Soil erosion is generally recognized as the dominant process of land degradation. The formation and expansion of gullies is often a highly significant process of soil erosion. However, our ability to ...assess and simulate gully erosion and its impacts remains very limited. This is especially so at regional to continental scales. As a result, gullying is often overlooked in policies and land and catchment management strategies. Nevertheless, significant progress has been made over the past decades. Based on a review of >590 scientific articles and policy documents, we provide a state-of-the-art on our ability to monitor, model and manage gully erosion at regional to continental scales. In this review we discuss the relevance and need of assessing gully erosion at regional to continental scales (Section 1); current methods to monitor gully erosion as well as pitfalls and opportunities to apply them at larger scales (section 2); field-based gully erosion research conducted in Europe and European Russia (section 3); model approaches to simulate gully erosion and its contribution to catchment sediment yields at large scales (section 4); data products that can be used for such simulations (section 5); and currently existing policy tools and needs to address the problem of gully erosion (section 6). Section 7 formulates a series of recommendations for further research and policy development, based on this review. While several of these sections have a strong focus on Europe, most of our findings and recommendations are of global significance.
Gully erosion damages land resources and endangers human productivity and life, making it a key issue in global research on soil erosion nowadays. Gully headcut retreat (GHR) is the main form of ...gully erosion. Tiny concave features can be found in many retreating gully heads worldwide, and they are referred to as “niche terrain” in this study. To investigate the association between niche terrain and GHR, relevant research was reviewed on niches and stability analysis of gully heads with niches was modelled and analysed. Studies have shown that not all niches worldwide are identical due to regional differences in internal material–external environmental conditions. Special soil properties, joints, and cracks are the internal material conditions that lead to the formation of niche. External conditions include climate conditions, vegetation conditions, and topography. Water is the driving force for the formation of niche, while vegetation and topography are key factors. Niches can be regarded as the initial stage of GHR in areas where gully erosion is intense. In general, GHR is a composite cyclical process dominated by hydraulic erosion in the early stage and gravitational erosion in the late stage, including niche formation, inward concave formation, free face formation, overhanging soil collapse, and niche reformation. In this study, a model of gully head stability is applied, and it is found that the stability‐based factor of safety decreases exponentially with increasing niche height and crack depth, increases exponentially with increasing niche angle, and decreases quadratically with increasing catchment slope. Summarizing the common characteristics of niche terrains worldwide can facilitate the study of the evolution of gully erosion globally.
Niches can be regarded as the initial stage of gully head retreat. The mechanism of niches varies with regional internal material–external environmental conditions. Gully head retreat is a composite cycle process dominated by early hydraulic erosion and later gravity erosion.
Despite over a century of investigations into gullies and gully erosion, the characterization and categorization of gullies and the varied definitions, nomenclatures and terminology used has caused ...some confusion in understanding and communicating the relationships of gully forms and processes around the world. We firstly review the gully literature and highlight how a lack of consistency in gully definition and characterization prevents unifying theory from being developed within this important field of research, since it is often unclear whether different landscape features being discussed are comparable. We propose that conventionally employed qualitative planform and cross‐sectional characteristics of gullies alone are inadequate to define gully types, yet both these features remain central to most modern gully descriptions. We discuss the need to revise and augment these basic characteristics with clearly defined morphogenetic attributes such as landscape context, soil material characteristics, erosion processes, hydrological integrity, modes of development, and head/side‐wall morphology for an effective, practicable, generic gully classification scheme. Central to a gully classification scheme is the need for a clear definition of what a gully is – and is not – for which geomorphological criteria are proposed to differentiate a ‘gully’ from other ‘incisional land surface forms’. This gully definition hinges largely on the identification of a retreating head scarp and the internal erosion by mass‐movement and other sidewall slope erosion processes, coupled with the transport of the soil materials from the gully void. By defining a gully and synthesizing descriptions of gully ‘types’ from the literature and our own experience, we propose key morphogenetic attributes of gullies necessary to form a framework for a systematic gully classification scheme. An initial, eclectic classification framework is presented as both a summation and a synthesis of the literature review, and as a progenitor to a dynamic generic classification scheme that is proposed in a follow‐up article.
From reviewing the gully erosion literature for definitions, terminology, and categorization we conclude that a systematic classification of gullies is necessary to overcome the apparent disorder. Thus, we propose key morphogenetic attributes of gullies to form a framework for a generic gully classification scheme. An initial classification framework is presented as both a summation and a synthesis of the literature, and as a progenitor to a dynamic classification scheme that is proposed in a follow up article.
