A Manual of Instructional Problems

A Manual of Instructional Problems for the USGS MODFLOW Model contains twenty problems (including data sets on diskette) solved using the popular MODFLOW model. The purpose of this MODFLOW manual is both educational and to provide verification tests for MODFLOW. The problems are designed to cover modeling principles, specifics of input/output, options available to the modeler, rules of thumb, and common modeling mistakes. The Manual of Instructional Problems for the USGS MODFLOW Model fills a void between ground-water modeling textbooks, which deal primarily with theoretical aspects of modeling, and code documentations, which usually deal with the programming aspects of particular models. Although developed specifically for the MODFLOW model, the principles discussed in the manual can be extended to other models.

A recent report by the U.S. EPA Modeling Policy Study Group offered several approaches to training agency staff in the application of ground-water modeling. They identified the problem that current training efforts tend to be of short duration (one week or less) with a lack of in-house programs to reinforce training received in a formal setting. The study group suggested, among other things, the alternative of self-study coupled with obtaining experience under the guidance of a senior modeling specialist.

In order for ground-water modeling self-study to be viable, a curriculum must exist that allows the student to have hands-on experience with the practical application of models. Available resources do not meet this need. They usually include one or two test problems for verification purposes. Journal articles or USGS publications best fit the need for learning about the practical application of models. However, these sources either do not give enough information to reproduce results or involve data setup that is too complicated to allow a student to efficiently have hands-on experience with the model.

This new manual for MODFLOW is intended to meet the need described above. Twenty documented problems for MODFLOW, complete with problem statements, input data sets, and discussion of results are presented. The problems are designed to cover modeling principles, specifics of input/output, options available to the modeler, rules of thumb and common modeling mistakes.

Data set preparation time and execution time have been minimized by simplifying the problems to small size and to focus only on the aspect that is under consideration. Model grids are generally smaller and more homogeneous than would be used in practice; however, the intent and result of each exercise are not compromised by the simplification.

The user of this manual for MODFLOW should attempt to solve the problems as described in the problem statement portion of each exercise. The model setup can be checked in the data set listing given in the model input section of each problem. Results can be checked by the pertinent portions given in the model output section. Some training on the structure and input of MODFLOW as well as some training on the theory of ground-water modeling is assumed. The user will need to refer to the MODFLOW manual on some occasions. The abbreviated input instructions given in the MODFLOW manual are included as Appendix A to the manual.

A secondary function of this manual is for verification purposes. Although the MODFLOW code has been extensively applied, very little documentation of its testing and verification is available in the literature. To address this situation, where possible, model-generated results are compared to analytical solutions, results of other models, or to simulations with alternative boundary conditions or configurations. In addition to providing an informal bench-marking of MODFLOW, these problems can be used to verify the correct installation of the code on a particular computer system or to verify that certain user modifications have not altered the integrity of the program. The results of the MODFLOW simulations may vary slightly (approximately +/-0.02 ft or m) from one computer to another.

All the packages of MODFLOW have been utilized at least twice in this series of problems. Input and output files are included on the diskette (included) for the data sets listed in the manual. The diskette included with this document does not include a copy of MODFLOW. It is assumed the user has obtained a copy of MODFLOW. The problems given in the manual for MODFLOW are intended to be useful without changes or additions. However, the problems may also be useful as a stepping stone to more detailed analysis. Rather than creating new data sets, the analyst can modify existing MODFLOW data sets to fill a particular need.

A Manual for MODFLOW Requirements: PC 386/486/Pentium with 2 MB RAM.