首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
ROCESSES OF EPHEMERAL GULLY EROSION   总被引：2，自引：0，他引：2  
IINTRoDUCTIONEphemeralgulliesaresmallerosionalchannelsonagriculturalIandscapescausedbytheconcentrationofoverlandflowtypicallybetweentwoopposingslopes(ahollow),oftenformedduringasingIerainfaIlevent.Sincethescouredsoilvolumeisnotverylargewithinthesegullies,farmerscaneasilyrefillthem.Ingeneral,ephemeralgulliescanreappearatornearthesamelocationonayearlybasisbecausethesurfacetopograPhyofthefielddoesnotchangeappreciably.Mostephemeralgulliesoccuroncultivatedfieldswithhighlyerodiblesoils,withlit…  相似文献   

2.
Concentrated flow erosion in Mediterranean cultivated areas is considered a major process of land degradation. Rills and ephemeral gullies in a 6.4 ha olive orchard catchment located in an intensive commercial farm, which could represent a common degradation scenario in hilly areas, were measured and compared with the sediment loads at the outlet. Four GPS survey campaigns were carried out between March 2009 and March 2014, for periods with cumulative precipitation ranging between 728 and 121 mm. Chopped pruning residues were kept on the lanes during campaigns 2–4, whereas a grass cover crop was seeded in campaign 4. Rainfall, runoff and sediment loads were measured in a flume gauge station at the catchment outlet. The ratio of concentrated flow erosion to catchment sediment load varied between 1.0 and 35.0. Total concentrated flow erosion ranged between 25.0 and 0.1 t ha−1. Rill erosion was the dominant process on ephemeral gullies for three campaigns, with a mean contribution to the total concentrated flow erosion of 55%. Rills clearly followed tractor tracks along the most parallel lanes to the maximum slope. Therefore, a change in traffic direction would be helpful to reduce the connectivity, controlled by the spatial distribution of rows and lanes in the farm. Olive plantation distributions should prioritize hydrological criteria to adapt traffic patterns in olive farms, as long as the tractor manoeuvrability and risk of overturning are not adversely affected. Although the farmer only kept the cover crop for one campaign, it proved to be an efficient measure for interrupting rills along the lanes, whereas pruning residues were effective for the control of interrill erosion. On-site application of pruning residues reduced their handling and transport costs, while increasing the soil fertility and soil cover. However, guidelines for the efficient application of pruning residues are still necessary in terms of residue rates and orientation.  相似文献   

3.
On hillslopes and agricultural fields, discrete areas of intense, localized soil erosion commonly take place in the form of migrating headcuts. These erosional features significantly increase soil loss and landscape degradation, yet the unsteady, transient, and migratory habits of headcuts complicate their phenomenological and erosional characterization. Here a unique experimental facility was constructed to examine actively migrating headcuts typical of upland concentrated flows. Essential components of the facility include a deep soil cavity with external drainage, rainfall simulator, capacity for overland flow, and a video recording technique for data collection. Results from these experiments show that： （1） after a short period of adjustment, headcut migration attained a steady-state condition, where the rate of migration, scour hole geometry, and sediment discharge remain constant with time; （2） boundary conditions of higher rates of overland flow, steeper bed slopes, and larger initial headcut heights produced systematically larger scour holes with higher rates of soil erosion; and （3） during migration, the turbulent flow structure within the scour hole remained unchanged, consisting of an overfall nappe at the brink transitioning into a reattached wall jet with two recirculation eddies within the plunge pool. The systematic behavior of headcut development and migration enabled the application of modified jet impingement theory to predict with good success the characteristics of the impinging jet, the depth of maximum scour, the rate of headcut migration, and the rate of sediment erosion. These laboratory data and the analytical formulation can be used in conjunction with soil erosion prediction technology to improve the management of agricultural areas impacted by headcut development and ephemeral gully erosion.  相似文献   

