Accounting for Water in the San Joaquin Valley

SJV ave balance

Water Balance Inflow/Outflow Diagram (from Excel File). Parameter and source calculation details are explained in Appendix A of “Water Stress and a Changing San Joaquin Valley (PPIC, 2017)

by Brad Arnold1, Alvar Escriva-Bou1,2, Jay Lund1, and Ellen Hanak2

  1. University of California – Davis, Center for Watershed Sciences
  2. Public Policy Institute of California

Accounting for water supplies and uses is fundamental to good water management, but it is often difficult and controversial to implement. As with other types of accounting, this task is harder and costlier when information is not well organized.

Here we present a 30-year set of water balances for the San Joaquin Valley, California’s largest agricultural region and home to more than half of the state’s irrigated acreage. The valley has multiple sources of surface water and is the largest user of groundwater in California. Of particular interest in this region is understanding the extent of long-term depletion of water stored in aquifers (overdraft). This practice will need to be curbed as water users implement the Sustainable Groundwater Management Act (SGMA). Ending overdraft can be achieved by augmenting other water supplies and reducing net water use.

Annual estimates for water use and availability are available from California’s Department of Water Resources (DWR) and the U.S. Bureau of Reclamation (USBR). However, this information is often difficult to navigate and piece together, and has some important gaps. State water balances (e.g., DWR Bulletin 160 – California Water Plan Updates) are sometimes hindered by missing or inadequate data. They also are produced with significant lags; the state’s last published water balances are for 2010, and do not include any of the latest drought years.

To develop a high-level, up-to-date picture of water supplies and uses in the valley, we combined available public data to develop estimates of annual regional water balances for the years 1986 to 2015. Similar exercises should be done at the sub-basin and hydrologic region scales to enable local water users to develop and implement plans for bringing their basins into long-term balance under SGMA, using these balance data and information as planning tools.

The downloadable Excel file contains annual data, calculations, and sources (a detailed description of data and methods is provided in Technical Appendix A of PPIC, 2017). Changes in groundwater storage are calculated as the residual in the water balance—the difference between other water supplies and net water use. Total net water supply— from local and imported inflows, precipitation, and changes in storage (including groundwater overdraft or recharge)—must equal the sum of net water used or stored within the valley (in surface reservoirs and aquifers) plus exports and outflows.

These annual data show:

  • Local inflows from Sierra Nevada watersheds vary wildly between years, and drive regional groundwater pumping;
  • Net or “consumptive” water use—the water consumed by people or plants, evaporated into the air, or discharged into saline water bodies or groundwater basins—is fairly constant across these years. In drier years, stored surface water and groundwater pumping supplement annual inflows;
  • Variance in Delta imports from the State Water Project (SWP) and the Central Valley Project (CVP) is largely independent of other valley conditions. These imports are affected by water conditions in the Sacramento Valley, Delta pumping regulations, and water demand in other importing regions (especially Southern California);
  • San Joaquin River outflows also vary significantly, reflecting variable inflows from the Sierra Nevada watershed, as well as changes over time in environmental and water quality regulations on valley outflows.
  • Differences between annual water supplies and net water use result in changes in surface and groundwater storage. Wet years tend to increase storage and dry years tend to draw more water from reservoirs and aquifers.
Annual SJV balances

Annual Valley Inflow/Outflow Data.  Slight differences in totals are from changes in surface reservoir storage (not shown).

In most years, consumptive water use exceeds local surface and groundwater inflows, leading to overdraft of groundwater and concerns for long-term water use sustainability.  Valley-wide, just a few wet years saw net groundwater recharge. The 30-year average annual groundwater overdraft is roughly 1.8 million acre-feet per year (MAF/yr). It averaged 2.2 MAF/yr from 2001-2015—the driest 15-year period since the 1920s. Local watershed inflows average about 55 percent of total inflow; Bay-Delta inflows from SWP and CVP imports average about 25 percent of supplies, and direct diversions from the Delta by north-valley water users about 6 percent. Average shares of water sources in the San Joaquin Valley are in the charts below.

SJV water supply mix

San Joaquin Valley Annual Water Supply Breakdown (Periodic Averages). 
“Local supplies” indicates inflows from the Central and Southern Sierra Nevada and precipitation on the valley floor.

Our recent report, Water Stress and a Changing San Joaquin Valley, describes a range of approaches for bringing the valley’s water accounts into long-term balance. A variety of factors, including SGMA, water market opportunities, water rights, and other regulatory and management decisions, will lead water managers to rely increasingly on water accounting at the basin and sub-basin levels.

The valley’s overall dryness and the high variability between drought and wet years require better long-term water planning and more robust water accounting. Better water data collection and management—that is both more timely and transparent—is an important government role that will require stakeholders’ support. Improved accounting methods and data analysis across state and local agencies—as is common in several other western states—can facilitate better water management in this important region.

Excel File Notes:

  • Remember to ‘Enable Macros’ if prompted.
  • Sheets and workbook are protected to avoid accidental changes. As such, source data sheets are shown but formulas cannot be edited.

Further Reading:

Alvar Escriva-Bou, Henry McCann, Ellen Hanak, Jay Lund, Brian Gray (2016). Accounting for California’s Water. 28 pp. Public Policy Institute of California, San Francisco, CA.

Alvar Escriva-Bou, Henry McCann, Elisa Blanco, Brian Gray, Ellen Hanak, Jay Lund, Bonnie Magnuson-Skeels, and Andrew Tweet (2016). Accounting for Water in Dry Regions: A Comparative Review. 177 pp. Public Policy Institute of California, San Francisco, CA.

Ellen Hanak, Jay Lund, Brad Arnold, Alvar Escriva-Bou, Brian Gray, Sarge Green, Thomas Harter, Richard Howitt, Duncan MacEwan, Josué Medellín-Azuara, Peter Moyle, and Nathaniel Seavy (2017). Water Stress and a Changing San Joaquin Valley. 48 pp. Public Policy Institute of California, San Francisco, CA.

Jay Lund (2016). “Better Accounting Begets Better Water Management.” California WaterBlog.

Jay Lund (2016). “How Much Water was Pumped from the Delta’s Banks Pumping Plant? A Mystery.” California WaterBlog.

California Department of Water Resources (2013). Bulletin 160: California Water Plan Update 2013, Volume 2: Regional Reports – San Joaquin River Hydrologic Region. Division of Statewide Integrated Water Management: Strategic Water Planning.

