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Council adopts updated Stormwater Management Design Manual, incorporates wildfire runoff guidance
Summary
Flagstaff adopted a rewritten Stormwater Management Design Manual (2025) by resolution and read an ordinance adopting it by reference. The update replaces the 2009 manual, simplifies guidance, adds burned‑watershed and two‑dimensional flood modeling guidance and incorporates modern references for hydraulics and design.
Flagstaff — The City Council approved a rewritten Stormwater Management Design Manual on March 4 and authorized adoption of the document by reference into city code, replacing the 2009 manual.
Consultants and city stormwater staff said the new 2025 manual updates procedures and standards, clarifies definitions, and simplifies the document by referencing established, detailed design material where appropriate. Key additions include guidance for post‑wildfire burned watershed runoff, updated hydrology parameters specific to Flagstaff, and 2‑D flood modeling guidance to reflect modern practice.
Rick Schuler, consultant with Woodson (project consultant), described the approach: the team used existing county and regional manuals as a foundation, adapted hydraulics guidance from the Flood Control District of Maricopa County for detailed hydraulic methods, and retained Flagstaff‑specific hydrology where local calibration was important. Schuler said the review process included more than 30 local engineering reviewers and nearly 200 comments, many incorporated into the draft.
Ed Shank, stormwater section director, thanked the consultant and staff and said the update was overdue. The council read a resolution recognizing the manual as a public record and then read an ordinance adopting the manual by reference into Title 12 (Flood Plains). Both measures moved forward on affirmative votes.
What changed and why it matters
- The 2025 manual consolidates and simplifies chapters, moves deep technical procedures to referenced documents, and keeps Flagstaff‑specific hydrology calibrations in the manual.
- A new burned‑watershed chapter offers specific guidance and parameters for post‑wildfire flooding and erosion — a topic of growing relevance after recent regional wildfires.
- The manual explicitly incorporates modern hydraulic methods including 2‑D flood modeling and provides quick reference guides for designers and applicants.
Action taken
Council designated the 2025 Stormwater Management Design Manual a public record by resolution and read an ordinance adopting it into city code (Title 12). Both the resolution and ordinance passed on council votes. The manual will be used by city staff and consultants for drainage studies, permitting and construction plan review moving forward.
Ending
Staff said the manual will improve clarity and reduce back‑and‑forth with applicants by consolidating design expectations and referencing contemporary technical standards. The manual also aims to help the city respond to increased post‑wildfire flood risk through clearer, locally calibrated procedures.
