Groundwater modeling, assessment, and management strategies of the shallow aquifer of Quiaoit River Watershed, Ilocos Norte, Philippines

A groundwater modeling and assessment study was conducted in the shallow aquifer of the Quiaoit River Watershed in Ilocos Norte, Philippines. This research determined the water balance in the watershed using the Soil Water Assessment Tool (SWAT) Model and developed a groundwater flow model for the area using Visual MODFLOW Flex (version 8.0). The groundwater flow model was calibrated to match the observed groundwater levels (GWL) and used to predict GWL for the year 2050 (2036- 2065). The PAGASA climate projections under the RCP 8.5 scenario, representing the worst-case climate scenario with a high greenhouse gas emission pathway, were utilized. Additionally, the study developed a groundwater salinity distribution and a groundwater management plan (GMP) for the area. The groundwater modeling results fairly matched the observed groundwater patterns for 2012 and 2013. Future predictions indicate an overall increasing trend in GWL over the simulation period, with increases during wet (non-irrigated) seasons and decreases during dry (irrigated) seasons for the upper bound scenario. Despite these fluctuations, the recharge rate exceeds the decline rate, leading to an average increased amount of 0.21 m in GWL by 2050. An analysis of groundwater supply and demand on an annual basis shows that the supply is sufficient to meet both current and future demands. However, monthly projections reveal a water deficit during the dry season and a surplus during the wet season. In terms of groundwater quality, the Total Dissolved Solids (TDS), turbidity, and electrical conductivity (EC) levels indicate that the groundwater is generally unsuitable for drinking but slightly to moderately suitable for irrigation. Proper management of the groundwater resources in the study area involves both direct and indirect actions. Direct actions, such as controlling abstraction, directly affect the availability and quality of the groundwater supply. Indirect actions have a limited impact on groundwater quantity and quality. The study also identified suggested locations for future groundwater level and quality monitoring.