By BEX Staff for AZBEX
Decades of planning and discussion have not yet brought about the expansive flood control effort to solve issues with the Rio de Flag in Flagstaff, but an upcoming grant application could be an important interim step before the complete project is put in place.
The Rio de Flag Flood Control Project is a joint plan between Flagstaff and the Army Corps of Engineers that will reroute the river to its original course and eliminate flood risks and the floodway designation from Flagstaff’s Southside area.
The project has been planned ever since a major flood event in Feb 1993. Cost estimates over that time have grown from around $30M to current projection of $243M.
AZBEX has run three articles about the Rio de Flag project in our subscriber-only digital magazine. The first article in Oct. 2019 said the final design was nearly complete and the cost estimate had increased from $106M to $121M. A Feb 2020 report said the Corps of Engineers had pledged $52M from its 2020 civil works plan “to fully fund the project.”
It also quoted a local news article that said, “The $52M allocated by the Army Corps joins local dollars raised by the Flagstaff City Council. In 2018, the Council approved $33M in bonds to pay for the City’s share of the flood control project and paid for by use of the stormwater fee.”
In Sept. 2020, the project was reported as part of the then-recently approved Southside community plan.
It is currently listed as being in the design/plan review stage. According to a DATABEX project database update from early 2025, “The Army Corps of Engineers is administering the project, and they have not released a solicitation date. The design is supposed to be complete this summer but with the new administration in Washington DC, there could be changes or shifts in how the project is delivered.”
New Project Will Help Flooding in the Interim
A local news outlet recently reported the new grant for which the City is currently applying its part of the plan by Flagstaff and BNSF Railway that will replace and enlarge culverts running under the railroad tracks and Route 66 east of the Flagstaff Mall that contribute to flooding in the area, including the major flood of 1993.
Federal Railway Administration funding could cover up to 80% of the $15.6M project cost. BNSF and Flagstaff will each provide $3.9M. The City will apply for an AZ SMART Grant that could cover all of Flagstaff’s obligations, but officials do not expect to receive the full amount.
The culvert replacement will not completely eliminate flooding, but it should reduce the extent of future floods.
The Federal Emergency Management Administration has issued a floodway designation for the area, which restricts the kinds of development and redevelopment that can take place there.
Design for the culvert project is complete. Four new eight-foot culverts and one fine-foot culvert, which could also serve as a pedestrian underpass, will be installed. While FEMA estimates as much as 3,100 cubic feet of water/second could pass through the area in a flood event, the increased number and size of pipes in the culvert project could manage as much as 2,200, significantly reducing the scale of future events.
City officials said the project will reduce the flood risk in the Rio de Flag area and increase the rate of flow downstream. The expansion will help carry water away from developed areas and into spaces where it can drain safely.
If implemented as planned, development restrictions will be removed on approximately 200 acres.
Once the culvert project is implemented, BNSF plans to add tracks in the area, which will roughly double the size of the embankment.
BSNF operations will not be impacted by the construction. No start date has been announced.
