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1.
The objective of this study was to determine the changing characteristics of soil surface roughness under different rainfall intensities and examine the interaction between soil surface roughness and different water erosion processes. Four artificial management practices (raking cropland, artificial hoeing, artificial digging, and contour tillage) were used according to the local agriculture customs of the Loess Plateau of China to simulate different types of soil surface roughness, using an additional smooth slope for comparison purposes. A total of 20 rainfall simulation experiments were conducted in five 1 m by 2 m boxes under two rainfall intensities (0.68 and 1.50 mm min?1) on a 15° slope. During splash erosion, soil surface roughness decreased in all treatments except raking cropland and smooth baseline under rainfall intensity of 0.68 mm min?1, while increasing for all treatments except smooth baseline under rainfall intensity of 1.50 mm min?1. During sheet erosion, soil surface roughness decreased for all treatments except hoeing cropland under rainfall intensity of 0.68 mm min?1. However, soil surface roughness increased for the artificial hoeing and raking cropland under rainfall intensity of 1.50 mm min?1. Soil surface roughness has a control effect on sheet erosion for different treatments under two rainfall intensities. For rill erosion, soil surface roughness increased for raking cropland and artificial hoeing treatments, and soil surface roughness decreased for artificial digging and the contour tillage treatments under two rainfall intensities. Under rainfall intensity of 0.68 mm min?1, the critical soil surface roughness was 0.706 cm for the resistance control of runoff and sediment yield. Under rainfall intensity of 1.50 mm min?1, the critical soil surface roughness was 1.633 cm for the resistance control of runoff, while the critical soil surface roughness was 0.706 cm for the resistance control of sediment yield. These findings have important implications for clarifying the erosive nature of soil surface roughness and harnessing sloped farmland. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
2.
Rainfall erosivity represents the primary driver for particle detachment in splash soil erosion. Several raindrop erosivity indices have been developed in order to quantify the potential of rainfall to cause soil erosion. Different types of rainfall simulators have been used to relate rainfall characteristics to soil detachment. However, rainfall produced by different rainfall simulators has different characteristics, specifically different relationships between rainfall intensity and rainfall erosivity. For this reason, the effect of rainfall characteristics produced by a dripper‐type rainfall simulator on splash soil erosion (Ds) has been investigated. The simulated rainfall kinetic energy (KE) and drop size distribution (DSD) were measured using piezoelectric transducers, modified from the Vaisala RAINCAP® rain sensor. The soil splash was evaluated under various simulated rainfall intensities ranging from 10 to 100 mm h?1 using the splash‐cup method. The simulated rainfall intensity (I) and kinetic energy relationship (I–KE) was found to be different from natural rainfall. The simulated rainfall intensity and splash soil erosion relationship (I–Ds) also followed this same trend. The I–KE relationship was found to follow the natural rainfall trend until the rainfall intensity reached 30 mm h?1 and above this limit the KE started to decrease. This emphasizes the importance of the I–KE relationship in determining the I‐Ds relationship, which can differ from one rainfall simulator to another. Ds was found to be highly correlated with KE (r = 0·85, P < 0·001), when data produced by the rainfall intensity ranged from 10 to 100 mm h?1. However, when the threshold rainfall intensity (30 mm h?1) was considered, the correlation coefficient further improved (r = 0·89, P = 0·001). Accordingly, to improve the soil splash estimation of simulated rainfall under various rainfall intensities the I–KE characterization relationship for rainfall simulators has to be taken into account. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
3.
