A study commissioned by the town of Marana reduces the community’s floodplain area from 19 square miles to three.
The study, released Monday, may override recommendations by the Federal Emergency Management Agency which placed more than 2,000 Marana structures in a high-risk flood zone, consequently requiring flood insurance.
Town officials are confident that the 165-square-mile drainage study will be accepted by the federal agency in October.
“It is by far, better than any of our previous studies,” said Town Engineer Keith Brann.
FEMA’s maps would’ve placed approximately 2,000 structures in the flood zone. The new town study places 250 structures in the flood zone.
The situation began in September 2007, when FEMA distributed new flood maps that included many areas that were not previously in the floodplain.
FEMA’s original floodplain stretched from the Pinal County line, down to Massingale Road in an area covering the Marana town hall, the Gladden Farms development and Arizona Pavilions. The FEMA draft maps added about 19 square miles to the floodplain.
“They essentially changed everything downstream until it hit another floodplain,” Brann said.
The disputed floodplain is from runoff from the Tortolita Fan and not from the banks of the Santa Cruz River.
Town officials and residents were worried that the new maps would require flood insurance for houses that would’ve otherwise been protected by the levee-like structures of the Central Arizona Project canal, Union Pacific Railroad and Interstate 10. Those structures would do enough to stop or disperse water running from the nearby mountain range, Marana officials argued.
The week after the flood maps arrived in Marana, Congresswoman Gabrielle Giffords wrote a letter to FEMA officials asking for the agency to reconsider the structures’ levee-like properties. In early November 2007, Giffords introduced legislation calling for the recognition of such structures as substitutes for levees.
Also in November, the town council commissioned a new drainage study of the area to counter the FEMA flood maps.
To date, the study conducted by CMG Drainage cost the town $300,000, with a projected final cost of $350,000. Half a million dollars had originally been budgeted for the project.
“It’s very much money well spent,” Brann said.
After pressure from Giffords and Sen. Jon Kyl, FEMA officials agreed to give the town time to conduct a drainage study.
“By working closely with my congressional colleagues, town leaders and officials from the Federal Emergency Management Agency, we showed that collaboration can lead to common sense solutions,” Giffords wrote in an e-mail.
Mayor Ed Honea credits Giffords in getting the agency to reconsider the proposed maps.
“Had she not intervened, we may not be having this discussion at how fortunate we are,” Honea said.
The three-volume study included new rainfall data not used in the town’s previous flood maps, a soil study and a drainage simulation.
“All in all we have much better scientific data to look at,” Brann said.
The first two volumes, the rainfall and soil studies, were submitted to FEMA in April and June, respectively. The agency had approved the scope and methods of the study as well as these two volumes, Brann said.
The final volume, identifying flood zones, was submitted to FEMA Aug. 12. It was made public Monday.
If results from the new study are accepted, much of the area east of I-10, including portions of the San Lucas Development, will be in the floodplain.
The flood maps illustrate what will happen during a 100-year flood, something that, according to Brann, has not occurred since the town was incorporated in 1977.
A 100-year flood, or base flood, has a 1 percent chance of occurring each year, which is not the same as saying such floods only occur once every century. A flood of that magnitude actually has a 63 percent chance of happening in a 100-year period.
The flood in 2006 was classified as a 25-year flood. The deluges of 1983 and 1993 fell into the 50-70-year range, Brann said.
While FEMA could reject the study provided by Marana, town officials believe this to be unlikely as the agency has already approved earlier aspects of the study. FEMA’s deadline for approval is Oct. 1, but the town’s work in the issue doesn’t end there.
Later this year, new maps will be issued which determine which areas fall into which insurance rate. At that time the town will conduct an outreach program for the properties affected by the new rate maps.
Town officials also plan to further analyze flood-prone areas for capital improvement projects that could take those areas out of the flood zone.
FEMA officials could not be reached for comment as of press time.
November 1 – HR 4050, accounting for levee-like structures, introduced by Rep. Giffords
November 6, 2007 – Marana passes resolution to provide funding to perform drainage study
December 18, 2007 – FEMA headquarters sends letter to congressional staff acknowledging levee-like structures’ influence on flooding, allow Town to perform drainage study to influence insurance rate maps, request withdrawal of HR 4050
April 16, 2008 – FEMA accepts scope of study
April 25, 2008 –CMG Drainage submits volume 1 of study
June 16, 2008 – CMG submits volume 2 of study
August 12, 2008 – CMG submits volume 3 of study