scholarly journals Unsaturated Flow Characterization Utilizing Water Content Data Collected within the Capillary Fringe

2014 ◽  
Vol 7 ◽  
pp. ASWR.S13282
Author(s):  
Arthur L. Baehr ◽  
Timothy J. Reilly
Keyword(s):  
Water Content ◽  
Capillary Pressure ◽  
Unsaturated Zone ◽  
Unsaturated Flow ◽  
Agricultural Research ◽  
Specific Yield ◽  
Hydraulic Parameters ◽  
Capillary Fringe ◽  
Pressure Function

An analysis is presented to determine unsaturated zone hydraulic parameters based on detailed water content profiles, which can be readily acquired during hydrological investigations. Core samples taken through the unsaturated zone allow for the acquisition of gravimetrically determined water content data as a function of elevation at 3 inch intervals. This dense spacing of data provides several measurements of the water content within the capillary fringe, which are utilized to determine capillary pressure function parameters via least-squares calibration. The water content data collected above the capillary fringe are used to calculate dimensionless flow as a function of elevation providing a snapshot characterization of flow through the unsaturated zone. The water content at a flow stagnation point provides an in situ estimate of specific yield. In situ determinations of capillary pressure function parameters utilizing this method, together with particle-size distributions, can provide a valuable supplement to data libraries of unsaturated zone hydraulic parameters. The method is illustrated using data collected from plots within an agricultural research facility in Wisconsin.

scholarly journals Coupling saturated and unsaturated flow: comparing the iterative and the non-iterative approach

2021 ◽  
Vol 25 (7) ◽  
pp. 4041-4059
Author(s):  
Natascha Brandhorst ◽  
Daniel Erdal ◽  
Insa Neuweiler
Keyword(s):  
Unsaturated Zone ◽  
Unsaturated Flow ◽  
Lower Boundary ◽  
3D Models ◽  
Specific Yield ◽  
Model Parameters ◽  
Test Cases ◽  
Iterative Approach ◽  
Groundwater Model ◽  
Fully Integrated

Abstract. Fully integrated three-dimensional (3D) physically based hydrologic models usually require many computational resources. For many applications, simplified models can be a cost-effective alternative. The 3D models of subsurface flow are often simplified by coupling a 2D groundwater model with multiple 1D models for the unsaturated zone. The crucial part of such models is the coupling between the two model compartments. In this work we compare two approaches for the coupling. One is iterative where the 1D unsaturated zone models go down to the impervious bottom of the aquifer, and the other one is non-iterative and uses a moving lower boundary for the unsaturated zone. In this context we also propose a new way of treating the specific yield, which plays a crucial role in linking the unsaturated and the groundwater model. Both models are applied to three test cases with increasing complexity and analyzed in terms of accuracy and speed compared to fully integrated model runs. The non-iterative approach is faster but does not yield a good accuracy for the model parameters in all applied test cases, whereas the iterative one gives good results in all cases. Which strategy is applied depends on the requirements: computational speed vs. model accuracy.

scholarly journals Coupling saturated and unsaturated flow: comparing the iterative and the non-iterative approach

2021 ◽  
Author(s):  
Natascha Brandhorst ◽  
Daniel Erdal ◽  
Insa Neuweiler
Keyword(s):  
Unsaturated Zone ◽  
Unsaturated Flow ◽  
Three Dimensional ◽  
Lower Boundary ◽  
3D Models ◽  
Specific Yield ◽  
Iterative Approach ◽  
Groundwater Model ◽  
Iterative Coupling ◽  
Fully Integrated

Abstract. Fully integrated three dimensional (3D) physically based hydrologic models usually require many computational resources. For many applications, simplified models can be a cost effective alternative. 3D models of subsurface flow are often simplified by coupling a 2D groundwater model with multiple 1D models for the unsaturated zone. The crucial part of such models is the coupling between the two model compartments. In this work we compare two approaches for the coupling. One is iterative and the 1D unsaturated zone models go down to the impervious bottom of the aquifer and the other one is non-iterative and uses a moving lower boundary for the unsaturated zone. In this context we also propose a new way of treating the specific yield, which plays a crucial role in linking the unsaturated and the groundwater model. Both models are applied to three test cases with increasing complexity and analyzed in terms of accuracy and speed compared to fully integrated model runs. The non-iterative approach is faster while the iterative approach is more accurate and robust. Besides, for the iterative coupling method a calibration of the specific yield is not needed.

