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1.
David Dunkerley 《地球表面变化过程与地形》2002,27(2):165-175
Large roughness elements such as stones or plant stems (obstacles) influence the depth of overland flows in two ways. The first effect is a dynamic one, involving frictional retardation of the flow and associated reduction in flow speeds. The second influence is static, and arises from the upward volumetric displacement of flow depth because of the submerged volume of the obstacles. Depending upon the distribution of submerged obstacle volume with height above the soil surface, the proportion of the flow volume occupied (and so, the perturbation of flow depth arising from volumetric displacement) can vary irregularly or systematically with flow stage. Furthermore, the amount of volumetric displacement of flow depth would vary among surfaces carrying different cover fractions of identical obstacles. Consequently, estimates of the change in friction factors arising from the drag on flow traversing varying obstacle cover fractions are confounded with the parallel shift volumetric displacement. To understand the true frictional drag arising from obstacles, a correction must be made for the volumetric displacement. A method for making this correction is outlined. New laboratory experiments provide precise observations of depths and friction coefficients in laminar flows passing fields of regular obstacles. After making the proposed correction for volumetric displacement, increases of 40 to 75 per cent in the derived value of the Darcy–Weisbach friction factor, f, are found for an obstacle cover of 20 per cent. Many published studies of friction coefficients in shallow overland flows, such as those on stone‐covered dryland soils, involve larger obstacle cover fractions, and evidently involve the significant confounding effect of volumetric displacement. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
2.
The influence of stone cover on the generation and continuity of overland flow is a function of several variables, primarily stone size, distance (spacing) between stones, and stone position (on top of the soil surface or partially embedded). The initial hypothesis of the present study were that stone size affects overland flow generation by inducing ‘concentration overland flow’ and that the distance between stones affects overland flow continuity. With respect to stone size and distance between stones, opposing results have been found in the literature. Accordingly, the present paper reports on laboratory experiments which were conducted to investigate, systematically, the effect on overland flow of stone size, distance between stones, and stone position. The main conclusions were:
- 1 Stone cover tended to induce overland flow, relative to bare soil. Small stones, however, especially in a low-cover percentage setting, and when resting on top of the soil surface, produced less overland flow than bare soil.
- 2 Overland flow was positively related to stone size, but inversely related to distance between stones.
- 3 Overland flow yield was always greater when stones were embedded than when on top of the soil surface.
- 4 The effect of stone size on increasing the degree of overland flow was of greater significance than the effect of the distance between stones on reducing overland flow.
3.
David Dunkerley 《地球表面变化过程与地形》2002,27(1):45-58
This study investigates the contribution of surface tension forces to friction coefficients in shallow, laminar interrill flows. Friction coefficients in these flows are known to be increased greatly by organic litter and by stems. Fine litter provides extensive edges along which surface tension menisci can be drawn up, and evaluating the significance of this in the frictional retardation of flow was the primary objective of the experiments reported here. Using both standardized ‘litter particles’ (small wooden blocks of fixed dimensions) and natural plant litter, meniscus behaviour and the Darcy–Weisbach friction coefficient were evaluated in shallow flows on a laboratory sand board. For some tests, the surface tension of ordinary water was reduced by 40 per cent by the addition of a surfactant, and the friction coefficient redetermined. Results show that the presence of surface tension menisci flanking litter particles provides areas of deeper flow that are up to 7 mm in width and which can increase flow depths by 100–300 per cent. These zones support significantly higher flow speeds. Increased water depths within menisci are additionally associated with reduced depths beyond the menisci, so that an increase in the spatial variability of flow depths is a second consequence of meniscus formation. These modifications of flow depth by surface tension menisci are shown to reduce rather than increase the overall friction coefficient applicable to the flow. Consequently, additional frictional retardation does not arise within the menisci flanking litter particles and so cannot account for the greater drag arising from litter than from other surface features. Different factors, possibly the direct obstruction of flow paths, must therefore underlie the frictional drag. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
