TASK 9—REGIONAL GROUNDWATER MODELING

Construction of the regional numerical model should begin early in the time frame of the regional study, as soon as the preliminary hydrogeologic analysis is completed. Such a model could be useful in defining a framework for studying the system dynamics and in organizing field data even before calibration, prediction, and sensitivity analysis are performed (Anderson and Woessner, 1992). The PMP states that the task “Regional Model Development—Phase I" will begin in August 2003, directly following the task “Define Preliminary Hydrogeologic Framework.” However, the text suggests that much of the initial work on the modeling will be directed towards choosing an appropriate code and developing algorithms to handle density dependent flow. Although the final model is intended to be capable of handling density-dependent flow, initial regional-scale modeling efforts employing available codes that do not have the capability to handle variable density problems may still be useful to guide the test-drilling program and associated data acquisition as well as the aquifer performance test program. This is especially true in areas with lower salinity, or where pumping-induced gradients are high. Modifications can be made to this model as the acquired data warrant in parallel with development of models with density dependent flow capabilities. Overall, the PMP outlines a reasonable strategy for developing, calibrating, testing and documenting a regional model as well as high-resolution inset models of selected areas. The Project Delivery Team recognizes the many technical challenges that will need to be addressed. It is not clear if the potential importance of horizontal anisotropy in hydraulic parameters will be evaluated, as in Yobbi (2000). Given the generic nature of the modeling task description provided in the PMP, a more substantive critique of the modeling methodology is not possible at this time. Comments relevant to the water level and water chemistry data that may provide constraints on these models are included in the discussion of Subtask 6.4. Calibration efforts should also make use of flux targets wherever possible to provide improved constraints on model parameters and boundary conditions. The Project Delivery Team should be commended for including peer review of the methodology and of the resulting model throughout the development process.

ECOLOGICAL AND WATER QUALITY STUDIES— APPENDIX L AND TASKS 10–13

Tasks 1013 are, in general, not described in the Project Scope (section 3.0) in detail sufficient to evaluate the adequacy of the monitoring or experimental studies. Also, these task descriptions are not as fully developed as are those of Tasks 4, 6, 7 and 9, which also address field and laboratory studies and modeling efforts. Appendix L, Ecological and Water Quality Studies, provides far greater detail and clarifies many of the questions that are raised by the task descriptions. Overall, there appears to be a poor linkage between the task descriptions provided in the main body of the PMP and the descriptions of studies in Appendix L. The appendix provides much of the needed description of these tasks, but it is never cited in Section 3 of the PMP. Either information that is contained in Appendix L should be incorporated into the task descriptions, or there should be substantial citing of appropriate sections of the Appendix throughout. There also appear to be some inconsistencies between the task descriptions and the Appendix.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement