Shallow groundwater and river baseflow: Interconnection evidences and integrated water management strategies. Case study in the upper Descoberto watershed, Federal District, Brazil

Aquifer discharge in the form of baseflow is intimate related to river replenishment. In this manner, it is reasonable that water management practices consider an integrated approach including surface and groundwater. Effective regulatory measures, however, require the understanding of the mechanisms and the degree of such interconnection. In the Federal District, capital of Brazil, research focused on this theme are scarce, despite the relevance addressed by some authors. In the present study, shallow groundwater of Upper Descoberto Watershed was monitored for four years (2019-2023). The area responds to 60% of local population public water supply and has been facing land use conflicts and water crisis. Data were collected with 2-h resolution and compared to fluviometric stations discharge and water height records. Graphical analyses demonstrate that river baseflow is highly dependent on shallow aquifer discharge. The decrease of the phreatic aquifer water level results, in a short period, in streams flow reduction. This result is contrasting to the former agreement that considered the connection would take more time to be established. Statistical correlation coefficients are as high as 0.920 for the entire monitoring range and 0.998 for the dry season. The results evidence that soils have important reservoir and regulatory functions, even though they might not be relevant for high water demand activities. In this way, water grant process should account for correlated components, such as territory planning, estimation of total extraction by sensitive areas and properly characterization of insignificant uses, alternative and independent water sources evaluation, and definition of environmental constraints. The mitigation practices of hydric problems must include the implementation of artificial recharge devices, use of sustainable farming methods and control of rainwater overland flow. It is desirable the maintenance and enlargement of the current monitoring net so that former patterns that culminated in water crisis can be early identified and mitigated.