Mapping Water Table Depths using Electromagnetic Induction Methods to Develop Variable Rate Technologies

Abstract

Most of the agricultural fields are generally irrigated or drained uniformly without considering the variation in water table depths (WTD). Investigating these depths is important for scheduling irrigation, drainage system designs and water balance models. The objective of this study was to estimate the WTD using electromagnetic induction (EMI) method. Thirty observation wells were installed to calibrate the DualEM-2 for predicting the WTD within a soybean and a pasture field in central Nova Scotia, respectively. The horizontal co-planar (HCP) geometry, perpendicular co-planar (PRP) geometry and WTD were recorded simultaneously from each well for three consecutive days after every significant rainfall. Comprehensive surveys were conducted in selected fields to measure ground conductivity with DualEM-2 and a differential global positioning system (DGPS). The HCP component of the DualEM-2 was better than PRP component for estimating WTD because of its greater sensing depth. The preliminary results showed significant correlations between the actual WTD and HCP measured with DualEM-2 in both fields. The regression equation was utilized to predict WTD from ground conductivity survey data (BEEC: R2 ranged from 0.76 to 0.93; p-value<0.01, Boulden: R2 ranged from 0.69 to 0.85; p-value<0.01).The predicted WTD maps were generated in ArcGIS 9.3 software. This information could also be used for measuring the depletion of WTD, site-specific irrigation and drainage design with time after the application of irrigation or rainfall.