Gully Erosion (gully + erosion)

Distribution by Scientific Domains

Selected Abstracts

Gully erosion in mountain areas: processes, measurement, modelling and regionalization

John Wainwright
No abstract is available for this article. [source]

High resolution quantification of gully erosion in upland peatlands at the landscape scale

Martin Evans
Abstract The upland peatlands of the UK are severely eroded, with large areas affected by gully erosion. The peatlands are important areas of carbon storage and provide a range of other ecosystem services including water supply and biodiversity all of which are negatively impacted by erosion of the upland surface. The magnitude of the gully erosion, and consequent adjustment of the peatland morphology, is such that in degraded peatlands the extent and magnitude of erosion is a major control on peatland function. Accurate mapping of gully form is therefore a necessary precondition to the understanding and management of these systems. This paper develops an approach to extracting gully maps from high resolution digital elevation models (DEMs). Gully maps of the Bleaklow Plateau in northern England were derived from a 2,m LiDAR DEM by combining areas of low difference from mean elevation and high positive plan curvature. Gully depth was modelled by interpolating between gully edges. Testing of the gully mapping and depth modelling against aerial photography, manual interpretation of the DEM and ground survey revealed that gully plan form is well represented and gully width and depth are modelled with tolerances close to the horizontal and vertical resolution of the LiDAR imagery. Estimates of gully width and depth were less reliable for gullies with total width of less than four pixels. The approach allows for the first time the derivation of accurate estimates of gully extent and magnitude over large areas and provides the basis for modelling a range of processes controlled by gullying. The approach has wider applicability to mapping gully erosion in a wide range of environments. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Dynamics of soil erosion rates and controlling factors in the Northern Ethiopian Highlands , towards a sediment budget

Jan Nyssen
Abstract This paper analyses the factors that control rates and extent of soil erosion processes in the 199 ha May Zegzeg catchment near Hagere Selam in the Tigray Highlands (Northern Ethiopia). This catchment, characterized by high elevations (2100,2650 m a.s.l.) and a subhorizontal structural relief, is typical for the Northern Ethiopian Highlands. Soil loss rates due to various erosion processes, as well as sediment yield rates and rates of sediment deposition within the catchment (essentially induced by recent soil conservation activities), were measured using a range of geomorphological methods. The area-weighted average rate of soil erosion by water in the catchment, measured over four years (1998,2001), is 14·8 t ha,1 y,1, which accounts for 98% of the change in potential energy of the landscape. Considering these soil loss rates by water, 28% is due to gully erosion. Other geomorphic processes, such as tillage erosion and rock fragment displacement by gravity and livestock trampling, are also important, either within certain land units, or for their impact on agricultural productivity. Estimated mean sediment deposition rate within the catchment equals 9·2 t ha,1 y,1. Calculated sediment yield (5·6 t ha,1 y,1) is similar to sediment yield measured in nearby catchments. Seventy-four percent of total soil loss by sheet and rill erosion is trapped in exclosures and behind stone bunds. The anthropogenic factor is dominant in controlling present-day erosion processes in the Northern Ethiopian Highlands. Human activities have led to an overall increase in erosion process intensities, but, through targeted interventions, rural society is now well on the way to control and reverse the degradation processes, as can be demonstrated through the sediment budget. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Using Rock-Eval 6 pyrolysis for tracking fossil organic carbon in modern environments: implications for the roles of erosion and weathering

Yoann Copard
Abstract This work relates to the debate on the fossil organic carbon (FOC) input in modern environments and its possible implication for the carbon cycle, and suggests the use of Rock-Eval 6 pyrolysis as a relevant tool for tracking FOC in such environments. Considering that such a delivery is mainly due to supergene processes affecting the continental surface, we studied organic matter in different reservoirs such as bedrocks, alterites, soils and rivers in two experimental catchments at Draix (Alpes de Haute Provence, France). Samples were subjected to geochemical (Rock-Eval 6 pyrolysis) investigations and artificial bacterial degradations. After comparing the geochemical fingerprint of samples, geochemical markers of FOC were defined and tracked in the different reservoirs. Our results confirm the contribution of FOC in modern soils and rivers and display the various influences of weathering and erosional processes on the fate of FOC during its exchange between these pools. In addition, the contrasting behaviour of these markers upon the supergene processes has also highlighted the refractory or labile characters of the fossil organic matter (FOM). Bedrock to river fluxes, controlled by gully erosion, are characterized by a qualitative and quantitative preservation of FOM. Bedrock to alterite fluxes, governed by chemical weathering, are characterized by FOC mineralization without qualitative changes in deeper alterites. Alterite to soils fluxes, controlled by (bio)chemical weathering, are characterized by strong FOC mineralization and qualitative changes of FOM. Thus weathering and erosional processes induce different FOM evolution and affect the fate of FOC towards the global carbon cycle. In this study, gully erosion would involve maintenance of an ancient sink for the global carbon cycle, while (bio)chemical processes provide a source of CO2. Finally, this study suggests that Rock-Eval 6 pyrolysis can be considered as a relevant tool for tracking FOC in modern environments. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Geomorphic changes in a complex gully system measured from sequential digital elevation models, and implications for management