Vegetation stems and litter cover have different effects on sediment transport capacity under the same experimental conditions, which in essence, may be due to differences in their hydraulic properties, but the availability of comparative studies is limited. This study aimed to compare the hydraulic properties affected by litter and stem cover, compare differences in the drag forces exerted by litter and stems on overland flow, and develop new Manning's n and flow velocity equations for litter cover. Two series of flume experiments were conducted with the same slope gradients (8.8%, 17.6%, 26.8%) and flow discharge rates (0.5, 1.0 × 10−3 m3 s−1). Artificial Gramineae stems with a 0%–30% cover level and Pinus tabulaeformis litter with a 0%–70% cover level were used in series 1 and series 2, respectively. The flow velocity and depth were measured. The results showed that the Froude number and flow velocity affected by stem cover were much lower than those affected by litter cover, while the opposite trend was observed in the relative magnitude of the Reynolds number, flow depth and shear stress. The form resistance caused by stems was 22–57 times greater than that caused by litter for the same cover level, which suggests that stem cover contributes more than litter cover to increasing the flow resistance and reducing the flow's ability for sediment detachment and transport. Two new equations for calculating Manning's n and flow velocity under the influence of litter cover were developed, with R2 and NSE values of 0.96. The results of this study contribute to revealing the mechanisms of the differences of the effects of stem and litter cover on soil erosion. 相似文献
5.
Soil erosion by concentrated flow can cause serious environmental damage. Erosion‐control geotextiles have considerable potential for reducing concentrated flow erosion. However, limited data are available on the erosion‐reducing potential of geotextiles. In this study, the effectiveness of three biological geotextiles in reducing soil losses during concentrated flow is investigated. Hereto, runoff was simulated in a concentrated flow flume, filled with an erodible sandy loam on three slope gradients (13·5, 27·0 and 41·5%). Treatments included three biological geotextiles (borassus, buriti and bamboo) and one bare soil surface. Darcy–Weisbach friction coefficients ranged from 0·01 to 2·84. The highest values are observed for borassus covered soil surfaces, followed by buriti, bamboo and bare soil, respectively. The friction coefficients are linearly correlated with geotextile thickness. For the specific experimental conditions of this study, borassus geotextiles reduced soil detachment rate on average to 56%, buriti geotextiles to 59% and bamboo geotextiles to 66% of the soil detachment rate for bare soil surfaces. Total flow shear stress was the hydraulic parameter best predicting soil detachment rate for bare and geotextile covered surfaces (R2 = 0·75–0·84, p <0·001, n = 12–15). The highest resistance against soil detachment was observed for the borassus covered soil surfaces, followed by buriti, bamboo and bare soil surfaces, respectively. Overall, biological geotextiles are less effective in controlling concentrated flow erosion compared with interrill erosion. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
6.
Plant litter can be incorporated into topsoil by a natural process, affecting the soil erosion process. This is a widespread phenomenon in erosion-prone areas. This study was conducted to investigate the effect of litter incorporation on the process of soil detachment on the Loess Plateau, China. Four common plant litters (Bothriochloa ischaemum L. Keng., Artemisia sacrorum Ledeb., Setaria viridis L. Beauv., and Artemisia capillaris Thunb.) were collected, then incorporated into the silt loam soil at five rates (0.1, 0.4, 0.7, 1.0, and 1.3 kg m−2) on the basis of our field investigation. Twenty litter–soil treatments and one bare soil control were prepared. After 50 days of natural stabilization, 30 soil samples of each treatment were collected. We used a flume test to scour the soil samples under six flow shear stress conditions (5.66, 8.31, 12.21, 15.55, 19.15, and 22.11 Pa). The results showed that the different incorporated litter masses and morphological characteristics, such as litter tissue density (ranging from 0.52 to 0.68 g cm−3), length density (2.34 to 91.00 km m−3), surface area density (LSAD; 27.9 to 674.2 m2 m−3), and volume ratio (0.003 to 0.050 m3 m−3), caused varied soil detachment capacities (0.043 to 4.580 kg·m−2·s−1), rill erodibilities (0.051 to 0.237 s m−1), and critical shear stresses (2.02 to 6.83 Pa). The plant litter incorporated within the soil reduced the soil detachment capacities by 38%–59%, lowered the rill erodibilities by 32%–46%, and increased the critical shear stresses by 98%–193% compared with the bare soil control. The soil containing B. ischaemum (L.) Keng. litter was more resistant to erosion. By comparing different parameters, we found that the contact area between the litter and soil was the main factor affecting the soil detachment process. The soil erosion resistance increased with the increasing contact area between the soil and litter. Furthermore, the litter incorporation effect on rill erodibility can be comprehensively reflected by LSAD (R2 = .93; Nash–Sutcliffe efficiency = 0.79), which could be used to adjust the rill erodibility parameter in physical process-based soil erosion models. 相似文献
7.
