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1.
Landform evolution models are powerful tools for determining long-term erosional stability and denudation rates spanning geological timescales. SIBERIA, CAESAR and CHILD are examples of these model. The newly developed State Space Soil Production and Assessment Model (SSSPAM) coupled soilscape-landform evolution model has the ability to assess overall erosion rates of catchment scale landforms either using short-term precipitation events, variable precipitation or time-averaged precipitation (annual average). In addition, SSSPAM has the capability of developing the subsurface soil profile through weathering and armouring. In SSSPAM, physical processes of pedogenesis such as erosion and armouring, diffusion, sediment deposition and weathering are modelled using a state space matrix approach. In this article we simulate the short-term evolution (100 years) of a proposed post-mining landform using both SIBERIA and SSSPAM and compare the erosion and sediment output results. For the short-term simulations SSSPAM's armouring capability was disabled. The models were then used to simulate the evolution of the catchment for 10,000 years. Results demonstrate that the short-term SSSPAM simulation results compare well with the results from the established landform evolution model SIBERIA. The long-term armouring disabled SSSPAM simulations produces simulated erosion rates comparable with SIBERIA simulations both of which are similar to upper limit of field measured denudation rates. The SSSPAM simulation using armouring demonstrated that armouring reduced the erosion rate of the catchment by a factor of 4 which is comparable with the lower limit of field measured denudation rates. This observation emphasizes the importance of armouring in long-term evolution of landforms. Soil profile cross-sections developed from the same results show that SSSPAM can also reproduce subsurface soil evolution and stratification and spatial variability of soil profile characteristics typically observed in the field.  相似文献   

2.
Sediment flux dynamics in fluvial systems have often been related to changes in external drivers of topography, climate or land cover. It is well known that these dynamics are non‐linear. Recently, model simulations of fluvial activity and landscape evolution have suggested that self‐organization in landscapes can also cause internal complexity in the sedimentary record. In this contribution one particular case of self‐organization is explored in the Sabinal field study area, Spain, where several dynamic zones of sedimentation and incision are observed along the current river bed. Whether these zones can be caused by internal complexity was tested with landscape evolution model (LEM) LAPSUS (Landscape Process Modelling at Multi‐dimensions and Scales). During various 500 year simulations, zones of sedimentation appear to move upstream and downstream in eroding river channels (‘waves’). These waves are visualized and characterized for a range of model settings under constant external forcing, and the self‐organizing process behind their occurrence is analysed. Results indicate that this process is not necessarily related to simplifications in the model and is more generic than the process of bed‐armouring that has recently been recognized as a cause for complexity in LEM simulations. We conclude that autogenic sediment waves are the result of the spatial propagation in time of feedbacks in local transport limited (deposition) and detachment limited (erosion) conditions. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

3.
The development and evolution of gullies on soil-mantled hillslopes can devastate agricultural regions and cause widespread soil and landscape degradation. Since 2000, international symposia have been organized to address gully erosion processes, and this paper and special issue provide additional context for the 7th International Symposium on Gully Erosion held at Purdue University in 2016. Several important themes of gully erosion emerged during this symposium that warranted additional discussion here. These topics include the importance and impact of technology transfer, disciplinary fragmentation as an impediment for research advancement, the difficulty in defining the erodibility of sediment within gullies, and the opportunities afforded by remote sensing technology. It is envisioned that such symposia will continue to enhance the capabilities of researchers and practitioners to monitor, model, and manage these important geomorphic processes and to mitigate landscape degradation. © 2018 John Wiley & Sons, Ltd.  相似文献   

4.
Incised coastal gullies (ICGs) are dynamic features found at the terrestrial‐coastal interface. Their geomorphic evolution is driven by the interactions between processes of fluvial knickpoint migration and coastal cliff erosion. Under scenarios of future climate change the frequency and magnitude of the climatological drivers of both terrestrial (fluvial and hillslope) and coastal (cliff erosion) processes are likely to change, with an adjunct impact on these types of coastal features. Here we explore the response of an incised coastal gully to changes in both terrestrial and coastal climate in order to elucidate the key process interactions which drive ICG evolution. We modify an extant landscape evolution model, CHILD, to incorporate processes of soft‐cliff erosion. This modified version, termed the Coastal‐Terrestrial‐CHILD (CT‐CHILD) model, is then employed to explore the interactions between changing terrestrial and coastal driving forces on the future evolution of an ICG found on the south‐west Isle of Wight, UK. It was found that the magnitude and frequency of storm events will play a key role in determining the future trajectory of ICGs, highlighting a need to understand the role of event sequencing in future projections of landscape evolution. Furthermore, synergistic (positive) and antagonistic (negative) interactions were identified between coastal and terrestrial parameters, such as wave height intensity and precipitation duration, which act to modulate the impact of changes in any one parameter. Of note was the role played by wave height intensity in driving coastal erosion, which was found to play a more important role than sea‐level rise in determining rates of coastal erosion. This highlights the need for a greater focus on wave height in studies of soft‐cliff erosion. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

