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Journal Details
Format
Journal
eISSN
1338-4333
First Published
28 Mar 2009
Publication timeframe
4 times per year
Languages
English

Search

Volume 66 (2018): Issue 2 (June 2018)

Journal Details
Format
Journal
eISSN
1338-4333
First Published
28 Mar 2009
Publication timeframe
4 times per year
Languages
English

Search

13 Articles
Open Access

Thematic Issue on HYDRUS Software Applications to Subsurface Fluid Flow and Contaminant Transport

Published Online: 06 Feb 2018
Page range: 129 - 132

Abstract

Open Access

New features of version 3 of the HYDRUS (2D/3D) computer software package

Published Online: 06 Feb 2018
Page range: 133 - 142

Abstract

Abstract

The capabilities of the HYDRUS-1D and HYDRUS (2D/3D) software packages continuously expanded during the last two decades. Various new capabilities were added recently to both software packages, mostly by developing new standard add-on modules such as HPx, C-Ride, UnsatChem, Wetland, Fumigant, DualPerm, and Slope Stability. The new modules may be used to simulate flow and transport processes in one- and two-dimensional transport domains and are fully supported by the HYDRUS graphical user interface (GUI). Several nonstandard add-on modules, such as Overland, Isotope, and Centrifuge, have also been developed, but are not fully supported by the HYDRUS GUI. The objective of this manuscript is to describe several additional features of the upcoming Version 3 of HYDRUS (2D/3D), which was unveiled at a recent (March 2017) HYDRUS conference and workshop in Prague. The new features include a flexible reservoir boundary condition, expanded root growth features, and new graphical capabilities of the GUI. Mathematical descriptions of the new features are provided, as well as two examples illustrating applications of the reservoir boundary condition.

Keywords

  • HYDRUS
  • Reservoir boundary condition
  • Pumping well
  • Root growth
  • Graphical user interface
Open Access

Effect of temporal averaging of meteorological data on predictions of groundwater recharge

Published Online: 06 Feb 2018
Page range: 143 - 152

Abstract

Abstract

Accurate estimates of infiltration and groundwater recharge are critical for many hydrologic, agricultural and environmental applications. Anticipated climate change in many regions of the world, especially in tropical areas, is expected to increase the frequency of high-intensity, short-duration precipitation events, which in turn will affect the groundwater recharge rate. Estimates of recharge are often obtained using monthly or even annually averaged meteorological time series data. In this study we employed the HYDRUS-1D software package to assess the sensitivity of groundwater recharge calculations to using meteorological time series of different temporal resolutions (i.e., hourly, daily, weekly, monthly and yearly averaged precipitation and potential evaporation rates). Calculations were applied to three sites in Brazil having different climatological conditions: a tropical savanna (the Cerrado), a humid subtropical area (the temperate southern part of Brazil), and a very wet tropical area (Amazonia). To simplify our current analysis, we did not consider any land use effects by ignoring root water uptake. Temporal averaging of meteorological data was found to lead to significant bias in predictions of groundwater recharge, with much greater estimated recharge rates in case of very uneven temporal rainfall distributions during the year involving distinct wet and dry seasons. For example, at the Cerrado site, using daily averaged data produced recharge rates of up to 9 times greater than using yearly averaged data. In all cases, an increase in the time of averaging of meteorological data led to lower estimates of groundwater recharge, especially at sites having coarse-textured soils. Our results show that temporal averaging limits the ability of simulations to predict deep penetration of moisture in response to precipitation, so that water remains in the upper part of the vadose zone subject to upward flow and evaporation.

Keywords

  • Groundwater recharge
  • Meteorological data
  • Temporal averaging
  • HYDRUS-1D
  • Infiltration
  • Evaporation
Open Access

Operational validation of HYDRUS (2D/3D) for capillary barriers using data of a 10-m tipping trough

Published Online: 06 Feb 2018
Page range: 153 - 160

Abstract

Abstract

Capillary barriers are an interesting alternative component for cover systems of landfills and contaminated sites. Provided they are sufficiently validated, soil hydrological models could be fast and powerful tools for the dimensioning of capillary barriers. Outflow rates measured in a 10 m long tipping trough for one material combination and two slopes from stationary periods were compared to simulation results of HYDRUS (2D/3D), Version 2.05. The measured outflow rates show a typical pattern with slope-dependent threshold values indicating the efficiency of the capillary barrier. This flow pattern could not be reproduced with HYDRUS (2D/3D) that for different input setups produced smooth patterns without thresholds. The input setup was varied for different soil hydraulic models (van Genuchten-Mualem vs. Brooks-Corey), homogeneous and heterogeneous transport domains (no scaling vs. stochastically distributed scaling factors considering the Miller-Miller similitude), different HYDRUS versions (standard vs. alternative; i.e., with material properties assigned either to finite element nodes or finite elements, respectively), and different lower boundary conditions (seepage face vs. free drainage). Differences between measured and simulated outflow patterns could be caused by the measurements, the application of the model, or by the model itself. The van Genuchten-Mualem model may not be suitable to describe the soil hydrological relationships of these particular materials. The reason for the mismatch, however, could not be identified yet.

