An assessment of groundwater recharge from agricultural land in Malta

Abstract

A comprehensive understanding of groundwater recharge processes is essential for ensuring the sustainability of the scarce freshwater resources in Malta, where groundwater is the only source of naturally replenishing freshwater. Infiltration plays a pivotal role in controlling the amount of water that enters the soil and contributes to groundwater recharge. The variability in soil properties significantly affects infiltration rates, underscoring the need for field-specific evaluations of hydraulic conductivity. This study aims to assess groundwater recharge from Malta’s agricultural lands, which provide a significant proportion of the permeable area, through the evaluation of hydraulic conductivity. Two field measurement techniques—the double-ring infiltrometer (DRI) and the mini disk infiltrometer (MDI)—were compared and used to determine saturated hydraulic conductivity (Ks). The study found the Ks to be high for the determined soil texture, with values ranging from 0.32 to 1.16 × 10-2cm/s using the DRI. A significant discrepancy was observed between the Ks results obtained from the industry-standard DRI method and the more portable MDI method, with the MDI values being higher by a factor of difference ranging from 3.03 to 7.19. In addition, QGIS-SWAT modeling revealed that agricultural lands contribute to a minor proportion of Malta’s total direct groundwater recharge due to the controlling factors of soil depth and the hydraulic conductivity of the underlying bedrock. Despite this, these lands significantly contribute to recharge indirectly through the generation of surface and underground runoff, which flows downslope into Malta’s valleys. This finding suggests that management techniques aimed at retaining runoff in valleys could enhance groundwater recharge.