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Oroville Dam

What We’ve Learned From California’s 2017 Floods So Far

Heavy rains in the last few weeks have caused severe localized flooding and tested the strength of California’s levees and dams. As we take stock of all the events, some important lessons have emerged, writes U.C. Davis’ Jay Lund.

Written by Jay Lund Published on Read time Approx. 4 minutes
This aerial view on February 15, 2017, looks east toward Oroville Dam and Lake Oroville, showing the damaged spillway with its outflow of 100,000 cubic feet per second at the Butte County site.Dale Kolke, California Dept. of Water Resources

What a wild water month! Floods, spillway damage and levee failures! Mass evacuations!

And Donald Trump and Barack Obama are not even remotely to blame!

Flood control and preparation are vitally important for California. Now we remember.

This year, we see California’s raw, boisterous and often irresistible flood potential. And we see the value and cost for being prepared for floods, even in dry years.

Here are some recent flood observations.

Oroville Spillway

Size matters. Recent flows at for Oroville spillway are 50,000 cfs (cubic feet per second), a modest flood flow. This flow is equivalent to about 200,000 basketballs of volume or 3.1 million pounds of water per second. Few structures can resist such assaults for long, and people should stay away from this.

The safety and prosperity of nearly 200,000 people along the Feather River rely on Oroville Dam’s spillways. Today, all water outlets from Oroville Dam are damaged or inoperable – reducing downstream flood safety for the first time since the dam was completed in 1968. Fortunately, enough spillway capacity has remained to draw the lake down to near-normal levels, for now. Lake Oroville’s spillway conditions will remain a nail-biter for operators, officials and downstream residents for the remaining months of this wet season and perhaps through spring snowmelt.

Our flood control system clearly needs sustained attention, overall. The governor seems to agree.

Retrospectives of the Oroville failures will examine the many decisions and events that led to this month’s frightening conditions. Past inspections, comments and criticisms will be poured over. But not all comments are damning. Most reflect normal professional thinking needed to drive and inform discussions of safety and costs to support immediate and long-term improvements. Dam operators and engineers should specifically identify urgent concerns. But public safety can be compromised if reactions to professional reports and concerns become hypersensitized, muting depth and long-term detailed reporting. Complete reports from experts and frank discussion of dam risks, objectives, maintenance and updates are vital for effective long-term flood protection.

Building on California’s existing dam safety program, funding is needed to assess and upgrade the state’s dams, spillways and outlet works, and update many flood operation manuals. Such funding should be sustained, since dam safety and periodic upgrades are not one-time expenses. California has a poor record of sustainable funding for flood control, relying on irregular pulses of bond funds.

The Oroville situation deserves attention, but not panic. It is going to be a long winter at Oroville, but the situation is under some control for now and good people are working on it.

Delta Levees

Two Delta islands have flooded so far this year (Van Sickle and McCormack-Williamson). Tyler Island was narrowly saved, after an evacuation order. The Delta’s subsided islands remain subject to flooding. Fortunately, the counties and state have allowed little housing in these low places. The two islands flooding this year were being considered for restoration as tidal habitat anyway. Liberty Island, which accidentally flooded in 1998, has become one of the Delta’s most successful habitat restoration “actions.” Perhaps this year’s Delta flooding is an opportunity to save some time and money. Continued vigilance is needed to keep remaining islands afloat, and judicious (and alas perhaps judicial) decisions will be needed for making island repairs – or not. Our response to Delta island failures is a primary mechanism for Delta policy, as we sometimes fail into long-term policies.

Local Flooding

The northern California town of Maxwell flooded and I-5 partially shut down. Last week, parts of San Jose’s Coyote Creek flooded homes and forced evacuation of 14,000 people. These are sizable local disasters. Wet years like this also bring tremendous local flooding of streets, roads and drainage systems, erosion of canals and banks as well as landslides affecting roads and buildings, etc. These damages are individually less than the flooding of neighborhoods, but are quite common, with sizable costs to cities, counties and state-wide. Local governments pay most of these costs through utility fees and tax revenues. Tallying such local costs is often neglected, but these costs add up substantially across the state. Over time, local funding has become harder. The state needs to facilitate the abilities of local governments to solve and raise funds for local problems – Proposition 218 poses special problems for local flood management.

Main Flood Systems

California’s flood systems are enormous, elaborate and, so far, mostly functioning well in this extraordinary wet year (Oroville being the big exception). With so much rain and snow, the wettest on record so far, some flooding will happen and some levees and other flood infrastructure will break or be damaged. But local and state authorities have responded well. Many reservoirs and rivers are near their normal flood release and storage capacities, and some have exceeded flood channel capacities (such as New Don Pedro and the Lower San Joaquin River).

So far, flooding downstream of New Don Pedro seems mostly agricultural and is less severe than in 1997. But the San Joaquin Valley has been reminded that it faces a sizable flood threat, and some environmental opportunities from restoring floodplain habitat. Flooding poses special safety challenges for urbanization in low-lying parts of San Joaquin County.

The Sacramento Valley’s Yolo Bypass (built mostly in the 1920s) is inundated, but is running at about half of its design capacity. Fremont weir, the bypass’ largest inflow, is currently at 160,000 cfs (five thousand tons of water per second), about half of its capacity. Major reservoirs have little empty storage. Things are moderately tight, and being actively inspected and managed.

Lessons So Far

Two months of this wet season remain, followed by a sizable snowmelt. Continued vigilance is needed, like every winter since the founding of California.

This is a good year for state and local policymakers to think about how to improve base funding for local, regional and state flood control, and how major flood infrastructure should be assessed, repaired, upgraded and funded, long-term.

The views expressed in this article belong to the author and do not necessarily reflect the editorial policy of Water Deeply.

This story first appeared on California Water Blog, published by the U.C. Davis Center for Watershed Sciences.

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