Keywords

  • Capillary barriers
  • Funneled flow
  • Landfills
  • Cover systems
  • Operational validation
  • HYDRUS (2D/3D)
Open Access

Further tests of the HYPROP evaporation method for estimating the unsaturated soil hydraulic properties

Published Online: 06 Feb 2018
Page range: 161 - 169

Abstract

Abstract

Many soil, hydrologic and environmental applications require information about the unsaturated soil hydraulic properties. The evaporation method has long been used for estimating the drying branches of the soil hydraulic functions. An increasingly popular version of the evaporation method is the semi-automated HYPROP© measurement system (HMS) commercialized by Decagon Devices (Pullman, WA) and UMS AG (München, Germany). Several studies were previously carried out to test the HMS methodology by using the Richards equation and the van-Genuchten-Mualem (VG) or Kosugi-Mualem soil hydraulic functions to obtain synthetic data for use in the HMS analysis, and then to compare results against the original hydraulic properties. Using HYDRUS-1D, we carried out independent tests of the HYPROP system as applied to the VG functions for a broad range of soil textures. Our results closely agreed with previous findings. Accurate estimates were especially obtained for the soil water retention curve and its parameters, at least over the range of available retention measurements. We also successfully tested a dual-porosity soil, as well as an extremely coarse medium with a very high van Genuchten n value. The latter case gave excellent results for water retention, but failed for the hydraulic conductivity. In many cases, especially for soils with intermediate and high n values, an independent estimate of the saturated hydraulic conductivity should be obtained. Overall, the HMS methodology performed extremely well and as such constitutes a much-needed addition to current soil hydraulic measurement techniques.

Keywords

  • Soil hydraulic properties
  • Evaporation method
  • HYPROP
  • HYDRUS-1D
  • van Genuchten-Mualem equations
Open Access

Inverse estimation of soil hydraulic properties and water repellency following artificially induced drought stress

Published Online: 06 Feb 2018
Page range: 170 - 180

Abstract

Abstract

Global climate change is projected to continue and result in prolonged and more intense droughts, which can increase soil water repellency (SWR). To be able to estimate the consequences of SWR on vadose zone hydrology, it is important to determine soil hydraulic properties (SHP). Sequential modeling using HYDRUS (2D/3D) was performed on an experimental field site with artificially imposed drought scenarios (moderately M and severely S stressed) and a control plot. First, inverse modeling was performed for SHP estimation based on water and ethanol infiltration experimental data, followed by model validation on one selected irrigation event. Finally, hillslope modeling was performed to assess water balance for 2014. Results suggest that prolonged dry periods can increase soil water repellency. Inverse modeling was successfully performed for infiltrating liquids, water and ethanol, with R2 and model efficiency (E) values both > 0.9. SHP derived from the ethanol measurements showed large differences in van Genuchten-Mualem (VGM) parameters for the M and S plots compared to water infiltration experiments. SWR resulted in large saturated hydraulic conductivity (Ks) decrease on the M and S scenarios. After validation of SHP on water content measurements during a selected irrigation event, one year simulations (2014) showed that water repellency increases surface runoff in non-structured soils at hillslopes.

Keywords

  • Inverse modeling
  • Water and ethanol infiltration
  • SHP estimation
  • Water dynamics
  • HYDRUS (2D/3D)
Open Access

The influence of stony soil properties on water dynamics modeled by the HYDRUS model

Published Online: 06 Feb 2018
Page range: 181 - 188

Abstract

Abstract

Stony soils are composed of two fractions (rock fragments and fine soil) with different hydrophysical characteristics. Although stony soils are abundant in many catchments, their properties are still not well understood. This manuscript presents an application of the simple methodology for deriving water retention properties of stony soils, taking into account a correction for the soil stoniness. Variations in the water retention of the fine soil fraction and its impact on both the soil water storage and the bottom boundary fluxes are studied as well. The deterministic water flow model HYDRUS-1D is used in the study. The results indicate that the presence of rock fragments in a moderate-to-high stony soil can decrease the soil water storage by 23% or more and affect the soil water dynamics. Simulated bottom fluxes increased or decreased faster, and their maxima during the wet period were larger in the stony soil compared to the non-stony one.

