A proposed wash project in northern Scottsdale around the Loop 101 freeway would protect thousands of properties and critical city infrastructure in the event of a 100-year flood.
The currently-unfunded project is one of many being considered for inclusion in a potential bond election that the City Council is expected to vote on in April.
The project would protect against a flood that would have flows greater than that of the Colorado River through the Grand Canyon.
Currently, there is a 7.5-square-mile FEMA-designated floodplain in Scottsdale that originates in the McDowell Mountains near Pinnacle Peak Road and extends south to Frank Lloyd Wright Boulevard.
The flood plain encompasses 4,600 properties and the Scottsdale Water Campus, a critical piece of city infrastructure that provides both potable and reclaimed water treatment for a significant portion of the city.
The proposed Reata Wash Floodplain project would create a channel along the eastern end of the current floodplain and divert flows into that channel and away from properties.
If approved, the city would only be on the hook for a fraction of the project’s total cost.
Couch said about 75 percent of the project has already been paid for by DC Ranch and Windgate Ranch communities and the city would split the remaining 25 percent with the Maricopa County Flood Control District through a grant awarded to the city.
The grant is contingent upon the city coming up with its portion of the funding, Couch said.
The project would cost the city $27.3 million with the county flood control district paying the same amount.
C. Ashley Couch, drainage and flood control manager and floodplain administrator for the City of Scottsdale, said the city estimated that in the event of a 100-year flood at least 1,000 properties in the plain would be flooded.
The designation “100-year flood” refers to a flood that “has a 1 in 100 chance of being equaled or exceeded in any 1 year,” according to the U.S. Geological Survey.
A 100-year flood could happen multiple times in a given generation, but there is a one percent chance it will happen in a given year.
Even lesser weather events, such as the recent storms that brought substantial rain and even some snow to Scottsdale, can affect homes and properties in the floodplain.
Rains last month caused some road closures in the floodplain and threatened to flood some condominiums in the Tom’s Thumb area, and “that was not even a five-year flood,” Couch said, adding that the wash program “would solve that problem.”
Some detractors have questioned why the entire city should be asked to pay for the flood control project instead of just the residents who live in the floodplain.
Couch said a bond is the appropriate approach because “there are major benefits to people living in the floodplain, but there are also benefits to people in greater Scottsdale.”
If the Water Campus were flooded or knocked off line, that would affect the city’s water supply.
Facilities at the Scottsdale Water Campus treat 70 percent of the city’s drinking water and 50 percent of the city’s recycled water, said Nicole Sherbert, spokesperson for Scottsdale Water Department.
“The Scottsdale Water Campus is the hub of Scottsdale Water’s operation,” Sherbert said.
There are also public safety issues to consider as the floodplain is home to a Scottsdale Police station and a planned Scottsdale Fire station near Loop 101 and Hayden Road.
Couch said a 100-year flood would flood out roads in the area, which could affect the ability to respond to emergency situations.
For residents within the floodplain, the flood control project could also remove the federal requirement for flood insurance at a total savings of $1.8 million, a city report says.
City Records show that the City Council approved in March 2018 a contract for $667,424 with Wood Patel Associates for design services for the Reata Wash Project so that the city could submit a Conditional Letter of Map Revision, or CLOMR, to FEMA.
Couch said that as long as the project is built according to a plan approved by FEMA, he anticipates the floodplain would be revised and the insurance requirement removed.
“We are not going to build a project that FEMA won’t approve,” Couch said.
Couch said it would likely take at least a year after the project is built for FEMA to review the project and revise the floodplain.
At a recent community open house on bond projects hosted by the city, the floodplain project drew the interest of several residents.
Joe Janick listed it as one of his top priorities along with a proposed bridge on Thompson Peak Parkway over Reata Wash, city solar energy projects and projects to support the fire department.
Not everyone is a fan of the project.
Couch said some people are convinced that there is no flood danger.
Couch said some people may be lulled into a false sense of security because the city has not experienced a 100-year flood in the area since rain has been measured in the area around 30 years ago.
The largest flood to date was a 20-year flood on Sept. 8, 2014, Couch said.