Study shows flow classification tool can be adapted to distinguish intermittent and ephemeral streams in Southwest

Posted May 5, 2018

SCCWRP and its partners have shown in a proof-of-concept study that a flow classification tool that can rapidly distinguish intermittent streams from ephemeral streams in the Pacific Northwest is feasible for application in the U.S. Southwest.

The tool, which determines a stream’s flow duration based on easily observed field indicators, was originally developed by the U.S. Environmental Protection Agency. Researchers are  now adapting and refining the tool for use across California, Arizona and New Mexico. Researchers also are developing a comparable tool in parallel for use in the adjacent Western Mountains region.

New Mexico’s Santa Fe River, left, is classified as an intermittent stream under a new flow classification tool co-developed by SCCWRP, while New Mexico’s Arroyo Chamiso, right, is classified as an ephemeral stream. The tool relies, in part, on visual observations of the plant community to determine classification. Willows and other water-loving vegetation thrive in the Santa Fe River, which is sustained by groundwater, while sagebrush and other upland vegetation dominate in the drier Arroyo Chamiso.

Watershed managers need to be able to distinguish intermittent streams from ephemeral because, in certain cases, they are subject to different regulatory requirements. Intermittent streams are defined as streams that have sustained seasonal flows from snow melt and groundwater, whereas ephemeral streams only experience brief surface flows from runoff.

The proof-of-concept study found that certain biological indicators – including riparian plants and aquatic invertebrates that prefer perennially flowing water – are particularly effective at distinguishing stream types.

Researchers will spend the next year finalizing the Southwest tool; they will particularly focus on how to account for the long-term variability observed in Southern California stream flow patterns.


More news related to: Bioassessment, Ecohydrology