Keywords

  • Rock fragments
  • Soil water retention
  • Water storage
  • Outflow
  • Numerical modeling
  • HYDRUS-1D
Open Access

Can a change in cropping patterns produce water savings and social gains: A case study from the Fergana Valley, Central Asia

Published Online: 06 Feb 2018
Page range: 189 - 201

Abstract

Abstract

The study examines possible water savings by replacing alfalfa with winter wheat in the Fergana Valley, located upstream of the Syrdarya River in Central Asia. Agricultural reforms since the 1990s have promoted this change in cropping patterns in the Central Asian states to enhance food security and social benefits. The water use of alfalfa, winter wheat/fallow, and winter wheat/green gram (double cropping) systems is compared for high-deficit, low-deficit, and full irrigation scenarios using hydrological modeling with the HYDRUS-1D software package. Modeling results indicate that replacing alfalfa with winter wheat in the Fergana Valley released significant water resources, mainly by reducing productive crop transpiration when abandoning alfalfa in favor of alternative cropping systems. However, the winter wheat/fallow cropping system caused high evaporation losses from fallow land after harvesting of winter wheat. Double cropping (i.e., the cultivation of green gram as a short duration summer crop after winter wheat harvesting) reduced evaporation losses, enhanced crop output and hence food security, while generating water savings that make more water available for other productive uses. Beyond water savings, this paper also discusses the economic and social gains that double cropping produces for the public within a broader developmental context.

Keywords

  • HYDRUS-1D
  • Food security
  • Crop evapotranspiration
  • Water budget
  • Syrdarya River
Open Access

Reassessment of the Goiânia radioactive waste repository in Brazil using HYDRUS-1D

Published Online: 06 Feb 2018
Page range: 202 - 210

Abstract

Abstract

In September 1987 an accident occurred with a cesium chloride (CsCl) teletherapy source taken from a cancer therapy institute in Goiânia, Brazil. Misuse of the abandoned source caused widespread contamination of radioactive material (about 50 TBq of 137Cs) in the town of Goiânia. Decontamination of affected areas did lead to about 3,500 m3 of solid radioactive wastes, which were disposed in two near-surface repositories built in concrete in 1995. This paper documents a safety assessment of one of the low-level radioactive waste deposits containing 137Cs over a time period of 600 years. Using HYDRUS-1D, we first obtained estimates of water infiltrating through the soil cover on top of the repository into and through the waste and its concrete liners and the underlying vadose zone towards groundwater. Calculations accounted for local precipitation and evapotranspiration rates, including root water uptake by the grass cover, as well as for the effects of concrete degradation on the hydraulic properties of the concrete liners. We next simulated long-term water fluxes and 137Cs transport from the repository towards groundwater. Simulations accounted for the effects of 137Cs sorption and radioactive decay on radionuclide transport from the waste to groundwater, thus permitting an evaluation of potential consequences to the environment and long-term exposure to the public. Consistent with previous assessments, our calculations indicate that very little if any radioactive material will reach the water table during the lifespan of the repository, also when accounting for preferential flow through the waste.

Keywords

  • Cs-137 transport
  • Goiânia radioactive waste repository
  • HYDRUS-1D
  • Safety assessment
Open Access

The HPx software for multicomponent reactive transport during variably-saturated flow: Recent developments and applications

Published Online: 06 Feb 2018
Page range: 211 - 226

Abstract

Abstract

HPx is a multicomponent reactive transport model which uses HYDRUS as the flow and transport solver and PHREEQC-3 as the biogeochemical solver. Some recent adaptations have significantly increased the flexibility of the software for different environmental and engineering applications. This paper gives an overview of the most significant changes of HPx, such as coupling transport properties to geochemical state variables, gas diffusion, and transport in two and three dimensions. OpenMP allows for parallel computing using shared memory. Enhancements for scripting may eventually simplify input definitions and create possibilities for defining templates for generic (sub)problems. We included a discussion of root solute uptake and colloid-affected solute transport to show that most or all of the comprehensive features of HYDRUS can be extended with geochemical information. Finally, an example is used to demonstrate how HPx, and similar reactive transport models, can be helpful in implementing different factors relevant for soil organic matter dynamics in soils. HPx offers a unique framework to couple spatial-temporal variations in water contents, temperatures, and water fluxes, with dissolved organic matter and CO2 transport, as well as bioturbation processes.

