Coconino County Flood Control District advances local floodplain maps for Tucson; board hearing set for Dec. 9

Coconino County Flood Control District staff told the Town Council that they will present an ordinance adopting locally derived floodplain maps for the Tucson watershed at the Coconino County Board of Supervisors meeting on Dec. 9, with public notice planned for about Nov. 9. The district says the maps are intended to reflect the best available science, not to block or encourage development.

Lucinda, a Flood Control District representative, said the change responds to decades-old FEMA Zone A maps that were often drawn from paper contours and digitized with errors. “We needed to stop speculating and use the very good science that we have today,” she said, introducing the technical team.

Ian Sharp, a civil engineer with JE Fuller Hydrology, presented the modeling and results. The study analyzed a roughly 59‑square‑mile watershed, used field reconnaissance and the August 2023 flood to calibrate models, and produced design discharges and water‑surface elevations for recurrence intervals including 10‑, 25‑, 100‑ and 500‑year events. Sharp cited example discharges at the wastewater treatment plant: a 10‑year event of about 940 cubic feet per second (CFS), a 25‑year event of about 3,500 CFS and a 100‑year event around 10,200 CFS; the August 2023 event produced about 1,400 CFS at the…