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1.
Soils in post‐wildfire environments are often characterized by a low infiltration capacity with a high degree of spatial heterogeneity relative to unburned areas. Debris flows are frequently initiated by run‐off in recently burned steeplands, making it critical to develop and test methods for incorporating spatial variability in infiltration capacity into hydrologic models. We use Monte Carlo simulations of run‐off generation over a soil with a spatially heterogenous saturated hydraulic conductivity (Ks) to derive an expression for an aerially averaged saturated hydraulic conductivity ( ) that depends on the rainfall rate, the statistical properties of Ks, and the spatial correlation length scale associated with Ks. The proposed method for determining is tested by simulating run‐off on synthetic topography over a wide range of spatial scales. Results provide a simplified expression for an effective saturated hydraulic conductivity that can be used to relate a distribution of small‐scale Ks measurements to infiltration and run‐off generation over larger spatial scales. Finally, we use a hydrologic model based on to simulate run‐off and debris flow initiation at a recently burned catchment in the Santa Ana Mountains, CA, USA, and compare results to those obtained using an infiltration model based on the Soil Conservation Service Curve Number.  相似文献   

2.
D. Markovic  M. Koch 《水文研究》2015,29(7):1806-1816
Hydrological processes commonly exhibit long‐term persistence, also known as the ‘Hurst phenomenon’. Here, we examine long‐term precipitation and streamflow time series from the Elbe River Basin to quantify differences in the spectral properties and in the Hurst parameter estimates () of the individual hydrological cycle components. Precipitation‐runoff modelling is performed for the Elbe River sub‐catchment Striegis using the Soil and Water Assessment Tool (SWAT). For 38 daily 50 years long streamflow time series from the Elbe River Basin, baseflow separation and spectral analysis is performed. The results show a spectral shift towards low‐frequency scales (>2 years) from precipitation to baseflow, with a parallel increase of from 0.52 (precipitation) to 0.65 (baseflow). The SWAT model is able to reproduce both, the main low‐frequency mode (≈7 yr.) and the (0.62) of the observed Striegis River flow time series. The baseflow appears to be the main component which shapes the low‐frequency response and of streamflow in the Elbe River Basin to the input precipitation. This conclusion is further confirmed through PMWIN‐MODFLOW groundwater modelling of a hypothetic phreatic stream‐connected aquifer system that consists of various soils (sand, loamy sand and silt). A power shift towards lower frequencies and an increase of for the hydraulic heads is obtained, as the aquifer's lateral dimensions increase and its hydraulic conductivity decreases. The average of the groundwater heads is 0.80, 0.90 and 1.0 for sand, loamy sand and silt aquifers, respectively. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

3.
Release of nitrogen compounds into groundwater, particularly those compounds from excessive agricultural fertilization, is a major concern in an aquifer recharge. Among the nitrogen compounds, ammonium ( ) is a common one. In order to assess the risk of agricultural fertilizer contamination to an aquifer through infiltration, adsorption onto a loamy agricultural soil profile (0–0.60 m depth) was studied using a soil column experiment and modelling simulation. The soil used in the experiment was drawn from an agricultural field in Xinzhen, Fangshan district, Beijing, China, and reconstituted in laboratory soil columns. Column experiments were conducted using bromide (conservative tracer) and ‐bearing aqueous solutions. The ammonium concentrations in the soil water samples were measured, and their values were plotted as the breakthrough curves. The chemical's soil–water distribution coefficients (Kd) were calculated using breakthrough curves. Then the retardation factor (R) in saturated soil was calculated. For the ‐bearing aqueous solutions, the strongest adsorption occurred at the soil depth of 0.30–0.45 m. The convection–dispersion equation model and chemical non‐equilibrium model in Hydrus‐1D were used to simulate transport in the loamy soil. The two‐site chemical non‐equilibrium model in Hydrus‐1D was best to simulate transport through the soil column. Parameter sensitivity study was conducted to investigate the influences of solute transport by Kd, the fraction of exchange sites assuming to be in equilibrium with the solution phase (f), the longitudinal dispersivity (λ), and the first‐order rate coefficients (ω). The sensitivity analysis results indicate Kd is the most critical parameter.  相似文献   

