Riparian zone evapotranspiration estimation from diurnal groundwater level fluctuations

Riparian vegetation typically has a great influence on groundwater level and groundwater-sustained stream baseflow. By modifying the well-known method by White [White, W.N., 1932. Method of estimating groundwater supplies based on discharge by plants and evaporation from soil – results of investigation in Escalante Valley, Utah – US Geological Survey. Water Supply Paper 659-A, 1–105] an empirical and hydraulic version of a new technique were developed to calculate evapotranspiration (ET) from groundwater level readings in the riparian zone. The method was tested with hydrometeorological data from the Hidegvíz Valley experimental catchment, located in the Sopron Hills region at the western border of Hungary. ET rates of the proposed method lag behind those of the Penman–Monteith method but otherwise the two estimates compare favorably for the day. At nights, the new technique yields more realistic values than the Penman–Monteith equation. On a daily basis the newly-derived ET rates are typically 50% higher than the ones obtainable with the original White method. Sensitivity analysis showed that the more reliable hydraulic version of our ET estimation technique is most sensitive (i.e., linearly) to the laboratory- and/or slug-test derived values of the saturated hydraulic conductivity and specific yield taken from the riparian zone.