4.
Concentrated flow erosion is the dominant form of winter erosion in northern France. This study correlates the ephemeral rill and gully volumes measured in 20 cultivated catchments (4–95 ha) for three consecutive winters with the size of the potential runoff-contributing areas. These areas were identified by characterizing soil surface state through crust development stage, importance of surface wheel tracks and roughness grade. A single and significant relationship was found between the size of runoff-contributing areas, estimated by this criterion, and the rill and gully volumes. This identified the proportion of the catchment area occupied by fields with a degraded surface structure as the main factor controlling the variability of erosion in a context of concentrated flow erosion on cultivated land. The extension of degraded areas was shown to be controlled by dynamic interactions between weather, land occupation and soil physical properties. This criterion accounts for the uneven distribution of rainfall in space and time. Morphological factors, such as talweg length and slope, are believed to determine part of the residual variability.  相似文献   

5.
1 INTRODUCTION Erosion caused by ephemeral flows is a frequent phenomenon in nature and contributes to the shape of the landscape. This type of erosion may cause great soil losses in agricultural areas, which are quickly transferred to the watershed outlets through the rill and gully network (Bennett et al., 2000; Poesen et al., 2003). Concentrated flow erosion is controlled by the erodibility of surface materials, climate, soil use and management, and watershed topography. Several metho…  相似文献   

6.
Knowledge of soil loss rates by water erosion under given climate, soil, topography, and management conditions is important for establishing soil conservation schemes. In Galicia, a region with Atlantic climatic conditions in Spain, field observations over the last decade indicate that interrill, rill and ephemeral gully erosion may be an important sediment source. The aim of this work was to assess concentrated erosion rates, describe types of rills and ephemeral gullies and determine their origin, evolution and importance as sediment sources. Soil surface state and concentrated flow erosion were surveyed on medium textured soils, developed over basic schists of the Ordenes Complex series (Coruña province, Spain) from 1997 to 2006. Soil surface state was characterized by crust development, tillage features and roughness degree. Soil erosion rate was directly measured in the field. Concentrated flow erosion took place mainly on seedbeds and recently tilled surfaces in late spring and by autumn or early winter. During the study period, erosion rates were highly variable and the following situations could be distinguished: (a) no incision or limited rill incision, i.e. below 2 Mg ha?1 year?1; (b) generalized rill and ephemeral gully incision in the class of mean values between 2·5 and 6·25 Mg ha?1 year?1, this was the most common erosion pattern; and (c) heavy erosion as observed during an extremely wet winter period, between October 2000 and February 2001, with erosion figures that may be about ten orders of magnitude higher, up to 55–60 Mg ha?1 year?1. Therefore, low values of soil losses are dominant, but also large values of rill and ephemeral gully erosion occurred during the study period. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

7.
Few models can predict ephemeral gully erosion rates (e.g. CREAMS, EGEM). The Ephemeral Gully Erosion Model (EGEM) was specifically developed to predict soil loss by ephemeral gully erosion. Although EGEM claims to have a great potential in predicting soil losses by ephemeral gully erosion, it has never been thoroughly tested. The objective of this study was to evaluate the suitability of EGEM for predicting ephemeral gully erosion rates in Mediterranean environments. An EGEM‐input data set for 86 ephemeral gullies was collected: detailed measurements of 46 ephemeral gullies were made in intensively cultivated land in southeast Spain (Guadalentin study area) and another 40 ephemeral gullies were measured in both intensively cultivated land and abandoned land in southeast Portugal (Alentejo study area). Together with the assessment of all EGEM‐input parameters, the actual eroded volume for each ephemeral gully was also determined in the field. A very good relationship between predicted and measured ephemeral gully volumes was found (R2 = 0·88). But as ephemeral gully length is an EGEM input parameter, both predicted and measured ephemeral gully volumes have to be divided by this ephemeral gully length in order to test the predictive capability of EGEM. The resulting relationship between predicted and measured ephemeral gully cross‐sections is rather weak (R2 = 0·27). Therefore it can be concluded that EGEM is not capable of predicting ephemeral gully erosion for the given Mediterranean areas. A second conclusion is that ephemeral gully length is a key parameter in determining the ephemeral gully volume. Regression analysis shows that a very significant relation between ephemeral gully length and ephemeral gully volume exists (R2 = 0·91). Accurate prediction of ephemeral gully length is therefore crucial for assessing ephemeral gully erosion rates. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

