Beta Streamflow Duration Assessment Method for the Arid West
The beta Streamflow Duration Assessment Method (SDAM) for the Arid West is a scientific tool to provide a rapid assessment framework to distinguish between ephemeral, intermittent, and perennial stream flow at the reach scale. The agencies are making this beta SDAM available for a one-year preliminary implementation period while we continue an expanded data collection effort in 2021 to inform the refinement of the final SDAM for the Arid West. We welcome user comments during the preliminary implementation period.
On this page:
- What is the method used for?
- How was the method developed?
- Additional information on how to apply the method
- Training opportunities
- Contacts
- Documents, tools, and data
What Is the Method Used For?
Long-term hydrologic data to assess streamflow duration is often limited, especially for streams that do not flow year-round. SDAMs are rapid field assessment methods that use hydrological, geomorphological, and/or biological indicators, observable in a single site visit, to classify streamflow duration as perennial, intermittent, or ephemeral at the reach scale. Regulators and water resource managers can use rapid, reach-scale methods to determine streamflow duration classifications (i.e., perennial, intermittent, ephemeral) and to help implement many federal, state, and local programs.
For instance, this information could help determine whether a stream may be subject to jurisdiction under the Clean Water Act, although use of the method is not a requirement for determining jurisdiction.
This method is also useful where knowledge of streamflow duration improves ecological assessment, management, and decision-making.
While use of this method may inform a more robust stream assessment, it was specifically developed for the purpose of determining streamflow duration class and does not provide a stand-alone assessment of stream function or condition.
This method does not imply or represent a change in the definition of Waters of the United States under the Clean Water Act.
How Was the Method Developed?
Learn more about the development of streamflow duration assessment methods for nationwide coverage, including the steps for developing a regional method.
The beta SDAM for the Arid West results from a multi-year study conducted at 90 stream reaches across the Arid West following the process described in Fritz et al. (2020). Twenty-one candidate indicators expected to control or respond to streamflow duration were tested at sites of known flow duration class. Through statistical analyses, the agencies identified the subset of indicators with the highest diagnostic accuracy of flow duration classification and constructed the current data-driven beta method. In October 2023 errors were found in the coding of the beta SDAM calculation of “at least intermittent” and “needs more information” classifications. This error has now been corrected in the web application and in the November 2023 updates to the User Manual and supporting documents. Users of the beta SDAM that have resulted in “at least intermittent” or “needs more information” classification results prior to these updates should consult the updated web application or classification table in the User Manual to correct possible errors in their classification results.
An expanded data collection effort began in 2021 to inform the refinement of the final SDAM for the Arid West. The objectives of the expanded effort are to test the beta method at more sites across the Arid West to improve upon the precision and accuracy of the beta method, and address any shortcomings or limitations identified during the preliminary period when the beta method is in use.
Study results, including data analyses for development of the beta method, are available (see below), as are study data.
Additional Information on How to Apply the Method
The information below is intended to clarify how to apply certain elements of this method. If you have other questions, feel free to share inquiries with contacts listed below.
1. How is the assessment reach defined for:
1.1 Unconstrained settings:
Assessments should be made over the length of a stream reach, rather than at one point. The assessment reach chosen should be representative of the stream, and should have a length equivalent to 40 channel widths. For narrow streams, the length of the assessment reach should be a minimum of 40 meters. The agencies recommend walking the stream prior to choosing an assessment reach.
1.2 Constrained settings (e.g., within highway right-of-way or a single tax lot):
If it is not possible to assess a reach that is 40 channel widths in length, then apply the method for the entire length of stream that you can access. Make a note of your reach length and constraints on the data sheet. If possible, inspect upstream and downstream sections of the stream and make a note of your observations.
2. Are the results from using this method the same as a jurisdictional determination?
No. Jurisdictional determinations are made by the regulatory agencies based on federal law and current guidance and policy, and method outputs are not a jurisdictional determination. Rather, the method provides information that may be useful for the agencies to make timely decisions because it helps determine the duration of streamflow.
3. Can this method be applied to created or altered channels?
Yes, the method can be used, in combination with best professional judgment, to assess the flow duration of created channels or streams that have been highly modified. The agencies have observed that some hydrologic and biologic indicators tend to persist (wetland plants, for instance, may occur on the margins of the channel) even with frequent maintenance of the created or altered channels. When applying the method in created channels or modified streams be sure to note that the site is a “disturbed site/difficult situation” and describe it in the “notes.”
4. What part of the stream do I assess when working in a braided stream system?
Identify the extent of the channels, based on the outer limits of ordinary high water marks, and apply the method to that area as a whole. Some indicators may be present or more apparent in the main channel versus the side channels; make a note of those differences on the field assessment form.
5. Is the method applicable when a stream goes subsurface in a portion of the assessment reach?
Streams observed flowing subsurface during the assessment visit may flow on the surface during wetter times of the year; therefore, it is important to check the entire reach for indicators of streamflow. In addition, the accuracy of an assessment can be improved by conducting a follow-up visit during a wetter time of the year.
Training Opportunities
Contacts
User comments are welcome during the preliminary implementation period. Detailed instructions on how to provide comments are available in the Joint Public Notice of Availability.
EPA:
- (Region 6) Loribeth Tanner (tanner.lori@epa.gov), 214-665-8153.
- (Region 8) Rachel Harrington (harrington.rachel@epa.gov), 303-312-6870.
- (Region 9) Joe Morgan (morgan.joseph@epa.gov), 415-972-3309.
Army Corps of Engineers:
- (Los Angeles District) Aaron Allen (Aaron.O.Allen@usace.army.mil), 805-585-2148.
- (Sacramento District) James Robb (James.T.Robb@usace.army.mil), 916-557-7610.
Documents, Tools, and Data
- Updated November 2023 User Manual for the Beta SDAM for the Arid West (pdf)
- Updated November 2023 Field Forms for the Beta SDAM for the Arid West (pdf)
- Joint Public Notice of Availability for the Beta SDAM for the Arid West
- Updated November 2023 Online Report Generating Tool – an optional electronic application that allows users to input SDAM for the Arid West data to generate a report of their results.
- Data Used to Develop the Beta SDAM for the Arid West
- Journal Article Describing the Development of the Beta SDAM for the Arid West
- Review of Scientific Literature Informing Method Development
- Training material Distribution Hub