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1.
Hillslopes turn precipitation into runoff and thus exert important controls on various Earth system processes. It remains difficult to collect reliable data necessary for understanding and modeling these Earth system processes in real catchments. To overcome this problem, controlled experiments are being conducted at the Landscape Evolution Observatory at Biosphere 2, The University of Arizona. Previous experiments have revealed differences in hydrological response between 2 landscapes within Landscape Evolution Observatory, even though both landscapes were designed to be identical. In an attempt to discover where the observed differences stem from, we use a fully 3‐dimensional hydrological model (CATchment HYdrology) to show the effect of soil water retention characteristics and saturated hydraulic conductivity on the hydrological response of these 2 hillslopes. We also show that soil water retention characteristics can be derived at hillslope scale from experimental observations of soil moisture and matric potential. It is found that differences in soil packing between the 2 landscapes may be responsible for the observed differences in hydrological response. This modeling study also suggests that soil water retention characteristics and saturated hydraulic conductivity have a profound effect on rainfall–runoff processes at hillslope scale and that parametrization of a single hillslope may be a promising step in modeling rainfall–runoff response in real catchments.  相似文献   

2.
Rainfall retention and runoff detention are likely the most important ecosystem services provided by extensive green roofs (EGRs) that contribute to urban stormwater mitigation and management. However, the hydrological performance and runoff generation mechanisms of mature, well-established EGRs in tropical regions remain poorly understood. This study evaluated the rainfall retention, discharge detention times and processes of runoff generation in two neighbouring 20-year-old EGRs with different slopes (2° and 14° for EGRns and EGRws, respectively) and management practices in Mexico City; results were compared with those obtained in a conventional roof (CR, 2° slope). Precipitation, substrate moisture and storm runoff were continuously measured during the 2017 and 2018 rainy seasons (May–November). Results showed spatial differences in substrate properties and moisture within and between green roofs. In general, higher bulk densities and a wide range of variation in water content characterized the bare substrate areas compared to those below vegetation. Greatest increases in substrate moisture and storm runoff were observed in the steeper green roof. Subsurface flow was the dominant process controlling the amount and timing of stormflow in the EGRs. The occurrence of saturation excess overland flow was small and detected when large rain events were preceded by high wetness conditions. The main factors influencing the hydrological responses of the green roofs were their substrate hydrophysical properties, related mostly to vegetation cover, management and age, and to much lesser extent to slope and substrate depth. On average, rainfall retention was ~60% in the EGRs with significantly longer delays and prolonged runoff times (100 and 340 min, respectively) compared to CR (3%, 20 min, and 258 min, respectively). Overall, these findings highlight the potential of EGRs in reducing stormflow and peak discharges for most rainfall in Mexico City, and thus mitigating the risk of saturation and overflow of urban drainages.  相似文献   

3.
The hydraulic properties of the topsoil control the partition of rainfall into infiltration and runoff at the soil surface. They must be characterized for distributed hydrological modelling. This study presents the results of a field campaign documenting topsoil hydraulic properties in a small French suburban catchment (7 km2) located near Lyon, France. Two types of infiltration tests were performed: single ring infiltration tests under positive head and tension‐disk infiltration using a mini‐disk. Both categories were processed using the BEST—Beerkan Estimation of Soil Transfer parameters—method to derive parameters describing the retention and hydraulic conductivity curves. Dry bulk density and particle size data were also sampled. Almost all the topsoils were found to belong to the sandy loam soil class. No significant differences in hydraulic properties were found in terms of pedologic units, but the results showed a high impact of land use on these properties. The lowest dry bulk density values were obtained in forested soils with the highest organic matter content. Permanent pasture soils showed intermediate values, whereas the highest values were encountered in cultivated lands. For saturated hydraulic conductivity, the highest values were found in broad‐leaved forests and small woods. The complementary use of tension‐disk and positive head infiltration tests highlighted a sharp increase of hydraulic conductivity between near saturation and saturated conditions, attributed to macroporosity effect. The ratio of median saturated hydraulic conductivity to median hydraulic conductivity at a pressure of − 20 mm of water was about 50. The study suggests that soil texture, such as used in most pedo‐transfer functions, might not be sufficient to properly map the variability of soil hydraulic properties. Land use information should be considered in the parameterizations of topsoil within hydrological models to better represent in situ conditions, as illustrated in the paper. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