8.
Vegetative filter strips (VFSs) can effectively trap sediment in overland flow, but little information is available on its performance in controlling high‐concentration sediment and the runoff hydraulics in VFS. Flume experiments were conducted to investigate the sediment deposition, hydraulics of overland flow and their relationships in simulating VFS under a great range of sediment concentrations with four levels of vegetation cover (bare slope and 4%, 11% and 17%) and two flow rates (15 and 30 L min?1). Sediment concentrations varied from 30 to 400 kg m?3 and slope gradient was 9°. Both the deposited sediment load and deposition efficiency in VFS increased as the vegetation cover increased. Sediment concentration had a positive effect on the deposited load but no effect on deposition efficiency. A lower flow rate corresponded to greater deposition efficiency but had little effect on deposited load. Flow velocities decreased as vegetation cover increased. Sediment concentration had a negative effect on the mean velocity but no effect on surface velocity. Hydraulic resistance increased as the vegetation cover and sediment concentration increased. Sediment deposition efficiency had a much more pronounced relationship with overland flow hydraulics compared with deposited load, especially with the mean flow velocity, and there was a power relationship between them. Flow regime also affected the sediment deposition efficiency, and the efficiency was much higher under subcritical than supercritical flow. The results will be useful for the design of VFS and the control of sediment flowing into rivers in areas with serious soil erosion. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

9.
Erosion caused by concentrated flows in agricultural areas is responsible for important soil losses, and rapid sediment transfer through the channel network. The main factors controlling concentrated flow erosion rates include the erodibility of soil materials, soil use and management, climate and watershed topography. In this paper, two topographic indices, closely related to mathematical expressions suggested by different authors, are used to characterize the influence of watershed topography on gully erosion. The AS1 index is defined as the product of the watershed area and the partial area‐weighted average slope. The AS2 index is similar to the AS1 but uses the swale slope as the weighting factor. Formally, AS2 is the product of the watershed area and the length‐weighted average swale slope. From studies made using different ephemeral gully erosion databases, it is shown that a high correlation consistently exists between the topographic indices and the volume of eroded soil. The resulting relationships are therefore useful to assess soil losses from gully erosion, to identify the most susceptible watersheds within large areas, and to compare the susceptibility to gully erosion among different catchments. This information is also important in studying the response of natural drainage network systems to different rainfall inputs. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

10.
Many studies attribute the effects of vegetation in reducing soil erosion rates to the effects of the above‐ground biomass. The effects of roots on topsoil resistance against concentrated flow erosion are much less studied. However, in a Mediterranean context, where the above‐ground biomass can temporarily disappear because of fire, drought or overgrazing, and when concentrated flow erosion occurs, roots can play an important role in controlling soil erosion rates. Unfortunately, information on Mediterranean plant characteristics, especially root characteristics, growing on semi‐natural lands, and knowledge of their suitability for gully erosion control is often lacking. A methodological framework to evaluate plant traits for this purpose is absent as well. This paper presents a methodology to assess the suitability of plants for rill and gully erosion control and its application to 25 plant species, representative for a semi‐arid Mediterranean landscape in southeast Spain. In this analysis determination of suitable plants for controlling concentrated flow erosion is based on a multi‐criteria analysis. First, four main criteria were determined, i.e. (1) the potential of plants to prevent incision by concentrated flow erosion, (2) the potential of plants to improve slope stability, (3) the resistance of plants to bending by water flow and (4) the ability of plants to trap sediments and organic debris. Then, an indicator or a combination of two indicators was used to assess the scores for the four criteria. In total, five indicators were selected, i.e. additional root cohesion, plant stiffness, stem density, the erosion‐reducing potential during concentrated flow and the sediment and organic debris obstruction potential. Both above‐ and below‐ground plant traits were taken into account and measured to assess the scores for the five indicators, i.e. stem density, sediment and organic debris obstruction potential, modulus of elasticity of the stems, moment of inertia of the stems, root density, root diameter distribution, root area ratio and root tensile strength. The scores for the indicators were represented on amoeba diagrams, indicating the beneficial and the weak plant traits, regarding to erosion control. The grasses Stipa tenacissima L. and Lygeum spartum L. and the shrub Salsola genistoides Juss. Ex Poir. amongst others, were selected as very suitable plant species for rill and gully erosion control. Stipa tenacissima can be used to re‐vegetate abandoned terraces as this species is adapted to drought and offers a good protection to concentrated flow erosion and shallow mass movements. Lygeum spartum can be used to vegetate concentrated flow zones or to obstruct sediment inflow to channels at gully outlets. Stipa tenacissima and Salsola genistoides can be used to stabilize steep south‐facing slopes. The methodology developed in this study can be applied to other plant species in areas suffering from rill and gully erosion. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

