Better sensitivity analyses

The sensitivities calculated by programs, such as MODFLOWP and UCODE, can be used as described in the Methods and Guidelines Report and textbook by Hill and Tiedeman (2007) to show clearly such things as the amount of information provided for the estimation of defined parameters by available data, and the likely importance of each parameter to predictions of interest. For example, in figure 1 below, composite scaled sensitivities show that the available data provide the most information about parameters T2, T3, and RCH1; associated parameter correlation coefficients also would need to be considered in an actual application, but are not shown here. In figure 2 below, one-percent scaled sensitivites are used to show that the prediction of concern, in this case the directional components of advective travel, are all influenced most by parameters T3 and T4. Thus, for this illustrative example, the estimation of T4 would be of concern because the available information provide little information about T4, while it is important to the predictions of interest. A next step would be to use similar methods to determine whether additional quantities could be measured to provide additional information about parameter T4.

Figure 1: Composite scaled sensitivities. Black bars indicate parameters estimated by regression; gray bars indicate parameters that were not estimated by regression. The values shown are for illustrative purposes only and are not associated with an actual synthetic or field problem.

Figure 2A
Figure 2B
Figure 2C

Figure 2: One-percent scaled sensitivities for the directional components of advective travel, derived using the ADV program. The bars show the range and average of values calculated for particles started in adjacent cells. Large absolute values are assoiciated with parameters that are important to the calculation of advective travel in the noted direction.

Methods and Guidelines Report
ADV program

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URL:www/projects/GW_ModUncert/mchill/Ideas/bettersenitivity/index.html
Project Contact Information:Mary C. Hill
Page Contact Information:Charmaine Gunther
Page Last Modified: September 12, 2011