fields accords with observations of large infilled gully systems in cultivated areas in eastern Belgium. The permanent gullies observed under forest are attributed to the fact that after severe gully erosion, this area was reforested or abandoned. Therefore, the sediment source was cut off and the gully was not filled in by sediment deposition.

A Runoff Capability Classification System Based on Surface Features Criteria on Semi-Arid Areas of West Africa

Article

Jan 1992
J HYDROL

An analysis of the factors influencing infiltration and runoff was carried out using data obtained under simulated rainfall conditions on 87 plots in arid and semi-arid areas of West Africa, arranged in a hierarchical sequence. One of the key factors to emerge from this typological classification is the type of surface crust. Together with faunal activity, vegetation cover and surface roughness, this parameter permits the inclusion of a ‘unit surface’ factor in the classification system. Each unit surface is characterized in terms of genetic, morphological and hydrological properties.At a higher level, the combination of these unit surfaces allows a ‘soil surface features unit’ to be defined, based on an original mapping method. The samples, once defined in this system, were found to correspond to homogeneous criteria both in terms of evolution dynamics and hydrological behaviour. Furthermore, such cartography could be successfully extrapolated through remote sensing image analysis, making possible a classification of the runoff capability of small watersheds based on objective and standardized criteria.

Streamflow responses to afforestation with Eucalyptus grandis and Pinus patula and to felling in the Mokobulaan experimental catchments, South Africa

Article

Dec 1997
J HYDROL

The reductions in streamflow following the afforestation of grassland with Eucalyptus grandis and Pinus patula in the Mokobulaan research catchments on the Mpumalanga escarpment, and the subsequent response in streamflow to clearfelling of the eucalypts are presented. Afforestation with eucalypts of an entire catchment with a virgin annual runoff of 236 mm, caused a statistically significant decrease in streamflow in the third year after planting and the stream dried up completely in the ninth year after planting. The eucalypts were clearfelled when 16 years old but full perennial streamflow did not return until five years later. Afforestation with pines of an entire catchment with a virgin annual runoff of 217 mm, produced a significant decrease in streamflow in the fourth year after planting and caused the stream to dry up completely in the twelfth year after planting.The drying up of the streams was not altogether surprising as the annual runoff was lower than the expected reductions owing to complete afforestation. The delayed return of streamflow in the clearfelled catchment is surprising though, and is attributed to the desiccation of deep, soil-water stores by the eucalypts. These stores had to be replenished before the streams could return to normal behaviour.

Human impact on the environment in the Ethiopian and Eritrean Highlands - a state of art

Article

Feb 2004
EARTH-SCI REV

This review analyses the environmental evolution of the Ethiopian highlands in the late Quaternary. The late Pleistocene (20,000–12,000 ¹⁴C years BP) was cold and dry, with (1) low lake levels in the Rift Valley, (2) large debris fans on the flanks of Lake Abhé basin, and (3) the Blue Nile transporting coarse bedload. Then, a period with abundant and less seasonal rains existed between 11,500 and 4800 ¹⁴C years BP, as suggested by increased arboreal pollen, high river and lake levels, low river turbidities and soil formation. Around 5000–4800 ¹⁴C years BP, there was a shift to more arid conditions and more soil erosion. Many phenomena that were previously interpreted as climate-driven might, however, well be of anthropic origin. Thick sediment deposits on pediments as well as an increase of secondary forest, scrub and ruderal species in pollen diagrams are witnesses of this human impact.

Sediment deposition and pedogenesis in exclosures in the Tigray Highlands, Ethiopia

Article

Jun 2006
GEODERMA

In the Tigray highlands of Northern Ethiopia, the establishment of exclosures (i.e., areas closed for grazing and agriculture) has become an important measure to combat land degradation and restore vegetative cover. Exclosures are commonly found on steep slopes and downslope from a sediment source area. In this study their sediment trapping capacity and controlling factors were investigated. Total sediment depth turned out to be related to vegetation cover, sediment source area and in some cases slope gradient. Thickness of recent, short-term (< 20 years) sediment deposits was strongly related to distance from the top edge of the closed area, slope gradient, vegetation cover and characteristics of the sediment source area. Mean sediment deposition rates ranged between 26 and 123 Mg ha− 1 yr− 1. Under influence of vegetation and sediment deposition dark soils rich in organic matter (Phaeozems) develop. In view of their high sediment trapping capacity, exclosures are highly valued as efficient soil conservation measures in the Tigray highlands.

