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Low impact development (LID) practices are rarely implemented on slopes due to concerns about their poor hydrological performance and the potential impact on slope stability. Implementing LIDs on slopes, involving alterations to surface topography and subsurface hydrology (specifically, the formation of a groundwater mound), can pose challenges in maintaining slope stability. However, sloping areas often require LIDs for sustainable development. It is imperative to supplement the conventional design standard to address these challenges. Before proposing specific solutions, the impact of LIDs on slope stability should be understood first. This includes quantifying the extent of changes in slope stability before and after LID implementation, as well as identifying the key factors that influence stability. To address these, we developed a numerical model in HYDRUS‐2D to simulate the hydrological and geotechnical processes of slopes implemented with a two‐stepped bioretention cell (BC) system. The numerical model was calibrated and validated using monitoring data from a stepped BC in Cincinnati, Ohio, USA. Simulation scenarios encompassed three generic slope angles (15°, 20°, and 25°) with and without BCs, two initial groundwater table positions and two inflow volumes. The hydrological process was characterized by the evolution of the groundwater mound, and the geotechnical process was quantified using the factor of safety (FoS). Our findings indicated slope cutting and filling was likely to enhance stability with an increase in the FoS of 0.1. However, the formation of groundwater mounds, resulting from exfiltration, led to an approximate 0.1–0.2 reduction in the FoS, depending on the inflow volume. The subsequent groundwater mound evolution had no further impact on stability. Ultimately, the FoS was slightly reduced by around 0–0.1 due to the combined effect of cutting and filling operations and groundwater mounds. It was generally safe to implement LIDs on 15° slopes. For steeper slopes, special design considerations are necessary, such as reducing the drainage area to strike a balance between hydrological performance and slope safety. [ABSTRACT FROM AUTHOR]

Ecological water conveyance is an effective measure to mitigate or reverse vegetation ecosystem degradation in arid regions, which can lead to frequent fluctuations in the groundwater table. The depth of soil water that vegetation takes up varies in response to groundwater table fluctuations in arid environments. To better characterize the root water uptake process under dynamic changes in the groundwater table in arid regions, this study proposed a new model for simulating root water uptake. The model reduces the dominant effect of root density on water uptake by introducing a correction factor and accounts for the effect of changes in the water content profile on root water uptake in arid areas. The new model was incorporated into the HYDRUS code and tested against the monitoring data of typical vegetation in the arid region of northwestern China. The results demonstrated that the soil water content simulated by the new model matched well with the observed data, which was consistent with the water uptake process under the fluctuations of the groundwater table at the study site. Compared with other models, this model can flexibly alter water uptake layers according to soil moisture conditions in arid conditions, thus providing a new method to depict the dynamic process of water uptake influenced by fluctuations in the groundwater table. [ABSTRACT FROM AUTHOR]

Engineered carbon‐based nanoparticles are increasingly used for environmental, industrial, and medical purposes. Thus, understanding their interaction with and transport through materials is important. We examine the impact of nanoparticle hydrophobicity and porous medium surface area on the transport of carbon nanoparticles through sand‐packed columns under saturated and unsaturated conditions. The fluorescent carbon nanoparticles (FCNs) used in this study, synthesized from citric acid and ethanolamine, exhibit synthesis‐temperature‐dependent hydrophobicity. To quantify the impact of hydrophobicity on retention, we use FCNs synthesized at four temperatures: 190°C (FCN190), 210°C (FCN210), 230°C (FCN230), and 250°C (FCN250). Several observations are noted. First, the more hydrophobic particles (FCN230 and FCN250) attain lower outlet concentrations and mass recovery than more hydrophilic particles (FCN190 and FCN210). For instance, while 77% of the FCN190 was recovered after passing through a fine‐sand‐packed column, only 23% of the FCN250 was recovered. Second, sand surface area significantly impacts FCN recovery. A 17‐fold increase in sand surface area yields a 30% decrease in the recovery of FCN210. Third, no significant difference in the mass recovery of the FCNs was observed between the unsaturated and saturated conditions, which is attributed to the small size of the FCNs relative to the water film thickness surrounding sand grains. Fourth, the particle transport model in HYDRUS‐1D successfully simulated FCN transport, showing approximately a tenfold increase in the attachment coefficient for hydrophobic FCNs. In summary, through experiments and modeling, we show that hydrophobicity is a major factor impacting FCN transport. Key Points: The synthesis‐temperature‐dependent hydrophobicity reduces the transport of fluorescent carbon nanoparticles through sand‐packed columnsA two‐kinetic sites transport model describes the transport of fluorescent carbon nanoparticles in porous mediaFluorescent carbon nanoparticles are not trapped in the meniscus under unsaturated conditions at the tested moisture contents [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Northern peatlands faced compounding disturbances that transformed such critical ecosystems from long‐term carbon sinks into carbon sources. Considerable investment is therefore directed for restoring their carbon sequestration potential through large‐scale rewetting/rehabilitation. However, rapid need to transform their carbon dynamics contrasts with millennial timescales over which peat profiles that control key ecohydrological processes within these ecosystems have developed. This study demonstrates the sensitivity of vadose zone hydrology of northern peatlands to hydrophysical properties of the very near‐surface peat layer and therefore the potential capability of at least some ecohydrological processes to respond rapidly to developments in peat properties as a result of restoration. HYDRUS 1‐D Monte Carlo simulations were undertaken of near‐surface peat layers of various species and depths overlying degraded peat layer during periods of sustained drying. The modelling results showed that shallow additions of newly developed Sphagnum peat, just a couple of centimetres in depth, substantially modified near‐surface hydrology of peat profiles and significantly altered the time taken for reaching important ecohydrological pressure heads. Whilst a degraded peat layer reached threshold pressure head (TP) of −100 cm in 119 h, addition of 2.5‐cm layer of S. magellancium reduced the average time to TP by 18 hours, whilst S. fuscum and amalgamated Sphagnum overlying degraded peat across initial WTDs (5, 10, 15 and 20 cm) increased average time to TP by 304 and 540 h, respectively. This demonstrates that whilst peat hydrophysical properties have developed over millennia, ecohydrological dynamics of these systems rapidly adjusted through restoration approaches in response to disturbances. Significance Statement: Peat profiles accumulate over millennia forming hydrophysical properties that regulate the transfer of water from the saturated zone to the peat surface for evaporation and to support growth. Whilst this legacy effect of past peatland development on current ecohydrology function can be considered comparatively fixed over long time periods, we show through exploratory modelling that the very near‐surface peat (that may be impacted rapidly by disturbance or reclamation) provides the dominant control on these dynamics, thus making the peat profile more adaptable and resilient to change. [ABSTRACT FROM AUTHOR]

This study simulates the dynamics of exchange fluxes between Brazos River Alluvium Aquifer and the Brazos River, TX. Seven conceptual models for the connection between the river and the aquifer were simulated in HYDRUS 2D using small‐scale, high‐resolution transects across the river. These models assumed varying aquifer lithology and river incision depths and considered processes such as riverbed clogging and seepage face flows. Observed river stage values were used to specify a time‐variable head boundary, and the simulations were tested against observed hydraulic heads in two nearby monitoring wells. The nearly 1.5 years of sub‐hourly measurements spanned both flood and drought periods. The best‐fit conceptual model supported a hypothesized hydraulic disconnection between the subsurface near the river and the wider alluvial aquifer. In contrast to the assumptions of previous studies, these data were more consistent with the presence of a thin, low‐K structure (such as an abandoned paleochannel) rather than riverbed clogging. Across the range of models evaluated, the average net exchange between the river and the aquifer ranged from 0.016 to 12.4 m3/d/m. Most of the variability was attributed to baseflow across the riverbed, which ranged from 0.18 to 13.1 m3/d/m depending on the model. The ranges of exchange fluxes across the seepage face (0.004 to 2.37 m3/d/m) and recharge from the river to the aquifer (0.1 to 5.63 m3/d/m) were significant, but not as influential. Based on these values, the choice of conceptual model could have a profound impact on the accuracy of numerical models used for river management. Extrapolated across the entire reach, this uncertainty would amount to ±83 m3/s of discharge, equivalent to 34% of the river's discharge near its outlet. [ABSTRACT FROM AUTHOR]

This study presents a conceptual Dual‐Permeability Non‐Equilibrium (DPNE) model that accounts for both physical and chemical non‐equilibria to describe the reactive solute transport through a porous medium. A semi‐analytical solution of the DPNE model is derived in the Laplace domain, which is then numerically inverted to obtain concentrations in different domains at different times and depths. The derived semi‐analytical solution is validated using experimental data and existing analytical (for simple problems) and numerical solutions. The Global Sensitivity Analysis (GSA) is performed to identify model parameters with an impact on nonreactive tracer breakthrough curves (BTC) for a selected data set. A sensitivity‐based calibration of the DPNE model's parameters is carried out to simulate a BTC with multiple inflection points. The DPNE model can better describe the experimental datasets than the model based on the dual‐porosity (MIM) concept with first‐order mass transfer. Since the DPNE model considers detailed sorption and mass transfer dynamics, it is suitable for process‐based investigations. Key Points: Semi‐analytical solution for non‐equilibrium solute transport in a dual‐permeability porous system with an immobile region is presentedThe global sensitivity analysis is carried out for input parameters for a non‐reactive soluteAn insight into intra‐ and inter‐aggregate mass transfers is presented [ABSTRACT FROM AUTHOR]

