The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Nadia Carluer - One of the best experts on this subject based on the ideXlab platform.
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Shallow Water Table effects on Water, sediment, and pesticide transport in vegetative filter strips – Part 1: nonuniform infiltration and soil Water redistribution
Hydrology and Earth System Sciences, 2018Co-Authors: R. Muñoz Carpena, C. Lauvernet, Nadia CarluerAbstract:Vegetation buffers like vegetative filter strips (VFS) are often used to protect Water bodies from surface runoff pollution from disturbed areas. Their typical placement in bottomland often results in the presence of a seasonal Shallow Water Table (WT) that can decrease soil infiltration and increase surface pollutant transport during a rainfall/runoff event. Simple and robust components of hydrological models are needed to analyse the impacts of WT in the landscape. To simulate VFS infiltration under realistic rainfall conditions with WT, we propose a generic infiltration solution (Shallow Water Table INfiltration algorithm: SWINGO) based on a combination of approaches by Salvucci and Entekhabi (1995) and Chu (1997) with new integral formulae to calculate singular times (time of ponding, shift time, and time to soil profile saturation). The algorithm was tested successfully on 5 distinct soils both against Richards’s numerical solution and experimental data in terms of infiltration and soil moisture redistribution predictions, and applied to study the combined effects of varying WT depth, soil type, and rainfall intensity and duration. The results show the robustness of the algorithm and its ability to handle various soil hydraulic functions, and initial non-ponding conditions under unsteady rainfall. The effect of a WT on infiltration under ponded conditions was found effectively decoupled from surface infiltration/excess runoff processes for depths larger than 1.2 to 2 m, Shallower for fine soils and shorter events. For non-ponded initial conditions, the influence of WT depth also varies with rainfall intensity. Also, we observed that soils with a marked air entry (bubbling pressure) exhibit a distinct behaviour with WT near the surface. The features and good performance of SWINGO support its coupling with an existing VFS model in the companion paper, where the potential effects of seasonal or permanent WTs on VFS pollutant transport and control are studied.
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Shallow Water Table effects on Water sediment and pesticide transport in vegetative filter strips part 1 nonuniform infiltration and soil Water redistribution
Hydrology and Earth System Sciences, 2017Co-Authors: Rafael Munozcarpena, C. Lauvernet, Nadia CarluerAbstract:Vegetation buffers like vegetative filter strips (VFS) are often used to protect Water bodies from surface runoff pollution from disturbed areas. Their typical placement in bottomland often results in the presence of a seasonal Shallow Water Table (WT) that can decrease soil infiltration and increase surface pollutant transport during a rainfall/runoff event. Simple and robust components of hydrological models are needed to analyse the impacts of WT in the landscape. To simulate VFS infiltration under realistic rainfall conditions with WT, we propose a generic infiltration solution (Shallow Water Table INfiltration algorithm: SWINGO) based on a combination of approaches by Salvucci and Entekhabi (1995) and Chu (1997) with new integral formulae to calculate singular times (time of ponding, shift time, and time to soil profile saturation). The algorithm was tested successfully on 5 distinct soils both against Richards’s numerical solution and experimental data in terms of infiltration and soil moisture redistribution predictions, and applied to study the combined effects of varying WT depth, soil type, and rainfall intensity and duration. The results show the robustness of the algorithm and its ability to handle various soil hydraulic functions, and initial non-ponding conditions under unsteady rainfall. The effect of a WT on infiltration under ponded conditions was found effectively decoupled from surface infiltration/excess runoff processes for depths larger than 1.2 to 2 m, Shallower for fine soils and shorter events. For non-ponded initial conditions, the influence of WT depth also varies with rainfall intensity. Also, we observed that soils with a marked air entry (bubbling pressure) exhibit a distinct behaviour with WT near the surface. The features and good performance of SWINGO support its coupling with an existing VFS model in the companion paper, where the potential effects of seasonal or permanent WTs on VFS pollutant transport and control are studied.