4.
The atmospheric chloride mass balance (CMB) method allows spatial evaluations of the average diffuse aquifer recharge by rainfall () in large and varied territories when long‐term steady conditions can be assumed. Often, the distributed average CMB variables necessary to calculate have to be estimated from the available variable‐length data series, which may be of suboptimal quality and spatial coverage. This paper explains the use of these data and the reliability of the results in continental Spain, chosen as a large and varied territory. The CMB variables have been regionalized by ordinary kriging at the same 4976 nodes of a 10 km × 10 km grid. Nodal values vary from 14 to 810 mm year–1, 90% ranging from 30 to 300 mm year–1. The recharge‐to‐precipitation ratios vary from 0.03 in low‐permeability formations and semiarid areas to 0.65 in some carbonate massifs. Integrated average results for the whole of continental Spain yield a potential aquifer recharge of 64 km3 year?1, the net recharge over permeable formations (40% of the territory) being 32 km3 year?1. Two main sources of uncertainty affecting (given by the coefficient of variation, CV), induced by the inherent natural variability of the variables (CVR) and from mapping (), have been segregated. The average CVR is 0.13 and could be improved with longer data series. The average is 0.07 and may be decreased with better data coverage. The estimates were compared with other regional and local recharge estimates, being 4% and 1% higher, respectively. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

5.
Urban stream features can be used to promote nutrient retention; however, their interactions with different hydrological regimes impact nutrient cycling, decrease their retention capacity, and inhibit stream ecosystem functioning. This study analysed the temporal and spatial dynamics of the uptake of three nutrients (nitrate, ammonium, and phosphorus) in an urban drainage stream during high flows. In particular, we studied variations in net uptake along the right margin (with native vegetation and a roots mat) comparatively to the left margin (a non‐rooted grassy bank). Applying the spiralling approach within each subreach on either side, we determined nutrient subreach (sr) retention metrics: uptake rate coefficients , mass transfer rates , and areal uptake rates . Our results showed nitrate (NO3) and ammonium (NH4) net uptakes on the right side were higher and more frequent along subreaches where the root mat was more abundant ( [μg m?2 s?1] = 22.80 ± 1.13 for NO3 and 10.50 ± 0.81 for NH4), whereas on the left side both nutrients showed patchy and inconsistent net uptake patterns despite the homogeneous grass distribution. Net uptake for filtered reactive phosphorus (FRP) was not observed on either side at any flow rate. The impact of hydrological factors such as discharge, travel time, water depth, and concentration, on uptake metrics was studied. Despite increases in travel time as the flow decreased, there was a reduction in net uptake rates, and , on either side. This was attributed to a reduction in water level with declining flows, which decreased hydrologic connectivity with the stream banks, combined with a decrease in water velocity and a reduction in nutrient concentrations. We concluded the rooted bank acted as an effective retention area by systematically promoting net uptake resulting in a twofold increased dissolved inorganic nitrogen (DIN) retention relative to the non‐rooted side where net uptake was spatially localized and highly dynamic. Overall, this work emphasized the importance of strategically sampling close to biologically active surfaces to more accurately determine areas where gross uptake surpasses release process.  相似文献   