Exploring the variation characteristics and influencing factors of gully agricultural production transformation (GAPT) in the Loess Plateau (LP) can provide scientific reference for the evolution of ...rural human-environment relationship and agricultural multi-functional development in the context of green high-quality development. In this paper, Taking Yan'an City of loess hilly and gully region (LHGR) as the study area, 30m resolution Landsat TM/OLI data in the year of 1995, 2000, 2005, 2010, and 2018 were selected, and kernel density estimation and geographic detector model were used to analyzes the process of GAPT, and to explore the driving force of GAPT in the LP and its spatial-temporal differentiation pattern. The results show that: (1) In the past 20 years, the gully agricultural production in the Yan'an LHGR has shown a divergent distribution and phased expansion, and the overall trend of fluctuating shrinkage. The gully agricultural production transformation center of gravity in the study area has shifted from the middle-altitude to the low-altitude area. (2) The gully agricultural production in the study area is transforming to agglomeration at small spatial scales. GAPT mostly occurs in the water supply belts near river waters, and in the area close to roads and areas near rural settlements which are closely related to human activities. (3) The process of GAPT mainly driven by socio-economic factors and policy factors, and it presents three evolution characteristics: contiguous distribution of traditional agricultural production, transformation of modern gully agricultural production functions, and modern agricultural and tourism multi-functional three-industry integration. The essence is the functional transformation of gully agricultural land. (4) GAPT in the LP is driven by many factors. Behavior subjects at different levels would promote the GAPT in different directions under the background of major national and regional development policies. The research results can provide scientific reference for crop planting mode adjustment, sustainable land use management, and the similar regional agriculture green transformation, thus supporting the realization of the strategic objectives of high-quality agricultural development and rural revitalization in the Yellow River Basin.
•The concept of the gully agricultural production transformation (GAPT) was proposed.•We quantified GAPT 's trends and characteristics of loess hilly and gully region of Yan’an, China.•The gully agricultural production is transforming to agglomeration at small spatial scales.•GAPT in the Loess Plateau is driven by many factors and has different driving mechanisms at different stages.
•A field investigation of gully erosion was conducted in a 393 km2 area.•Larger ridge orientation angle and sunny slope were conducive to gully development.•Gully volume can be well predicted by a ...power function of gully area.•Soil loss caused by gully erosion occupied by 65% in northeast China.
Gully erosion, one of the most damaging forms of land degradation, destroys farmlands and threatens grain and ecological stability. Approximately 295,000 gullies have formed in the Mollisols region of northeast China (NEC), while the actual severity of gully erosion remains unclear. This study aims to clarify gully morphology, factors influencing gully morphology, and contribution of gully erosion to soil loss through a 393 km2 field investigation in a typical and representative Mollisols region of NEC. There were 1048 gullies observed, with an average length, top width, depth and width-depth ratio of 522.32 m, 15.05 m, 2.77 m and 7.16, respectively. Over 70% of gullies had a length, top width and depth of 100–500 m, 3–20 m and 0.5–3 m, respectively. The three types of gullies, classified based on where the gully head developed (GF, farmland; GR, unpaved road; GW, woodland), had significantly distinct morphologies, with GW being broader and deeper and GF being longer. Notably, 56.2% of gullies are GF, accounted for 74.84% of the total gully area and 67.04% of the total gully volume (V). V of GF, GR and GW could be well explained by a power function of gully area (A). Gully density (gully length per unit area, GD, km km−2) and ground lacerative degree (gully area per unit area, GLD, km km−2) increased with slope gradient, and first increased and then decreased with slope length. Gully development was more favorable of sunny slope and a larger angle between gully and ridge orientation. The annual eroded soil from the gully was 1.86 times of that from the hillslope across the region during 2013–2018, contributing 65% of region eroded soil. This clearly identifies the severity of gully erosion and substantiates gully erosion risks to valuable mollisols and therefore food security. An urgent need exists to implement gully erosion control practices in this area.
Intersecting views of gully erosion in South Africa Olivier, George; Van De Wiel, Marco J.; De Clercq, Willem P.
Earth surface processes and landforms,
January 2023, 2023-01-00, 20230101, Letnik:
48, Številka:
1
Journal Article
Recenzirano
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Gully erosion is an environmental problem recognized as one of the worst land degradation processes worldwide. Insight into regional gully perturbations is required to combat the serious on‐ and ...off‐site impacts of gullying on a catchment management scale. In response, we intersect different perspectives on gully erosion‐specific views in South Africa (SA), a country that exhibits various physiographic properties and spans 1.22 million km2. While the debate surrounding gully origin continues, there is consensus that anthropogenic activities are a major contemporary driver. The anthropogenic impact caused gullying to transcend climatic, geomorphic, and land‐use boundaries, although it becomes more prominent in central to eastern SA. Soil erodibility plays a crucial role in what extent of gully erosion severity is attained from human impact, contributing to the east–west imbalance of erosion in SA. Soil erosion rates from gullying and badlands are limited but suggest that it ranges between 30 and 123 t ha−1 yr−1 in the more prominent areas. These soil loss rates are comparable to global rates where gullying is concerned; moreover, they are up to four orders of magnitude higher than the estimated baseline erosion rate. On a national scale, the complexity of gullying is evident from the different temporal timings of (re)activation or stabilizing and different evolution rates. Continued efforts are required to understand the intricate interplay of human activities, climate, and preconditions determining soil erodibility. In SA, more medium‐ to long‐term studies are required to understand better how changing control factors affect gully evolution. More research is needed to implement and appraise mitigation measures, especially using indigenous knowledge. Establishing (semi)‐automated mapping procedures would aid in gully monitoring and assessing the effectiveness of implemented mitigation measures. More urgently, the expected changes in climate and land‐use necessitate further research on how environmental change affects short‐term gully erosion dynamics.
