Vallejo Times-Herald


How Vallejo stays low, dry
City no desert, but has a lot of factors allowing for minimal heavy rain damage


By MATTHIAS GAFNI/Times-Herald staff writer
Vallejo Times Herald
Sunday, January 8, 2006


First in a two-part series

Precariously close to the ever-flooding Napa River and near the mouth of the Sacramento Delta and its crumbling levee system, at a measly 60 feet above sea level, sits Vallejo.

Seemingly a prime target for monumental flooding, Vallejo has, so far at least, managed to avoid catastrophic deluges.

In last weekend's intense rainstorm, Vallejo suffered flooding, $1.86 million worth in damages, according to the Solano County Office of Emergency Services. However, compared to nearby Vacaville's $25.8 million, Fairfield's $23.5 million and Napa County's $135 million in losses, Vallejo escaped relatively unscathed.

So, how has Vallejo avoided major flood woes, while its neighbors suffer so? Some of it's luck, some foresight and some learning from past mistakes.

In a post-Hurricane Katrina world, with an intense microscope on areas with levees and man-made infrastructure protecting people from water, Vallejo finds itself surprisingly unaffected.

With few levees nearby, Vallejo's biggest concerns lie with levees protecting half of its drinking water in the Delta and farmland its agency owns. Nothing life threatening.

Lake Chabot Dam once caused great concern in Vallejo, threatening a subdivision of thousands below it, but improvements have negated concerns.

Nature helped ease pressure from the Napa River, with bounties of wetlands providing a flood barrier and crucial environment for endangered species. However, the new formidable Highway 37 may have provided the ultimate levee protecting the city's northwest shore from the Napa River.

All in all, Vallejo officials feel confident that the city will hold up if a catastrophic flood hits the region.

Napa River

Every winter it rains and the Napa River reaches its banks. And more often than residents care for, the river spills over its banks. So much so that Napa is in the middle of a $255 million flood control project that likely won't be completed until 2011.Considering Napa County suffered an estimated $135 million in damages just from last weekend's rains, it may seem like a bargain.

That same flood-prone river moves south through Napa and American Canyon and empties into Mare Island Strait at Vallejo.

So, how has Vallejo dodged the Napa River flooding? Well, it has and it hasn't. Vallejo has topography on its side.

While the Napa River forms a C-shape around the city of Napa and often bottlenecks under low-lying bridges, the body of water straightens and widens at Vallejo, says Ron Matheson, Vallejo Sanitation and Flood District manager.

The river also has the luxury of surrounding wetlands reaching out to Sears Point.

Even with the geographical advantages, Vallejo hasn't always dodged the brown Napa River.

White Slough

In the early 1960s, the wetlands along Highway 37 between Sacramento Street and Sonoma Boulevard were dry and served as a small local airport. The Napa River had no access to the area: it was completely blocked by levees.

Later in the 1960s, there was a breach of those levees, flooding the White Slough area. The Army Corps of Engineers cleaned up and fixed the levee. Again in the 1970s, the levee was breached, flooding the area. Again the Corps fixed it. However, they told the local property owners it would be their responsibility from then on, Matheson said.

Finally, in the late 1970s, the levee was breached again, and water filled the empty White Slough land. The water remained for over a year, officially making it a federal wetlands, Matheson said, providing it numerous environmental protections.

Property owners still own land in White Slough, Matheson said, however it's all permanently submerged.

Environmentally, the addition of White Slough was vital for endangered species, Matheson said. The largest environment for the California Clapper rail is in White Slough, he said.

"It's surprising how rapidly it went back to nature," Matheson said.

As wetlands, White Slough provides a quasi-flood plain for any spillage from the Napa River, along with acres of wetlands west toward Sears Point.

"Our saving grace is Caltrans came in and built Highway 37 so big that it's protecting us and we won't face a flooding issue," said Matheson, who's worked 26 years for the flood district. "Highway 37 would have to fail and it's a large man-made structure and couldn't fail, I believe."

Caltrans also added a state-of-the-art culvert system under Highway 37 to allow tidal influences on White Slough.

Those wetlands still get large amounts of water during heavy storms, but the east side, along Sonoma Boulevard, was built up to prevent flooding there.

Lake Chabot Dam

During the city's last 100-year flood in 1982, Lake Chabot dam spilled over its banks, causing significant flooding in the Lofas subdivision below. Residents were forced to flee homes by boat, and panic arose when reports of the dam breaking surfaced.

The dam never collapsed, but city and state officials quickly worked to shore it up.

Again, during heavy storms in 1986, media began reporting that Lake Chabot Dam may burst after hearing police and fire radio traffic calling for immediate evacuations because of an impending break.

Residents frantically left their homes throughout the area, finding out later that the dam was not breaking.

The dam was built in 1870 to create Lake Chabot, early Vallejoans' first drinking water system. The dam lies at the north tip of Lake Chabot, along Dan Foley Park and Six Flags Marine World.

The dam is 47 feet high, with a capacity of 504 acre feet of water and a reservoir area of 61 acres. It's an earth-filled dam, instead of a concrete dam. Water feeds into Lake Chabot through Blue Rock Springs Creek.