Information on water balance components such as evapotranspiration and groundwater recharge are crucial for water management. Due to differences in physical conditions, but also due to limited budgets, there is not one universal best practice, but a wide range of different methods with specific advantages and disadvantages. In this study, we propose an approach to quantify actual evapotranspiration, groundwater recharge and water inflow, i.e. precipitation and irrigation, that considers the specific conditions of irrigated agriculture in warm, arid environments. This approach does not require direct measurements of precipitation or irrigation quantities and is therefore suitable for sites with an uncertain data basis. For this purpose, we combine soil moisture and energy balance monitoring, remote sensing data analysis and numerical modelling using Hydrus. Energy balance data and routine weather data serve to estimate ET0. Surface reflectance data from satellite images (Sentinel‐2) are used to derive leaf area indices, which help to partition ET0 into energy limited evaporation and transpiration. Subsequently, first approximations of water inflow are derived based on observed soil moisture changes. These inflow estimates are used in a series of forward simulations that produce initial estimates of drainage and ETact, which in turn help improve the estimate of water inflow. Finally, the improved inflow estimates are incorporated into the model and then a parameter optimization is performed using the observed soil moisture as the reference figure. Forward simulations with calibrated soil parameters result in final estimates for ETact and groundwater recharge. The presented method is applied to an agricultural test site with a crop rotation of cotton and wheat in Punjab, Pakistan. The final model results, with an RMSE of 2.2% in volumetric water content, suggest a cumulative ETact and groundwater recharge of 769 and 297 mm over a period of 281 days, respectively. The total estimated water inflow accounts for 946 mm, of which 77% originates from irrigation. [ABSTRACT FROM AUTHOR]

Differences in vertical root distributions are often assumed to create resource uptake trade‐offs that determine plant growth and coexistence. Yet, most plant roots are in shallow soils, and data linking root distributions with resource uptake and plant abundances remain elusive.Here we used a tracer experiment to describe the vertical distribution of absorptive roots of dominant species in a shrub–steppe ecosystem. To describe how these different rooting distributions affected water uptake in wet and dry soils across a growing season, we used a soil water movement model. Root traits were then correlated with plant landscape abundances.Deeper root distributions extracted more soil water, had larger unique hydrological niches and were more abundant on the landscape. Though most (>50%) root biomass and tracer uptake occurred in shallow soils (0–32 cm), the depth of 50% of tracer uptake varied from 11 to 32 cm across species and species with deeper rooting distributions were more abundant on the landscape (R2 =.95). The water flow model revealed that deeper rooting distributions should extract more soil water (i.e. a range of 60–113 mm of soil water) because shallow roots were often in dry soils. These potential water uptake values were tightly correlated with species' abundances on the landscape (R2 =.90). Finally, each species' rooting distribution demonstrated a depth and time at which it could extract more soil water than any other rooting distribution, and the size of these unique hydrological niches indices was also well correlated with species' abundances (R2 =.89).Synthesis. Our results demonstrate not only a correlation between root distributions and species abundance, but also the mechanism through which differences in rooting distributions can determine resource uptake and niche partitioning, even when most roots are found in shallow soils. [ABSTRACT FROM AUTHOR]

Food contamination is responsible for thousands of deaths worldwide every year. Plants represent the most common pathway for chemicals into the human and animal food chain. Although existing dynamic plant uptake models for chemicals are crucial for the development of reliable mitigation strategies for food pollution, they nevertheless simplify the description of physicochemical processes in soil and plants, mass transfer processes between soil and plants and in plants, and transformation in plants. To fill this scientific gap, we couple a widely used hydrological model (HYDRUS) with a multicompartment dynamic plant uptake model, which accounts for differentiated multiple metabolization pathways in plant's tissues. The developed model is validated first theoretically and then experimentally against measured data from an experiment on the translocation and transformation of carbamazepine in three vegetables. The analysis is further enriched by performing a global sensitivity analysis on the soil‐plant model to identify factors driving the compound's accumulation in plants' shoots, as well as to elucidate the role and the importance of soil hydraulic properties on the plant uptake process. Results of the multilevel numerical analysis emphasize the model's flexibility and demonstrate its ability to accurately reproduce physicochemical processes involved in the dynamic plant uptake of chemicals from contaminated soils. Key Points: A dynamic plant uptake module is coupled with the HYDRUS model to simulate the translocation of chemicals in the soil‐plant continuumTheoretical and experimental scenarios are used to validate the coupled model and demonstrate its flexibilityThe model satisfactorily reproduces the measured carbamazepine translocation and transformation in three vegetables [ABSTRACT FROM AUTHOR]

