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Section Descri tion <br />1.0 Model Calibration Overview <br />2.0 Calibration Process <br />3.0 Selection of Calibration Targets <br />3.1 Calibration Time Periods <br />3.2 Groundwater Level Tar ets <br />3.3 Streamflow Targets <br />3.4 Stream Gain/Loss Targets <br />3.5 Other Targets <br />3.6 Development of Target Database <br />4.0 Selection of Calibration Criteria <br />4.1 Target Criteria <br />4.2 Ob ~ective Ftunction <br />4.3 WeialntinQ Factors <br />5.0 Summar and Conclusions <br />6.0 Recommendations <br />1.0 Model Calibration Overview <br />Model calibration is an iterative process where selected sensitive model parameters are adjusted <br />within predetermined ranges until the simulation results match observed data to an acceptable <br />degree (Anderson & Woessner 1992). A calibrated model simulates historical conditions within <br />an acceptable range of tuncertainty, thus representing the effects of past inflows and outflows. <br />Calibration is by its nature non-unique, i.e. many comb>lnations of model parameters may <br />results in a model that fits the field data. If sufficient data exist, calibrated models maybe used <br />to simulate other historical time periods un order to verify that the model is able to adequately <br />represent fine system response for a period that was not used for the calibration. This process is <br />termed model validation. Calibrated models that adequately simulate the validation period are <br />considered to be even more robust lln their ability to reproduce the processes that have occurred <br />historically iIn the area modeled. Models are most commonly used for evaluating future <br />conditions. A calibrated model maybe used to estimate future and past conditions with <br />confidence if the stresses imposed on the model are comparable to those imposed during the <br />calibration and validation period. <br />The field data used for comparison against simulation results are termed calibration targets in <br />this TM. Calibration targets are defined un terms of the type of measurement, its location and <br />date of measurement, and measurement value. The SPDSS alluvial groundwater flow model <br />will be calibrated using the following: <br />• Water levels observed at wells <br />• Stream Flow, Diversions and Gain-Loss <br />• Groundwater Budget, including groundwater evapotranspiration (ET) <br />• Other Non-Numeric Data (e.g. dry cells, flooded cells) <br />The calibration criteria define fine acceptable differences between tlne measured and simulated <br />values for each calibration target. The relative importance of the calibration targets will be <br />P~ SPDSS T~8 2 Final TM 10-08-0t~.doc 2 <br />