Both mnw1 and mnw2 allow a water level limit to be

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Unformatted text preview: 0 -5.864026E+00 -5.857332E+00 -5.848033E+00 -5.833587E+00 -5.803555E+00 63 Appendix 3—Program to Convert MNW1 Input Data to MNW2 Input Data 65 Appendix 3—Program to Convert MNW1 Input Data to MNW2 Input Data By A.W. Harbaugh Overview of Program The MNW2 Package will supercede the older MNW1 Package in new releases of MODFLOW. Therefore, model users who have input datasets compatible with MNW1 will have to edit and modify those datasets to use MNW2. MNW1to2 is a utility program that automatically converts input data for the MNW1 Package to input data for the MNW2 Package. The overall capabilities of both packages are similar, but the organization of the input data differs, and a few incompatible features and processes exist between the two packages. MNW1 reads all of the attributes for all of the nodes of a multi-node well every stress period the well is used. MNW2 defines most attributes for all multi-node wells up front, and then a well is activated within a stress period by indicating its name and pumping rate. Both MNW1 and MNW2 allow a water-level limit to be specified for wells, but MNW2 does not support all the functionality of MNW1. The fundamental capability supported by both packages is an absolute water-level limit (input variable Hlim in both MNW1 and MNW2). MNW1 also supports specifying the limit as a drawdown (or head build up for recharging wells) from a reference level (input variable Href in MNW1). Although MNW2 does not directly support specification of the limit as a drawdown, MNW1to2 will compute Hlim for use in MNW2 from the MNW1 Hlim and Href values. MNW1 further allows the reference head to be specified as a water level computed during the simulation, and MNW1to2 does not have a way to deal with this, except that MNW1to2 notifies the user if the drawdown limit is being used. The user is then asked to choose to either deactivate the water-level limit for all wells with a drawdown limit or allow MNW1to2 to compute Hlim from the specified Href. MNW1 does not require well names, but MNW2 requires well names. MNW1to2 generates well names if none exist. The name is generated in the following form: WcccrrrL1L2…Lx, where ccc is a 3-digit number that is the grid column of the first node of the well, rrr is a 3-digit number that is the grid row of the first node of the well, L1,L2…Lx is a series of 2-digit numbers that are the layers of the nodes in the well. For example, if there is a multi-node well in nodes (column, row, layer) (17,43,3), (17,43,4), and (17,43,5), then the generated well number will be W017043030405. MNW1 allows 32-character names, and MNW2 limits well names to 20 characters. If a name is longer than 20 characters, then MNW1to2 uses the first 16 characters of the MNW1 name and appends a 4-digit number to make 20 characters. MNW1 does not require unique well names within a stress period as required by MNW2. MNW1to2 checks the wells defined for each stress period to make sure that the names are unique. If there are duplicate names, then the program writes an error message and stops. Further, MNW1 allows many of the attributes of a well to change each stress period, and MNW2 does not allow those changes. The attributes that can change in MNW1 and not in MNW2 are LOSSTYPE, use of a water-level limit, the specific nodes incorporated in the well, well radius, and any of the well-loss constants. The well discharge (Qdes) and the value of the water-level limit are allowed to change every stress period in MNW2. MNW1to2 checks for an invalid change in well attributes each stress period. If a change is detected, then those new attributes are represented by creating a new well by appending a single uppercase letter to the name of the well. MNW2 implements five alternative models of well loss, which are specified using input variable LOSSTYPE. Table A3–1 describes how the value of LOSSTYPE for MNW2 is determined from MNW1 data. 66 Revised Multi-Node Well (MNW2) Package for MODFLOW Ground-Water Flow Model Table A3–1. Inferred equivalence in MNW1to2 of LOSSTYPE options in MNW1 to those in MNW2.  MNW1 data Rw=0 Rw<0 LOSSTYPE=SKIN and Skin≤0 LOSSTYPE=SKIN and Skin>0 LOSSTYPE=LINEAR LOSSTYPE=NONLINEAR MNW2 LOSSTYPE NONE SPECIFYcwc THIEM SKIN General, with C=0 General When the MNW2 LOSSTYPE is Skin, MNW2 requires that the skin radius (Rskin) and the skin hydraulic conductivity (Kskin) be defined. MNW1to2 computes these from MNW1 data. In MNW1 (Halford and Hanson, 2002, eq. 3), Skin is defined as , (A3–1) where T is the aquifer transmissivity in the cell (L2/T) and TSkin is the transmissivity in the skin region (L2/T). A node is assumed to be screened in the entire thickness of the cell, so , (A3–2) where K is the aquifer hydraulic conductivity (L/T) and KSkin is the hydraulic conductivity in the area around the well (L/T). Skin and Rw are specified in the MNW1 data file, and K is determined from data in the flow package file. MNW1to2 determines the flow package being used from the MODFLOW Name File. The two flow packages supported by MNW1to2 are the Block-Centered Flow (BCF) and Layer-Property Flow (LPF) Packages. When K is different in the x- and y-directions, K is defined as . Equation 2 can be used to determine either KSkin or RSkin if the other is known. To avoid having the user interactively enter one of the values, MNW1to2 assumes that RSkin=2 Rw. Using equation 2, KSkin is then computed to be . (A3–3) Running MNW1to2 When MNW1to2 is started, it prompts for a MODFLOW Name File. The Name File is used to determine the MNW1 input file, the Discretization (DIS) File, and the flow package file. If the MNW1 option to compute waterlevel limits based on drawdown is used, then MNW1to2 asks the user to specify whether or not to compute the MNW2 Hlim from the MNW1 Hlim and Href values. If the response is “No”, then the MNW1 water-level limit is ignored for all wells for which a drawdown limit is specified. MNW1to2 writes two output files. Mnw1to2.lst contains information about the conversion, including the original MNW1 input data. Mnw1to2.mnw is the converted MNW2 data file. The MNW2 data file has comments at the end of lines to indicate the input data contained on the lines. MNW1to2 does not use dynamic memory allocation, which results in limits on the number of wells and the number of nodes associated with each well. The limits are 10,000 multi-node wells and 50 nodes per well. MNW1to2 also limits the number of stress periods to 100. Although MNW1to2 will usually be successful in generating an equivalent dataset for MNW2 from a MNW1 dataset, the conversion is based on a number of implicit assumptions, as discussed above, and the conversion may not always be 100 percent complete nor be precisely as anticipated by the user. Thus, it is recommended that the Appendix 3—Program to Convert MNW1 Input Data to MNW2 Input Data user carefully inspect the MNW2 input file generated by this utility program. The user should also review the Mnw1to2.lst output file to see if any warning messages were generated during the conversion process. The executable code for MNW1to2 is available for downloading from a USGS software repository, which for ground-water models can be found at http://water.usgs.gov/software/ground_water.html. 67 Konikow and others—Revised Multi-Node Well (MNW2) Package for MODFLOW Ground-Water Flow Model—Techniques and Methods 6–A30 Printed on recycled paper...
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