Landscape‐scale reconstruction and prescription of soil cover systems following oil sands mining is challenging due to the quality of available reclamation materials and the subhumid climate of the Boreal Plains of Canada. In an experimental reclaimed watershed (Sandhill Fen Watershed), basin‐scale upland landforms (i.e., hummocks) were designed to provide groundwater to adjacent lowlands, necessitating adequate recharge following establishment of forest vegetation. Volumetric water contents, soil water pressure heads, and groundwater levels were monitored for four years throughout the watershed and used to calibrate and verify numerical models in HYDRUS. Using a variably saturated two‐dimensional domain, we identified a threshold‐like relationship between recharge (or upflux) and upland hummock height, where upland hummocks not tall enough to limit root water uptake from the saturated zone decreased recharge or resulted in net upflux. Recharge varied with soil cover texture (higher in coarser‐textured) and associated soil hydraulic parameters. Furthermore, scenario tests indicated the importance and relative influence that maximum rooting depths, forest floor placement thicknesses, and leaf area indices (all associated with forest development) had on recharge. Simulations utilizing a historical climate record indicated that interannual climatic variability was as influential as variation in soil cover texture in determining recharge. Reclamation practitioners should recognize that the water balances of reconstructed landscapes are largely influenced by the trade‐off between optimizing forest productivity and sourcing water to downgradient landscape positions. Key Points: A tradeoff exists between optimizing forest productivity and facilitating groundwater recharge at reclaimed mines in sub‐humid regionsRecharge exhibited a threshold‐like relationship to landform height, driven by the distance between the water table and rooting zone.Factors associated with forest development, such as maximum rooting depth, were key controls on recharge over the long‐term. [ABSTRACT FROM AUTHOR]

Abstract: Thermal conductivity is an essential component in multiphysics models and coupled simulation of heat transfer, fluid flow, and solute transport in porous media. In the literature, various empirical, semiempirical, and physical models were developed for thermal conductivity and its estimation in partially saturated soils. Recently, Ghanbarian and Daigle (GD) proposed a theoretical model, using the percolation‐based effective‐medium approximation, whose parameters are physically meaningful. The original GD model implicitly formulates thermal conductivity λ as a function of volumetric water content θ. For the sake of computational efficiency in numerical calculations, in this study, we derive an explicit λ(θ) form of the GD model. We also demonstrate that some well‐known empirical models, e.g., Chung‐Horton, widely applied in the HYDRUS model, as well as mixing models are special cases of the GD model under specific circumstances. Comparison with experiments indicates that the GD model can accurately estimate soil thermal conductivity. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background To compare the reduction of intraocular pressure (IOP) and glaucoma medications following selective laser trabeculoplasty (SLT) versus stand-alone placement of the Hydrus microstent, a microinvasive glaucoma surgery device. Design Prospective interventional case-series. University practice. Participants Fifty six eyes (56 patients) with uncontrolled primary open-angle glaucoma. Methods Patients received either SLT ( n = 25) or Hydrus implantation ( n = 31) in two centres. Patients were evaluated at baseline and 1, 7 days, 1, 3, 6 and 12 months after surgery. Main Outcome Measures Intraocular pressure and number of glaucoma medications variations inter-groups and intra-groups. Results There were no significant differences at baseline between groups, but the mean deviation was worse in the Hydrus group (−8.43 ± 6.84 dB, confidence limits (CL)−2.8/−3.3 vs.−3.04 ± 0.65 dB, CL−6/−10.8; P < 0.001). After 12 months, there was a significant decrease in IOP and medications in the Hydrus group compared with baseline values. In the SLT group, only the decrease in IOP was significant. There was 3-fold greater reduction in medication use in the Hydrus group compared with SLT (−1.4 ± 0.97 vs.−0.5 ± 1.05, P = 0.001). 47% of patients were medication free at 12 months in the Hydrus group (4% in the SLT group). No complications were recorded in the SLT group. In the Hydrus group, three patients experienced a temporary reduction of visual acuity post-operatively, and two patients had post-operative IOP spikes that resolved within one week. Conclusions Both SLT and Hydrus implantation reduced IOP without serious adverse events. Hydrus implantation led to a significant and further reduction in medication dependence at 12 months. [ABSTRACT FROM AUTHOR]

