The computationally expensive variable density and salt transport numerical models hinder the implementation of simulation-optimization routines for coastal aquifer management. To reduce the computational cost, surrogate models have been utilized in pumping optimization of coastal aquifers. However, it has not been previously addressed whether surrogate modelling is effective given a limited number of numerical simulations with the seawater intrusion model. To that end, two surrogate-based optimization (SBO) frameworks are employed and compared against the direct optimization approach, under restricted computational budgets. The first, a surrogate-assisted algorithm, employs a strategy which aims at a fast local improvement of the surrogate model around optimal values. The other, balances global and local improvement of the surrogate model and is applied for the first time in coastal aquifer management. The performance of the algorithms is investigated for optimization problems of moderate and large dimensionalities. The statistical analysis indicates that for the specified computational budgets, the sample means of the SBO methods are statistically significantly better than those of the direct optimization. Additionally, the selection of cubic radial basis functions as surrogate models, enables the construction of very fast approximations for problems with up to 40 decision variables and 40 constraint functions.
15Variable-fidelity modelling has been utilized in several engineering optimization 16 studies to construct surrogate models. However, similar approaches have received 17 much less attention in coastal aquifer management problems. A variable-fidelity 18 optimization framework was developed utilizing a lower-fidelity and 19 computationally cheap model of seawater intrusion, based on the sharp interface 20 assumption, and a simple correction process. The variable-fidelity method was 21 compared to the direct optimization with the high-fidelity variable density and salt 22 transport model and to conventional surrogate-based optimization. The surrogate-23
Highlights 1) Distributed groundwater models were linked together with a river model via the OpenMI software platform. 2) Kriging metamodels were applied to facilitate analysis with the integrated models. 3) The overall computational savings were in the range of 70-90%. 4) Monte Carlo simulations demonstrate that metamodels were in good agreement with the responses of the integrated models. 5) Sensitivity Analysis using the metamodels accurately identified the important parameters.
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