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Shallow Water Table effects on Water, sediment and pesticide transport in vegetative filter strips: Part A. non-uniform infiltration and soil Water redistribution
2017Co-Authors: R. Muñoz Carpena, C. Lauvernet, Nadia CarluerAbstract:Abstract. Vegetation buffers like vegetative filter strips (VFS) are often used to protect Water bodies from surface runoff pollution from disturbed areas. Their typical placement in bottomland often results in the presence of a seasonal Shallow Water Table (WT) that can decrease soil infiltration and increase surface pollutant transport during a rainfall/runoff event. Simple and robust components of hydrological models are needed to analyse the impacts of WT in the landscape. To simulate VFS infiltration under realistic rainfall conditions with WT, we propose a generic infiltration solution (Shallow Water Table INfiltration algorithm: SWINGO) based on a combination of approaches by Salvucci and Entekhabi (1995) and Chu (1997) with new integral formulae to calculate singular times (time of ponding, shift time, and time to soil profile saturation). The algorithm was tested successfully on 5 distinct soils both against Richards’s numerical solution and experimental data in terms of infiltration and soil moisture redistribution predictions, and applied to study the combined effects of varying WT depth, soil type, and rainfall intensity and duration. The results show the robustness of the algorithm and its ability to handle various soil hydraulic functions, and initial non-ponding conditions under unsteady rainfall. The effect of a WT on infiltration under ponded conditions was found effectively decoupled from surface infiltration/excess runoff processes for depths larger than 1.2 to 2 m, Shallower for fine soils and shorter events. For non-ponded initial conditions, the influence of WT depth also varies with rainfall intensity. Also, we observed that soils with a marked air entry (bubbling pressure) exhibit a distinct behaviour with WT near the surface. The features and good performance of SWINGO support its coupling with an existing VFS model in the companion paper, where the potential effects of seasonal or permanent WTs on VFS pollutant transport and control are studied.
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Adding the influence of a Shallow Water Table on hydrology, sediment and pesticide transport in a vegetative filter strip model
2013Co-Authors: C. Lauvernet, R. Muñoz Carpena, Nadia CarluerAbstract:A Shallow Water Table can significantly affect soil infiltration and surface runoff during a rainfall event. We develop here an algorithm based on an approximate non-uniform Green-Ampt time-implicit integral form solutions to the infiltration case for ponded soils bounded by a Water Table under initial hydrostatic equilibrium. The coupling into VFSMOD is then developed, and a global sensitivity analysis to study the influence of the Water Table into the coupled model.
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Evaluation of a mechanistic algorithm to calculate the influence of a Shallow Water Table on hydrology sediment and pesticide transport through vegetative filter strips by sensitivity analysis
2012Co-Authors: C. Lauvernet, R. Muñoz Carpena, Nadia CarluerAbstract:Natural or man-introduced areas of vegetation, also known as vegetative filter strips (VFS), are a common environmental control practice to protect surface Water bodies from human influence. In Europe, VFS are often set along the hydrographic network to protect it from agrochemical drift during applications and from field surface runoff. The VFS position in low lands near Water bodies often implies the presence of a seasonal Shallow Water Table, which may have a significant impact on buffer zone’s efficiency.
C. Lauvernet - One of the best experts on this subject based on the ideXlab platform.
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Shallow Water Table effects on Water, sediment, and pesticide transport in vegetative filter strips – Part 1: nonuniform infiltration and soil Water redistribution
Hydrology and Earth System Sciences, 2018Co-Authors: R. Muñoz Carpena, C. Lauvernet, Nadia CarluerAbstract:Vegetation buffers like vegetative filter strips (VFS) are often used to protect Water bodies from surface runoff pollution from disturbed areas. Their typical placement in bottomland often results in the presence of a seasonal Shallow Water Table (WT) that can decrease soil infiltration and increase surface pollutant transport during a rainfall/runoff event. Simple and robust components of hydrological models are needed to analyse the impacts of WT in the landscape. To simulate VFS infiltration under realistic rainfall conditions with WT, we propose a generic infiltration solution (Shallow Water Table INfiltration algorithm: SWINGO) based on a combination of approaches by Salvucci and Entekhabi (1995) and Chu (1997) with new integral formulae to calculate singular times (time of ponding, shift time, and time to soil profile saturation). The algorithm was tested successfully on 5 distinct soils both against Richards’s numerical solution and experimental data in terms of infiltration and soil moisture redistribution predictions, and applied to study the combined effects of varying WT depth, soil type, and rainfall intensity and duration. The results show the robustness of the algorithm and its ability to handle various soil hydraulic functions, and initial non-ponding conditions under unsteady rainfall. The effect of a WT on infiltration under ponded conditions was found effectively decoupled from surface infiltration/excess runoff processes for depths larger than 1.2 to 2 m, Shallower for fine soils and shorter events. For non-ponded initial conditions, the influence of WT depth also varies with rainfall intensity. Also, we observed that soils with a marked air entry (bubbling pressure) exhibit a distinct behaviour with WT near the surface. The features and good performance of SWINGO support its coupling with an existing VFS model in the companion paper, where the potential effects of seasonal or permanent WTs on VFS pollutant transport and control are studied.
