Lunch & Learn: Getting It Right at the Water’s Edge — Practical Insights into OHWM and SDAM

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Webinar Summary: 📝

Practical Tips for OHWM & SDAM Field Work

Guest Expert: Cheryl Creer, Senior Botanist & Wetland Specialist, Stantec

Hosted by: Wildnote

Date: December 2025

Overview

This webinar focused on practical, field-driven guidance for performing Ordinary High Water Mark (OHWM) delineations and using the Streamflow Duration Assessment Methods (SDAM) across regions—especially the Arid West and Western Mountains. Cheryl shared real-world examples, time-saving advice, and how new federal regulatory changes may shape future field protocols.

Key Themes & Takeaways

1. The Relationship Between Wetland Delineations, OHWM & SDAM

  • Modern “wetland delineations” are more accurately aquatic resource delineations.

  • Field teams must often complete:

    • A wetland determination form

    • OHWM form

    • SDAM

    • Sometimes additional region-specific tools (e.g., MESA protocol in CA desert solar projects)

  • OHWM determines where the aquatic resource is; SDAM determines flow regime (perennial, intermittent, ephemeral).

2. Why SDAM Matters More Than Ever

Changes in the definition of Waters of the United States (WOTUS) made ephemeral streams non-jurisdictional.

→ Accurately distinguishing ephemeral vs. intermittent now directly affects federal jurisdiction.

SDAM:

  • Provides a quantitative, standardized way to determine flow regime.

  • Reduces back-and-forth with the Army Corps.

  • Prevents costly rework and delays.

Case Example:

A project without SDAM data received a Corps request for additional information, delaying approval by six weeks. Another project required 75 additional data points—forcing a full extra mobilization.

3. Practical Field Tips for SDAM Pre-Field Planning

  • Read the manual — this is not a form you can “wing.”

  • Understand which indicators feed the actual statistical model (R code).

Tools Cheryl Recommends

  • PocketMacros app – free, photo-based dichotomous key for aquatic invertebrates

  • Percentage Cover app – inexpensive, accurate alternative to a convex spherical densiometer

  • Ocular estimation is still acceptable for:

    • Canopy cover

    • Streambed slope

    • Depth measurements

Time-Consuming SDAM Elements

  • Mapping upstream/downstream boundaries for each assessment reach

  • Dip-netting and identifying aquatic macroinvertebrates

  • Measuring canopy with prescribed methods

  • Detailed vegetation documentation within ½ streambed width

These steps add ~20 minutes per site, based on participant feedback.

Cheryl’s “Streamlined SDAM Approach”

  • Build a stripped-down version of the form collecting only indicators used by the SDAM model.

  • Enter results into the web calculator after returning from the field.

  • Include a strong note: “Do not select flow regime until model results are obtained.”

4. Practical Field Tips for OHWM

National Rapid OHWM Form vs. Regional Forms

  • The 2024 National Rapid OHWM form is being promoted across districts.

  • LA District requires it; Sacramento and San Francisco list both national and Arid West forms.

  • Cheryl’s take:

    • The Arid West OHWM form prompts better thinking about geomorphic units.

    • The National form’s open-ended fields may lead inexperienced staff to miss features like:

      • Floodplains

      • Low-flow channels

      • Islands & bars

    • Always confirm district preference.

Calibration is Critical

  • Have the field team walk sites together early in a project.

  • Discuss indicators: cut banks, scour, sorting, wrack, vegetation shifts, etc.

Hybrid Forms Improve Efficiency

Cheryl uses:

  • A combined OHWM + SDAM hybrid form in Wildnote

  • Logic-driven question display (e.g., only show compound-system questions when applicable)

  • Added fields not included in federal forms (e.g., top of bank, riparian canopy) to support state agencies like CDFW

5. Integrating Wildnote & SDAM (R-Code Model)

  • The finalized SDAM protocol uses R code (version 3.0.1).

  • EPA representative Brian Topping encouraged use of the newest version.

  • Wildnote is exploring potential future integration with the SDAM model to automate regime calculations and eliminate tedious data entry.

6. Regulatory Watch: Proposed WOTUS Definition (Nov 2025)

Cheryl flagged that proposed revisions:

  • Could reshape wetland determination requirements

  • Introduce new expectations for documenting continuous surface connections

  • Potentially increase data burdens even while reducing federal jurisdiction

Recommendation:

Read the fact sheet and submit comments.

7. Questions & Notable Clarifications

  • When do you use OHWM vs. SDAM?

    → You need both for any non-wetland aquatic feature (streams, washes).

  • Do you need cross-sections?

    → Required in Arid West OHWM; optional in National form (but helpful).

  • Slope measurement tools?

    → No reliable app yet; most practitioners use ocular estimation.

  • Bankfull vs. top of bank vs. OHWM?

    → Still a gray area; varies by region and interpretation.

  • How precise must measurements be?

    → Corps guidance suggests engineering-grade accuracy, but currently treated as recommended, not required.

8. Closing Notes

  • Hybridizing forms and workflows can reduce fatigue and error in large teams.

  • Work smarter: streamline in the field, process the heavy lifting back in-office.

  • The Wildnote team is actively developing improved workflows and future integration options for SDAM modeling.