title: A nested rediscretization method to improve pathline resolution by eliminating weak sinks representing wells.
abstract: This paper discusses a method for overcoming the problem of weak sinks representing wells that result from spatial discretization effects when using MODPATH, the particle-tracking postprocessor for the ground water flow model MODFLOW. Weak sink cells are model cells that represent a well that does not discharge at a sufficiently large rate to capture all of the flow entering the cell; therefore, flowpaths within these cells cannot be uniquely defined because it is impossible to know whether a given water particle discharges to the well or passes through the cell. Creating a submodel of the well cell by using the nested rediscretization method can eliminate this ambiguity by converting the weak sink cell into a strong sink cell. The method is designed to be run manually for each well and for steady-state conditions. Other advantages, disadvantages, technical considerations, and limitations of the method are presented. Software created for the method consists of five Fortran programs that are operated using a set of instructions. A practical application of the method is presented by using an example wellhead-protection problem that demonstrates that nested rediscretization can provide more accurate particle-tracking results than those obtained by using a coarsely discretized model alone.
authors.affiliation: U.S. Geological Survey Water Resources Division, 810 Bear Tavern Rd., West Trenton, NJ 08628, USA.
authors.forename: F J
authors.initials: FJ
authors.lastname: Spitz
authors.forename: R S
authors.initials: RS
authors.lastname: Nicholson
authors.forename: D A
authors.initials: DA
authors.lastname: Pope
mesh_terms: D008962:Models, Theoretical; D012987:Soil; D014872:Water Movements; D014881:Water Supply
chemical_list: D012987:Soil