Depleção fluvial associada ao bombeamento de poços entre rios paralelos: solução analítica e aplicação no sistema aquífero urucuia.

Abstract

The pumping of wells in aquifers can reduce the base flows of adjacent rivers, a phenomenon known as streamflow depletion. The main factors that control depletion are the hydraulic diffusivity of the aquifer and the distance between the well and the river. This study presents an analytical model for the assessment of river depletion resulting from well pumping in an unconfined aquifer hydraulically connected to parallel rivers. For this, the Glover and Balmer (1954) solution was used in conjunction with the image method. Four types of input signals were considered to represent pumping: step, impulse, ramp, and sinusoidal. The results showed that the aquifer's response time is the most influential variable in the assessment of depletion and has the ability to dampen its amplitude in cases of sinusoidal pumping, leading to reduced seasonal variation of this component. To mitigate this effect, a 90% attenuation was established, allowing depletion to reach the river with a significant lag relative to pumping. This lag can be adjusted to coincide with the flood season. The methodology was applied to an area in western Bahia, a region characterized by intense agricultural activity and the use of groundwater through the Urucuia Aquifer System (UAS). The analysis of the current INEMA regulations concerning well drilling in the UAS suggests that, in addition to well spacing and pumped flow rate, the hydrological conditions of the river and the definition of the maximum allowable flow that can be withdrawn from the base flow are essential for the efficient management of the region’s water resources. The model proved satisfactory for the intended purpose, offering a relevant contribution to water resource management in western Bahia and other regions with similar characteristics.