Assessing and modelling hard rock aquifer recharge based on complementary metho...

• Author(s): Paralta, Eduardo ; Oliveira, M.
• Date: 2005
• Persistent ID: http://hdl.handle.net/10400.9/474
• Origin: Repositório do LNEG
• Subject(s): Aquíferos; Balanço hídrico; Piezometria; Sistema Aquífero dos Gabros de Beja (Portugal)
• Document Type: Other
• Language: English

Description

The "Gabbros of Beja" Aquifer System extends for approximately 350 km2 and is one of the most important reservoirs of groundwater in the context of hard rocks aquifers of South Portugal (Alentejo Region). The average annual rainfall in the area is about 500 to 600 mm. Groundwater resources are used for public supply over 3 councils and irrigation. During drought cycles consumption increases and pumping rates decrease with correspondent management difficulties and conflicts between private and public interests. The correct assessment of annual recharge is of utmost importance for regional planning and management of groundwater resources under semiarid climate conditions. Moreover the aquifer was recently declared vulnerable to nitrate diffuse pollution of agriculture origin and recharge mechanisms are the major natural factor controlling contamination of shallow waters in the "Gabbros of Beja" aquifer. Recharge assessment and modelling was performed on the base of several complementary methodologies: 1) water balance based on historical data of annual pumping rates; 2) chloride mass balance between groundwater and rainfall compositions; 3) daily sequential water balance modelling of hydrological parameters using Balseq model, and 4) soil and vadose zone daily water balance modelling using lumped model Earth and piezometric water level curves for calibration. Results of direct and indirect methods show that annual average recharge should be between 10% and 20% or even more of annual rainfall.