Development of an Alpine Hydrogeology Model and Water Budget Evaluation– a Case Study of the Upper Beinan River, Taiwan

The mountainous aquifer system plays an important role in the entire hydrological cycle, facilitating the redistribution of seasonal water resources and providing water supply to downstream watersheds. Due to severely environments and complex geological conditions, it is still a challenge to establish a conceptual model to comprehensively describe the system. Accordingly, this study aims to focus on constructing an alpine hydrogeological model and evaluating the water budget in mountain areas. The selected study site is located at the upstream tributaries of the Beinan River in Taituung County, Taiwan. Through establishment of hydrological monitoring facilities of surface and subsurface and conduction a series of field experiments, such as electrical resistivity tomography (ERT), fiber-optic distributed temperature sensor (FO-DTS) measurements, hillslope infiltration tests, and cross-borehole tracer tests, the aquifer properties, flow paths, and recharge mechanisms can be evaluated. The preliminary results indicate that the shallow aquifer contributed a significantly amount of water to the stream, piratically during the dry seasons. Infiltrated water was primarily passes through the regolith, while flow within the bedrock is predominantly controlled by fractures. Groundwater was mainly stored in the regolith but the water within the fractured rocks may serve as the buffer for the downstream water supply. The conceptual model and water flow paths for high mountain hydrogeology developed in this study can provide a theoretical basis for understanding the hydrological characteristics, hydrological processes, and storage of groundwater resources in mountainous areas. This preliminary model can serve as a reference for subsequent analyses of the impact and feedback of climate change and land use changes on the hydrogeological environment of high mountain areas.