HYDRUS 1D Research Articles

Surfactant flow and transport in the vadose zone: a numerical experiment

The presence of surfactants in the unsaturated zone is one of the scenarios where the flow depends on the solute concentration. The simulation of flow and transport of surfactants requires the coupling of flow and transport, where the surfactant concentration-dependent changes to water retention (i.e. changes in surface tension and/or contact angle) and hydraulic conductivity need to be considered. This research presents a numerical experiment that compares surfactant flow and transport under intermittent boundary conditions to that of a conservative tracer. A modified version of Hydrus 2D, with the concentration-dependent surface tension and viscosity effects, is used. The numerical experiment examines the effect of surfactant infiltration, redistribution and flushing in a low-water content unsaturated porous medium with a deep water table. The numerical experiment encompasses not only the hysteresis as a result of transient localised drainage and rewetting associated with the surfactant-induced pressure gradients, and the intermittent boundary conditions. The comparison of surfactant flow to that of a conservative tracer indicates significant differences for the same boundary conditions. The results from this experiment will be beneficial for the design and optimisation of infiltration galleries employing surfactants for soil and ground water remediation, as well as for the understanding the flow and transport of grey water in the unsaturated zone.

Análise da capacidade de infiltração para atenuação de alagamento em um ponto crítico na cidade do Recife

A crescente urbanização de Recife (PE) acarreta em uma diminuição das áreas naturais permeáveis, aumento do escoamento superficial, redução na recarga das águas subterrâneas e geração de alagamentos que, embora pontuais, ocasionam diversos transtornos à população. Esse cenário, juntamente com a deficiência no sistema de drenagem local, cria a necessidade de estudos de técnicas sustentáveis para minimizar os impactos dos eventos chuvosos. Sendo assim, o objetivo desse trabalho foi estimar o comportamento hidrodinâmico de um solo da cidade do Recife utilizando registros reais de precipitação, a fim de verificar seu potencial de infiltração na atenuação de alagamentos e seus consequentes benefícios para o abastecimento do fluxo subterrâneo próximo a um ponto de alagamento. Para isso, foi escolhida a área coberta por solo natural adjacente a um local crítico em época chuvosa. As características hidrodinâmicas do solo foram estimadas a partir da metodologia Beerkan. No software Hydrus 1D, as simulações foram realizadas com os dados meteorológicos do mês de julho de 2000 e consideraram a situação mais desfavorável de infiltração, ou seja, menor condutividade hidráulica saturada obtida (Ks = 0,0047 mm/s). As simulações mostraram a influência de Ks nos resultados que evidenciaram que o solo possuía uma boa capacidade drenante a curto e médio prazo, conforme as análises diárias e mensal, além de ter se observado benefícios para o abastecimento humano e para as obras civis devido a ocorrência da recarga do nível freático.

Determining the Unsaturated Hydraulic Properties of Cohesionless Soils: An Integrated Experimental and Inverse Modeling Approach

Abstract A simple, inexpensive and quick method for measuring the van Genuchten soil water retention curve (SWRC) model parameters for cohesionless soil is presented. The proposed method is an integration of laboratory testing and numerical modeling. The experimental testing consists of multistage bottom-top water imbibition of a dry sand column while recording pore pressure at the inlet. The experiment is then simulated numerically using Hydrus 1D, and the van Genuchten SWRC model parameters are determined through inverse modeling to match the recorded pore pressures. The soil column flushing includes multiple flow stoppages and resumptions, all before permeating one pore volume of water. The flow stoppage results in a time-dependent redistribution of moisture near the waterfront that is controlled by the unsaturated hydraulic properties of the soil and is reflected by changes in the pore pressure measurements. The uniqueness of this method comes from the simple experimental setup and the multistage flushing that can reduce the testing time by a factor of 30 compared with other methods. The results from testing three different sands with different grain size distributions are presented. The new method generated consistent results from multiple specimens tested at a range of flow rates for the three sands. The hypothesis behind moisture redistribution during flow stoppage was confirmed through a combination of experimental and numerical observations. The van Genuchten SWRC parameters obtained from the new method were comparable to those obtained using the conventional hanging column test for Sands B and C and available data in the literature. Sand A could not be tested using the hanging column test because of its large particle size, which demonstrates the wide range of soils that can be tested using the new proposed method.

