Analysis of the long-term effects of groundwater extraction on the water balance in part of the Urucuia Aquifer System in Bahia - Brazil

Abstract

In agricultural regions where there is insufficient rainwater for cultivation, understanding the dynamics of surface water and groundwater is critical to assess the impact of increased well pumping on the water balance. The western region of the state of Bahia-Brazil, the largest area of agribusiness in the state, has experienced progressive occupation since the 1980s, resulting in pressure on water resources - mainly after the introduction of irrigation - and conflicts among water users. This study analyzed the effects of groundwater extraction by wells in a portion of the Urucuia Aquifer System. The methodology used was the simulation of groundwater flow in steady-state for three scenarios: i) without withdrawal of water by pumping wells; (ii) with current withdrawal rates; and (iii) with 60% additional extraction. After defining well production rates from field surveys (4.6 m3 s-1) and modeling of the aquifer base geometry (maximum thickness of 535 m), the steady-state models with and without pumping show that, in the long term, groundwater storage decreases by 2 km3 (0.8 m on average in the aquifer) without interference in the regional flow direction. The mass balance shows that the base flow of the main rivers is reduced by approximately 6% after current groundwater extraction and an additional 2.5% after additional extraction. The results point to a greater impact on surface water caused by a reduction in groundwater storage and related river base flow. This indicates the importance of maintaining and expanding the groundwater-level monitoring network.

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“…The municipalities with the smallest WSF (between 0 and 165 m 3 -eq kg -1 ) were inserted in the west, south coast, and extreme south of Bahia. However, according to Oliveira et al (2019), the west region of Bahia is the largest agribusiness area in the state and has faced pressure on water resources, mainly due to irrigation, causing conflicts between water users.…”

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“…The combined effects on the surrounding environment are not considered, even though the combined and simultaneous pumping by the two wells may cause serious groundwater depletion or deterioration of groundwater quality, thereby further complicating groundwater contamination. Oliveira et al (2019) have reported that unequal distribution of the wells and the extraction water from multiple wells in some points can contribute to overexploitation of groundwater and deteriorated groundwater quality. In many cases, well owners are trying to resolve contamination problems by simply closing the wells and not using contaminated groundwater (Baek & Lee, 2011).…”