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1.
This study aimed to investigate the changing characteristics of microrelief of purple soil and its erosional response during successive stages of water erosion, including splash erosion, sheet erosion, and rill erosion. Methods employed included a rainfall simulator and the use of a laser scanner to generate a digital elevation model. Three artificial tillage practices, including conventional tillage (CT), artificial digging (AD), and ridge tillage (RT), were used to simulate different microrelief patterns. Eighteen artificial rainfall experiments were conducted using three 2 × 1 m boxes with a rainfall intensity of 1.5 mm min?1 on a 15° slope. The results showed that the soil roughness (SR) index values for the tillage slopes were RT > AD > CT. The combined effects of detachment by raindrop impact and transport by run‐off decreased the SR index, whereas rill erosion increased the SR index during rainfall event. Microtopography and drainage networks have strong multifractal behaviours. The multifractal parameters of microtopography reflect the overall characteristics as well as the characteristics of the local soil surface. Within a certain range of threshold values, higher microrelief causes less soil erosion. However, when the parameters of spatial heterogeneity of microtopography exceed the threshold values, a higher degree of microrelief can increase soil erosion. These results help clarify the effect of microtopography on soil erosion and provide a theoretical foundation to guide future tillage practices on sloping farmland of purple soil. 相似文献
2.
Agricultural use of soils implies tillage and often compaction and therefore influences processes on soil surface and affects infiltration of water into the subsoil. Although many studies on soil surface processes or flow patterns in soils exist, works relating both are rare in literature. We did two tracer experiments with Brilliant Blue FCF on a tilled and compacted plot and a non‐tilled one to investigate water storage on the soil surface during simulated rainfall and changes of soil microtopography, to analyse the associated flow patterns in the soil and to relate both to tillage and compaction. Our results show that storage was larger on the tilled and compacted plot than on the non‐tilled one. After tillage, transport processes above the plough pan were partly disconnected from those underneath because macropores were disrupted and buried by the tillage operation. However, preferential flow along cracks occurred on both plots and the macropores buried below the tillage pan still functioned as preferential flow paths. Therefore, we conclude that the studied soil is susceptible to deep vertical solute propagation at dry conditions when cracks are open, irrespective of tillage and compaction. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
3.
Sayjro K. Nouwakpo Mark A. Weltz Kenneth C. McGwire Jason C. Williams Al‐Hamdan Osama Colleen H.M. Green 《地球表面变化过程与地形》2017,42(4):681-696
In arid and semi‐arid rangeland environments, an accurate understanding of runoff generation and sediment transport processes is key to developing effective management actions and addressing ecosystem response to changes. Yet, many primary processes (namely sheet and splash and concentrated flow erosion, as well as deposition) are still poorly understood due to a historic lack of measurement techniques capable of parsing total soil loss into these primary processes. Current knowledge gaps can be addressed by combining traditional erosion and runoff measurement techniques with image‐based three‐dimensional (3D) soil surface reconstructions. In this study, data (hydrology, erosion and high‐resolution surface microtopography changes) from rainfall simulation experiments on 24 plots in saline rangelands communities of the Upper Colorado River Basin were used to improve understanding on various sediment transport processes. A series of surface change metrics were developed to quantify and characterize various erosion and transport processes (e.g. plot‐wide versus concentrated flow detachment and deposition) and were related to hydrology and biotic and abiotic land surface characteristics. In general, erosivity controlled detachment and transport processes while factors modulating surface roughness such as vegetation controlled deposition. The extent of the channel network was a positive function of slope, discharge and vegetation. Vegetation may deflect runoff in many flow paths but promoted deposition. From a management perspective, this study suggests that effective runoff soil and salt load reduction strategies should aim to promote deposition of transported sediments rather than reducing detachment which might not be feasible in these resource‐limited environments. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
4.