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Shallow Water Table effects on Water sediment and pesticide transport in vegetative filter strips part 1 nonuniform infiltration and soil Water redistribution
Hydrology and Earth System Sciences, 2017Co-Authors: Rafael Munozcarpena, C. Lauvernet, Nadia CarluerAbstract:Vegetation buffers like vegetative filter strips (VFS) are often used to protect Water bodies from surface runoff pollution from disturbed areas. Their typical placement in bottomland often results in the presence of a seasonal Shallow Water Table (WT) that can decrease soil infiltration and increase surface pollutant transport during a rainfall/runoff event. Simple and robust components of hydrological models are needed to analyse the impacts of WT in the landscape. To simulate VFS infiltration under realistic rainfall conditions with WT, we propose a generic infiltration solution (Shallow Water Table INfiltration algorithm: SWINGO) based on a combination of approaches by Salvucci and Entekhabi (1995) and Chu (1997) with new integral formulae to calculate singular times (time of ponding, shift time, and time to soil profile saturation). The algorithm was tested successfully on 5 distinct soils both against Richards’s numerical solution and experimental data in terms of infiltration and soil moisture redistribution predictions, and applied to study the combined effects of varying WT depth, soil type, and rainfall intensity and duration. The results show the robustness of the algorithm and its ability to handle various soil hydraulic functions, and initial non-ponding conditions under unsteady rainfall. The effect of a WT on infiltration under ponded conditions was found effectively decoupled from surface infiltration/excess runoff processes for depths larger than 1.2 to 2 m, Shallower for fine soils and shorter events. For non-ponded initial conditions, the influence of WT depth also varies with rainfall intensity. Also, we observed that soils with a marked air entry (bubbling pressure) exhibit a distinct behaviour with WT near the surface. The features and good performance of SWINGO support its coupling with an existing VFS model in the companion paper, where the potential effects of seasonal or permanent WTs on VFS pollutant transport and control are studied.
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Shallow Water Table effects on Water, sediment and pesticide transport in vegetative filter strips: Part A. non-uniform infiltration and soil Water redistribution
2017Co-Authors: R. Muñoz Carpena, C. Lauvernet, Nadia CarluerAbstract:Abstract. Vegetation buffers like vegetative filter strips (VFS) are often used to protect Water bodies from surface runoff pollution from disturbed areas. Their typical placement in bottomland often results in the presence of a seasonal Shallow Water Table (WT) that can decrease soil infiltration and increase surface pollutant transport during a rainfall/runoff event. Simple and robust components of hydrological models are needed to analyse the impacts of WT in the landscape. To simulate VFS infiltration under realistic rainfall conditions with WT, we propose a generic infiltration solution (Shallow Water Table INfiltration algorithm: SWINGO) based on a combination of approaches by Salvucci and Entekhabi (1995) and Chu (1997) with new integral formulae to calculate singular times (time of ponding, shift time, and time to soil profile saturation). The algorithm was tested successfully on 5 distinct soils both against Richards’s numerical solution and experimental data in terms of infiltration and soil moisture redistribution predictions, and applied to study the combined effects of varying WT depth, soil type, and rainfall intensity and duration. The results show the robustness of the algorithm and its ability to handle various soil hydraulic functions, and initial non-ponding conditions under unsteady rainfall. The effect of a WT on infiltration under ponded conditions was found effectively decoupled from surface infiltration/excess runoff processes for depths larger than 1.2 to 2 m, Shallower for fine soils and shorter events. For non-ponded initial conditions, the influence of WT depth also varies with rainfall intensity. Also, we observed that soils with a marked air entry (bubbling pressure) exhibit a distinct behaviour with WT near the surface. The features and good performance of SWINGO support its coupling with an existing VFS model in the companion paper, where the potential effects of seasonal or permanent WTs on VFS pollutant transport and control are studied.
