When performing automated parameter estimation, a set of head and flow observations are defined using points, arcs, and polygons in the Map module. When entering the point and flow observations, care should be taken when entering the calibration interval and confidence values. These values are used to determine the weights assigned to each observation in the inverse model. The weight is multiplied by the residual for the observation in the objective function. The weight that is sent to the inverse model input files by GMS is computed as 1/[(standard deviation)^2*Group Weight]. Note that GMS will automatically convert from an interval and a confidence to a standard deviation or you can directly enter the standard deviation.
Related Links:
Confidence Interval and Standard Deviation