5.
Drainage network extension in semi‐arid rangelands has contributed to a large increase in the amount of fine sediment delivered to the coastal lagoon of the Great Barrier Reef, but gully erosion rates and dynamics are poorly understood. This study monitored annual erosion, deposition and vegetation cover in six gullies for 13 years, in granite‐derived soils of the tropical Burdekin River basin. We also monitored a further 11 gullies in three nearby catchments for 4 years to investigate the effects of grazing intensity. Under livestock grazing, the long‐term fine sediment yield from the planform area of gullies was 6.1 t ha‐1 yr‐1. This was 7.3 times the catchment sediment yield, indicating that gullies were erosion hotspots within the catchment. It was estimated that gully erosion supplied between 29 and 44% of catchment sediment yield from 4.5% of catchment area, of which 85% was derived from gully wall erosion. Under long‐term livestock exclusion gully sediment yields were 77% lower than those of grazed gullies due to smaller gully extent, and lower erosion rates especially on gully walls. Gully wall erosion will continue to be a major landscape sediment source that is sensitive to grazing pressure, long after gully length and depth have stabilised. Wall erosion was generally lower at higher levels of wall vegetation cover, suggesting that yield could be reduced by increasing cover. Annual variations in gully head erosion and net sediment yield were strongly dependent on annual rainfall and runoff, suggesting that sediment yield would also be reduced if surface runoff could be reduced. Deposition occurred in the downstream valley segments of most gullies. This study concludes that reducing livestock grazing pressure within and around gullies in hillslope drainage lines is a primary method of gully erosion control, which could deliver substantial reductions in sediment yield. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

6.
Despite growing interest in soil erosion on agricultural land, relatively little attention has been paid to the influence of erosion processes on the pattern of contemporary landform evolution. This in part reflects the problems associated with up-scaling the results of short-term process studies to temporal and spatial scales relevant to the study of landform evolution. This paper presents a new approach to examining the influence of erosion processes on landform evolution on agricultural land which employs: caesium-137 (137Cs) measurements to provide medium-term (c. 40 years) estimates of rates of landform change; experimental data and a topographic-based model to simulate soil redistribution by tillage; a mass-balance model of 137Cs redistribution to separate the water erosion and tillage components of the 137Cs ‘signatures’; and field observations of water erosion for validation. This approach is used to examine the relative importance of water erosion and tillage processes for contemporary landform evolution at contrasting sites near Leuven, in Belgium, and near Yanan, in Shaanxi Province, China. This application of the approach provides good agreement between the derived water erosion rates and field observations, and hitherto unobtainable insights into medium-term patterns and rates of contemporary landform evolution. At Huldenberg in Belgium, despite rill incision of slope concavities and ephemeral gully incision of the valley floor, contemporary landform evolution is dominated by infilling of slope and valley concavities (rates >0.5 mm a−1) and gradual lowering of slope angles as a result of tillage. In contrast, at Ansai (near Yanan) the slope is characterized by increase in slope angle over most of the length, recession of the steepest section at a rate >5 mm a−1 and by increasing planform curvature. At this site, contemporary landform evolution is dominated by water erosion. The constraints on the approach are examined, with particular attention being given to limitations on extrapolation of the results and to the sensitivity of the models to parameter variation. © 1997 by John Wiley & Sons, Ltd.  相似文献   