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Shallow Water Table effects on Water sediment and pesticide transport in vegetative filter strips part 2 model coupling application factor importance and uncertainty
Hydrology and Earth System Sciences, 2017Co-Authors: C. Lauvernet, Rafael MunozcarpenaAbstract:Abstract. Vegetative filter strips are often used for protecting surface Waters from pollution transferred by surface runoff in agricultural Watersheds. In Europe, they are often prescribed along the stream banks, where a seasonal Shallow Water Table (WT) could decrease the buffer zone efficiency. In spite of this potentially important effect, there are no systematic experimental or theoretical studies on the effect of this soil boundary condition on the VFS efficiency. In the companion paper (Munoz-Carpena et al., 2018), we developed a physically based numerical algorithm (SWINGO) that allows the representation of soil infiltration with a Shallow Water Table. Here we present the dynamic coupling of SWINGO with VFSMOD, an overland flow and transport mathematical model to study the WT influence on VFS efficiency in terms of reductions of overland flow, sediment, and pesticide transport. This new version of VFSMOD was applied to two contrasted benchmark field studies in France (sandy-loam soil in a Mediterranean semicontinental climate, and silty clay in a temperate oceanic climate), where limited testing of the model with field data on one of the sites showed promising results. The application showed that for the conditions of the studies, VFS efficiency decreases markedly when the Water Table is 0 to 1.5 m from the surface. In order to evaluate the relative importance of WT among other input factors controlling VFS efficiency, global sensitivity and uncertainty analysis (GSA) was applied on the benchmark studies. The most important factors found for VFS overland flow reduction were saturated hydraulic conductivity and WT depth, added to sediment characteristics and VFS dimensions for sediment and pesticide reductions. The relative importance of WT varied as a function of soil type (most important at the silty-clay soil) and hydraulic loading (rainfall + incoming runoff) at each site. The presence of WT introduced more complex responses dominated by strong interactions in the modeled system response, reducing the typical predominance of saturated hydraulic conductivity on infiltration under deep Water Table conditions. This study demonstrates that when present, the WT should be considered as a key hydrologic factor in buffer design and evaluation as a Water quality mitigation practice.
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Adding the influence of a Shallow Water Table on hydrology, sediment and pesticide transport in a vegetative filter strip model
2013Co-Authors: C. Lauvernet, R. Muñoz Carpena, Nadia CarluerAbstract:A Shallow Water Table can significantly affect soil infiltration and surface runoff during a rainfall event. We develop here an algorithm based on an approximate non-uniform Green-Ampt time-implicit integral form solutions to the infiltration case for ponded soils bounded by a Water Table under initial hydrostatic equilibrium. The coupling into VFSMOD is then developed, and a global sensitivity analysis to study the influence of the Water Table into the coupled model.
Mark Ross - One of the best experts on this subject based on the ideXlab platform.
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Comparison of IHM and MIKE SHE Model Performance for Modeling Hydrologic Dynamics in Shallow Water Table Settings
Vadose Zone Journal, 2015Co-Authors: Jing Zhang, Mark RossAbstract:Modeling hydrologic dynamics behavior in Shallow Water Table settings provides unique challenges for integrated hydrologic models. The Integrated Hydrologic Model (IHM), a comprehensive distributed-parameter model, was developed based on deterministic and physically based soil and vegetative properties. In the paper, the IHM was compared with the popular MIKE SHE model in the study of a Shallow Water Table site in west-central Florida. The theoretical basis and integration pathways of IHM are discussed. The models were compared in terms of their performance in predicting streamflow and Water Table depth. Performance was evaluated using the coefficient of determination (R2) and the Nash–Sutcliffe efficiency (Ens). The P factor and R factor were used as uncertainty statistics, comparing observed data with the 95% prediction band. Both models performed reasonably well and reliably in predicting monthly Water Table depth and streamflow, with accepTable R2 values (0.49–0.86) and Ens values (0.41–0.78) over a 3-yr period. Overall, MIKE SHE was the more robust model, producing slightly better streamflow predictions than IHM. However, there was no major difference in the ability of the models to predict depth of the Water Table, using existing parameter sets. The generalized likelihood uncertainty estimation (GLUE) was used to quantify parameter sensitivity and the uncertainty of predictions made by the IHM and MIKE SHE models. A sensitivity analysis (SA) was conducted in the form of Sobol’s method with first- and second-order sensitivity indices, based on the Ens values for the two models. Pair-wise correlations between parameters as well as uncertainties associated with equifinality in model parameter estimation were also explored. It is concluded that both models performed adequately after calibration, andparameter identification in both was subject to considerable uncertainties.
