Innovations clarify which state waterways are protected under the Clean Water Act

The flow and regulation of water in the arid Southwest is unique. The complexities of whether the state of Arizona or the federal government has jurisdiction over waterways—both continually flowing and not—impact recreation, agriculture, industrial use and drinking water all over Arizona.

So when 1,400 water bodies needed to be reevaluated in response to the 2020 federal Navigable Waters Protection Rule (NWPR), the Arizona Department of Environmental Quality needed to optimize the process as much as possible. The new rule redefined which water bodies were protected under the Clean Water Act. ADEQ needed to start the substantial analysis effort while also continuing to make progress on other mission-critical objectives, such as air quality testing, addressing groundwater chemicals and more.

At issue was the classification of waterways that only flow after precipitation. Known as ephemeral drainages, they were no longer protected under the federal Clean Water Act while the NWPR was in effect. What were still protected were intermittent waterways, which have seasonal flow, as well as continuously flowing streams and rivers. 

After launching an Arizona Management System problem-solving effort, ADEQ came up with three innovative ways to simplify how to figure out which Arizona waterways were likely intermittent and therefore regulated by the Clean Water Act while the NWPR was in effect. 

To determine which waterways were intermittent, ADEQ needed to know the flow patterns. Yet at the time, 83 percent of the waterways in question had no data to indicate their flow. To do these analyses without having to send staff to every streambed, ADEQ used satellite imagery, snowpack records and groundwater depth to zero in on likely intermittent waters. 

“These tools are mostly based on published and peer-reviewed Arizona-specific science done at our state universities,” said Trevor Baggiore, ADEQ Water Quality Division director. “Being able to leverage this local research from world-class institutions is critical to understanding our unique waterways and how we can best protect the water that flows through them.”

Because the presence of robust plant life in a waterway indicates seasonal flow, ADEQ used satellite imagery and Geographic Information System software to measure the shrubs and vegetation that grow in riparian environments within the water channel in question. If more than 50% of the channel has vegetation, that implies an intermittent flow. Less than that implies an ephemeral flow. 

Elevation and snowpack records were also used to identify waterways that were likely affected by snowmelt for more than 30 days. Headwaters at 6,500 feet elevation or higher were determined to be potentially intermittent, narrowing down the scope for analysts, who cross-referenced snowpack records from the Salt River Project. 

Finally, groundwater depth was used to determine the likelihood of an intermittent waterway. Since research indicates that shallow groundwater may mean a higher likelihood of intermittent flow, ADEQ determined the Arizona Department of Water Resources Groundwater Site Inventory Database could be used to figure out which waterways may be seasonal. 

Within a year of the NWPR becoming effective, ADEQ had used their new tools to determine the likely status for 764 waters in Arizona. Automating these tools also saved hundreds of hours of staff time, including a 75% reduction in the time it took to analyze groundwater data (saving nearly 600 hours of work time). All told, 5,712 miles of waterways were analyzed in this effort.

While the NWPR is no longer effective (as it was vacated by a federal court in August 2021), these innovations continue to impact Arizona water users and set a standard for other states. Flow characteristics of water remain central to federal surface water jurisdiction and a new Arizona Surface Water Protection Program. ADEQ continues to showcase these tools to a national audience and was awarded the National Association of Environmental Professionals 2022 Environmental Excellence Award for Best Available or Innovative Technology.

“These tools enable ADEQ to better protect the quality of Arizona's surface waters. With drought continuing to impact our water supply, it's more important than ever to ensure our lakes, rivers and streams are healthy today and for generations to come,” said Baggiore.