7.
Loess gullies are the most active and changeable landform unit on the Loess Plateau of China. Under the influence of inhomogeneous internal and external forces, various gully morphologies have been identified as specific forms of asymmetrical loess gullies in the northeastern Loess Plateau. Thus, the formation mechanisms of asymmetrical gullies should be examined to better understand the gully evolution processes in this area. In this study, a typical asymmetrical gully area and its geological background in the northeastern Loess Plateau are investigated. Then, the asymmetrical gullies are extracted and ordered under different watershed hierarchies using 5 m horizontal resolution digital elevation models. The asymmetrical gullies are characterized using the gully deviation index and gully asymmetrical coefficient to quantitatively and qualitatively describe the gully formation from the perspective of gully morphology. Subsequently, environmental factors, such as the bedrock, climate, vegetation and interactions with neighbouring watersheds, are combined to achieve an in-depth understanding of the mechanisms of asymmetrical gully formation. The results show that most watersheds shift to the right side of the watershed geometric centre line, thereby forming a specific asymmetrical gully morphology. The phenomenon in which the asymmetrical degree characteristics decrease with the increase in drainage area suggests evident morphological differences on both sides of the main channel on a small scale, and relatively weak morphological differences on both sides of the main channel on a large scale. The degree of loess gully asymmetry appears higher in the area where only the windward slope is covered by loess than in areas where all slopes are covered by loess. The interaction between adjacent watersheds also influences the formation of asymmetrical gullies. These results support the understanding of asymmetrical gully formation in relation to the underlying bedrock structure and gully reorganization, thereby contributing to the development of process-based gully evolution models.  相似文献   

8.
Process dynamics in fluvial‐based dryland environments are highly complex with fluvial, aeolian, and alluvial processes all contributing to landscape change. When anthropogenic activities such as dam‐building affect fluvial processes, the complexity in local response can be further increased by flood‐ and sediment‐limiting flows. Understanding these complexities is key to predicting landscape behavior in drylands and has important scientific and management implications, including for studies related to paleoclimatology, landscape ecology evolution, and archaeological site context and preservation. Here we use multi‐temporal LiDAR surveys, local weather data, and geomorphological observations to identify trends in site change throughout the 446‐km‐long semi‐arid Colorado River corridor in Grand Canyon, Arizona, USA, where archaeological site degradation related to the effects of upstream dam operation is a concern. Using several site case studies, we show the range of landscape responses that might be expected from concomitant occurrence of dam‐controlled fluvial sand bar deposition, aeolian sand transport, and rainfall‐induced erosion. Empirical rainfall‐erosion threshold analyses coupled with a numerical rainfall–runoff–soil erosion model indicate that infiltration‐excess overland flow and gullying govern large‐scale (centimeter‐ to decimeter‐scale) landscape changes, but that aeolian deposition can in some cases mitigate gully erosion. Whereas threshold analyses identify the normalized rainfall intensity (defined as the ratio of rainfall intensity to hydraulic conductivity) as the primary factor governing hydrologic‐driven erosion, assessment of false positives and false negatives in the dataset highlight topographic slope as the next most important parameter governing site response. Analysis of 4+ years of high resolution (four‐minute) weather data and 75+ years of low resolution (daily) climate records indicates that dryland erosion is dependent on short‐term, storm‐driven rainfall intensity rather than cumulative rainfall, and that erosion can occur outside of wet seasons and even wet years. These results can apply to other similar semi‐arid landscapes where process complexity may not be fully understood. Published 2015. This article is a U.S. Government work and is in the public domain in the USA  相似文献   

9.
Landscape evolution models provide a way to determine erosion rates and landscape stability over times scales from tens to thousands of years. The SIBERIA and CAESAR landscape evolution models both have the capability to simulate catchment–wide erosion and deposition over these time scales. They are both cellular, operate over a digital elevation model of the landscape, and represent fluvial and slope processes. However, they were initially developed to solve research questions at different time and space scales and subsequently the perspective, detail and process representation vary considerably between the models. Notably, CAESAR simulates individual events with a greater emphasis on fluvial processes whereas SIBERIA averages erosion rates across annual time scales. This paper describes how both models are applied to Tin Camp Creek, Northern Territory, Australia, where soil erosion rates have been closely monitored over the last 10 years. Results simulating 10 000 years of erosion are similar, yet also pick up subtle differences that indicate the relative strengths and weaknesses of the two models. The results from both the SIBERIA and CAESAR models compare well with independent field data determined for the site over different time scales. Representative hillslope cross‐sections are very similar between the models. Geomorphologically there was little difference between the modelled catchments after 1000 years but significant differences were revealed at longer simulation times. Importantly, both models show that they are sensitive to input parameters and that hydrology and erosion parameter derivation has long‐term implications for sediment transport prediction. Therefore selection of input parameters is critical. This study also provides a good example of how different models may be better suited to different applications or research questions. Copyright © 2010 John Wiley & Sons, Ltd and Commonwealth of Australia  相似文献   