A database composed of 673 natural rainfall events with sediment concentration measurements at the field or plot scale was analysed. Measurements were conducted on similar soil type (loess soils prone to sealing phenomenon) to apprehend the variability and complexity involved in interrill erosion processes attributable to soil surface conditions. The effects of the dominant controlling factors are not described by means of equations; rather, we established a classification of potential sediment concentration domain according to combination of the dominant parameters. Thereby, significant differences and evolution trends of mean sediment concentration between the different parameter categories are identified. Further, when parameter influences interact, it allows us to discern the relative effects of factors according to their respective degree of expression. It was shown that crop cover had a major influence on mean sediment concentration, particularly when soil surface roughness is low and when maximum 6‐min intensity of rainfall events exceeds 10 mm h?1: mean sediment concentration decreases from 8·93 g l?1 for 0–20 per cent of coverage to 0·97 g l?1 for 21–60 per cent of coverage. The established classification also indicates that the increase of the maximum 6‐min intensity of the rainfall factor leads to a linear increase of mean sediment concentration for crop cover over 21 per cent (e.g. from 2·96 g l?1 to 14·44 g l?1 for the 1–5 cm roughness class) and to an exponential increase for low crop cover (e.g. from 3·92 g l?1 to 58·76 g l?1 for the 1–5 cm roughness class). The implication of this work may bring perspective for erosion prediction modelling and give references for the development of interrill erosion equation. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
8.
To date, most studies of the effectiveness of geotextiles on soil erosion rates and processes have been conducted in laboratory experiments for less than 1 h. Hence, at Hilton (52°33′ N, 2°19′ W), UK, the effectiveness of employing palm‐mat geotextiles for soil erosion control under field conditions on arable loamy sands was investigated. Geotextile‐mats constructed from Borassus aethiopum (Borassus palm of West Africa) and Mauritia flexuosa (Buriti palm of South America) leaves are termed Borassus mats and Buriti mats, respectively. Duplicate runoff plots (10 m × 1 m on a 15° slope) had five treatments (bare, permanent grass, Borassus total plot cover, Borassus buffer strip and Buriti buffer strip). Borassus covered plots had about 72% ground cover and to differentiate between this treatment and Borassus buffer strips, the former treatment is termed Borassus completely‐covered. Runoff and eroded soil were collected from each bounded plot in a concrete gutter, leading to a receptacle. Results from 08/01/2007–23/01/2009 (total precipitation = 1776·5 mm; n = 53 time intervals) show that using Borassus buffer strips (area coverage ～10%) on bare soil decreased runoff volume by about 71% (P > 0·05) and soil erosion by 92% (P < 0·001). Bare plots had nearly 29·1 L m?2 runoff and 2·36 kg m?2 soil erosion during that period. Borassus buffer strip, Buriti buffer strip and Borassus completely‐covered plots had similar effects in decreasing runoff volume and soil erosion. Runoff volumes largely explain the variability in soil erosion rates. Although buffer strips of Borassus mats were as effective as whole plot cover of the same mats, the longevity of Borassus mats was nearly twice that of Buriti mats. Thus, use of Borassus mats as buffer strips on bare plots is highly effective for soil erosion control. The mechanisms explaining the effectiveness of buffer strips require further studies under varied pedo‐climatic conditions. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
9.