Keywords

  • HYDRUS
  • HPx
  • Numerical modeling
  • Reactive transport
  • Organic matter
  • Bioturbation
Open Access

Simulating vertical flow wetlands using filter media with different grain sizes with the HYDRUS Wetland Module

Published Online: 06 Feb 2018
Page range: 227 - 231

Abstract

Abstract

In this study, the simulation results of four vertical flow wetland systems using the HYDRUS Wetland Module are presented. The four wetland systems comprise three single-stage pilot scale systems and one full-scale two-stage system. The main difference between these systems is the filter media used, referred to as fine media, i.e., sand with a grain size distribution 0.063–4 mm, or coarse media, i.e., sand with grain size distributions between 1–4 mm, respectively. The water-flow simulation of each system is carried out using the single porosity van Genuchten-Mualem model. A good match between measured and simulated volumetric effluent flow rates could be achieved for all wetland systems. For reactive transport simulations, the CW2D biokinetic model was applied. First, simulations were run using the standard CW2D parameter set. For some systems, adjustments of the parameter set were needed in order to avoid unlimited bacteria growth. To better fit measured COD, NH4-N, and NO3-N effluent concentrations, adjustments of few parameters of the standard parameter set were required. The results show that for the VF wetlands with fine sand, no adjustments of the CW2D standard parameter set were needed, while for systems with coarser filter media as the main layer, the standard parameter set had to be adjusted to match simulated and measured effluent concentrations.

Keywords

  • Treatment wetlands
  • Vertical flow
  • French VF wetland
  • HYDRUS Wetland Module
  • CW2D
Open Access

Coupling DSSAT and HYDRUS-1D for simulations of soil water dynamics in the soil-plant-atmosphere system

Published Online: 06 Feb 2018
Page range: 232 - 245

Abstract

Abstract

Accurate estimation of the soil water balance of the soil-plant-atmosphere system is key to determining the availability of water resources and their optimal management. Evapotranspiration and leaching are the main sinks of water from the system affecting soil water status and hence crop yield. The accuracy of soil water content and evapotranspiration simulations affects crop yield simulations as well. DSSAT is a suite of field-scale, process-based crop models to simulate crop growth and development. A “tipping bucket” water balance approach is currently used in DSSAT for soil hydrologic and water redistribution processes. By comparison, HYDRUS-1D is a hydrological model to simulate water flow in soils using numerical solutions of the Richards equation, but its approach to crop-related process modeling is rather limited. Both DSSAT and HYDRUS-1D have been widely used and tested in their separate areas of use. The objectives of our study were: (1) to couple HYDRUS-1D with DSSAT to simulate soil water dynamics, crop growth and yield, (2) to evaluate the coupled model using field experimental datasets distributed with DSSAT for different environments, and (3) to compare HYDRUS-1D simulations with those of the tipping bucket approach using the same datasets. Modularity in the software design of both DSSAT and HYDRUS-1D made it easy to couple the two models. The pairing provided the DSSAT interface an ability to use both the tipping bucket and HYDRUS-1D simulation approaches. The two approaches were evaluated in terms of their ability to estimate the soil water balance, especially soil water contents and evapotranspiration rates. Values of the d index for volumetric water contents were 0.9 and 0.8 for the original and coupled models, respectively. Comparisons of simulations for the pod mass for four soybean and four peanut treatments showed relatively high d index values for both models (0.94–0.99).

Keywords

  • System Modeling
  • Crop Growth
  • Soil water
  • Unsaturated zone
  • DSSAT
  • HYDRUS-1D
Open Access

Simulations of freshwater lens recharge and salt/freshwater interfaces using the HYDRUS and SWI2 packages for MODFLOW

Published Online: 06 Feb 2018
Page range: 246 - 256

Abstract

Abstract

The paper presents an evaluation of the combined use of the HYDRUS and SWI2 packages for MODFLOW as a potential tool for modeling recharge in coastal aquifers subject to saltwater intrusion. The HYDRUS package for MODFLOW solves numerically the one-dimensional form of the Richards equation describing water flow in variablysaturated media. The code computes groundwater recharge to or capillary rise from the groundwater table while considering weather, vegetation, and soil hydraulic property data. The SWI2 package represents in a simplified way variable-density flow associated with saltwater intrusion in coastal aquifers. Combining these two packages within the MODFLOW framework provides a more accurate description of vadose zone processes in subsurface systems with shallow aquifers, which strongly depend upon infiltration. The two packages were applied to a two-dimensional problem of recharge of a freshwater lens in a sandy peninsula, which is a typical geomorphologic form along the Baltic and the North Sea coasts, among other places. Results highlighted the sensitivity of calculated recharge rates to the temporal resolution of weather data. Using daily values of precipitation and potential evapotranspiration produced average recharge rates more than 20% larger than those obtained with weekly or monthly averaged weather data, leading to different trends in the evolution of freshwater-saltwater interfaces. Root water uptake significantly influenced both the recharge rate and the position of the freshwater-saltwater interface. The results were less sensitive to changes in soil hydraulic parameters, which in our study were found to affect average yearly recharge rates by up to 13%.

