Using streambed temperature sensors to monitor flow events in the san pedro river, southeast Arizona and north-central Sonora, Mexico

Abstract

Streamflow gaging stations commonly are spaced too far apart to provide detailed spatial information on flowing and non-flowing reaches. Synoptic surveys can provide good spatial information, but with little temporal resolution. Therefore, a new technique is needed to monitor both the spatial and temporal distribution of streamflow in desert streams. Streambed temperature is an easily measured variable from which patterns of streamflow frequency and duration can be inferred. To determine the effectiveness of this technique, a network of 42 temperature sensors was installed in the San Pedro River Basin from the headwaters in Sonora, Mexico, to near the confluence with the Gila River in Arizona (approximately 220 kilometers). Streambed temperature was measured every half hour, at a depth of approximately 10 centimeters. Data were evaluated on the basis of long-term diurnal fluctuations in streambed temperature. In a dry stream channel, the fluctuation can be as much as 30°C. During periods of streamflow, however, the fluctuation is dampened. Perennial reaches exhibit a constant dampening with little variation throughout the year. Ephemeral reaches exhibit temperature dampening in response to precipitation events that is usually short in duration. Intermittent reaches exhibit temperature dampening as shallow water tables rise in response to decreased evapotranspiration. This dampening can last for many months. Because perennial, ephemeral, and intermittent flows have a different effects on streambed temperature, it is possible to recognize these flow events on a streambed thermograph, making this method ideal for classifying flowing and non-flowing reaches of a desert stream.