Water flow in unsaturated soils subjected to multiple infiltration events

2020 ◽  
Vol 57 (3) ◽  
pp. 366-376
Author(s):  
Xiaokun Hou ◽  
Sai K. Vanapalli ◽  
Tonglu Li
Keyword(s):  
Water Content ◽  
Water Flow ◽  
Unsaturated Zone ◽  
Unsaturated Soils ◽  
Water Infiltration ◽  
Wetting Front ◽  
Influx Rate ◽  
The Relationship ◽  
Stable Zone

In this paper, water flow in a 4 m height column with an unsaturated soil that is subjected to multiple infiltration events for a 62 day period is investigated. One-dimensional (1D) numerical analysis is also undertaken to analyze the flow, extending the seepage theory for unsaturated soils. Results highlight the formation of two wetting fronts; namely, wetting front I and wetting front II that are induced by the first and subsequent infiltration events, respectively. There is a stable zone where the water content is approximately constant; it forms between the two fronts. A conceptual model of the suction profile is proposed for interpreting in situ water flow by dividing the unsaturated zone into four distinct zones; namely, active, steady, transition, and capillary fringe zones. This division is helpful for providing a rational explanation of water flow in different zones. Novel contributions from this study include a relationship between the hydraulic properties in the steady zone and the flow velocity, which is determined by an average influx rate. In addition, the rate of groundwater recharge can also be estimated using the average influx rate. Results of the present study are useful to understand and interpret the relationship between water infiltration and suction or water content profile in the unsaturated zone as well as variation of groundwater table level.

scholarly journals Bayesian inverse modelling of in situ soil water dynamics: using prior information about the soil hydraulic properties

2011 ◽  
Vol 8 (1) ◽  
pp. 2019-2063 ◽  
Author(s):  
B. Scharnagl ◽  
J. A. Vrugt ◽  
H. Vereecken ◽  
M. Herbst
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Vadose Zone ◽  
Hydraulic Properties ◽  
Prior Information ◽  
Hydraulic Parameters ◽  
Soil Hydraulic Properties ◽  
Soil Hydraulic Parameters ◽  
Soil Hydraulic

Abstract. In situ observations of soil water state variables under natural boundary conditions are often used to estimate field-scale soil hydraulic properties. However, many contributions to the soil hydrological literature have demonstrated that the information content of such data is insufficient to reliably estimate all the soil hydraulic parameters. In this case study, we tested whether prior information about the soil hydraulic properties could help improve the identifiability of the van Genuchten-Mualem (VGM) parameters. Three different prior distributions with increasing complexity were formulated using the ROSETTA pedotransfer function (PTF) with input data that constitutes basic soil information and is readily available in most vadose zone studies. The inverse problem was posed in a formal Bayesian framework and solved using Markov chain Monte Carlo (MCMC) simulation with the DiffeRential Evolution Adaptive Metropolis (DREAM) algorithm. Synthetic and real-world soil water content data were used to illustrate our approach. The results of this study corroborate and explicate findings previously reported in the literature. Indeed, soil water content data alone contained insufficient information to reasonably constrain all VGM parameters. The identifiability of these soil hydraulic parameters was substantially improved when an informative prior distribution was used with detailed knowledge of the correlation structure among the respective VGM parameters. A biased prior did not distort the results, which inspires confidence in the robustness and effectiveness of the presented method. The Bayesian framework presented in this study can be applied to a wide range of vadose zone studies and provides a blueprint for the use of prior information in inverse modelling of soil hydraulic properties at various spatial scales.

