Coconino County, Town of Tusayan outline multi‑phase plan to reduce flood risk around Grand Canyon gateway

Coconino County flood‑control staff and town officials presented a multidiscipline drainage master plan on Tuesday that pairs large detention basins upstream on Coconino Wash with in‑town storm‑drain and channel improvements in Tusayan to reduce the community’s exposure to high‑volume floods.

The plan lays out a staged approach: upstream flood‑retarding basins on National Forest lands (including a large basin at Tusayan Pines and a second at the Echo Draw/10x meadow) to capture and attenuate runoff, plus in‑town conveyance upgrades (dual large pipes and a reconstructed channel) designed to meet Arizona Department of Transportation standards for Highway 64 and to protect the town’s wastewater treatment plant from a 100‑year event. "We've reached a consensus as to the preferred alignment of the flood mitigation both through town as well as the measures proposed upstream of town on Forest," Flood Control Director Lucinda Andriani told the board.

Why it matters: The August 2023 storm that flowed through the watershed produced observed flows that county engineers now model as roughly a 10‑ to 25‑year event; the modelled 100‑year discharge on Coconino Wash is several thousand cubic feet per second. County and consultant modeling shows that selected upstream basins plus the in‑town improvements will remove surface flow from most streets for a 25‑year event, provide 100‑year protection to the wastewater plant, and reduce the peak flows routed through Tusayan for larger storms.

Engineering and next steps: Consultants said they evaluated a dozen potential basin and alignment locations before selecting five sites that provide the greatest mitigation benefit per cost. "Coconino Wash is the big contributor to volumetric flood. In order to attenuate that flow, you need very large basins," consultant Joe Leverage said. The recommended measures rely on extensive geotechnical testing and utility surveys before 30% design can be completed; county staff stressed those field investigations require rights‑of‑entry from landowners and Forest Service permitting for facilities on federal land.

Funding and permitting strategy: The town and county plan to apply to the Federal Lands Access Program (FLAP) this fall so the town can meet a grant‑application requirement associated with an earlier state smart‑grant award. Staff said FLAP does not require a local cash match but that a local match improves competitiveness. County staff also identified FEMA mitigation and other federal grant programs as possible funding sources; they emphasized the work will likely be completed in stages and will require a mix of local, state, and federal funding.

Officials noted permitting questions remain — including whether ADWR or Forest Service permitting pathways will be required for flood‑retarding structures — and that those items will determine feasibility and final costs. "This is not a one‑and‑done project," Andriani said. "It's a long‑term effort that's going to take multiple funding sources." Mayor (Town of Tusayan) joined county staff and said the town strongly supports the partnership and will continue to pursue grant opportunities.

What’s next: Staff will conduct geotechnical borings, utility locates and environmental assessments during the next phase so the design concept report (30% design) can be completed; the town plans to consider the plan on its November 4 agenda. County staff will pursue a FLAP application this fall and continue coordination with ADOT, US Forest Service, ADWR and FEMA as design advances.

Ending: County and town leaders framed the plan as a coordinated, multi‑year program that must pair upstream watershed work on federal land with in‑town infrastructure improvements and broad funding support to reduce both roadway closures on Highway 64 and flood risk to critical facilities in Tusayan.