A simple conceptual hydrological model that explicitly includes the lateral movement of soil water and operates efficiently at the landscape scale is outlined. It is applied to five areas of ecological interest in the UK to provide distributed mean monthly soil moisture on a 50 m grid. As the model's driving variables—daily rainfall and potential evapotranspiration—are assumed constant over each of the tracts of land, the variability in soil moisture is due to different soil types and to topographic effects. Box plots of the mean monthly simulated soil moisture clearly show the spread of values occasioned by modelling the lateral water movement down the hillslope. The general magnitude of the results are compared with published data wherever possible and there is some discussion of the form of the curve used in the model to describe the attenuation of evapotranspiration with decreasing soil moisture. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
5.
Variation in soil saturated hydraulic conductivity along the hillslope of collapsing granite gullies 总被引：2，自引：0，他引：2
Saturated hydraulic conductivity (Ks) affects the soil hydrological process and is influenced by many factors that exhibit strong spatial variations. To accurately measure Ks and its scale, spatial variability and relationship with collapsing gullies, we analysed four double-ring infiltrometer diameters in three soil layers during in situ experiments designed to measure Ks in two typical collapsing gullies (three slope sites) in Tongcheng County of China. The results showed that Ks increased with increasing inner ring diameter, but no significant difference existed between inner diameters of 30 and 40 cm. The Ks in red soil layers was higher than that in sandy soil layers, the transition layers had the lowest values. Ks also varied with slope position, gradually decreasing with distance from the gully head. The suggestion is that the spatial variation in Ks is affected not only by the intrinsic soil properties but also by the interaction with the collapsing gully. 相似文献
6.
2012年8月,在新疆博斯腾湖13个站点进行表层沉积物采集,分析无机碳及其碳、氧稳定同位素的含量和空间分布特征,探讨该湖表层沉积物无机碳(TIC)的空间变化影响因素.结果表明:2012年,博斯腾湖表层沉积物TIC含量平均值为5.5%,变幅为3.8%~9.8%,而δ13Ccarb和δ18Ocarb平均值分别为0.71‰和-4.4‰,范围为-0.23‰~2.27‰和-5.53‰~-2.55‰.从空间来看,湖泊北岸TIC值明显高于南岸,最高值出现在湖泊西北部的黄水沟水域,而河口区和湖心区最低.总体上,博斯腾湖表层沉积物TIC主要是湖泊自生的,其空间分布主要受开都河、黄水沟等入湖河水的影响,导致水体矿化度和营养盐的空间差异,进而影响了碳酸盐的析出与沉淀.另外,湖泊局部的水动力条件也影响TIC的保存与分布.δ13Ccarb与δ18Ocarb的极显著正相关说明近几年博斯腾湖封闭程度较好,尤其是东部大湖区,属于封闭环境碳酸盐沉淀. 相似文献
7.
D. S. L. Lawrence 《地球表面变化过程与地形》1997,22(4):365-382
The hydraulics of overland flow on rough granular surfaces can be modelled and evaluated using the inundation ratio rather than the flow Reynolds number, as the primary dimensionless group determining the flow behaviour. The inundation ratio describes the average degree of submergence of the surface roughness and is used to distinguish three flow regimes representing partially inundated, marginally inundated and well-inundated surfaces. A heuristic physical model for the flow hydraulics in each regime demonstrates that the three states of flow are characterized by very different functional dependencies of frictional resistance on the scaled depth of flow. At partial inundation, flow resistance is associated with the drag force derived from individual roughness and therefore increases with depth and percentage cover. At marginal inundation, the size of the roughness elements relative to the depth of flow controls the degree of vertical mixing in the flow so that frictional resistance tends to decrease very rapidly with increasing depth of flow. Well-inundated flows are described using rough turbulent flow hydraulics previously developed for open channel flows. These flows exhibit a much more gradual decrease in frictional resistance with increasing depth than that observed during marginal inundation. A data set compiled from previously published studies of overland flow hydraulics is used to assess the functional dependence of frictional resistance on inundation ratio over a wide range of flow conditions. The data confirm the non-monotonic dependence predicted by the model and support the differentiation of three flow regimes based on the inundation ratio. Although the percentage cover and the surface slope may be of importance in addition to the inundation ratio in the partially and marginally inundated regimes, the Reynolds number appears to be of significance only in describing well-inundated flows at low to moderate Reynolds numbers. As these latter conditions are quite rare in natural environments, the inundation ratio rather than the Reynolds number should be used as the primary dimensionless group when evaluating the hydraulics of overland flow on rough surfaces. © 1997 by John Wiley & Sons, Ltd. 相似文献
8.