Considering all the alterations on hydrology and water quality that urbanization process brings, permeable pavement (PP) is an alternative to traditional impermeable asphalt and concrete pavement. The goal of the PP and other low impact development devices is to increase infiltration and reduce peak runoff flows. These structures are barely used in Brazil aiming stormwater management, one of the big hydrological issues in cities throughout the country, with increasing urbanization rates. The main objective of this paper is the hydraulic characterization of a PP and the assessment of its hydrological efficiency from the point of view of the infiltration process. The study focuses on a pilot area in a parking lot in an urban area (Recife, Brazil). Soil elements filling the voids between concrete elements were sampled (particle size density, water contents) and tested with water infiltration experiments at several points of the 3 m × 1.5 m surface pilot area. Beerkan Estimation of Soil Transfer parameters algorithm was applied to the infiltration experiment data to obtain the hydraulic characteristics of the soil composing the PP surface layer, the concrete grid pavers (with internal voids filled with natural soil) permeability being neglected. Results show that the soil hydraulic characteristics vary spatially within the pilot area and that the soil samples have different hydraulic behaviours. The hydraulic characteristics derived from Beerkan Estimation of Soil Transfer parameters analysis were implemented into Hydrus code to simulate runoff, infiltration and water balance over a year. The numerical simulation showed the good potential of the PP for rainfall-runoff management, which demonstrates that PP can be used to retrofit existing parking infrastructure and to promote hydrological behaviour close to natural soils. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Forests play a determinant role in the hydrologic cycle, with water being the most important ecosystem service they provide in semiarid regions. However, this contribution is usually neither quantified nor explicitly valued. The aim of this study is to develop a novel hydroeconomic modeling framework for assessing and designing the optimal integrated forest and water management for forested catchments. The optimization model explicitly integrates changes in water yield in the stands (increase in groundwater recharge) induced by forest management and the value of the additional water provided to the system. The model determines the optimal schedule of silvicultural interventions in the stands of the catchment in order to maximize the total net benefit in the system. Canopy cover and biomass evolution over time were simulated using growth and yield allometric equations specific for the species in Mediterranean conditions. Silvicultural operation costs according to stand density and canopy cover were modeled using local cost databases. Groundwater recharge was simulated using HYDRUS, calibrated and validated with data from the experimental plots. In order to illustrate the presented modeling framework, a case study was carried out in a planted pine forest ( Pinus halepensis Mill.) located in south-western Valencia province (Spain). The optimized scenario increased groundwater recharge. This novel modeling framework can be used in the design of a 'payment for environmental services' scheme in which water beneficiaries could contribute to fund and promote efficient forest management operations. [ABSTRACT FROM AUTHOR]

Determination of saturated hydraulic conductivity, Ks, and the shape parameters α and n of the water retention curve, θ(h), is of paramount importance to characterize the water flow in the vadose zone. This work presents a modified upward infiltration method to estimate Ks, α and n from numerical inverse analysis of the measured cumulative upward infiltration (CUI) at multiple constant tension lower boundary conditions. Using the HYDRUS-2D software, a theoretical analysis on a synthetic loam soil under different soil tensions (0, 0-10, 0-50 and 0-100 cm), with and without an overpressure step of 10 cm high from the top boundary condition at the end of the upward infiltration process, was performed to check the uniqueness and the accuracy of the solutions. Using a tension sorptivimeter device, the method was validated in a laboratory experiment on five different soils: a coarse and a fine sand, and a 1-mm sieved loam, clay loam and silt-gypseous soils. The estimated α and n parameters were compared to the corresponding values measured with the TDR-pressure cell method. The theoretical analysis demonstrates that Ks and θ(h) can be simultaneously estimated from measured upward cumulative infiltration when high (>50 cm) soil tensions are initially applied at the lower boundary. Alternatively, satisfactory results can be also obtained when medium tensions (<50 cm) and the Ks calculated from the overpressure step at the end of the experiment are considered. A consistent relationship was found between the α ( R2 = 0.86, p < 0.02) and n ( R2 = 0.97, p < 0.001) values measured with the TDR-pressure cell and the corresponding values estimated with the tension sorptivimeter. The error between the α (in logarithm scale) and n values estimated with the inverse analysis and the corresponding values measured with pressure chamber were 3.1 and 6.1%, respectively. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Data from six monitoring stations were combined with a soil-water dynamics model (HYDRUS 1D) to achieve physically-based estimates of shallow water-table recharge in representative hydropedological settings of the glaciated midwestern U.S.A. Calibration involved inverse modeling that yielded optimized hydraulic parameters. Root mean square errors for modeled versus measured soil moisture contents were generally within 3% for all soil layers at the six study sites. The optimized models also accurately simulated recharge values that corresponded to observed water-table fluctuations. Optimized parameter values were consistent with estimates from a pedotransfer function, lab analyses, and field experiments. Forward modeling indicated that shallow water-table recharge in mid-continent glacial settings is approximately 35% of precipitation, but interannual and monthly variability is significant. Soil parent materials and horizon characteristics influence recharge primarily through their control on Ks with clay-rich till parent materials producing values as low as 16% and coarse-grained outwash parent materials producing values as high as 58% of precipitation. During the three-year study period, distinct seasonality of recharge was observed with most recharge occurring in the winter (seasonal mean of all sites was 66% of precipitation) and lesser but interannually stable amounts in the spring (44%), summer (13%), and autumn (16%). This research underscores the importance of incorporating pedological information into models of soil-water dynamics and groundwater recharge. © 2015 The Authors. Hydrological Processes published by John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

