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 15 毫秒
1.
Wind erosion characteristics of Sahelian surface types   总被引：1，自引：0，他引：1  
The assessment of wind erosion magnitudes for a given area requires knowledge of wind erosion susceptibilities of the dominant local surface types. Relative wind erosion potentials of surfaces can hardly be compared under field conditions, as each erosion event is unique in terms of duration, intensity and extent. The objective of this study was to determine and compare relative wind erosion potentials of the most representative surface types over a transect comprising most parts of southwestern Niger. For this purpose, mobile wind tunnel experiments were run on 26 dominant surface types. The effects of surface disturbance were additionally determined for 13 of these surfaces. The results, namely measurements of wind fields and mass fluxes, can be classified according to specific surface characteristics. Three basic surface groups with similar emission behaviour and aerodynamic characteristics were identified: (1) sand surfaces, (2) rough stone surfaces and (3) flat crusted surfaces. Sand surfaces feature a turbulent zone close to the surface due to the development of a saltation layer. Their surface roughness is medium to high, as a consequence of the loss of kinetic energy of the wind field to saltating particles. Sand surfaces show the highest mass fluxes due to the abundance of loose particles, but also fairly high PM10 fluxes, as potential dust particles are not contained in stable crusts or aggregates. Rough stone surfaces, due to their fragmented and irregular surface, feature the highest surface roughness and the most intense turbulence. They are among the weakest emitters but, due to their relatively high share of potential dust particles, PM10 emissions are still average. Flat crusted surfaces, in contrast, show low turbulence and the lowest surface roughness. This group of surfaces shows rather heterogeneous mass fluxes, which range from moderate to almost zero, although the share of PM10 particles is always relatively high. Topsoil disturbance always results in higher total and PM10 emissions on sand surfaces and also on flat crusted surfaces. Stone surfaces regularly exhibit a decrease in emission after disturbance, which can possibly be attributed to a reorganization which protects finer particles from entrainment. The results are comparable with field studies of natural erosion events and similar wind tunnel field campaigns. The broad range of tested surfaces and the standardized methodology are a precondition for the future regionalization of the experimental point data. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

2.
Changes in wind speed and sediment transport are evaluated at a gap and adjacent crest of a 2 to 3 m high, 40 m wide foredune built by sand fences and vegetation plantings on a wide, nourished fine sand beach at Ocean City, New Jersey. Anemometer masts, cylindrical sand traps and erosion pins were placed on the beach and dune during two obliquely onshore wind events in February and March 2003. Results reveal that: (1) changes in the alongshore continuity of the beach and dune system can act as boundaries to aeolian transport when winds blow at an angle to the shoreline; (2) oblique winds blowing across poorly vegetated patches in the dune increase the potential for creating an irregular crest elevation; (3) transport rates and deflation rates can be greater within the foredune than on the beach, if the dune surface is poorly vegetated and the beach has not had time to dry following tidal inundation; (4) frozen ground does not prevent surface deflation; and (5) remnant sand fences and fresh storm wrack have great local but temporary effect on transport rates. Temporal and spatial differences due to sand fences and wrack, changes in sediment availability due to time‐dependent differences in surface moisture and frozen ground, combined with complex topography and patchy vegetation make it difficult to specify cause–effect relationships. Effects of individual roughness elements on the beach and dune on wind flow and sediment transport can be quantified at specific locations at the event scale, but extrapolation of each event to longer temporal and spatial scales remains qualitative. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

3.
Aeolian sand transport is a complicated process that is affected by many factors (e.g. wind velocity, sand particle size, surface microtopography). Under different experimental conditions, erosion processes will therefore produce different results. In this study, we conducted a series of wind tunnel experiments across a range of wind velocities capable of entraining sand particles (8.0, 10.0, 12.0, and 14.0 m s-1) to study the dynamic changes of the shear velocity, aerodynamic roughness length, and sand transport. We found that the shear velocity and aerodynamic roughness length are not constant; rather, they change dynamically over time, and the rules that describe their changes depend on the free-stream air velocity. For wind tunnel experiments without feeding sand into the airflow, the sand bed elevation decreases with increasing erosion time, and this change significantly affected the values of shear velocity and aerodynamic roughness length. A Gaussian distribution function described the relationships between the sand transport rate (qT) and the duration of wind erosion (T). It is therefore necessary for modelers to consider both deflation of the bed and the time scale used when calculating sand transport or erosion rates. © 2018 John Wiley & Sons, Ltd.  相似文献   