10.
Landscapes respond in complex ways to external drivers such as base level change due to damming events. In this study, landscape evolution modelling was used to understand and analyse long‐term catchment response to lava damming events. PalaeoDEM reconstruction of a small Turkish catchment (45 km2) that endured multiple lava damming events in the past 300 ka, was used to derive long‐term net erosion rates. These erosion rates were used for parameter calibration and led to a best fit parameter set. This optimal parameter set was used to compare net erosion landscape time series of four scenarios: (i) no uplift and no damming events; (ii) no uplift and three damming events; (iii) uplift and no damming events; and (iv) uplift and three damming events. Spatial evolution of net erosion and sediment storage of scenario (iii) and (iv) were compared. Simulation results demonstrate net erosion differences after 250 000 years between scenarios with and without dams. Initially, trunk gullies show less net erosion in the scenario with damming events compared with the scenario without damming events. This effect of dampened erosion migrates upstream to smaller gullies and local slopes. Finally, an intrinsic incision pulse in the dam scenario results in a higher net erosion of trunk gullies while decoupled local slopes are still responding to the pre‐incision landscape conditions. Sediment storage differences also occur on a 100 ka scale. These differences behaved in a complex manner owing to different timings of the migration of erosion and sediment waves along the gullies for each scenario. Although the specific spatial and temporal sequence of erosion and deposition events is sensitive to local parameters, this model study shows the manner in which past short‐lived events like lava dams have long‐lasting effects on catchment evolution. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

11.
Balkas (large Quaternary gullies) of the south‐western part of the East European Plain (and their analogues in Central and Western Europe) are considered in terms of their geomorphology, lithology, sedimentology, modern surface processes, stratigraphy and palaeogeography. Features attributed to balkas in comparison with regular gullies and small river valleys are described. Balkas are widespread elements of the modern landscape with the same characteristic gentle‐concave bottom as regular gullies, and with or without weakly incised river channels. Buried gully incisions of different ages (post‐Gelasian) with the same shape are also revealed below modern Balkas. They are infilled by characteristic balka alluvial, slope and even lacustrine‐bog deposits, in places representing compound sequences of fluvial‐aeolian sedimentation. The fluvial part reflects multiple series of ephemeral episodes of increased water and sediment supply within temporary streams. Two conspicuous series supposedly fall within the final stages of the Dnieper (late Middle Pleistocene) and Valdai (Late Pleistocene) glaciations. Different ideas concerning the increase of surface runoff and erodibility of soils that might favour active balkas under conditions of land‐ice decay and permafrost, including its degradation, are discussed. The development of balkas included relatively short phases of incision and accumulation interrupted by much longer periods of inactivity, when they were subjected to surface processes in a subaerial environment or left as a relic. However, during active phases they served as important and powerful depositories and arteries of rill–gully–balka sedimentation systems, collecting and transmitting eroded material to the river valleys. These phases are related to climatic oscillations and were to some degree independent of fluvial processes affecting the permanent streams. Most of the Middle‐Late Pleistocene balkas retained their primary features, having subsequently been incorporated into the erosional network. In contrast, some of them were totally infilled and disappeared from the landscape. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

12.
Two gullies located in the Protva River basin （central part of European Russia, 100 Ion southwest of Moscow） were studied to investigate the history of their development during Late Holocene. This case study included detailed topographic and geomorphologic surveys, geological cross-sections, and radiocarbon dating of organic matter in gully sediments. For both gullies, incision of the long profile occurred for most of the Holocene, as indicated by the limited presence of infill sediment. However, interruptions of incisions occurred in both gullies during the last -3.5 ka （the Chugunkin gully） or -2.0 ka （the Uzkiy gully）, as evident from stratigraphic interpretation of the sediment record. Periods of surface stabilization are represented by buried soil horizons, whereas relatively thick sediment layers suggest periods of predominant aggradation. Similarities and differences in discovered sequences of erosion and accumulation stages for the two gullies point out the importance of distinguishing between local and regional controls. Evidence of the role of internal system behavior and self-development in the gully long-term evolution is clear from asynchronous response of different parts of gullies. In recent times （-500 years）, active agricultural development of the study territory resulted in accelerated incisions, followed by deposition of catchment-derived material. The latter was limited to the upper parts of the gullies, while incisions have continued in the middle and lower parts. The impact of human activities （-500 years） has been very limited. This suggests that within the forest zone of the Russian Plain many gullies which were earlier attributed to anthropogenic factors are, in realitv, due to natural phenomena.  相似文献   

