UPPER KLAMATH BASIN GROUND-WATER STUDY

 Approach

The preliminary ground-water model developed during phase II will be used as an investigative tool to improve our understanding of how the flow-system functions. In phase III, the primary goal of modeling will be to develop a tool that can be used for predictive purposes. The exact approach to developing the predictive model in phase III depends on results from the modeling design work conducted in phases I and II. For planning purposes, a possible strategy to construct and calibrate steady-state and transient models is described below.

 As previously described, a simple, steady-state model would be developed during phase II. This model will probably have a coarse grid and few layers so that it can be run efficiently, and used to test concepts of the flow system. As a better understanding of the flow system is developed, more detail will be incorporated into the model. A limited amount of calibration will be done using this model.

At the beginning of phase III, the model grid would be refined so that the model would have the appropriate resolution for the data available to calibrate it, and for eventual predictive use. This refined steady-state model would then be carefully calibrated. When a reasonable match with predevelopment conditions is achieved, the model will be used to simulate initial conditions for the transient calibration period.

During the later part of phase II and the early part of phase III, historical stress data will be compiled (recharge and pumpage) for the period between predevelopment and current conditions. Available hydrologic response data (heads, stream flux) will also be compiled and used to complete a transient calibration of the model; this calibration period would probably have annual or longer stress periods. Finally, the model would be calibrated to transient conditions during the 1998-2001 period of intensive data collection for this study; this calibration period will probably be simulated with monthly to quarterly stress periods.

Once the model is calibrated, a few representative management scenarios will be framed by the cooperating agencies. The USGS will develop model input data based on the scenarios and demonstrate the use the model to simulate the effects of these scenarios on hydrologic conditions in the basin. The results of these simulations will be presented in the report describing the model and its calibration.

The ground-water model will be sufficiently detailed so that the effects of managed changes in water use can be evaluated at a scale commensurate with the scale of management questions in the basin. Ground-water interaction with canals, rivers, and lakes will be represented at appropriate scales that produce useful estimates of effects of management scenarios on these features. The uncertainty in model predictions will be estimated and reported so that it may be considered in any management decisions formulated on the basis of model results.

Although the modeling described in this proposal is only designed to define flow at a regional scale, it may be possible to utilize embedded-mesh techniques (Leake and Lilly, 1997; Claar, 1998) to build more detailed sub-regional models of site specific areas within the larger regional model to evaluate management at a smaller scale. The regional model would provide boundary fluxes to such an effort; therefore, the entire Upper Klamath Basin would not have to be modeled in uniformly small space and time increments.

It is anticipated that OWRD staff will be involved in all phases of model development and implementation. While all cooperators will be involved in developing scenarios for testing with the model, OWRD will maintain technical expertise for operating the model and interpreting the results. Ultimately, the model will be transferred to OWRD's computer for use after the project.

Finally, using the information and data compiled in phases I and II, a long-term hydrologic monitoring plan will be designed for the basin. At the end of phase II, data collection for this study will be significantly reduced, however, it is important that an adequate monitoring network be maintained beyond this study to support future water resource assessments in the basin.