California Department of Water Resources (2013). Bulletin 160: California Water Plan Update 2013, Volume 2: Regional Reports – Tulare Lake Hydrologic Region. Division of Statewide Integrated Water Management: Strategic Water Planning.

Posted in Uncategorized | 2 Comments

California’s drought and floods are over and just beginning

California is weird

California’s weather is weird and wild.  California has more extreme precipitation years (dry and wet) per average year that any other state.  Coefficient of variation for annual precipitation at weather stations for 1951-2008.  Larger values have greater year-to-year variability. SOURCE: M. Dettinger, et al. 2011. “Atmospheric Rivers, Floods and the Water Resources of California.” Water 3(2), 445-478.

By Jay Lund 

California is a land of extremes – where preparing for extremes must be constant and eternal.

The last six years demonstrated California’s precipitation extremes. From 2012-2015, California endured one of its driest years of record.  2016 was an additional near-average year, classified into drought because water storage levels were so low.

2017 will likely be the wettest year on record in northern California and one of the wettest years ever in most of California.  Most of California has over 160% of average precipitation, with over 150% of average snowpack. Reservoirs today are about 2 million acre feet above their long-term average for this date (having been about 8 million acre ft below average 2 years ago).

After wondering for years if the drought would end, the drought is definitively over, even as some impacts to forests, fish populations, and groundwater levels will persist for decades.  Last Friday, Governor Brown lifted his drought emergency declaration for the state, with a few exceptions.  But to keep drought lessons alive, this lifting also stressed a need to reduce wasteful water use and was accompanied by a state plan to make “conservation as a way of life.”

What should we have learned (or re-learned) from this decade’s dance with extremes?

  • California is a land of water extremes. California is a dry place, that is sometimes much drier than usual for long periods of time – we call these droughts.  California also can become very wet – which can cause floods if inadequately managed and prepared for.
  • California must manage for both extremes. Wet years allow gathering water into aquifers and reservoirs, but we can never economically capture all water in wet years. Even in dry years, we need to prepare for floods, in preparing infrastructure and emergency management. In all years we need to improve capabilities and coordination among water agencies (local, state, and federal).
  • Conditions can change quickly. The drought took two years to develop and two years to end (although some effects will last for decades).  Floods move faster and more violently, as Oroville’s spillways tore themselves apart in mere hours.
  • Groundwater is key to sustainability and prosperity for California’s human water uses. Increased groundwater pumping replaced about 70% of the drought’s agricultural water shortage. Groundwater provides by far the most water storage in California, and is the predominant storage for longer droughts.  The 2014 Sustainable Groundwater Management Act shows that this lesson was learned, but implementation remains a challenge.
  • The southern Central Valley will see large reductions in net water use. This uncomfortable truth is now widely accepted following the drought. About 15 percent of the southern Central Valley’s agricultural land depends on groundwater overdraft. Problems in the Delta and increased outflows for the San Joaquin River threaten perhaps another 15 percent of supplies.  Soil salinization, urbanization of agricultural land, technology, and climate change will also mostly push to reduce irrigated acreage.
  • Preparation is key to managing extremes – for both droughts and floods. Most cities and farmers did well in the recent drought and floods. A roughly 30% loss of water supply reduced statewide agricultural revenue by about 2-3% and urban losses were financially inconvenient but economically negligible.  Local impacts were sometimes much worse, especially for some rural communities. The biggest losses were in areas least prepared. Ecosystems were unprepared for this drought, with often devastating effects.  This wet year saw widespread minor flooding, but little major flooding, and identified some areas needing more attention and funding.
  • Future droughts and floods will be a bit different. This drought was worsened by higher temperatures, hit an agricultural economy with many more permanent (and more profitable) crops, and hit a system with more effective water supply agency cooperation, and a different composition of species in the Delta ecosystem.  We need to prepare for future droughts (and floods).
  • We need to do better. The extreme drought and wet year served to identify weaknesses in California’s water management. We must learn from these tests, and improve local, regional, and statewide water management.  Learning from past droughts and floods has make California’s water management as successful as it has been, and remains vital for sustaining a major dynamic civilization in such a dry and increasingly variable climate.

The last few years have shown some major problems:

  • Groundwater. Implementing the Sustainable Groundwater Management Act remains one of California’s greatest water challenges.
  • The Sacramento-San Joaquin Delta is a second key to sustainability and prosperity for California’s water system. We are still struggling with this one.
  • Rural water supplies. California still has 1-2% of its population with substandard drinking water quality. The drought highlighted the problems of these mostly small rural water systems. Some progress is occurring, but will require stronger county responsibility, oversight, and capability, aided by others.
  • Ecosystem management. The drought showed the weakness of remaining native ecosystems and pretty dreadful drought capability and preparation by agencies for their environmental responsibilities. State and federal agencies are neither organized nor funded to succeed here.
  • Investments in flood infrastructure. While most of California’s flood infrastructure did pretty well, the floods showed a need to invest in maintenance and updating of major flood infrastructure – and Californians will need to pay for this.
  • California lacks a coherent state water technical and scientific program, integrated across agencies. Lack of a common effective water balance, inadequately organized, transparent and expeditious data and modeling, fragmented science, and incoherent fragmentation of technical efforts add confusion, delays, costs, and hassles.  The state’s major drought, flood, groundwater, water right, rural drinking water, and environmental management problems mostly span agency responsibilities, requiring a common coherent technical program.  State effectiveness is hobbled without this.

As a mostly dry place with a highly variable climate, California’s water problems are eternal and will always be punctuated by floods, droughts, and other emergencies.  These are tests which invite, focus attention, and can help guide improvements.

If we want to continue to move forward, we cannot go back.

Jay Lund is a professor of civil and environmental engineering and director of the Center for Watershed Sciences at UC Davis. @jrlund113

Further reading

Alvar Escriva-Bou, Henry McCann, Ellen Hanak, Jay Lund, and Brian Gray (2016), Improving California’s Water Accounting, 28 pp. Public Policy Institute of California, San Francisco, CA.

Hanak, Lund, Dinar, Gray, Howitt, Mount, Moyle, and Thompson. 2011, Managing California’s Water: From Conflict to Reconciliation, Public Policy Institute of California, San Francisco, CA.

