Modeling the water balance of transboundary aquifers for assessing groundwater flow along the Latvia-Estonia national border

Coordinating transboundary aquifer management is becoming increasingly important worldwide to minimize adverse transboundary impacts. Moreover, the global trend of groundwater consumption is increasing, and groundwater abstraction exceeds sustainable limits in many parts of the world. To avoid future international disputes and maximize the rational and equitable use of common transboundary aquifers, it is imperative to accurately and comprehensively assess groundwater resources' development potential in these aquifers.

As part of this study, a transient hydrogeological model using MODFLOW-NWT was developed to assess the changes in groundwater balance and groundwater flow in the transboundary area between Estonia and Latvia in northeast Europe. The model consists of eleven layers that discretize four main aquifers (Quaternary aquifer, Upper-Devonian aquifer, Upper-Middle-Devonian aquifer, and Lower-Middle-Devonian-Silurian aquifer) and represents an area of 45 000 km². The cell size of the model varies from 0.25 to 1.00 km. The model was used to simulate three scenarios: (1) the base case scenario, which involved no abstraction, (2) the current abstraction, and (3) the maximum abstraction allowed. A detailed water balance for eight transboundary groundwater bodies for all three scenarios was calculated to assess water balance changes and groundwater flow along the national border.

Model results indicate that the groundwater balance between groundwater bodies remained the same in Simulations 1 (base case scenario) and 2 (current water extraction), which indicates that the existing water extraction in the territory does not significantly affect the transboundary groundwater flow. Some minor changes were observed in Simulation 3 (maximum water abstraction rates), mostly in the Upper-Devonian groundwater bodies. However, significant changes in cross-border groundwater flow patterns were not expected even with the maximum possible water abstraction.

The study has been founded by Iceland, Liechtenstein and Norway through the EEA and Norway Grants Fund for Regional Cooperation project No.2018-1-0137 “EU-WATERRES: EU-integrated management system of cross-border groundwater resources and anthropogenic hazards”.