For many scientific and practical tasks, it is important to estimate the soil-water percolation fluxes. This paper builds on measurements with large horizontal time-domain reflectometry water content sensors in a loamy Mollisol. The sensors were installed into pre-drilled holes and the gaps between them, and the soil was filled with a slurry of local soil with water. This gave rise to envelopes around them that contained artificial macropores. The sensors reacted to intensive rains by a rapid increase of their readings, often above the native soil's porosity, followed by an almost equally rapid decrease. The paper explores the feasibility of quantifying the rapid percolation, based on these anomalous water content peaks, and demonstrates that this is possible in principle, if the processes are simulated by a suitable model. A two-dimensional dual porosity non-equilibrium (mobile-immobile) model was tried. The envelope around the sensor was modelled as an annulus with higher porosity and hydraulic conductivity, which attracts preferential flow and amplifies the percolation signal. With the model at hand, the flux hydrographs can be derived from model simulations and measured precipitation. For contrast, the Durner equilibrium dual porosity model was tried but was found little suitable. However, even the mobile-immobile model did not perform perfectly. Simulated water contents were similar to the measured ones at some depths but not in the others, and the percolation fluxes were overestimated, compared to cumulative soil-water balance. Efforts to improve model performance were not successful. Hence, the model structure needs to be improved. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Because groundwater is Earth's largest pool of freshwater, understanding the sensitivity of deep drainage to climate, soils, and land cover is critical in managing water resources. To better understand controls on this critical flux in the context of woody encroachment, we determined the sensitivity of deep drainage to climate, soil texture, soil compaction, rooting depth, growing season duration, and plant-water stress response using Hydrus-1D to simulate deep drainage. To evaluate the simulation results, we compared these results with ground measurements at two anchor sites. At both anchor sites, Hydrus-1D predictions of deep drainage matched measured values within the errors inherent in ground measurements. Sensitivity analysis suggested greatest sensitivity of deep drainage to climate (24 mm yr−1) and rooting depth (12 mm yr−1), moderate sensitivity to growing season duration (5 mm yr−1) and soil texture (4 mm yr−1), and lowest sensitivity to topsoil compaction and plant-water stress response (3 mm yr−1). The sensitivity analysis indicated the relative importance of the plant-related factors considered, which, in decreasing order, were rooting depth, growing season duration, and plant-water stress response - factors that change concomitantly as a result of forestation or woody encroachment. Further ground-truth measurements of woody encroachment effects on deep drainage are needed to confirm or refine the results of this simulation modelling study. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The effects of land use changes on the ecology and hydrology of natural watersheds have long been debated. However, less attention has been given to the hydrological effects of forest roads. Although less studied, several researchers have claimed that streamflow changes related to forest roads can cause a persistent and pervasive effect on hillslope hydrology and the functioning of the channel system. The main potential direct effects of forest roads on natural watersheds hydrologic response are runoff production on roads surfaces due to reduced infiltration rates, interruption of subsurface flow by road cutslopes and rapid transfer of the produced runoff to the stream network through roadside ditches. The aforementioned effects may significantly modify the total volume and timing of the hillslope flow to the stream network. This study uses detailed field data, spatial data, hydro-meteorological records, as well as numerical simulation to investigate the effects of forest roads on the hydrological response of a small-scale mountain experimental watershed, which is situated in the east side of Penteli Mountain, Attica, Greece. The results of this study highlight the possible effects of forest roads on the watersheds hydrological response that may significantly influence direct runoff depths and peak flow rates. It is demonstrated that these effects can be very important in permeable watersheds and that more emphasis should be given on the impact of roads on the watersheds hydrological response. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The soil moisture state partitions both mass and energy fluxes and is important for many hydro-geochemical cycles, but is often only measured within the surface layer. Estimating the amount of soil moisture in the root-zone from this information is difficult due to the nonlinear and heterogeneous nature of the various processes which alter the soil moisture state. Data-driven methods, such as artificial neural networks (ANN), mine data for nonlinear interdependencies and have potential for estimating root-zone soil moisture from surface soil moisture observations. To create an ANN root-zone model that was nonsite-specific and physically constrained, a training set was generated by forcing HYDRUS-1D with meteorological observations for different soil profiles from the unsaturated soil hydraulic database. Ensemble ANNs were trained to provide soil moisture at depths of 10, 20, and 50 cm below the surface using surface soil moisture observations and local meteorological information. Insights into the processes represented by the ANNs were derived from a clamping sensitivity analysis and by changing the ANNs input data. Further model testing based on synthetic soil moisture profiles from three McMaster Mesonet and three USDA soil climate analysis network sites suggests that ANNs are a flexible tool capable of predicting root-zone soil moisture with good accuracy. It was found that ANNs could well represent soil moisture as estimated by HYDRUS-1D, but performance was reduced in comparison to in situ soil moisture observations outside the training conditions. The transferability of the model appears limited to the same geographic region. [ABSTRACT FROM AUTHOR]