Keywords

  • Groundwater recharge
  • Freshwater lenses
  • HYDRUS
  • SWI2
  • MODFLOW
  • Vadose zone
13 Articles
Open Access

Thematic Issue on HYDRUS Software Applications to Subsurface Fluid Flow and Contaminant Transport

Published Online: 06 Feb 2018
Page range: 129 - 132

Abstract

Open Access

New features of version 3 of the HYDRUS (2D/3D) computer software package

Published Online: 06 Feb 2018
Page range: 133 - 142

Abstract

Abstract

The capabilities of the HYDRUS-1D and HYDRUS (2D/3D) software packages continuously expanded during the last two decades. Various new capabilities were added recently to both software packages, mostly by developing new standard add-on modules such as HPx, C-Ride, UnsatChem, Wetland, Fumigant, DualPerm, and Slope Stability. The new modules may be used to simulate flow and transport processes in one- and two-dimensional transport domains and are fully supported by the HYDRUS graphical user interface (GUI). Several nonstandard add-on modules, such as Overland, Isotope, and Centrifuge, have also been developed, but are not fully supported by the HYDRUS GUI. The objective of this manuscript is to describe several additional features of the upcoming Version 3 of HYDRUS (2D/3D), which was unveiled at a recent (March 2017) HYDRUS conference and workshop in Prague. The new features include a flexible reservoir boundary condition, expanded root growth features, and new graphical capabilities of the GUI. Mathematical descriptions of the new features are provided, as well as two examples illustrating applications of the reservoir boundary condition.

Keywords

  • HYDRUS
  • Reservoir boundary condition
  • Pumping well
  • Root growth
  • Graphical user interface
Open Access

Effect of temporal averaging of meteorological data on predictions of groundwater recharge

Published Online: 06 Feb 2018
Page range: 143 - 152

Abstract

Abstract

Accurate estimates of infiltration and groundwater recharge are critical for many hydrologic, agricultural and environmental applications. Anticipated climate change in many regions of the world, especially in tropical areas, is expected to increase the frequency of high-intensity, short-duration precipitation events, which in turn will affect the groundwater recharge rate. Estimates of recharge are often obtained using monthly or even annually averaged meteorological time series data. In this study we employed the HYDRUS-1D software package to assess the sensitivity of groundwater recharge calculations to using meteorological time series of different temporal resolutions (i.e., hourly, daily, weekly, monthly and yearly averaged precipitation and potential evaporation rates). Calculations were applied to three sites in Brazil having different climatological conditions: a tropical savanna (the Cerrado), a humid subtropical area (the temperate southern part of Brazil), and a very wet tropical area (Amazonia). To simplify our current analysis, we did not consider any land use effects by ignoring root water uptake. Temporal averaging of meteorological data was found to lead to significant bias in predictions of groundwater recharge, with much greater estimated recharge rates in case of very uneven temporal rainfall distributions during the year involving distinct wet and dry seasons. For example, at the Cerrado site, using daily averaged data produced recharge rates of up to 9 times greater than using yearly averaged data. In all cases, an increase in the time of averaging of meteorological data led to lower estimates of groundwater recharge, especially at sites having coarse-textured soils. Our results show that temporal averaging limits the ability of simulations to predict deep penetration of moisture in response to precipitation, so that water remains in the upper part of the vadose zone subject to upward flow and evaporation.

Keywords

  • Groundwater recharge
  • Meteorological data
  • Temporal averaging
  • HYDRUS-1D
  • Infiltration
  • Evaporation
Open Access

Operational validation of HYDRUS (2D/3D) for capillary barriers using data of a 10-m tipping trough

Published Online: 06 Feb 2018
Page range: 153 - 160

Abstract

Abstract

Capillary barriers are an interesting alternative component for cover systems of landfills and contaminated sites. Provided they are sufficiently validated, soil hydrological models could be fast and powerful tools for the dimensioning of capillary barriers. Outflow rates measured in a 10 m long tipping trough for one material combination and two slopes from stationary periods were compared to simulation results of HYDRUS (2D/3D), Version 2.05. The measured outflow rates show a typical pattern with slope-dependent threshold values indicating the efficiency of the capillary barrier. This flow pattern could not be reproduced with HYDRUS (2D/3D) that for different input setups produced smooth patterns without thresholds. The input setup was varied for different soil hydraulic models (van Genuchten-Mualem vs. Brooks-Corey), homogeneous and heterogeneous transport domains (no scaling vs. stochastically distributed scaling factors considering the Miller-Miller similitude), different HYDRUS versions (standard vs. alternative; i.e., with material properties assigned either to finite element nodes or finite elements, respectively), and different lower boundary conditions (seepage face vs. free drainage). Differences between measured and simulated outflow patterns could be caused by the measurements, the application of the model, or by the model itself. The van Genuchten-Mualem model may not be suitable to describe the soil hydrological relationships of these particular materials. The reason for the mismatch, however, could not be identified yet.