Surface runoff plays an important role in contaminant transport, nutrient loss, soil erosion and peak discharges in streams and rivers. Because it is the result of a variety of complex hydrological processes, estimating surface runoff using physically based hydrological models is challenging. Upscaling of physical soil properties is necessary to cope with the limits of computational power in surface runoff modelling. In flat landscapes, the (micro)topographic surface controls the onset and progression of surface runoff on saturated soils during rain events. Therefore, its proper representation is crucial when attempting to model and predict surface runoff. In this study, the influence of microtopography (centimetre scale) on estimations of maximum depression storage (MDS), random roughness (RR) and the connectivity threshold (CT) is explored. These properties are selected because they often serve as surface runoff indicators in hydrological modelling. To characterize microtopography, a terrestrial laser scanner (TLS) is used to generate a digital terrain model (DTM) of the study site with a horizontal spatial resolution of 5 cm. MDS, RR and CT are then calculated and compared to the values generated from the publicly available Dutch national DTM dataset with a resolution of 50 cm. Our results show considerable differences in MDS, RR and CT when calculated for the different input resolution datasets. Using DTMs that do not sufficiently capture microtopography leads to underestimation of MDS and RR, and to overestimation of CT. Our findings indicate that surface runoff indicators, and thereby the surface runoff response of a saturated surface to rainfall events, are defined at scales smaller than the scales of typically available DTMs. Understanding surface runoff through modelling studies therefore requires a framework that accounts for this lack of information arising from using coarser resolution DTMs. We demonstrate a linear relationship between MDS values generated from the different resolution DTMs. This opens the possibility of using empirical scaling relationships between high- and lower-resolution DTMs to account for microtopography. Repetition of our measurements on similar surfaces would contribute to establishing such empirical scaling relationships. Our results should be seen as indicative of flat landscapes and surfaces where centimetre scale microtopography is relevant. 相似文献
9.
Pingping Zhang 《水文科学杂志》2013,58(1):96-110
AbstractKnowledge of the variability of soil water content (SWC) in space and time plays a key role in hydrological and climatic modelling. However, limited attention has been given to arid regions. The focus of this study was to investigate the spatio-temporal variability of surface soil (0–6 cm) water content and to identify its controlling factors in a region of the Gobi Desert (40 km2). The standard deviation of SWC decreased logarithmically as mean water content decreased, and the coefficient of variation of SWC exhibited a convex upward pattern. The spatial variability of SWC also increased with the size of the investigated area. The spatial dependence of SWC changed over time, with stronger patterns of spatial organization in drier and wetter conditions of soil wetness and stochastic patterns in moderate soil water conditions. The dominant factors regulating the variability of SWC changed from combinations of soil and topographical properties (bulk density, clay content and relative elevation) in wet conditions to combinations of soil and vegetation properties (bulk density, clay content and shrub coverage) in dry conditions. This study has important implications for the assessment of soil quality and the sustainability of land management in arid regions. 相似文献
10.