Gully Erosion and Environmental Change: Importance and Research Needs

Article

Jan 2003
CATENA

Assessing the impacts of climatic and, in particular, land use changes on rates of soil erosion by water is the objective of many national and international research projects. However, over the last decades, most research dealing with soil erosion by water has concentrated on sheet (interrill) and rill erosion processes operating at the (runoff) plot scale. Relatively few studies have been conducted on gully erosion operating at larger spatial scales.Recent studies indicate that (1) gully erosion represents an important sediment source in a range of environments and (2) gullies are effective links for transferring runoff and sediment from uplands to valley bottoms and permanent channels where they aggravate off site effects of water erosion. In other words, once gullies develop, they increase the connectivity in the landscape. Many cases of damage (sediment and chemical) to watercourses and properties by runoff from agricultural land relate to (ephemeral) gullying. Consequently, there is a need for monitoring, experimental and modelling studies of gully erosion as a basis for predicting the effects of environmental change (climatic and land use changes) on gully erosion rates.In this respect, various research questions can be identified. The most important ones are:(1)What is the contribution of gully erosion to overall soil loss and sediment production at various temporal and spatial scales and under different climatic and land use conditions?(2)What are appropriate measuring techniques for monitoring and experimental studies of the initiation and development of various gully types at various temporal and spatial scales?(3)Can we identify critical thresholds for the initiation, development and infilling of gullies in different environments in terms of flow hydraulics, rain, topography, soils and land use?(4)How does gully erosion interact with hydrological processes as well as with other soil degradation processes?(5)What are appropriate models of gully erosion, capable of predicting (a) erosion rates at various temporal and spatial scales and (b) the impact of gully development on hydrology, sediment yield and landscape evolution?(6)What are efficient gully prevention and gully control measures? What can be learned from failures and successes of gully erosion control programmes?These questions need to be answered first if we want to improve our insights into the impacts of environmental change on gully erosion. This paper highlights some of these issues by reviewing recent examples taken from various environments.

Soil Erosion by Water: Some Measures for its Control in Cultivated Lands

Article

Jan 1965

Evolution du relief et pédogenèse dans la basse vallée du Wabi-Shebelli (Ethiopie)

Article

Jan 1971

Review of information on interactions between vegetation and groundwater

Article

Apr 1999
WATER SA

Copyright: 1999 Water Research Commission Vegetation plays key roles in the interactions between groundwater and surface-water systems, because of its direct and indirect influence on recharge and because of the dependence of vegetation communities on groundwater. Despite this, groundwater and surface water have traditionally been treated as separate legal entities in South Africa and scientific disciplines have also tended to view them as separate, or at least separable, hydrological systems. This situation is beginning to change as South Africa’s new Water Act recognizes them both as inseparable elements of the hydrological cycle. The Act also requires that water resources be managed sustainably and a much greater understanding of these interactions is needed to meet this obligation. This paper provides a review of what is known about groundwater - vegetation interactions based on local and international literature and on information from the “grey” literature and unpublished sources. Changes in vegetation cover and structure, particularly from low vegetation such as grassland to tall vegetation such as a forest can have a significant impact on groundwater recharge by altering components of the hydrological cycle such as interception and transpiration. Recent research has shown that root systems often extend to more than the 1 m maximum used in defining agricultural soils and frequently to more than 10 m deep where the physical conditions permit root penetration. Woody plants have the deepest root systems and are capable of extracting large volumes of water from depths of 10 m or more. In South Africa the impacts of vegetation changes on base flow or groundwater have been documented in both humid and sub-humid catchments but the greatest changes in groundwater levels have followed type conversions in semi-arid savanna and on the coastal plains of Zululand. Transpiration of water by plants accounts for about half of the largest changes in the water balance associated with vegetation type conversions. Many plant communities, particularly those of wetlands and riparian strips are highly susceptible to changes in the depth to the groundwater, both annual and seasonal. The rate of change (positive or negative) in water-table levels may be important but the data are not conclusive. Interactions between groundwater and vegetation appear to be generally more pervasive and important than was believed in the past.

