Last Updated July 17, 2017
The key to modeling the vadose zone is predicting an accurate surface boundary condition. VADOSE/W computes this surface flux boundary by coupling ground heat, mass and vapor flow with actual climate data.
VADOSE/W extends the concepts found in the popular SoilCover program into two dimensions. Critical to the formulation of VADOSE/W is its ability to predict actual evaporation as a function of the soil water stress state, rather than simply using soil water content, drying time, or empirical user-defined relationships. Instead, VADOSE/W uses the rigorous Penman-Wilson method to compute actual evaporation as a function of soil water pressure, a stress state variable. It is the only 2D product using this state-of-the-art approach.
Actual Evaporation (AE) is only equal to Potential Evaporation (PE) when the soil is saturated. If the soil at the ground surface is not saturated, the AE rate can be much less than the PE rate. Wilson (1990, 1994) showed that the only way AE can be predicted correctly for all soil types and climatic conditions is to base the calculation on both the negative pore-water pressures and temperatures in the ground. Wilson modified the Penman (1948) method to make the actual evaporation rate dependent on the relative humidity of the soil and the air. The relative humidity in the soil can only be known if the soil temperature and water pressure are known and solved for simultaneously. To solve this complex set of equations, it is necessary to include vapor flow in the soil. VADOSE/W meets all these requirements, and is fully coupled in two dimensions.
Wilson, G. W., 1990. Soil Evaporative Fluxes for Geotechnical Engineering Problems. Ph.D. Thesis, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Wilson, G. W., Fredlund, D. G. & Barbour, S. L. 1994. Coupled soil-atmosphere modelling for soil evaporation. Canadian Geotechnical Journal, 31(2): 151-161.
Penman, H. L., 1948. Natural evapotranspiration from open water, bare soil and grass. Proc. R. Soc. London Ser. A. 193: 120-245.
VADOSE/W is formulated to analyze transient 2-dimensional oxygen or radon gas diffusion, dissolution and decay in response to changing heat and moisture conditions in the ground. The gas transport analysis is carried out simultaneously with the coupled heat and mass transfer solution. This feature can be used to determine gas concentrations and mass flows into or out of the ground in response to pre-set or user input concentration boundary conditions.
When VADOSE/W analyzes an evaporative flux problem, it computes data regarding:
Infiltration and ponding resulting from high rainfall event
Specific computed parameters include:
Comparison of upslope and downslope cover base flow on a shallow sloped cover
Soil surface results data includes (for each time interval, or cumulative since Day 1):
Upslope saturation profiles during a 365 day simulation in a shallow sloped cover.
Water Balance data includes cumulative:
Cover layer interface results data includes:
Using finite element computed pore-water pressures in SLOPE/W makes it possible to model the effects of evaporative flux on stability. For example, you can analyze changes in stability as the pore-water pressure changes over time due to the evaporative flux process. Also use VADOSE/W data in CTRAN/W contaminant transport analysis.