Techniques and Methods 6-A30
Wells that are open to multiple aquifers can provide preferential pathways to flow and solute transport that short-circuit normal fluid flowlines. Representing these features in a regional flow model can produce a more realistic and reliable simulation model. This report describes modifications to the Multi-Node Well (MNW) Package of the U.S. Geological Survey (USGS) three-dimensional ground-water flow model (MODFLOW). The modifications build on a previous version and add several new features, processes, and input and output options. The input structure of the revised MNW (MNW2) is more well-centered than the original verion of MNW (MNW1) and allows the user to easily define hydraulic characteristics of each multi-node well. MNW2 also allows calculations of additional head changes due to partial penetration effects, flow into a borehole through a seepage face, changes in well discharge related to changes in lift for a given pump, and intraborehole flows with a pump intake located at any specified depth within the well. MNW2 also offers an improved capability to simulate nonvertical wells. A new output option allows selected multi-node wells to be designated as “observation wells” for which changes in selected variables with time will be written to separate output files to facilitate postprocessing. MNW2 is compatible with the MODFLOW–2000 and MODFLOW–2005 versions of MODFLOW and with the version of MODFLOW that includes the Ground-Water Transport process (MODFLOW–GWT).
Posted August 2009
For additional information, please contact Leonard F. Konikow.
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Konikow, L.F., Hornberger, G.Z., Halford, K.J., and Hanson, R.T., 2009, Revised multi-node well (MNW2) package for MODFLOW ground-water flow model: U.S. Geological Survey Techniques and Methods 6–A30, 67 p.
Conceptual Model and Numerical Implementation
Simulation of Pumping and Nonpumping Wells
Head Loss Terms
Calculation of Water Level and Flow in the Multi-Node Well
Specifying the Location of Multi-Node Wells
Model Features and Processes
Description of Test Problems
Fully Penetrating Pumped Well in Ideal Confined Aquifer (Lohman Problem)
Long, Unpumped Observation Well (Reilly Problem)
Constraints on Pumping Rate
Flowing Wells: Special Application of Constraints on Pumping Rate
Horizontal and Slanted Wells
Well Screen Variability
Flow Routing in Borehole
Summary and Conclusions
Appendix 1—Data Input Instructions for Multi-Node Well (MNW2) Package
Appendix 2—Selected Input Data and Printed Results for Sample Problem
Appendix 3—Program to Convert MNW1 Input Data to MNW2 Input Data