What are ephemeral streams and why are they important?

Ephemeral streams flow during and after rain. They are different than intermittent streams, which flow continuously for part of the year because of seasonal snow melt or a high water table. While ephemeral streams do not flow continuously, they connect the arid landscape to rivers, lakes, reservoirs, and underground aquifers.

Arizona’s ephemerals streams perform four critical functions:

  1. Protect surface water and groundwater quality
  2. Buffer and protect downstream private property by conveying flood waters and sediment flows
  3. Replenish groundwater levels for agriculture and communities
  4. Provide habitat for birds and other wildlife

What impacts ephemeral streams?

Land development in Arizona (particularly prior to the Clean Water Act) significantly altered the network of streams across the landscape. Ephemeral streams have been particularly impacted, as their essential contributions to wildlife, groundwater recharge, and water quality are more important than their dry appearance may suggest. Many ephemeral streams and the surrounding uplands have been filled in and paved, channelized and built for urban flood control, altered for road construction, and used as dumpsites.

What is the current threat to ephemeral streams?

The recently finalized Navigable Waters Protection Rule (the “new rule”) reduces the number of waters—including in Arizona—that will receive water quality protections through the federal Clean Water Act. The new rule excludes ephemeral streams from “waters of the United States” and, as a consequence, they are excluded from federal water quality protection.

The Arizona Department of Environmental Quality (ADEQ) has implemented the federal Clean Water Act for several decades but lacks authority under state law to protect Arizona waters that are no longer protected by the federal government. As ADEQ contemplates how to continue to protect the water quality of rivers, streams, and wetlands in the wake of the new federal rule, the inclusion of ephemeral streams in a state water quality protection program must be considered—and Audubon is active in this process.

Whether a river or stream flows year-round or a few weeks per year, both the water and the streambeds through which they flow support water supplies, wildlife, native vegetation, and local communities and developments. Without regulatory protection, those benefits are at risk.

Learn more in Audubon's new analysis, The Importance of Arizona’s Ephemeral Streams.

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