Gully erosion and desiccation of the landscape in Tigray (North-Ethiopia) MSc thesis, Department of Land Manage-ment Fighting desertification in the Ethiopian highlands: The stone bund technique and it's risk of developing a soil fertility gradient

Jan 2004

Van Damme
A Belgium
K Vancampenhout
Desta J Nyssen
Deckers J Gebremichael
Mitiku J Poesen
Haile

Van Damme A. 2004. Gully erosion and desiccation of the landscape in Tigray (North-Ethiopia). MSc thesis, Department of Land Manage-ment, University of Leuven, Belgium. Vancampenhout K, Nyssen J, Desta Gebremichael, Deckers J, Poesen J, Mitiku Haile, Moeyersons J. 2005. Fighting desertification in the Ethiopian highlands: The stone bund technique and it's risk of developing a soil fertility gradient. Soil and Tillage Research (in press).

Working Paper 1. Soils and land classification Hunting Technical Services: Hemel Hempstead Impact of gully formation on the evolution of the agricultural system in two villages in Dogu'a Tembien A review of information on interactions between vegetation and groundwater

Jan 1974
137-152

Le D Maitre
D Scott
C Colvin

Hunting 1974. Central Tigre Development Study, Working Paper 1. Soils and land classification. Hunting Technical Services: Hemel Hempstead. Kassa Teka 2003. Impact of gully formation on the evolution of the agricultural system in two villages in Dogu'a Tembien. Report of Practical Attachment with Zala-Daget Project. Mekelle University, Ethiopia. Le Maitre D, Scott D, Colvin C. 1999. A review of information on interactions between vegetation and groundwater. Water SA 25(2): 137– 152.

Stuwmeren in Tigray (Noord-Ethiopië): kenmerken, sedimentatie en sedimentbronnen MSc thesis, Department of Geo-graphy

Jan 2003

De J K U Wit
Leuven
Belgium
K Descheemaeker
Rossi J J Nyssen
Mitiku J Poesen
Haile

De Wit J. 2003. Stuwmeren in Tigray (Noord-Ethiopië): kenmerken, sedimentatie en sedimentbronnen. MSc thesis, Department of Geo-graphy, K.U. Leuven, Belgium. Descheemaeker K, Nyssen J, Rossi J, Poesen J, Mitiku Haile, Moeyersons J, Deckers J. 2005. Sediment deposition and pedogenesis in exclosures in the Tigray Highlands, Ethiopia. Geoderma (in press).

Conséquence de la forêt sur le bilan d'écoulement annuel

Jan 1999
63

Cosandey C

Cosandey C. 1999. Conséquence de la forêt sur le bilan d'écoulement annuel. Bulletin de la Société Géographique du Liège 37: 63-73.

Erosion processes and soil conservation in a tropical mountain catchment under threat of anthropogenic desertification – a case study from Northern Ethiopia Vertic movements and the developments of stone covers and gullies

Jan 2000
145-164

J K U Nyssen
Leuven
Belgium
Moeyersons J J Nyssen
Mitiku Haile

Nyssen J. 2001. Erosion processes and soil conservation in a tropical mountain catchment under threat of anthropogenic desertification – a case study from Northern Ethiopia. PhD thesis, Department of Geography, K.U. Leuven, Belgium. Nyssen J, Moeyersons J, Deckers J, Mitiku Haile, Poesen J. 2000a. Vertic movements and the developments of stone covers and gullies, Tigray Highlands, Ethiopia. Zeitschrift für Geomorphologie, N.F. 44(2): 145–164.