4.
Soil surface crusts are widely reported to favour Hortonian runoff, but are not explicitly represented in most rainfall‐runoff models. The aim of this paper is to assess the impact of soil surface crusts on infiltration and runoff modelling at two spatial scales, i.e. the local scale and the plot scale. At the local scale, two separate single ring infiltration experiments are undertaken. The first is performed on the undisturbed soil, whereas the second is done after removal of the soil surface crust. The HYDRUS 2D two‐dimensional vertical infiltration model is then used in an inverse modelling approach, first to estimate the soil hydraulic properties of the crust and the subsoil, and then the effective hydraulic properties of the soil represented as a single uniform layer. The results show that the crust hydraulic conductivity is 10 times lower than that of the subsoil, thus illustrating the limiting role the crust has on infiltration. Moving up to the plot scale, a rainfall‐runoff model coupling the Richards equation to a transfer function is used to simulate Hortonian overland flow hydrographs. The previously calculated hydraulic properties are used, and a comparison is undertaken between a single‐layer and a double‐layer representation of the crusted soil. The results of the rainfall‐runoff model show that the soil hydraulic properties calculated at the local scale give acceptable results when used to model runoff at the plot scale directly, without any numerical calibration. Also, at the plot scale, no clear improvement of the results can be seen when using a double‐layer representation of the soil in comparison with a single homogeneous layer. This is due to the hydrological characteristics of Hortonian runoff, which is triggered by a rainfall intensity exceeding the saturated hydraulic conductivity of the soil surface. Consequently, the rainfall‐runoff model is more sensitive to rainfall than to the subsoil's hydrodynamic properties. Therefore, the use of a double‐layer soil model to represent runoff on a crusted soil does not seem necessary, as the increase of precision in the soil discretization is not justified by a better performance of the model. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

5.
In the semi‐arid Mediterranean environment, the rainfall–runoff relationships are complex because of the markedly irregular patterns in rainfall, the seasonal mismatch between evaporation and rainfall, and the spatial heterogeneity in landscape properties. Watersheds often display considerable non‐linear threshold behavior, which still make runoff generation an open research question. Our objectives in this context were: to identify the primary processes of runoff generation in a small natural catchment; to test whether a physically based model, which takes into consideration only the primary processes, is able to predict spatially distributed water‐table and stream discharge dynamics; and to use the hydrological model to increase our understanding of runoff generation mechanisms. The observed seasonal dynamics of soil moisture, water‐table depth, and stream discharge indicated that Hortonian overland‐flow was negligible and the main mechanism of runoff generation was saturated subsurface‐flow. This gives rise to base‐flow, controls the formation of the saturated areas, and contributes to storm‐flow together with saturation overland‐flow. The distributed model, with a 1D scheme for the kinematic surface‐flow, a 2D sub‐horizontal scheme for the saturated subsurface‐flow, and ignoring the unsaturated flow, performed efficiently in years when runoff volume was high and medium, although there was a smoothing effect on the observed water‐table. In dry years, small errors greatly reduced the efficiency of the model. The hydrological model has allowed to relate the runoff generation mechanisms with the land‐use. The forested hillslopes, where the calibrated soil conductivity was high, were never saturated, except at the foot of the slopes, where exfiltration of saturated subsurface‐flow contributed to storm‐flow. Saturation overland‐flow was only found near the streams, except when there were storm‐flow peaks, when it also occurred on hillslopes used for pasture, where soil conductivity was low. The bedrock–soil percolation, simulated by a threshold mechanism, further increased the non‐linearity of the rainfall–runoff processes. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

6.
The impact of three-dimensional subsurface heterogeneity in the saturated hydraulic conductivity on hillslope runoff generated by excess infiltration (so-called Hortonian runoff) is examined. A fully coupled, parallel subsurface–overland flow model is used to simulate runoff from an idealized hillslope. Ensembles of correlated, Gaussian random fields of saturated hydraulic conductivity are used to create uncertainty in spatial structure. A large number of cases are simulated in a parametric manner with the variance of the hydraulic conductivity varied over orders of magnitude. These cases include rainfall rates above, equal and below the geometric mean of the hydraulic conductivity distribution. These cases are also compared to theoretical representations of runoff production based on simple assumptions regarding (1) the rainfall rate and the value of hydraulic conductivity in the surface cell using a spatially-indiscriminant approach; and (2) a percolation-theory type approach to incorporate so-called runon. Simulations to test the ergodicity of hydraulic conductivity on hillslope runoff are also performed. Results show that three-dimensional stochastic representations of the subsurface hydraulic conductivity can create shallow perching, which has an important effect on runoff behavior that is different than previous two-dimensional analyses. The simple theories are shown to be very poor predictors of the fraction of saturated area that might runoff due to excess infiltration. It is also shown that ergodicity is reached only for a large number of integral scales (∼30) and not achieved for cases where the rainfall rate is less than the geometric mean of the saturated hydraulic conductivity.  相似文献   