Using electromagnetic induction technology to identify atrazine leaching potential at field scale

Atrazine is an herbicide commonly used to control weeds in corn crop. Atrazine becomes an environmental concern when it moves off-site to surface and ground waters. Understanding how atrazine moves in the field is important for developing management controls. Electromagnetic induction (EMI) has been used to map certain contaminant transport at the field scale. This study was developed to evaluate the efficacy of EMI technology for identifying surface soil atrazine concentration in a corn crop field. The research was conducted in a corn silage field with silt, clay and loam soils at the U.S. Meat Animal Research Center (USMARC), Clay Center, NE – USA, and it was divided in three stages; i) EMI data collection and a response surface sampling design for collection of bulk soils and soil core samples, ii) atrazine transport parameters were obtained by Breakthrough Curves using the bulk soil and numerical adjustments using STANMOD (HYDRUS package), and iii) Modeling atrazine parameters through EMI signal data with posterior atrazine’s movement simulations through the soil using HYDRUS 2D. Atrazine’s retardation factor, partition coefficient, and transfer coefficient were strongly correlated with EMI signal exhibiting a strong correlation with apparent electrical conductivity (ECa). The low values for RMSE and RRMSE and the high values for Willmott and Pearson coefficients indicate EMI technology can be used to predict atrazine movement parameters. HYDRUS 2D quantitatively simulates the atrazine concentration leaching and how the temporal scale of this contamination would be. Combining EMI technology with HYDRUS 2D modeling provides researcher with additional information for developing better management practices for controlling atrazine movement to surface water; however, further studies are needed determine the effectiveness of this approach for other soil types.

Comportamento da infiltração de água no solo em parque urbano

The objective of this work is to evaluate the infiltration capacity and to determine the hydrodynamic parameters of three surfaces (community use, children's recreation and gardens) in an urban park in Recife/PE. The Beerkan methodology was used to determine the parameters of the water retention curve and the hydraulic conductivity curve from 24 infiltration tests. Besides that, the surfaces’ water balance subjected to 365 days of rainfall was simulated with the aid of the Hydrus 1D model. The garden areas presented the higher values for maximum infiltration rates (553.58 mm.h-1), followed by children's recreation areas (116.70 mm.h-1) and and community use area (18.75 mm.h-1). The areas’ predominant textures had no direct correlation with the saturated hydraulic conductivity (Ks), presenting values between 25.38 and 306.65 mm.h -1 for sandy loam soils (gardens); 7.67 and 542.2 mm.h-1 for sandy clay loam (gardens and community use); and 4.07 and 256.86 mm.h -1 for loamy sand (recreation). The water retention capacity was lower in the gardens, with opposite behavior in the community use areas. The Hydrus’ simulations resulted in higher values of runoff and evaporation in the gardens. They showed that there is no difference in the values of cumulative infiltration in the three areas.

Nitrate-leaching and groundwater vulnerability mapping in North Bihar, India

Aquifer vulnerability assessment is crucial for studying the impact of increasing pollution load scenarios on the quantification of contaminant concentration with movement of plume for protecting groundwater resources. Only a few recent studies have focused on the performance evaluation of vulnerability assessment methods using process-based modeling approach. However, the moisture flow and pollutant transport through partially saturated zone plays a crucial role under varying hydrogeological conditions, which are generally ignored in index-based methods. Thus, the objective of this research is to evaluate the vulnerability of groundwater resources to nitrate in Samastipur, Darbhanga and Madhubani districts of Bihar State, India, using soil moisture flow and solute transport modeling. Richard’s equation integrated with the classical advection dispersion equation is simulated using HYDRUS 1D by incorporating a constant head and atmospheric boundary conditions. The time taken to reach the nitrate peak concentration at groundwater table is considered to estimate vulnerability index (VI). Results have shown that high risk in terms of nitrate-leaching vulnerability in southern part of study area is dominated by Gangetic kankar in subsurface. Further, high pollution risk was reported in eastern north part of study area having alluvial deposition in subsurface. The main causes of high risk were due to the short depth of water table, little discharge and more hydraulic conductivity presence in the subsurface media. Moreover, comparatively low vulnerability was observed in area having clay capping of 2–4 m from surface. This research may help in better implementation of agricultural, soil–water conservation practices and urban/industrial infrastructure development in and around the study area.

