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1.
Infiltration into frozen soil plays an important role in soil freeze–thaw and snowmelt-driven hydrological processes. To better understand the complex thermal energy and water transport mechanisms involved, the influence of antecedent moisture content and macroporosity on infiltration into frozen soil was investigated. Ponded infiltration experiments on frozen macroporous and non-macroporous soil columns revealed that dry macroporous soil produced infiltration rates reaching 103 to 104 mm day−1, two to three orders of magnitude larger than dry non-macroporous soil. Results suggest that rapid infiltration and drainage were a result of preferential flow through initially air-filled macropores. Using recorded flow rates and measured macropore characteristics, calculations indicated that a combination of both saturated flow and unsaturated film flow likely occurred within macropores. Under wet conditions, regardless of the presence of macropores, infiltration was restricted by the slow thawing rate of pore ice, producing infiltration rates of 2.8 to 5.0 mm day−1. Reduced preferential flow under wet conditions was attributed to a combination of soil swelling, due to smectite-rich clay (that reduced macropore volume), and pore ice blockage within macropores. In comparison, dry soil column experiments demonstrated that macropores provided conduits for water and thermal energy to bypass the frozen matrix during infiltration, reducing thaw rates compared with non-macroporous soils. Overall, results showed the dominant control of antecedent moisture content on the initiation, timing, and magnitude of infiltration and flow in frozen macroporous soils, as well as the important role of macropore connectivity. The study provides an important data set that can aid the development of hydrological models that consider the interacting effects of soil freeze–thaw and preferential flow on snowmelt partitioning in cold regions.  相似文献   

2.
Markus Weiler   《Journal of Hydrology》2005,310(1-4):294-315
Simulating infiltration in soils containing macropores still provides unsatisfactory results, as existing models seem not to capture all relevant processes. Recent studies of macropore flow initiation in natural soils containing earthworm channels revealed a distinct flow rate variability in the macropores depending on the initiation process. When macropore flow was initiated at the soil surface, most of the macropores received very little water while a few macropores received a large proportion of the total inflow. In contrast, when macropore flow was initiated from a saturated or nearly saturated soil layer, macropore flow rate variation was much lower. The objective of this study was to develop, evaluate, and test a model, which combines macropore flow variability with several established approaches to model dual permeability soils. We then evaluate the INfiltration–INitiation–INteraction Model (IN3M) to explore the influence of macropore flow variability on infiltration behavior by performing a sensitivity analysis and applying IN3M to sprinkling and dye tracer experiments at three field sites with different macropore and soil matrix properties. The sensitivity analysis showed that the flow variability in macropores reduces interaction between the macropores and the surrounding soil matrix and thus increases bypass flow, especially for surface initiation of macropore flow and at higher rainfall intensities. The model application shows reasonable agreement between IN3M simulations and field data in terms of water balance, water content change, and dye patterns. The influence of macropore flow variability on the hydrological response of the soil was considerable and especially pronounced for soils where initiation occurs at the soil surface. In future, the model could be applied to explore other types of preferential flow and hence to get a generally better understanding of macropore flow.  相似文献   

3.
Earlier modelling studies have shown the difficulty of accurately simulating snowmelt infiltration into frozen soil using the hydraulic model approach. Comparison of model outputs and field measurements have inferred the occurrence of rapid flow even during periods when the soil is still partly frozen. A one-dimensional, physically based soil water and heat model (SOIL) has been complemented with a new two-domain approach option to simulate preferential flow through frozen layers. The ice is assumed to be first formed at the largest water filled pore upon freezing. Infiltrating water may be conducted rapidly through previously air-filled pores which are not occupied by ice. A minor fraction of water is slowly transferred within the liquid water domain, which is absorbed by the solid particles. A model validation with field measurements at a location in the middle-east of Sweden indicated that the two-domain approach was suitable for improving the prediction of drainage during snowmelting. In particular, the correlation between simulated and observed onset of drainage in spring was improved. The validation also showed that the effect of the high flow domain was highly sensitive to the degree of saturation in the topsoil during freezing, as well as to the hydraulic properties at the lower frost boundary regulating the upward water flow to the frozen soil and ice formation.  相似文献   