7.
The forest floor plays an important role in runoff rate, soil erosion and soil infiltration capacity by protecting mineral soils from the direct impact of falling raindrops. Forest floor consists of different kinds of litter with different hydraulic properties. In this study, the inverse method was used to estimate the hydraulic properties of three kinds of forest floor (broad‐leaved, needle‐leaved and mixed‐stand) at three replications in a completely random design. Forest floor samples were collected from the Gilan Province, Iran. The samples were piled up to make long columns 40.88 cm high with an inner diameter of 18.1 cm. Artificial rainfall experiments were conducted on top of the columns, and free drainage from the bottom of the columns was measured in the laboratory. Saturated hydraulic conductivity (Ks), saturated water content and water retention curve parameters (van Genuchten equation) were estimated by the inverse method. The results showed that the Ks of needle‐leaved samples differed significantly (p < 0.05) from those of broad‐leaved and mixed‐stand samples, whereas the latter two did not differ in this regard. No significant differences emerged in the water retention function parameters of van Genuchten (θr, β and α) in the three forest floor samples. The saturated water content of mixed‐stand samples was significantly different (p < 0.05) from that of broad‐leaved and needle‐leaved treatments with the latter two samples showing no significant difference. The good agreement between simulated and observed free drainage for all forest floor samples in the validation period indicates that the estimated hydraulic properties efficiently characterize the unsaturated water flow in the forest floor. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

8.
Modeling unsaturated flow in porous media requires constitutive relations that describe the soil water retention and soil hydraulic conductivity as a function of either potential or water content. Often, the hydraulic parameters that describe these relations are directly measured on small soil cores, and many cores are needed to upscale to the entire heterogeneous flow field. An alternative to the forward upscaling method using small samples are inverse upscaling methods that incorporate soft data from geophysical measurements observed directly on the larger flow field. In this paper, we demonstrate that the hydraulic parameters can be obtained from cross borehole ground penetrating radar by measuring the first arrival travel time of electromagnetic waves (represented by raypaths) from stationary antennae during a constant flux infiltration experiment. The formulation and coupling of the hydrological and geophysical models rely on a constant velocity wetting front that causes critical refraction at the edge of the front as it passes by the antennae. During this critical refraction period, the slope of the first arrival data can be used to calculate (1) the wetting velocity and (2) the hydraulic conductivity of the wet (or saturated) soil. If the soil is undersaturated during infiltration, then an estimate of the saturated water content is needed before calculating the saturated hydraulic conductivity. The hydraulic conductivity value is then used in a nonlinear global optimization scheme to estimate the remaining two parameters of a Broadbridge and White soil.  相似文献   

9.
In 1989, in a hydrological research programme within a deacidification project in the Gårdsjön area in southwest Sweden, flow paths and residence times of soil water and groundwater in microcatchments were examined to support the interpretation of the hydrochemical changes. Saturated hydraulic conductivity and soil water retention were analysed on more than 100 cylinder samples. The catchments have shallow sandy-silty till soil with a mean depth in the main catchment of 43 cm. Porosity of the mineral soil in the main catchment was high and ranged from 38 to 85%. The samples from the B-horizon had generally higher porosity. Porosity and the content of organic matter were correlated. The soil water retention was relatively high at all tensions, likely owing to the high content of organic matter. Dissolved organic substances were most probably transported from the shallow soil on the steep sides of the catchment down to the valley where it precipitated. The high porosities could be a consequence of long-term weathering, provided that the organic substances present have increased the leaching of the weathering products. Measured values of saturated hydraulic conductivity were close to log-normally distributed with a mean for all samples of 3 × 10−5 m s−1. There was a significant increase in conductivity toward the ground surface with the mean conductivity of the samples in the uppermost 10 cm of the mineral soil of 4 × 10−5 m s−1, which was about 13 times higher than the conductivity of 3 × 10−6 m s−1 at 1 m depth. From the relationship between runoff at the catchment outlet and groundwater levels, the conductivity was estimated to be 15–200 times higher in the upper soil layer than in the deeper ones. In one profile, 44–64% of the yearly lateral flow was estimated to occur above 30 cm depth. The conductivity was correlated with the content of drainable water, which indicated the importance of the largest pores for the saturated hydraulic conductivity.  相似文献   