Vegetation analysis. In Rehabili-tation of Degraded and Degrading Areas of Tigray-Northern Ethiopia

May 1994
20-75

E Feoli
Teklehaimanot M Fernetti
Tewoldeberhane Haileselassie
Zerihun Gebreegziabher
Woldu

Feoli E, Fernetti M, Teklehaimanot Haileselassie, Tewoldeberhane Gebreegziabher, Zerihun Woldu, 1994. Vegetation analysis. In Rehabili-tation of Degraded and Degrading Areas of Tigray-Northern Ethiopia. Progress Report of Research Activities until March 31, 1994, Feoli E (ed.). Scientific report, STD3 Project. Commission of European Communities: 20–75.

Tigré, Ethiopie; Résistance et limites d'une ancienne civilisation agraire; Conséquences sur la dégradation des terres. Mémoire. CNEARC: Montpellier. Nigussie Haregeweyn Specific sediment yield in Tigray-Northern Ethiopia: Assessment and semi-quantitative modelling

Jan 2001
315-331

Naudts J J Poesen
J Nyssen
G Verstraeten
Govers J G Vente

Naudts J. 2001. Land use in Dogua Tembien, Tigray Ethiopia. Unpublished M.Sc. thesis. Department of Land Management, University of Leuven, 173 pages. Naudts J. 2002. Les Hautes Terres de Tembien, Tigré, Ethiopie; Résistance et limites d'une ancienne civilisation agraire; Conséquences sur la dégradation des terres. Mémoire. CNEARC: Montpellier. Nigussie Haregeweyn, Poesen J, Nyssen J, Verstraeten G, de Vente J, Govers G, Deckers J, Moeyersons J. 2005. Specific sediment yield in Tigray-Northern Ethiopia: Assessment and semi-quantitative modelling. Geomorphology 69: 315–331.

The methodology of the participatory research approach

Jan 1980
167-185

J Nyssen

J. Nyssen et al. Copyright © 2006 John Wiley & Sons, Ltd. Earth Surf. Process. Landforms 31, 167–185 (2006) Bryceson D, Manicom L, Kassam Y. 1981. The methodology of the participatory research approach. In Research for the People, Research by the People: Selected Papers from the International Forum on Participatory Research in Ljubljana, Yugoslavia, 1980, Erasmie T, de Vries J, Dubell F (eds). Linköping University: 94–109.

Ravijnontwikkeling en -erosiecontrolemaatregelen in een tropisch bergrivierbekken Soil and erosion features of the Central Plateau region of Tigrai, Ethiopia

Jan 1978
131-157

M Veyret-Picot
Belgium
K Virgo
Munro

Veyret-Picot M. 2001. Ravijnontwikkeling en -erosiecontrolemaatregelen in een tropisch bergrivierbekken. MSc thesis, Department of Geography, University of Leuven, Belgium. Virgo K, Munro R. 1978. Soil and erosion features of the Central Plateau region of Tigrai, Ethiopia. Geoderma 20: 131–157.

Agricultural Systems in Ethiopia Centre for Agricultural Publishing and Documentation: Wageningen. WFW Working for Water. Department of Water Affairs and Forestry: South Africa An introduction to participatory appraisal techniques: sharing experience from China and Nepal

Jan 1975

E Westphal
D Young
Hinton

Westphal E. 1975. Agricultural Systems in Ethiopia. Centre for Agricultural Publishing and Documentation: Wageningen. WFW. 2005. Working for Water. Department of Water Affairs and Forestry: South Africa. http://www.dwaf.gov.za/wfw/ [accessed 16.12.2005] Young D., Hinton R. 1996. An introduction to participatory appraisal techniques: sharing experience from China and Nepal. London, VSO.

Forests and their importance for soil conservation in Ethiopia

Jan 1988
161

Fiedler HJ

Fiedler HJ, Gebeyehu Belay, 1988. Forests and their importance for soil conservation in Ethiopia. Archiv für Naturschutz und Landschaftsforschung 28: 161-175.