Quantifying the relative proportions of soil losses due to interrill and rill erosion processes during erosion events is an important factor in predicting total soil losses and sediment transport and deposition. Beryllium‐7 (7Be) can provide a convenient way to trace sediment movement over short timescales providing information that can potentially be applied to longer‐term, larger‐scale erosion processes. We used simulated rainstorms to generate soil erosion from two experimental plots (5 m × 4 m; 25° slope) containing a bare, hand‐cultivated loessal soil, and measured 7Be activities to identify the erosion processes contributing to eroded material movement and/or deposition in a flat area at the foot of the slope. Based on the mass balance of 7Be detected in the eroded soil source and in the sediments, the proportions of material from interrill and rill erosion processes were estimated in the total soil losses, the deposited sediments in the flat area, and in the suspended sediments discharged from the plots. The proportion of interrill eroded material in the discharged sediment decreased over time as that of rill eroded material increased. The amount of deposited material was greatly affected by overland flow rates. The estimated amounts of rill eroded material calculated using 7Be activities were in good agreement with those based on physical measurements of total plot rill volumes. Although time lags of 45 and 11 minutes existed between detection of sediment being removed by rill erosion, based on 7Be activities, and observed rill initiation times, our results suggest that the use of 7Be tracer has the potential to accurately quantify the processes of erosion from bare, loessal cultivated slopes and of deposition in flatter, downslope areas that occur in single rainfall events. Such measurements could be applied to estimate longer‐term erosion occurring over larger areas possessing similar landforms. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
Effects of patterned Artemisia capillaris on overland flow velocity under simulated rainfall 总被引：2，自引：0，他引：2
Vegetation cover is an important factor for erosion control. Laboratory‐simulated rainfall experiments were conducted to quantify the effectiveness of patchy distributed Artemisia capillaris in retarding overland flow velocity. Simulated storms (60, 90, 120, and 150 mm h?1) were applied on a bare plot (CK) and four different plant patterns, a banded pattern perpendicular to the slope direction (BP), a single long strip parallel to slope direction (LP), small patches distributed like a checkerboard (SP1), and small patches distributed like a letter “X” (SP2). All treatments had three replicates. Each plot underwent two sets of experiments, intact plant plots and root plots (the above‐ground parts were removed, only roots were reserved), respectively. Results showed that flow velocity increased with rainfall intensity, and the lower slope velocity (Vl) was higher than the upper slope velocity (Vu). The removal of grass shoots increased flow velocity. Compared with bare soil plot, intact plants reduced mean flow velocity by 14%–60%, whereas the reduction declined to <40% for the root plots. BP and both SP treatments performed more effectively than LP in retarding flow velocity, whereas no significant differences were identified between BP and SP. The contributions of A. capillaris shoots and roots to the reductions in flow velocity under different rainfall intensities were different. The shoots made greater contribution of 53%–97% at 60 and 90 mm h–1, and the roots contributed more (51%–81%) at 120 and 150 mm h–1. Runoff and sediment rate had significant (p < 0.05) linear correlations with mean flow velocity. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
11.
This study examines how the sediment transport capacity of interrill overland flow varies with stone cover and stone size at two flow intensities. Six series of flume experiments were conducted on two slopes (2° and 10°) with stones of three sizes (28·0, 45·5 and 91·3 mm) serving as roughness elements. Bed sediment size, water discharge and simulated rainfall intensity were the same in all experiments. It was found (1) that transport capacity is positively related to stone size, with the relation becoming stronger as stone cover increases and flow intensity decreases; and (2) that transport capacity is negatively related to stone cover at the high flow intensity and curvilinearly related to stone cover at the low flow intensity. The curvilinear relations are concave‐upward with the lowest transport capacities occurring at stone covers between 0·40 and 0·60. The highest transport capacities are found at stone covers of 0 and 1, with the transport capacity being greater at the former stone cover than at the latter. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
12.