Kelley, Robert (1989), Battling the Inland Sea: Floods, Public Policy, and the Sacramento Valley, University of California Press, Berkley, CA.

Lund, J., “The banality of California’s ‘1,200-year’ drought,”, 23 September 2015.

Lund, J. “You Can’t Always Get What You Want – A Mick Jagger Theory of Drought Management”, 21 February 2016.

Lund, J. and E. Hanak, “Resistance is futile: Inevitable changes to water management in California”, 7 January 2014

Posted in Uncategorized | 5 Comments

Down the DRAIN: California gets a jump on Delta tunnels

The intake structure for the first Delta tunnel was completed and began to transport water this winter to the central Delta. Photo source: Gus Tolley

by Nan W. and Dunlay J. Frobish

California took a step towards replumbing its archaic Delta water infrastructure by completing the first part of a contentious project. An intake for the first Delta tunnel was completed this fall, and with the return of wet weather, began transporting flows that will eventually bypass the Delta entirely.

Officially named the “Diversion Restoring Almonds Intake,” or DRAIN, the diversion intake conveys water into the central Delta to improve water quality and combat damage to water supplies and Delta ecosystems done by salt-water intrusion during the recent drought.

“The writing was on the wall for California’s big infrastructure projects,” said Rowe Foote, a legislative aide in the governor’s office. “The tunnels and the bullet train are our biggest goals. We need to get them done. We took a page from recent national election rhetoric: build now, get buy-in and pay later.”

Map of proposed Bay Delta Conservation Plan Dual Conveyance tunnel project. One of multiple potential intake locations was selected for the DRAIN. Source: California Natural Resources Agency

Since Californians have yet to approve full project funding, the first tunnel could only be partially completed using existing discretionary funds and a loan from Proposition 1 funds to improve access to south-of-Delta storage. Fiscal hawks in the governor’s office demanded that construction be limited to structures within the available budget, and that would provide on-going benefit regardless of whether future phases were ultimately approved.

The open bell-mouth DRAIN is unique for intake designs, and was selected because it physically limits diversions to surplus flows and can passively operate until future bonds and plans are approved. The passive structure means that intake flows will mimic the hydrograph, peaking when flows are high and receding as flows are low. Studies have shown that this kind of direct “functional flow” strategy helps preserve complex stream processes without overly complex interventions.

Record low reservoirs following the 2011-2016 drought gave California ample opportunity to complete construction of the bell-mouth intake for the first Delta tunnel. Photo credit: Dagon Jones.

The impetus behind fast-tracking the DRAIN’s construction came when poor water quality for local Delta intakes coincided with increasing reports of marine animals in streams and canals. Sea lions have been reported in Knights Landing, Dixon, and Vacaville, and several reports of whales in the Sacramento River.

Spectators watch as one of two humpback whales partially surfaces near the Port of Sacramento. Image source: U.S. Coast Guard via EPA.

“Our environmental flow policy is barely enough to keep fish the size of Delta smelt in the right place,” said Chuck Laird, a spokesperson for the state’s Natural Resources Agency. “It’s really no surprise that with the amount of salt-water intrusion, we’re starting to see marine mammals in places that used to be reliably fresh water habitat.”

“While California’s drought may be easing, the environment has essentially been in a drought for decades,” said the Center for Watershed Sciences LeRoy Tempe. “Combine the salt-water intrusion with flow reversals from the Delta pumps, and you’ve got whales swimming into our rivers while [Delta] smelt and juvenile salmon don’t know which way to go.”

Delta flows are notoriously convoluted. It is the hub of California’s critical infrastructure, conveying fresh water from the wetter northern part of the state to farms and cities in the drier south. But tidal “sloshing” greatly exceeds Delta outflows: as a result, inland channels like the dredged Sacramento Deep Water Ship channel has extended tidal mixing, bringing salty, tidal water up the channel. Experts have long warned that fresh water to the environment has been under-allocated in the Delta, and that its ecosystem won’t recover until those flows are restored.

The DRAIN’s use will be limited until Phase 2 can be implemented: the construction of a device to Prevent/Limit Unnecessary Gushing (the PLUG) can be fitted to improve the reliability of water deliveries.

Nan W. Frobish is an occasional contributor to the California Waterblog and director of life enrichment for the UC Davis Center for Watershed Sciences. Dunlay J. Frobish performs multiphase fluid flow experiments throughout the Delta.

Further reading

Bay Delta Conservation Plan. 2013 Public Review Draft BDCP.

Yarnell et al. 2015. Functional flows in modified riverscapes: hydrographs, habitats and opportunities. Bioscience.

Fleenor et al. 2017. Episode 1: “Unraveling the Knot” Water movement in the Sacramento-San Joaquin Delta. California WaterBlog.

Fleenor et al. 2017. Episode 2: “Unraveling the Knot” Water movement in the Sacramento-San Joaquin Delta. California WaterBlog.

California WaterBlog. 2015. Q & A on survival of California’s Delta smelt.


Posted in April Fools' Day, California Water, Delta | 13 Comments

Pumping out the Inland Sea – Delta exports in a time of plenty


Cumulative exports March 2017

Cumulative total SWP + CVP Delta water exports for recent years, Data source: CDEC

By Jay Lund

This is northern California’s wettest year of record, so far.  The Yolo Bypass has been flooded for most of this wet season, and is still flowing.  Are Delta water exports going to exceed the previous record exports from 2011 (6.5 maf)?  The figure above compares this year’s Delta water exports compare with other years before and after the 2007 Wanger Decision, and the drought years (2012-2016).

So far, the State Water Project and Central Valley Project together have pumped a little less than in 2011, 2006 (another wet year), or 2007. They are all pretty close (with most of these highest-export water years falling after CVPIA and Endangered species restrictions on Delta pumping).

Compared to the drought years, the first two years of drought were less dry and exports were supplemented by water drawn from California’s large northern-of-Delta surface reservoirs. By 2014 and 2015, surface storage for drought exports was substantially depleted. This surface storage depletion partially refilled in 2016 and is now fully filled.

The State Water Project pumped at record daily rates in January, in the figure below.  Daily maximum pumping was 10,426 cfs on February 2, exceeding the 8,500 cfs daily maximum from 2006-2016 and even Banks Pumping Plant’s listed capacity of 10,300 cfs.  This compares to several hundred thousand cfs of Delta outflow during January.

Harvey O. Banks Pumping Plant. SF Chronicle Graphic by John Blanchard.