6.
Evapotranspiration (ET) can cause diel fluctuations in the elevation of the water table and the stage in adjacent streams. The diel fluctuations of water levels change head gradients throughout the day, causing specific discharge through near‐stream sediment to fluctuate at the same time scale. In a previous study, we showed that specific discharge controls the residence time of groundwater in streambed sediment that, in turn, exerted the primary control on removal from groundwater passing through the streambed. In this study, we examine the magnitude of diel specific discharge patterns through the streambed driven by ET in the riparian zone with a transient numerical saturated–unsaturated groundwater flow model. On the basis of a first‐order kinetic model for removal, we predicted diel fluctuations in stream concentrations. Model results indicated that ET drove a diel pattern in specific discharge through the streambed and riparian zone (the removal zones). Because specific discharge is inversely proportional to groundwater travel time through the removal zones and travel time determines the extent of removal, diel changes in ET can result in a diel pattern in concentration in the stream. The model predictions generally matched observations made during summertime base‐flow conditions in a small coastal plain stream in Virginia. A more complicated pattern was observed following a seasonal drawdown period, where source components to the stream changed during the receding limb of the hydrograph and resulted in diel fluctuations being superimposed over a multi‐day trend in concentrations. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

7.
Although changes in rainfall characteristics have been noted across the world, few studies have reported those in mountainous areas. This study was undertaken to clarify spatial and temporal variations in rainfall characteristics such as annual rainfall amount (Pr), mean daily rainfall intensity (η), and ratio of rain days (λ) in mountainous and lowland areas in Taiwan. To this aim, we examined spatial and year‐to‐year variations and marginal long‐term trends in Pr, η, and λ, based on rainfall data from 120 stations during the period 1978–2008. The period mean rainfall () at the lowland stations had strong relationships with the period mean daily rainfall intensity () and the period mean ratio of rain days () during those 31 years. Meanwhile, was only strongly related to at mountainous stations, indicating that influences on spatial variations in were different between lowland and mountainous stations. Year‐to‐year variations in Pr at each station were primarily determined from the variation in η at most stations for both lowland and mountainous stations. Long‐term trend analysis showed that Pr and η increased significantly at 10% and 31% of the total 120 stations, respectively, and λ decreased significantly at 6% of the total. The increases in Pr were mostly accompanied by increases in η. Although stations with significant η increases were slightly biased toward the western lowland area, increases or decreases in Pr and λ were not common. These results contribute to understanding the impacts of possible climate changes on terrestrial hydrological cycles. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

8.
Non-unique solutions of inverse problems arise from a lack of information that satisfies necessary conditions for the problem to be well defined. This paper investigates these conditions for inverse modeling of water flow through multi-dimensional variably saturated porous media. It shows that in order to obtain a unique estimate of hydraulic parameters, along each streamline of the flow field (1) spatial and temporal head observations must be given; (2) the number of spatial and temporal head observations required should be greater or equal to the number of unknown parameters; (3) the flux boundary condition or the pumping rate of a well must be specified for the homogeneous case and both boundary flux and pumping rate are a must for the heterogeneous case; (4) head observations must encompass both saturated and unsaturated conditions, and the functional relationships for unsaturated hydraulic conductivity/pressure head and for the moisture retention should be given, and (5) the residual water content value also need to be specified a priori or water content measurements are needed for the estimation of the saturated water content.For field problems, these necessary conditions can be collected or estimated but likely involve uncertainty. While the problems become well defined and have unique solutions, the solutions likely will be uncertain. Because of this uncertainty, stochastic approaches are deemed to be appropriate for inverse problems as they are for forward problems to address uncertainty. Nevertheless, knowledge of these necessary conditions is critical to reduce uncertainty in both characterization of the vadose zone and the aquifer, and prediction of water flow and solute migration in the subsurface.  相似文献   

9.
N. Subba Rao 《水文研究》2012,26(22):3344-3350
A pollution index of groundwater (PIG) is proposed for quantification of water contamination. PIG quantifies the status of concentrations of water quality measures with respect to their drinking water quality standards. The validity of the proposed index is verified by choosing the data of groundwater quality of the Varaha River Basin (Visakhapatnam District, Andhra Pradesh, India) as a case study. The computed index from the study area varies from 0.83 to 2.55. The index disseminates the area into zones of insignificant (PIG <1.0), low (PIG: 1.0 to 1.5), moderate (PIG: 1.5 to 2.0), high (PIG 2.0 to 2.5) and very high (PIG >2.5) pollution. Insignificant pollution zone is observed from the upstream area, where the groundwater is dominated by , and very high pollution zone from the downstream area, where the groundwater is associated with Cl?. This indicates that the quality of groundwater in the study area is mainly influenced by the source of geogenic origin, but it is subsequently modified by the effects of anthropogenic and marine sources. Geochemical ratios (Na+ : Cl?, : Cl?, Na+ : Ca2+ and Mg2+ : Ca2+) also form the quantitative basis of the index. The present study paves the way to implement appropriate management strategies at a specific site to circumvent the pollution. As the classification of the pollution zones with PIG depends upon the drinking water quality standards, it becomes a universal assessment tool for groundwater contamination at any test area. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

