Determining soil water flux and pore water velocity by a heat pulse technique

A method is presented for measuring soil water nux density (J) with: a ther mo-TDR (time domain reflectometry) probe, Constant heat input during a smal l time interval (15 s) is used to emit a heat pulse from a line heat source . Asymmetry in the thermal field near the heat source is quantified by comp uting the maximum dimensionless temperature difference (MDTD) between upstr eam and downstream locations, Heat transfer theory was used to relate MDTD to J, A thermo-TDR probe was used to obtain measurements of MDTD in water-s aturated soil materials of different textures (sand, sandy loam, and clay l oam) with imposed water flux densities ranging from 1.16 x 10(-5) to 6.31 x 10(-5) m(3) m(-2) s(-1). A nearly linear relationship between measured MDT Ds and fluxes was observed for all soil materials. Measured and predicted M DTDs agreed well for now experiments in sand, Greater discrepancies were ob served for now experiments in sandy loam and clay loam. Despite the lack of universal agreement between measured and predicted MDTDs, the experimental results indicate that the proposed method may provide a useful means of me asuring J, The method presented herein improves upon earlier methods by red ucing distortion of the water now field and minimizing heat-induced soil wa ter redistribution. Because the thermo-TDR probe can be used to make TDR-ba sed measurements of volumetric water content (theta), the proposed method a lso may permit measurement of pore water velocity (J/theta).