An Innovative Approach to Determination of Double-Porosity Fractured Aquifers Hydraulic Parameters Using Artificial Neural Network

Accurate determination of hydraulic parameter values is the first step to the sustainable development of an aquifer. Since Theis (1935), type curve matching technique (TCMT) has been used to estimate the aquifer parameters from pumping test data. The TCMT is subjected to graphical error. To eliminate the error an Artificial Neural Network (ANN) is developed as an alternative to the conventional TCMT by modeling the Bourdet-Gringaten’s well function for the determination of the fractured double porosity aquifer parameters. The neural network model is developed in a six-step protocol based on multi-layer perceptron (MLP) networks architecture and is trained for the well function of double porosity aquifers by the back propagation method and the Levenberg-Marquardt optimization algorithm. By applying the principal component analysis on the training input data and through a trial-and-error procedure the optimum structure of the network is fixed with the topology of [3×6×3]. The replicative, predictive and structural validity of the developed network are evaluated with synthetic and real field data. The developed network provides an automatic and fast procedure for the double porosity aquifer parameter determination that eliminates graphical errors inherent in the conventional TCMT. The network receives pumping test data and provides the user with the aquifer parameter values.

Aquifer parameter estimation for the Zhagu subcatchment (Tibetan Plateau) based on geophysical methods

<p>The aquifers on the Tibetan Plateau (TP) constitute as origin for major river systems, which are supplying millions of people all over Asia. Increasing population and tourism activities leading to larger water consumption. Hence, water supply is getting increasingly important. The TP is a sensitive system and is noticeable reacting climate change. Past decades are marked with, increasing trends of precipitation, melting of glaciers and degradation of permafrost and have generally lead to rising water levels in lakes on the TP. To ensure future water supply, aquifer characterisation and future prognosis on groundwater behavior are therefore necessary. However, due to the remote character of the TP, knowledge according to hydrogeological parameter is scarce. The aim of this study is therefore to estimate a range for aquifer parameter based on geophysical methods. The Zhagu basin, situated in the Nam Co Lake basin (second largest lake on the TP), is used as a case study. This project is part of the International Research Training Group “Geoecosystems in transition on the Tibetan Plateau” (TransTiP), funded by the DFG.</p><p>During several field work campaign in July 2018, May 2019 and September 2019 disturbed sediment samples were taken and were analyzed for grain size distribution. Selected sediment layer in the laboratory were tested. Outcome of this analysis is the porosity for each selected sediment layer. Another measurement during field work has been conducted, namely electrical resistivity tomography measurements (ERT). To get better approximation of porosity and sediment characteristics, Archie’s Law is used as model to estimate those properties and later on to compare it to field and laboratory results. Two approaches are implemented (i) calculates the bulk resistivity based on known porosity from the laboratory and known conductivity of pore water measured during field work (ii) calculates the porosity with known conductivity of pore water and the bulk conductivity. For analysis saturated sediment layers were chosen.</p><p>The investigation shows that both approaches are largely applicable and leading to almost same results and trends of each sediment layer. The best percentage deviation of the modeled bulk resistivity results to the measurement in the field could be achieved by position D11 which is situated near the Nam Co Lake showing a deviation of around 7%. Inside the catchment the percentage deviation is largely increasing. However, the application of Archie’s Law in combination with field and laboratory measurements allows to construct a porosity ranges for future groundwater flow calibration. In addition, the results emphasising the zonation of the subsurface in (un)saturated zones due to the small amount of resistivity.</p><p>Sediment profiles, ERT measurements, observations, interpretation and conclusion including the comparison of simulated resistivity and simulated porosity to field resistivity and porosity based on laboratory analysis will be shown and discussed in the contribution.</p>

A hybrid optimization approach for parameter estimation of confined and leaky confined aquifers

The main objective of this study is to propose a linked simulation–optimization approach for solving aquifer parameter estimation problems from pumping test results. In the simulation part of the proposed approach, the drawdowns at given monitoring points and times are calculated by considering the Theis and Hantush approaches for confined and leaky confined aquifers, respectively. This simulation part is then integrated to a newly proposed hybrid optimization approach, namely DE–Solver, which integrates the differential evolution (DE) algorithm and generalized reduced gradient (GRG) method of the spreadsheet Solver add-in. The performance of the proposed approach is evaluated by considering two pumping test data for confined and leaky confined aquifers. Identified results indicate that the proposed approach provides better results than those obtained by using different approaches in the literature.

IDENTIFICATION AQUIFER PARAMETERS THROUGH SINGLE WELL PUMPING TEST SERIES AT PT. KALTIM KARIANGAU TERMINAL, BALIKPAPAN, EAST KALIMANTAN

Aquifer Parameters are very important in groundwater and well management. The objective of this research is to determine aquifer parameter in order to be used in determining suitable production rate of well. Research was carried out in PT. Kaltim Kariangau Terminal, which is administratively, located in Balikpapan City, East Kalimantan, Indonesia. PT. Kaltim Kariangau Terminal has developed four wells with distance of each of well is between 50 and 300 meters, but it is a pity because just one well was completed by pumping test without observation well. Result of constant pumping test analyzing through Cooper – Jacob method has shown that value of Transmissivity (T) of aquifer is 319.0718283 m2/day, and it is known from geophysical logging and well construction design that the thickness of aquifer is 48 m, so hydraulic conductivity (K) of aquifer is 6.6473 m/day. Coefficient of aquifer loss is 0.0013 and coefficient of well loss is 0.0000008. Factors development of well could be classified as very effective with the well condition is properly designed and developed.

Aquifer parameter and zonation structure estimation using meshless local Petrov–Galerkin method and particle swarm optimization

The simulation-optimization (SO) modeling approach can be effectively used for aquifer parameter estimation. In this study, a numerical approach based on meshless local Petrov–Galerkin (MLPG) method is used for groundwater flow simulation and coupled with particle swarm optimization model for optimization. The study deals with the identification of the most suitable model structure for a hypothetical heterogeneous confined aquifer from a number of alternate models using zonation method of parameter estimation. A range of alternate models starting from homogeneous to more complex model structures are considered for the zonation. Inverse modeling of different model structures is carried out based on weighted least square performance criterion. The suitable models are selected and reliability analysis ascertained by computing three parameters of composite scaled sensitivity, coefficient of variation, and confidence interval, and the best model is selected. Sensitivity of estimated parameters is investigated by considering different sets of head data involving possible measurement errors. The solutions are compared with another inverse model using the MLPG and Levenberg–Marquardt algorithm. Based on the results, it is found that the proposed methodology can be utilized in the estimation of different unknown parameters in a regional groundwater system.