State Water Project pumping began to plummet as San Luis Reservoir filled and damage was found at the intake to the pumping plant’s Clifton Court Forebay.  State Water Project pumping will be curtailed or stopped until this is repaired, with deliveries made good from San Luis Reservoir.  Spring is likely to remain wet, with substantial additional pumping later in the season.

Finding places to store pumped water south of the Delta is becoming difficult. MWD of Southern California has reduced its use of Colorado River water to employ and store this Northern California abundance.  About half of recent pumping has gone to filling San Luis Reservoir, which is essentially full.  The San Joaquin and Tulare basins are also wet, filling reservoirs locally and likely helping refill some of the region’s drought-depleted groundwater.

It may be worthwhile to invest in additional groundwater or surface storage, water infiltration capacity, and conveyance to places with more infiltration capacity.  But justifying such expensive decisions requires more economic calculations. For now, water managers throughout California are trying to avoid flooding, while maximizing the capture of flows for surface and groundwater storage.

Damage to the Clifton Court Forebay and lack of south-of-Delta storage (or conveyance to storage) are likely to keep this record-wet year from becoming a record Delta export year.  Recent SWP and CVP water allocations are not yet at 100% for all contractors, but will likely increase, and seem limited mostly by conveyance and storage infrastructure this year.  But for water users statewide, it is a welcome very wet year nonetheless.

This year is testing California’s water system in wet extreme conditions – for floods and capture of “surplus” flows, following five years of drought testing.  For California water, every year is a test.  Every year’s tests identify problems and opportunities.  Hopefully learn from these tests.

Maximum SWP exports

Data from DWR’s wondrous CDEC:

Jay Lund is the Director of the Center for Watershed Sciences and a Professor of Civil and Environmental Engineering at the University of California – Davis. He is grateful that the people of California pay him.

Further reading

Episode 3: “Unraveling the Knot” Water Movement in the Sacramento-San Joaquin Delta – Managing Flows, CaliforniaWaterBlog, 29 January 2017

Harter, Thomas. Post-drought groundwater in California: Like the economy after a deep “recession,” recovery will be slow,, 19 March 2017

Nguyen, Megan, Yolo Bypass: the inland sea of Sacramento,, 20 February 2017


Posted in Delta | 7 Comments

Post-drought groundwater in California: Like the economy after a deep “recession,” recovery will be slow

by Thomas Harter

The 2012-2016 drought has made many of us keenly aware of how “empty” our groundwater “reservoirs” have become. As the recent series of atmospheric rivers have left us with a massive snowpack, full surface water reservoirs (with some exceptions in southern California), and soggy soils, some questions are frequently asked:

Is the drought over, even for groundwater – if not, when will well owners see full recovery of their water table?  And could the massive amounts of runoff be captured to accelerate replenishment of our depleted groundwater aquifers?

The short answers: while the surface water drought is over, the groundwater drought is not. How much longer may it last? As a rule of thumb, in many areas it will take as many above average to wet years to recover our groundwater storage, as it has taken to draw it down. And while excess runoff can be used for recharge, California currently lacks the infrastructure and capacity to divert and hold flows like those released over the Oroville spillways for infiltration and groundwater storage.

Why does groundwater storage recovery take so much time? Groundwater is by far our largest of the four water reservoir systems in California, where agriculture and urban users consume about 40 million acre-feet (MAF) each year, mostly from spring to fall:

  • Mountain snowpack, in an average winter and spring, holds about 15 MAF
  • Surface water storage reservoirs have a total capacity of 40 MAF
  • Soils store many 10s of MAF of our winter precipitation for use by natural vegetation, crops, and urban landscaping
  • Groundwater reservoirs are endowed with well over 1,000 MAF of freshwater

With this endowment, groundwater storage works like a large bank account. We run deficits in dry times, taking out more than we deposit (more pumping than recharge); and we run savings in wet times, depositing more into the account than what we withdraw (more recharge than pumping). Ideally, over the longer term, the savings match the withdrawals – groundwater recharge matches groundwater pumping.

Dynamics of groundwater storage and water level change – a history lesson

Groundwater levels are the indicators that show how this bank account is performing. Rising groundwater levels mean increasing storage – more savings. Falling groundwater levels mean decreasing storage – running a deficit.

How much and when groundwater levels rise and fall varies greatly around the state. But there are some common patterns. Seasonal variations occur due to California winters being wet and cold while summers are dry and hot. Water levels rise during winter and spring due to recharge from precipitation and recharge from streams that carry winter runoff (plenty of bank deposits), while groundwater pumping is limited (small account withdrawals). On the other hand, groundwater levels decline during the summer and fall, when pumping exceeds local recharge.

Groundwater levels (and storage) also change over the longer term, in response to drought or wet years. In dry years, it is common to see water levels recover less during the (dry) winter. With the early onset of irrigation in the spring and lack of surface water leading to replacement with groundwater pumping, water levels drop quickly in the summer following a dry winter.  In wet years, the opposite occurs: water levels recover more strongly after a wet winter and groundwater levels are not drawn down as much in the summer, resulting in a net year-over-year rise in water levels.

In some regions, such as the Borrego Valley basin, the depletion has been a steady decline: each summer, water levels are drawn down more than they recover in the following winter, regardless of how wet the winter may be. In other places, the decline in groundwater levels may be less obvious:  year-over-year water levels fall during drought, but recover during wet years. But the recovery during a series of wet years doesn’t make up for the depletion during dry years, resulting in long-term overdraft.

Over the past 100 years, overdraft has drained groundwater resources by 150-200 MAF, with most of that depletion occurring in the middle and southern Central Valley, and in southern California. The overall decline in groundwater storage, time and again, has led to costly replacement of wells that have become too shallow to dip into a falling water table, land subsidence, seawater intrusion in coastal basins, water quality degradation in other basins, and depletion of streams that depend on groundwater for base flow during California’s long dry season.

The decline has also created groundwater storage space to replenish with extra water in wet years. For the past half century, Orange, LA, and Santa Clara counties have been busy building a diversity of water projects to take advantage of that additional groundwater storage space. During wet years, they refill it with excess water from local streams, the state and federal water supply system, urban runoff, and recycled urban water:

Figure 1: Average depth to groundwater in Santa Clara Valley, where overdraft began in the 1920s and continued for 40 years. It has taken another 40 years to recover from that overdraft. From: Santa Clara Valley Water District.