After the 1971 San Fernando Valley earthquake, the state began looking at old dams across California, Fred Sage, state Division of Safety of Dams' chief of field branch, said.

"We found that many dams were not built to modern earthquake standards," Sage said.

Lake Chabot dam was one. In the late 1970s, crews reinforced the lower section with a berm, basically compacting dirt on top to make it thicker, Sage said.

Following the overflow during the 1982 floods, the dam's spillway was strengthened. Flood district trustees also voted to create a larger storm drainage system to move the spillway water quickly out of the Lofas neighborhood.

Now, the dam is completely safe, Sage says.

"There's nothing wrong with the dam. It should be able to pass any flood," Sage said.

Sage and his agency inspect the dam every year, checking for plant growth, rodent activity, erosion and anything else that could weaken the dirt structure.

During inspections, the state can mark deficiencies in the dam. Lake Chabot dam has no such deficiencies, Sage said.

Of the 1,200 dams Sage's agency inspects throughout the state, none of the Solano County dams appear on the agency's problem dam list.

The nearest trouble dam is the Milliken Creek Dam above the Napa River. That dam, owned by the city of Napa, is under water restriction.

Eight miles northeast of Napa, off Highway 121, the concrete arch dam is restricted from holding too much water out of stability concerns in the event of an earthquake, Sage said.

"A historic fill could be a problem. At a restricted level it should not be a problem. The water pressure is low enough," Sage said.

If the dam were breached, the water would flow down into the upper Napa River and surrounding communities, Sage said.

Levees

The levee breaks in New Orleans after last year's Hurricane Katrina and subsequent loss of human life, and recent Bay Area floods have local officials scrambling to secure the state's aging Delta levee system.

In Thursday's State of the State Address, Gov. Arnold Schwarzenegger outlined a massive infrastructure bond that would send $35 billion to improving flood control and water supplies.

Despite all public safety concerns over levee breaks, residents of Vallejo have little to fear, officials say.

"I don't think anything would really impact Vallejo if we had a Delta levee failure," Matheson said. "No levees protect the people in the city of Vallejo."

However, the area's drinking water could suffer from a breach near the Northbay Aqueduct. But Vallejo only gets half its drinking water from that regional water hub near Travis Air Force Base. The other half comes from a relatively safe Lake Berry-essa. (see page ??, for related story)

One of Matheson's biggest levee concerns doesn't even lie within Vallejo's city limits. The Vallejo Sanitation and Flood District owns 1,800 acres of farmland near Sears Point that 100-year-old levees protect from Sonoma and Tulay creeks and San Pablo Bay.

The district contracts a farmer to grow wheat on the farm land, netting the agency about $100,000 a year. In addition, the district can truck sludge from its wastewater facility to the farm, which uses it as fertilizer.

By not having to truck those bio-solids to an out-of-town dump, the district saves about $900,000 a year, Matheson said, keeping Vallejo sewer rates low.

So, the farmland is a $1 million-a-year cash crop, so to speak.

However, the levees are fragile. The farmer maintains and keeps watch on most of the levees, on the district's dime.

"He's fairly vigilant with the levee. He's the eyes and ears out there," Matheson said.

About a decade ago, Matheson said the farmland suffered a major levee failure during a set of major storms.

"It flooded the whole island. We had zero crops that year," Matheson said.

"If we lost that island it would cost us $1 million a year in additional costs because we'd have to haul (sludge) to a landfill," Matheson said.

All things considered, Matheson said the levees are in "pretty good shape." "We work on them every couple of years," he said, adding the levees fared fine in the recent rains.

Flood zones

Vallejoans may not have to worry about getting rescued off their rooftops from helicopters like New Orleans flood victims, but that doesn't mean there still isn't inconvenient and even costly flooding in this city.

The flood district received about 20 different claims from flooded residences and businesses from last weekend's storm, Matheson said.

Most of those were in the Hampshire and Mississippi streets neighborhood, off Couch Street. "It's simply a low spot," Matheson said. "And there was too much rain."

A past problem area, Lake Dalwigk, off Curtola Parkway, poses a limited threat now, Matheson said. In the past, the lake - which serves as a flood basin before water can be piped into Mare Island Strait - has flooded, leaving up to 6 feet of water in the surrounding Lemon Street neighborhood.

Since the flood district widened and drained the lake, and created a larger storm channel to the strait, Lake Dalwigk has behaved, Matheson said.

Sandy Beach, an unincorporated strip of dozens of homes along Mare Island Strait, still receives landslides from the cliff above them, Matheson said.

To coordinate which areas of Vallejo are vulnerable, the Federal Emergency Management Agency (FEMA) designates cities' flood zones.

"They are areas in town that would flood in a 100-year storm," City Engineer Gary Leach said. "As improvements are made, they can be taken out of flood zones too."

The zones aren't an exact indicator either, he said. "A lot of those areas (in the flood zone) have never flooded and some areas that flood a lot aren't named in flood zones," Leach said.

However, a flood zone designation means if you own a home there, the mortgage company usually requires you to have flood insurance.

E-mail Matthias Gafni at mgafni@thnewsnet.com or call 553-6825.


http://www.timesheraldonline.com/portlet/article/html/fragments/print_article.jsp?article=3383460