You have entered the website of the Water and Environmental Research Institute of the Western Pacific (WERI) at the University of Guam. We are currently six faculty and five staff and our mission is to seek solutions through research, teaching and outreach programs, to issues and problems associated with the location, production, distribution and management of freshwater resources in Guam, the CNMI and the FSM.
This study deals with the application of a two-dimensional, salt-water intrusion model (SWIGS2D) to the lens in northern Guam. The model uses finite element theory and the Galerkin, weighted-residual approach as its basis. A description of the model and program is provided in WERI Technical Report No. 26. The northern Guam lens was discretized into 299 linear, triangular elements and 189 nodes. The model was calibrated using 1978 hydrologic data. Elevations of the impervious basement of the aquifer were obtained from a seismic-refraction study. Hydrologic data necessary as input to the program consisted of recharge to the aquifer, water-production figures of all wells and elevations of the ocean. The recharge was obtained from an analysis of rainfall and streamflow in southern Guam. Results from the model were compared with the measured water levels in six observation wells. Calibration consisted of varying the permeability and porosity in the aquifer until acceptable agreement was obtained between measured and predicted water levels in all six wells. The calibrated values of permeability and porosity were then used to verify the model using 1979 data. The agreement between measured and predicted water levels in the six wells was good, the errors being slightly lower than those obtained in the calibration run.
A calibrated model can be used to make an infinite variety of management and planning studies. In this study, a few applications are provided that demonstrate the behavior and characteristics of the aquifer. Steady-state runs were made to compare the four conditions of (1) no pumping, (2) 1978 pumping levels, (3) twice 1978 pumping levels, and (4) five times 1978 pumping levels. The differences in the conditions are shown in plan [view] and in cross-sections of the aquifer. The effect of zero recharge to the aquifer is demonstrated for conditions existing during 1978. An additional run shows how long the aquifer takes to reach steady-state when the pumping rate is increased from the 1978 pumping level to twice that value. The program can be used for numerous other studies for management and planning purposes.
