The floodwaters that swept through south Louisiana over the past week may have reached 31 percent of the homes in Baton Rouge and the eight surrounding parishes, according to a detailed but preliminary economic analysis of the disaster released Friday.

The report from the Baton Rouge Area Chamber translates that figure into an estimate of roughly 110,000 homes, valued at $20.7 billion, that could have flooded because they were located in neighborhoods where water pooled. The homes included in the analysis are spread across East Baton Rouge, Livingston, Ascension, East Feliciana, Iberville, Pointe Coupee, St. Helena, West Baton Rouge and West Feliciana.

The potential damage figure is far higher than any put forward thus far. State officials have said over the past week that at least 40,000 homes were thought to have flooded, although BRAC officials cautioned that the 110,000 homes in flooded areas may not all have taken on water, accounting for some of the discrepancy.

The new analysis makes clear that Livingston Parish was the hardest-hit parish, with a whopping 86.6 percent of its homes located in flooded areas. Just 21.7 percent Livingston Parish homes are covered by flood insurance, suggesting that perhaps three-fourths of those who flooded will be forced to go into debt or tap savings to rebuild.

That group, in Livingston Parish alone, could number in the tens of thousands, the analysis suggests.

Regionally, the data show there were about 52,896 flood insurance policies in effect – about half the estimated number of homes that flooded. But because some people with flood insurance did not experience flooding, the proportion of flood victims with flood insurance is probably far lower than 50 percent.

The good news is that the three parishes that appear to have suffered the most damage -- Livingston, East Baton Rouge and Ascension, according to the report -- are the ones with the highest proportion of insured people and the greatest number of flood policies. Still, BRAC’s numbers suggest that at least 42,000 households in those three parishes may have flooded and didn’t have insurance policies.

Across the capital region, an average of just 15 percent of households have flood insurance. The highest “take-up” rates are in Ascension and Livingston, at 23 and 22 percent, respectively.

BRAC’s analysis represents the first complex effort that attempts to measure the impact of the flooding that has ruined thousands of homes and forced thousands of families to evacuate to shelters across the region. As such, it comes with a series of caveats.

The biggest is that the analysis is not an actual count of damaged properties, but an estimate of how many might have flooded.

That may explain why BRAC data for West Baton Rouge Parish, for instance, suggests there was far more damage from flooding than there actually was. The report puts more than 3,000 homes in the “flood zone,” but West Baton Rouge Parish President Riley "Pee Wee" Berthelot told The Advocate that only approximately 30 homes received "minor damage" from flooding.

BRAC President and CEO Adam Knapp said that his agency's numbers should not be considered a damage estimate, which he said the Federal Emergency Management Agency will calculate. The $20.7 billion figure of the value of homes in flooded areas cited in the report is only meant to represent how much the homes are worth.

The chamber expects FEMA to calculate damages that cost far less.

"This is something that is always going to be a living analysis," Knapp said. "It could change today, it could change tomorrow, it's been changing over the course of the week."

Knapp also noted that the numbers for flooding in Ascension Parish are still in great flux and may rise, as flooding there has been ongoing throughout the week even as other parishes have started to dry.

It should come as no surprise that getting a fix on the extent of damage is taking some time. After Hurricane Katrina devastated New Orleans and the Gulf Coast in 2005, it took many months for local leaders to estimate how many homes had flooded and how much damage had occurred. Six months after the storm, state and federal officials were still squabbling over how many homes were damaged by Katrina and Rita, with the feds pegging the number at 167,000 and Louisiana leaders putting the number at around 212,000.

BRAC conducted its analysis by using geographic information system data of areas that were affected by the flood; the chamber counted the homes and residences that fall in the flood-affected areas.

"We're being careful not to say there are a specific number of damaged homes, but the number of potentially damaged is more than 2.5 times the number that we've been looking at thus far," Knapp said.

New flooding numbers that City Hall released Friday for East Baton Rouge Parish also do not sync up closely with BRAC's data. The city-parish data shows floodwaters inundated more than 58 percent of the parish over the past week, suggesting more than 50,000 homes flooded -- far more than what BRAC estimated.

City-parish officials and Knapp both said the City Hall data is more up-to-date and accurate. The city-parish gathered its information by using the 100-year floodplain map and adding data sets for calls for rescue, calls to 911, calls to 311 for flooding or sewer backups and more.

But like the BRAC data, the city-parish data does not assess precisely how many homes took on water, but rather how many homes are located in areas that were inundated.

Both the city-parish and BRAC are still trying to tweak their data to make it as accurate as possible, and asked for help from the public in doing so.

"We've already had comments from some people that were in the 100-year flood zone that did not receive any flooding," said city-parish Director of Information Services Eric Romero. He encouraged people to look at the map and point out incorrect information in it by emailing gis@brgov.com.

BRAC also estimated that more than 7,000 businesses that employ nearly 74,000 people are in flood-affected areas in the capital region.

The businesses in areas that flooded make up 21 percent of businesses in the overall area. The data shows that retail, construction, healthcare, manufacturing, and food and drink services are the hardest-hit sectors.

Staff Writer Terry L. Jones also contributed to this report.

Follow Andrea Gallo on Twitter, @aegallo.​