On the basis of detailed rill surveys carried out on bare plots of different lengths at slopes of 12 per cent, basic rill parameters were derived. Rill width and maximum depth increased with plot length, whereas rill amount and cross‐sectional area, expressed per unit length, remained similar. On smaller plots, all rills were connected in a continuous transport system reaching the plot outlet, whilst on larger plots (10 and 20 m long) part of the rills ended with a deposition areas inside the plots. Amounts of erosion, calculated from rill volume and soil bulk density, were compared with soil loss measured at the plot outlets. On plots 10 and 20 m long, erosion estimated from volume of all rills was larger than measured soil loss. The latter was larger than erosion estimated from volume of contributing rills. To identify contributing soil loss area on these plots, two methods were applied: (i) ratio of total soil loss to maximum soil loss per unit area, and (ii) partition of plot area according to the ratio of contributing to total rill volume. Both methods resulted in similar areas of 21·8–23·5 m2 for the plot 10 m long and 31·2 m2 for the plot 20 m long. Identification of contributing areas enabled rill (5·9 kg m?2) and interrill (2·6 kg m?2) erosion rate to be calculated, the latter being very close to the value predicted from the Universal Soil Loss Equation. Although rill and interrill rates seemed to be similar on all plots, their ratio increased slightly with plot length. Application of this ratio to compute slope length factor of the Revised Universal Soil Loss Equation resulted in similar values to those predicted with the model. The achieved balance of soil loss suggested that all the sediment measured at the plot outlet originated from contributing rills and associated contributing rill areas. The results confirmed the utility of different plot lengths as a research tool for analysing the dynamic response of soil to rainfall–runoff. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
13.
Sergio A. Prats Óscar González-Pelayo Flavio C. Silva Koen J. Bokhorst Jantiene E.M. Baartman Jan J. Keizer 《地球表面变化过程与地形》2019,44(14):2837-2848
Mulching with forest residues has proved to be highly effective in reducing post-fire soil losses at the plot scale. However, its effectiveness has not been quantified at the application rates that are typically used in operational post-fire land management (2–3 Mg ha-1 using straw), as well as at scales larger than 100 m2. The present study compared post-fire erosion rates for six convergent hillslopes or swales of 500 to 800 m2, three of which were left untreated while the other three were mulched immediately after the fire with shredded eucalypt bark at a rate of 2.4 Mg ha-1. Erosion rates were monitored at irregular intervals during the first three post-fire years, whilst ground cover was assessed yearly. Selected topsoil properties (0–2 cm) such as organic matter content and aggregate stability were determined at a single occasion – two years after the wildfire, for three micro-environments separately: bare soil, and under mulch/litter and vegetation. Soil losses on the untreated swales decreased with post-fire year from 2.2 to 0.4 and 0.11 Mg ha-1 yr-1 (respectively for the first, second and third post-fire years), while the mulched swales produced 84%, 77% and 38% less soil losses than the untreated swales. Soil losses also depended on slope aspect, with the north-facing swales producing less erosion than the west-facing ones. This could be linked to their significant differences in bare soil, vegetation and stone cover, or a combination thereof. The type of micro-environment also played a significant role in topsoil properties (stone content, bulk density, resistance to penetration/shear stress, porosity and organic matter content). The present results add to the increasing evidence that forest residues should be duly considered for operational post-fire land management. Forest residues were highly effective in reducing erosion from swales at application rates as low as the typical 2 Mg ha-1 of post-fire straw mulch. © 2019 John Wiley & Sons, Ltd. © 2019 John Wiley & Sons, Ltd. 相似文献
14.