Notably, it has taken those basins two to four decades to recover from their deep overdraft accumulated during the early groundwater exploration in the 1920s through 1960s – a recovery often interrupted by droughts (1977, 1988-92).

Recharge as the driver for groundwater recovery after drought.

Recharge drives the amount of groundwater level recovery. Let’s take a closer look: Some of the recharge comes from precipitation that infiltrates into the soil, in excess of the soil water holding capacity. During dry years, that may be less than an inch in southern California and a few inches in central California. In a soggy, wet winter, some areas (especially on sandy soils) may see over a foot of recharge from precipitation. For the 10+ million acre Central Valley aquifer, this accounts for a significant portion of natural recharge. Streams and irrigation water returns provide the other significant portion of recharge. Intentional recharge through groundwater banking, aquifer storage and recovery, and intentional flooding of natural depressions can further enhance that recharge.

In the Central Valley, recharge in a critically dry year may be well below 10 MAF while pumping may far exceed 15 MAF – thus groundwater storage in a critically dry year may decrease by 3-7 MAF. The opposite occurs in a wet year like 2017 – groundwater pumping may be as little as 10 MAF, while recharge is well over 12 MAF, leading to storage gains of 2-5 MAF (see Figure 2 below). Hence a wet year’s gain is roughly of the same magnitude as a dry year’s loss.

The important point about this: the amount of recharge in a single wet year cannot wipe out three or four or five years of drought losses.

Figure 2: Annual (bars) and cumulative (lines) change in groundwater storage in the Central Valley aquifer between 2005 and 2010. Upper and lower best limits for a best estimate are obtained by assuming aquifer specific yields of 7% (blue) to 17% (green). From: DWR Water Plan 2013

How will a wet winter help drought-affected well owners?

Back to our wet winter of 2017. What will drought recovery be like for domestic, irrigation, and public water supply wells? For well owners that have kept water level records over the past 30 years, a good estimate of the time needed for recovery is to look at their records during the years after the 1988-1992 drought. Alternatively, the annual recovery rates during the wet winters of 2005-2006 and 2010-2011 may provide some good indication for recovery rates this year.

Where those records are not available, a look at DWR’s Water Data Library, with its easy-to-use map interface, may be helpful: clicking on a few wells in the area of interest will quickly reveal some examples of water level hydrographs and recovery rates, especially during the mid- to late 1990s (a series of rather wet years). Figure 3 shows some good examples from the Sacramento Valley (Yolo County) and the southern Central Valley (Tulare County):

Figure 3: Water level hydrographs for wells in Yolo and Tulare County, 1950 – current. Wells are identified by their DWR well identification number. Notice the decline in water levels during drought periods. Year-to-year recovery rates during the wetter periods of the 1980s and late 1990s mirror the rates of year-to-year decline in drought years. Data were obtained from DWR’s Water Data Library.

If neither of these resources are at hand, consider the rate at which water levels have fallen over the past five years: recovery may likely happen at about the same rate as water levels have fallen. For example, if water levels have fallen about 15 feet each year (spring to spring), this year may yield a water level increase of about 10 – 20 feet (spring to spring).

Additional recharge to accelerate groundwater recovery?

Could we not accelerate the process by recharging, for example, much of the over 2 MAF released from the Oroville dam during the three weeks of emergency releases in February (not counting Lake Shasta and other releases)?

Some of that water has in fact become recharge, directly from the Yuba River into the Central Valley aquifer system, from Marysvville and along the Sacramento River, as well as along the flooded Yolo Bypass to the Delta. But the Bypass contains fine-grained floodplain soils with very low infiltration capacity – about one-tenth of a foot per month (one of the reasons the  Bypass is ideal for rice fields). The Yolo Bypass is 60,000 acres – recharge from there may add about 0.01 MAF to the Central Valley aquifer system, a tiny fraction of the reservoir releases. Letting the floodwaters fill more of its original floodplains can increase that fraction, which is important to local groundwater.

If we dedicate some of the lighter soils with higher infiltration rates for use as intentional recharge basins, a likely recharge rate would be on the order of one or perhaps even a few feet of recharge in one month.  We would need 1-2 million acres of these lands just to put away the surplus Oroville outflow in February!

Another option is to systematically use agricultural land for winter irrigation while taking advantage of some of these flood flows.  Intentional winter recharge in the agricultural landscape could be coupled with smart reoperation of surface storage reservoirs to better match the slower groundwater infiltration rates with the intensive but short availability of flood waters.  Irrigating suitable agricultural land with surplus winter water may allow recharge of one-half to two feet of water between December and March – allowing for additional intentional recharge in wet years of perhaps 2-6 MAF across the Central Valley, if and where water rights, infrastructure, and agricultural chemicals could also be managed appropriately (Water Foundation, 2015). Considering that the Central Valley is irrigated with about 20 MAF between April and October each year, intentional agricultural winter recharge of 2-6 MAF during wet winters is not an unreasonable proposal. This type of recharge could indeed make a significant difference to the typical wet year groundwater storage gains of 2-5 MAF – theoretically doubling the current water level recovery rate during a post-drought winter like 2017 (Harter and Dahlke, 2014; DWR, 2017).

Figure 4: Soil Agricultural Groundwater Banking Index showing recharge suitability of soils in California’s agricultural regions. Potential recharge rates on “excellent” soils may exceed several tens of feet per year, where subsurface “storage space” exists; in contrast, “very poor” soils may allow for recharge of as little as 1 foot per year, even under ponding conditions.

Thomas Harter is a groundwater specialist with the UC Davis Center for Watershed Sciences.

Additional Resources:

Santa Clara County Water District. Groundwater: Where does our water come from?

California Department of Water Resources. California Water Plan 2013.

California Department of Water Resources. Water Data Library.

Water Foundation. 2015. Creating an opportunity on farm recharge.

Harter, T. and Dahlke, H.E. 2014. Out of sight but not out of mind: California refocuses on groundwater.

California Department of Water Resources. 2017. Sustainable Groundwater Management: Water available for replenishment.

Soil Agricultural Groundwater Banking Index.

