Coconino County’s Flood Control District presented a technical update Oct. 21 on the Tusayan Drainage Master Plan and a proposed local floodplain for the town of Tusayan. Engineers described a multi‑element approach that combines several upstream detention basins in the forested watershed with new storm‑drain and channel work through town to reduce flood exposure for Highway 64, the Tusayan wastewater treatment plant and town streets.

Lucinda Andriani, the district director, said the engineering team has reached consensus on a preferred set of measures and has advanced from conceptual planning into the design concept phase. The work includes:

- Watershed measures: Five primary upstream locations were identified to store and attenuate flows, including a large basin near Tusayan Pines and a second large basin at the Echo Draw/10X meadow; smaller basins were recommended on Water Tank, Middle Wash and Long Jim tributaries. Engineers said the combined effect reduces peak flows entering town.

- In‑town measures: The preferred alignment includes multiple underground storm pipes (6‑foot and dual ~7½‑foot pipes in critical reaches), reconstruction of a concrete channel along the wastewater treatment plant and local crossing improvements (box culverts/bridges) to carry flows safely beneath roadways. Project modeling shows the proposed combined measures can meet ADOT’s 25‑year standard for Highway 64, provide 100‑year protection for the wastewater treatment plant and 25‑year mitigation through the town, with full 100‑year mitigation for two smaller tributaries.

Engineers described the Aug. 2023 flood that produced a calculated peak discharge of about 1,400 cubic feet per second at the wastewater plant and summarized design storm discharges used in modeling: roughly 940 cfs (10‑year), 3,200 cfs (25‑year) and 10,000 cfs (100‑year) for the watershed. The designers said Tusayan Pines basin capacity could exceed 600 acre‑feet, requiring downstream conveyance be sized for extended outflows after a storm.

Next steps include geotechnical testing, survey and utility locates within town, environmental and permitting coordination (U.S. Forest Service, ADWR dam/jurisdictional reviews) and completion of 30% design. The town of Tusayan previously secured a $2.4 million federal “SMART” planning grant for the master plan; district staff also said they will prepare an application for the Federal Lands Access Program (FLAP) to seek construction funding for transportation‑related improvements. Andriani said a FLAP application would not require a local match but would strengthen competitiveness if the town or district provided matching funds.

The Flood Control District also proposed establishing a “local floodplain” to reflect updated modeling that shows greater inundation than the FEMA Zone A maps. JE Fuller engineer Ian Sharp said the district’s FEMA‑standard modeling produces a larger, more accurate inundation area; county staff said they will return to the board with an ordinance amendment in December to enable the district to designate local floodplains. County and town officials said local floodplain authority would allow the county and town to regulate development and require no‑adverse‑impact analyses using the best available information while FEMA map updates proceed (a process that can take several years).

Tusayan Mayor Clarinda Veil and multiple supervisors praised staff and engineers for the technical work and emphasized that the program will require staged funding and multiple federal and state grants to implement.