Estimating transmissivity and storativity in a karst aquifer by direct and indirect methods

Abstract

The karst aquifer located in the Environmental Protection Area of Lagoa Santa, Minas Gerais, Brazil, exhibits the characteristic morphological features of an evolved karst environment, including large caves, sinkholes, and copious springs. Understanding the hydrogeological characteristics of karst aquifers is crucial for effective management of public resources and prevention of contamination, as these aquifers are highly vulnerable, making it essential to identify and mitigate potential risks. Given the ongoing economic and population growth in this region, the assessment of the hydrogeological parameters that control the dynamics of local flow becomes relevant for the proper evaluation of hydrogeological models and the management of water resources. Four classical pumping test analysis methods were compared to quantify the flow and storativity of the aquifer: Theis (1935), Neuman (1972), Moench (1984), and Agarwal (1980). In addition, indirect estimation methods based on the identification of capture zones and the analysis of recession curves of water courses were employed, since these approaches are cheaper and easier to apply in areas with low information. The statistical analysis of the results suggests that classical solutions can be applied to the karst aquifer to estimate hydrogeological parameters, apart from the Storage Coefficient obtained using the Neuman method. In general, the indirect estimation methods tend to produce values that are consistent with those obtained through direct methods, albeit with some reservations. The transmissivity values obtained from the pumping tests were approximately 3.0 × 10−4 m2/s, while the storage coefficient is estimated to be around 3.7 × 10−3. The indirect estimation methods yield transmissivity values of about 1.8 × 10−4 m2/s using the capture zone method, and storage coefficient values of 4.0 × 10−3 and 3.9 × 10−2 using recession curve analysis.