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• the location of groundwater ET, <br />• fl1e number and distribution of flooded and dry model cells, <br />• the spatial distribution of residuals from the objective function. <br />Each of these targets are described in more detail in Section 3. <br />Steady-state and transient model simulations >IZ a series that result in the best fit (i.e. lowest <br />objective function value) will be evaluated against other non-numeric calibration criteria not <br />included in t11e objective function. T11e set of input parameters that result in simulations t11at <br />meet t11e calibration criteria will be used as inputs for the model validation dine period, and t11e <br />results will be evaluated. If the criteria are not met for the validation period (January 1950 to <br />October 2006) then the model inputs and model objective function will be re-evaluated and the <br />model simulation process will begin again (Figure 2-2). The model will be considered calibrated <br />when the calibration criteria are met over the validation period. <br />The last step in the modeling process is a formal parameter sensitivity analysis that describes <br />the calibrated models sensitive to various parameters. During this formal sensitivity analysis, <br />calibrated values for hydraulic conductivity, streambed hydraulic conductivity, recharge, and <br />boundary conditions will be systematically varied within acceptable ranges. The results of a <br />sensitivity analysis allow one to evaluate the effect of individual parameters on the calibrated <br />model. This analysis will help identify the parameters that could benefit from additional data <br />collection in the future, which would help reduce model uncertainty. <br />3.0 Selection of Calibration Targets <br />This section describes the general methodology and steps used to identify and select the field <br />data that will be used for calibrating and validating the Phase 4 alluvial groundwater model. <br />The selected tinge periods for t11e steady-state, transient and validation periods are presented >11 <br />Section 3.1. The groundwater level measurement (head) targets are defined and discussed in <br />Section 3.2. Streamflow targets are discussed in Section 3.3. Stream gain/loss targets used for <br />model calibration are discussed in Section 3.4. Targets that will be used in a manual calibration <br />step, including water mass balance, groundwater budget, diversions and locations of flooded <br />and dry cells, are discussed >11 Section 3.5. The methods used to develop the calibration target <br />database are discussed in Section 3.6. <br />3.1 Calibration Time Periods <br />In order to increase the efficiency of the calibration process, tinge periods shorter than the full <br />study period of 1950 to 2006 were selected for the initial calibration. For the steady-state <br />calibration period (1991-1994), a period with relatively steady or consistent conditions was <br />selected. For the transient calibration period (1999-2005), a period contaululg years with large <br />variation in climatic and streamflow conditions was selected. This section describes how these <br />calibration tune periods were selected. <br />Streamflow, precipitation and water level data were used in this analysis. Pumping data were <br />not readily available, so the pattern of alluvial well development based on decrees, was used. <br />P~ SPDSS T~8 2 Final TM 10-08-0t~.doc 5 <br />