According to informal surveys following the February evacuations ordered in response to the Oroville Dam crisis, a large segment of the local population said they stayed at home rather than leave for higher ground.

From the looks of an inundation map created by graduate students at the UC Irvine Department of Civil and Environmental Engineering, those residents who stayed behind might have wanted to rethink things.

The recent study conducted by the graduate program forecasts the potential destruction that could have followed a complete failure of the emergency spillway at Lake Oroville.

"If you know the hazard you are potentially facing, you can make more informed decisions on how to protect yourself and your property," said Adam Luke, a graduate student who took part in the department's FloodRISE project.

The study showed that if Lake Oroville was completely full with a water elevation of about 901 feet on Feb. 12, and the emergency spillway failed, about 451,830 acre-feet of water would have rushed into the valley.

The map estimates the different areas that would have experienced the most destruction, or were threatened by the possibility of being washed away completely.

"The main goal is to show this type of information is technologically available," Luke said. "We are trying to show we can do a lot more for emergency response and planning, so people can have a better understanding of their area's risk."

The FloodRISE project, which is in its last year, is a four-year program funded by the National Science Foundation. Graduate students were tasked with creating inundation models that could potentially help counties and emergency responders with flood risk mitigation.

Luke said the grad program started the Lake Oroville study on Feb. 20, which took about two weeks to complete.

The flood simulation model is considered to be roughly 60-80 percent accurate, meaning it isn't intended for official planning purposes and cannot be relied upon in emergency planning, but Luke said it might help residents better understand potential risks.

"Because we didn't do detailed surveying of the levee systems in the area, it cannot be considered official," Luke said. "In order to make a map for official emergency responding and planning, you'd have to go into the study with accurate information about the levee system."

The study takes into account the average capacity of the system downstream — roughly 170,000 cubic feet per second can be held within the levees at a given time — and shows what would happen when water from the breached emergency spillway overtopped the levees.

"There are a couple reasons we are comfortable with what we did. One being the amount of water that would go through the breach is around 600,000 cfs," Luke said. "With the levee capabilities downstream, the map shows levees overtopping, though it's not a precise measure of elevations. But we expect that much water from a breach at the emergency spillway, so we expect the levees would overtop."

The study

The good news: Communities like Sutter, Olivehurst, Linda and Wheatland were forecast to experience little to no impacts from an emergency spillway breach. The bad news: Practically every other city and town along the river system from Biggs to just north of Sacramento County would experience flooding.

Areas along the Feather River, notably portions of Yuba City and Marysville, would see widespread structural home damage or, worse, homes being washed away completely. The power of the water would be great enough to crack concrete, cars would be displaced and people wouldn't be able to walk without being toppled.

Downtown areas in Yuba City and Marysville would be under more than 51⁄2 feet of water. For areas further away from the Feather River, water depth would range from about half a foot of water to about 2 feet of water, likely to erode exposed soils and even vegetated terrain.

It would take about four to eight hours for water to reach Biggs and Gridley, according to the inundation map. Yuba City and Marysville would experience flooding eight to 16 hours after an emergency spillway breach. After about 32 hours, water would have flowed around the northside of the Sutter Buttes and touched the Meridian area, as well as inundated Robbins and Nicolaus.

"It was interesting to see just how much water, the extent of flooding and how far down the Central Valley it would make it," Luke said. "I was surprised how close the water got to Sacramento. Also, the flooding projected for the Yuba-Sutter area was also surprising because before running the models you just don't really know the extent of things."

Useful, not official

At the time of the Feb. 12 evacuation, Sutter County public information officer Chuck Smith said the only inundation maps that were available to the public involved a failure of the actual dam.

It wasn't until after the incident occurred when the Department of Water Resources created an inundation map for the emergency spillway, which hasn't been released to the public, Smith said. Still, he said the public shouldn't assume either map is 100 percent correct.

"What's important is that this type of technology is out there, and I think if people were to spend some time thinking a little more about these scenarios it would be a good thing," Smith said. "But the map shouldn't be relied upon by people to make decisions on whether or not to leave, because a lot of things could happen that cannot be accounted for."

Smith said the UC Irvine map doesn't take into account the high water that was already in the Feather River at the time of the emergency evacuation — approximately 85,000 cfs. Also, he said the modeling assumes the water would only overtop the levees and not cause a breach.

"If water overtops the levee, it's going to erode and break, so it's hard to really know where water is going to go and how fast it is going to get there," Smith said.

Aside from the many variables that cannot be demonstrated in such a map, Smith said these types of inundation maps are important because they could end up saving someone's life.

"I think it's a noble effort to create this," Smith said. "It's like an emergency plan itself. You have a plan and you try and work it, but things don't always happen according to the plan."

CONTACT Jake Abbott at 749-4769 and on Twitter (@JakeAbbott_AD).

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