4.
Research shows that water repellency is a key hydraulic property that results in reduced infiltration rates in burned soils. However, more work is required in order to link the hydrological behaviour of water repellent soils to observed runoff responses at the plot and hillslope scale. This study used 5 M ethanol and water in disc infiltrometers to quantify the role of macropore flow and water repellency on spatial and temporal infiltration patterns in a burned soil at plot (<10 m2) scale in a wet eucalypt forest in south‐east Australia. In the first summer and winter after wildfire, an average of 70% and 60%, respectively, of the plot area was water repellent and did not contribute to infiltration. Macropores (r > 0·5 mm), comprising just 5·5% of the soil volume, contributed to 70% and 95%, respectively, of the field‐saturated and ponded hydraulic conductivity (Kp). Because flow occurred almost entirely via macropores in non‐repellent areas, this meant that less than 2·5% of the soil surface effectively contributed to infiltration. The hydraulic conductivity increased by a factor of up to 2·5 as the hydraulic head increased from 0 to 5 mm. Due to the synergistic effect of macropore flow and water repellency, the coefficient of variation (CV) in Kp was three times higher in the water‐repellent soil (CV = 175%) than under the simulated non‐repellent conditions (CV = 66%). The high spatial variability in Kp would act to reduce the effective infiltration rate during runoff generation at plot scale. Ponding, which tend to increase with increasing scale, activates flow through macropores and would raise the effective infiltration rates at larger scales. Field experiments designed to provide representative measurements of infiltration after fire in these systems must therefore consider both the inherent variability in hydraulic conductivity and the variability in infiltration caused by interactions between surface runoff and hydraulic conductivity. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

5.
Macropores are important preferential pathways for the migration of water and contaminants through the vadose zone. The objective of this study was to examine small‐scale preferential flow processes during infiltration in macroporous, low permeability soils. A series of tension infiltration tests were conducted using Brilliant Blue dye tracer at two field sites in southwestern Ontario, Canada. The maximum applied pressure head was varied for each test and the resulting dye stain patterns and macropore networks were characterized by excavation, mapping, photography, and image analysis. Worm burrows were the dominant macropore type, with average macropore densities exceeding 400 m?2 and peak densities of more than 750 m?2 at 30 cm depth at both sites. Flow in macropores became significant at infiltration pressures > ? 3 cm, with corresponding increases in infiltration rate, soil water content variability (spatially and temporally), and depth of dye staining. The results demonstrated clear evidence for partially saturated macropore flow under porewater tension conditions and the associated importance of macropore–matrix interaction in controlling this flow. Field observations of transient infiltration showed that film and rivulet flow along macropores yielded vertical flow velocities exceeding 40 m d?1. Simple calculations showed that film flow along the walls and corners of irregularly shaped macropores could explain the observed results. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

6.
In cold climates, the process of freezing–thawing significantly affects the ground surface heat balance and water balance. To better understand the mechanism of evaporation from seasonally frozen soils, we performed field experiments at different water table depths on vegetated and bare ground in a semiarid region in China. Soil moisture and temperature, air temperature, precipitation, and water table depths were measured over a 5‐month period (November 1, 2016, to March 14, 2017). The evaporation, which was calculated by a mass balance method, was high in the periods of thawing and low in the periods of freezing. Increased water table depth in the freezing period led to high soil moisture in the upper soil layer, whereas lower initial groundwater levels during freezing–thawing decreased the cumulative evaporation. The extent of evaporation from the bare ground was the same in summer as in winter. These results indicate that a noteworthy amount of evaporation from the bare ground is present during freezing–thawing. Finally, the roots of Salix psammophila could increase the soil temperature. This study presents an insight into the joint effects of soil moisture, temperature, ground vegetation, and water table depths on the evaporation from seasonally frozen soils. Furthermore, it also has important implications for water management in seasonally frozen areas.  相似文献   

