Program

UNSAT-H: Unsaturated Soil Water and Heat Flow Model

The UNSAT-H computer code is used to understand the movement of water, heat, and vapor in soils so more informed decisions can be made about land use, waste disposal, and climate change.

An illustration showing how water flows into the layers of the subsurface.

UNSAT-H is a FORTRAN computer code used to simulate the one-dimensional flow of water, vapor, and heat in soils. The code addresses the processes of precipitation, evaporation, plant transpiration, storage, and deep drainage.

The UNSAT-H computer code is used to understand the movement of water, heat, and vapor in soils. Use of the code allows for better informed decisions to be made about land use, waste disposal, and climate change. Example tests and typical applications include studies of the water balance behavior of surface covers over shallow land burial waste sites and studies of land disturbance effects on recharge rates.

Get UNSAT-H

UNSAT-H Version 3.0 can be downloaded from our GitHub site: https://github.com/pnnl/unsat_h

This open source software was developed by PNNL in 2000. The user guide, also found in GitHub as "UNS_V30.pdf" is available here. 

About UNSAT-H

The UNSAT-H model was developed at PNNL to assess the water dynamics of arid sites and, in particular, estimate recharge fluxes for scenarios pertinent to waste disposal facilities. This model received significant support from the Immobilized Waste Program (IWP) of the Hanford Site’s River Protection Project. This program was interested in designing and assessing the performance of on-site disposal facilities to receive radioactive wastes that were stored in single- and double-shell tanks at the Hanford Site. The IWP was interested in estimates of recharge rates for current conditions and long-term scenarios involving the vadose zone disposal of tank wastes. 

To achieve the above goals for assessing water dynamics and estimating recharge rates, the UNSAT-H model addresses soil water infiltration, redistribution, evaporation, plant transpiration, deep drainage, and soil heat flow as one-dimensional processes. The UNSAT-H model simulates liquid water flow using Richards’ equation, water vapor diffusion using Fick’s law, and sensible heat flow using the Fourier equation.

The UNSAT-H 3.0 User Guide details development of UNSAT-H Version 3.0, including the bases for the conceptual model and its numerical implementation, benchmark test cases, example simulations involving layered soils and plants, and the code manual. New features include hysteresis, an iterative solution of head and temperature, an energy balance check, the modified Picard solution technique, additional hydraulic functions, multiple-year simulation capability, and general enhancements.  

This guide includes eight example problems. The first four are verification tests of UNSAT-H capabilities, three of which are repeats of the tests used for previous versions of UNSAT-H.

  • The first test examines the ability of UNSAT-H to simulate infiltration compared to separate analytical and numerical solutions. This test was repeated using the modified Picard solution technique.
  • The second test examines the ability of UNSAT-H to simulate drainage compared to measurements and a numerical solution.
  • The third test examines the ability of UNSAT-H to simulate heat conduction compared to an analytical solution.
  • The fourth test is new for UNSAT-H and examines the ability of UNSAT-H to simulate hysteresis compared to measurements and a numerical solution.
  • The results of all four tests showed that the tested processes were correctly implemented in UNSAT-H. The repeat of the first test with the modified Picard solution technique successfully demonstrated a 10^4 to 10^5 reduction in mass balance errors.

The second four example problems are demonstrations of real-world situations.

  • The first three are repeat problems from previous versions of UNSAT-H.
  • The first demonstration involves a 1-year simulation of the water dynamics of a layered soil without heat flow or plants.
  • The second demonstration repeats the first for a 3-day period but with the addition of heat flow. This demonstration was repeated with the new energy balance check; a 4x reduction in the heat balance error was obtained.
  • The third demonstration involves a 1-year simulation of the water dynamics of a sandy soil with plants.
  • The fourth and final demonstration is a 35-year simulation of the water dynamics of a sandy loam soil without plants to highlight the new multiyear capability.

The Code Custodian

Catherine Yonkofski

Catherine Yonkofski is the code custodian for UNSAT-H. An environmental engineer, her technical specialty is in the development and application of subsurface simulation codes for use in characterization and interpretation of complex flow systems, predictive fate and transport modeling, and optimization of engineered subsurface systems. Dr. Yonkofski earned her PhD in environmental engineering and science at Clemson University.

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