Purification Efficiency for Treated Waste Water in Case of Joint Infiltration with Water Originating from Precipitation

The decentralized treatment of wastewater and its on-site infiltration is common practice, especially in rural areas. However, uncertainties exist on the degradation potential of treated wastewater constituents mixed with additional infiltration of large quantities of water originating from precipitation. The intermixture of these waters is causing a reduction of residence times of the treated wastewater as well as an increased water saturation within the unsaturated soil zone. This can lead to a negative influence on the purification efficiency. Laboratory-scale 1D column experiments, accompanied by numerical simulations of water flow using the software code HYDRUS 1D, have been performed to evaluate the risks for a reduction of the degradation efficiency. Water content measurements and analysis of relevant organic substances in samples taken at different depths were the basis for evaluating the influence of the joint infiltration on the purification efficiency. The results highlight that a joint infiltration of treated wastewater and additional water originating from precipitation is not affecting the degradation efficiency for treated wastewater constituents. Degradation rates under these conditions were similar to the infiltration of treated wastewater alone. Timeframes with high water saturation were limited to the duration of the precipitation event.

Machine Learning vs. Physics-Based Modeling for Real-Time Irrigation Management

Real-time monitoring of soil matric potential has now become a common practice for precision irrigation management. Some crops, such as cranberries, are susceptible to both water and anoxic stresses. Excessive variations in soil matric potential in the root zone may reduce plant transpiration, due to either saturated or dry soil conditions, thereby reducing productivity. A timely supply of the right amount of water is, therefore, fundamental for efficient irrigation management. In this paper, we compare the capabilities of a machine learning-based model and a physics-based model to predict soil matric potential in the root zone. The machine learning model is a random forest algorithm, while the physics-based model is a two-dimensional solver of Richards equation (HYDRUS 2D). After training and calibration on a dataset collected in a cranberry field located in Quebec (Canada), the performance of the two models is evaluated for 30 different time frames of 72-h soil matric potential forecasts. The results highlight that both models can accurately forecast the soil matric potential in the root zone. The machine learning-based model can achieve better performance when compared to the physics-based model, but forecasting accuracy decreases rapidly toward the end of the 72-h lead time, while the error for the Richards equation-based model does not increase with time and remain small compared to the typical measurement error.

Modelling groundwater evapotranspiration in a shallow aquifer in a semi-arid environment

The use of diurnal or seasonal water table fluctuation (WTF) to estimate groundwater evapotranspiration (ETG) at different land uses and climate conditions is increasing applied in ecohydrological studies. In this study, we applied the WTF method for a shallow aquifer in an urbanized area in Senegal over the dry season 2000–2013.To analyze the applicability and validity of the WTF method for this site, and to understand the impact of the parameters used in this method, the unsaturated /saturated system was first simulated using the HYDRUS 1D model. The drawdown of the water table ranges from 18.1 to 113.2 cm and 10.4 to 101.9 cm for a bare soil and a perennial grass scenario and is highly related to the annual rainfall of the previous rainy season. The results indicate that the mean daily FAO-PM reference evapotranspiration rates for this area ranged from 2 to 4 mmd−1 and that the estimated actual evapotranspiration (ETa) from the HYDRUS 1D model ranged between 0.22 to 1.11 and 0.23 to 1.27 mmd−1 in bare soil and vegetative condition, respectively. ETa and ETG were well correlated for the vegetated scenario. However, the WTF method slightly overestimates ETa fluxes in the bare soil scenario. The study shows that the decline of ETa with water table depth can be simulated by an exponential function. The overall results indicate that higher ETa values were observed when the water table is shallow, suggesting that ETa is mainly driven by the water table depth at this site.