7.
Preferential flow is known to influence hillslope hydrology in many areas around the world. Most research on preferential flow has been performed in temperate regions. Preferential infiltration has also been found in semi‐arid regions, but its impact on the hydrology of these regions is poorly known. The aim of this study is to describe and quantify the influence of preferential flow on the hillslope hydrology from small scale (infiltration) to large scale (subsurface stormflow) in a semi‐arid Dehesa landscape. Precipitation, soil moisture content, piezometric water level and discharge data were used to analyse the hydrological functioning of a catchment in Spain. Variability of soil moisture content during the transition from dry to wet season (September to November) within horizontal soil layers leads to the conclusion that there is preferential infiltration into the soils. When the rainfall intensity is high, a water level rapidly builds up in the piezometer pipes in the area, sometimes even reaching soil surface. This water level also drops back to bedrock within a few hours (under dry catchment conditions) to days (under wet catchment conditions). As the soil matrix is not necessarily wet while this water layer is built up, it is thought to be a transient water table in large connected pores which drain partly to the matrix, partly fill up bedrock irregularities and partly drain through subsurface flow to the channels. When the soil matrix becomes wetter the loss of water from macropores to the matrix and bedrock decreases and subsurface stormflow increases. It may be concluded that the hillslope hydrological system consists of a fine matrix domain and a macropore domain, which have their own flow characteristics but which also interact, depending on the soil matrix and macropore moisture contents. The macropore flow can result in subsurface flow, ranging from 13% contribution to total discharge for a large event of high intensity rainfall or high discharge to 80% of total discharge for a small event with low intensity rainfall or low discharge. During large events the fraction of subsurface stormflow in the discharge is suppressed by the large amount of surface runoff. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

8.
Spatial distribution of soil macroporosity was determined for a forest podzol from tension infiltrometer measurements at the soil surface. Surface‐derived macroporosity values were compared with point infiltration characteristics obtained from soil water content and soil water chemistry measurements during an experimental irrigation, and with parameters of a kinematic wave model applied to soil water content data. Macroporosity estimated by the tension infiltrometer ranged from 0·00087 to 0·0219% of soil volume, and infiltration at these two sites was dominated by propagation of a well‐defined wetting front through the soil profile and bypass flow via soil macropores, respectively. Infiltration at sites with intermediate macroporosities reflected a combination of these two processes, although results were inconclusive at one site owing to lateral flow at the base of the soil profile. There was no agreement between macroporosities estimated by the tension infiltrometer and the kinematic wave model. The maximum soil conductance parameter within the profile at a site, however, was related directly to the surface‐derived macroporosity. The partial agreement between surface‐derived macroporosity estimates and point infiltration characteristics shown here supports the use of tension infiltrometry as a rapid, non‐destructive method of assessing spatial variations in the relative contribution of macropore flow to the infiltration process. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

9.
Despite the potential impact of winter soil water movements in cold regions, relatively few field studies have investigated cold‐season hydrological processes that occur before spring‐onset of snowmelt infiltration. The contribution of soil water fluxes in winter to the annual water balance was evaluated over 5 years of field observations at an agricultural field in Tokachi, Hokkaido, Japan. In two of the winters, soil frost reached a maximum depth of 0·2 m (‘frozen’ winters), whereas soil frost was mostly absent during the remaining three winters (‘unfrozen’ winters). Significant infiltration of winter snowmelt water, to a depth exceeding 1·0 m, occurred during both frozen and unfrozen winters. Such infiltration ranged between 126 and 255 mm, representing 28–51% of total annual soil water fluxes. During frozen winters, a substantial quantity of water (ca 40 mm) was drawn from deeper layers into the 0–0·2 m topsoil layer when this froze. Under such conditions, the progression and regression of the freezing front, regulated by the thickness of snow cover, controlled the quantity of soil water flux below the frozen layer. During unfrozen winters, 13–62 mm of water infiltrated to a depth of 0·2 m, before the spring snowmelt. These results indicate the importance of correctly evaluating winter soil water movement in cold regions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

