An Evaluation of Unsaturated Flow Models in an Arid Climate

Dixon, J. Michael

doi:10.2172/759261

Cited by 7 publications

(9 citation statements)

References 13 publications

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“…Figure 4 displays the daily evaporation corresponding to the SCL medium-textured soil-type case computed by all codes, except code HYDRUS-1D that was forced by the half hourly evaporation output from SABAE-HW. A quick overdrying of soil surface wetness by SHAW is noted, which corresponds to the same conclusion by Dixon (1999). Furthermore, while CLASS continues evaporating surface moisture before and after the precipitation day, SABAE-HW curbs the rate, joining the evaporation curves corresponding to SHAW.…”

Section: Test 1: Infi Ltra On In Three Diff Erent Soilssupporting

confidence: 74%

“…Moreover, the faster moving wetting fronts by HYDRUS-1D can be noticed in plots corresponding to the 222.5 cm depth, with a lag time of about 10 d for the medium SCL soil. Th e study by Dixon (1999) already noted this behavior when comparing HYDRUS-1D and SHAW model predictions, a direct consequence of the greater unsaturated hydraulic conductivity evaluated from the Mualem model used in HYDRUS-1D. Th e CLASS early wetting fronts are associated with numerical error arising from the coarse layer.…”

Section: Test 1: Infi Ltra On In Three Diff Erent Soilsmentioning

confidence: 88%

“…Furthermore, it was noted that SHAW generally overestimated evaporation and underestimated water storage change and drainage. The effectiveness of HYDRUS‐1D and SHAW models was also evaluated in a study by Dixon (1999) for an arid test site. It was noticed that the SHAW model's overprediction of evaporation occurs immediately after precipitation events, which overdries the near‐surface soil and induces a subsequent underprediction.…”

Section: Other Model Descriptionsmentioning

confidence: 99%

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SABAE‐HW: An Enhanced Water Balance Prediction in the Canadian Land Surface Scheme Compared with Existing Models

Loukili

Woodbury

Snelgrove

2008

Vadose Zone Journal

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The Canadian Land Surface Scheme (CLASS) is a numerical model pioneered at the Canadian Atmospheric Environment Service by Verseghy (1991) and Verseghy et al. (1993) to evaluate the vertical transfer of energy and water between the atmosphere and three surface soil layers. This article introduces SABAE‐HW (soil atmosphere boundary, accurate evaluations of heat and water), a new model built using the modeling framework of CLASS version 2.6 that allows a user to specify depth and number of soil layers. The physically based calculations of heat and moisture transfer are adequately extended in the new code to fit the desired refined mesh. The generalized minimal residual (GMRES) iterative method is used to resolve new soil heat flux terms. Moreover, a water table lower boundary condition is added to allow eventual coupling with groundwater models. The results of SABAE‐HW are validated for some synthetic runs under real‐like seasonal weather conditions and various soil types. Then the model prediction capability is confirmed for a location within the Assiniboine Delta Aquifer using North American Regional Reanalysis (NARR) atmospheric data. Intercomparisons of results to simulation outputs from CLASS, SHAW, HYDRUS‐1D, and HELP models demonstrate the capability of SABAE‐HW to predict reasonable moisture profiles and water budget terms. Under warm weather conditions, SABAE‐HW and SHAW yield similar water content profiles and bottom drainages. Also, in the freezing–thawing situations, detailed moisture profiles by SABAE‐HW are contrasted to both CLASS and SHAW solutions.

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Section: Test 1: Infi Ltra On In Three Diff Erent Soilssupporting

confidence: 74%

Section: Test 1: Infi Ltra On In Three Diff Erent Soilsmentioning

confidence: 88%

Section: Other Model Descriptionsmentioning

confidence: 99%

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SABAE‐HW: An Enhanced Water Balance Prediction in the Canadian Land Surface Scheme Compared with Existing Models

Loukili

Woodbury

Snelgrove

2008

Vadose Zone Journal

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“…Free drainage was selected for the lower boundary. The most important factor for successful application of unsaturated flow theory to actual field problems is obtaining the parameters for the governing transfer equation (Dixon 1999). The hydraulic parameters used in this study for hydraulic conductivity function were optimized by neural network prediction (Van Genuchten et al 1992).…”

Section: Wfps Simulationmentioning

confidence: 99%

Hierarchical Bayesian models for soil CO₂flux using soil texture: a case study in central Hokkaido, Japan

Ishikura

Wang

et al. 2014

Soil Science and Plant Nutrition

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Hierarchical Bayesian (HB) methods are useful tools for modeling multifaceted, nonlinear phenomena such as those encountered in ecology, and have been increasingly applied in environmental sciences, e.g., to estimate soil gas flux from different soil textures or sites. We have developed a model of soil carbon dioxide (CO 2) flux based on soil temperature (T, 5 cm depth) and water-filled pore space (WFPS, 5 cm depth) using HB theory. The HB model was calibrated using a dataset of CO 2 flux measured from bare soils belonging to four texture classes in 14 upland field sites in a watershed in central Hokkaido, Japan, in the nonsnow-cover season from 2003 to 2011. The numerical software HYDRUS-1D was used to simulate daily WFPS, and the estimated values were significantly correlated with the measured WFPS (R 2 = 0.68, P < 0.001). Compared to a nonhierarchical Bayesian model (Bayesian pooled model), the CO 2 predictions with the HB model more accurately represented texture-specific observations. The simulation-observation fit of the CO 2 flux model was R 2 = 0.64 (P < 0.001). More than 90% of the observed daily data were within the 95% confidence interval. The HB model exhibited high uncertainty for high CO 2 flux values. The HB model calibration revealed differing sensitivity of CO 2 flux to T and WFPS in different soil texture classes. CO 2 flux increased with an increase in T, and it increased to a lesser degree with a finer texture, possibly because the clay and silt facilitated soil aggregation, thus reducing temperature fluctuations. WFPS values between 0.48 and 0.64 resulted in optimal conditions for CO 2 flux. The minimum WFPS value increased with an increase in clay content (P < 0.05). Although only a small number of soil types were studied in only one season in this study, the HB model may provide a method for predicting how the effects of soil temperature and moisture on CO 2 flux change with texture, and soil texture could be regarded as an upscaling factor in future research on regional extrapolation.