10.
T. H. Brikowski 《水文研究》2015,29(7):1746-1756
Adaptation and mitigation efforts related to global trends in climate and water scarcity must often be implemented at the local, single‐catchment scale. A key requirement is understanding the impact of local climate and watershed characteristics coupled with these regional trends. For surface water, determination of multi‐parameter runoff elasticities is a promising tool for achieving such understanding, as explored here for two surface‐water dependent basins in Texas. The first basin is the water supply for Dallas‐Ft. Worth (DFW), and exhibits relatively high precipitation elasticity (proportional change in runoff to change in precipitation) εP = 2.64, and temperature elasticity εT = ? 0.41. Standard precipitation–temperature elasticity diagrams exhibit unusual concave contours of runoff change, indicating influence of additional parameters, which can be isolated using multi‐parameter approaches. The most influential local parameter in DFW is unexpected reduced runoff fraction in cooler wetter years. Those years exhibit increased summer (JJA) precipitation fraction, but predominant cracking soils in DFW minimize JJA runoff, yielding negative . A comparative basin near Houston shows positive , reflecting the local impact of tropical cyclones and lesser abundance of cracking soils. Both basins exhibit positive elasticity to 1‐year previous precipitation (e.g. DFW εP ? 1 = 1.24), reflecting the influence of soil moisture storage. Only DFW exhibits negative elasticity to 2‐year previous precipitation (εP ? 2 = ? 0.65), reflecting multi‐year influence of vegetation growth and increased evapotranspiration. Using these elasticities, analysis of historical multi‐decadal climate departures for DFW indicates the 80% decrease in runoff during the 1950–1957 drought of record was primarily caused by reduced precipitation. Runoff 56% above‐normal during an unprecedented 1986–1998 wet period was primarily caused by increased precipitation. Since 2000, despite precipitation slightly above normal, runoff has decreased 20%, primarily in response to ～ 1°C warming. Future precipitation droughts superimposed on this new drier normal are likely to be much more severe than historical experience would indicate. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

11.
The modeling of thick vadose zones is particularly challenging because of difficulties in collecting a variety of measured sediment properties, which are required for parameterizing the model. Some models rely on synthetic data, whereas others are simplified by running as homogeneous sediment domains and relying on a single set of sediment properties. Few studies have simulated flow processes through a thick vadose zone using real and comprehensive data sets comprising multiple measurements. Here, we develop a flow model for a 7-m-thick vadose zone. This model, combining the numerical codes CTRAN/W with SEEP/W, includes the measured sediment hydraulic properties of the investigated vadose zone and incorporates the actual climate and subsurface conditions of the study site (precipitations, water-table elevations, and stable isotope data). The model is calibrated by fitting the simulated and measured vertical profiles of water content. Our flow model calculates a transit time of 1 year for the travel of water through the 7-m vadose zone; this estimate matches stable isotope-based results obtained previously for this site. A homogeneous sediment domain flow model, which considers only a single set of sediment properties, produces a transit time that is approximately half the duration of that of the heterogeneous flow model. This difference highlights the importance of assuming heterogeneous material within models of thick vadose zones and testifies to the advantage gained when using real sediment hydraulic properties to parametrize a flow model.  相似文献   

