Assessing Snowpack Melt Rates Using Penta-Needle Heat Pulse Probes and Snowmelt Lysimeters.

The fate of snowmelt is not only important for water supply, but also a crucial input to hydrological modeling for flood forecasting. Snowmelt measurements are desirable for monitoring networks but lysimeters are expensive and challenging to manage. A Penta-needle Heat-Pulse Probe (PHPP) has a central heater needle surrounded by two pairs of orthogonally arranged temperature sensing needles. In situ calibration of the apparent spacing between each heater-thermistor needle pair is critical for accurate water flux estimates. The calibration and complexity of fitting soil-thermal property and heat flux estimates from temperature rise data has been automated and simplified with microprocessor-based optimization and SDI-12 communication, yielding a user-friendly and multifunctional research tool. Heat-pulse measurements used to assess water flux in soil have shown promise for determination of infiltration rates ranging from about 1 to 1000 cm d^-1. Snow melt-based soil water flux estimates may exceed 10 cm d^-1 being proportional to the up- and down-stream temperature differences among needle pairs. Additional applications of the PHPP for water flux estimates include monitoring stream beds, riparian zones and irrigated soils.