Comparative analysis of recharge estimation methods for a microbasin in Reserva Florestal Adolpho Ducke, Manaus - AM

Abstract

Groundwater recharge is a key element of the hydrological cycle and for the integrated management of water resources. This study aimed to quantify and compare the direct recharge rates of a groundwater aquifer located in a primary forest region adjacent to the city of Manaus using the water budget (WB), water table fluctuation (WTF) and darcyan methods (DM). Precipitation and atmospheric temperature data from 2013 to 2015 were obtained from the weather station located at the Reserva Florestal Adolpho Ducke (RFAD). Groundwater level measurements and slug-tests to determine hydraulic conductivity were executed in seven piezometers installed in a small catchment of the RFAD. Specific yield (Sy) was measured in undisturbed soil samples. WB results show a recharge rate of 47% (1,583 mm) in 2013, 46% (1,277 mm) in 2014, and 20% (680 mm) in 2015. Total precipitation in 2014 was 18% lower than in 2013, and 21% lower in 2015 when compared to 2014 data due to the El Niño phenomenon, sharply reducing groundwater recharge only in the last year. Groundwater level was measured between February and July 2013 for the DM, generating a recharge rate estimate of 28% (624 mm). Applying the WTF method, a recharge rate of 52% (2,229 mm) was estimated for the period from February 2014 to August 2015. The results indicate greater consistency between WB and WTF. The recharge rates here are higher than those obtained in areas with similar hydrogeological settings in other regions of Brazil. © 2021 Universidade de Sao Paulo. All rights reserved.