scholarly journals Optimal estimation of unconfined aquifer parameters in uncertain environment based on fuzzy transformation method

2018 ◽  
Vol 19 (2) ◽  
pp. 444-450
Author(s):  
Atefeh Delnaz ◽  
Gholamreza Rakhshandehroo ◽  
Mohammad Reza Nikoo
Keyword(s):  
Test Data ◽  
Statistical Error ◽  
Optimal Estimation ◽  
Pumping Test ◽  
Transformation Method ◽  
Unconfined Aquifer ◽  
Uncertain Variable ◽  
Specific Yield ◽  
Pumping Rate ◽  
Fuzzy Transformation

Abstract In this paper, a fuzzy simulation–optimization model coupled with the genetic algorithm based on Boulton's equation is presented to estimate transmissibility (T), storage coefficient (S), specific yield (Sy) and leakage factor (Dt) of an unconfined aquifer. This model is capable of minimizing the deviation between observed and calculated drawdowns of pumping test data. To assess the applicability of the model, its results are compared with the graphically obtained solutions from Boulton's equation. To this end, real pumping test data obtained from an unconfined aquifer in Dayton, Ohio, are considered as the case problem to evaluate the efficacy of the model. In the fuzzy approach, pumping rate is considered as an uncertain variable. For evaluation of the model, several statistical error indices are utilized. Results show better matches for the model as evidenced by much smaller errors. As an example, mean absolute relative error for the proposed model and graphical Boulton's solution is 2.52% and 4.98%, respectively. It is concluded that the model is accurate and may replace the graphical Boulton's solution. T and Sy were found to be more sensitive to uncertainty in the pumping rate measurement, when compared with S and r/Dt.

Unusual drawdown curves for a pumping test in an unconfined aquifer at Lachenaie, Quebec: field data and numerical modeling

2005 ◽  
Vol 42 (4) ◽  
pp. 1133-1144 ◽  
Author(s):  
Robert P Chapuis ◽  
Djaouida Chenaf ◽  
Nelson Acevedo ◽  
Denis Marcotte ◽  
Michel Chouteau
Keyword(s):  
Numerical Modeling ◽  
Numerical Models ◽  
Field Tests ◽  
Pumping Test ◽  
Unconfined Aquifer ◽  
Specific Yield ◽  
Characteristic Functions ◽  
Constant Flow Rate ◽  
Monitoring Wells ◽  
Highly Nonlinear

An unconfined aquifer was instrumented with monitoring wells over a surface area of about 100 m × 100 m. The aquifer is a sand deposit overlying a thick nonfissured layer of Champlain Sea clay. The paper presents the results of a pumping test at a constant flow rate. None of the curves of drawdown versus time presented the S shape of current theories; however, all drawdowns indicated that the aquifer was homogeneous. The values for the specific yield were too low and varied with distance and time instead of being constant. The theories for steady and unsteady states provided different values for the saturated hydraulic conductivity. To understand the field behavior that differs from theoretical predictions, the pumping test conditions were modeled numerically using a finite element method. The transmissivity was derived from the Dupuit equation, and different curves for capillary retention and unsaturated permeability were examined. The numerical drawdowns agree with the experimental drawdowns. Several numerical models were investigated. All of them solved the inverse problem correctly for steady-state conditions and fairly well for transient conditions with highly nonlinear characteristic functions. The best solution to the transient problem was obtained using trial and error, by considering how the drawdown curves might be modified due to anisotropy and stratification. According to these field tests and the numerical analysis, the S shape is not the rule, and a different shape can be perfectly normal due to the complexity of unsaturated flow.Key words: pumping, unconfined aquifer, permeability, drawdown, numerical modeling.

Using groundwater levels and Specific Yield to Estimate the Recharge, South of Erbil, Kurdistan Region, Iraq

2018 ◽  
Vol 7 (4) ◽  
pp. 191
Author(s):  
Sherwan Sh. Qurtas
Keyword(s):  
Unconfined Aquifer ◽  
Middle Part ◽  
Water Levels ◽  
Specific Yield ◽  
Aquifer System ◽  
Groundwater Levels ◽  
Monitoring Wells ◽  
Water Table Fluctuation Method ◽  
Recharge Estimation ◽  
Fluctuation Method

Recharge estimation accurately is crucial to proper groundwater resource management, for the groundwater is dynamic and replenished natural resource. Usually recharge estimation depends on the; the water balance, water levels, and precipitation. This paper is studying the south-middle part of Erbil basin, with the majority of Quaternary sediments, the unconfined aquifer system is dominant, and the unsaturated zone is ranging from 15 to 50 meters, which groundwater levels response is moderate. The purpose of this study is quantification the natural recharge from precipitation. The water table fluctuation method is applied; using groundwater levels data of selected monitoring wells, neighboring meteorological station of the wells, and the specific yield of the aquifers. This method is widely used for its simplicity, scientific, realistic, and direct measurement. The accuracy depends on the how much the determination of specific yield is accurate, accuracy of the data, and the extrapolations of recession of groundwater levels curves of no rain periods. The normal annual precipitation there is 420 mm, the average recharge is 89 mm, and the average specific yield is around 0.03. The data of one water year of 2009 and 2010 has taken for some technical and accuracy reasons.

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