11.
In Mediterranean areas the dynamics of gully development act as an important indicator of desertification. However, little is known about the influence of climate and land‐use changes, and almost no field data exist to assess the sensitivity of a landscape to gully erosion. Two important components of gully erosion studies are the prediction of where gullies begin and where they end. To address some of these issues, topographical thresholds for gully initiation and sedimentation in six different Mediterranean study areas were established. Field measurements of local soil surface slope (S) and drainage‐basin area (A) at the point of initiation of ephemeral gullies in intensively cultivated fields (five datasets) and permanent gullies in rangelands (three datasets) were carried out. A negative power relationship of the form S = aA−b was fitted through all datasets, and defined as the mean topographical threshold for gullying in the respective area. Topographically controlled slopes of sedimentation at the gully bottom were also measured. Compared to theoretical relationships for channel initiation by overland flow, relatively low values for b are obtained, suggesting a dominance of overland flow and an influence of subsurface flow. The influence of landsliding at steeper slopes appeared from the flattening of the overall negative trend in the higher slope range (S > 0·30) of the integrated dataset. Comparing the threshold lines of our datasets to the average trend lines through data found in literature revealed that vegetation type and cover could better explain differences in topographical thresholds level than climatic conditions. In cultivated fields, soil structure and moisture conditions, as determined by the rainfall distribution, are critical factors influencing topographical thresholds rather than daily rainfall amounts of the gully‐initiating events. In rangelands, vegetation cover at the time of incision appears to be the most important factor differentiating between topographical thresholds, overruling the effect of average annual rainfall amounts. Soil texture and rock fragment cover contributed little to the explanation of the relative threshold levels. Differences in regression slopes (b) between the S–A relationships found in this study have been attributed to the soil characteristics in the different study areas, determining the relative importance of subsurface flow and Hortonian overland flow. Sedimentation slopes where both ephemeral and permanent gullies end were generally high because of the high rock fragment content of the transported sediment. A positive relationship was found between the rock fragment content at the apex of the sedimentation fan and the slope of the soil surface at this location. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

12.
The objective of this study is to explore in a critical way the potential of high-altitude (stereo) aerial photographs for the assessment of ephemeral gully erosion rates. On 28 May 1995, an intensive rainfall event (30 mm h−1 during 30 min, return period = 3 years) occurred in central Belgium. Ephemeral gullies formed within an area of 218 ha (study area 1) were mapped and measured both in the field and by high-altitude aerial photos taken at the same time. Comparison of these two methods shows that if only one of the two surveying techniques had been used, only 75 per cent of the total ephemeral gully length would have been detected, so that the combination of aerial and field data leads, in fact, to the best possible determination of total gully length within the selected area. A correction factor (C) is proposed, so that the results of an ephemeral gully erosion survey based on high-altitude (stereo) aerial photos can be adjusted for the undetected gullies. Next, a sequential series of high-altitude stereo aerial photographs, taken in six different years, was analysed in order to determine ephemeral gully erosion rates in three selected study areas (study areas 2, 3 and 4). Selection criteria were chosen so that these three areas were similar to study area 1 and representative for the cultivated areas in central Belgium where intense soil erosion regularly occurs. Ephemeral gullies were mapped and their total length was measured from the aerial photos. Using a mean gully cross-section of 0·2635 m2 (determined in study area 1), the average eroded volume is 1·89 m3 ha−1 in six months for study area 1, 0·86 m3 ha−1 in six months for area 2, 1·44 m3 ha−1 in six months for area 3, and 2·37 m3 ha−1 in six months for area 4. According to the correction factor (C), these mean ephemeral gully erosion volumes have to be increased by 44 per cent. The ephemeral gully erosion rates based on high-altitude stereo aerial photos, correspond well with the results of other surveys carried out in the Belgian loess belt. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