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Evading Dam-Nation to Build a Working Floodplain on the Cosumnes River

Flooding at the Cosumnes River Preserve on February 14, 2017 along Franklin Blvd. in the lower Cosumnes River Watershed. Source: Tom Palmer

by Michelaina Johnson

This winter’s barrage of rain storms has driven most Central Valley rivers to the point of near record-breaking flooding, and the Cosumnes River is no exception. On February 10th, the Cosumnes hit the second highest peak flow in its recorded flow history: 45,400 cubic feet per second at Michigan Bar.

The Cosumnes is the only river draining the western Sierra Nevada Mountains that has no major dam. As a result, the river’s natural floods have limited – but not eliminated – development and agriculture in the Cosumnes’ lower watershed while also sustaining some of the best native habitat remaining in the Central Valley. Today, the 50,000+ acre Cosumnes River Preserve (CRP) protects the lower watershed’s exceptional habitat using a unique public-private partnership model that weaves together the seemingly conflicting human and environmental demands of the landscape – ultimately benefitting both.

When the earliest settlers came to the lower Cosumnes River watershed in the late 1840s and early 1850s, they found a landscape that was far different from today’s. The ranches and crop fields were once a marshland filled with tules and willow thickets. The Plains Miwok managed the landscape through controlled burning and hunting, among other practices. Even the Cosumnes’ acclaimed oak riparian forest stands did not exist in the lower watershed a century and a half ago.

Early settlers diked and drained the lower watershed, which converted the marshland into productive farm and grazing land in just a few decades. By the late 1870s, agriculture and cattle dominated the region. Due to this extensive reclamation and the damming of most of the Central Valley’s rivers, the Valley lost nearly all of its native habitat with a few notable exceptions, such as the Cosumnes River watershed.

Between 1900 and 1974, there were five distinct water projects totaling more than 30 dams proposed for the Cosumnes River. The most notable one was the Cosumnes River Project, which was part of the Central Valley Project (CVP) and called for the construction of six dams and reservoirs on the Cosumnes River, the largest being a 900,000 acre-foot reservoir on the Cosumnes’ main stem, at a cost of $180 million. Each of the proposals failed due to high costs, the inability to secure water rights, and farmer resistance, among other reasons.

The absence of a major dam on the Cosumnes River meant that the river flooded nearly every year, which relegated farmers to growing annual crops and ranchers to grazing livestock. These two land uses happened to be compatible with waterfowl and some native habitat types like vernal pools and riparian forests. Over the course of a century and a half, farming and ranching activities worked to unintentionally preserve these flora and fauna.

Even though vernal pools did not historically evolve with extensive grazing, two studies found that vernal pool landscapes in the Sacramento Valley have come to depend on this land use (Barry, 1998; Marty, 2005). The lower watershed has a long history of grazing dating back to the late 1840s, which, due to the river’s frequent flooding, remained a driving force behind the unintentional preservation of a significant percentage of vernal pools remaining in the Central Valley. The CRP today protects 14,141 acres of vernal pools, which is about ten percent of the total 137,100 acres remaining in the Central Valley.

Perhaps more surprisingly, cattle grazing also partly enabled the growth of riparian forest in the lower watershed where it didn’t “naturally” occur before reclamation. Limited coring of the remnant forests on the Preserve suggests that the oldest forest stands appeared around the turn of the twentieth century, only decades after the diking and draining of the lower watershed’s marshland was completed. As other watersheds suffered reclamation and damming, California lost 90% of the estimated 922,000 to 1.6 million acres of its historic riparian forests. But in the Cosumnes, the combination of reclaimed land and annual floodwaters created the environmental conditions necessary for riparian forests to take root and grow. Cattle grazing along the riparian corridor ensured that only the understory rather than the trees were consumed, leaving the largest oak riparian forest remaining in California in the lower Cosumnes River watershed.

Riparian forest in the lower watershed flooded from January’s strong rainstorms. Source: Mike Eaton.

As well as promoting new habitats, the reconciled use of the Cosumnes River watershed also supports long-present species. Unlike the riparian forest stands in the lower watershed, waterfowl have resided in the region, as well as the rest of the Central Valley, for more than a million years. The birds stop over in the Central Valley during their annual winter migration to fuel up for their journey to the wetlands of northern Alaska and western Canada. When early settlers converted 90% of the Central Valley’s original four million acres of seasonal and perennial wetlands to other land uses, principally agriculture, beginning in the early 1850s, the waterfowl turned to whatever food sources became available, including rice, alfalfa, wheat, corn, and pasture land. Due to the Cosumnes’ annual flooding, farmers opted to grow crops that could be planted and harvested before the unregulated deluge could destroy their agricultural investment. These annual crops, specifically wheat and corn, happened to serve as food sources for waterfowl –  much to the chagrin of farmers, some of whom shot the birds to keep them away from the fields. Since the Preserve’s founding in 1987, more than 200 species of birds have been observed within the preserve’s boundaries, including the state listed threatened Greater Sandhill Crane.

The Nature Conservancy (TNC) became interested in the Cosumnes’ riparian forest stands in the early 1980s and decided to establish the Cosumnes River Preserve in 1987. TNC, along with its myriad partners, quickly realized that other rare habitat types and bird species resided in the lower watershed and capitalized on their presence to create a cutting-edge conservation model for the Delta. The Preserve uses conservation easements to ensure that the historic, wildlife compatible land uses present on 21,271 acres, or 46% of the Preserve’s property, continue in perpetuity. The CRP also leases preserve land to farmers and ranchers to allow them to cultivate annual crops that can also function as food sources for waterfowl.       

The Cosumnes River Preserve today protects the Cosumnes’ free flow, floodplain, and rare native habitats. Through experimental, cutting-edge restoration techniques, such as levee breaching, the Preserve, in partnership with researchers from UC Davis, has shown that the restoration of the floodplain will lead to the regrowth of riparian forests, increase aquatic and avian wildlife habitat, and improve groundwater recharge through reconnection with the floodplain – all while remaining compatible with agriculture. This type of restoration has made the lower Cosumnes River watershed into an exemplary working floodplain. As a result of the Cosumnes River Preserve’s innovative public-private partnership management model and restoration techniques, state policymakers today look to the Cosumnes River as a restoration model for other rivers in the Central Valley and for the Delta.

Michelaina Johnson is a senior at UC Berkeley majoring in History and double minoring in Spanish and Conservation and Resource Studies. She completed her senior honors thesis, “Evading Dam-Nation: Land Use History of the Lower Cosumnes River Watershed, ca. 1820-2016,” last December and based this article on her research. She plans to pursue a career in either environmental journalism or water policy after graduating. 