Calibration and application of quality-scoring functions using soil-forest productivity relationships in land reclamation

Soil-forest productivity has been studied over decades, especially for North American boreal forests; however, there has been little effort to quantitatively incorporate this relationship into frameworks of soil quality assessment (SQA). The need for such framework is critical as land reclamation and ecosystem restoration are expected to quantitatively demonstrate the redevelopment of functional soil-plant systems in spatial and/or temporal dimensions for closure of disturbed sites. The objective of this research was to assess three potential options for calibrating soil-forest productivity relationships into a SQA framework using scoring functions, while demonstrating applications in land reclamation. Using Alberta oil sands reclamation as a case study, soil-forest productivity was calibrated by i) stepwise regression of soil and forest productivity indicators, ii) use of GYPSY to model pre-disturbance growth trajectories while treating soil as categorical variable, and iii) use of process based models HYDRUS 1D and BIOMES-BGC to estimate soil and plant productivity parameters such as available water holding capacity, leaf area index and net primary productivity. All three approaches provided adequate data for calibrating the relationship into existing SQA frameworks producing soil quality-scoring functions (SQF), although the regression approach will require more rigorous validation and constraining of the SQF in comparison to the other two options. Applications of the SQF include temporal assessments of plant’s growth rate of reclaimed stands and testing the effect of reclamation cover design factors on forest productivity.

Combining Historical Remote Sensing, Digital Soil Mapping and Hydrological Modelling to Produce Solutions for Infrastructure Damage in Cosmo City, South Africa

Urbanization and hydrology have an interactive relationship, as urbanization changing the hydrology of a system and the hydrology commonly causing structural damage to the infrastructure. Hydrological modelling has been used to quantify the water causing structural impacts, and to provide solutions to the issues. However, in already-urbanized areas, creating a soil map to use as input in the modelling process is difficult, as observation positions are limited and visuals of the natural vegetation which indicate soil distribution are unnatural. This project used historical satellite images in combination with terrain parameters and digital soil mapping methods to produce an accurate (Kappa statistic = 0.81) hydropedology soil map for the Cosmo City suburb in Johannesburg, South Africa. The map was used as input into the HYDRUS 2D and SWAT hydrological models to quantify the water creating road damage at Kampala Crescent, a road within Cosmo City (using HYDRUS 2D), as well as the impact of urbanization on the hydrology of the area (using SWAT). HYDRUS 2D modelling showed that a subsurface drain installed at Kampala Crescent would need a carrying capacity of 0.3 m3·h−1·m−1 to alleviate the road damage, while SWAT modelling shows that surface runoff in Cosmo City will commence with as little rainfall as 2 mm·month−1. This project showcases the value of multidisciplinary work. The remote sensing was invaluable to the mapping, which informed the hydrological modelling and subsequently provided answers to the engineers, who could then mitigate the hydrology-related issues within Cosmo City.

Study of moisture transfer through unsaturated zone and groundwater recharge at the emergency site of the Solikamsk-2 Mine (Verkhnekamskoye salt deposit, Russia)

The article provides the results of assessing groundwater recharge at the emergency site of the Solikamsk-2 Mine (Solikamsk, Russia). The assessment was performed using two separate approaches, including the study of the results of groundwater level observations and numerical modeling of soil moisture transfer through the unsaturated zone. The analysis of the groundwater level fluctuations in observation wells made it possible to estimate the recharge rate in natural and anthropogenic (after the accident) conditions. To study the soil moisture transfer in the upper part of the unsaturated zone two moisture sensors were installed at a depth of 0.4 and 0.65 m. To interpret sensors data the numerical model was developed using the HYDRUS 1D software. The modeling results allowed estimating the recharge rate at a depth of 0.65 m and the main water balance components (evaporation, transpiration, surface runoff). A comparison of the two methods showed similar results, allowing them to use for estimating and predicting groundwater recharge in the annual cycle.

