ABSTRACT
Recharge rate is the most important component in water balance computation and groundwater modeling. Also, it is the critical factor in optimal planning and management of groundwater resources in the arid and semi-arid regions such as the eastern part of Iran. There are different techniques to quantify the recharge amount. Each of these methods has been developed in separate hydro-geological conditions and they will estimate completely different recharge value in an identical region. In this study, based on available hydro-geological information, four of these methods were selected to estimate the groundwater recharge. All of these methods are based on the water balance principle (rainfall-groundwater level relationship), including CRD (Cumulative Rainfall Departure), RIB (Rainfall Infiltration Breakthrough), WTFs (Water Table Fluctuations), and HBM (Hydrological Budget Method). These methods were useful, easy to be utilized, cost effective, simple, requiring few non-deterministic data such as groundwater level measurements, rainfall, aquifer properties, and groundwater extraction dataset. These methods were used to provide the percentage of irrigation return flow and the precipitation contribute to natural groundwater recharge. In order to apply the first three methods (WTFs, CRD, and RIB that are distributed techniques), the study area was classified to Thiessen polygons based on the existing observation wells. Thus, the natural recharge rate was estimated for each Thiessen polygon in monthly scale. Utilizing of these three methods, groundwater level was simulated and also the optimization technique was applied to minimize the Root Mean Square Error (RMSE) between the simulated and observed groundwater level. The results were shown that the simulated groundwater level was matched well with the observed amount. The forth method (HBM) was a lumped technique and it estimated an annual recharge rate of Neyshabour plain, from 378.73 to 448.95 MCM for 2000 to 2010. Finally, the estimated groundwater recharge of each method compared with each other and also the results showed that CRD, RIB and WTF methods provided more reliable groundwater recharge.