4.
A portable field wind tunnel was used to assess the sediment flux rates of loam and sand textured soils in the Mallee region of southeastern Australia. Three levels of crust disturbance (nil, moderate and severe) simulating stock trampling were investigated. The results demonstrated the importance of cryptogamic crusts in binding the soil surface and providing roughness after the soil was moderately disturbed. On the loamy soil, the crust helped maintain sediment flux rates below the erosion control target to 5 g m−1 s−1 for a 65 km h−1 wind measured at 10 m height. Once the crust was severely disturbed, sediment fluxes increased to 1·6 times the erosion target. On the sandy soil, even with no crust disturbance the sediment flux was 1·6 times the erosion control target. Disturbing the crust increased sediment fluxes to a maximum of 6·7 times the erosion control target. Removal of the crust also decreased the threshold wind velocity that resulted in an increase to the risk of erosion from <5 per cent to 20 per cent. © 1998 John Wiley & Sons, Ltd.  相似文献   

5.
Strong winds are a characteristic feature of UK upland areas. Despite this, understanding of aeolian processes in upland environments of the UK is limited. This paper presents direct measurements and observations of blanket peat erosion by wind action during a two week period of desiccation in the North Pennines, Northern England. A circular configuration of mass flux sediment samplers was used to collect peat eroded by wind action from 16 cardinal compass directions. Meteorological conditions (wind speed, wind direction, precipitation and temperature) were recorded by an automatic weather station set up adjacent to the site. Surface desiccation led to peat crust erosion and dust deflation. During short (≤1 hour) periods of precipitation, wind‐driven rainfall also caused erosion. Typically, dust flux rates were up to two orders of magnitude lower than recorded during periods of sustained wet weather. Measurements demonstrate the hitherto unreported rapid switch in process regime between wind‐driven rainfall and dry blow deflation in blanket peat environments. Dry blow processes of blanket peat erosion may become more important in UK upland areas if climate change promotes more frequent surface desiccation. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

6.
Wind erosion modelling efforts, both ?eld and wind tunnel studies, have traditionally focused on saltation‐based processes for estimating dust emissions from high wind events. This approach gives generally good results when saltation‐sized particles, 90 µm to 2 mm mean diameter, are prevalent on the exposed soil surface. The Columbia Plateau, located in north‐central Oregon and south‐central Washington, is a region with extensive loess deposits where up to 90 per cent of sieved particles (by mass) are less than 100 µm mean diameter. During high‐wind events, large amounts of soil and ?ne particulate matter are suspended. However, ?eld surfaces typically show little evidence of surface scouring or saltation, e.g. soil drifts or covered furrows. Velocity pro?le analysis of two high‐wind events and additional data from a third event show evidence of direct suspension process where saltation is not a major mechanism for eroding soil or generating dust emissions. Surface roughness heights are less than saltation roughness height estimates during peak wind speeds. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