10.
Topographic controls upon soil macropore flow   总被引：1，自引：0，他引：1  
Macropores are important components of soil hydrology. The spatial distribution of macropore flow as a proportion of saturated hydraulic conductivity was tested on six humid–temperate slopes using transects of tension infiltrometer measurements. Automated water table and overland flow monitoring allowed the timing of, and differentiation between, saturation‐excess overland flow and infiltration‐excess overland flow occurrence on the slopes to be determined and related to tension‐infiltrometer measurements. Two slopes were covered with blanket peat, two with stagnohumic gleys and two with brown earth soils. None of the slopes had been disturbed by agricultural activity within the last 20 years. This controlled the potential for tillage impacts on macropores. The proportion of near‐surface macropore flow to saturated hydraulic conductivity was found to vary according to slope position. The spatial patterns were not the same for all hillslopes. On the four non‐peat slopes there was a relationship between locations of overland flow occurrence and reduced macroporosity. This relationship did not exist for the peat slopes investigated because they experienced overland flow across their whole slope surfaces. Nevertheless, they still had a distinctive spatial pattern of macropore flow according to slope position. For the other soils tested, parts of slopes that were susceptible to saturation‐excess overland flow (e.g. hilltoes or flat hilltops) tended to have least macropore flow. To a lesser extent, for the parts of slopes susceptible to infiltration‐excess overland flow, the proportion of macropore flow as a component of infiltration was also smaller compared with the rest of the slope. The roles of macropore creation and macropore infilling by sheet wash are discussed, and it is noted that the combination of these may result in distinctive topographically controlled spatial patterns of macropore flow. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

11.
Preferential flow is of high relevance for runoff generation, transport of chemicals and nutrients, and the transit time distribution of water in the soil or watershed. However, preferential flow effects are generally ignored in lumped hydrological models. And even most physically‐based models ignore macropores and preferential flow features at the soil and hillslope scale. Keith Beven was never satisfied with this situation and he tried again and again to convince the scientific community to focus their research on the complex topic of macropore and preferential flow. Although he recognized how difficult it is to correctly include preferential flow in hydrological models, he made substantial progress defining and describing macropore flow and showing its relevance, developing models to simulate preferential flow, and in particular, the interaction between macropores and the soil matrix. In this short commentary, I reflect on these achievements and outline a vision for research in preferential flow experiments and modeling.  相似文献   

12.
The effects of vegetation root distribution on near‐surface water partitioning can be two‐fold. On the one hand, the roots facilitate deep percolation by root‐induced macropore flow; on the other hand, they reduce the potential for deep percolation by root‐water‐uptake processes. Whether the roots impede or facilitate deep percolation depends on various conditions, including climate, soil, and vegetation characteristics. This paper examines the effects of root distribution on deep percolation into the underlying permeable bedrock for a given soil profile and climate condition using HYDRUS modelling. The simulations were based on previously field experiments on a semiarid ponderosa pine (Pinus ponderosa) hillslope. An equivalent single continuum model for simulating root macropore flow on hillslopes is presented, with root macropore hydraulic parameterization estimated based on observed root distribution. The sensitivity analysis results indicate that the root macropore effect dominates saturated soil water flow in low conductivity soils (Kmatrix below 10?7 m/s), while it is insignificant in soils with a Kmatrix larger than 10?5 m/s, consistent with observations in this and other studies. At the ponderosa pine site, the model with simple root‐macropore parameterization reasonably well reproduces soil moisture distribution and some major runoff events. The results indicate that the clay‐rich soil layer without root‐induced macropores acts as an impeding layer for potential groundwater recharge. This impeding layer results in a bedrock percolation of less than 1% of the annual precipitation. Without this impeding layer, percolation into the underlying permeable bedrock could be as much as 20% of the annual precipitation. This suggests that at a surface with low‐permeability soil overlying permeable bedrock, the root penetration depth in the soil is critical condition for whether or not significant percolation occurs. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