We intersect different perspectives on gully erosion‐specific views in South Africa, a country that exhibits various physiographic properties and spans 1.22 million km2, to provide insight into regional‐scale gully perturbations. Gully origin is still being debated; however, contemporary gully erosion has a significant anthropogenic imprint, reaching unsustainable soil losses in certain regions. Further efforts are required to expand the geographic location of gully research sites and establish long‐term datasets, and to address how underground processes and environmental change conditions will impact gully evolution.
The world is experiencing serious soil losses. Soil erosion has become an important environmental problem in certain regions and is strongly affected by climate and land use changes. By selecting and ...reviewing 13 extensively used soil water erosion models (SWEMs) from the published literature, we summarize the current model-based knowledge on how climate factors (e.g., rainfall, freeze-thaw cycles, rainstorms, temperature and atmospheric CO2 concentrations) and land use change impact soil erosion worldwide. This study also provides a critical review of the application of these 13 SWEMs. By comparing model structures, features, prediction accuracies, and erosion processes, we recommend the most suitable SWEMs for different regions of the globe (Asia, Europe, Africa and the America) based on the evaluations of 13 SWEMs. Future soil erosion could be simulated using the RUSLE, LISEM, WEPP v2010.1, SWAT, EPIC, KINEROS and AGNPS models in Asia; the RUSLE, WEPP v2010.1, SWAT, EPIC, WATEM-SEDEM, MEFIDIS, AGNPS and AnnAGNPS models in Europe; the RUSLE, LISEM, SWAT, and AGNPS models in Africa; and the WEPP v2010.1, SWAT, EPIC, KINEROS, AGNPS and AnnAGNPS models in America. Finally, the limitations and challenges of the 13 SWEMs are highlighted.
•Evaluate the applications of soil water erosion models (SWEMs) at the global scale.•Recommend suitable SWEMs for Asia, Europe, Africa and America.•Identify how to improve SWEMs to cope with climate and land use changes in future.
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•The gully erosion at the regional scale was strongly affected by pedodiversity.•The factors influencing gully occurrences changed with the elevation of soil groups.•The SOC and silt ...content significantly influenced the gully intensity.•Gullies in specific soil zones predominantly affected by vegetation and topography.
How to assess gully erosion at large spatial scales is a major challenge, and few previous regional-scale studies have identified the vegetation and topography as the main factors of gully erosion, while little attention has been paid to the effects of soil properties on the regional gully occurrence and intensity. The Hengduan Mountain region has high pedodiversity owing to its significant horizontal and vertical zonation, and gully erosion is an important soil loss process in this region. This study aimed to identify the occurrence, intensity, and key influencing factors of gully erosion in the different soil zones of the Hengduan Mountain region. A total of 2,300 investigation quadrats were randomly set around the region with the size of 1 km × 1 km, and the gully erosion within each quadrat was investigated using Google Earth images. Approximately 25.5 % of the quadrats contained gullies (Qeg), 96.1 % of which was concentrated in 13 major soil groups. The annual temperature, vegetation, and slope were the key factors that influenced the occurrence of gullies in the alpine (>3,700 m a.s.l.), middle mountain (2,000–3,700 m a.s.l.), and low mountain (<2,000 m a.s.l.) soil zones, respectively. The average gully density (GD) and number of gullies (GN) were 2.22 km km−2 and 20.4 in the region, respectively, and both the average GD and GN of each main soil group exhibited significant exponentially decreasing relationships with the soil properties, including the soil organic matter (SOC) and silt content (0.43 < R2 < 0.76, P < 0.001). Within a specific soil zone, the vegetation (NDVI) and topography (elevation and slope) became the key influencing factors on GD and GN. These results show that, at the regional scale, gully erosion is initially controlled by the geographic pattern of the soil. Within the same soil zone, the vegetation and topography (slope and elevation) predominantly influence the occurrence and intensity of gully erosion.
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