Project Name:
Ephemeral Channels
Collaborators:
USDA-ARS Tucson hydrologists and rangeland scientists
Goals/purpose:
Streams in the water-limited West are often termed "losing streams", as opposed to the "gaining streams" in the east. In losing streams, the water table is below the stream, so water infiltrates into the channel bed, and the flow declines with distance downstream. 
Flow Chart of WGEW Sub-Watersheds:Ephemeral flow is the term used for those streams with flashy flows during and immediately after precipitation. For streams where the water table is high enough to be connected to the stream seasonally, the resulting flow that is not directly associated with storms is termed intermittent. Typically, intermittent and ephemeral flows are mapped together, as in the National Hydrography Dataset (NHD, 2008), which showed 94%, 89%, 88%, and 79% of the stream lengths in Arizona, Nevada, New Mexico, and Utah as either intermittent or ephemeral. A recent article in Science (Brinkerhoff et al., 2024) estimated that 55% of the flow in the continental US originated in ephemeral streams. Ephemeral streams supply water, sediment, nutrients, and biota downstream, and are a key source of groundwater recharge. Although non-perennial streams are gauged much less than perennial streams, we can study the hydrology of ephemeral streams on the Walnut Gulch Experimental Watershed which was designed to systematically measure ephemeral flows in nested subwatersheds.