13.
Most vegetated land surfaces contain macropores that may have a significant effect on the rate of infiltration of water under ponded conditions on the ground surface. Owing to the small-scale variations of the land topography (microtopography), only portions of the land area may get ponded during the process of overland flow. As the macropores transmit water at much higher rates than the primary soil matrix, higher macropore activation in ponded areas produces larger effective infiltration rates into the soil. Therefore, overland flow and infiltration into the macroporous vadose zone are interrelated. Representing the microtopographic variation of the land surface by a simple sine wave function, a method was developed to relate the ponding area to the average ponding depth which was determined by overland flow. A numerical model coupling overland flow and infiltration into the macroporous vadose zone was developed. Overland flow was simulated using the St. Venant equations with the inertia terms neglected. A single macropore model was used to simulate the infiltration into the macroporous vadose zone. The interaction between overland flow and the infiltration into the macroporous vadose zone was analyzed for a hypothetical watershed. The sensitivity analysis revealed that the interaction of macropore flow and overland flow is significant. For the conditions tested, the macropore flow and the overland flow were found to be more sensitive to the macroporosity and less sensitive to the microtopographic surface variation.  相似文献   

14.
Soil macropore networks are subsurface connected void spaces caused by processes such as fracture of soils, micro‐erosion and fauna burrows. Axial X‐ray computed tomography (CT) scanning provides a convenient means of recording the spatial structure of soil macropore networks. The objective of this study were to (1) based on CT technique and GIS digitized image method, construction a new technique for tracing, visualizing and measuring the soil macropore networks and (2) investigate the effects of farming activities on soil macropore networks characteristics. Our technique uses left‐turning and nine‐direction judgment methods, a combination of the layer‐by‐layer analysis method and the up‐down tracking algorithm. The characteristics for the overall structure patterns of macropores, the spatial distribution of the macropore networks and each single macropore network can be conveniently identified by our technique. Eight undisturbed soil columns from fields with two distinct land uses (under cultivation and not been cultivated) and four different depths (0–20, 20–40, 40–60 and 60–80 cm) were investigated. The soil columns were scanned using X‐ray CT at a voxel resolution of 0.075 × 0.075 × 3.000 mm. Results indicate that farming activities can destroy the initial structure of macropores, and those remaining are mainly small‐sized and medium‐sized networks with lower extension and hydraulic conductivity. The network properties show a significant difference between upper and lower layer. The results can provide beneficial reference to further research centered on non‐equilibrium flow prediction and chemical transport modeling in field soils. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

15.
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16.
Seasonal changes over 2 years (2004–2006) in soil moisture content (θv) of frozen alpine frost meadow soils of the Qinghai‐Tibet plateau permafrost region under three different levels of vegetation cover were investigated. Vegetation cover and air temperature changes had significant effects (synergistic effect) on θv and its distribution in the soil profile. During periods of soil freezing or thawing, the less the vegetation cover, the quicker the temperature drop or rise of soil water, and the shorter the duration of the soil water freeze–thaw response in the active soil layer. Under 30% and 65% vegetation cover the amplitude of variation in θv during the freezing period was 20–26% greater than that under 93% cover, while during the thawing period, it was 1·5‐ to 40·5‐fold greater. The freezing temperature of the surface soil layer, fTs, was 1·6 °C lower under 30% vegetation cover than under 93% vegetation cover. Changes in vegetation cover of the alpine frost meadow affected θv and its distribution, as well as the relationship between θv and soil temperature (Ts). As vegetation cover decreased, soil water circulation in the active layer increased, and the response to temperature of the water distribution across the soil profile was heightened. The quantity of transitional soil phase water at different depths significantly increased as vegetation cover decreased. The influence of vegetation cover and soil temperature distribution led to a relatively dry soil layer in the middle of the profile (0·70–0·80 m) under high vegetation cover. Alpine meadow θv and its pattern of distribution in the permafrost region were the result of the synergistic effect of air temperature and vegetation cover. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