Soil water is an important limiting factor for restoring alpine meadows on the northern Tibetan Plateau. Field studies of soil‐water content (SWC), however, are rare due to the harsh environment, especially in a mesoscale alpine‐meadow ecosystem. The objective of this study was to assess the spatial variability of SWC and the temporal variation of the spatial variability in a typical alpine meadow using a geostatistical approach. SWC was measured using a neutron probe to a depth of 50 cm at 113 locations on 22 sampling occasions in a 33.5‐hm2 alpine meadow during the 2015 and 2016 growing seasons. Mean SWC in the study plot for the two growing seasons was 18.7, 14.0, 13.9, 14.3, and 14.8% for depths of 10, 20, 30, 40, and 50 cm, respectively, and SWC was significantly larger at 10 cm than at other depths. SWC was negatively correlated with its spatial variability, and the spatial variability was higher when SWC was lower. Thirty‐three sampling locations in this study plot met the requirement of accuracy of the central limit theorem. A Gaussian model was the best fit for SWC semivariance at depths of 10, 20, and 30 cm, and the spatial structural ratio was between 0.997 and 1, indicating a strong spatial dependence of SWC. The sill and range fluctuated temporally, and the nugget and spatial structural ratio did not generally vary with time. The sill was significantly positively correlated with SWC and was initially stable and then tend to increase with SWC. The nugget, range, and spatial structure ratio, however, were not correlated with SWC. These results contribute to our understanding of SWC spatial distribution and variation in alpine meadows and provide basic empirical SWC data for mesoscale model simulations, optimizing sampling strategies and managing meadows on the Tibetan Plateau. 相似文献
11.
Numerous models and risk assessments have been developed in order to estimate soil erosion from agricultural land, with some including estimates of nutrient and contaminant transfer. Many of these models have a slope term as a control over particle transfer, with increased transfer associated with increased slopes. This is based on data collected over a wide range of slopes and using relatively small soil flumes and physical principals, i.e. the role of gravity in splash transport and flow. This study uses laboratory rainfall simulation on a large soil flume to investigate interrill soil erosion of a silt loam under a rainfall intensity of 47 mm h?1 on 3%, 6% and 9% slopes, which are representative of agricultural land in much of northwest Europe. The results show: (1) wide variation in runoff and sediment concentration data from replicate experiments, which indicates the complexities in interrill soil erosion processes; and (2) that at low slopes processes related to surface area connectivity, soil saturation, flow patterns and water depth may dominant over those related to gravity. Consequently, this questions the use of risk assessments and soil erosion models with a dominant slope term when assessing soil erosion from agricultural land at low slopes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
12.
Terracettes are repeating step-like microtopographic features roughly following the contours of hillslopes that are often associated with livestock tracks. These common features in many semi-arid rangelands have been shown to alter soil moisture, slope stability, sediment transport, infiltration rates and coincident vegetation patterns. The spatial extent and distribution of terracettes is currently unknown and therefore their landscape-scale hydrological influence is absent in modelling and land management decision making. When viewed in uncalibrated very-high-resolution satellite imagery, terracettes appear as repetitious parallel lines within a specific frequency range. Here we used the two-dimensional discrete Fourier transform to identify terracettes at three test sites in the Inland Pacific Northwest, USA. We created an automated rule-based classification of terracetted sites based on spatial frequency, orientation, slope angle and land-use class. Results show a detection accuracy of 77% based on an optimized spatial frequencies search window between 0.3 and 0.7 m−1. Terracette orientation did not contribute significantly to detection accuracy because orientations varied ±50° from digital elevation model-derived aspects. We found terracettes occurred predominantly on north-facing slopes at our test sites, although this estimate may be exaggerated by the timing of image capture. We feel that the method developed in this paper provides a way forward to map terracettes at large scales and enable new insights into the functions of terracettes in the landscape. © 2020 John Wiley & Sons, Ltd. 相似文献
13.