scholarly journals In situ measurement of meltwater percolation flux in seasonal alpine snowpack using self potential and capillary pressure sensors

2017 ◽  
Author(s):  
Wilson S. Clayton
Keyword(s):  
Capillary Pressure ◽  
Unsaturated Flow ◽  
Snow Water Equivalent ◽  
Pressure Sensors ◽  
Average Error ◽  
Glacier Mass Balance ◽  
Column Test ◽  
Constitutive Parameters ◽  
Self Potential

Abstract. Downward flux of percolating meltwater was measured quantitatively in an in situ vertical profile, in an alpine snowpack, at a remote location. Three separate measurement systems were used to obtain multiple parameters required to calculate percolation flux. Brooks-Corey constitutive parameters were measured in a 0 °C isothermal snow sample test cell, and then applied to an on-site snow column test. The instrumented column test allowed calculation of fluxes, that were then calibrated to measured outflow to empirically determine an appropriate value of zeta potential. In situ measurements with data logging of self-potential (SP) and capillary pressure sensors then allowed calculation of flux from SP measurements (qsp), expressed as darcy velocity, over a multi-day period. The results strongly reflected diurnal snow melt dynamics, and daily peak qsp ranged from 5.6 to 105 cm/d. qsp was comparable to actual fluxes, represented by changes in snow water equivalent (SWE) (2.5 to 5.3 cm/d) measured at an adjacent USDA SNOTEL station. The average error in qsp was 8 % over a four-day period, with total calculated flux of 18.1 cm, compared to a 16.8 cm change in SNOTEL SWE. Daily (24-hour period) errors ranged from +26 % to −47 %. The methodology developed herein can combine SP with either capillary pressure or saturation measurements. The ability to measure meltwater percolation flux in snowpacks may support mathematical modeling of unsaturated flow processes in melting snow, and may supplement studies of snowmelt-groundwater and snowmelt-runoff interactions and glacier mass balance studies.

New Method for Estimation of Contaminant Travel Rate in Unsaturated Zone under Irrigated Soils

1993 ◽  
Vol 27 (7-8) ◽  
pp. 173-178 ◽  
Author(s):  
M. Zilberbrand
Keyword(s):  
Water Content ◽  
Unsaturated Zone ◽  
Sandy Loam ◽  
Chestnut Soil ◽  
Deep Penetration ◽  
Groundwater Recharge Rate ◽  
Capillary Tension ◽  
Travel Rate ◽  
Tracer Experiments ◽  
Irrigated Soils

In a thick unsaturated zone, when quick deep penetration of rain and irrigation water is absent, at the depths below 3-5 m there exists a zone of downwards quasi-steady water flow. Darcy's water velocity in this zone remains constant with depth and equal to the groundwater recharge rate; unit hydraulic head gradient occurs above the capillary fringe. Therefore, contaminant travel rate is equal to the ratio of hydraulic conductivity (K) and effective volumetric water content (θef). Field tracer experiments and laboratory K and θef determinations were carried out for several representative irrigated lots in the South Ukraine. The dependence of θef on capillary tension was studied for the first time. For loess loam with a capillary tension decreasing from 46 kPa to 0, θef nonlinearly increases from 12% to 27-28%. The effective water content portion (β1) of the total water content increases nonlinearly from 0.38 to 0.65-0.7. The β1 values were estimated for different unsaturated sedimentary rocks. For a capillary tension of about 5 kPa β1 values were: 0.88-0.99 for sands, about 0.65 for loess loam and chestnut soil, about 0.6 for sandy loam, about 0.32 for limestone and about 0.07 for clay. Calculated chloride travel rates in loess loams under irrigated soils fit the values of 0.001-0.003 m/day, determined by the results of field tracer experiments.

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