Spatial and Temporal Variability of Vertical Hydrologic Fluxes at The San Pedro River, AZ

Abstract

Precipitation patterns in semi-arid river systems of the southwestern U.S. make stream-aquifer exchanges an important source of water in perennial rivers. Nonetheless, the spatial and temporal evolution of surface and ground water interaction are not fully understood. This research utilizes diurnal temperature oscillations as a tracer of vertical water fluxes by applying Stallman's analytical solution to a series of temperature time series recorded in the stream and in the streambed of the San Pedro River. Temperature measurements were recorded at four spatial extents using a nested hierarchy during four different periods since last flood. Time since last flood did not affect vertical fluxes significantly, but fluxes exhibited spatial dependence at lengths of 6-24 m. Stream geomorphic features influenced the magnitude of vertical fluxes; runs were more downwelling than riffles. The data suggests that the spatial distribution of vertical fluxes becomes more homogeneous as time since last flood increases.