Knowledge of soil microtopography and its changes in space and over time is important to the understanding of how tillage influences infiltration, runoff generation and erosion. In this study, the use of a terrestrial laser scanner (TLS) is assessed for its ability to quantify small changes in the soil surface at high spatial resolutions for a relatively large surface area (100 m2). Changes in soil surface morphology during snow cover and melt are driven by frost heave, slaking, pressure exertion by the snowpack and overland flow (erosion and deposition). An attempt is undertaken to link these processes to observed changes at the soil surface. A new algorithm for soil surface roughness is introduced to make optimal use of the raw point cloud. This algorithm is less scale dependent than several commonly used roughness calculations. The results of this study show that TLSs can be used for multitemporal scanning of large surfaces and that small changes in surface elevation and roughness can be detected. Statistical analysis of the observed changes against terrain indices did not yield significant evidence for process differentiation. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. © 2019 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd. 相似文献
14.
Soil moisture is essential for plant growth and terrestrial ecosystems, especially in arid and semi‐arid regions. This study aims to quantify the variation of soil moisture content and its spatial pattern as well as the influencing factors. The experiment is conducted in a small catchment named Yangjuangou in the loess hilly region of China. Soil moisture to a depth of 1 m has been obtained by in situ sampling at 149 sites with different vegetation types before and after the rainy season. Elevation, slope position, slope aspect, slope gradient and vegetation properties are investigated synchronously. With the rainy season coming, soil moisture content increases and then reaches the highest value after the rainy season. Fluctuation range and standard deviation of soil moisture decrease after a 4‐month rainy season. Standard deviation of soil moisture increases with depth before the rainy season; after the rainy season, it decreases within the 0‐ to 40‐cm soil depth but then increases with depths below 40 cm. The stability of the soil moisture pattern at the small catchment scale increases with depth. The geographical position determines the framework of soil moisture pattern. Soil moisture content with different land‐use types is significantly increased after the rainy season, but the variances of land‐use types are significantly different. Landform and land‐use types can explain most of the soil moisture spatial variations. Soil moisture at all sample sites increases after the rainy season, but the spatial patterns of soil moisture are not significantly changed and display temporal stability despite the influence of the rainy season. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
15.
Site‐average values of local gradient, defined as the steepest slope angle measured at a point, are a powerful predictor of long‐term rates of soil loss as measured by erosion pins on the non‐channel floor portions of ten badland study sites in the Karoo area of South Africa. Local gradient may be easily measured using a smartphone clinometer. The successful use of local gradient here is in strong contrast to the previous failure of other site‐specific attributes, including other measures of gradient and relief, to explain between‐site variation in erosion rate on these study sites. Each measurement of local gradient may be thought of as a sample of the site's microtopography. Microrelief is a strong determinant of the emergent patterns of inter‐channel overland flow, and hence of the patterns of inter‐channel erosion by flow. Local gradient changes most rapidly during the initial stages of channel incision. When channels are established, local gradient changes more slowly leading to almost‐parallel retreat of channel sidewalls. A sensitivity analysis suggests that measurements of local gradient are not all equal with regard to prediction of long‐term erosion rate. A greater share of predictive power is contributed by measurements made on very steep or vertical channel side wall areas, and a lesser share is contributed by measurements made on interfluves. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
16.
Mark A. Nearing 《地球表面变化过程与地形》2000,25(9):1035-1043
One of the important methods used to evaluate the effectiveness of soil erosion models is to compare the predictions given by the model to measured data from soil loss collected on plots taken under natural rainfall conditions. While it is recognized that plot data contain natural variability, this factor is not quantitatively considered during such evaluations because our knowledge of natural variability between plots which have the same treatments is very limited. The goal of this study was to analyse sufficient replicated plot data and present methodology to allow the model evaluator to take natural, within‐treatment variability of erosion plots into account when models are tested. A large amount of data from pairs of replicated erosion plots was evaluated and quantified. The basis for the evaluation method presented is that if the difference between the model prediction and a measured plot data value lies within the population of differences between pairs of measured values, then the prediction is considered ‘acceptable’. A model ‘effectiveness’ coefficient was defined for studies undertaken on large numbers of prediction versus measured data comparisons. This method provides a quantitative criterion for taking into account natural variability and uncertainty in measured erosion plot data when those data are used to evaluate erosion models. Published in 2000 by John Wiley & Sons, Ltd. 相似文献
17.