Keywords

  • Capillary barriers
  • Funneled flow
  • Landfills
  • Cover systems
  • Operational validation
  • HYDRUS (2D/3D)
Open Access

Further tests of the HYPROP evaporation method for estimating the unsaturated soil hydraulic properties

Published Online: 06 Feb 2018
Page range: 161 - 169

Abstract

Abstract

Many soil, hydrologic and environmental applications require information about the unsaturated soil hydraulic properties. The evaporation method has long been used for estimating the drying branches of the soil hydraulic functions. An increasingly popular version of the evaporation method is the semi-automated HYPROP© measurement system (HMS) commercialized by Decagon Devices (Pullman, WA) and UMS AG (München, Germany). Several studies were previously carried out to test the HMS methodology by using the Richards equation and the van-Genuchten-Mualem (VG) or Kosugi-Mualem soil hydraulic functions to obtain synthetic data for use in the HMS analysis, and then to compare results against the original hydraulic properties. Using HYDRUS-1D, we carried out independent tests of the HYPROP system as applied to the VG functions for a broad range of soil textures. Our results closely agreed with previous findings. Accurate estimates were especially obtained for the soil water retention curve and its parameters, at least over the range of available retention measurements. We also successfully tested a dual-porosity soil, as well as an extremely coarse medium with a very high van Genuchten n value. The latter case gave excellent results for water retention, but failed for the hydraulic conductivity. In many cases, especially for soils with intermediate and high n values, an independent estimate of the saturated hydraulic conductivity should be obtained. Overall, the HMS methodology performed extremely well and as such constitutes a much-needed addition to current soil hydraulic measurement techniques.

Keywords

  • Soil hydraulic properties
  • Evaporation method
  • HYPROP
  • HYDRUS-1D
  • van Genuchten-Mualem equations
Open Access

Inverse estimation of soil hydraulic properties and water repellency following artificially induced drought stress

Published Online: 06 Feb 2018
Page range: 170 - 180

Abstract

Abstract

Global climate change is projected to continue and result in prolonged and more intense droughts, which can increase soil water repellency (SWR). To be able to estimate the consequences of SWR on vadose zone hydrology, it is important to determine soil hydraulic properties (SHP). Sequential modeling using HYDRUS (2D/3D) was performed on an experimental field site with artificially imposed drought scenarios (moderately M and severely S stressed) and a control plot. First, inverse modeling was performed for SHP estimation based on water and ethanol infiltration experimental data, followed by model validation on one selected irrigation event. Finally, hillslope modeling was performed to assess water balance for 2014. Results suggest that prolonged dry periods can increase soil water repellency. Inverse modeling was successfully performed for infiltrating liquids, water and ethanol, with R2 and model efficiency (E) values both > 0.9. SHP derived from the ethanol measurements showed large differences in van Genuchten-Mualem (VGM) parameters for the M and S plots compared to water infiltration experiments. SWR resulted in large saturated hydraulic conductivity (Ks) decrease on the M and S scenarios. After validation of SHP on water content measurements during a selected irrigation event, one year simulations (2014) showed that water repellency increases surface runoff in non-structured soils at hillslopes.

Keywords

  • Inverse modeling
  • Water and ethanol infiltration
  • SHP estimation
  • Water dynamics
  • HYDRUS (2D/3D)
Open Access

The influence of stony soil properties on water dynamics modeled by the HYDRUS model

Published Online: 06 Feb 2018
Page range: 181 - 188

Abstract

Abstract

Stony soils are composed of two fractions (rock fragments and fine soil) with different hydrophysical characteristics. Although stony soils are abundant in many catchments, their properties are still not well understood. This manuscript presents an application of the simple methodology for deriving water retention properties of stony soils, taking into account a correction for the soil stoniness. Variations in the water retention of the fine soil fraction and its impact on both the soil water storage and the bottom boundary fluxes are studied as well. The deterministic water flow model HYDRUS-1D is used in the study. The results indicate that the presence of rock fragments in a moderate-to-high stony soil can decrease the soil water storage by 23% or more and affect the soil water dynamics. Simulated bottom fluxes increased or decreased faster, and their maxima during the wet period were larger in the stony soil compared to the non-stony one.