12.
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13.
In arid to semi-arid regions, groundwater is a critical water resource heavily relied upon, with the recharge sources and patterns being predominantly shaped by climate change and regional disparities. To compare the characteristics of groundwater in the endorheic and exorheic river basins with the climate transition zone of Gansu Province, this study uses isotopic hydrochemical analyses. This study summarizes the differences in regional groundwater recharge and evolutionary patterns. The results shows that the distribution patterns of precipitation isotopes in endorheic and exorheic river basins are opposite to those of groundwater isotopes. Specifically, the precipitation in the endorheic areas is more depleted in heavy isotopes, whereas the groundwater is more enriched. Both endorheic areas and exorheic areas exhibit similar characteristics of groundwater hydrochemical evolution, evolving from low-mineralization Mg2+ HC O 3 − recharge water to Na+ Cl− type water with saline characteristics. The former is primarily replenished by surface water, whereas the latter is primarily replenished by precipitation. Variations in recharge patterns along with the differences in climatic conditions lead to distinct groundwater conditions in the two regions.  相似文献   

14.
In subsurface porous media, the soil water retention curve (WRC) and unsaturated hydraulic conductivity curve (UHC) are two important soil hydraulic property curves. Spatial heterogeneity is ubiquitous in nature, which may significantly affect soil hydraulic property curves. The main theme of this paper is to investigate how spatial heterogeneities, including their arrangements and amounts in soil flumes, affect soil hydraulic property curves. This paper uses a two‐dimensional variably saturated flow and solute transport finite element model to simulate variations of pressure and moisture content in soil flumes under a constant head boundary condition. To investigate the behavior of soil hydraulic property curves owing to variations of heterogeneities and their arrangements as well, cases with different proportions of heterogeneities are carried out. A quantitative evaluation of parameter variations in the van Genuchten model (VG model) resulting from heterogeneity is presented. Results show that the soil hydraulic properties are strongly affected by variations of heterogeneities and their arrangements. If the pressure head remains at a specific value, the soil moisture increases when heterogeneities increase in the soil flumes. On the other hand, the unsaturated hydraulic conductivity decreases when heterogeneities increase in the soil flumes under a constant pressure head. Moreover, results reveal that parameters estimated from both WRC and UHC also are affected by shapes of heterogeneity; this indicates that the parameters obtained from the WRC are not suitable for predicting the UHC of different shapes in heterogeneous media. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

15.
The fate and transport of contaminants in the vicinity of septic fields remains poorly understood in many hydrogeomorphological environments. We report hydrometric data from an intensive hillslope‐scale experiment conducted between 29 August and 11 November 1998 at a residential leach field in New York State. The objective of our study was to characterize water flux within the vadose zone, understand the physical controls on the flux, and predict how this ultimately will affect subsurface water quality. Soil‐water flux was calculated using matric potential measurements from a network of 25 tensiometer nests, each nest consisting of three tensiometers installed to depths of 10, 50 and 130 cm. Unsaturated hydraulic conductivity curves were derived at each depth from field‐determined time‐domain reflectometry–tensiometry moisture‐release curves and borehole permeametry measurements. Flownets indicated that a strong upward flux of soil water occurred between rainstorms. Following the onset of (typically convective) rainfall, low near‐surface matric potentials were rapidly converted to near‐saturated and saturated conditions, promoting steep vertical gradients through the near‐surface horizons of the hillslope. Lateral hydraulic gradients were typically 10 times smaller than the vertical gradients. Resultant flow vectors showed that the flux was predominantly vertical through the vadose zone, and that the flux response to precipitation was short‐lived. The flux response was controlled primarily by the shape of the unsaturated hydraulic conductivity curves, which indicated a rapid loss of conductivity below saturation. Thus, soil water had a very high residence time in the vadose zone. The absence of rapid wetting at 130 cm and the delayed and small phreatic zone response to rainfall indicated that water movement through macropores did not occur on this hillslope. These results are consistent with a Cl tracing experiment, which demonstrated that the tracer was retained in the vadose zone for several months after injection to the system. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