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Numerical modeling of Shallow Water Table behavior with Lisse effect
Chinese Geographical Science, 2011Co-Authors: Jing Zhang, Mark Ross, Huili Gong, Demin ZhouAbstract:Air entrapment is an important consideration in environments with Shallow Water Tables and sandy soil, like the condition of highly conductive sandy soils and flat topography in Florida, USA. It causes Water Table rises in soils, which are significantly faster and higher than those in soils without air entrapment. Two numerical models, Integrated Hydrologic Model (IHM) and HYDRUS-1D (a single-phase, one-dimensional Richards’ equation model) were tested at an area of west central Florida to help further understanding the Shallow Water Table behavior during a long term air entrapment. This investigation employed field data with two modeling approaches to quantify the variation of air pressurization values. It was found that the air pressurization effect was responsible at time up to 40 cm of Water Table rise being recorded by the observation well for these two models. The values of air pressurization calculated from IHM and HYDRUS-1D match the previously published values. Results also indicated that the two numerical models did not consider air entrapment effect (as the predictive parameters remain uncertain) and thus results of depth to Water Table from these models did not compare to the observations for these selected periods. Incorporating air entrapment in prediction models is critical to reproduce Shallow Water Table observations.
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modelling vadose zone moisture dynamics in Shallow Water Table settings with the integrated hydrologic model field scale testing and application
Water and Environment Journal, 2010Co-Authors: Jing Zhang, Mark Ross, Jeffrey Geurink, Huili GongAbstract:Reproducing the moisture retention behaviour of the vadose zone in Shallow Water Table settings, especially for the near-surface Water Table aquifer of the Florida coastal plain, provides unique challenges for integrated hydrological models. A comprehensive distributed parameter model, the Integrated Hydrologic Model (IHM), is developed based on deterministic and physically based soil and vegetative properties. The theory and vertical behaviour of IHM is examined through comparisons with data collected at a study site in west-central Florida. The objectives of this exploration are to test a model of the vertical processes controlling Water Table behaviour, and to also investigate model parameter effects and offer recommendations for improvements and parameterization for regional model application. Rigorous testing is performed to better understand the robustness and/or the limitations of the methodology of the IHM for vadose zones. Simulation results indicate that IHM is capable of providing reasonable predictions of infiltration, depth to Water Table (DTWT) elevation response, evapotranspiration (ET) distributions from the upper, lower soil and Water Table while incorporating field-scale variability of soil and land cover properties.
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variability in specific yield under Shallow Water Table conditions
Journal of Hydrologic Engineering, 2009Co-Authors: Nirjhar Shah, Mark RossAbstract:Investigation is provided concerning the variable behavior of specific yield ( SY ) under Shallow Water Table conditions ( <2 m below land surface). Traditionally, specific yield has been defined as the Water released from pumping of a phreatic aquifer down by a unit head. It is often used as a fixed value in groundWater flow models. This study seeks to elucidate SY variability due to natural processes of evapotranspiration (ET) and recharge. SY variability is of fundamental importance for modeling hydrologic response from stresses and for determination of Water budget of a catchment. HYDRUS 1D—a numerical model solving Richard’s equation for saturated—unsaturated flow in one dimension is used to simulate the behavior of specific yield for a soil type representative of west central Florida. It was found, that for various cases examined (e.g., ET and infiltration), the magnitude of specific yield varied with depth to Water Table. For infiltration response, the variation in the specific yield exhibited stro...
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Variability in Specific Yield under Shallow Water Table Conditions
Journal of Hydrologic Engineering, 2009Co-Authors: Nirjhar Shah, Mark RossAbstract:Investigation is provided concerning the variable behavior of specific yield ( SY ) under Shallow Water Table conditions (
Rafael Munozcarpena - One of the best experts on this subject based on the ideXlab platform.