Groundwater recharge estimation using HYDRUS 1D model in Alaşehir sub-basin of Gediz Basin in Turkey.

Gediz Basin, located in the western part of Turkey constituting 2% land of the country, has an important groundwater potential in the area. Alasehir sub-basin, located in the southeast of the Gediz Basin and subject to the extensive withdrawal for the irrigation, constitutes the study area. Natural recharge to the sub-basin due to precipitation is numerically investigated in this study. For this purpose, 25 research wells, whose depths range from 20 to 50 m, were drilled to observe the recharge and collect the necessary field data for the numerical model. Meteorological data were collected from 3 weather stations installed in the study area. The numerical model HYDRUS was calibrated using the field water content data. Soil characterization was done on the core samples; the aquifer characterization was performed, and the alluvial aquifer recharge due to precipitation was calculated. As a result, the computed recharge value ranges from 21.78 to 68.52 mm, with an average value of 43.09 mm. According to the numerical model, this amount of recharge corresponds to 10% of the amount of annual rainfall.

Effect of Biochar Application Rates on the Hydraulic Properties of an Agricultural-Use Boreal Podzol

Boreal agriculture struggles with soils of lower agronomic value, most of which are sandy with a low water holding capacity (WHC) and prone to nutrient leaching. Biochar amendments are associated with positive effects on soil hydraulic properties and enhanced nutrient retention. However, these effects are strongly related to feedstock type and pyrolysis parameters and depend on biochar application rates and soil types. While biochar could increase the productivity of boreal agriculture by improving water and nutrient use efficiency, little is known about its effects on hydraulic processes in podzol. In this study, we investigated the effects of biochar rates (10, 20, 40, 80 Mg carbon ha−1) and maturity on soil hydrology for an agriculturally used Podzol in Labrador, Canada. The in-situ soil water content (SWC) and weather data over an entire growing season were analysed. Hydrus 1D simulations were used to estimate changes in water fluxes. SWC showed clear differentiation among storage parameters (i.e., initial, peak and final SWC) and kinetic parameters (i.e., rate of SWC change). Storage parameters and soil wetting and drying rates were significantly affected by biochar rates and its maturity. The magnitude of the changes in SWC after either wetting or drying events was statistically not affected by the biochar rate. This confirms that biochar mostly affected the WHC. Nevertheless, reductions in cumulative lower boundary fluxes were directly related to biochar incorporation rates. Overall, biochar had positive effects on hydrological properties. The biochar rate of 40 Mg C ha−1 was the most beneficial to agriculturally relevant hydraulic conditions for the tested Podzol.

Influence of agroforestry plant species on the infiltration of S-Metolachlor in buffer soils

Agroforestry practices have been acknowledged for reducing pesticide losses while maintaining land productivity. Pesticide removal from overland flow results from great infiltration capacities of the buffer soils. This can in turn threaten the quality of groundwater in case of poor pesticide sorption and degradation in the root-influenced zone. These mechanisms and their balance are likely to be influenced by plant species. However, little is known about the role of agroforestry species in the infiltration of herbicides. The aim of this study was thereby to evaluate how popular agroforestry species modulate the infiltration of water and of a widely used herbicide. We established large buffer microcosms by planting Brome grass, Black walnut, Pin oak and Poplar trees in repacked soil columns. After a growth season of 4 months, we performed ponded infiltration experiments with bromide and S-Metolachlor. We used then the HYDRUS 1D model to compare the hydrodynamic properties and S-Metolachlor transport patterns between the microcosms. In addition, we compared the sorption properties of the rhizosphere and bulk soils. We found that the tree species increased the sorption of S-Metolachlor in soil with Kd being 3 times greater than in the un-vegetated and Brome grass microcosms. Poplar trees increased the hydraulic conductivity (Ksat) compared to the control and was associated to a low retardation of S-metolachlor, which increases the risk of groundwater contamination. With slightly reduced Ksat and retardation factor in the root zone, 1.6 to 1.8 times greater than in the control treatment, Black walnut appears as an optimal species for mitigating S-Metolachlor. The Brome grass and oak microcosms had the lowest Ksat of all treatments and S-Metolachlor retardation factors were equal and slightly increased compared to the control, respectively. These results show that agroforestry buffer's efficiency can be optimized by selecting appropriate species.