Keywords

  • Rock fragments
  • Soil water retention
  • Water storage
  • Outflow
  • Numerical modeling
  • HYDRUS-1D
Open Access

Can a change in cropping patterns produce water savings and social gains: A case study from the Fergana Valley, Central Asia

Published Online: 06 Feb 2018
Page range: 189 - 201

Abstract

Abstract

The study examines possible water savings by replacing alfalfa with winter wheat in the Fergana Valley, located upstream of the Syrdarya River in Central Asia. Agricultural reforms since the 1990s have promoted this change in cropping patterns in the Central Asian states to enhance food security and social benefits. The water use of alfalfa, winter wheat/fallow, and winter wheat/green gram (double cropping) systems is compared for high-deficit, low-deficit, and full irrigation scenarios using hydrological modeling with the HYDRUS-1D software package. Modeling results indicate that replacing alfalfa with winter wheat in the Fergana Valley released significant water resources, mainly by reducing productive crop transpiration when abandoning alfalfa in favor of alternative cropping systems. However, the winter wheat/fallow cropping system caused high evaporation losses from fallow land after harvesting of winter wheat. Double cropping (i.e., the cultivation of green gram as a short duration summer crop after winter wheat harvesting) reduced evaporation losses, enhanced crop output and hence food security, while generating water savings that make more water available for other productive uses. Beyond water savings, this paper also discusses the economic and social gains that double cropping produces for the public within a broader developmental context.

Keywords

  • HYDRUS-1D
  • Food security
  • Crop evapotranspiration
  • Water budget
  • Syrdarya River
Open Access

Reassessment of the Goiânia radioactive waste repository in Brazil using HYDRUS-1D

Published Online: 06 Feb 2018
Page range: 202 - 210

Abstract

Abstract

In September 1987 an accident occurred with a cesium chloride (CsCl) teletherapy source taken from a cancer therapy institute in Goiânia, Brazil. Misuse of the abandoned source caused widespread contamination of radioactive material (about 50 TBq of 137Cs) in the town of Goiânia. Decontamination of affected areas did lead to about 3,500 m3 of solid radioactive wastes, which were disposed in two near-surface repositories built in concrete in 1995. This paper documents a safety assessment of one of the low-level radioactive waste deposits containing 137Cs over a time period of 600 years. Using HYDRUS-1D, we first obtained estimates of water infiltrating through the soil cover on top of the repository into and through the waste and its concrete liners and the underlying vadose zone towards groundwater. Calculations accounted for local precipitation and evapotranspiration rates, including root water uptake by the grass cover, as well as for the effects of concrete degradation on the hydraulic properties of the concrete liners. We next simulated long-term water fluxes and 137Cs transport from the repository towards groundwater. Simulations accounted for the effects of 137Cs sorption and radioactive decay on radionuclide transport from the waste to groundwater, thus permitting an evaluation of potential consequences to the environment and long-term exposure to the public. Consistent with previous assessments, our calculations indicate that very little if any radioactive material will reach the water table during the lifespan of the repository, also when accounting for preferential flow through the waste.

Keywords

  • Cs-137 transport
  • Goiânia radioactive waste repository
  • HYDRUS-1D
  • Safety assessment
Open Access

The HPx software for multicomponent reactive transport during variably-saturated flow: Recent developments and applications

Published Online: 06 Feb 2018
Page range: 211 - 226

Abstract

Abstract

HPx is a multicomponent reactive transport model which uses HYDRUS as the flow and transport solver and PHREEQC-3 as the biogeochemical solver. Some recent adaptations have significantly increased the flexibility of the software for different environmental and engineering applications. This paper gives an overview of the most significant changes of HPx, such as coupling transport properties to geochemical state variables, gas diffusion, and transport in two and three dimensions. OpenMP allows for parallel computing using shared memory. Enhancements for scripting may eventually simplify input definitions and create possibilities for defining templates for generic (sub)problems. We included a discussion of root solute uptake and colloid-affected solute transport to show that most or all of the comprehensive features of HYDRUS can be extended with geochemical information. Finally, an example is used to demonstrate how HPx, and similar reactive transport models, can be helpful in implementing different factors relevant for soil organic matter dynamics in soils. HPx offers a unique framework to couple spatial-temporal variations in water contents, temperatures, and water fluxes, with dissolved organic matter and CO2 transport, as well as bioturbation processes.