Deforestation, gully development and desertification in sub-Saharan tropical and subtropical Africa. Poster presented at Second International Conference on Tropical Climatology, Meteorology and Hydrology Medium-term evolution of a gully developed in a loess-derived soil

Jan 2002
12-143

Moeyersons J J Nachtergaele
Oostwoud J D Poesen
L Vandekerckhove

Moeyersons J. 2001. Deforestation, gully development and desertification in sub-Saharan tropical and subtropical Africa. Poster presented at Second International Conference on Tropical Climatology, Meteorology and Hydrology, Brussels, 12–14 December 2001. Nachtergaele J, Poesen J, Oostwoud Wijdenes D, Vandekerckhove L. 2002. Medium-term evolution of a gully developed in a loess-derived soil. Geomorphology 46(3-4): 223–239.

Simple approaches to predicting rates and extent of gully development

Jan 1997
1125-1130

I D Rutherfurd
I P Prosser

Rutherfurd ID, Prosser IP, Davis J. 1997. Simple approaches to predicting rates and extent of gully development. In Proceedings of the Conference on Management of Landscapes Disturbed by Channel Incision, Wang SSY, Langendoen EJ, Shields Jr (eds) Center for Computational Hydroscience and Engineering, University of Mississippi, USA. 1125-1130.

Geomorphological and sedimentary records of Holocene climatic changes and human impact in the Highlands of Northern Ethiopia

Jan 1997
167-185

Copyright
Berakhi
L Brancaccio
G Calderoni
Dramis M F Coltorti
Belay Tegene
Mohammad Umer

Copyright © 2006 John Wiley & Sons, Ltd. Earth Surf. Process. Landforms 31, 167–185 (2006) Ogbaghebriel Berakhi, Brancaccio L, Calderoni G, Coltorti M, Dramis F, Belay Tegene, Mohammad Umer. 1997. Geomorphological and sedimentary records of Holocene climatic changes and human impact in the Highlands of Northern Ethiopia. In 4th International Conference an Geomorphology – Abstracts, Federici PR (ed.). Geografia Fiscia e Dinamica Quaternaria, Supp. 3: T1:77.

Stuwmeren in Tigray (Noord-Ethiopië): kenmerken, sedimentatie en sedimentbronnen

Jan 2003

De Wit

De Wit J. 2003. Stuwmeren in Tigray (Noord-Ethiopië): kenmerken, sedimentatie en sedimentbronnen. MSc thesis, Department of Geography, K.U. Leuven, Belgium.

The methodology of the participatory research approach

Jan 1980
94-109

D Bryceson
L Manicom
Y Kassam

Bryceson D, Manicom L, Kassam Y. 1981. The methodology of the participatory research approach. In Research for the People, Research by the People: Selected Papers from the International Forum on Participatory Research in Ljubljana, Yugoslavia, 1980, Erasmie T, de Vries J, Dubell F (eds). Linköping University: 94-109.

An introduction to participatory appraisal techniques: sharing experience from China and Nepal

Youngd
Hintonr

Young D., Hinton R. 1996. An introduction to participatory appraisal techniques: sharing experience from China and Nepal. London, VSO.

Les Hautes Terres de Tembien, Tigré, Ethiopie; Résistance et limites d'une ancienne civilisation agraire; Conséquences sur la dégradation des terres

Jan 2002

Naudts

Naudts J. 2002. Les Hautes Terres de Tembien, Tigré, Ethiopie; Résistance et limites d'une ancienne civilisation agraire; Conséquences sur la dégradation des terres. Mémoire. CNEARC: Montpellier.

Fighting desertification in the Ethiopian highlands: The stone bund technique and it's risk of developing a soil fertility gradient. Soil and Tillage Research

Jan 2005

K Vancampenhout
J Nyssen
Desta Gebremichael
J Deckers
J Poesen
Mitiku Haile
J Moeyersons

Vancampenhout K, Nyssen J, Desta Gebremichael, Deckers J, Poesen J, Mitiku Haile, Moeyersons J. 2005. Fighting desertification in the Ethiopian highlands: The stone bund technique and it's risk of developing a soil fertility gradient. Soil and Tillage Research (in press).

Assessment of gully erosion rates through interviews and measurements: A case study from northern Ethiopia

Abstract

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