Evaluation of confidence intervals for a steady-state leaky aquifer model

✍ Scribed by S. Christensen; R.L. Cooley

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 752 KB
• Volume: 22
• Category: Article
• ISSN: 0309-1708
• DOI: 10.1016/s0309-1708(98)00055-4

✦ Synopsis

The fact that dependent variables of groundwater models are generally nonlinear functions of model parameters is shown to be a potentially signi®cant factor in calculating accurate con®dence intervals for both model parameters and functions of the parameters, such as the values of dependent variables calculated by the model. The Lagrangian method of Vecchia and Cooley [Vecchia, A.V. & Cooley, R.L., Water Resources Research, 1987, 23(7), 1237±1250] was used to calculate nonlinear Sche e-type con®dence intervals for the parameters and the simulated heads of a steady-state groundwater ¯ow model covering 450 km 2 of a leaky aquifer. The nonlinear con®dence intervals are compared to corresponding linear intervals. As suggested by the signi®cant nonlinearity of the regression model, linear con®dence intervals are often not accurate. The commonly made assumption that widths of linear con®dence intervals always underestimate the actual (nonlinear) widths was not correct. Results show that nonlinear eects can cause the nonlinear intervals to be asymmetric and either larger or smaller than the linear approximations. Prior information on transmissivities helps reduce the size of the con®dence intervals, with the most notable eects occurring for the parameters on which there is prior information and for head values in parameter zones for which there is prior information on the parameters.