ABSTRACT The evapotranspiration (ET) demands of growing trees or plants are required for designing groundwater drafts due to plantation over a long period. The principle of high water extractive demand of growing trees could be useful for designing biodrainage systems for reclamation and managing waterlogged salt-affected soils as well as seepage interception. The search for a practical method of estimation of tall growing ET trees suitable for biodrainage over a long period of time using simple weather parameters is still going on. Modeling of ET based on weather parameters and tree parameters may avoid the associated complexity of direct ET measurement. Eucalyptus is the most commonly used tree species for bio-drainage. ET of the eucalyptus is dependent on interrelated weather parameters and the age of the tree. A geometrical similarity (GS) between weather parameters (Epan) and ET of plants was observed, and an Epan-based GS Model was hypothesized. Modeled ET values of eucalyptus by an analytical model of Singh & Verma were used for developing Epan based GS model and predicting ET values for 10 years. Monthly characteristic constants (CEpan) of GS Model were worked out. ET values predicted by GS Model for the year 2004, 2008 and 2013 were compared with the modeled values of ET by Singh and Verma model for different months. Overall average percent deviation of predicted ET values by Epan-based GS Model was only 12.49% compared to the analytically modeled ET values. Average per cent deviations of ET values by the Epan-based GS Model were .07, 21.3 and 8.11% for 2004, 2008 and 2013, respectively. The proposed model is a simple method for the estimation of ET of eucalyptus trees for field application.

Keywords: Biodrainage, evapotranspiration, geometrical similarity, subsurface drainage, waterlogging