Keywords

  • HYDRUS
  • HPx
  • Numerical modeling
  • Reactive transport
  • Organic matter
  • Bioturbation
Open Access

Simulating vertical flow wetlands using filter media with different grain sizes with the HYDRUS Wetland Module

Published Online: 06 Feb 2018
Page range: 227 - 231

Abstract

Abstract

In this study, the simulation results of four vertical flow wetland systems using the HYDRUS Wetland Module are presented. The four wetland systems comprise three single-stage pilot scale systems and one full-scale two-stage system. The main difference between these systems is the filter media used, referred to as fine media, i.e., sand with a grain size distribution 0.063–4 mm, or coarse media, i.e., sand with grain size distributions between 1–4 mm, respectively. The water-flow simulation of each system is carried out using the single porosity van Genuchten-Mualem model. A good match between measured and simulated volumetric effluent flow rates could be achieved for all wetland systems. For reactive transport simulations, the CW2D biokinetic model was applied. First, simulations were run using the standard CW2D parameter set. For some systems, adjustments of the parameter set were needed in order to avoid unlimited bacteria growth. To better fit measured COD, NH4-N, and NO3-N effluent concentrations, adjustments of few parameters of the standard parameter set were required. The results show that for the VF wetlands with fine sand, no adjustments of the CW2D standard parameter set were needed, while for systems with coarser filter media as the main layer, the standard parameter set had to be adjusted to match simulated and measured effluent concentrations.

Keywords

  • Treatment wetlands
  • Vertical flow
  • French VF wetland
  • HYDRUS Wetland Module
  • CW2D
Open Access

Coupling DSSAT and HYDRUS-1D for simulations of soil water dynamics in the soil-plant-atmosphere system

Published Online: 06 Feb 2018
Page range: 232 - 245

Abstract

Abstract

Accurate estimation of the soil water balance of the soil-plant-atmosphere system is key to determining the availability of water resources and their optimal management. Evapotranspiration and leaching are the main sinks of water from the system affecting soil water status and hence crop yield. The accuracy of soil water content and evapotranspiration simulations affects crop yield simulations as well. DSSAT is a suite of field-scale, process-based crop models to simulate crop growth and development. A “tipping bucket” water balance approach is currently used in DSSAT for soil hydrologic and water redistribution processes. By comparison, HYDRUS-1D is a hydrological model to simulate water flow in soils using numerical solutions of the Richards equation, but its approach to crop-related process modeling is rather limited. Both DSSAT and HYDRUS-1D have been widely used and tested in their separate areas of use. The objectives of our study were: (1) to couple HYDRUS-1D with DSSAT to simulate soil water dynamics, crop growth and yield, (2) to evaluate the coupled model using field experimental datasets distributed with DSSAT for different environments, and (3) to compare HYDRUS-1D simulations with those of the tipping bucket approach using the same datasets. Modularity in the software design of both DSSAT and HYDRUS-1D made it easy to couple the two models. The pairing provided the DSSAT interface an ability to use both the tipping bucket and HYDRUS-1D simulation approaches. The two approaches were evaluated in terms of their ability to estimate the soil water balance, especially soil water contents and evapotranspiration rates. Values of the d index for volumetric water contents were 0.9 and 0.8 for the original and coupled models, respectively. Comparisons of simulations for the pod mass for four soybean and four peanut treatments showed relatively high d index values for both models (0.94–0.99).

Keywords

  • System Modeling
  • Crop Growth
  • Soil water
  • Unsaturated zone
  • DSSAT
  • HYDRUS-1D
Open Access

Simulations of freshwater lens recharge and salt/freshwater interfaces using the HYDRUS and SWI2 packages for MODFLOW

Published Online: 06 Feb 2018
Page range: 246 - 256

Abstract

Abstract

The paper presents an evaluation of the combined use of the HYDRUS and SWI2 packages for MODFLOW as a potential tool for modeling recharge in coastal aquifers subject to saltwater intrusion. The HYDRUS package for MODFLOW solves numerically the one-dimensional form of the Richards equation describing water flow in variablysaturated media. The code computes groundwater recharge to or capillary rise from the groundwater table while considering weather, vegetation, and soil hydraulic property data. The SWI2 package represents in a simplified way variable-density flow associated with saltwater intrusion in coastal aquifers. Combining these two packages within the MODFLOW framework provides a more accurate description of vadose zone processes in subsurface systems with shallow aquifers, which strongly depend upon infiltration. The two packages were applied to a two-dimensional problem of recharge of a freshwater lens in a sandy peninsula, which is a typical geomorphologic form along the Baltic and the North Sea coasts, among other places. Results highlighted the sensitivity of calculated recharge rates to the temporal resolution of weather data. Using daily values of precipitation and potential evapotranspiration produced average recharge rates more than 20% larger than those obtained with weekly or monthly averaged weather data, leading to different trends in the evolution of freshwater-saltwater interfaces. Root water uptake significantly influenced both the recharge rate and the position of the freshwater-saltwater interface. The results were less sensitive to changes in soil hydraulic parameters, which in our study were found to affect average yearly recharge rates by up to 13%.

Keywords

  • Groundwater recharge
  • Freshwater lenses
  • HYDRUS
  • SWI2
  • MODFLOW
  • Vadose zone

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