This article investigates the soil moisture dynamics within two catchments (Stanley and Krui) in the Goulburn River in NSW during a 3-year period (2005-2007) using the HYDRUS-1D soil water model. Sensitivity analyses indicated that soil type, and leaf area index were the key parameters affecting model performance. The model was satisfactorily calibrated on the Stanley microcatchment sites with a single point rainfall record from this microcatchment for both surface 30 cm and full-profile soil moisture measurements. Good correlations were obtained between observed and simulated soil water storage when calibrations for one site were applied to the other sites. We extended the predictions of soil moisture to a larger spatial scale using the calibrated soil and vegetation parameters to the sites in the Krui catchment where soil moisture measurement sites were up to 30 km distant from Stanley. Similarly good results show that it is possible to use a calibrated soil moisture model with measurements at a single site to extrapolate the soil moisture to other sites for a catchment with an area of up to 1000 km2 given similar soils and vegetation and local rainfall data. Site predictions were effectively improved by our simple data assimilation method using only a few sample data collected from the site. This article demonstrates the potential usefulness of continuous time, point-scale soil moisture data (typical of that measured by permanently installed TDR probes) and simulations for predicting the soil wetness status over a catchment of significant size (up to 1000 km2). Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The connectivity and upscaling of overland runoff and sediment transport are important issues in hillslope hydrology to identify water flux and sediment transport within landscape. These processes are highly variable in time and space with regard to their interactions with vegetation and soil surface conditions. The generation of overland runoff and its spatial connectivity were examined along a slope to determine the variations in the transport mechanism of runoff and soil particles by rain splash and overland runoff. Field experiments were conducted by erosion plots on a steep hillslope at lengths of 5, 10, and 15 m. The overland runoff connectivity and flow transport distance decreased with the slope length, while spatial variability of infiltration increased significantly with the slope length. Observation of subsurface flow revealed that surface soil and litter layer could have important role in water transport. However, the surface soil water content and water flux transport along the slope was highly variable for different storm events; the variability was related to the complexity of the system, mainly by way of the initial wetness conditions and infiltration characteristics. Only net rain-splashed soil was measurable, but examination of the water flux, overland runoff and sediment transport connectivity, characteristics of sheetwash, and the variability in spatial infiltration indicated an increase in the contribution of the rain splash transport mechanism along the slope. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

•Deep root water uptake in tropical Amazonian forests has been a major discovery during the last 15 yr. However, the effects of extended droughts, which may increase with climate change, on deep soil moisture utilization remain uncertain. •The current study utilized a 1999–2005 record of volumetric water content (VWC) under a throughfall exclusion experiment to calibrate a one-dimensional model of the hydrologic system to estimate VWC, and to quantify the rate of root uptake through 11.5 m of soil. •Simulations with root uptake compensation had a relative root mean square error (RRMSE) of 11% at 0–40 cm and < 5% at 350–1150 cm. The simulated contribution of deep root uptake under the control was c. 20% of water demand from 250 to 550 cm and c. 10% from 550 to 1150 cm. Furthermore, in years 2 (2001) and 3 (2002) of throughfall exclusion, deep root uptake increased as soil moisture was available but then declined to near zero in deep layers in 2003 and 2004. •Deep root uptake was limited despite high VWC (i.e. > 0.30 cm3 cm−3). This limitation may partly be attributable to high residual water contents ( θr) in these high-clay (70–90%) soils or due to high soil-to-root resistance. The ability of deep roots and soils to contribute increasing amounts of water with extended drought will be limited. [ABSTRACT FROM AUTHOR]