10.
A pore‐scale model based on measured particle size distributions has been used to quantify the changes in pore space geometry of packed soil columns resulting from a dilution in electrolyte concentration from 500 to 1 mmol l?1 NaCl during leaching. This was applied to examine the effects of particle release and re‐deposition on pore structure and hydraulic properties. Two different soils, an agricultural soil and a mining residue, were investigated with respect to the change in hydraulic properties. The mining residue was much more affected by this process with the water saturated hydraulic conductivity decreasing to 0·4% of the initial value and the air‐entry value changing from 20 to 50 cm. For agricultural soil, there was little detectable shift in the water retention curve but the saturated hydraulic conductivity decreased to 8·5% of the initial value. This was attributed to localized pore clogging (similar to a surface seal) affecting hydraulic conductivity, but not the microscopically measured pore‐size distribution or water retention. We modelled the soil structure at the pore scale to explain the different responses of the two soils to the experimental conditions. The size of the pores was determined as a function of deposited clay particles. The modal pore size of the agricultural soil as indicated by the constant water retention curve was 45 µm and was not affected by the leaching process. In the case of the mining residue, the mode changed from 75 to 45 µm. This reduction of pore size corresponds to an increase of capillary forces that is related to the measured shift of the water retention curve. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

11.
This study analyses some hydrological driving forces and their interrelation with surface‐flow initiation in a semiarid Caatinga basin (12 km2), Northeastern Brazil. During the analysis period (2005 – 2014), 118 events with precipitation higher than 10 mm were monitored, providing 45 events with runoff, 25 with negligible runoff and 49 without runoff. To verify the dominant processes, 179 on‐site measurements of saturated hydraulic conductivity (Ksat) were conducted. The results showed that annual runoff coefficient lay below 0.5% and discharge at the outlet has only occurred four days per annum on average, providing an insight to the surface‐water scarcity of the Caatinga biome. The most relevant variables to explain runoff initiation were total precipitation and maximum 60‐min rainfall intensity (I60). Runoff always occurred when rainfall surpassed 31 mm, but it never occurred for rainfall below 14 mm or for I60 below 12 mm h?1. The fact that the duration of the critical intensity is similar to the basin concentration time (65 min) and that the infiltration threshold value approaches the river‐bank saturated hydraulic conductivity support the assumption that Hortonian runoff prevails. However, none of the analysed variables (total or precedent precipitation, soil moisture content, rainfall intensities or rainfall duration) has been able to explain the runoff initiation in all monitored events: the best criteria, e.g. failed to explain 27% of the events. It is possible that surface‐flow initiation in the Caatinga biome is strongly influenced by the root‐system dynamics, which changes macro‐porosity status and, therefore, initial abstraction. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

12.
Rainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface. For a given cover level, rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation. Compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface. For the same cover level, rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer. The effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage. Micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by Poesen (1986): i.e. runoff generated as rock flow or as Horton overland flow can (partly) infiltrate into the unsealed soil surface under the rock fragments, provided that they are not completely embedded in the top layer. Hence, rock fragment position, beside other rock fragment properties, should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers. A simple model, based on the proportions of bare soil surface, soil surface occupied by embedded rock fragments, and soil surface covered with rock fragments resting on the soil surface, describes the runoff coefficient data relatively well.  相似文献   

13.
Low Impact Development (LID) aims to mitigate the hydrological impacts of urbanization by replication of processes in natural catchments. Green roofs covered with vegetation and pervious substrate are one alternative among a wide range of LID tools. Water retention of green roofs depends on many factors (e.g. local climate), and measurements remain crucial in evaluating their performance. The simulation of green roof retention by a hydrological model is one option to evaluate their potential benefits before implementation. In this paper, we evaluated the ability of the recently introduced LID green roof module of the stormwater management model to replicate runoff from monitored green roof test beds under Nordic climate conditions. A parameter sensitivity analysis was conducted to identify calibration parameters. The model showed an overall acceptable performance, and the results indicated the importance of accurately estimating potential evapotranspiration rates for inter‐event periods, which is essential in representing the retention capacity regeneration. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