Further Reading:

Ahearn, Dylan S, Richard W Sheibley, Randy A Dahlgren, and Kaylene E Keller. “Temporal Dynamics of Stream Water Chemistry in the Last Free-Flowing River Draining the Western Sierra Nevada, California.” Journal of Hydrology 295, no. 1–4 (2004): 47–63.

Barry, Sheila J. “Managing the Sacramento Valley Vernal Pool Landscape to Sustain the Native Flora.” In Ecology, Conservation, and Management of Vernal Pool Ecosystems – Proceedings from a 1996 Conference, edited by C.W. Witham, E.T. Bauder, D. Belk, W.R. Ferren Jr., and R. Ornduff, 236-240. Sacramento: California Native Plant Society, 1998.

Bennett, Karen Louise. “The River That Got Away: An Investigation into the Proposed Development Projects, the Players and the Political Climate That Helped Shape the Fate of the Cosumnes River.” Master’s Thesis, California State University, Sacramento, 1997.

Marty, Jaymee T. “Effects of Cattle Grazing on Diversity in Ephemeral Wetlands.” Conservation Biology 19, no. 5 (2005): 1626-1627.

Robinson, April, Samuel Safran, and Julie Beagle, “A Delta Renewed: A Guide to Science-Based Ecological Restoration in the Sacramento-San Joaquin,” San Francisco Estuary Institute—Aquatic Science Center, a report of SFEI-ASC’s Resilient Landscapes Program, publication #799, Richmond, CA, 2016.

Steding, Anna. “Restoring Riparian Forests and Natural Flood Regimes: The Cosumnes River Preserve.” In Sustainable Use of Water: California Success Stories, edited by Lisa Owens-Viani, Arlene K. Wong, and Peter H. Gleick, 229-239. Oakland: Pacific Institute for Studies in Development, Environment, and Society, 1999.

Whipple AA, Grossinger RM, Rankin D, Stanford B, Askevold RA. “Sacramento-San Joaquin Delta Historical Ecology Investigation: Exploring Pattern and Process.” Prepared for the California Department of Fish and Game and Ecosystem Restoration Program. A report of SFEI-ASC’s Historical Ecology Program, publication #672, San Francisco-Estuary Institute-Aquatic Science Center, Richmond, CA, 2012.

Posted in flood, Floodplains | Tagged | 6 Comments

What do stream fish do during flood flows?

Catch from a single seine haul (top to bottom): largemouth bass, black crappie, bluegill, two golden shiners and a green sunfish.

Catch from a single seine haul (top to bottom): largemouth bass, black crappie, bluegill, two golden shiners and a green sunfish. Photo by Peter Moyle.

By Peter B. Moyle

My local stream, Putah Creek, looks like a river these days.  Water is pouring down the Glory Hole of Lake Berryessa and rushing in muddy turmoil from the ‘dry’ creeks that are its main tributaries.   The creek’s deeply incised and leveed channel is containing the flows that once would have spread across the landscape.  As a fish biologist, I am often asked: what’s going on with the fish?  Are they all being flushed downstream into the Sacramento River and Delta?


The Morning Glory Hole Spillway by Monticello Dam. Photo by Gus Tolley.

My response is this. Some unlucky fish are being flushed into places they would rather not be, causing freshwater fishes to be found in places normally too salty for them.  But most fish manage to stay near home or are carried to places they want to be, especially to food-rich floodplains.


Jess Vargas and Zachary Bess sampling Putah Creek , February 21, 2017. Photo by Peter Moyle.

For stay-at-home fish, the key is to get out of the main channel and into side channels, among the trees and bushes, where they shelter from the current. A few days ago, I led a small expedition (4 enthusiastic fish people) to look for fish in the backwaters of Putah Creek.  We used a seine and pulled it on flooded roadways, where the currents were weak and the bottom free of logs and vegetation.  In an hour of somewhat difficult sampling, we caught eight species of fish: largemouth bass, bluegill, green sunfish, black crappie, golden shiner, fathead minnow, Sacramento pikeminnow, and threespine stickleback.  With the exception of the single stickleback, these are all fishes that we have collected sampling during low summer flows. The stickleback probably washed in from upstream; it is common just below the Putah Creek Diversion Dam.  What we did not find were juvenile Chinook salmon; I am hopeful that the small juveniles (alevins) will emerge soon from where they are buried deep in the gravel below the dam, and will migrate downstream.  We will be looking for them.

The juvenile salmon are an example of native fish that can benefit from being carried downstream by high flows, if they wind up on the flooded fields of the Yolo Bypass. Previous studies from the UCD Center for Watershed Sciences have shown  that young salmon thrive on the floodplains, growing at rapid rates, and then moving off the floodplains as the water recedes (Holmes waterblog, March 20, 2016).  A five year study of the Cosumnes River showed that other native fishes, like the salmon, arrived on the floodplain early and then bailed out as it drained (Moyle et al. 2007).  Many of the non-native fishes were not so fortunate; they arrived on the floodplain late, moving up and in from the permanent sloughs, and then became food for pelicans after they were trapped in shallow floodplain ponds.

The key concept here is that stream fishes have evolved to handle high flows, which most streams experience.  Native fishes are especially well adapted for the fairly predictable timing of high flows in California.  Even the non-native fishes, such as bass and sunfish, show behavioral adaptations to move to sheltered locations during floods, but they appear to be less well equipped to handle the particular seasonal flow regimes found in California streams..

As the flows recede in Putah Creek and elsewhere, native fishes like Sacramento sucker and pikeminnow move upstream and start spawning in the emerging riffles.   Their young will rear in the flooded vegetation at the edges, which should be in abundance.  The non-native fishes, in contrast, will have their reproduction delayed as high flows keep water temperatures cool and prevent them from spawning in quiet pools and vegetated areas.

In short, stream fishes are adapted for living with floods.  The flood of 2017 should favor native fishes, from salmon to suckers.  We expect to see a big increase in the abundance of juvenile natives in the coming summer.   How well they survive to reproduce themselves will depend on how well we manage our dammed rivers in the coming years.

Peter Moyle is a UC Davis Professor Emeritus of fish biology and an associate director of the Center for Watershed Sciences. 

Further reading

Moyle P.B., Crain P.K., and Whitener K. 2007.  Patterns in the use of a restored California floodplain by native and alien fishes.  San Francisco Estuary and Watershed Science 5(3):1-27.

