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1.
An inexpensive, mobile field rainfall simulator and runoff plot frame were developed for use on hillside vineyards. The simulator framework and components were lightweight, readily available and easily manageable such that they can be handled by one person during transport, set–up and operation. The vineyard rainfall simulator was simpler than many of the machines in recent use for similar studies, yet offered equal or improved performance for small‐plot studies. The system developed consistent sized 2·58 mm raindrops at intensities ranging from 20 to 90 mm/h. The average distribution uniformity coefficient at an intensity of 60 mm/h was 91·7%, with a deviation of only 2·2%. This coefficient was similar to the range reported for a more complex rotating disk simulator, and was notably greater than that obtained for other similar devices. The system water capacity of 40 l allowed for 1‐h storm durations at 60 mm/h, usually sufficient time for commencement of erosion and runoff. The runoff plot frame was designed to be quickly installed, and to discourage sediment deposition in the routing of runoff to collect containers. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

2.
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   

3.
Investigating the causes of soil erosion is difficult in natural conditions owing to the presence of other factors. Without simplifying the experimental conditions, studying soil behavior with its numerous parameters while considering factors such as vegetation cover, topography, and rainfall is difficult and in most conditions impossible. The application of simulation approaches is therefore necessary to simplify the prototype. In this research, the effects of physical soil factors such as texture and antecedent soil moisture, along with land slope and vegetation cover were evaluated in the Taleghan watershed, Iran, using a rainfall simulator and soil erosion plots. For this purpose, a 89 × 120 cm rainfall simulator producing 24.5 and 32 mm/h rainfall intensities of 30 min duration, as a common condition of the study area, was used at 144 locations over soil erosion plots with dimensions of 95 × 125 cm. Plots had slope classes of 12-20 and 20-30 %, different soil textures, different antecedent soil moistures, and medium to poor vegetation cover conditions. It was found that for 24.5 and 32 mm/h rainfall intensities, the sediment yield had high correlations of-0.771 and -0.796 with vegetation cover and slight correlations of 0.045 and 0.029 with land slope respectively. Regression equations for predicting the sediment yield were also developed for different conditions.  相似文献   

4.
Evaluating the benefits of sediment and runoff reduction in different vegetation types is essential for studying the mechanisms of soil and water conservation on the Loess Plateau.The experiment was conducted in shrub-grass plots with nine levels of mixed vegetation coverage from 0%to 70%,three slopes(10,15,and 20)and two rainfall intensities(1.0 and 2.5 mm/min).The results showed that the vegetation coverage and slope gradient significantly affect runoff and sediment yield.Shrub-grass vegetation coverage had a significant effect on the runoff start-time,runoff flow velocity,runoff rate,and soil erosion rate on hillslopes.Mixed vegetation coverage could effectively delay the runoff starttime and decrease the runoff flow velocity.However,the effects of the slope gradient on runoff and sediment yield are opposite to those of vegetation coverage.Shrub-grass vegetation coverage could effectively increase runoff and sediment yield reduction benefits,while their benefits were affected by the rainfall intensity.At the 1.0 mm/min rainfall intensity,the reduction in the sediment production rate was greater than that under the 2.5 mm/min intensity.However,when the shrub-grass vegetation coverage exceeded 42%,the runoff reduction benefit was more obvious at higher rainfall intensities.The cumulative sediment yield increased with increasing cumulative runoff,and the rate of increase in the cumulative runoff was greater than that of the cumulative sediment yield with increasing of shrub-grass vegetation coverage.Moreover,there was a power function relationship between cumulative sediment yield and cumulative runoff yield(P<0.05).Our paper is expected to provide a good reference on the ecological environment and vegetation construction on the Loess Plateau.  相似文献   