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Shallow Water Table effects on Water sediment and pesticide transport in vegetative filter strips part 1 nonuniform infiltration and soil Water redistribution
Hydrology and Earth System Sciences, 2017Co-Authors: Rafael Munozcarpena, C. Lauvernet, Nadia CarluerAbstract:Vegetation buffers like vegetative filter strips (VFS) are often used to protect Water bodies from surface runoff pollution from disturbed areas. Their typical placement in bottomland often results in the presence of a seasonal Shallow Water Table (WT) that can decrease soil infiltration and increase surface pollutant transport during a rainfall/runoff event. Simple and robust components of hydrological models are needed to analyse the impacts of WT in the landscape. To simulate VFS infiltration under realistic rainfall conditions with WT, we propose a generic infiltration solution (Shallow Water Table INfiltration algorithm: SWINGO) based on a combination of approaches by Salvucci and Entekhabi (1995) and Chu (1997) with new integral formulae to calculate singular times (time of ponding, shift time, and time to soil profile saturation). The algorithm was tested successfully on 5 distinct soils both against Richards’s numerical solution and experimental data in terms of infiltration and soil moisture redistribution predictions, and applied to study the combined effects of varying WT depth, soil type, and rainfall intensity and duration. The results show the robustness of the algorithm and its ability to handle various soil hydraulic functions, and initial non-ponding conditions under unsteady rainfall. The effect of a WT on infiltration under ponded conditions was found effectively decoupled from surface infiltration/excess runoff processes for depths larger than 1.2 to 2 m, Shallower for fine soils and shorter events. For non-ponded initial conditions, the influence of WT depth also varies with rainfall intensity. Also, we observed that soils with a marked air entry (bubbling pressure) exhibit a distinct behaviour with WT near the surface. The features and good performance of SWINGO support its coupling with an existing VFS model in the companion paper, where the potential effects of seasonal or permanent WTs on VFS pollutant transport and control are studied.
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Shallow Water Table effects on Water sediment and pesticide transport in vegetative filter strips part 2 model coupling application factor importance and uncertainty
Hydrology and Earth System Sciences, 2017Co-Authors: C. Lauvernet, Rafael MunozcarpenaAbstract:Abstract. Vegetative filter strips are often used for protecting surface Waters from pollution transferred by surface runoff in agricultural Watersheds. In Europe, they are often prescribed along the stream banks, where a seasonal Shallow Water Table (WT) could decrease the buffer zone efficiency. In spite of this potentially important effect, there are no systematic experimental or theoretical studies on the effect of this soil boundary condition on the VFS efficiency. In the companion paper (Munoz-Carpena et al., 2018), we developed a physically based numerical algorithm (SWINGO) that allows the representation of soil infiltration with a Shallow Water Table. Here we present the dynamic coupling of SWINGO with VFSMOD, an overland flow and transport mathematical model to study the WT influence on VFS efficiency in terms of reductions of overland flow, sediment, and pesticide transport. This new version of VFSMOD was applied to two contrasted benchmark field studies in France (sandy-loam soil in a Mediterranean semicontinental climate, and silty clay in a temperate oceanic climate), where limited testing of the model with field data on one of the sites showed promising results. The application showed that for the conditions of the studies, VFS efficiency decreases markedly when the Water Table is 0 to 1.5 m from the surface. In order to evaluate the relative importance of WT among other input factors controlling VFS efficiency, global sensitivity and uncertainty analysis (GSA) was applied on the benchmark studies. The most important factors found for VFS overland flow reduction were saturated hydraulic conductivity and WT depth, added to sediment characteristics and VFS dimensions for sediment and pesticide reductions. The relative importance of WT varied as a function of soil type (most important at the silty-clay soil) and hydraulic loading (rainfall + incoming runoff) at each site. The presence of WT introduced more complex responses dominated by strong interactions in the modeled system response, reducing the typical predominance of saturated hydraulic conductivity on infiltration under deep Water Table conditions. This study demonstrates that when present, the WT should be considered as a key hydrologic factor in buffer design and evaluation as a Water quality mitigation practice.
Mahmood Nachabe - One of the best experts on this subject based on the ideXlab platform.