13.
Interrill erosion processes on gentle slopes are affected by mechanisms of raindrop impact, overland flow and their interaction. However, limited experimental work has been conducted to understand how important each of the mechanisms are and how they interact, in particular for peat soil. Laboratory simulation experiments were conducted on peat blocks under two slopes (2.5° and 7.5°) and three treatments: Rainfall, where rainfall with an intensity of 12 mm h?1 was simulated; Inflow, where upslope overland flow at a rate of 12 mm h?1 was applied; and Rainfall + Inflow which combined both Rainfall and Inflow. Overland flow, sediment loss and overland flow velocity data were collected and splash cups were used to measure the mass of sediment detached by raindrops. Raindrop impact was found to reduce overland flow by 10 to 13%, due to increased infiltration, and reduce erosion by 47% on average for both slope gradients. Raindrop impact also reduced flow velocity (80–92%) and increased roughness (72–78%). The interaction between rainfall and flow was found to significantly reduce sediment concentrations (73–85%). Slope gradient had only a minor effect on overland flow and sediment yield. Significantly higher flow velocities and sediment yields were observed under the Rainfall + Inflow treatment compared to the Rainfall treatment. On average, upslope inflow was found to increase erosion by 36%. These results indicate that overland flow and erosion processes on peat hillslopes are affected by upslope inflow. There was no significant relationship between interrill erosion and overland flow, whereas stream power had a strong relationship with erosion. These findings help improve our understanding of the importance of interrill erosion processes on peat. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

14.
Little attention has been paid to the role of sidewall processes in gully development. Simple estimates of linear incision/sidewall erosion ratios at two localities in New South Wales, Australia suggest that sidewall erosion is responsible for more than half the gully volume. Studies at three localities where overland flow and throughflow are limited to only one sidewall indicate that these processes are responsible for 10-30 per cent of gully volume. These observations have important implications for gully management.  相似文献   

15.
Physically based soil erosion simulation models require input parameters of soil detachment and sediment transport owing to the action and interactions of both raindrops and overland flow. A simple interrill soil water transport model is applied to a laboratory catchment to investigate the application of raindrop detachment and transport in interrill areas explicitly. A controlled laboratory rainfall simulation study with slope length simulation by flow addition was used to assess the raindrop detachment and transport of detached soil by overland flow in interrill areas. Artificial rainfall of moderate to high intensity was used to simulate intense rain storms. However, experiments were restricted to conditions where rilling and channelling did not occur and where overland flow covered most of the surface. A simple equation with a rainfall intensity term for raindrop detachment, and a simple sediment transport equation with unit discharge and a slope term were found to be applicable to the situation where clear water is added at the upper end of a small plot to simulate increased slope length. The proposed generic relationships can be used to predict raindrop detachment and the sediment transport capacity of interrill flow and can therefore contribute to the development of physically‐based erosion models. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

16.
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.  相似文献   

17.
The rangeland hydrology and erosion model (RHEM) is a new process‐based model developed by the USDA Agricultural Research Service. RHEM was initially developed for functionally intact rangelands where concentrated flow erosion is minimal and most soil loss occurs by rain splash and sheet flow erosion processes. Disturbance such as fire or woody plant encroachment can amplify overland flow erosion by increasing the likelihood of concentrated flow formation. In this study, we enhanced RHEM applications on disturbed rangelands by using a new approach for the prediction and parameterization of concentrated flow erosion. The new approach was conceptualized based on observations and results of experimental studies on rangelands disturbed by fire and/or by tree encroachment. The sediment detachment rate for concentrated flow was calculated using soil erodibility and hydraulic (flow width and stream power) parameters. Concentrated flow width was calculated based on flow discharge and slope using an equation developed specifically for disturbed rangelands. Soil detachment was assumed to begin with concentrated flow initiation. A dynamic erodibility concept was applied where concentrated flow erodibility was set to decrease exponentially during a run‐off event because of declining sediment availability. Erodibility was estimated using an empirical parameterization equation as a function of vegetation cover and surface soil texture. A dynamic partial differential sediment continuity equation was used to model the total detachment rate of concentrated flow and rain splash and sheet flow. The enhanced version of the model was evaluated against rainfall simulation data for three different sites that exhibit some degree of disturbance by fire and/or by tree encroachment. The coefficient of determination (R2) and Nash–Sutcliffe efficiency were 0.78 and 0.71, respectively, which indicates the capability of the model using the new approach for predicting soil loss on disturbed rangeland. By using the new concentrated flow modelling approach, the model was enhanced to be a practical tool that utilizes readily available vegetation and soil data for quantifying erosion and assessing erosion risk following rangeland disturbance. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

