Integrated Hydrometeorology Measurements on Quantifying Evapotranspiration and Infiltration of a Grass Covered Pilot Site

I-Chieh Tseng, Kuan-Yin Chen, and Ming-Hsu Li
Graduate Institute of Hydrological and Oceanic Sciences
National Central University

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Abstract

Evapotranspiration (ET) and infiltration are primary fluxes of water exchanges between land surface and atmosphere. Latent heat flux of ET further plays an important role in energy budget of land surface. How ET and infiltration affect soil moisture variations and subsequently shape groundwater levels remain great challenges in quantifications through different temporal scales. We established integrated hydrometeorology measurements, including radiation, wind speed, relative humidity, air temperature, soil temperature, soil moisture, pore water pressure, and groundwater levels, at the meteorology station inside the campus of National Central University in northern Taiwan to provide continuous field data supporting estimations of ET and infiltration. Tensiometers were installed at 0.4 m 1.2 m below surface with nearby capacitance probes measuring soil moisture at -0.1 m, -0.3 m, -0.5 m, -0.7 m, -1.0 m, -1.5 m, -2.0 m, -3.0 m, and -4.0 m to quantify soil water fluxes during rainfall events and after. A well logging drilled to 25 m to identify hydrogeology characteristics. Five groundwater wells drilled to 15 m on four corners of a square plot of roughly 10 m x 6 m and one in the center to monitor changes of groundwater levels. Pumping tests were performed to determine hydraulic conductivities. Water retention curves were determined from selected wet-to-dry and dry-to-wet events to support simulations of groundwater levels with three-dimensional variable saturated numerical models. Soil moisture and pore water pressures give good estimations of vertical soil water movement to quantify ET and infiltration. However, preliminary analysis shows significant lateral movements of soil moisture and groundwater during rainfall events owing to layers of gravel mixed between different layers of dominated silt clay at this site.