Soil erosion and nutrient losses with surface runoff in the loess plateau in China cause severe soil quality degradation and water pollution. It is driven by both rainfall impact and runoff flow that usually take place simultaneously during a rainfall event. However, the interactive effect of these two processes on soil erosion has received limited attention. The objectives of this study were to better understand the mechanism of soil erosion, solute transport in runoff, and hydraulic characteristics of flow under the simultaneous influence of rainfall and shallow clear‐water flow scouring. Laboratory flume experiments with three rainfall intensities (0, 60, and 120 mm h−1) and four scouring inflow rates (10, 20, 30, and 40 l min−1) were conducted to evaluate their interactive effect on runoff. Results indicate that both rainfall intensity and scouring inflow rate play important roles on runoff formation, soil erosion, and solute transport in the surface runoff. A rainfall splash and water scouring interactive effect on the transport of sediment and solute in runoff were observed at the rainfall intensity of 60 mm h−1 and scouring inflow rates of 20 l min−1. Cumulative sediment mass loss (Ms) was found to be a linear function of cumulative runoff volume (Wr) for each treatment. Solute transport was also affected by both rainfall intensity and scouring inflow rate, and the decrease in bromide concentration in the runoff with time fitted to a power function well. Reynolds number (Re) was a key hydraulic parameter to determine erodability on loess slopes. The Darcy–Weisbach friction coefficients (f) decreased with the Reynolds numbers (Re), and the average soil and water loss rate (Ml) increased with the Reynolds numbers (Re) on loess slope for both scenarios with or without rainfall impact. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
4.
The economic forest management is one of the main land use models on low hill gentle slope. In order to investigate the soil erosion properties of bare slope under economic forest, dynamic simulation on hydraulic characteristic values of overland flow was carried out under 0.5 mm min?1, 1.2 mm min?1 and 1.8 mm min?1 rainfall intensities. Results indicated that runoff shear stress increased with increasing of slope length and their relationship can be described by quadratic equation. There were abnormal points at the length of 4 m and 5.5 m under rainfall intensity of 1.8 mm min?1. The shallow flow was pseudo-laminar flow under 0.5 mm min?1, 1.2 mm min?1 and 1.8 mm min?1 rainfall intensities, and the runoff at upslope was sluggish flow then changed to torrential flow at downslope with increasing of slope length. Critical Reynolds number varied from sluggish flow to torrential flow with 1.8 mm min?1 rainfall intensity and was more than that under 0.5 mm min?1. Reynolds number can be estimated by power function of slope length. And there was a positive correlation between runoff shear stress and both Froude number Fr and Reynolds number Re. We hope this study can provide scientific gist for soil erosion control under economic forest. 相似文献
5.
A better knowledge of soil erosion by water is essential for planning effective soil and water conservation practices in semi‐arid Mediterranean environments. The special climatic and hydrological characteristics of these areas, however, make accurate soil loss predictions difficult, particularly in the absence of minimal data. Two zero‐order experimental microcatchments (328–759 m2), representative of an extensive semi‐arid watershed with a high potential erosion risk in the south‐east of Spain, were selected and monitored for 3 years (1991–93) in order to provide information on the hydrological and erosional response. A pluviogram and hydrograph recorded data at 1‐min intervals during each storm, after which the soil loss was collected and the particle size of the sediment was analysed. Runoff coefficients of about 9% and soil losses of between 84·83 and 298·9 g m?2 year?1 were observed in the area. Rapid response times (geometric mean values lower than 2 h) and low runoff thresholds (mean values between 3·5 to 5·9 mm) were the norm in the experimental areas. A rain intensity of over 15 mm h?1 was considered as ‘erosive rainfall’ in these areas because of the total soil loss and the transport capacity of the overland flow. Differences in pore‐size distribution explained the different hydrological responses observed between areas. The erosional response was more complex and basically seemed to be determined by soil aggregate stability and topographical properties. A greater proportion of finer particles in the eroded material than in the soil matrix indicated selective erosion and the transport of finer material. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
6.