18.
Estimating overland flow erosion capacity using unit stream power   总被引：2，自引：0，他引：2  
Soil erosion caused by water flow is a complex problem. Both empirical and physically based approaches were used for the estimation of surface erosion rates. Their applications are mainly limited to experimental areas or laboratory studies. The maximum sediment concentration overland flow can carry is not considered in most of the existing surface erosion models. The lack of erosion capacity limitation may cause over estimations of sediment concentration. A correlation analysis is used in this study to determine significant factors that impact surface erosion capacity. The result shows that the unit stream power is the most dominant factor for overland flow erosion which is consistent with experimental data. A bounded regression formula is used to reflect the limits that sediment concentration cannot be less than zero nor greater than a maximum value. The coefficients used in the model are calibrated using published laboratory data. The computed results agree with laboratory data very well. A one dimensional overland flow diffusive wave model is used in conjunction with the developed soil erosion equation to simulate field experimental results. This study concludes that the non-linear regression method using unit stream power as the dominant factor performs well for estimating overland flow erosion capacity.  相似文献   

19.
G. V. Wilson 《水文研究》2013,27(14):2032-2040
The internal erosion of soil pipes can induce pipe collapses that affect soil erosion processes and landform evolution. The objective of this study was to determine the spatial distribution of pipe collapses in agricultural fields of Goodwin Creek watershed. Ground survey was carried out to detect pipe collapses, and the location, size and surface elevation was measured with differential GPS. A total of 143 of the 145 pipe collapses were found in cropland, and the density was approximately 0.58 collapses per hectare. The spatial distribution of pipe collapses was not uniform as pipe collapses were concentrated in the flat alluvial plains where the land use was dominated by cropland. One of the four parcels had 90% of the pipe collapses with a density of 7.7 collapses per hectare. The mean depth, area and volume of these pipe collapses were 0.12 m, 0.34 m2 and 0.02 m3, respectively, and all these properties exhibited a skewed distribution. The drainage area–slope gradient equation, which has been widely used for erosion phenomenon prediction, did not represent pipe collapses in this study as the coefficient of determination was <0.01. This is clear evidence that subsurface flow is not represented by surface topographic characteristics. The pipe collapses were found to intercept runoff, thereby reducing the slope length factor by 6% and the drainage area by 7%. Both of these factors can reduce the sheet and rill erosion; however, the increased subsurface flow could enhance ephemeral gully erosion. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

20.
Recent research has indicated the large spatial and temporal variation in soil erosion resistance against concentrated flow (SER). This study analyzes this variability in relation to rill and gully initiation locations on slopes and the downslope eroded volumes. The soil erodibility (Kc) and critical flow shear stress (τcr), were estimated from topsoil properties and correlated to eroded rill and gully volumes and their initiation points on slopes in the Belgian loess belt. Therefore, concentrated flow paths and topsoil properties were measured in their vicinity. The results show that rill and gully initiation points, and hence the lengths of concentrated flow paths, depend on τcr, which is controlled by soil surface conditions and can be predicted from saturated soil shear strength. Soil erosion control measures that increase soil shear strength (e.g. thalweg compaction), can therefore decrease rill and gully lengths. Once a rill or an ephemeral gully is initiated, its cross‐section was found to depend on Kc, which can be estimated from the soil water content, dry bulk density, and the dry density of roots and crop residues incorporated in the topsoil. 74% of the variation in the channel cross‐sectional area measured in the study area could be predicted from the combined effect of flow intensity and these three soil properties, whereas flow intensity alone could only account for 31% of the variation. Soil conservation measures affecting one of the soil properties that control Kc (e.g. double drilling of the thalweg, conservation tillage) can therefore decrease the cross‐sections of the concentrated flow paths. These findings also indicate that rill and gully initiation points are not only topographically controlled but also depend on the SER, which in turn determines the dimensions of these concentrated flow paths. Hence, knowledge of the variability in SER is indispensable. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号