13.
Hydrogeomorphic processes influencing alluvial gully erosion were evaluated at multiple spatial and temporal scales across the Mitchell River fluvial megafan in tropical Queensland, Australia. Longitudinal changes in floodplain inundation were quantified using river gauge data, local stage recorders and HEC‐RAS modelling based on LiDAR topographic data. Intra‐ and interannual gully scarp retreat rates were measured using daily time‐lapse photographs and annual GPS surveys. Erosion was analysed in response to different water sources and associated erosion processes across the floodplain perirheic zone, including direct rainfall, infiltration‐excess runoff, soil‐water seepage, river backwater and overbank flood inundation. The frequency of river flood inundation of alluvial gullies changed longitudinally according to river incision and confinement. Near the top of the megafan, flood water was contained within the macrochannel up to the 100‐year recurrence interval, but river backwater still partially inundated adjacent gullies eroding into Pleistocene alluvium. In downstream Holocene floodplains, inundation of alluvial gullies occurred beyond the 2‐ to 5‐year recurrence interval and contributed significantly to total annual erosion. However, most gully scarp retreat at all sites was driven by direct rainfall and infiltration‐excess runoff, with the 24‐h rainfall total being the most predictive variable. The remaining variability can be explained by seasonal vegetative conditions, complex cycles of soil wetting and drying, tension crack development, near‐surface pore‐water pressure, soil block undermining from spalling and overland flow, and soil property heterogeneity. Implications for grazing management impacts on soil surface and perennial grass conditions include effects on direct rainfall erosion, water infiltration, runoff volume, water concentration along tracks, and the resistance of highly dispersible soils to gully initiation or propagation under intense tropical rainfall. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

14.
Large (>0.1 km2) gully–mass movement complexes (badass gullies) are significant contributors to the sediment cascade in New Zealand's steepland East Coast Region catchments. The scale of change taking place in these gully systems allows significant evolution in morphology and sediment dynamics to be tracked at annual to decadal timescales. Here we document changes in two adjacent badass gullies in Waipaoa catchment (Tarndale and Mangatu) to infer sediment generation processes and connectivity using a morphological budgeting approach. A baseline dataset for this study is provided by a LiDAR-derived digital elevation model (DEM) in 2005. We produced new DEMs and orthophoto mosaics using photogrammetry in 2017, 2018, and 2019 to quantify gully morphodynamics and associated volumes of sediment erosion and deposition in both systems as they co-evolved. Results indicate ongoing rapid development of both gully complexes. Severe erosion took place at the gully heads with lowering and migration (up to 25 m vertically and laterally) of the topographic divide separating the two gullies between 2005 and 2019. Over the same period, net lowering of each gully system was ~250 mm year−1. Key sediment-generating processes included surface erosion, deep-seated landslides, and debris flows. Longer term, the overall contribution of sediment from both badass gullies to the Waipaoa catchment has been declining. In the mid-20th century, both gullies yielded in excess of 300 kt year−1. From 2005 to 2019, 80 kt year−1 was yielded from Tarndale and 110 kt year−1 from Mangatu. Our most recent surveys demonstrated considerable variability in sediment yield, ranging from 76 kt year−1 (2017–2018) to 291 kt year−1 (2018–2019). The annual variability observed reflects the complex morphodynamics of discrete hillslopes and tributary fans in these badass gully systems and underlines the importance of integrating decadal and annual surveys when assessing system trajectory. © 2020 John Wiley & Sons, Ltd.  相似文献   

