🌵 Decoding Arizona's Streams: What's "Relatively Permanent" in the Desert?

The Main Idea

Arizona's streams are undergoing a complex classification process to determine which are "relatively permanent" under new Clean Water Act regulations.

The R&D

🏜️ Arizona's streams are feeling the heat, and not just from the desert sun! A recent study dives deep into the state's waterways, aiming to answer a crucial question: What exactly makes a stream "relatively permanent" in a place where water is as precious as gold?

This research comes hot on the heels of the 2023 Conforming Rule, which redefined "Waters of the United States" (WOTUS) under the Clean Water Act. With about 95% of Arizona's streams being nonperennial (meaning they don't flow year-round), this classification is more than just a drop in the bucket – it's a flood of implications!

📊 The study analyzed 70 stream reaches across Arizona, using over 30 years of daily flow data. They classified streams into three categories:

• Ephemeral: These fair-weather friends flow less than 25% of the time (think less than 3 months out of every 7.5 years).
• Intermittent: The middle-ground streams, flowing more than 25% but less than 100% of the time.
• Perennial: The overachievers, flowing 100% of the time (at least 9 out of 10 years).

🌡️ But wait, there's more! The ongoing megadrought since 1994 is reshaping Arizona's waterscape. Some streams are downgrading from perennial to intermittent, or even from intermittent to ephemeral. It's like a hydrological game of musical chairs, and when the music stops, some streams are left high and dry!

This research isn't just academic – it could shape how Arizona and other arid regions protect their precious water resources. So next time you're hiking in the desert and come across a dry streambed, remember – it might just be waiting for its moment to shine!

Concepts to Know

• Nonperennial Streams 🏞️: These are streams that don't flow year-round. They include both ephemeral (flowing only after rain) and intermittent (flowing seasonally) streams.
• Waters of the United States (WOTUS) 🇺🇸: A legal term defining which waters are protected under the Clean Water Act. The definition has been a subject of debate and legal challenges.
• Megadrought 🌵: An extended period of drought lasting two decades or longer. The southwestern United States is currently experiencing a megadrought that began around 1994.

Source: Julian, J.P.; Stuhldreher, C.; Wade, M.T. What Is Relatively Permanent? Flow Regimes of Arizona Streams within the Context of the 2023 Conforming Rule on the Revised Definition of “Waters of the United States”. Water 2024, 16, 2641. https://doi.org/10.3390/w16182641

From: Texas State University; University of Oklahoma