5.
Effects of rainfall patterns on runoff and rainfall-induced erosion   总被引：3，自引：0，他引：3  
Rainfall-induced erosion involves the detachment of soil particles by raindrop impact and their transport by the combined action of the shallow surface runoff and raindrop impact.Although temporal variation in rainfall intensity(pattern)during natural rainstorms is a common phenomenon,the available information is inadequate to understand its effects on runoff and rainfall-induced erosion processes.To address this issue,four simulated rainfall patterns(constant,increasing,decreasing,and increasing-decreasing)with the same total kinetic energy were designed.Two soil types(sandy and sandy loam)were subjected to simulated rainfall using 15 cm×30 cm long detachment trays under infiltration conditions.For each simulation,runoff and sediment concentration were sampled at regular intervals.No obvious difference was observed in runoff across the two soil types,but there were significant differences in soil losses among the different rainfall patterns and stages.For varying-intensity rainfall patterns,the dominant sediment transport mechanism was not only influenced by raindrop detachment but also was affected by raindrop-induced shallow flow transport.Moreover,the efficiency of equations that predict the interrill erosion rate increased when the integrated raindrop impact and surface runoff rate were applied.Although the processes of interrill erosion are complex,the findings in this study may provide useful insight for developing models that predict the effects of rainfall pattern on runoff and erosion.  相似文献   

6.
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   

7.
Rainfall was simulated on unconfined plots on regolith in debris flow source areas using a portable simulator. In total, 351 simulations were carried out on steep slopes (27–54°) with rainfall intensities of 28–291 mm/h. From these rainfall simulations the infiltration parameters sorptivity (S) and steady-state infiltration capacity (K) of the regolith, and a threshold for the occurrence of micro-scale mass movements, were obtained. Two evaluation methods were used to obtain the infiltration parameters K and S. The ‘infiltration envelope’ method uses rainfall intensity and time to ponding from multiple tests and fits an infiltration envelope through the data from which K and S can be obtained. The ‘constant runoff’ method uses rainfall intensity and overland flow intensity to calculate K, after which S can be calculated in several ways by using time to ponding. The constant runoff method produced K values of 16.6–128 mm/h, which usually show a log-normal distribution. K values depend on the regolith parent material and rainfall intensity. Using this method, S values are 0.088–0.381 cm/min1/2. The infiltration envelope method produced K values of 9.8–131 mm/h and S values of 0.14–0.32 cm/min1/2. It can be argued that both methods overestimate K as well as S, but quantitative relations between measured/calculated and actual values of K and S have not yet been obtained. At high rainfall intensities, typically 100 mm/h or more, micro-scale mass movements sometimes occur. A lower threshold curve for the occurrence of these micro-scale mass movements has been constructed. It is a function of both slope angle and rainfall intensity. The micro-scale mass movements could play an important part in the initiation of debris flows in the study area, possibly by delivering sediment to overland flow. On the very steep slopes, the sediment-rich overland flow can easily mobilize coarse material.  相似文献   

8.
Automated rainfall simulator for variable rainfall on urban green areas   总被引：1，自引：0，他引：1  
Rainfall simulators can enhance our understanding of the hydrologic processes affecting the total runoff to urban drainage systems. This knowledge can be used to improve urban drainage designs. In this study, a rainfall simulator is developed to simulate rainfall on urban green surfaces. The rainfall simulator is controlled by a microcomputer programmed to replicate the temporal variations in rainfall intensity of both historical and synthetic rainfall events with constant rainfall intensity on an area of 1 m2. The performance of the rainfall simulator is tested under laboratory conditions with regard to spatial uniformity of the rainfall, the kinetic energy of the raindrops, and the ability to replicate historical and synthetic rainfall events with temporally varying intensity. The rainfall simulator is applied in the field to evaluate its functionality under field conditions and the influence of wind on simulated rainfall. Finally, a field study is carried out on the relationship between runoff, soil volumetric water content, and surface slope. Performance and field tests show that the simulated rainfall has a uniform spatial distribution, whereas the kinetic energy of the raindrops is slightly higher than that of other comparable rainfall simulators. The rainfall simulator performs best in low wind speed conditions. The simulator performs well in replicating historical and synthetic rainfall events by matching both intensity variations and accumulated rainfall depth. The field study shows good correlation between rainfall, runoff, infiltration, soil water content, and surface slope.  相似文献   

