Quantifying Transmission Losses in a New Mexico Ephemeral Stream: A Losing Proposition

Under natural conditions, stormwater runoff in much of the semiarid Southwest drains through a network of unlined stream channels called arroyos. Dry during most of the year, arroyos are transformed into raging rivers for short periods of time following intense rain events. As stormwater travels downstream, a portion of the flow is lost to the highly permeable arroyo bed. The purpose of this study was to quantify these so-called transmission losses for a 13-km reach of one New Mexico arroyo. Infiltration rates were tested in the field using a double-ring infiltrometer. Test results varied considerably from 3.0 to 19.6cm/h, with a median rate of 9.4cm/h. Additionally, three stream-gauging stations were installed along the arroyo; for two storms in 2015, they measured a dramatic decrease in peak discharge (91 and 84%, respectively) and runoff volume (90 and 80%, respectively). Gauge data was used to successfully simulate transmission losses in a hydrologic model of the drainage system; the average loss rate for the arroyo was found to be 3.8cm/h. On average, infiltrometer results overestimated reach-scale loss rates by 60%.