Rill erosion is a serious concern in the hilly region of China with purple soil, and maize is extensively cultivated in this region. Evaluations of the dynamic mechanisms of rill erosion in sloping farmland areas are particularly important during the maize growing season to determine whether rill erosion can occur. A new ridge tillage (RT) system was designed using local agricultural methods in China. Twelve artificial rainfall experiments were conducted in three 1 × 2 m experimental plots with a slope of 15°, which is a typical slope in the study area. The rainfall intensities were designated as 1.0, 1.5, and 2.0 mm min?1. The rainfall experiments were performed in the field to determine the characteristics of run‐off and sediment transport related to rill erosion processes during different stages of maize growth and to analyse how hydraulic parameters and the sediment yield of the rill erosion process are related. The results showed that rill flow patterns were mainly classified as subcritical transition flow during all the growth stages of maize. The effects of hydrodynamic parameters on the sediment yield were ordered as follows: Reynolds number > stream power > Froude number > shear stress. The total sediment yield varied by stage as follows: seedling stage > jointing stage > mature stage > tasseling stage. The sediment yield and run‐off rate exhibited a linear relationship that was well described at the hillslope scale. To initiate soil loss in sloping farmland areas with purple soil during the maize growing season, the critical hydrodynamic shear stress and stream power must be at least 46.505 Pa and 1.541 N m?1 s?1, respectively. 相似文献
7.
Nozzle‐type rainfall simulators are commonly used in hydrologic and soil erosion research. Simulated rainfall intensity, originating from the nozzle, increases as the distance between the point of measurement and the source is decreased. Hence, rainfall measured using rain gauges would systematically overestimate the rainfall received at the ground level. A simple model was developed to adjust rainfall measured anywhere under the simulator to plot‐wide average rainfall at the ground level. Nozzle height, plot width, gauge diameter and height, and gauge location are required to compute this adjustment factor. Results from 15 runs at different rain intensities and durations, and with different rain gauge layouts, showed that a simple average of measured rain would overestimate the plot‐wide rain by about 20 per cent. Using the adjustment factor to convert measured rainfall for individual gauges before averaging improved the estimate of plot‐wide rainfall considerably. For the 15 runs considered, overall discrepancy between actual and measured rain is reduced to less than 1 per cent with a standard error of 0·97 mm. This model can be easily tested in the ?eld by comparing rainfall depths of different sized gauges. With the adjustment factor they should all give very similar values. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
8.
The variability of rainfall in space and time is an essential driver of many processes in nature but little is known about its extent on the sub‐kilometre scale, despite many agricultural and environmental experiments on this scale. A network of 13 tipping‐bucket rain gauges was operated on a 1·4 km2 test site in southern Germany for four years to quantify spatial trends in rainfall depth, intensity, erosivity, and predicted runoff. The random measuring error ranged from 10% to 0·1% in case of 1 mm and 100 mm rainfall, respectively. The wind effects could be well described by the mean slope of the horizon at the stations. Except for one station, which was excluded from further analysis, the relative differences due to wind were in maximum ±5%. Gradients in rainfall depth representing the 1‐km2 scale derived by linear regressions were much larger and ranged from 1·0 to 15·7 mm km?1 with a mean of 4·2 mm km?1 (median 3·3 mm km?1). They mainly developed during short bursts of rain and thus gradients were even larger for rain intensities and caused a variation in rain erosivity of up to 255% for an individual event. The trends did not have a single primary direction and thus level out on the long term, but for short‐time periods or for single events the assumption of spatially uniform rainfall is invalid on the sub‐kilometre scale. The strength of the spatial trend increased with rain intensity. This has important implications for any hydrological or geomorphologic process sensitive to maximum rain intensities, especially when focusing on large, rare events. These sub‐kilometre scale differences are hence highly relevant for environmental processes acting on short‐time scales like flooding or erosion. They should be considered during establishing, validating and application of any event‐based runoff or erosion model. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
9.
