Determining the influence of discharge observations on ground-water model calibration
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A model is a mathematical representation of a complex phenomenon and can be used to gather quantitative information about that phenomenon (McGarity 1985). Ground-water models are calibrated to hydrologic observations in order to derive model parameters (such as hydraulic conductivity) that cannot be independently measured. In this study, the relative influence of head observations and discharge observations on model calibration is compared. It is hypothesized that an increase in the number of flux observations along a stream will improve confidence in parameter estimation. This hypothesis was tested in the Ischua Creek Basin, where head observations have been previously determined and discharge measurements have previously been measured at many points along a stream. Discharge had been measured using temperature as an indicator of ground-water discharge. The influence of this unusually large number of discharge observations on model calibration will be tested by returning parameter optimization statistics to a spatial (GIS) database. This will be done by using newly created tools with Visual Basic for Applications (VBA). These tools will allow the calibration statistics to be spatially displayed in the GIS database. Multiple model runs will be compared statistically to test the hypothesis. After running multiple simulations, which included the known head and discharge observations as well as generated synthetic head and discharge observations, it was determined that discharge observations did have a large influence in the model calibration. Also, with the addition of more flux observations, the Observation Residual maps created showed a clear decrease in the magnitude of the residuals. From these results, the hypothesis was proven and it was concluded that an increase in flux observations along a stream did improve confidence in parameter estimation.