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“…• Hydrogeologic (IT, 1998Blout et al, 1995;Laczniak et al, 1996;Winograd and Thordarson, 1975) • Unsaturated Flow (Dixon, 1999;BN, 1998a) • Groundwater Recharge (Levitt and Yucel 2002a, b;Hokett and French, 1998) • Subsidence (DOE, 1998;Obi et al, 1996) • Source Term • Transport and Exposure (Cochran, Crowe, et al, 2001a; • Inadvertent Human Intrusion (BN, 2001;Black, 2001;Shott et al, 1998) • Biological (Hansen and Ostler, 2003;Winkel et al, 1995;Wirth et al, 1999) • General Performance Cochran, Beyeler, et al, 2001) Most scenarios for radionuclide release and transport ultimately involve some aspect of the hydrologic system. Additionally, the hydrologic environment affects monitoring, PA, and closure cover design decisions.…”

Section: Conceptual Models and Assessmentsmentioning

confidence: 99%

Characterization Report for the 92-Acre Area of the Area 5 Radioactive Waste Management Site, Nevada Test Site, Nevada

Nevada¹

2006

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Office (NNSA/NSO) manages two low-level Radioactive Waste Management Sites (RWMSs) at the Nevada Test Site (NTS). The Area 5 RWMS uses engineered shallow-land burial cells to dispose of packaged waste. This report summarizes characterization and monitoring work pertinent to the 92-Acre Area in the southeast part of the Area 5 RWMS. The southeast quadrant covers 37 hectare (ha) (92 acres [ac]), and is referred to as the "92-Acre Area."The cells in the 92-Acre Area include 13 boreholes, 16 narrow trenches, and 9 broader pits. The waste disposal units were gradually established during 45 years of waste operations. Only three disposal units within the 92-Acre Area are currently active. Most of the disposal units have been operationally closed with covers of at least 2.4 meters (m) (8 feet [ft]) of native fill. Closure of the 92-Acre Area disposal units is anticipated by 2011.Current closure plans organize the disposal cells of the 92-Acre Area into six closure units by physical location, waste types, and regulatory requirements. One of these closure units is Federal Facility Agreement and Consent Order Corrective Action Unit (CAU) 111: Retired Mixed Waste Pits. The CAU 111 pits and trenches were operated prior to the promulgation of the Resource Conservation and Recovery Act (RCRA) and may have received both low-level waste (LLW) and low-level mixed waste (LLMW). A proposed single final closure cover and a monitoring plan will meet the needs of all six closure units within the 92-Acre Area. Studies indicate a monolayer soil cover will provide the equivalent protection of a standard RCRA cover, and offer superior performance with respect to subsidence.The precursor to the Area 5 RWMS, the Sugar Bunker Dump, began receiving waste by 1960 and began burying waste in January 1961. The Area 5 RWMS was established in 1978 on a 296 ha (732-ac) site incorporating the existing Sugar Bunker Dump waste cells in the southeast corner. The thirteen 37-m (120-ft) boreholes were drilled in the 1980s for the Greater Confinement Disposal (GCD) program. The GCD program was terminated before all the boreholes were used.Both classified and unclassified materials are managed at this facility. Unclassified disposal records and historic records indicate waste types in the 92-Acre Area include LLW, LLMW, asbestiform waste, transuranic (TRU) waste, and mixed TRU waste. Most of the inventory is LLW, and much of the LLW contains radionuclides that will decay significantly over the next several decades. Most of the TRU and potential mixed TRU waste is in boreholes over 21 m (70 ft) below ground surface. Thorium waste is present in the lowest tier of one disposal pit. Two disposal units have been designated for asbestos waste. Much of the suspected LLMW was deposited at the oldest disposal units prior to the promulgation of RCRA. The contaminants are not readily released or transported, due to the structure (such as lead shielding). The waste acceptance criteria, packaging requirements, monitoring, and other factors in the operation of the interi...

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An Evaluation of Unsaturated Flow Models in an Arid Climate

Cited by 7 publications

References 13 publications

SABAE‐HW: An Enhanced Water Balance Prediction in the Canadian Land Surface Scheme Compared with Existing Models

SABAE‐HW: An Enhanced Water Balance Prediction in the Canadian Land Surface Scheme Compared with Existing Models

Hierarchical Bayesian models for soil CO₂flux using soil texture: a case study in central Hokkaido, Japan

Characterization Report for the 92-Acre Area of the Area 5 Radioactive Waste Management Site, Nevada Test Site, Nevada

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An Evaluation of Unsaturated Flow Models in an Arid Climate

Cited by 7 publications

References 13 publications

SABAE‐HW: An Enhanced Water Balance Prediction in the Canadian Land Surface Scheme Compared with Existing Models

SABAE‐HW: An Enhanced Water Balance Prediction in the Canadian Land Surface Scheme Compared with Existing Models

Hierarchical Bayesian models for soil CO2flux using soil texture: a case study in central Hokkaido, Japan

Characterization Report for the 92-Acre Area of the Area 5 Radioactive Waste Management Site, Nevada Test Site, Nevada

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Hierarchical Bayesian models for soil CO₂flux using soil texture: a case study in central Hokkaido, Japan