Low tide rainfall may represent an important but little studied process affecting sediment fluxes on intertidal mudflats. In this study, we simulated rainfall events on an intertidal mudflat (median grain size=18.4 μm) of low slope (1 in 300) then quantified effects on sediment erodibility. Treatments consisted of a high (4.1 mm min−1 for 6 min) and low (0.36 mm min−1 for 60 min) rain intensity, chosen to match naturally occurring events and experiments were conducted seasonally (May and August) to encompass variations in ambient sediment stability. Changes in bed elevation due to rainfall were estimated using marked rods and sediment erodibility parameters (mass of sediment eroded at a flow velocity of 0.3 m s−1 (ME-30, g m−2) and critical erosion velocity (Ucrit, m s−1)) were determined in annular flumes (bed area=0.17 m2). Ambient/control sediment erodibility in May (ME-30=211 g m−2, Ucrit=0.18 m s−1) was higher than in August (ME-30=30 g m−2, Ucrit=0.26 m s−1) and was correlated with changes in biological activity. In May, surface sediment was influenced by high densities of the bioturbating snail Hydrobia ulvae (1736 ind. m−2) and low biomass of the sediment stabilising microphytobenthos (5.7 μg chlorophyll a cm−2). In contrast, in August H. ulvae densities were low (52 ind. m−2) and microphytobenthic biomass higher (9.2 μg chlorophyll a cm−2). The high rain treatment caused a decrease in bed elevation of between 1.5 mm (May) and 4.4 mm (August) and significantly reduced sediment organic content and microphytobenthic biomass. Rainfall increased sediment erodibility; compared to ambient sediments ME-30 increased by a factor of 1.4× in May and 8.8× in August and caused a 10–30% decline in Ucrit. The seasonal difference in treatment effect was due to the change in ambient sediment stability. The low rain treatment in August had no effect on bed elevation, microphytobenthic biomass or sediment erodibility. In May, the same treatment caused a reduction in bed elevation (0.5 mm) and microphytobenthic biomass but counter-intuitively, a decrease in sediment erodibility (ME-30 was reduced by 40%, Ucrit increased by 5%) compared to controls. We attribute this result to removal by rainfall of easily eroded surface flocs and biogenic roughness which resulted in an underlying sediment with a smoother surface and greater resistant to erosion. Results suggest that high intensity rain events may destabilise intertidal sediments making them more susceptible to erosion by returning tidal currents and that the sediment eroded during such events may represent a considerable fraction (up to 25%) of the seasonal variation in shore elevation. The impact of natural rain events are likely to vary considerably due to variations in droplet size, intensity and duration and the interaction with ambient sediment stability. 相似文献
10.
Effects of rainfall and slope on runoff,soil erosion and rill development: an experimental study using two loess soils 总被引：3，自引：0，他引：3 
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下载免费PDF全文 Runoff generation and soil loss from slopes have been studied for decades, but the relationships among runoff, soil loss and rill development are still not well understood. In this paper, rainfall simulation experiments were conducted in two neighbouring plots (scale: 1 m by 5 m) with four varying slopes (17.6%, 26.8%, 36.4% and 46.6%) and two rainfall intensities (90 and 120 mm h?1) using two loess soils. Data on rill development were extracted from the digital elevation models by means of photogrammetry. The effects of rainfall intensity and slope gradient on runoff, soil loss and rill development were different for the two soils. The runoff and soil loss from the Anthrosol surface were generally higher than those from the Calcaric Cambisol surface. Higher rainfall intensity produced less runoff and more sediment for almost each treatment. With increasing slope gradient, the values of cumulative runoff and soil loss peaked, except for the treatments with 90 mm h?1 rainfall on the slopes with Anthrosol. With rainfall duration, runoff discharge decreased for Anthrosol and increased for Calcaric Cambisol for almost all the treatments. For both soils, sediment concentration was very high at the onset of rainfall and decreased quickly. Almost all the sediment concentrations increased on the 17.6% and 26.8% slopes and peaked on the 36.4% and 46.6% slopes. Sediment concentrations were higher on the Anthrosol slopes than on the Calcaric Cambisol slopes. At 90 mm h?1 rainfall intensity, increasingly denser rills appeared on the Anthrosol slope as the slope gradient increased, while only steep slopes (36.4% and 46.6%) developed rills for the Calcaric Cambisol soil. The contributions of rill erosion ranged from 36% to 62% of the cumulative soil losses for Anthrosol, while the maximum contribution of rill erosion to the cumulative soil loss was only 37.9% for Calcaric Cambisol. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
11.