A replicated field study using rainfall simulation and overland flow application was conducted in central Oahu, Hawaii, on a clay‐dominated Oxisol with a 9% slope. Three main treatment groups were examined: a bare treatment, a group of four rolled erosion control systems (RECSs) with open weave designs, and a group of five randomly oriented fibre RECSs. A total of 1122 measurements of runoff and erosion were made to examine treatment differences and to explore temporal patterns in runoff and sediment flux. All erosion control systems significantly delayed the time required to generate plot runoff under both simulated rainfall (35 mm h?1) and the more intense trickle flow application (114 mm h?1). Once runoff was generated during the rainfall application phase, the bare treatment runoff coefficients were significantly lower than those from the two groups of RECSs, as surface seal disruption by rilling is inferred to have enhanced infiltration in the bare treatments. During the more intense phase of overland flow application, the reverse pattern was observed. Interrill contributing‐area roughness was reduced on the bare treatment, facilitating increased runoff to well‐developed rill networks. Meanwhile, the form roughness associated with the RECSs delayed interrill flow to the poorly organized rills that formed under some of the RECSs. Regardless of runoff variations between treatments, sediment output was significantly lower from all surfaces covered by RECSs. The median cumulative sediment output from the bare surfaces was 6·9 kg, compared with 1·2 kg from the open‐weave RECSs and 0·2 kg from the random‐fibre RECSs. The random‐fibre systems were particularly effective under the more stressful overland flow application phase, with 63 times less sediment eroded than the bare treatments and 12 times less than that from the open‐weave systems. Architectural design differences between the two groups of RECSs are discussed in light of their relation to erosion process dynamics and shear stress partitioning. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
15.
Runoff and erosion processes can increase after wildfire and post-fire salvage logging, but little is known about the specific effects of soil compaction and surface cover after post-fire salvage logging activities on these processes. We carried out rainfall simulations after a high-severity wildfire and post-fire salvage logging to assess the effect of compaction (uncompacted or compacted by skid traffic during post-fire salvage logging) and surface cover (bare or covered with logging slash). Runoff after 71 mm of rainfall across two 30-min simulations was similar for the bare plots regardless of the compaction status (mean 33 mm). In comparison, runoff in the slash-covered plots averaged only 22 mm. Rainsplash in the downslope direction averaged 30 g for the bare plots across compaction levels and decreased significantly by 70% on the slash-covered plots. Sediment yield totalled 460 and 818 g m−2 for the uncompacted and compacted bare plots, respectively, and slash significantly reduced these amounts by an average rate of 71%. Our results showed that soil erosion was still high two years after the high severity burning and the effect of soil compaction nearly doubled soil erosion via nonsignificant increases in runoff and sediment concentration. Antecedent soil moisture (dry or wet) was the dominant factor controlling runoff, while surface cover was the dominant factor for rainsplash and sediment yield. Saturated hydraulic conductivity and interrill erodibility calculated from these rainfall simulations confirmed previous laboratory research and will support hydrologic and erosion modelling efforts related to wildfire and post-fire salvage logging. Covering the soil with slash mitigated runoff and significantly reduced soil erosion, demonstrating the potential of this practise to reduce sediment yield and soil degradation from burned and logged areas. 相似文献
16.
Although numerous studies have acknowledged that vegetation can reduce erosion, few process-based studies have examined how vegetation cover affect runoff hydraulics and erosion processes. We present field observations of overland flow hydraulics using rainfall simulations in a typical semiarid area in China. Field plots (5 × 2 m2) were constructed on a loess hillslope (25°), including bare soil plot as control and three plots with planted forage species as treatments—Astragalus adsurgens, Medicago sativa and Cosmos bipinnatus. Both simulated rainfall and simulated rainfall + inflow were applied. Forages reduced soil loss by 55–85% and decreased overland flow rate by 12–37%. Forages significantly increased flow hydraulic resistance expressed by Darcy–Weisbach friction factor by 188–202% and expressed by Manning's friction factor by 66–75%; and decreased overland flow velocity by 28–30%. The upslope inflow significantly increased overland flow velocity by 67% and stream power by 449%, resulting in increased sediment yield rate by 108%. Erosion rate exhibited a significant linear relationship with stream power. M. sativa exhibited the best in reducing soil loss which probably resulted from its role in reducing stream power. Forages on the downslope performed better at reducing sediment yield than upslope due to decreased rill formation and stream power. The findings contribute to an improved understanding of using vegetation to control water and soil loss and land degradation in semiarid environments. 相似文献
17.
