Exploring Limits of near-Surface Water Flux Determination From Penta-Needle Heat Pulse-Based Measurements.

The fate of precipitation and snowmelt are not only important sources for water supply, but also crucial inputs to hydrological modeling.  Presently subsurface water flux measurements are unavailable for monitoring networks despite the critical need for information on subsurface transport rates. The Penta-needle Heat-Pulse Probe (PHPP) has a central heater needle surrounded by two pairs of orthogonally arranged temperature sensing needles and has been shown to provide flux determination estimates within a plane normal to the heater needle. Heat-pulse measurements used to assess water flux in soil have shown promise for determination of infiltration rates ranging from about 1 to 1000 mm h^-1. While these flow rates exclude some finer textured and unsaturated soil transport rates, they capture rates equivalent to the mean saturated hydraulic conductivity of soils in several large databases (UNSODA, USDA), which are associated with significant rainfall and snowmelt events. A single sensor can provide estimates of soil-thermal properties, -moisture, -temperature and  flux estimates. Detailed results in soil columns evaluate the range of feasible flux rates under saturated conditions. The complexity of analyzing the PHPP sensor data has been simplified with microprocessor-based optimization of the thermal properties and flux values leading to a user-friendly and multifunctional research tool.