9.
A series of large rainfall simulator experiments was conducted in 2002 and 2003 on a small plot located in an experimental catchment in the North Island of New Zealand. These experiments measured both runoff and sediment transport under carefully controlled conditions. A physically based hydrological modelling system (SHETRAN) was then applied to reproduce the observed hydrographs and sedigraphs. SHETRAN uses physically based equations to represent flow and sediment transport, and two erodibility coefficients to model detachment of soil particles by raindrop erosion and overland flow erosion. The rate of raindrop erosion also depended on the amount of bare ground under the simulator; this was estimated before each experiment. These erodibility coefficients were calibrated systematically for summer and winter experiments separately, and lower values were obtained for the summer experiments. Earlier studies using small rainfall simulators in the vicinity of the plot also found the soil to be less erodible in summer and autumn. Limited validation of model parameters was carried out using results from a series of autumn experiments. The modelled suspended sediment load was also sensitive to parameters controlling the generation of runoff from the rainfall simulator plot; therefore, we found that accurate runoff predictions were important for the sediment predictions, especially from the experiments where the pasture cover was good and overland flow erosion was the dominant mechanism. The rainfall simulator experiments showed that the mass of suspended sediment increased post‐grazing, and according to the model this was due to raindrop detachment. The results indicated that grazing cattle or sheep on steeply sloping hill‐country paddocks should be carefully managed, especially in winter, to limit the transport of suspended sediment into watercourses. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

10.
Laminar sheetflows, transporting sediment at their capacity rates, both with and without rainfall disturbance, were investigated. Values of flow depth and relative submergence were very small. In the flows without rainfall, measured velocities exceeded the predictions of the smooth-surface, clear-water laminar model by an average of 12 per cent. Reduced flow resistance due to high sediment concentrations may explain this result. Velocities in the rainfall-disturbed flows were not significantly different from the predictions of the smooth-surface, clear-water model, and the velocity reduction due to rainfall was about 12 per cent. Although the uniformity of rainfall intensity under the single-nozzle rainfall simulator is high, variation of momentum and kinetic energy fluxes along the 1-5 m long flume was significant. The rainfall angle of incidence was highly correlated with deviations from expected flow velocities in the upper and lower sections of the flume.  相似文献   

11.
A small portable rainfall simulator is described which is inexpensive to construct and use and which requires relatively little water. Although drops are produced by drop-formers a satisfactory drop-size distribution is obtained by allowing the drops to break-up by falling onto a 3 mm wire mesh. The kinetic energy of the simulated rain is lower than that of natural rainfall because of the low fall height. Characteristics of the simulated rain are described and the use of the simulator briefly illustrated by results obtained from forested areas in Luxembourg.  相似文献   

12.
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   

13.
Agrichemical transport to coastal waters may have adverse ecological impact. This work examined atrazine fate and transport in a field adjacent to Puerto Rico’s Jobos Bay National Estuarine Research Reserve. The herbicide’s use was linked to residue detection in shallow groundwater and movement toward the estuary; however, data indicated that transport via this pathway was small. In contrast, surface runoff as tropical storm systems moved through the area appeared to have high potential for atrazine transport. In this case, transport to the estuary was limited by runoff event timing relative to atrazine application and very rapid atrazine dissipation (DT50 = 1–3 days) in field soil. Soil incubation studies showed that accelerated degradation conditions had developed in the field due to repeated atrazine treatment. To improve weed management, atrazine replacement with other herbicide(s) is recommended. Use of products that have greater soil persistence may increase runoff risk.  相似文献   

14.
Reservoir sedimentation resulting fromwater erosion is an important environmental issue inmany countries where storage of water is crucial for economic and agricultural development.Therefore,this paper reports results from analysis of the soil hydrological response,i.e.soil water erosion,to simulated rainfall resulting in sediment accumulation at the reservoir of Ekbatan Dam(Hamedan province,Iran).Also,another objective of this study was to simulate the future trends in reservoir sedimentation(soil loss rate;SLR)from indoor rainfall simulator data by multiple linear regression(MLR)and Artificial Neural Networks(ANNs).For this research,three sampling points with different types of soils were chosen including clayey sand soil(SC-SM),silty soil(ML),and clayey soil(CL).The input parameters were slope gradient(sin θ),soil type(St),water content(w),dry density(γd),shear strength(τ),unconfined compressive strength(qu),permeability(k),and California bearing ratio(CBR).Using MLR and ANN methods,7 models were developed with 2 constant predictors(i.e.sin θ and St)and 6 free predictors which were added in each step one by one.Among MLR models,model 5 with St,sin θ,γd,τ,w,and qu as input parameters was statistically significant.Among ANN models,model 4 with St,sin θ,?d,τ,and w as input parameters,9 nodes,and 1 hidden layer was statistically significant.The root mean square error(RMSE),mean error(ME),and correlation coefficient(R)values were 1.433 kg/m^2 h,0.0195 kg/m^2 h,and 0.698 for the MLRmodel and 0.38 kg/m^2 h,0.151 kg/m^2 h,and 0.98 for the ANN model,respectively.These results show that the ANN model could better predict the SLR in comparison to the MLR model.The results also demonstrate that shear strength,among the strength parameters,had a greater impact on the SLR than compressive strengths(qu and CBR).Last but not the least,the reservoir sedimentationwas estimated for all methods and compared with the observed data.The results indicate that the ANN model is more appropriate for forecasting/simulating the sediment yield for a small watershed.  相似文献   