17.
This paper concerns heat transfer and water infiltration into a homogeneous, unsaturated, frozen soil. A numerical analysis of the processes, which is based on the local volume averaging formulation of transport phenomena in porous media, is described. Simultaneous heat and mass transfers with phase changes are considered. The results of the simulations provide an insight into the mechanics of the infiltration process. They suggest that infiltration involves primarily two flow regimes, a transient regime and a quasi-steady-state regime. Once the quasi-steady-state regime is reached, the energy needed to increase soil temperature at depth is supplied by latent heat released from freezing of water in the upper layers of soil. The effects of surface saturation, initial soil saturation and initial soil temperature on infiltration are examined.  相似文献   

18.
Macropores are a relatively small proportion of the soil volume, but they play an important role in the movement of water and chemicals owing to occasional rapid fluxes through them. The occurrence of macropore flow does not depend on the water content (or potential) of the bluk matrix unless the soil is close to saturation, but depends instead principally upon surface boundary conditions. Accordingly, three control situations of infiltration are recognized: macropore control, application control, and matrix control. These three situations indicate that the two-domain system may be a proper approach for the simulation of macropore soil. In this conceptualization, macropores are defined as channeling pores of different radii in which the flux density (with unit hydraulic gradient) occurring in the minimum sizes of such pores is greater than or equal to the saturated matrix hydraulic conductivity. Recognizing the two structural domains of the macropore and matrix, and possible water flow situations, three flow regions are suggested: matrix, macropore, and transaction. The matrix and the macropore are the two domains, and the transaction represents the exchange of water between the matrix and the macropore. The classic approach of the Richards equation is applicable to describe the flow in the matrix domain. The Hagen-Poiseuille and the Chezy-Manning equations for tube flow can be applied to represent the relationship between the hydraulic conductivity of the macroporosity and the total macroporosity, where the total macroporosity is defined as the ratio of the summed macropore cross-sectional area and the total soil cross-sectional area. An equation describing water flow in the macropore domain is then obtained.  相似文献   

19.
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20.
Climate change and thawing permafrost in the Arctic will significantly alter landscape hydro‐geomorphology and the distribution of soil moisture, which will have cascading effects on climate feedbacks (CO2 and CH4) and plant and microbial communities. Fundamental processes critical to predicting active layer hydrology are not well understood. This study applied water stable isotope techniques (δ2H and δ18O) to infer sources and mixing of active layer waters in a polygonal tundra landscape in Barrow, Alaska (USA), in August and September of 2012. Results suggested that winter precipitation did not contribute substantially to surface waters or subsurface active layer pore waters measured in August and September. Summer rain was the main source of water to the active layer, with seasonal ice melt contributing to deeper pore waters later in the season. Surface water evaporation was evident in August from a characteristic isotopic fractionation slope (δ2H vs δ18O). Freeze‐out isotopic fractionation effects in frozen active layer samples and textural permafrost were indistinguishable from evaporation fractionation, emphasizing the importance of considering the most likely processes in water isotope studies, in systems where both evaporation and freeze‐out occur in close proximity. The fractionation observed in frozen active layer ice was not observed in liquid active layer pore waters. Such a discrepancy between frozen and liquid active layer samples suggests mixing of meltwater, likely due to slow melting of seasonal ice. This research provides insight into fundamental processes relating to sources and mixing of active layer waters, which should be considered in process‐based fine‐scale and intermediate‐scale hydrologic models. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

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