Changes to the MNW2 Package for MODFLOW-2005 version 1.10.0 (Nov.-Dec. 2012) A bug was fixed that affected simulations in which a composite well screen was generated when specifying multiple open intervals by elevation. In this case, some nodes were inadvertently excluded from the second interval. With the fix, all nodes of the multi-node well will be represented. Some output format adjustments were also made. If a single-node multi-node well with a nonzero specified discharge were located in an inactive cell (IBOUND=0), it could generate a divide-by-zero error and halt execution of the program. The code was fixed to preclude such a floating-point error from occurring. A new warning message is now also written to the output file if this condition is detected. If the well yield (and pumping rate) was reduced because of the seepage face calculations, an incorrect message (indicating erroneously that the cause was the head constraint) was written to the output file. The code was fixed so that possible causes of reduced puming rates are accurately printed. The code was modified to eliminate separate processing for single-node MNW2 wells, which eliminated some inconsistencies in handling single-node wells. If the computed value for the head in single-node wells drops below the bottom of the cell, it invokes the seepage face calculation, which will reduce or eliminate the desired Q from the well. In cases where the Qdes is thereby reduced, the actual head in the well is indeterminate, but will be reported in separate MNWI output files as the limiting value of the bottom elevation of the cell together with an informaiton note that the actual value may be lower than that reported value. If Qdes is reduced to zero, the well is deactivated and that information is reported in the MNWI optional MNW2 observation well file. At the end of the first paragraph on p. 32 of the documentation report, it states that the alternate calculations for CWC for nonvertical wells will be performed automatically when LOSSTYPE = THIEM, SKIN, or GENERAL. Unfortunately, the code did not check this condition, and erroneously performed these calculations when LOSSTYPE = SPECIFYCWC. The corrected code now uses the specified values of CWC for nonvertical wells when it is supposed to. The code automatically estimates the maximum number of nodes (NODTOT) as required for allocation of arrays. However, if a large number of horizontal wells are being simulated, or possibly for other reasons, this default estimate proves to be inadequate, a new input option has been added to alow the user to directly specify a value for NODTOT. If this is a desired option, then it can be implemented by specifying a negative value for "MNWMAX"--the first value listed in Record 1 (Line 1) of the MNW2 input data file. If this is done, then the code will assume that the very next value on that line will be the desired value of "NODTOT". The model will then reset "MNWMAX" to its absolute value. The value of "IWL2CB" will become the third value on that line, etc. The code included several coding errors in the calculation of cell-to-well conductances for nonvertical wells. There was also an error in the calculation of the length of closed casing between sequential, but non-adjacent, active nodes of a nonvertical MNW2 well (a value only used for informational purposes in the output file). All of these errors have now been fixed. ________________________________________________________________________________________ Changes to the MNW2 Package for MODFLOW-2005 version 1.9 (March, 2012) A bug was fixed that affected simulations when both MNW2 and the HUF Package were used in the same simulation in conjunction with the partial penetration correction. The variable KY is now declared as a Double Precision variable instead of being implicitly assumed (incorrectly) to be an Integer variable. A number of minor changes were made in Format statements to produce a cleaner output file. In Subroutines GWF2MNW27BCF and GWF2MNW27HUF, corrections were made to assure the correct check is made for steady-state or transient conditions and to prevent a divide by zero error if a cell is dry. A bug was fixed for the calculation of angles theta and omega for slanted wells with an orientation into the southwest directional quadrant. References 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.