7.
Dust emission from wet and dry playas in the Mojave Desert,USA   总被引：1，自引：0，他引：1  
The interactions between playa hydrology and playa‐surface sediments are important factors that control the type and amount of dust emitted from playas as a result of wind erosion. The production of evaporite minerals during evaporative loss of near‐surface ground water results in both the creation and maintenance of several centimeters or more of loose sediment on and near the surfaces of wet playas. Observations that characterize the texture, mineralogic composition and hardness of playa – surfaces at Franklin Lake, Soda Lake and West Cronese Lake playas in the Mojave Desert (California), along with imaging of dust emission using automated digital photography, indicate that these kinds of surface sediment are highly susceptible to dust emission. The surfaces of wet playas are dynamic surface texture and sediment availability to wind erosion change rapidly, primarily in response to fluctuations in water‐table depth, rainfall and rates of evaporation. In contrast, dry playas are characterized by ground water at depth. Consequently, dry playas commonly have hard surfaces that produce little or no dust if undisturbed except for transient silt and clay deposited on surfaces by wind and water. Although not the dominant type of global dust, salt‐rich dusts from wet playas may be important with respect to radiative properties of dust plumes, atmospheric chemistry, windborne nutrients and human health. Published in 2007 by John Wiley & Sons, Ltd.  相似文献   

8.
Sediment distribution is investigated applying grain size analysis to 279 surface samples from the transitional zone between high mountains (Qilian Shan) and their arid forelands (Hexi Corridor) in north‐western China. Six main sediment types were classified. Medium scale (103 m) geomorphological setting is carefully considered as it may play an important role concerning sediment supply and availability. A tripartite distribution of sedimentological landscape units along the mountain to foreland transition is evident. Aeolian sediments (e.g. loess and dune sands) are widespread. They are used to identify aeolian transport pathways. The mU/fS‐ratio (5–11 µm/48–70 µm) among primary loess opposes the two grain size fractions being most sensitive to varying accumulation conditions. The first fraction is attributed to long‐distance transport in high suspension clouds whereas the latter represents local transport in saltation mode. The ratio shows strong correlation with elevation (R2 = 0.77). Thus, it indicates a relatively higher far‐traveled dust supply in mountainous areas (>3000 m above sea level [a.s.l.]) compared to the foreland. The contribution of westerlies to high mountain loess deposits is considered likely. Hereby, the influence of the geomorphological setting on grain size composition of aeolian sediments becomes apparent: the contribution from distant dust sources is ubiquitous in the study area. However, the far‐distance contribution may be reduced by the availability of fine sand provided in low topography settings. Plain foreland areas support fine sand deflation from supplying river beds, allowing the formation of sandy loess in foreland areas and intramontane basins. In contrast, high mountain topography inhibits strong sand deflation into loess deposits. Eastern parts of the Hexi Corridor show higher aeolian sand occurrence. In contrast, the western parts are dominated by gravel gobi surfaces. This is attributed to higher sand supply in eastern parts provided by the Badain Jaran Desert and fluvial storages as sand sources. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

9.
A wind tunnel study examined the effect of distributions of saltating particles on sediment surfaces which were characterized by distributions of their tensile strength. The sediments consisted of varying proportions of large sand‐sized particles with a fine particle cement. The energies of the impacting particles and the surface strengths were compared with the mass of material lost from the surface. It is important to consider distributions of parameters rather than mean values only, since abrasion and erosion may occur from surfaces not predicted from average strength and saltation velocities. At the impact velocities used in this study (mean velocity 4·4 m s?1, with standard deviation of 0·51), surfaces containing less than 12 per cent fine material were easily eroded, but insignificant erosion occurred when the fine particle content exceeded 60 per cent. Small amounts of cementing material were easily ruptured, allowing the large sand grains to be moved (largely in creep) by the bombarding particles. A significant amount of energy was lost to the bed. As the percentage of fine material increased, the surface became more difficult to break up and less energy was lost to the bed. The probability that erosion will occur for known energy distributions of impacting particles and surface strength can be calculated and the mass loss increases exponentially with a decrease in the percentage of fine cementing particles. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

