Determination of Evaporation from Free Surface Water in Mazandaran Plain (Dazmirkandeh Abbandan) and Compared with Seven Experimental Methods

Evaporation is one of the important and effective processes in water cycle that causes loss of large volumes of lake and Abbandan’s water wich its measurement has great importance in water resources planning. In this research, the amount of evaporation in six months (from April to September in 2016) from the free surface of Dazmirkande Abbandan located at Mazandaran Province has been measured by floating evaporation pan and amount of evaporation has been calculated by Meyer, USBR, Shahthin, Hefner, Penman, Marciano and Ivanov formulas with Dashte-e-Naz station data compared. It was found that by using statistical criteria Ivanov methods, USBR and shahthin provides high precision for determining evaporation from the free surface in this region. Root mean square errors values, deviation and t-test results in the best models are 1/36, 0/18 and 0/95, respectively. Due to the accuracy of Ivanov formula for humid areas, the amounts of daily evaporation have been calculated based on Ivanov formula. For determination of pan coefficient, According to Ivanov formula for this region, amounts of daily evaporation measured with 0/6, 0/7, 0/75, 0/8, 0/85 and 0/9 coefficient. Due to the statistical results, the coefficient of 0/75 with minimum amount of RMSE and MBE and t, has been chosen as the best coefficient for floating evaporation pan. The results indicate a 18 percent of the total volum of Abbandan reservoir evaporation in the study period. Minimizing of evaporation it could be used a wind break, floating objects or proper planning of water resources change to minimize the amount.