Flood insurance reforms, set to take effect Oct. 1, may make it impossible for some homeowners in Marion and Mattapoisett’s waterfront communities to afford insurance as annual rates could climb to $20,000 per year — or perhaps more.

To rein in the taxpayer cost of the National Flood Insurance Program, the Biggert-Waters Flood Insurance Reform Act dropped two key provisions that kept rates where they are now. Flood insurance will no longer be subsidized by tax dollars for homes that pre-date the flood insurance program. And homes that met flood-zone requirements when they were built, but have since been placed in a higher risk flood zone, will no longer be “grandfathered” in to previous insurance rates.

To Congresspeople sitting in Washington, that simply meant that everyone will be paying for insurance based on the actual risk posed to each actual home. To homeowners in Marion Village, Crescent Beach in Mattapoisett, and other neighborhoods, it could mean a 2014 flood insurance bill that dwarfs other insurance and property tax costs combined.

Blame global warming or just a stretch of freaky, vicious weather, but the cost to the federal government of insuring coastal property has skyrocketed.

Because of the risk involved in flood insurance, it is only offered through the federal government program. As Katrina flattened New Orleans and Sandy swept into New York and New Jersey, insurance claims made it clear that flood insurance premiums were insufficient to cover the costs.

The Federal Emergency Management Agency estimates that homeowners will only see premiums higher than $20,000 “in rare cases,” but local insurance agents say if the program is not revised, homeowners in the South Coast area will likely see premiums in excess of $20,000.

“I think it’s absolutely devastating to the economy, and we need change,” said David Dunn, who runs G.H. Dunn Insurance locations in West Wareham, Mattapoisett, and Buzzards Bay.

U.S. Rep. Bill Keating (D) said lawmakers must craft legislation that would properly fund the flood insurance program while providing relief for homeowners

“As someone who has heard from families in Southeastern Massachusetts seeing premium increases, I believe more work is needed to ensure the solvency and affordability of the flood insurance program,” said Keating.

“Yet, I am disappointed to see that many homeowners will face sudden devastating hikes to flood insurance rates. While there is no question that a comprehensive long-term solution is needed, we need immediate action to help homeowners in Massachusetts and across the country.”

Keating co-sponsored the Flood Insurance Implementation Reform bill (H.R. 2199), which would delay some legislation provisions if passed. Oddly enough, U.S. Rep. Maxine Waters (Calif.) – co-author of the original legislation – has also joined the Flood Insurance Reform bill as a co-sponsor.

The bill would allow homeowners to avoid the impending rate increases, according to Keating’s spokeswoman Ganesan Annamalai. Just how much rates will increase depends on the property. Homeowners’ whose primary home pre-dates the flood insurance program will keep their current subsidy until their property is sold or their policy lapses.

For owners of secondary homes that pre-date the flood insurance program, annual flood insurance rates will increase by 25 percent until rates reach what FEMA deems is a necessary premium for the property’s risk of flooding.

When their flood insurance plans expire, homeowners will be required to get an elevation certificate from a surveyor, which, in essence, ensures the building is properly elevated.

Homeowners will have to foot the bill for the elevation certificate, which can cost $700 to $1,000, and bring it to an insurance company to receive a new rate.

While flooding insurance is optional for those who own their homes outright, all mortgage-holders require that mortgaged properties most susceptible to flooding be insured, making the program particularly worrisome for homeowners on tight budgets.

Jim Austin, of Cape Cod Five Cents Savings Bank’s Marion office, says he recently sold a mortgage to someone who purchased in a flood zone, but cautioned the client that insurance rates will increase due to Biggert-Waters.

“We should be concerned because this law is going to take somebody’s housing cost and throw it right through the roof,” said Austin. But the program, if not revised,  will make it more difficult for homeowners to sell their homes.

Adding insult to injury, homebuyers currently have the option to “buy in” to the previous owner’s subsidized flood insurance rate until the policy expires, but once the policy expires, the new rates go into effect.

The legislation comes on the heels of the recent redrawing of flood insurance maps, which put many homeowners in a higher risk flood zone, and thus, made  their homes more expensive to insure.

Some residents have already dropped coverage. Longtime Crescent Beach resident Russ Gleason cancelled his policy last year when faced with a 33 percent increase not tied to the new law.

Gleason, who owned the property since 1942, said the cost of insurance was higher than the risk he faced from bad weather: “If a hurricane comes - our house is 15 feet up - then God is telling me to get out of here.”

For more information, visit the National Flood Insurance Program’s website, www.floodsmart.gov.