Volume-weighted particle-tracking method for solute-transport modeling; Implementation in MODFLOW–GWT

Techniques and Methods 6-A58
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Abstract

In the traditional method of characteristics for groundwater solute-transport models, advective transport is represented by moving particles that track concentration. This approach can lead to global mass-balance problems because in models of aquifers having complex boundary conditions and heterogeneous properties, particles can originate in cells having different pore volumes and (or) be introduced (or removed) at cells representing fluid sources (or sinks) of varying strengths. Use of volume-weighted particles means that each particle tracks solute mass. In source or sink cells, the changes in particle weights will match the volume of water added or removed through external fluxes. This enables the new method to conserve mass in source or sink cells as well as globally. This approach also leads to potential efficiencies by allowing the number of particles per cell to vary spatially—using more particles where concentration gradients are high and fewer where gradients are low. The approach also eliminates the need for the model user to have to distinguish between “weak” and “strong” fluid source (or sink) cells. The new model determines whether solute mass added by fluid sources in a cell should be represented by (1) new particles having weights representing appropriate fractions of the volume of water added by the source, or (2) distributing the solute mass added over all particles already in the source cell. The first option is more appropriate for the condition of a strong source; the latter option is more appropriate for a weak source. At sinks, decisions whether or not to remove a particle are replaced by a reduction in particle weight in proportion to the volume of water removed. A number of test cases demonstrate that the new method works well and conserves mass. The method is incorporated into a new version of the U.S. Geological Survey’s MODFLOW–GWT solute-transport model.

Suggested Citation

Winston, R.B., Konikow, L.F., and Hornberger, G.Z., 2018, Volume-weighted particle-tracking method for solute-transport modeling; Implementation in MODFLOW–GWT: U.S. Geological Survey Techniques and Methods, book 6, chap. A58, 44 p., https://doi.org/10.3133/tm6A58.

ISSN: 2328-7055 (online)

Table of Contents

  • Abstract 
  • Introduction
  • Governing Equations 
  • Numerical Methods
  • Model Testing and Evaluation 
  • Summary and Conclusions 
  • Acknowledgments
  • Software 
  • References Cited
  • Appendix 1. Revised Data Input Instructions for Groundwater Transport Process (GWT) with MOCWT Option

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Volume-weighted particle-tracking method for solute-transport modeling; Implementation in MODFLOW–GWT
Series title Techniques and Methods
Series number 6-A58
DOI 10.3133/tm6A58
Year Published 2018
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) National Research Program - Eastern Branch
Description v, 44 p.
Larger Work Type Report
Larger Work Subtype USGS Numbered Series
Larger Work Title Section A: Groundwater in Book 6: Modeling techniques
Public Comments This report is Chapter 58 of Section A: Groundwater in Book 6 Modeling techniques.
Online Only (Y/N) Y
Additional Online Files (Y/N) N