UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY RESTON, VA. 22092 In Reply Refer To: June 18, 1985 WGS-Mail Stop 411 GROUND WATER BRANCH TECHNICAL MEMORANDUM NO. 85.03 Subject: PUBLICATIONS--Release of New Report Entitled "SUTRA: Saturated-Unsaturated Transport, a finite- element simulation model for saturated- unsaturated, fluid- density-dependent ground water flow with energy transport or chemically-reactive single-species solute transport" by Clifford I. Voss The subject report has recently been approved and printed as Water-Resources Investigations Report 84-4369. Copies are being sent under separate cover to all District Offices and some Subdistricts. The report documents a state-of-the-art ground-water transport- simulation model known as SUTRA. In addition, the report provides an excellent description and explanation of the physics of ground- water flow and transport. We recommend that this very thorough work be read by all individuals interested in attaining an understanding of density-dependent ground-water flow and transport in addition to those individuals interested in applying the computer code. Simulation using SUTRA is in two space dimensions in either the areal plane or in a cross-sectional plane. The third dimension is accounted for by allowing the thickness to vary from point to point. The spatial coordinate system may be either Cartesian (x,y) or radial-cylindrical (r,z). Areal simulation is usually physically unrealistic for two-dimensional variable-density fluid problems. Ground-water flow is simulated through numerical solution of a fluid-mass-balance equation. The ground-water system may be either saturated, or partly or completely unsaturated. Fluid density may be constant, or vary as a function of either solute concentrations or fluid temperature. SUTRA tracks the transport of either solute mass or energy (heat) in the flowing ground water through a unified equation which represents the transport of either solute or energy. Solute transport is simulated through numerical solution of a solute- mass-balance equation where solute concentration may affect fluid density. The single-solute species may be transported conservatively, or it may undergo equilibrium sorption (through linear, Freundlich, or Langmuir isotherms). In addition, the solute may be produced or decayed through first- or zero-order processes. Energy transport is simulated through numerical solution of an energy-balance equation. The solid grains of the aquifer matrix and fluid are assumed to have equal temperature locally, and fluid density and viscosity may be temperature dependent. SUTRA is a very powerful, and accordingly very complex, numerical simulator. Because of the complexity of the physics governing the systems and the approximations made by the numerical algorithms, extreme care must be taken to properly use and interpret results generated by this method. The author provides some insight and guidelines as to proper discretization and problem formulation for optimal use of this numerical simulator. (s) Thomas E. Reilly Hydrologist WRD Distribution: A, B, S, FO, PORelease of New Report Entitled "SUTRA: Saturated-Unsaturated Transport, a finite-element simulation model for saturated-unsaturated, fluid- density-dependent ground water flow with energy transport or chemically-reactive single-species solute transport"