Estimating Anisotropic Aquifer Parameter by Artificial Neural Networks
Date Issued
2010
Date
2010
Author(s)
Lin, Hsien-Tsung
Abstract
Obtaining reasonable hydrological parameters is a key challenge in groundwater modeling. The analysis of the temporal evolution of pump-induced drawdown is a common approach to estimate the effective transmissivity and storage coefficients in the heterogeneous aquifer. In this study, we compared modified ANN model, modified PCA-ANN model cooperated with Papadopoulos solution, and applied them to the estimation of effective aquifer parameters with better precision. Results show that modified ANN model and modified PCA-ANN model can efficiently obtain the most representative (or effective) aquifer parameters wich are close to geometric means. In-situ time-drawdown from Shi-Chou station on the Choushui River alluvial fan, Taiwan, is further adopted to test the applicability and reliability of the proposed methods, as well as provide a basis for comparison with the Straight-line method (SLM) and the Type-curve method (TCM). Results show that both of the modified methods give better estimation than SLM and TCM in terms of RRMSE. Besides, model uncertainties could be easily induced with the application of the TCM or SLM for not using a systematic approach to optimize the parameters of well functions. In order to diminish the uncertainties, relationships between well function and simulated drawdown are established by modified ANN and modified PCA-ANN to automatically optimize those parameters. Aforementioned methods are further applied to optimize the location of pumping wells in a local-scaled numerical model, MODFLOW-96. The optimal zone for exploiting groundwater could be initially decided by modeling the groundwater flow distribution, and validated by Hill method. Pumping tests are carried out in the optimal zone to generate time-drawdown data for modified ANN method to estimate the value and direction of transmissivities. Optimization of the location of the pumping wells is conducted in the direction with major transmissivities in order to increase pumping efficiency. This study expects to develop a mechanism of parameters optimization for groundwater management.
Subjects
modified ANN model
modified PCA-ANN
pumping test
Hill method
effective hydrological parameters
Type
thesis
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