15.
Soil erosion processes have been studied intensively throughout the last decades and rates have been measured at the plot scale as well as at larger scales. However, the relevance of this knowledge for the modelling of long-term landscape evolution remains a topic of considerable debate. Some authors state that measurements of current rates are irrelevant to landscape evolution over a longer time span, as they are inconsistent with some fundamental characteristics of landscapes, such as the fact that the long-term sediment delivery ratio needs to be equal to 1 and that extrapolation of current rates would imply that all soils in Europe should have disappeared by now (e.g. Parsons, A.J., Wainwright, J., Brazier, R.E., Powell, D.M., 2006. Is sediment delivery a fallacy? Earth Surface Processes and Landforms 31, 1325–1328). In this study, we investigate if and to what extent estimates of long-term erosion rates are consistent with information obtained over much shorter time spans for the Loam Belt of Belgium.In a first step, observed short-term and long-term patterns in the Belgian loess area are compared statistically by classifying the study area into landscape element classes and comparing average erosion values per class. This analysis shows that the erosion intensities on the two temporal scales are of the same order of magnitude for each landscape element class. Next, the spatially distributed model WaTEM LT (Water and Tillage Erosion Model Long Term) is calibrated based on the available short-term data by optimising average erosion values for the same landscape element classes. Finally, the calibrated model is used to simulate long-term landform evolution, and is validated using long-term data based on soil profile truncation. We found that the model allows simulating landscape evolution on a millennial time scale using information derived from short-term erosion and deposition data. However, it is important that land use is taken into account for the calibration in order to obtain realistic patterns on a longer time scale. Our analysis shows that, at least for the study area considered, data obtained on erosion and deposition rates over various temporal scales have the same orders of magnitude, thereby demonstrating that measurements of current rates of processes can be highly relevant for interpreting long-term landscape evolution.  相似文献   

16.
This paper reviews the role of alluvial soils in vegetated gravelly river braid plains. When considering decadal timescales of river evolution, we argue that it becomes vital to consider soil development as an emergent property of the developing ecosystem. Soil processes have been relatively overlooked in accounts of the interactions between braided river processes and vegetation, although soils have been observed on vegetated fluvial landforms. We hypothesize that soil development plays a major role in the transition (speed and pathway) from a fresh sediment deposit to a vegetated soil‐covered landform. Disturbance (erosion and/or deposition), vertical sediment structure (process history), vegetation succession, biological activity and water table fluctuation are seen as the main controls on early alluvial soil evolution. Erosion and deposition processes may not only act as soil disturbing agents, but also as suppliers of ecosystem resources, because of their role in delivering and changing access (e.g. through avulsion) to fluxes of water, fine sediments and organic matter. In turn, the associated initial ecosystem may influence further fluvial landform development, such as through the trapping of fine‐grained sediments (e.g. sand) by the engineering action of vegetation and the deposit stabilization by the developing aboveground and belowground biomass. This may create a strong feedback between geomorphological processes, vegetation succession and soil evolution which we summarize in a conceptual model. We illustrate this model by an example from the Allondon River (Switzerland) and identify the research questions that follow. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

17.
Landscape evolution models (LEMs) quantitatively simulate processes of sedimentation and erosion on millennial timescales. An important aspect of human impact on erosion is sediment redistribution due to agriculture, referred to herein as tillage erosion. In this study we aim to analyse the potential contribution of tillage erosion to landscape development using LEM LAPSUS. The model is calibrated separately for a water erosion process (i) without tillage and (ii) with tillage. The model is applied to the ~250 km2 Torrealvilla case study catchment, SE Spain. We were able to simulate alternating sequences of incision and aggradation, that are important on longer (millennial) timescales. Generally, model results show that tillage erosion adds to deposition in the lower floodplain area, but neither water erosion alone nor water with tillage erosion together could exactly reproduce the observed amounts of erosion and sedimentation for the case study area. In addition, scale effects are apparent. On hillslopes, tillage may contribute importantly to erosion and may fill local depressions. If assessed on the catchment scale, sediments from tillage erosion eventually reach the lower floodplain area where they contribute to deposition. However, water erosion was observed in the model simulations to be the most important process on the catchment scale. This is the first time that tillage erosion has been explicitly included in a landscape evolution model at a millennial timescale and large catchment scale. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