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evapotranspiration of two vegetation covers in a Shallow Water Table environment
Soil Science Society of America Journal, 2005Co-Authors: Mahmood Nachabe, Nirjhar Shah, Mark Ross, Jeff VomackaAbstract:A method is introduced to estimate evapotranspiration (ET) in Shallow Water Table environments. The method involves measuring the diurnal fluctuations in total soil moisture above the Water Table to estimate (i) the net lateral and vertical subsurface flux in the aquifer and (ii) evapotranspiration from the vegetation cover. In a hillslope discharge zone, the net lateral subsurface flux was calculated from the recovery rate of soil moisture between midnight and 0400 h. Evapotranspiration was then estimated from a daily Water balance in a soil column that included the Water Table. The method was tested on two vegetation covers, a pasture in a groundWater recharge area, and a riparian zone with woody vegetation in a groundWater discharge area. A moisture probe carrying eight sensors was used in each area to estimate the total soil moisture in a sandy soil environment. The observed Water Table fluctuated between land surface and a depth of 1.2 m during the study period, allowing observation and estimation of the total soil moisture in a soil column that included the Water Table. The results of this investigation support another hypothesis that, in humid, Shallow Water Table environments, ET demand may be supported by adjacent ecosystems. This method provided reasonable results for the two landscapes investigated and was able to capture the variability of evapotranspiration in heterogeneous vegetation covers. It provided a relatively inexpensive alternative to characterize ET within regionally heterogeneous but microhomogenous landscapes. Though tested for coarse-textured soil, the method involving soil moisture monitoring can be easily adapted to other soil types with Shallow Water Table. Another advantage of using this method is that ET can be successfully estimated without detailed knowledge of soil hydraulic properties, subsurface flow patterns, or vegetation characteristics.
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evapotranspiration of two vegetation covers in a Shallow Water Table environment
Soil Science Society of America Journal, 2005Co-Authors: Mahmood Nachabe, Nirjhar Shah, Mark Ross, Jeff VomackaAbstract:A method is introduced to estimate evapotranspiration (ET) in Shallow Water Table environments. The method involves measuring the diurnal fluctuations in total soil moisture above the Water Table to estimate (i) the net lateral and vertical subsurface flux in the aquifer and (ii) evapotranspiration from the vegetation cover. In a hillslope discharge zone, the net lateral subsurface flux was calculated from the recovery rate of soil moisture between midnight and 0400 h. Evapotranspiration was then estimated from a daily Water balance in a soil column that included the Water Table. The method was tested on two vegetation covers, a pasture in a groundWater recharge area, and a riparian zone with woody vegetation in a groundWater discharge area. A moisture probe carrying eight sensors was used in each area to estimate the total soil moisture in a sandy soil environment. The observed Water Table fluctuated between land surface and a depth of 1.2 m during the study period, allowing observation and estimation of the total soil moisture in a soil column that included the Water Table. The results of this investigation support another hypothesis that, in humid, Shallow Water Table environments, ET demand may be supported by adjacent ecosystems. This method provided reasonable results for the two landscapes investigated and was able to capture the variability of evapotranspiration in heterogeneous vegetation covers. It provided a relatively inexpensive alternative to characterize ET within regionally heterogeneous but microhomogenous landscapes. Though tested for coarse-textured soil, the method involving soil moisture monitoring can be easily adapted to other soil types with Shallow Water Table. Another advantage of using this method is that ET can be successfully estimated without detailed knowledge of soil hydraulic properties, subsurface flow patterns, or vegetation characteristics.
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analytical expressions for transient specific yield and Shallow Water Table drainage
Water Resources Research, 2002Co-Authors: Mahmood NachabeAbstract:[1] New closed-form expressions are introduced to capture the dependence of specific yield on time and depth to Water Table. The expressions allow the user to convert observations of Water Table fluctuations to volumes of Water released from storage in a Shallow Water Table aquifer. Whereas a linear relationship between Water Table fluctuations and released volumes holds for a deep Water Table aquifer, this relationship is nonlinear for Shallow Water Table aquifers. The dependence of specific yield on time stems from the slow drainage of soil Water from pores above the Water Table. The new expressions allow determination of transient specific yield and time to drain the soil Water profile for a given Water Table fluctuation. If the time step in a numerical groundWater model is longer than the time for limiting specific yield, then a constant (time independent) specific yield can be justifiably adopted. The new expressions are easy to use and require knowledge of soil hydraulic properties which are readily available from soil Water retention data and surveys.