As Governor Jerry Brown asks for additional federal assistance following February’s heavy storms, a larger question looms as to how California should pay to repair – and improve – its defense against floods.

In the request dated March 19, Brown asked President Donald Trump to declare a major disaster for the state, estimating the total damage at more than $539 million.

That sum, however, represents just a fraction of the billions of dollars experts say are needed to protect Californians from the threat of flood.

According to “California’s Flood Future,” a 2013 joint report from the state’s Department of Water Resources and the U.S. Army Corps of Engineers, one in five Californians live in an area at risk for flood

For Oroville resident William Bynum, the threat of flood is more than a distant hypothetical.

Bynum was forced to evacuate in February, when the security of the nearby Oroville Dam was threatened. The dam’s spillways were eroding, threatening to unleash a 30-foot wall of water on downstream communities.

Nearly 200,000 people were subject to the emergency evacuation order.

“We were looking at the dam when we got the phone call saying we needed to get out in 45 minutes,” Bynum said. “When we got here, our car got stuck in the mud, so we couldn’t load our horses. My wife’s panicking … her daughter’s panicking.”

Bynum said it took three trips back to their Oroville ranch the next day to evacuate their horses. But even though the waters have subsided, emotions still run high.

“What really frustrates me is I don’t think anything is really going to be done about it,” Bynum said.

At the state capitol, leaders are reacting to February’s storms with a slate of actions.

In late February, Senate President Pro Tem Kevin de Leon amended SB-5, a bill that, if approved by voters, would provide $500 million for flood protection and repairs.

“I’m not a keen expert on the projections as to what it’s going to take, but half a billion dollars — $500 million – is a good sum to put up right now,” de Leon told ABC10 News.

The day after de Leon introduced the changes to SB-5, Brown announced a four-point plan for dam safety and flood protection that would include $437 million in flood control and emergency response actions.

Nearly $1 billion in combined emergency funding sounds like a lot of money – and it is. But state agency officials and public policy experts warn that what California really needs, more than an emergency bandage, is sustainable funding to repair and improve the state’s aging infrastructure on a continual, ongoing basis.

“All is unknown how we’re going to get that funding, because the numbers are so large,” said Jeffrey Mount, Public Policy Institute of California senior fellow.

Mount’s organization has estimated that there’s a funding gap in the state for flood control and protection ranging from $800 million to $1 billion each year.

The Department of Water Resources and Army Corps of Engineers report, “California’s Flood Future,” identified the “immediate need for more than $50 billion” to complete currently identified flood management projects at local, state and federal agencies.

Meanwhile, the Central Valley Flood Protection Plan (CVFPP), updated in December, says the region, which includes the Sacramento and San Joaquin river basins, will need $17 to $21 billion in investments over the next three decades.

Bond funding has allowed agencies to spend more on flood projects since 2007, but that source of funding is set to dry up shortly.

The Central Valley Flood Protection Board, which oversaw the development of the protection plan, says current funding mechanisms at historical spending levels could provide $4 to $5 billion – less than a quarter of what the board has said it needs over the next 30 years.

“You’ve got to have a revenue stream which is reliable, long-term and large,” Mount agreed.

The Central Valley Flood Protection Plan calls for more spending from existing sources, like increasing contributions from the state general fund, as well as instituting new funding mechanisms, such as a state flood insurance program and a river basin assessment program.

Additionally, the plan says it depends on “successfully passing new State bonds with unprecedented amounts and frequency for flood management investments.”

While politicians have moved quickly in the wake of February’s storms, there is reason to doubt the commitment to creating new, long-term plans for spending.

“Twenty-one billion dollars over 30 years is obviously a lot of money,” de Leon told ABC10 News when asked whether the CVFPP’s goals sounded feasible. “I think we should take a comprehensive review – make sure to deal with the most immediate, pressing needs right now, which is why we need to move that $500 million, then take a look at the rest of California, Central Valley, and elsewhere.”

Put aside the fact that the CVFPP is supposed to be that comprehensive review. Historically, the state has not executed on long-term plans as well as many experts would like.

“The problem is that we get everyone’s attention when we see the water as high as it is right now, but when you’re in a drought, it’s hard to convince people to put a priority on flood work,” Chris Unkel said. Unkel is with the advocacy group American Rivers.

Mount says he’s optimistic now that flood protection has the attention of the legislature, but also points to the year 1997 – a year of devastating floods from northern to central California. Despite an estimated $2 billion in damages, it took nearly a decade – and Hurricane Katrina – for California to pass flood legislation to repair its aging levees.

“What they failed to do in 2006 was come up with a flood mechanism to improve this system,” Mount said. “What I’m hopeful now is that 10 years later, we have another year miss, but the legislature will wake up and come up with a funding system.”

The experts agree that the window of time for action is short – and growing shorter.

“The flood-memory half-life is short – if history shows, it’s about nine months,” Mount said. “There’s about a nine-month period in which, if the legislature does not act, we will move on to other problems.”