Characterisation of the aquifer and river-aquifer interaction in an agricultural area of the lower Natuba River sub-basin – Pernambuco, Brazil

Abstract

Aquifers play a fundamental role in the hydrological cycle and in the maintenance of surface water sources. However, excessive use for agricultural irrigation can reduce their potentiometric levels. This study aimed to characterize the unconfined aquifer of an agricultural region in Vitória de Santo Antão-PE and its interaction with the local river, through monitoring between June/2023 and May/2024. Eight 4 m deep piezometers were installed and the following were performed: (a) slug tests to estimate hydraulic conductivity and effective porosity; (b) weekly measurements of static levels; (c) estimation of aquifer recharge; and (d) evaluation of the vertical hydraulic conductivity of the riverbed. The average hydraulic conductivity was 8.69 x 10⁻⁶ m/s, ranging from 10⁻⁵ to 10⁻⁸ m/s, reflecting the heterogeneous granulometry of the area, with an average drainable porosity of 13.62%. The variations in hydraulic loads indicated good recovery of levels due to rainfall. The estimated average recharge was 27.10%. Infiltration into the riverbed was 3.72 x 10⁻⁶ m/s in winter and 1.74 x 10⁻⁶ m/s in summer. The predominant flow was from the aquifer to the river, evidencing that excessive pumping can make the river effluent due to the decrease in hydraulic load.