The program 'HOTWTR' is a block-centered finite difference model for simulating three-dimensional steady-state groundwater flow and heat transport in an isotropic, heterogeneous confined aquifer system with uniform thermal properties and no change of state. The interblock transmissivities are calculated as the harmonic mean of the adjacent blocks. Driving forces on the system are external hydrologic conditions of recharge from precipitation and fixed hydraulic head boundaries. The IGWMC version also includes the effects of pumping and recharging wells. Heat flux includes geothermal heat flow (in-flux), conduction from aquifer to the land surface, advection (heat conveyed by water) from areal recharge, and advection to or from fixed-head boundaries. Furthermore, the IGWMC version includes heat in-flux from recharging wells and heat loss through pumping wells.

The program uses an iterative procedure that alternatively solves the groundwater- and heat-flow equations, updating advective flux after solution of the groundwater flow equation, and updating hydraulic conductivity after solution of the heat flow equation. The coupling is based on linear interpolation of hydraulic conductivity-viscosity-temperature tables. The finite difference equations for both groundwater- and heat-flow are solved using a direct method. Density is considered constant in space.

The model supports variable grid block lengths in X-, Y-, and Z-direction. Necessary data for this program include the distribution of hydraulic conductivities and porosity, the water level at recharge or discharge sites, recharge from precipitation, temperature of recharged water, land-surface temperature, geothermal heat flow, average thermal conductivity of the water-saturated rock, distance from land surface to top of aquifer, and volumetric heat of the fluid. In addition, the IGWMC version requires, if present, recharge well water flux rates and temperature, and discharge well water flow rates. Input of hydraulic conductivity and porosity is either given per layer per zone, where each zone represents an area of uniform parameters, or per individual cell. There are up to 9 zones allowed in the model. Recharge for the top active layer, distance from land surface to top of aquifer, geothermal heat flow (heat flux into bottom layer of model), and initial head and temperatures for each layer are entered on a cell-by-cell basis.

All output files are ASCII text files. One of the files created by the model contains a complete echo of the model input, including the actual, cell-by-cell values for porosity and initial hydraulic conductivity. Also, the model results are given in three files, one containing X-, Y-, and Z-coordinates and final heads for each cell; one containing X-, Y-, and Z-coordinates and final temperatures for each cell; and one containing iteration progress, final heat flux and groundwater flux balances, computed temperature and head distribution, and final temperature-corrected hydraulic conductivities. Finally, a 'log' file is created with information on simulation progress. An IGWMC-written utility is included to prepare two-dimensional head and temperature distribution files for graphic postprocessing.

HOTWTR facilitates limited dynamic allocation of arrays. It can handle various grid sizes, limited by a maximum of 200 elements in either direction and with (M*N*2+1)*(M*N*L/2)< 1,480,000, where M, N, and L indicate the number of rows, columns, and layers, respectively.

HOTWTR is a public domain MS-DOS based model. It runs in a DOS window under MS Windows 3.1. HOTWTR is distributed on DOS formatted disks containing source code, executable image, and example data sets. The documentation includes installation instructions and a user's manual.

SYSTEM REQUIREMENTS

Intel 80486 or 80386 processor with math coprocessor, 16 Mb RAM, DOS 5.0 or higher, 2 Mb free disk space for program and example files.

Authors: J. Reed (U.S. Geological Survey); modified by P.K.M. van der Heijde (IGWMC).