Assessment of the impact of different vegetation patterns on soil erosion processes on semiarid loess slopes 总被引：6，自引：0，他引：6 下载免费PDF全文
下载免费PDF全文 Tianjiao Feng Wei Wei Liding Chen Jesús Rodrigo‐Comino Chen Die Xinran Feng Kemeng Ren Eric C. Brevik Yang Yu 《地球表面变化过程与地形》2018,43(9):1860-1870
Soil erosion hinders the recovery and development of ecosystems in semiarid regions. Rainstorms, coupled with the absence of vegetation and improper land management, are important causes of soil erosion in such areas. Greater effort should be made to quantify the initial erosion processes and try to find better solutions for soil and water conservation. In this research, 54 rainfall simulations were performed to assess the impacts of vegetation patterns on soil erosion in a semiarid area of the Loess Plateau, China. Three rainfall intensities (15 mm h‐1, 30 mm h‐1 and 60 mm h‐1) and six vegetation patterns (arbors‐shrubs‐grass ‐A‐S‐G‐, arbors‐grass‐shrubs ‐A‐G‐S‐, shrubs‐arbors‐grass ‐S‐A‐G‐, shrubs‐grass‐arbors ‐S‐G‐A‐, grass‐shrubs‐arbors ‐G‐S‐A‐ and grass‐arbors‐shrubs ‐G‐A‐S‐) were examined at different slope positions (summits, backslopes and footslopes) in the plots (33.3%, 33.3%, 33.3%), respectively. Results showed that the response of soil erosion to rainfall intensity differed under different vegetation patterns. On average, increasing rainfall intensity by 2 to 4 times induced increases of 3.1 to 12.5 times in total runoff and 6.9 to 46.4 times in total sediment yield, respectively. Moreover, if total biomass was held constant across the slope, the patterns of A‐G‐S and A‐S‐G (planting arbor at the summit position) had the highest runoff (18.34 L m‐2 h‐1) and soil losses (197.98 g m‐2 h‐1), while S‐A‐G had the lowest runoff (5.51 L m‐2 h‐1) and soil loss (21.77 g m‐2 h‐1). As indicated by redundancy analysis (RDA) and Pearson correlation results, a greater volume of vegetation located on the back‐ and footslopes acted as effective buffers to prevent runoff generation and sediment yield. Our findings indicated that adjusting vegetation position along slopes can be a crucial tool to control water erosion and benefit ecosystem restoration on the Loess Plateau and other similar regions of the world. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
12.
Effects of rainfall intensity and slope gradient on the application of vetiver grass mulch in soil and water conservation 总被引：3，自引：1，他引：2
The objective of this study is to investigate the effect of rainfall intensity and slope gradient on the performance ofvetiver grass mulch (VGM) in soil and water conservation.The study involved field ... 相似文献
13.
Derege Tsegaye Meshesha Atsushi Tsunekawa Mitsuru Tsubo Nigussie Haregeweyn Enyew Adgo 《水文科学杂志》2013,58(12):2203-2215
AbstractKnowledge of rainfall characteristics is important for estimating soil erosion in arid areas. We determined basic rainfall characteristics (raindrop size distribution, intensity and kinetic energy), evaluated the erosivity of rainfall events, and established a relationship between rainfall intensity I and volume-specific kinetic energy KEvol for the Central Rift Valley area of the Ethiopian highlands. We collected raindrops on dyed filter paper and calculated KEvol and erosivity values for each rainfall event. For most rainfall intensities the median volume drop diameter (D50) was higher than expected, or reported in most studies. Rainfall intensity in the region was not high, with 8% of rain events exceeding 30 mm h-1. We calculated soil erosion from storm energy and maximum 30-min intensity for soils of different erodibility under conditions of fallow (unprotected soil), steep slope (about 9%) and no cover and management practice on the surface, and determined that 3 MJ mm ha-1 h-1 is the threshold erosivity, while erosivity of >7 MJ mm ha-1 h-1 could cause substantial erosion in all soil types in the area.
