The State of Arizona has more than 100,000 known miles of surface water drainages at medium resolution in the National Hydrography Dataset | Learn More on the USGS Website >

These surface waters are divided into segments, known individually as a reach. A reach is a section of a stream or river along which similar hydrologic conditions exist. These hydrologic conditions are described as flow regimes in statute as follows:

• Perennial means a surface water or portion of surface water that flows continuously through the year.
• Intermittent means a surface water or portion of surface water that flows continuously only at certain times of the year and more than in direct response to precipitation, such as when it receives water from a spring, elevated groundwater table or another surface source, such as melting snowpack.
• Ephemeral means a surface water or portion of surface water that flows or pools only in direct response to precipitation.

See Arizona Revised Statutes Title 49, Chapter 2, Article 1 | View >

ADEQ assigns each surface water reach, lake, pond or other type of surface water an identification number known as a Waterbody Identification Number or WBID. Through analysis of available and credible data, ADEQ assigns each WBID one of the flow regimes. ADEQ utilizes eMaps to display the known flow regimes for perennial, intermittent and ephemeral waters on the layer listed as Flow Regimes - Perennial Intermittent and Ephemeral Streams | View eMap >

To assign additional flow regimes and to confirm or adjust existing flow regimes, ADEQ developed an algorithm that can be applied to a Geographic Information System (GIS) to analyze available credible flow related data and observations for a WBID. This algorithm applies:

• Types of observation data where measured flow data (e.g. USGS stream gauges) and on-the-ground observations (e.g., wet-dry mapping, site visits and flow measurements by staff) receive greater weight for scoring over other indirect data (e.g., satellite imagery review, modeling)
• Scope or extent, where data that indicate a flow regime along the entire reach receives a greater weight than for data that are related to a partial segment of the reach or point on the reach

How GIS algorithm works | Learn More >

Submit additional or new sources of data or provide input regarding flow regimes | Email >

The flow regime information may be applied in jurisdictional evaluations of surface waters to help the agency evaluate waters for assessment and permitting under the Clean Water Act or the State Surface Water Protection Program for inclusion on Arizona’s Protected Surface Waters List | More Information >

To request the ADEQ GIS files for flow regime eMaps, including the data analyzed to assign flow regime, fill out an online request form through the ADEQ Records Center | Learn How >

Monthly Updates

ADEQ updates the eMap layer monthly. Updates will be listed below for the current month and previous two months.

January 2024

• No updates made
  
  

December 2023

• No updates made
  
  

November 2023

• No updates made
  
  

Additional Resources

• White Paper: Application of flow gauge data utilizing a USGS approach to identify ephemeral and intermittent flow regimes in Arizona | View/Download >
• White Paper: Analysis of percent riparian vegetation for estimating flow regimes in Arizona | View/Download >
• White Paper: Analysis of snowpack for estimating flow regimes in Arizona | View/Download >
• White Paper: Analysis of depth to groundwater for estimating flow regimes in Arizona | View/Download >
• Regional Streamflow Duration Assessment Methods (SDAMs) | Learn More on the EPA Website >
• Antecedent Precipitation Tool (APT) | Learn More on the EPA Website >

Disclaimer: ADEQ has compiled this data as a service to our customers using information from various sources. ADEQ cannot ensure that the information is 100 percent accurate, current or complete. Neither the information presented nor maps derived from them are official documents. All data are provided "as is" and may contain errors. The data are for reference and illustration purposes and are not suitable for site-specific decision-making by themselves. Other available data, information, and analysis may be necessary to make final jurisdictional determinations related to a WOTUS. Information found here should not be used for making financial or any other commitments. Conclusions drawn from such information are the responsibility of the user. ADEQ assumes no responsibility for errors arising from misuse of the data or maps derived from the data. ADEQ disclaims any liability for injury, damage or loss that might result from the use of this information. In no event shall ADEQ become liable to users of these data and maps, or any other party, arising from the use or modification of the data. Anyone using the information for commercial purposes must contact the ADEQ Records Management Center pursuant to Arizona law.