Techniques of Water-Resource Investigations (TWRI) Report, Book 6, Chapter A1, "A Modular Three-Dimensional Finite-difference Ground-Water Flow Model," In Reply Refer To: June 17, 1988 WGS-Mail Stop 411 OFFICE OF GROUND WATER TECHNICAL MEMORANDUM NO.88.05 Subject: PUBLICATIONS--Techniques of Water-Resources Investigations (TWRI) Report, Book 6, Chapter A1, "A Modular Three-Dimensional Finite-Difference Ground-Water Flow Model," by M. G. McDonald and A. W. Harbaugh The subject report replaces Open-File Report 83-875. The new report is similar to the old one, but many sections of the text have been modified to add more detailed explanations. Also, a number of changes were made to the model program, but it functions just as the previous version did. Most of the program changes were made for the purpose of converting it to FORTRAN 77. This version should be even more portable than the original FORTRAN 66 version. For example, it runs on IBM Personal Computers under Microsoft FORTRAN without any modification. Datasets used with the original version of the program should produce identical results when used with the new version. The new report may be ordered from the Books and Open-File Reports Section at the Denver Federal Center by submitting Form 9-1986. There is no charge if ordered for official use by USGS employees however, if more than four copies are being ordered, Form 9-1986 must be sent through Kathleen Iseri in Reston. The cost to the public is $27. Water-Resources Division employees may obtain the new version of the model program in several ways: 1. Use the Software Exchange (SoftEx) on the QVARSB Prime computer to obtain the program as a single file. The SoftEx entry number is VAKJH00011. 2. Issue the following command from your own Prime computer to obtain the program as a single file: FTR SOFTEX>M.SOURCE>VAKJH00011 xxx -SS QVARSB where "xxx" is the pathname for the program on your computer. 3. Send electronic mail to Mike McDonald or Arlen Harbaugh (EDOC identifiers are given below) requesting the program. You will receive the program in multiple files (one file per model package), sample problem input data, and compilation instructions. Include in the request the name of the directory that you want the files sent to. The program that is sent by any of the above methods has two changes from what is published in the new TWRI report. It has the BAS Package input unit set to 5 (rather than 1) as is usual on Prime computers, and the X array is dimensioned to 350000 rather than 30000. Please report any problems with the new report or program to Mike McDonald (FTS 959-5805, EDOC user identifier MGMCDONALD) or Arlen Harbaugh (FTS 959-5615, EDOC user identifier AHARBAUGH). Eugene P. Patten Chief, Office of Ground Water WRD Distribution: A, B, S, FO, PO