Estimation of water table depth using DUALEM2 system Abstract   Most of the agricultural fields are generally irrigated or drained uniformly without considering the spatial and temporal variation in water table depth (WTD). Investigating WTD is important for scheduling irrigation, drainage system designs and water balance models. The objective of this study was to develop a software interface to estimate the variations in WTD via electromagnetic induction (EMI) methods using frequencies of a DUALEM2 system. Two fields (Field 1: 45.38xc2xb0N, 63.23xc2xb0W and Field 2: 45.37xc2xb0N, 63.25xc2xb0W) were selected and thirty perforated observation wells were installed to calibrate the DUALEM2 for predicting WTD. Boundaries of the selected sites and location of the wells were marked using a real time kinematics global positioning system (RTKGPS). The user interface program was developed in Delphi 5.0 software and imported in a laptop computer to retrieve data from the DUALEM2 system. The horizontal coplanar (HCP) geometry, perpendicular coplanar (PRP) geometry and WTD were recorded simultaneously from each well before and after every significant rainfall for three consecutive days. Comprehensive surveys were conducted to measure apparent ground conductivity (ECa) with DUALEM2 and corresponding locations of the sampling points using Trimble Ag GPS 332. The regression model showed significant correlation between the HCP and WTD with coefficient of determination (R2xc2xa0xc2xa00.71) for field 1 and (R2xc2xa0xc2xa00.53) for field 2. Maps were generated in ArcGIS 10 software to examine the accuracy of predicted WTD in comparison with actual values. Results indicated that the DUALEM2 system was efficient in mapping variation rapidly and reliably in WTD in a nondestructive fashion rather than following conventional way of repeated well drilling for WTD determination. This information could be used for measuring the depletion of WTD during dry periods (droughts), sitespecific irrigation and drainage design with the aided advantage of labor and time savings in case of observing precision water management practices at large fields.

SpatioTemporal Variations in Groundwater Revealed by GRACE and Its Driving Factors in the HuangHuaiHai Plain, China The HuangHuaiHai (3H) Plain is the major cropproducing region in China. Due to the longterm overexploitation of groundwater for irrigation, the groundwater funnel is constantly expanding and the scarcity of water resources is prominent in this region. In this study, Gravity Recovery and Climate Experiment (GRACE) and hydrological models were used to estimate the spatialtemporal changes of groundwater storage (GWS) and the driving factors of GWS variations were discussed in the 3H Plain. The results showed that GRACEbased GWS was depleted at a rate of xe2x88x921.14 xc2xb1 0.89 cmy in the 3H Plain during 2003 to 2015. The maximum negative anomaly occurred in spring due to agricultural irrigation activities. Spatially, the loss of GWS in the Haihe River Basin is more serious than that in the Huaihe River Basin, presenting a decreasing trend from south to north. Conversely, the blue water footprint (WFblue) of wheat exhibited an increasing trend from south to north. During the drought years of 2006, 2013, and 2014, more groundwater was extracted to offset the surface water shortage, leading to an accelerated decline in GWS. This study demonstrated that GWS depletion in the 3H Plain is well explained by reduced precipitation and groundwater abstraction due to anthropogenic irrigation activities.