15.
Improved knowledge of the effects of grass and shrub cover in overland flow can provide valuable information for soil and water conservation programs.Laboratory simulated rainfall studies were conducted to determine effects of grass and shrub on runoff and soil loss and to ascertain the relationship between the rate of soil loss and the unit stream power of runoff for a 20°slope subjected to rainfall intensities of 45,87,and 127 mm/h.The results indicated that the average runoff rates ranged from 4.2 to 73.1 mm/h for grass plots and from 9.3 to 58.2 mm/h for shrub plots.Runoff rates from shrub plots were less than those from grass plots for all but the 45 mm/h rainfall intensity regime. Average soil loss rates varied from 5.7 to 120.3 g/min.m~2 for grass plots and from 5.6 to 84.4 g/min.m~2 for shrub plots.Soil loss rates from shrub plots were generally lower than those from grass plots.Runoff and soil loss were strongly influenced by soil surface conditions due to the formation of erosion pits and rills.The rate of soil loss increased linearly with the unit stream power of runoff on both grass and shrub plots.Critical unit stream power values were 0.0127 m/s for grass plots and 0.0169 m/s for shrub plots.Shrub plots showed a greater stability to resist soil detachment and transport by surface flow than grass plots.  相似文献   

16.
Two rainfall simulators of different plot sizes were used to test whether sediment in runoff could be used to measure aggregate breakdown in the surface of a cracking clay soil under rain. Plots were prepared with either levelled or furrowed surfaces. Samples of the soil surface under rain were taken from furrow ridges or levelled surfaces, and from areas of deposited sediment. These were compared with samples of sediment in runoff taken at the same times. On both furrowed and levelled plot surfaces and for both simulators, aggregate sizes were significantly finer in sediment in runoff than in samples of the soil surface taken with a spatula. No significant differences in surface aggregate size distributions were found between rainfall simulators, or between furrowed and levelled plot surfaces. Regression lines fitted to the data on size distributions of sediment or of aggregates in the soil surface showed no significant changes through time. The fitted lines showed sediment in runoff to be still significantly finer than aggregates in the soil surface after 50 min rain at 95 mm h?1, except for levelled plots under the rotating disc rainfall simulator, where extreme variability of data meant that even relatively large differences were not statistically significant. Size distributions of deposited sediment were similar to those of the surface of adjacent furrow ridges exposed to raindrop impact. This provides evidence that sampling the soil surface with a spatula gives a representative sample of the material available for rain-flow transport.  相似文献   

17.
This study examines the size characteristics of sediment removed from a semiarid hillslope by interrill overland flow. Rainfall simulation experiments were conducted on a runoff plot 18 m wide and 35 m long established on a piedmont hillslope in southern Arizona. The top of the plot coincided with the hillslope divide, and its outlet was located within a shallow rill. Samples of runoff were obtained from two cross-sections located in the interrill portion of the plot upslope of the rill and from a calibrated flume through which was directed interrill overland flow reaching the bottom of the plot. Analyses of sediment contained in these samples showed that sediment in interrill flow is finer than the matrix soil. The fineness of the interrill sediment compared to the matrix soil appears to be due to the inability of interrill overland flow to transport the coarser fraction of the sediment supplied to it by raindrop detachment. This finding implies that the rate of soil erosion in interrill areas is not. as is commonly supposed, limited by the rate at which raindrops can detach sediment but by the rate at which they detach sediment of a size that the overland flow is competent to transport. The relative fineness of sediment eroded from this hillslope is consistent with other evidence for the recent evolution of shrub-covered hillslopes in southern Arizona.  相似文献   