14.
Water infiltration rate and hydraulic conductivity in vegetated soil are two vital hydrological parameters for agriculturists to determine availability of soil moisture for assessing crop growths and yields, and also for engineers to carry out stability calculations of vegetated slopes. However, any effects of roots on these two parameters are not well‐understood. This study aims to quantify the effects of a grass species, Cynodon dactylon, and a tree species, Schefflera heptaphylla, on infiltration rate and hydraulic conductivity in relation to their root characteristics and suction responses. The two selected species are commonly used for ecological restoration and rehabilitation in many parts of the world and South China, respectively. A series of in‐situ double‐ring infiltration tests was conducted during a wet summer, while the responses of soil suction were monitored by tensiometers. When compared to bare soil, the vegetated soil has lower infiltration rate and hydraulic conductivity. This results in at least 50% higher suction retained in the vegetated soil. It is revealed that the effects of root‐water uptake by the selected species on suction were insignificant because of the small evapotranspiration (<0.2 mm) when the tests were conducted under the wet climate. There appears to have no significant difference (less than 10%) of infiltration rates, hydraulic conductivity and suction retained between the grass‐covered and the tree‐covered soil. However, the grass and tree species having deeper root depth and greater Root Area Index (RAI) retained higher suction. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

15.
Sustainable strategies such as green roofs have been implemented as stormwater management tools to mitigate disturbance of the hydrologic cycle resulting from urbanization. Green roofs, also referred to as vegetated roofs, can improve the urban landscape by reducing heat island effects, providing ecosystem services, and facilitating the retention and treatment of stormwater. Green roofs have received particular attention because they do not require acquisition and development of land and represent an application of biomimicry in design and construction. In this paper, we evaluate the effects of precipitation, evapotranspiration (ET), antecedent dry period (ADP), and seasonal variation on the run‐off quantity and distribution of an extensive, sedum covered, green roof on a commercial building in Syracuse, NY, USA. The green roof greatly facilitated retention of precipitation events without significant changes over the 4‐year study. The green roof retained on average 95.9 ± 3.6% (6.5 ± 5.6 mm) per rainfall event, with a range from 75% to 99.6% (33.2 to 3.3 mm). However, as precipitation quantity increased, the retention of water decreased. This high water retention capacity was the result of the combined effects of ET, stormwater storage (plants, growth media, and stormwater retention layer), and limited surface run‐off from the roof deck due to variation in the sloping of the green roof and the tapered insulation to the deck drains. The water retention capacity of the green roof did not change significantly between growing and nongrowing seasons. Slightly greater precipitation during the growing season coincided with increased ET. Average potential ET during the growing season was approximately 3 times greater than during the nongrowing season. The hydrologic performance of the green roof was not significantly impacted by an ADP greater than 2 days.  相似文献   

16.
Surface soil hydraulic properties are key factors controlling the partition of rainfall and snowmelt into runoff and soil water storage, and their knowledge is needed for sound land management. The objective of this study was to evaluate the effects of three land uses (native grass, brome grass and cultivated) on surface soil hydraulic properties under near‐saturated conditions at the St Denis National Wildlife Area, Saskatchewan, Canada. For each land use, water infiltration rates were measured using double‐ring and tension infiltrometers at ?0·3, ?0·7, ?1·5 and ?2·2 kPa pressure heads. Macroporosity and unsaturated hydraulic properties of the surface soil were estimated. Mean field‐saturated hydraulic conductivity (Kfs), unsaturated hydraulic conductivity at ?0·3 kPa pressure head, inverse capillary length scale (α) and water‐conducting macroporosity were compared for different land uses. These parameters of the native grass and brome grass sites were significantly (p < 0·1) higher than that of the cultivated sites. At the ?0·3 kPa pressure head, hydraulic conductivity of grasslands was two to three times greater than that of cultivated lands. Values of α were about two times and values of Kfs about four times greater in grasslands than in cultivated fields. Water‐conducting macroporosity of grasslands and cultivated fields were 0·04% and 0·01% of the total soil volume, respectively. Over 90% of the total water flux at ?0·06 kPa pressure head was transmitted through pores > 1·36 × 10?4 m in diameter in the three land uses. Land use modified near‐saturated hydraulic properties of surface soil and consequently may alter the water balance of the area by changing the amount of surface runoff and soil water storage. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

