Groundwater Recharge Estimating in Mashhad-Chenaran Aquifer using water table fluctuations method (MRC algorithm)

Mashhad-Chenaran Aquifer with an area of about 2527 km2, as the most sustainable resource supplying the drinking water of Mashhad city, is the most important alluvial aquifer in Khorasan Razavi Province. In this study, groundwater recharge has been estimated using the water table fluctuations method and MRC algorithm in a period of 15 years (Sep. 2001 to Sep. 2016) measured in 31 observation wells. Results suggested that recharge in Mashhad-Chenaran Aquifer follows a certain pattern depend on rainfall fluctuations. Seasonal rainfall starts from the end of October and reaches its maximum in April. The trend of increasing groundwater recharge continues until the end of March, and then, with the beginning of the spring season, the amount of recharge is significantly reduced. The most important reason for the decrease in recharge rate during this period is the lag time between the beginning of rainfall and its impact on the groundwater. The highest amount of recharge takes place in January, February and March and the lowest in August and September. During the 15-year period, the lowest and the highest amounts of recharge were 87.2 MCM (12.4% of rainfall) and 221.7 MCM (29% of rainfall) respectively in 2002-2003 and 2011-2012 water years. During this period, the average annual recharge is about 122 MCM (19% of rainfall). Recharge events less than 5 MCM have the highest frequency and high amounts also have the lowest frequency. Assessing the ratio of recharge to precipitation indicates the correct estimation of recharge by water level fluctuations method and MRC algorithm.