Quantifying Ephemeral Streambed Infiltration from Downhole Temperature Measurements Collected Before and After Streamflow

A constant flux infiltration experiment was conducted to determine the feasibility of using downhole temperature measurements to estimate infiltration flux. Temperatures measured using a downhole thermistor within a 15.4‐m‐deep borehole compare well with temperatures measured with buried thermocouples in an adjacent borehole to 5 m depth. Numerical forward model simulations were conducted using VS2DI. A numerical sensitivity analysis showed that the temperature profile was most sensitive to the average temperature of the infiltrating water, the infiltration flux, and the specific heat capacity of dry soil. The high sensitivity of these variables allows for a simple sequential optimization to be used to estimate the average temperature of the infiltrating water, the water flux, and the specific heat capacity of dry soil from numerical inversion of temperature measurements. Downhole temperature measurements could be a useful complement to shallow streambed temperature methods, allowing for better quantification of the contribution of streambed infiltration to basin‐scale recharge.