Editor Z.W. Kundzewicz; Associate Editor Q. Zhang 相似文献
14.
ABSTRACTKnowledge of rainfall characteristics such as drop-size distribution is essential for the development of erosion-mitigation strategies and models. This research used an optical disdrometer to elucidate the relationships between raindrop-size distribution, median volume drop diameter (D50), kinetic energy and radar reflectivity (dBz) of simulated rainfall of different intensities. The D50 values were higher for the simulated rain than for natural rain at almost all rainfall intensities, perhaps due to variations in rainfall types and the turbulence in natural rain that breaks up large drops. The kinetic energy ranged from 26.67 to 5955.51 J m?2 h ?1, while the median volume drop diameter (D50) was in the range 1.94–7.25 mm, for intensities between 1.5 and 202.6 mm h?1. The relationship between radar reflectivity (Z) and the intensity (R) of the simulated rain was best described by a power law function (Z = aRb), with a and b coefficients in the ranges 162–706 and 0.94–2.46, respectively, throughout the range of rainfall intensities (1.5–202.6 mm h?1). 相似文献
15.
The on- and off-site effects of soil erosion in many environments are well known, but there is still limited understanding of the soil loss fluxes in downstream direction due, among other factors, to scarce and poor quality. A four year study to (i) evaluate water and sediment fluxes at different spatio-temporal scales and (ii) interpret the results in terms of processes involved and the controlling factors, was conducted in Thukela basin, South Africa. Five hierarchically nested catchments; namely microcatchment (0.23 km2), subcatchment (1.20 km2), catchment (9.75 km2), sub-basin (253 km2) and basin (29,038 km2), were used in addition to fifteen (1 m2) microplots and ten (10 m2) plots on five locations within the microcatchment. The results showed 19% decrease of unit-area runoff (q) from 3.1 L m−2 day−1 at microplot to 2.5 L m−2 day−1 at plot scale followed by steeper (56%) decrease at microcatchment scale. The q decreased in downstream direction to very low level (q ≤ 0.26 L m−2 day−1). The changes in q were accompanied by initial 1% increase of soil loss (SL) from 18.8 g m−2 day−1 at microplot to 19.1 g m−2 day−1 at plot scale. The SL also decreased sharply (by 39 fold) to 0.50 g m−2 day−1 at microcatchment scale, followed by further decrease in downstream direction. The decrease of q with spatial scale was attributed to infiltration losses, while initial increase of SL signified greater competence of sheet than splash erosion. The decrease of SL beyond the plot scale was attributed to redistribution of the soil on the hillslope and deposition on the stream channel upstream of the microcatchment outlet. Therefore, erosion control strategies focussing on the recovery of vegetation on the slope and stabilisation of gullies are recommended. 相似文献
16.
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
17.
Comparing grain size distribution of sediment and original soil under raindrop detachment and raindrop-induced and flow transport mechanism 总被引：3，自引：0，他引：3
The grain size distribution (GSD) of sediment in comparison with the original soil GSD is discussed under different slopes (5, 15 and 25%) and rainfall intensities (30, 60 and 90 mm h–1 with respective duration of 30, 15 and 10 min) but identical runoff (15 mm). The sediment quantification was carried out by raindrop-induced flow transport (RIFT) or/and transport by flow (FT) using a rainfall simulator and a 6 × 1 m2 erosion plot and a silt loam. The results show a high degree of enrichment for size classes of 2–4 and 4–8 μm and a high degree of depletion for size classes of >63 μm under different slopes and rainfall intensities. In addition, the results show that the experimental enrichment ratio (ER) for particle size <16 μm under different slopes and rainfall intensities was greater than 1, while the ER for particle size >32 μm was less than 1. 相似文献
18.
