Estimation of water table depth using DUALEM-2 system

摘要

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 DUALEM-2 system. Two fields (Field 1: 45.38 degrees N, 63.23 degrees W and Field 2: 45.37 degrees N, 63.25 degrees W) were selected and thirty perforated observation wells were installed to calibrate the DUALEM-2 for predicting WTD. Boundaries of the selected sites and location of the wells were marked using a real time kinematics global positioning system (RTK-GPS). The user interface program was developed in Delphi 5.0 software and imported in a laptop computer to retrieve data from the DUALEM-2 system. The horizontal co-planar (HCP) geometry, perpendicular co-planar (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 DUALEM-2 and corresponding locations of the sampling points using Trimble Ag GPS 332. The regression model showed significant correlation between the HCP and WTD with co-efficient of determination (R-2 = 0.71) for field 1 and (R-2 = 0.53) 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 DUALEM-2 system was efficient in mapping variation rapidly and reliably in WTD in a non-destructive 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), site-specific irrigation and drainage design with the aided advantage of labor and time savings in case of observing precision water management practices at large fields.