Influence of Fluctuating Groundwater Table on Volatile Organic Chemical Emission Flux at a Dissolved Chlorinated‐Solvent Plume Site

AbstractGroundwater elevation fluctuation has been recognized as one mechanism causing temporal indoor air volatile organic chemical (VOC) impacts in vapor intrusion risk assessment guidance. For dissolved VOC sources, groundwater table fluctuation shortens/lengthens the transport pathway, and delivers dissolved contaminants to soils that are alternating between water saturated and variably saturated conditions, thereby enhancing volatilization potential. To date, this mechanism has not been assessed with field data, but enhanced VOC emission flux has been observed in lab‐scale and modeling studies. This work evaluates the impact of groundwater elevation changes on VOC emission flux from a dissolved VOC plume into a house, supplemented with modeling results for cyclic groundwater elevation changes. Indoor air concentrations, air exchange rates, and depth to groundwater (DTW) were collected at the study house during an 86‐d constant building underpressurization test. These data were used to calculate changes in trichloroethylene (TCE) emission flux to indoor air, during a period when DTW varied daily and seasonally from about 3.1 to 3.4 m below the building foundation (BF). Overall, TCE flux to indoor air varied by about 50% of the average, without any clear correlation to changes in DTW or its change rate. To complement the field study, TCE surface emission fluxes were simulated using a one‐dimensional model (HYDRUS 1D) for conditions similar to the field site. Simulation results showed time‐averaged surface TCE fluxes for cyclic water‐table elevations were greater than for stationary water‐table conditions at an equivalent time‐averaged water‐table position. The magnitudes of temporal TCE emission flux changes were generally less than 50% of the time‐averaged flux, consistent with the field site observations. Simulation results also suggested that TCE emission flux changes due to groundwater fluctuation are likely to be significant at sites with shallow groundwater (e.g., < 0.5 m BF) and permeable soil types (e.g., sand).

Evaluate the Probability of Failure in Rainfall-Induced Landslides Using a Fuzzy Point Estimate Method

Traditional slope stability analysis mostly adopts the limit equilibrium method, which predetermines the slope failure surface and assumes that failure occurs simultaneously at all points of the failure surface. The method is based on the balance of forces and torques. The slope stability is represented by the factor of safety. The lowest factor of safety obtained after repeated analysis indicates the most failure-prone slope surface. However, the factor of safety for only one slope failure surface is obtained when applying this method. The distribution and changes of factor of safety in the interior of the slope are not identified. In addition, the analysis of factor of safety is influenced by the uncertainty in soil mechanical parameters, whereas uncertainty is not quantified in the traditional deterministic analysis. Therefore, a probabilistic approach, which uses the probability distribution function to explain the randomness of parameters, is proposed for quantifying the uncertainty. Nonetheless, when the observation data are not sufficient for determining the probability distribution function, the fuzzy theory can be an alternative method for the analysis. The fuzzy theory is based on fuzzy sets. It expresses the ambiguity of incomplete sets of information using a membership function. Moreover, a correct judgment can be made without verbose iterations. Hence, the aim of this study is to examine the uncertainty in soil mechanical parameters. The membership functions between soil mechanical parameters, i.e., cohesion and angle of internal friction, were constructed based on the fuzzy theory. The fuzzy point estimation was used in combination with the hydrologic and mechanical coupling model on HYDRUS 2D and the Slope Cube Module. The local factor of safety at different depths of the slope was determined using the local factor of safety theory. The probability of failure at different depths was calculated through reliability analysis, which could serve as an early warning for subsequent slope failures.