Jos‐Manuel Nicolau 《水文研究》2002,16(3):631-647
The aim of this study was to identify the mechanisms of runoff generation and routing and their controlling factors at the hillslope scale, on artificial slopes derived from surface coal mining reclamation in a Mediterranean–continental area. Rainfall and runoff at interrill and microcatchment scales were recorded for a year on two slopes with different substrata: topsoil cover and overburden cover. Runoff coefficient and runoff routing from interrill areas to microcatchment outlets were higher in the overburden substratum than in topsoil, and greater in the most developed rill network. Rainfall volume is the major parameter responsible for runoff response on overburden, suggesting that this substratum is very impermeable—at least during the main rainfall periods of the year (late spring and autumn) when the soil surface is sealed. In such conditions, most rainfall input is converted into runoff, regardless of its intensity. Results from artificial rainfall experiments, conducted 3 and 7 years after seeding, confirm the low infiltration capacity of overburden when sealed. The hydrological response shows great seasonal variability on the overburden slope in accordance with soil surface changes over the year. Rainfall volume and intensities (I30, I60) explain runoff at the interrill scale on the topsoil slope, where rainfall experiments demonstrated a typical Hortonian infiltration curve. However, no correlation was found at the microcatchment level, probably because of the loss of functionality of the only rill as ecological succession proceeded. The runoff generation mechanism on the topsoil slope is more homogeneous throughout the year. Runoff connectivity, defined as the ratio between runoff rates recorded at the rill network scale and those recorded at the interrill area scale in every rainfall event, was also greater on the rilled overburden slope, and in the most developed rill network. The dense rill networks of the overburden slope guarantee very effective runoff drainage, regardless of rainfall magnitude. Rills drain overland flow from interrill‐sealed areas, reducing the opportunity of reinfiltration in areas not affected by siltation. Runoff generation and routing on topsoil slopes are controlled by grass cover and soil moisture content, whereas on overburden slopes rill network density and soil moisture content are the main controlling factors. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
18.
Frederick B. Pierson Corey A. Moffet C. Jason Williams Stuart P. Hardegree Patrick E. Clark 《地球表面变化过程与地形》2009,34(2):193-203
Changing fire regimes and prescribed‐fire use in invasive species management on rangelands require improved understanding of fire effects on runoff and erosion from steeply sloping sagebrush‐steppe. Small (0·5 m2) and large (32·5 m2) plot rainfall simulations (85 mm h–1, 1 h) and concentrated flow methodologies were employed immediately following burning and 1 and 2 years post‐fire to investigate infiltration, runoff and erosion from interrill (rainsplash, sheetwash) and rill (concentrated flow) processes on unburned and burned areas of a steeply sloped sagebrush site on coarse‐textured soils. Soil water repellency and vegetation were assessed to infer relationships in soil and vegetation factors that influence runoff and erosion. Runoff and erosion from rainfall simulations and concentrated flow experiments increased immediately following burning. Runoff returned to near pre‐burn levels and sediment yield was greatly reduced with ground cover recovery to 40 per cent 1 year post‐fire. Erosion remained above pre‐burn levels on large rainfall simulation and concentrated flow plots until ground cover reached 60 per cent two growing seasons post‐fire. The greatest impact of the fire was the threefold reduction of ground cover. Removal of vegetation and ground cover and the influence of pre‐existing strong soil‐water repellency increased the spatial continuity of overland flow, reduced runoff and sediment filtering effects of vegetation and ground cover, and facilitated increased velocity and transport capacity of overland flow. Small plot rainfall simulations suggest ground cover recovery to 40 per cent probably protected the site from low‐return‐interval storms, large plot rainfall and concentrated flow experiments indicate the site remained susceptible to elevated erosion rates during high‐intensity or long duration events until ground cover levels reached 60 per cent. The data demonstrate that the persistence of fire effects on steeply‐sloped, sandy sagebrush sites depends on the time period required for ground cover to recover to near 60 per cent and on the strength and persistence of ‘background’ or fire‐induced soil water repellency. Published in 2009 by John Wiley & Sons, Ltd. 相似文献
19.