10.
This study provides fundamental examination of mass fluvial erosion along a stream bank by identifying event timing, quantifying retreat lengths, and providing ranges of incipient shear stress for hydraulically driven erosion. Mass fluvial erosion is defined here as the detachment of thin soil layers or conglomerates from the bank face under higher hydraulic shear stresses relative to surface fluvial erosion, or the entrainment of individual grains or aggregates under lower hydraulic shear stresses. We explore the relationship between the two regimes in a representative, US Midwestern stream with semi‐cohesive bank soils, namely Clear Creek, IA. Photo‐Electronic Erosion Pins (PEEPs) provide, for the first time, in situ measurements of mass fluvial erosion retreat lengths during a season. The PEEPs were installed at identical locations where surface fluvial erosion measurements exist for identifying the transition point between the two regimes. This transition is postulated to occur when the applied shear stress surpasses a second threshold, namely the critical shear stress for mass fluvial erosion. We hypothesize that the regimes are intricately related and surface fluvial erosion can facilitate mass fluvial erosion. Selective entrainment of unbound/exposed, mostly silt‐sized particles at low shear stresses over sand‐sized sediment can armor the bank surface, limiting the removal of the underlying soil. The armoring here is enhanced by cementation from the presence of optimal levels of sand and clay. Select studies show that fluvial erosion strength can increase several‐fold when appropriate amounts of sand and clay are mixed and cement together. Hence, soil layers or conglomerates are entrained with higher flows. The critical shear stress for mass fluvial erosion was found to be an order of magnitude higher than that of surface fluvial erosion, and proceeded with higher (approximately 2–4 times) erodibility. The results were well represented by a mechanistic detachment model that captures the two regimes. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

11.
Rainfall simulation was used to examine runoff generation and sediment transport on roads, paths and three types of agricultural fields in Pang Khum Experimental Watershed (PKEW), in mountainous northern Thailand. Because interception of subsurface flow by the road prism is rare in PKEW, work focused on Horton overland flow (HOF). Under dry antecedent soil moisture conditions, roads generated HOF in c. 1 min and have event runoff coefficients (ROCs) of 80 per cent, during 45 min, c. 105 mm h−1 simulations. Runoff generation on agricultural fields required greater rainfall depths to initiate HOF; these surfaces had total ROCs ranging from 0 to 20 per cent. Footpaths are capable of generating erosion‐producing overland flow within agricultural surfaces where HOF generation is otherwise rare. Paths had saturated hydraulic conductivity (Ks) values 80–120 mm h−1 lower than those of adjacent agricultural surfaces. Sediment production on roads exceeded that of footpaths and agricultural lands by more than eight times (1·23 versus < 0·15 g J−1). Typically, high road runoff volumes (owing to low Ks, c. 15 mm h−1) transported relatively high sediment loads. Initial road sediment concentrations exceeded 100 g l−1, but decayed with time as loose surface material was removed. Compared with the loose surface layer, the compacted, underlying road surface was resistant to detachment forces. Sediment concentration values for the road simulations were slightly higher than data obtained from a 165 m road section during a comparable natural event. Initial simulation concentration values were substantially higher, but were nearly equivalent to those of the natural event after 20 min simulation time. Higher sediment concentration in the simulations was related to differences in the availability of loose surface material, which was more abundant during the dry‐season simulations than during the rainy season natural event. Sediment production on PKEW roads is sensitive to surface preparation processes affecting the supply of surface sediment, including vehicle detachment, maintenance activities, and mass wasting. The simulation data represent a foundation from which to begin parameterizing a physically based runoff/erosion model to study erosional impacts of roads in the study area. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

12.
Airflow patterns through a saucer blowout are examined from wind speed and direction measurements made during a chinook wind event. The blowout long‐axis is oriented east–west with a broad depositional apron on the east side. Wind directions during the event rotated from south‐westerly to westerly, permitting an assessment of oblique and axis‐parallel flows. Results show that airflow passing over the windward rim of the saucer blowout expands and decelerates, leading to flow separation and a small re‐circulation zone on sheltered lee slopes. Near the deflation basin, airflow re‐attaches to the blowout surface and accelerates up to a small opening in the east rim, where it can be up to 50% faster than on the windward edge. Beyond the downwind rim the airflow expands and decelerates and sand is deposited onto a broad apron. Similar to coastal trough blowouts, the degree of airflow steering and acceleration along the deflation basin is determined by the angle of incidence between the approach wind and the long‐axis of the blowout. As the angle of incidence increases wind speed accelerates at 0·3 m above the surface of the deflation basin and the degree of airflow steering increases. Overall, a two‐fold process is identified, where south‐westerly flows have greater potential for eroding the deflation basin, while westerly flows have greater potential for evacuating sand from within the blowout. Visual observations indicate that sand eroded from the deflation basin during south‐westerly flows is re‐distributed to adjacent zones of low wind speed until axis‐parallel winds evacuate the sand through the opening in the east rim. Morphometric changes since 1994 indicate that the blowout morphology has remained relatively constant, suggesting a persistent interplay between oblique and axis‐parallel wind erosion events. Collectively, these findings indicate that the angle of approach winds is an important control on saucer blowout morphodynamics. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