17.
Post‐wildfire runoff was investigated by combining field measurements and modelling of infiltration into fire‐affected soils to predict time‐to‐start of runoff and peak runoff rate at the plot scale (1 m2). Time series of soil‐water content, rainfall and runoff were measured on a hillslope burned by the 2010 Fourmile Canyon Fire west of Boulder, Colorado during cyclonic and convective rainstorms in the spring and summer of 2011. Some of the field measurements and measured soil physical properties were used to calibrate a one‐dimensional post‐wildfire numerical model, which was then used as a ‘virtual instrument’ to provide estimates of the saturated hydraulic conductivity and high‐resolution (1 mm) estimates of the soil‐water profile and water fluxes within the unsaturated zone. Field and model estimates of the wetting‐front depth indicated that post‐wildfire infiltration was on average confined to shallow depths less than 30 mm. Model estimates of the effective saturated hydraulic conductivity, Ks, near the soil surface ranged from 0.1 to 5.2 mm h?1. Because of the relatively small values of Ks, the time‐to‐start of runoff (measured from the start of rainfall), tp, was found to depend only on the initial soil‐water saturation deficit (predicted by the model) and a measured characteristic of the rainfall profile (referred to as the average rainfall acceleration, equal to the initial rate of change in rainfall intensity). An analytical model was developed from the combined results and explained 92–97% of the variance of tp, and the numerical infiltration model explained 74–91% of the variance of the peak runoff rates. These results are from one burned site, but they strongly suggest that tp in fire‐affected soils (which often have low values of Ks) is probably controlled more by the storm profile and the initial soil‐water saturation deficit than by soil hydraulic properties. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

18.
Excessive application of poultry litter to pastures in the Sand Mountain region of north Alabama has resulted in phosphorus (P) contamination of surface water bodies and buildup of P in soils of this region. Since surface runoff is recognized as the primary mechanism of P transport, understanding surface runoff generation mechanisms are crucial for alleviating water quality problems in this region. Identification of surface runoff generation mechanisms is also important for delineation of hydrologically active areas (HAAs). Therefore, the specific objective of this study was to identify surface runoff generation mechanisms (infiltration excess versus saturation excess) using distributed surface and subsurface sensors and rain gauge. Results from three rainfall events (2·13–3·43 cm) of differing characteristics, and sensor data at four locations with differing soil hydraulic properties along the hillslope showed that the main surface runoff generation mechanism in this region is infiltration excess. Because of this, rainfall intensity and soil hydraulic conductivity were found to play dominant roles in surface runoff generation in this region. Further, only short periods of a few rainfall events during which the rainfall intensity is high produce surface runoff. This study indicates that perhaps subsurface flows and transport of P in subsurface flows need to be quantified to reduce P contamination of surface water bodies in this region. Current studies at this location are identifying spatial and temporal distribution of HAAs, quantifying rainfall characteristics that generate runoff, and estimating runoff volume that results from connected HAAs. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

19.
Chronosequences provide suitable sources for the study of changes in soil hydraulic behaviour as a result of long-term pedogenesis. For a podsol chronosequence in the Scottish Highlands, data are presented to indicate the changes that have occurred over 13000 years in the saturated hydraulic conductivity (Ksat) in each horizon. As the soil profile has evolved into a differentiated sequence of three horizons, the resulting hydrological changes can be both measured and quantified by relating Ksat to textural properties and bulk density. The results are significant for interpretation of changing runoff processes and slope stability.  相似文献   

20.
Andosol soils formed in volcanic ash provide key hydrological services in montane environments. To unravel the subsurface water transport and tracer mixing in these soils we conducted a detailed characterization of soil properties and analyzed a 3-year data set of sub-hourly hydrometric and weekly stable isotope data collected at three locations along a steep hillslope. A weakly developed (52–61 cm depth), highly organic andic (Ah) horizon overlaying a mineral (C) horizon was identified, both showing relatively similar properties and subsurface flow dynamics along the hillslope. Soil moisture observations in the Ah horizon showed a fast responding (few hours) “rooted” layer to a depth of 15 cm, overlying a “perched” layer that remained near saturated year-round. The formation of the latter results from the high organic matter (33–42%) and clay (29–31%) content of the Ah horizon and an abrupt hydraulic conductivity reduction in this layer with respect to the rooted layer above. Isotopic signatures revealed that water resides within this soil horizon for short periods, both at the rooted (2 weeks) and perched (4 weeks) layer. A fast soil moisture reaction during rainfall events was also observed in the C horizon, with response times similar to those in the rooted layer. These results indicate that despite the perched layer, which helps sustain the water storage of the soil, a fast vertical mobilization of water through the entire soil profile occurs during rainfall events. The latter being the result of the fast transmissivity of hydraulic potentials through the porous matrix of the Andosols, as evidenced by the exponential shape of the water retention curves of the subsequent horizons. These findings demonstrate that the hydrological behavior of volcanic ash soils resembles that of a “layered sponge,” in which vertical flow paths dominate.  相似文献   

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