Water erosion on hillslopes is a worldwide environmental problem, which is a rainfall‐induced process, especially extreme rainfall. The great intensity of extreme rainfall strongly enhances the power of overland flow to detach soil and transport sediment. Plant litter is one of the most important constituents of ecosystems that often covers the soil surface and can be incorporated into topsoil. However, little attention has been paid to its effect on flow hydraulics owing to the veiled nature. This study aimed to examine the effects of incorporated litter on the hydraulic properties under extreme rainfall condition. To reach this goal, six litter rates of 0, 0.05, 0.10, 0.20, 0.35, and 0.50 kg m?2 and four litter types collected from deciduous trees, coniferous trees, shrubs, and herbs were incorporated into topsoil. Then, simulated rainfall experiments were performed on five slope gradients (5°, 10°, 15°, 20°, and 25°) with an extreme rainfall intensity of 80 mm h?1. The results showed that Froude number and flow velocity of the overland flow decreased, whereas flow resistance increased exponentially with litter incorporation rate. Litter type had an influence on flow hydraulics, which can mainly be attributed to the variations in surface coverage of the exposed litter and the litter morphology. Flow velocity and Darcy–Weisbach coefficient increased markedly with slope gradient. However, the variation of slope gradient did not modify the relationships between flow hydraulics and incorporated litter rate. The random roughness, resulting from heterogeneous erosion due to the uneven protection of surface exposed litter, increased linearly with litter incorporated rate. As rainfall proceeded, flow hydraulics varied with incorporated litter rate and slope gradient complicatedly due to the increases in flow rate and coverage of the exposed litter and the modification of soil surface roughness. 相似文献
19.
Abstract Soil erosion vulnerability and extreme rainfall characteristics over the Mediterranean semi-arid region of Tunisia are crucial input for estimation of siltation rate in artificial reservoirs. A comprehensive high-resolution database on erosive rainfall, together with siltation records for 28 small reservoirs, were analysed for this region, the Tunisian Dorsal (the easternmost part of the Atlas Mountains). The general life-span of these reservoirs is only about 14 years. Depending on the soil degradation in the different catchments, the corresponding reservoirs display a wide range of soil erosion rates. The average soil loss was 14.5 t ha?1 year?1 but some catchments display values of up to 36.4 t ha?1 year?1. The maximum 15-min duration rainfall intensity was used to determine the spatial distribution of rainfall erosivity. The northwestern parts of the Tunisian Dorsal display the most extreme rainfall erosivity. Spatial erosion patterns are to some extent similar; however, they vary greatly according to their location in the “soil degradation cycle”. This cycle determines the soil particle delivery potential of the catchment. In general, the northwestern parts of the Dorsal display modest soil erosion patterns due to the already severely degraded soil structure. Here, the soil surface is often the original bedrock. However, the greatest soil erosion occurs in the mid-eastern parts of the Dorsal, which represents the “degradation front”. The latter corresponds to the area with highest erosion, which is continuously progressing westward in the Dorsal. The large variation between the erosive rainfall events and the annual soil loss rates was explained by two important factors. The first relates to the soil degradation cycle. The second factor corresponds to the degradation front with the highest soil loss rates. At present this front is located at 300 m altitude and appears to be moving along an 80-km westward path starting from the east coast. A better understanding of the above can be used to better manage soils and soil covers in the Tunisian Dorsal area and, eventually, to decrease the soil erosion and reservoir siltation risk. Citation Jebari, S., Berndtsson, R., Bahri, A. & Boufaroua, M. (2010) Spatial soil loss risk and reservoir siltation in semi-arid Tunisia. Hydrol. Sci. J. 55(1), 121–137. 相似文献
20.
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