13.
Surfactants are chemical compounds that can change the contact angle of a water drop on solid surfaces and are commonly used to increase infiltration into water repellent soil. Since production fields with water repellent soil often contain areas of wettable soil, surfactants applied to such fields worldwide will likely be applied to wettable soil, with unknown consequences for irrigation‐induced erosion, runoff, or soil water relations. We evaluated surfactant and simulated sprinkler irrigation effects on these responses for three wettable, Pacific Northwest soils, Latahco and Rad silt loams, and Quincy sand. Along with an untreated control, we studied three surfactants: an alkyl polyglycoside (APG) in solution at a concentration of 18 g active ingredient (AI) kg?1, a block copolymer at 26 g kg?1, and a blend of the two at 43 g kg?1. From 2005 to 2009 in the laboratory, each surfactant was sprayed at a rate of 46·8 l ha?1 onto each soil packed by tamping into 1·2‐ by 1·5‐m steel boxes. Thereafter, each treated soil was irrigated twice at 88 mm h?1 with surfactant‐free well water. After each irrigation, runoff and sediment loss were measured and soil samples were collected. While measured properties differed among soils and irrigations, surfactants had no effect on runoff, sediment loss, splash loss, or tension infiltration, compared to the control. Across all soils, however, the APG increased volumetric water contents by about 3% (significant at p≤0·08) at matric potentials from 0 to ? 20 kPa compared to the control. With a decrease in the liquid–solid contact angle on treated soil surfaces, surfactant‐free water appeared able to enter, and be retained in pores with diameters ≥ 15 µm. All told, surfactants applied at economic rates to these wettable Pacific Northwest soils posed little risk of increasing either runoff or erosion or harming soil water relations. Moreover, by increasing water retention at high potentials, surfactants applied to wettable soils may allow water containing pesticides or other agricultural chemicals to better penetrate soil pores, thereby increasing the efficacy of the co‐applied materials. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

14.
Winter wheat–summer fallow is the conventional cropping system employed on >1·5 million ha within the Columbia Plateau of eastern Washington and northern Oregon. Wind erosion contributes to poor air quality in the region, yet little is known concerning the magnitude of soil and PM10 (particulate matter of ≤10 µm in aerodynamic diameter) loss from agricultural lands. Therefore, loss of soil and PM10 was assessed from a silt loam in eastern Washington during 2003 and 2004. Field sites were maintained in fallow using conventional tillage practices in 2003 (9 ha field) and 2004 (16 ha field) and instrumented to assess horizontal soil flux and PM10 concentrations at the windward and leeward positions in the field during high‐wind events. Soil flux was measured using creep and airborne sediment collectors while PM10 concentrations were measured using high‐volume PM10 samplers. Aggregate size distribution of parent soil and eroded sediment was characterized by rotary and sonic sieving. Six high‐wind events occurred over the two year period, with soil loss ranging from 43 kg ha?1 for the 12–22 September 2003 event to 2320 kg ha?1 for the 27–29 October 2003 event. Suspension‐sized particulates (<100 µm in diameter) comprised ≥90 per cent of the eroded sediment, indicating that direct suspension may be an important process by which the silt loam eroded. The corresponding loss of PM10 for these two events ranged from 5 to 210 kg ha?1. Loss of PM10 comprised 9–12 per cent of the total soil loss for the six events. This study suggests that the relatively small loss of PM10 from eroding agricultural fields maintained in summer fallow can affect air quality in the Columbia Plateau. Therefore, alternative tillage practices or cropping systems are needed for minimizing PM10 emissions and improving air quality in the region. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

