Floods are a serious threat to Southern California, say C.S.U.F. geologists

http://www.ocregister.com/2017/09/19/floods-are-a-serious-threat-to-southern-california-say-csuf-geologists/Opens in new window

Dr. Matthew Kirby and Dr. Joe Carlin

September 19, 2017

Seeing the devastation that Hurricanes Harvey and Irma inflicted, it’s tempting to take solace that Southern California escapes anything but the rare remnant of a tropical storm.

But that doesn’t mean we’re spared flooding, reminded two Cal State Fullerton geologists in the wake of Harvey and Irma.

Our water events might not have names, but they can wreak havoc on our beaches, canyons and low-lying communities. Just ask anyone who lived here in 1938.

The 1938 storm dropped 8 inches of rain in the days leading up to March 3, when the Santa Ana River overflowed its banks. The storm affected the entire region, including Fullerton, Placentia and Los Angeles, but Anaheim was particularly hard hit.

“Floods are a serious threat to our region,” said Matthew E. Kirby, professor of geological sciences, after Hurricane Harvey left vast swaths of Texas underwater. “Land-falling hurricanes are highly unlikely in Southern California, but they are not out of the realm of possibility.”

A bigger threat comes from large atmospheric rivers connected to Pacific Ocean-sourced winter cyclones, Kirby said. These rivers of water in the sky contain huge amounts of vapor and usually bring heavy precipitation to the West Coast.

Several such events occurred earlier this year, ending the state’s five-year drought while dropping massive quantities of water that often had nowhere to go.

In 1938, five days of rain bloated the Santa Ana River, sending it spilling over its banks, killing about 100 people in the region, sending cows paddling down streets and wiping out entire neighborhoods. The Prado Dam is one legacy of the disaster.

Southern California’s low-lying areas adjacent to river channels, creeks and flood-control basins or downstream from dams, as well as coastal areas, are most vulnerable to flooding, noted Joe Carlin, assistant professor of geological sciences. Carlin, a Dallas native, in 2015 investigated flood deposits in the Gulf of Mexico from the Brazos River, which flows west of Houston and experienced record flooding due to Hurricane Harvey.

C.S.U.F. researchers are studying California’s water history, including floods and droughts, to better understand the region’s risks.

“Perhaps the most important lesson we can learn is rather than being worried about it, we need to recognize this risk and be prepared,” Carlin said.

The two men are collaborating with C.S.U.F. mathematics faculty members Kevin Nichols and Reza Ramezan and U.C.L.A. geography professor Glen MacDonald on a three-year research project to reconstruct the history of floods, drought, fire and vegetation in California over the past 3,000 years.

C.S.U.F. students Judith Avila, left, and Jenifer Leidelmeijer, right, with Jiwoo Han, a doctoral student from U.C.L.A., prep a sediment core retrieved from Barley Lake in the Mendocino National Forest. The students, with C.S.U.F. geological sciences faculty members Matthew E. Kirby and Joe Carlin, conducted field work in August as part of a collaborative National Science Foundation-funded research project with U.C.L.A. to reconstruct the history of floods, drought, fire and vegetation in California over the past 3,000 years.
Funded by a nearly $550,000 joint grant from the National Science Foundation, the team in August conducted its first season of fieldwork for the project at Barley Lake in the Mendocino National Forest.

“In this latest study, we’ll look into whether large floods produced precipitation events more frequently during past wet climates,” Kirby said. “How global climate change will change flood risk or probability in Southern California remains a debate.”

Other flood research at Cal State Fullerton includes:

–Carlin and his students are working on a project in Upper Newport Bay to determine whether sedimentation in marshes and mudflats is sufficient to keep pace with sea-level rise.

–Kirby, who studies the history of precipitation in California, is investigating lake and wetland mud sediments. His N.S.F.-funded research focuses on understanding the past 10,000 years of the state’s water history — why and how water varies across the state.

–Geology grad student Jen Palermo is working on a Southern California flood history using sediments from Crystal Lake in the San Gabriel Mountains.

–Kirby and his students also have submitted a journal paper documenting a large flood event in Lake Elsinore about 4,800 years ago.

“It is highly likely that this flood is larger than anything we’ve seen in the historical record (in Southern California),” Kirby said.