Impacts of nonideal field conditions on vertical water velocity estimates from streambed temperature time series

Analytical solutions to the 1‐D heat transport equation can be used to quantify surface‐groundwater interactions directly from temperature time series data in streams and their streambeds. The solutions rely on three assumptions: purely vertical flow, no thermal gradient with depth in the streambed and sinusoidal temperature signals. Here numerical models of heat transport in streambeds are used to generate synthetic time series data under conditions that violate the aforementioned assumptions. These synthetic records are used to evaluate the impact of violations of model assumptions on vertical water velocity estimates. Analytical methods using the amplitude ratio to derive flux are less prone to error than methods that use lag time under nonideal field conditions. The greatest source of error is nonvertical flow in the streambed. Errors from analytical solutions for flux are comparable to or smaller than errors inherent to Darcy‐based flux estimates and therefore the use of temperature data to quantify flux across the streambed is a promising alternative to more commonly used approaches, such as Darcy flux calculations.