Integration of hydrologic and groundwater models: Is it profitable?

TETIS is a distributed hydrological model represented conceptually by seven interconnected storage tanks. These tanks simulate various hydrological processes through water balance equations, resulting in the generation of three flow components: overland flow, interflow and base flow.

In relation to base flow, TETIS utilizes a storage tank that receives water from percolation, loses a portion of it due to deep percolation, and stores the remaining volume, which is subsequently released as base flow. This process is governed by a discharge coefficient, whose value depends on spatial and temporal scales, saturated horizontal hydraulic conductivity, and one of the eight correction factors involved in the calibration process of TETIS.

As is well known, base flow results from the interplay of various groundwater processes, including river-aquifer interaction, groundwater pumping, and others. Additionally, other factors significantly influence the base flow component, such as hydrogeological units, which often extend beyond hydrographic boundaries. This leads to inter-basin hydrogeological interactions, a phenomenon that exceeds the modeling capabilities of TETIS.

To address this limitation, an integration between TETIS and MODFLOW, a widely recognized groundwater model, has been implemented. In this framework, TETIS supplies recharge values to MODFLOW, while MODFLOW provides the base flow component to TETIS, enabling mutual feedback between the two models. As a result, the integration of both models is expected to yield improved hydrological modeling through their dynamic interaction.

To evaluate the performance of the TETIS-MODFLOW model, it has been implemented in Requena-Utiel aquifer, located in Valencia, Spain. This aquifer has been classified as being in a poor quantitative state since 2016, primarily due to the overexploitation of groundwater resources resulting from the transition from rain-fed agriculture to drip irrigation systems. The implementation results have been satisfactory in the sense that the integrated TETIS-MODFLOW model delivers better outcomes compared to the initially implemented individual models.