18.
Gully erosion of cultural sites in Grand Canyon National Park is an urgent management problem that has intensified in recent decades, potentially related to the effects of Glen Canyon Dam. We studied 25 gullies at nine sites in Grand Canyon over the 2002 monsoon–erosion season to better understand the geomorphology of the gully erosion and the effectiveness of erosion‐control structures (ECS) installed by the park under the direction of the Zuni Conservation Program. Field results indicate that Hortonian overland flow leads to concentrated flow in gullies and erosion focused at knickpoints along channels as well as at gully heads. Though groundcover type, soil shear strength and permeability vary systemat‐ically across catchments, gradient and, to a lesser degree, contributing drainage area seem to be the first‐order controls on gully extent, location of new knickpoints, and ECS damage. The installed ECS do reduce erosion relative to reaches without them and initial data suggest woody checkdams are preferable to rock linings, but maintenance is essential because damaged structures can exacerbate erosion. Topographic data from intensive field surveys and detailed photogrammetry provide slope–contributing area data for gully heads that have a trend consistent with previous empirical and theoretical formulations from a variety of landscapes. The same scaling holds below gully heads for knickpoint and ECS topographic data, with threshold coefficients the lowest for gully heads, slightly higher for knickpoints, and notably higher for damaged ECS. These topographic thresholds were used with 10‐cm digital elevation models to create simple predictive models for gully extent and structure damage. The model predictions accounted for the observed gullies but there are also many false‐positives. Purely topographical models are probably inadequate at this scale and application, but models that also parameterize the variable soil properties across sites would be useful for predicting erosion problems and ECS failure. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

19.
Severe soil erosion occurs on the Loess Plateau in China, which makes the Yellow River the most sediment-laden river in the world. Construction of about 60,000 sediment check dams has remarkably controlled soil erosion on the Loess Plateau and reduced the sediment load of the middle and lower Yellow River. Nonetheless, little is known about the mechanism of erosion control and vegetation development of sediment check dams. The function of a single check dam mainly is trapping sediment, while the function of a train of check dams comprising dozens of or over hundreds of check dams in a gully encompasses controlling bed incision and reducing erosion energy. A formula was proposed to calculate the potential energy of bank failure and slope failure in a gully, which essentially constitutes the erosion energy. The erosion energy increases when gully incision occurs, which is induced by the incision of the Yellow River and its tributaries on the Loess Plateau. Sediment deposition in many gullies due to construction of check dams reduces the erosion energy to almost zero, which in turn greatly reduces soil erosion and sediment yield. Construction of check dams promotes vegetation development. The vegetation-erosion dynamics model was used to study the effect of check dams on vegetation development. Simulation results show that reforestation without check dam construction might result in an increase of vegetation cover in the first ten years and then a drop of vegetation cover to less than 10% in the later years. The check dams provide a foundation for vegetation development.  相似文献   

20.
Gully erosion is a major environmental threat on the Moldavian Plateau (MP) of eastern Romania. The permanent gully systems consist of two main gully types. These are: (1) discontinuous gullies, which are mostly located on hillslopes and (2) large continuous gullies in valley bottoms. Very few studies have investigated the evolution of continuous gullies over the medium to longer term. The main objective of this study was to quantitatively analyse the development of continuous gullies over six decades (1961–2020). The article aimed at predicting temporal patterns of gully head erosion based on field data from multiple gullies. Fourteen representative continuous gullies were selected near the town of Barlad, most of them having catchment areas < 500 ha. Linear gully head retreat (LGHR) and areal gully growth (AGG) rates were quantified for six decades. Two main periods were distinguished and compared (i.e., the wet 1961–1980 period and the drier 1981–2020 period). Results indicate that gully erosion rates have significantly decreased since 1981. The mean LGHR of 7.7 m yr−1 over 60 years was accompanied by a mean AGG of 213 m2 yr−1. However, erosion rates between 1961 and 1980 were 4.0 times larger for LGHR and 5.9 times more for AGG compared to those for 1981–2020. Two regression models indicate that annual precipitation depth (P) is the primary controlling factor, explaining 57% of LGHR and 53% of AGG rate. The contributing area (CA) follows, with ~33%. Only 43% of total change in LGHR and 46% of total change in AGG results from rainfall-induced runoff during the warm season. Accordingly, the cold season (with associated freeze–thaw processes and snowmelt runoff) has more impact on gully development. The runoff pattern, when flow enters the trunk gully head, is largely controlled by the upper approaching discontinuous gully.  相似文献   

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