18.
This paper presents an erosion model, ARMOUR, which simulates time‐varying runoff, erosion, deposition and surface armour evolution down a hillslope either as a result of a single erosion event or as the cumulative impact of many events over periods up to decades. ARMOUR simulates sediment transport for both cohesive and non‐cohesive soil and dynamically differentiates between ‘transport‐limited’ and ‘source‐limited’ processes. A variety of feasible processes for entrainment of different size classes can be modelled and evaluated against data. The generalized likelihood of uncertainty estimation (GLUE) technique was used to calibrate and validate ARMOUR using data collected during rainfall simulator experiments at two contrasting sites: (1) non‐cohesive stony sediments at Ranger Uranium Mine, Northern Territory, Australia; and (2) cohesive silty sediments at Northparkes Gold Mine, NSW, Australia. The spatial and temporal variations of model predictions within the individual runoff events showed that some entrainment processes could not model the spikes in concentration and subsequent depletion, while the hiding model of Andrews and Parker best simulated the concentration trends for both calibrated and independent runoff events. ARMOUR also successfully captured the coarsening of the surface material, though small, over the duration of the rainfall simulator trials. This was driven by the depletion of the finest size class of the soil. For a constant discharge, ARMOUR simulated higher sediment flux at the start of the storm with the sediment flux and concentration diminishing with time. For natural rainfall a power law relationship between sediment flux and discharge was observed. The calibration exercise showed that sediment concentration and discharge alone are insufficient to calibrate all aspects of the physics, in particular the armour depth. This appears to be because the armouring during the short duration events is driven by depletion of the finest classes of the sediments (diameters less then 62·5 mm), which are not normally measured. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

19.
Based on observations of runoff plots and field investigations of gully cross-sections, impacts of various soil and water conservation measures on runoff and sediment yield are analyzed for different rainfall conditions. The results show that antecedent rainfall and rainfall intensity are the main factors affecting the runoff and soil erosion processes. Rainfall events with antecedent rainfall can produce high runoff and sediment yield. Large differences in the characteristics of two rainfall events will result in greater variations of total runoff and sediment yield from the same runoff plot. Under the same soil control measure and rainfall condition, soil and water conservation measures can reduce the impacts of antecedent rainfall and rainfall intensity on runoff and soil erosion. Among various measures, level terrace seems to be the greatest for soil conservation purposes. Combining with engineering measures,Vegetation measures is also effective in controlling runoff and soil erosion. In the initial stage of vegetation enclosure measures, engineering measure is necessary to improve the environment for ecological recovery. Gully head protection can control gully erosion effectively, but the effectiveness of gully head protection would be reduced when rainfall intensity increases. Therefore, the design of a gully head protection structure must be based on local hydrological conditions.  相似文献   

20.
The Qinghai–Tibet Plateau has a vast area of approximately 70×104 km2 of alpine meadow under the impacts of soil freezing and thawing, thereby inducing intensive water erosion. Quantifying the rainfall erosion process of partially thawed soil provides the basis for model simulation of soil erosion on cold-region hillslopes. In this study, we conducted a laboratory experiment on rainfall-induced erosion of partially thawed soil slope under four slope gradients (5, 10, 15, and 20°), three rainfall intensities (30, 60, and 90 mm h−1), and three thawed soil depths (1, 2, and 10 cm). The results indicated that shallow thawed soil depth aggravated soil erosion of partially thawed soil slopes under low hydrodynamic conditions (rainfall intensity of 30 mm h−1 and slope gradient ≤ 15°), whereas it inhibited erosion under high hydrodynamic conditions (rainfall intensity ≥ 60 mm h−1 or slope gradient > 15°). Soil erosion was controlled by the thawed soil depth and runoff hydrodynamic conditions. When the sediment supply was sufficient, the shallow thawed soil depth had a higher erosion potential and a larger sediment concentration. On the contrary, when the sediment supply was insufficient, the shallow thawed soil depth resulted in lower sediment erosion and a smaller sediment concentration. The hydrodynamic runoff conditions determined whether the sediment supply was sufficient. We propose a model to predict sediment delivery under different slope gradients, rainfall intensities, and thawed soil depths. The model, with a Nash–Sutcliffe efficiency of 0.95, accurately predicted the sediment delivery under different conditions, which was helpful for quantification of the complex feedback of sediment delivery to the factors influencing rainfall erosion of partially thawed soil. This study provides valuable insights into the rainfall erosion mechanism of partially thawed soil slopes in the Qinghai–Tibet Plateau and provides a basis for further studies on soil erosion under different hydrodynamic conditions.  相似文献   

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