Heat flux through shallow streambed sediments is often used to quantify streambed water exchange with groundwater. Although two-dimensional (2-D) and three-dimensional (3-D) models are available, one-dimensional (1-D) models still have advantages in terms of ease of use and cost effectiveness. This study investigated error associated with the vertical flow assumption for a lateral section of a synthetic channel of varying geometry, hydraulic gradient, and stage using 1-D and 2-D models. Hydraulic gradient had the greatest influence on total channel flux. Flux at the lateral edge of the channel was up to 8.3 times higher than at channel center, and seepage from the channel banks accounted for up to 50% of total flux. Despite this variation along the channel boundary, the difference between channel flux estimates using 1-D and 2-D models was less than 30%. The models were applied to data from a large irrigation canal, and 1-D channel flux estimates were 30% greater and 81% lower than from the 2-D model, using temperatures collected at channel center and at the left edge of the channel, respectively. These results stress the importance of placing probes to best capture water flux direction when using 1-D, temperature-based methods. [ABSTRACT FROM AUTHOR]

The heat pulse probe (HPP) has received more attention as it allows in situ, simultaneous, and automated measurements of soil hydraulic and thermal properties, as well as soil water fluxes. Although the currently used design allows many applications, changes in HPP design and analyses are needed to increase the sensitivity to smaller water fluxes. In this study, numerical simulations were used to evaluate the effects of (1) sensor locations and thermal properties of the HPP sensor body material, (2) the heater diameter and heat pulse intensity, and (3) vapor flow on HPP performance. A numerical study was carried out using the HYDRUS code for the HPP consisting of three parallel needles, spaced 6 mm apart. A heater of varying diameter in the center is surrounded by a pair of thermistor needles. Our results show that significantly different temperature responses will be obtained depending on the axial location of thermistors, and that only temperature measurements near the middle of the 33-mm-long heater fulfill the assumption of an infinite line heat source. It is shown that larger heater needle diameters allow larger heat pulses, leading to larger temperature differences between upstream and downstream thermistor needles and a higher sensitivity to water flux measurements. For example, for a standard 1-mm-diameter heater needle, ten times greater heat pulse input results in ten times greater sensitivity, but with the maximum temperature at the heater exceeding 100°C. This maximum temperature can be reduced to 80°C by increasing the heater diameter to 4 mm, while maintaining equal sensitivity. Consideration of vapor transport significantly reduced temperature increases near the heater caused by latent heat of vaporization. Larger heat pulses are beneficial for estimation of liquid water fluxes in the 1 cm d−1 range, provided vapor transport is considered. [ABSTRACT FROM AUTHOR]

A variety of analytical and numerical models have been developed during the past several decades to predict water and solute transfer processes between the soil surface and the groundwater table. While many models quantifying solute transport in soils usually consider only one solute and severely simplify various chemical interactions, others such as the geochemical module of HYDRUS-1D consider multiple solutes and their mutual interactions. In this study we use HYDRUS-1D to analyze water flow and solute transport in three soil lysimeters (1.2 m2 × 1 m) irrigated during the summer months with waters of different quality that were used to evaluate salinization and alkalization hazards. The soil monoliths were constructed in a Eutric Fluvisol in Alentejo, Portugal. The electrical conductivity (EC) of irrigation water varied between 0.4 and 3.2 dS m−1, and the sodium adsorption ratio (SAR) varied between 1 and 6 (mmol(c) L−1)0.5, while maintaining a ratio of Ca:Mg equal to 1:2. The soil monoliths were subjected to regular rainfall and leaching during the rest of the year. Water contents and fluxes, concentrations of individual ions (Na+, Ca2+, and Mg2+), electrical conductivity of the soil solution, SAR, and exchangeable sodium percentage (ESP) indices were monitored from May 2001 to September 2004 at four depths (10, 30, 50, and 70 cm) in all three soil monoliths. Irrigation water with EC up to 1.6 dS m−1 did not cause salinization or alkalization hazards. The rainfall water leached the salts accumulated during the irrigation period down to a depth of 100 cm. Rainfall, however, did not restore the salinity and sodicity of the soil to its original values below a depth of 60 cm for the lysimeter irrigated with water having an EC equal to 3.2 dS m−1. HYDRUS-1D successfully described field measurements of the water content ( R2 = 0.60), overall salinity ( R2 = 0.65), and the concentration of individual soluble cations ( R2 ranged between 0.62 and 0.78) as well as the sodium adsorption ratio ( R2 = 0.87) and the exchangeable sodium percentage ( R2 = 0.76). [ABSTRACT FROM AUTHOR]