New maps used to calculate flood insurance rates in Jefferson Parish may be delayed by up to two years as the Federal Emergency Management Agency works to incorporate information showing some areas of the parish may be lower than previously thought.

Review of the new data, which come from a U.S. Army Corps of Engineers study, will push back approval of the new flood maps until 2016 as FEMA tries to determine how the data will affect flood maps for the parish that had been under review, Jefferson Parish Director of Flood Plain Management Michelle Gonzales said.

The review of the flood maps, which had been nearing its end, will have to be restarted as the maps are redrawn and those affected by them are given time to comment on the changes. That means Jefferson Parish residents, developers and businesses will continue to have their flood insurance rates and standards based on nearly 20-year-old maps that do not take into account many of the new drainage and storm protection systems in the parish. “Never did we anticipate that process starting again,” Gonzales said.

The new elevation data were released in January. Due to a provision in the federal Biggert-Waters Act, which changed the way flood insurance is calculated, the new data have to be used in the creation of the new flood maps, Gonzales said.

It’s not clear to what extent the lower elevations are due to actual subsidence, a significant issue in the New Orleans area, and to what extent they result from more accurate technology being used to determine elevation, she said.

While the data show many areas of the parish at lower elevations than previously thought, how the new elevations will affect flood insurance ratings in Jefferson Parish is unclear, Gonzales said. FEMA has indicated that in most cases, the lower elevation may be accompanied by a decrease in the base flood elevation, which determines how high a property must be to avoid flood risks, she said.

Thus, while a home that had been listed at -5 feet — or 5 feet below sea level, which is the proposed base flood elevation on the 2012 maps — might be listed at -6 feet on the new maps, the base flood elevation may fall by a foot as well, canceling out the decrease’s effect on insurance ratings. The actual effect of the new elevations will not be apparent until the maps are released.

The current flood maps date from 1995 and do not incorporate the improvements the U.S. Army Corps of Engineers has made to the area’s hurricane protection system since the area flooded during Hurricane Katrina. They also do not account for the massive Southeast Louisiana Urban Flood Control Project, an ongoing effort to improve stormwater drainage in Jefferson, Orleans and St. Tammany parishes that was sparked by massive flooding in 1995, 10 years before Katrina.

Both the parish and individual homeowners are fighting for changes in the flood maps. The parish’s key concern is that FEMA underestimated the amount of water that can be carried in drainage canals, creating flaws in the model that suggest a higher risk of flooding in some areas. Jefferson is preparing data it says would correct that error; it expects to submit the data to FEMA by June.

Adding that information to the existing maps would have been a relatively quick process, but going through the procedures needed to revise the parishwide maps is expected to take at least 18 months, Gonzales said.

Parish President John Young, who fought against other aspects of the Biggert-Waters Act that would have led to increased premiums for some residents, said he wished there was a way to implement the revised maps for areas not affected by the new elevation data.

“We’d like to see it bifurcated, but at this point that doesn’t seem to be an option as far as the federal government’s concerned,” Young said.

Follow Jeff Adelson on Twitter, @jadelson.