15.
Quantitative estimation of the material transported by the wind under field conditions is essential for the study and control of wind erosion. A critical step of this calculation is the integration of the curve that relates the variation of the amount of the material carried by the wind with height. Several mathematical procedures have been proposed for this calculation, but results are scarce and controversial. One objective of this study was to assess the efficiency of three mathematical models (a rational, an exponential, and a simplified Gaussian function) for the calculation of the mass transport, as compared to the linear spline interpolation. Another objective of this study was to compare the mass transport calculated from field measurements obtained from a minimum of three discrete sampling heights with measurements of nine sampling heights. With this purpose, wind erosion was measured under low surface roughness conditions on an Entic Haplustoll during 25 events. The rational function was found to be mathematically limited for the estimation of wind eroded sediment mass flux. The simplified Gaussian model did not fit to the vertical mass flux profile data. Linear spline interpolation generally produced higher mass transport estimates than the exponential equation, and it proved to be a very flexible and robust method. Using different sampling arrangements and different mass flux models can produce differences of more than 45% in mass transport estimates, even under similar field conditions. Under the conditions of this study, at least three points between the soil surface and 1·5 m high, including one point as closest as possible to the surface, should be sampled in order to obtain accurate mass transport estimates. Additionally, the linear spline interpolation and the non‐linear regression using an exponential model, proved to be mathematically reliable methods for calculating the mass transport. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

16.
Alluvial gullies are often formed in dispersible sodic soils along steep banks of incised river channels. Field data collected by Shellberg et al. (Earth Surface Processes and Landforms 38: 1765–1778, 2013) from a gully outlet in northern Australia showed little hysteresis between water discharge and fine (<63 µm) and coarse (>63 µm) suspended sediment, indicating transport‐limited rather than source‐limited conditions. The major source of the fine (silt/clay) component was the sodic soils of upstream gully scarps, and the coarser (sand) component was sourced locally from channel bed material. In this companion paper at the same study site, a new method was developed for combining the settling velocity characteristics of these two sediment source components to estimate the average settling velocity of the total suspended sediment. This was compared to the analysis of limited sediment samples collected during flood conditions. These settling velocity data were used in the steady‐state transport limit theory of Hairsine and Rose (Water Resources Research 28: 237–243, 245–250, 1992) that successfully predicted field data of concentrations and loads at a cross‐section, regardless of the complexity of transport‐limited upstream sources (sheet erosion, scalds, rills, gullies, mass failure, bank and bed erosion, other disturbed areas). The analysis required calibration of a key model parameter, the fraction of total stream power (F ≈ 0.025) that is effective in re‐entraining sediment. Practical recommendations are provided for the prediction of sediment loads from other alluvial gullies in the region with similar hydrogeomorphic conditions, using average stream power efficiency factors for suspended silt/clay (Fw ≈ 0.016) and sand (Fs ≈ 0.038) respectively, but with no requirement for field data on sediment concentrations. Only basic field data on settling velocity characteristics from soil samples, channel geometry measurements, estimates of water velocity and discharge, and associated error margins are needed for transport limit theory predictions of concentration and load. This theory is simpler than that required in source‐limited situations. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

17.
Small scale features resulting from wind erosion are widespread in the Namib Desert. They include selective erosion of lithological variations (etching), flutes and grooves, facetting of clasts and residual boulders, and smoothing and polishing of rock surfaces. Large scale features are tentatively identified and are restricted to the southern Namib, with its high energy, unidirectional wind regime. Wind erosion features are best developed on fine-grained rocks of intermediate hardness. They are oriented towards or parallel to modern strong winds. The turbulent flow of wind armed only with dust particles is probably more important than wind driven sand in creating smooth polished rock surfaces, flutes, and grooves. Wind driven sand appears to be significant only in facetting rock masses.  相似文献   