Harley D. Betts
Abstract High-resolution digital elevation models (DEMs) were derived from sequential aerial photography of an active ,uvio-mass movement (gully) complex in New Zealand's North Island East Coast region, to measure geomorphic changes over approximately one year. The gully showed a complex behaviour, combining ,uvial and mass movement erosion, deposition, and reworking of materials stored in an active debris fan. During the measurement period 5200 ± 1700 m3 of material were eroded from the 8·7 ha gully complex and 670 ± 180 m3 from the 0·8 ha depositional fan, giving a total of 5870 ± 1710 m3 for the entire gully complex,fan system. The results provide a high-resolution description of gully behaviour over a short time period, and also demonstrate that mass movement (slumping and debris ,ows) accounted for almost 90 per cent (4660 ± 200 m3) of the sediment generated. This erosional response is described in terms of gully evolution by comparing the gully complex to other systems in the region in various stages of development. The effect of gully evolution on geomorphic coupling between the gully complex and channel system is described, and coupling is also shown to vary with the magnitude and frequency of rainfall events. From a land management perspective the success of strategies, such as tree planting, to mitigate against gully erosion depends on the stage of gully development , particularly on whether or not mass movement erosion has begun. In contrast to gully rehabilitation efforts elsewhere, basin-wide afforestation in the early stages of gully incision is favoured over riparian planting, given that mass movement assisted by excessive groundwater pressure is the main process leading to uncontrollable gully expansion. To protect land effectively against continuing gully erosion of headwater catchments and resulting downstream aggradation, it is necessary for land managers to understand the spatial and temporal variability of gully development fully so that mitigation efforts can be targeted appropriately. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Sediment production in large gullies of the Mediterranean area (NE Spain) from high-resolution digital elevation models and geographical information systems analysis

J. A. Martínez-Casasnovas
Abstract Recent studies in the Mediterranean area have shown gully erosion to have a very significant contribution to total soil loss. In the Penedès vineyard region (NE Spain), between 15 and 27% of the land is affected by large gullies and gully-wall retreat seems to be an ongoing process. Multi-date digital elevation model (DEM) analysis has allowed computation of sediment production by gully erosion, showing that the sediment production rates are very high by the, up-to-date, usual global standards. Here, we present a study carried out using large-scale multi-date (1975 and 1995) aerial photographs (1 : 5000 and 1 : 7000) to monitor sediment yield caused by large gullies in the Penedès region (NE Spain). High-resolution DEMs (1 m grid) were derived and analysed by means of geographical information systems techniques to determine the gully erosion rates. Rainfall characteristics within the same study period were also analysed in order to correlate with the soil loss produced. Mass movement was the main process contributing to total sediment production. This process could have been favoured by rainfalls recorded during the period: 58% of the events were of an erosive character and showed high kinetic energy and erosivity. A sediment production rate of 846 ± 40 Mg ha,1 year,1, a sediment deposition rate of 270 ± 18 Mg ha,1 year,1 and a sediment delivery ratio of 68·1% were computed for a gully area of 0·10 km2. The average net erosion within the study period (1975,95) was 576 ± 58 Mg ha,1 year,1. In comparison with other methods, the proposed method also includes sediment produced by processes other than only overland flow, i.e. downcutting, headcutting, and mass movements and bank erosion. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A simple validated GIS expert system to map relative soil vulnerability and patterns of erosion during the muddy floods of 2000,2001 on the South Downs, Sussex, UK

H. Faulkner
Abstract The soils of the South Downs in East Sussex, England (UK), are dominated by loessic silt (>70 per cent) and are prone to crusting. Continuing erosion of these soils means that they are thin, typically less than 25,cm thick and are becoming stonier, more droughty and less easier to work. Rates of erosion are relatively low but during extreme events, soils are vulnerable and on- and off-site erosion is a current and long-term risk. Property damage due to muddy flooding is of particular concern. Due to a long history of research interest, a rich database exists on the erosional history of an area of approximately 75,km2 of these thin, calcareous South Downs soils. In particular, during the winter of 2000,2001, Hortonian overland flow was common on certain crop types. Consequent sheet, rill and gully erosion was intense. The gullies and rills formed by runoff during these winter events were mapped in detail. In this paper, a method to estimate soil vulnerability to erosion is described and illustrated. Then, to validate the predictive efficacy of the algorithm used, the actual mapped distribution of rills and gullies following the winter events of 2001 on a particularly badly-affected site are compared with predictions from our soil erosion vulnerability model. Methods for adjusting the land-cover weightings to optimise the map fit are outlined. In a further survey of the utility of the map, it was discovered that farmers' recollections of events provided additional verification. Thus, one implication of our research is that erosion models can be validated by inviting farmers to comment on their efficacy to predict known histories. Copyright © 2010 John Wiley & Sons, Ltd. [source]

Conservation of gullies in susceptible riparian areas of alluvial soil regions

R. C. Yadav
Abstract The problem of gully erosion is very severe in the riparian areas of the alluvial deep soil region in India. Research and development have progressed in response to the change in social needs. The earlier strategy of maintenance of law and order has changed to one of reclamation and restoration of the productive capacity of riparian areas. Watershed management in the ravines has been adopted for development of food security, eco-restoration and pollution control. Case studies on the watershed management in watersheds projects initiated in the mid-1980s revealed the scope for bringing increased prosperity through crop diversification and eco-restoration. In consideration of the erosion process, new concepts of management zones and improved conservation and reclamation practices have been developed. The sociological factors have been rationally analysed, as they applied to watershed management in the ravines. A new paradigm of watershed management by group action is necessary in the future. Since the ways of combating the ravine problem and enhancing the productivity of ravine-degraded lands were made on rational process-based approach, there is scope for it to be implemented in other countries with similar land and socio-economic situations. Copyright © 2002 John Wiley & Sons, Ltd. [source]