lINTRoDUCTlONMicrotopography,oftenreferredtoassurfaceroughness,isanimportantsurfacecharacteristicthatinvariouswaysaffectssoilerosionprocessesonuplandareas.Theconventionalviewisthatmicrotopographyincreasesthesurfacestoragecapacityandreducesrunoffvelocityofexcessrain(MitchellandJones,1978;Onstad,l984;BroughandJarrett,l992),thusdecreasingtheerosivepowerofrunoffandtheproductionofsediment(Cogo,l983;Hairsineetal.,l992).Fora"fixed"surfacesuchasapavement,themicrotopographyeffectisinvariantduring… 相似文献
18.
针对油气勘探面临的圈闭规模小, 地质沉积相变快等复杂情形, 如果受地震分辨率不足的制约, 可以通过时频分析技术在时间域和频率域上进行精细的地震信号聚焦, 以达到提高识别小型油气目标精度的目的.本文在阐述时频分析技术原理的基础上, 与层序地层学分析有机结合, 确立了湖底扇有利砂体的能量团随频率变化的方向性及其响应强度等时频特征, 揭示了湖底扇砂体由于岩性、物性或孔隙流体性质变化所导致的时频特征的差异.研究结果表明, 以湖底扇频率响应分布特征为前提, 利用时频分析技术将涠洲A湖底扇各朵叶体甜点的瞬时频率变化特征类比能反映湖底扇有利砂体的优势频率变化的规律, 可以定性地预测湖底扇各朵叶储层甜点的岩性组合信息, 从而降低朵叶体甜点岩性解释的多解性, 为有利砂岩的发现及油气开发提供了技术支撑.
相似文献19.
研究了地震地面运动多点激励,即空间变化效应对装有铅芯橡胶支座(Lead Rubber Bearing)的连续梁桥地震反应的影响.首先,利用三角级数法生成了拟合规范反应谱的多点人工地震动时程;然后利用非线性时程分析法数值仿真并比较了某五跨LRB隔震连续梁桥在一致激励、仅考虑地震动行波效应、仅考虑地震动部分相干效应、同时考虑行波和部分相干效应以及同时考虑行波、部分相干和局部场地土效应等七种工况下结构的减震效果.行波效应和部分相干效应对铅芯橡胶支座隔震桥梁影响不大,而局部场地土效应对该类桥梁的地震反应分析影响很大,应该引起重视. 相似文献
20.
The relevance of bypass flow on water flow, solute or pesticide transport is becoming increasingly recognized. Recent investigations proved that soil salinization may be influenced by bypass flow, i.e. the rapid transport of water and solutes via macropores and/or shrinkage cracks to subsoil and groundwater. This paper explores the role of bypass flow in the process of accumulation and leaching of solutes, as well as of sodium, in a Mediterranean cracking soil irrigated with saline/sodic waters. The results of bypass flow experiments performed on undisturbed soil cores showed that leaching of solutes occurred in concomitance with bypass fluxes when a low salinity solution was alternated with a high salinity solution. Exchange of solutes between the incoming solution and the soil matrix occurred during the bypass flow events at the contact surfaces (cracks walls) between the solution and the soil matrix and where cracks terminated in the soil samples. Concomitant exchanges of sodium were indicated by measurements performed in the effluent solution during the bypass flow measurements. The amount of Sodium released from the soil during the bypass flow events, as well as that of the soluble salts leached from the soil, were found to depend on the degree of soil cracking. These results indicated that:
- 1 in management of irrigation in cracking soils, under the occurrence of bypass fluxes, alternating a low salinity/sodicity water with a high salinity/sodicity solution can be effective for preventing salinization and sodification:
- 2 greater efficiency of removal of sodium/soluble salts can be obtained if application of the leaching solution is performed when the soil is at a considerable degree of cracking.