Determination of the water regulation capacity of a typic hapludands by means of humidity retention curves and the modeling of its hydrophysical properties

In the watershed Centella , located in the upper river basin of the Dagua - Valle del Cauca, in nine farms with association coffee - banana, coffee - guamo, cane panelera and pastures, the water regulation capacity of the soil was studied by means of humidity retention curves obtained in the laboratory and by modeling its hydrophysical properties in Hydrus 2D. Properties such as texture, bulk density, porosity, organic matter, hydraulic conductivity, infiltration and humidity were determined. Subsequently, moistureretention curves were simulated using the hydraulic models of Van Genuchten, Brooks and Corey, Van Genuchten modified and Kosugi, evaluating the average errors and the dispersion of the data. Agreed to the results it is possible to point out that the soil under study has a high capacity for moisture retention ( > 18%), consequence of the high content of clays ( > 41%) and organic matter ( > 5%), characteristics of the Andisols of the Valle del Cauca. Finally, the best fitting model was compared statistically with the data of the curves obtained in the laboratory, finding that Van Genuchten and Van Genuchten models modified, are the most appropriate for obtaining the retention curves from the hydrophysical properties since they presented a lower mean error (ME) with a value not higher than -0.11 cm3 / cm3 and a value of the square root of the mean square error (RMSE) less than 0.11 cm3 / cm3.

Biochar Amendment Affects Soil Water and CO2 Regime during Capsicum Annuum Plant Growth

Recent studies on using soil enhancer material, such as biochar, provide varying results from a soil hydrological and chemical perspective. Therefore, research focusing on soil-biochar-plant interactions is still necessary to enhance our knowledge on complex effects of biochar on soil characteristics. The present study investigated the changes in soil water content (SWC) and soil respiration (belowground CO2 production) over time during the growth of Capsicum annuum (pepper) in pot experiments. Concurrently, we investigated the influence of grain husk biochar with the amount of 0, 0.5%, 2.5%, and 5.0% (by weight) added to silt loam soil. Pepper plants were grown under natural environmental conditions to better represent field conditions, and additional irrigation was applied. SWC among treatments showed minor changes to precipitation during the beginning of the study while plants were in the growing phase. The highest water holding throughout the experiment was observed in the case of BC5.0. CO2 production increased in biochar amended soils during the first few days of the experiments; while the overall cumulative CO2 production was the highest in control and the lowest in BC2.5 treatments. We used the HYDRUS 1D soil hydrological model to simulate changes in SWC, using the control treatment without biochar as a reference data source for model calibration. The simulated SWC dynamics fitted well the measured ones in all treatments. Therefore, the HYDRUS 1D can be an exceptionally valuable tool to predict the hydrological response of different amount of biochar addition to silt loam soil including plant growth.

Sensitivity of Percolation Estimates to Modeling Methodology: A Case Study at an Unlined Tailings Facility with Limited Monitoring Data

Calculation of water budgets is critical to developing long-term management and remediation plans for legacy mine waste facilities. The effects of several modeling decisions commonly made by practitioners constructing numerical hydrologic models can significantly alter estimates of percolation and resultant management strategies. We investigated the effects of variations in several common modeling decisions for an unlined legacy tailings emplacement in Lincoln County, Nevada using predictions from HYDRUS 1D and 2D simulations. Modeling decisions investigated include choice of hydraulic property model, hydraulic properties, numerical mesh discretization, boundary condition representation, dimensionality, and geometry. Hydrologic parameterization was informed by measurement of field-saturated hydraulic conductivity, in-situ density, field moisture content, bulk (dry) density, and water retention curve by hanging column, pressure plate, and chilled mirror hygrometer. Numerical hydrologic models resulted in percolation estimates from 0 to 24 mm/year through the tailings. Choice of hydraulic properties and temporal resolution of boundary condition data contributed the most to variations in percolation estimates. For comparison, percolation was predicted with a simple water balance model (HELP), resulting in a percolation rate of 51 mm/year. Such a wide range of percolation rate predictions demonstrates the potential for significant variability in model output within a range of defensible modeling decisions, assumptions, and parameterization methods. To appropriately bound this uncertainty, several model assumptions and iterations should be considered.