Soil Hydro-thermodynamics:Soil Hydro-thermodynamics

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The user guideline on running thermodynamic process in permafrost and seasonal freezing/thawing watershed thermo-hydrodynamic modeling in is described in the following document: HYDRO-THERMODYNAMIC PROCESS GUIDELINE REPORT.

For more theoretical information about the physical equations and fully coupled architecture, visit [1].

POC: Nawa Raj Pradhan at nawa.pradhan@usace.army.mil

Introduction

To account for the seasonal changes in the soil thermal and hydrological dynamics, the soil moisture state physical process defined by the Richards Equation is integrated with the soil thermal state defined by the numerical model of phase change based on the quasi-linear heat conductive equation. The numerical model of phase change is used to compute a vertical soil temperature profile using the soil moisture information from the Richards solver; the soil moisture numerical model, in turn, uses this temperature and phase, information to update hydraulic conductivities in the vertical soil moisture profile. Long-term simulation results from the test case, a head water sub-catchment at the peak of the Caribou Poker Creek Research Watershed, representing the Alaskan permafrost active region, indicated that freezing temperatures decreases infiltration, increases overland flow and peak discharges by increasing the soil ice content and decaying the soil hydraulic conductivity exponentially.

Method

The GIPL model is a stand-alone permafrost model that computes a 1D (vertical) soil temperature profile over time using static values of soil moisture at daily intervals. As implemented in GSSHA, GIPL is a subroutine that computes a profile of soil temperature in every 2D grid cell, including time-varying soil moisture and groundwater levels at varying time intervals. To accomplish this, several tasks were performed: The original GIPL permafrost model was converted from FORTRAN to C and C++ source code. Originally, GIPL parameters were 1D in the soil’s vertical profile but are lumped into the horizontal spatial extent of application. Significant effort was expended to make all the GIPL state variables and parameters horizontally distributed as grid based or permafrost soil type based before merging the C and C++ version of GIPL into GSSHA. Thus, the 1D limitations of GIPL are enhanced into multidimensional distributed applicability in the GSSHA distributed modeling framework. Originally, the GIPL numerical model of heat transport used daily or larger time-steps. As implemented in GSSHA, GIPL can have any time-step, as specified by the user. The default time-step is the infiltration time-step, which is now on the order of seconds or minutes. Several thermo-hydrodynamic formulations and modeling concepts developed by Pradhan et al. (2019) are implemented by Pradhan et al. (2024) as a methodology in linking GIPL and GSSHA for the development of a coupled framework that simulates interactive effects of soil thermal hydrological dynamics in the saturated and unsaturated permafrost layer. The following links between GIPL and GSSHA hydro- thermodynamic formulations are implemented to exchange the information between hydrodynamic infiltration process and thermodynamic heat transfer process: • Linking hydrodynamic and thermodynamic computational nodes • Linking GIPL soil thermodynamics with GSSHA soil moisture hydrodynamics • Linking soil temperature and hydraulic conductivity • Linking soil heat transfer effect on effective groundwater transmissivity

References

  • Nawa Raj Pradhan, Charles Downer, Sergey Marchenko, 2019, Catchment Hydrological Modeling with Soil Thermal Dynamics during Seasonal Freeze-Thaw Cycles Water 2019, 11, 116; doi:10.3390/w11010116.
  • Nawa Raj Pradhan, Charles W. Downer, and Sergey Marchenko, 2024, User guidelines on catchment hydrological modeling with soil thermal dynamics in Gridded Surface Subsurface Hydrologic Analysis (GSSHA). ERDC/CHL TR-24-4, Vicksburg, 
 MS: U.S. Army Engineer Research and Development Center. http://dx.doi.org/10.21079/11681/35777.



GSSHA User's Manual

22 Soil Hydro-thermodynamics


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