16.
Concentration–discharge (C–Q) relationships are widely used to assess the link between hydrological and biogeochemical processes at the catchment scale. C–Q relationships are mainly calibrated using mono-objective methods to represent, either concentrations or discharge-weighted concentrations (i.e., load). Based on its wide use in hydrological modelling, we test a multi-objective calibration for the C–Q relationship parameters, using both concentration and load, and compare it to a mono-objective calibration applied on either concentrations or load. This work is carried out on a high-frequency dataset (ORACLE-Orgeval Observatory, France). Our findings show that the multi-objective calibration yield a better representation of C–Q relationships parameters during the high and low-flow events. The multi-objective calibration can be used for all forms of C–Q relationships and avoids issues of under-representation of dilution processes characterized by high-discharge, low-concentration periods.  相似文献   

17.
In this work we study mixed finite element approximations of Richards’ equation for simulating variably saturated subsurface flow and simultaneous reactive solute transport. Whereas higher order schemes have proved their ability to approximate reliably reactive solute transport (cf., e.g. [Bause M, Knabner P. Numerical simulation of contaminant biodegradation by higher order methods and adaptive time stepping. Comput Visual Sci 7;2004:61–78]), the Raviart–Thomas mixed finite element method (RT0) with a first order accurate flux approximation is popular for computing the underlying water flow field (cf. [Bause M, Knabner P. Computation of variably saturated subsurface flow by adaptive mixed hybrid finite element methods. Adv Water Resour 27;2004:565–581, Farthing MW, Kees CE, Miller CT. Mixed finite element methods and higher order temporal approximations for variably saturated groundwater flow. Adv Water Resour 26;2003:373–394, Starke G. Least-squares mixed finite element solution of variably saturated subsurface flow problems. SIAM J Sci Comput 21;2000:1869–1885, Younes A, Mosé R, Ackerer P, Chavent G. A new formulation of the mixed finite element method for solving elliptic and parabolic PDE with triangular elements. J Comp Phys 149;1999:148–167, Woodward CS, Dawson CN. Analysis of expanded mixed finite element methods for a nonlinear parabolic equation modeling flow into variably saturated porous media. SIAM J Numer Anal 37;2000:701–724]). This combination might be non-optimal. Higher order techniques could increase the accuracy of the flow field calculation and thereby improve the prediction of the solute transport. Here, we analyse the application of the Brezzi-Douglas-Marini element (BDM1) with a second order accurate flux approximation to elliptic, parabolic and degenerate problems whose solutions lack the regularity that is assumed in optimal order error analyses. For the flow field calculation a superiority of the BDM1 approach to the RT0 one is observed, which however is less significant for the accompanying solute transport.  相似文献   

18.
We investigate fracture‐induced attenuation anisotropy in a cluster of events from a microseismic dataset acquired during hydraulic fracture stimulation. The dataset contains 888 events of magnitude ?3.0 to 0.0. We use a log‐spectral‐amplitude‐ratio method to estimate change in over a half‐hour time period where fluid is being injected and an increase in fracturing from S‐wave splitting analysis has been previously inferred. A Pearson's correlation analysis is used to assess whether or not changes in attenuation with time are statistically significant. P‐waves show no systematic change in during this time. In contrast, S‐waves polarised perpendicular to the fractures show a clear and statistically significant increase with time, whereas S‐waves polarised parallel to the fractures show a weak negative trend. We also compare between the two S‐waves, finding an increase in with time. A poroelastic rock physics model of fracture‐induced attenuation anisotropy is used to interpret the results. This model suggests that the observed changes in t* are related to an increase in fracture density of up to 0.04. This is much higher than previous estimates of 0.025 ± 0.002 based on S‐wave velocity anisotropy, but there is considerably more scatter in the attenuation measurements. This could be due to the added sensitivity of attenuation measurement to non‐aligned fractures, fracture shape, and fluid properties. Nevertheless, this pilot study shows that attenuation measurements are sensitive to fracture properties such as fracture density and aspect ratio.  相似文献   

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