14 / 2023-12-16 05:04:25

Calibration and Validation of Models for the Water Yield of San Diego Confined Aquifer, Venezuela

calibration,validation,models,water yield,confined aquifer

This article deals with calibration and validation of models for water yield of San Diego confined aquifer, Venezuela. Novelty consists in converting into coefficients those parameters associated with the well function proposed by Theis for non-stationary flow to a well in a confined aquifer. Based on the analysis of 28 lithological profiles provided by Ecosocialism Ministry, clay and fine to coarse sand strata were found at depths that varied between 43 and 96 m below the ground surface, which confirms the condition of a confined aquifer. Characterization of flow variables towards wells in confined aquifer of San Diego municipality was held by 21 undergraduate theses at University of Carabobo developed in period 2015 to  2019. From them, 20 pumping tests for variable flow were carried out measuring flow rate and water level in the wells. In undergraduate theses of Center for Hydrological and Environmental of the University of Carabobo (CIHAM-UC), a double-wire electrical tape graduated in meters was used, PLM model, Seba Hydrometrie. The properties associated to transmissivity (T) and storage coefficient (S) of the aquifer were determined by pumping a variable flow rate (Q) and measuring drawdown for various time intervals. Based on values of geophysical properties obtained in 28 lithological profiles from pumping wells of San Diego aquifer, the saturated thickness of the aquifer varied between 5 and 55 m, with 15 m being the most frequent value of occurrence (40%). Permeability in aquifer strata varied from 50 to 1,200 m/d, with the interval with the highest frequency of 65%. Highest Q values were measured in pumping wells located in areas of industrial use (15.6 L/s), recreational (23.9 L/s) and educational (19.7 L/s). The T and S parameters resulted in the highest frequency of occurrence (85%), corresponding to transmissivity values between 0 and 77 m²/d. Regarding the values of storage coefficient, values associated with high frequency (70%) were found in the order of 0.00001. Modification of Theis model for a confined aquifer was calibrated and validated, finding satisfactory fits for prediction of S and T parameters. Proposed models obtained determination coefficient in a magnitude between 75 and 85%, which indicated that the relationships of ho –h f(Q,T) and T f(S, r ² /t) were adequately described by the curvature of proposed functions. Validation stage demonstrated that improvement of models can be achieved by increasing the variable flow pumping tests carried out in San Diego aquifer.