In this study our main objective was to quantify water interrill erosion in the sloping lands of Southeast Asia, one of the most bio‐geochemically active regions of the world. Investigations were performed on a typical hillslope of Northern Laos subjected to slash and burn agriculture practiced as shifting cultivation. Situations with different periods of the shifting cultivation cycle (secondary forest, upland rice cultivation following a four‐year fallow period and three‐year continuous upland rice cultivation) and soil orders (Ultisols, Alfisols, Inceptisols) were selected. One metre square micro‐plots were installed to quantify the soil material removed by either detachment of entire soil aggregate or aggregate destruction, and the detached material transported by thin sheet flow, the main mechanisms of interrill erosion. In addition, laboratory tests were carried out to quantify the aggregate destruction in the process of water erosion by slaking, dispersion and mechanical breakdown. The average runoff coefficient (R) evaluated throughout the 2002 rainy season was 30·1 per cent and the interrill erosion was 1413 g m?2 yr?1 for sediments and 68 g C m?2 yr?1 for soil organic carbon, which was relatively high. Among the mechanisms of interrill water erosion, aggregate destruction was low and mostly caused by mechanical breakdown due to raindrops, thus leading to the conclusion that detachment and further transport by the shallow runoff of macro‐aggregates predominates. R ranged from 23·1 to 35·8 per cent. It decreased with the proportion of mosses on the soil surface and soil surface coverage, and increased with increasing proportion of structural crust, thus confirming previous results. Water erosion varied from 621 to 2433 g m?2 yr?1 for sediments and from 31 to 146 g C m?2 yr?1 for soil organic carbon, and significantly increased with increasing clay content of the surface horizon, probably due to the formation of easily detachable and transportable sand‐size aggregates, and proportion of macro‐aggregates not embedded in the soil matrix and prone to transport. In addition, water erosion decreased with increasing proportion of structural crusts, probably due to their higher hardness, and when cultivation follows a fallow period rather than after a long period of cultivation due to the greater occurrence of algae on the soil surface, which affords physical protection and greater aggregate stability through binding and gluing. This study based on simultaneous field and laboratory investigations allowed successful identification and quantification of the main erosion mechanisms and controlling factors of interrill erosion, which will give arguments to further set up optimal strategies for sustainable use of the sloping lands of Southeast Asia. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
20.
Estimating the mean speed of laminar overland flow using dye injection‐uncertainty on rough surfaces
David Dunkerley 《地球表面变化过程与地形》2001,26(4):363-374
A common method for estimating mean flow speeds in studies of surface runoff is to time the travel of a dye cloud across a measured flow path. Motion of the dye front reflects the surface flow speed, and a correction must be employed to derive a value for the profile mean speed, which is always lower. Whilst laminar flow conditions are widespread in the interrill zone, few data are available with which to establish the relationship linking surface and profile mean speeds, and there are virtually none for the flow range 100 < Re < 500 (Re = Reynolds number) which is studied here. In laboratory experiments on a glued sand board, mean flow speeds were estimated from both dye speeds and the volumetric flow relation v = Q/ wd with d measured using a computer‐controlled needle gauge at 64 points. In order to simulate conditions applicable to many dryland soils, the board was also roughened with plant litter and with ceramic tiles (to simulate surface stone cover). Results demonstrate that in the range 100 < Re < 500, there is no consistent relation between surface flow speeds and the profile mean. The mean relationship is v = 0·56 v surf, which departs significantly from the theoretical smooth‐surface relation v = 0·67 v surf, and exhibits a considerable scatter of values that show a dependence on flow depth. Given the inapplicability of any fixed conversion factor, and the dependence on flow depth, it is suggested that the use of dye timing as a method for estimating v be abandoned in favour of precision depth measurement and the use of the relation v = Q/ wd , at least within the laminar flow range tested. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献