Developing empirical monthly groundwater recharge equation based on evapotrairation in catchments without hydrometric station to estimate runoff Ghazal Kamran g.kamran@cv.iut.ac.ir Sep 21, 2020 Department of Civil Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc. Language: Farsi Supervisor: Dr. Mohammad Hossein Golmohammadi, m.golmohammadi@iut.ac.ir Dr. Hamid Reza Safavi, hasafavi@iut.ac.ir One of the biggest challenges and most important aims of planning and managing water resources is determining the amount of recharge and the runoff within watersheds using climate and hydrological parameters particularly in areas that lack a hydrological station. In order to predict hydrological processes precisely and accurately, hydrological models are used. Almost all hydrological models, calibrate through dividing and categorizing the area of study into hydrological results and examining the runoff of each result and aggregating runoff results within the hydrometric station and comparing it with runoff observation data. Calibrated parameters match the observational data of the exit point of the studied basin and every single hydrological result should be calibrated with its own data but in this case, since there are no hydrometric stations in each result, this is almost impossible. Based on similar studies in this field, it is indicated that the share of the produced runoff reported by the hydrological model in sub-basins without a hydrometric station is not accurate since calibration parameters in exit point of the area is randomly allocated to the upstream sub-basins and for each of these sub-basins, it's not be calibrated exclusively. Hence, in this study an empirical equation for calculating recharge based on climatic and landuse parameters in the form of factors such as precipitation and evapotrairation in a basin with a hydrometric station and adequate data from the water years of 1991 to 2011 with the coefficient of determination equal to (0.95) was developed. For this purpose, two parameters of maximum daylight hours (N) and extraterrestrial radiation (HA) were calculated using solar method daily and after that, potential evapotrairation (PET) was calculated using Penman’s method. In addition, with using satellite data, Budyko framework method and seasonal conversion CoKriging method. Also, by subtracting the average aquifer thickness from the DEM map, the bedrock raster map of the upstream Eskandari sub-basins was obtained. With the difference of these two raster maps, the mass volume of the porous aquifer space was calculated. By multiplying this with the aquifer storage coefficient, the volume of groundwater within the aquifer was obtained. By subtracting the groundwater in consecutive months, the changes in monthly water storage was calculated. Finally, by determining the volume of extractions and the amount of water returned from consumptions, the recharge volume from rainfall was calculated on a monthly basis from the water year 1991 to 2011 for sub-basins upstream of Eskandari station. In the end, in order to validate the results, the recharge amount obtained for three sub-basins of Buin-Maindasht, Damane-Daran and Chehel Khane from empirical equation were compared with the recharge amount resulted from groundwater balance. The correlation coefficient (R) of sub-basins were calculated as 0.95, 0.95 and 0.95, the Nash-Sutcliffe Efficiency (NSE) was calculated as 0.53, 0.22 and 0.75, the Index of Agreement (d) was calculated as 0.93, 0.9 and 0.95 respectively. The results indicate that the amount of recharge being simulated using empirical equation is very compatible with the amounts of recharge being calculated from the groundwater balance and this provides evidence for the efficiency of the proposed method. Keywords: Empirical Equation of Recharge, Evapotrairation, Surface and Groundwater Balance, Runoff, Watershed without hydrometric station