18.
Numerical simulation experiments of water erosion at the local scale (20 × 5 m) using a process‐based model [Plot Soil Erosion Model_2D (PSEM_2D)] were carried out to test the effects of various environmental factors (soil type, meteorological forcing and slope gradient) on the runoff and erosion response and to determine the dominant processes that control the sediment yield at various slope lengths. The selected environmental factors corresponded to conditions for which the model had been fully tested beforehand. The use of a Green and Ampt model for infiltration explained the dominant role played by rainfall intensity in the runoff response. Sediment yield at the outlet of the simulated area was correlated positively with rainfall intensity and slope gradient, but was less sensitive to soil type. The relationship between sediment yield (soil loss per unit area) and slope length was greatly influenced by all environmental factors, but there was a general tendency towards higher sediment yield when the slope was longer. Contribution of rainfall erosion to gross erosion was dominant for all surfaces with slope lengths ranging from 4 to 20 m. The highest sediment yields corresponded to cases where flow erosion was activated. An increase in slope gradient resulted in flow detachment starting upstream. Sediment exported at the outlet of the simulated area came predominantly from the zone located near the outlet. The microrelief helped in the development of a rill network that controlled both the ratio between rainfall and flow erosion and the relationship between sediment yield and slope length. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

19.
Simulated rainfall experiments were performed on bare, undecomposed litter layer and semi-decomposed litter layer slopes with litter biomasses of 0, 50, 100 and 150 g m−2, respectively, to evaluate the effect of the undecomposed layer and semi-decomposed layer of Quercus variabilis litter on the soil erosion process and the particle size distribution of eroded sediment. The undecomposed layer and semi-decomposed layer of litter reduced the runoff rate by 10.91–27.04% and 12.91–36.05%, respectively, and the erosion rate by 13.35–40.98% and 17.16–59.46%, respectively. The percentage of smaller particles (clay and fine silt particles) decreased and the percentage of larger particles (coarse silt and sand particles) increased with an increased rainfall duration on all treated slopes, while the extent of the eroded sediment particle content varied among the treated slopes with the rainfall duration, with bare slopes exhibiting the largest variability, followed by undecomposed litter layer slopes and finally semi-decomposed litter layer slopes. The clay and sand particles were transported as aggregates, and fine silt and coarse silt particles were transported as primary particles. Compared with the original soil, sediment eroded from all treated slopes was mainly enriched in smaller particles. Furthermore, the loss of the smaller particles from the undecomposed litter layer slopes was lower than that from the semi-decomposed litter layer slopes, indicating that the undecomposed litter layer alleviated soil coarsening to some extent. The findings from this study improve our understanding of how litter regulates slope erosion and provide a reference for effectively controlling soil erosion.  相似文献   

20.
A sample ord, a low section of beach characteristic of the Holderness coast, is examined as it moved southwards between 1977 and 1983 and its significant role in coast erosion is demonstrated. The reduction in beach level at the cliff foot by up to 3.9 m enabled most HWN tides to reach it, as compared with only some HWS tides along the inter-ord beach, and the volume of till eroded from the cliffs increased by eight times to an annual mean of 72m3m?1. The Holderness tills are shown to be composed of 31 per cent sand and coarser sediment which is the sediment range of the beaches. Where an ord is sited the massive injection of beach sediment goes to form the ord's most prominent constructional feature, the lower beach ridge which extends southwards from the centre of the ord. Analysis of 12 months' observer wave data collected at Withernsea in 1969/70 indicates that a net southward sand movement of 144 000 m3 occurred. Comparison of this rate with beach sediment input rates along the whole coast backed by till cliffs suggests a sediment deficit at the northern end and a surplus towards the southern end. This conclusion is supported by an overall increase in beach sediment volume southwards from Barmston. Within this longshore sediment transport system, the ords migrate southwards from their point of origin in the Barmston-Skipsea area, without losing their identity until reaching the tip of Spurn Head.  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