Jeffres, C. A., J. J. Opperman, and P. B. Moyle. 2008. Ephemeral floodplain habitats provide best growth conditions for juvenile Chinook salmon in a California river.  Environmental Biology of Fishes 83: 449-458.

Ribeiro, F., P. K. Crain, and P. B. Moyle. 2004.  Variation in condition factor and growth in young-of-year fishes in floodplain and riverine habitats of the Cosumnes River, California. Hydrobiologia 527:77-84.

Little, Jane B. We should better understand how to live with floods. Sacramento Bee. March 6, 2017.

Posted in Fish, flood, Floodplains, Salmon | Tagged | 1 Comment

California’s Floods of 2017, so far


Flooding in Maxwell, California, February 2017.  Photo Credit Hector Iniguez

by Jay Lund

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 pored 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.


Eroded primary spillway at Oroville Dam, February 2017. Photo credit: Eric Holmes

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

Last week, the northern California town of Maxwell flooded and I-5 partially shut down.  This 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 (Kelley, 1989).

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.

Jay Lund is a Professor of Civil and Environmental Engineering and Director of the University of California – Davis’ Center for Watershed Sciences.

Further Reading

Jack Ohman, The U.S. Army Corps of Engineers Dam Manual…, Sacramento Bee, 24 February 2017. [Awesome editorial cartoon!]

Kelley, Robert (1989), Battling the Inland Sea: Floods, Public Policy, and the Sacramento Valley, University of California Press, Berkley, CA.

Nguyen, M., Yolo Bypass: the inland sea of Sacramento,, February 20, 2017.

Sabolow, R. Oroville Dam: Can damaged spillway hold through California’s rainy season?, Sacramento Bee, 26 February 2017.

Breitler, A. San Joaquin River’s flood challenge, Stockton Record, 26 February 2017.

Feb 18, 2017 DWR video –

2017 Update to the Central Valley Flood Protection Plan, Public Draft, California Department of Water Resources, 2017.

2012 Central Valley Flood Protection Plan, California Department of Water Resources, 2011.

A wonderful map of the Sacramento Valley bypass system:sacramento-valley-flood-map

Posted in California Water, flood, Planning and Management, Stressors, Uncategorized | Tagged | 4 Comments

Yolo Bypass: the inland sea of Sacramento

A very flooded Yolo Bypass. Photo taken by Carson Jeffres on January 26, 2017. (In view is looking south at Interstate 5 just west of Woodland, in the distance is Interstate 80 between Davis and Sacramento)

A flooded Yolo Bypass, flowing much less than capacity. Photo taken by Carson Jeffres on January 26, 2017. (View looking south at Interstate 5 west of Woodland, in the distance is Interstate 80 between Davis and Sacramento)

By Megan Nguyen

Land or Sea? The recent rains early this year brought much needed relief from the five-year drought in California. Reservoirs are full, mountains are covered with snow, and flood control structures are being used, some for the first time since 2006. Interstate 80 causeway commuters frequently, though perhaps unknowingly, witness one of the most important floodplains in California – the Yolo Bypass is now filled with water as far as the eye can see.

The recent events at Oroville Dam help highlight the Yolo Bypass’ vital role in flood protection for the Sacramento area. Despite the risk of flooding from the potential failure of Oroville Dam’s emergency spillway last week, flood control managers and experts emphasized the limited risk to the Sacramento area. The Bypass was a big reason why communities near Sacramento didn’t experience the same risk as those closer to the dam. Understanding the Bypass helps explain why it functions so well in our regional flood control strategy. But it also emphasizes the scale of protection needed for a low-lying area like Sacramento.

Sacramento Valley and San Joaquin Valley historically flooded from major rainstorms or snowmelt. Most major floods in California are caused by “atmospheric rivers” from the Pacific Ocean.  Atmospheric rivers are warm, intense streams of tropical moisture that often produce several days of heavy precipitation in the Central Valley and over the mountains of California. By the time this blog is posted, forecasts say we will be drenched by one.

Prior to construction of large flood infrastructure and coordinated flood management, seasonal runoff would often cover the valley floor. Historically, floods could reach as large as 600,000 cfs (cubic feet per second) near Sacramento (one cubic foot is about the size of a basketball). Snow melt from the mountains and heavy rainfall would often overtop the river banks. Following hydraulic mining in the 1800s, immense quantities of sediment began to deposit in the river channels of the valley floor. The sediment essentially filled  the river channels and left no place for flood water to go.  The resulting floods covered large areas of the valley floor to great depth, with large property damage and loss of life.

To prevent future flood damage such as what happened in the flood of 1907, the state of California through the Central Valley Flood Protection Board and the Army Corps of Engineers developed the Sacramento River Flood Control Project (SRFCP). The SRFCP is a system of flood-relief structures and weirs that release Sacramento River and Feather River flows into a bypass system when flows exceed downstream channel capacity.

Video: This hydraulic model is a simulation of a swollen Sacramento River spilling over the Fremont weir into the Yolo Bypass as it floods as a result of high flow events. Notice that the floodwaters spread through individual irrigation ditches and drains.

The most downstream of the bypasses and a critical component of the SRFCP, the Yolo Bypass is a 59,000-acre floodway that serves as a flood relief valve and protects Sacramento and southern Sacramento Valley from seasonal inundation. At three miles wide and 40 miles long, the bypass can carry up to four times the flow of the river’s main channel during large floods. The Bypass lies within the Sacramento River’s historical floodplain and conveys floodwaters from major valley rivers including the Sacramento, American, and Feather Rivers, and west-side tributaries: Knights Landing Ridge Cut, Cache Creek, Willow Slough, and Putah Creek. The Bypass is designed for a capacity 500,000 cfs at the downstream end.

A schematic map of the Yolo Bypass. Courtesy of DWR. Point A shows the location of the Fremont Guage (FRE). Point B shows the location of the Yolo Bypass guage (YBY).

A schematic map of the Yolo Bypass. Courtesy of DWR. Point A is the location of the Fremont Guage (FRE). Point B is the location of the Yolo Bypass guage (YBY).

Weirs are lower, armored sections of levees that are used to divert high river flows through bypasses and ultimately to the Sacramento-San Joaquin Delta. Major weirs in the Yolo Bypass include the Fremont and Sacramento Weirs.

The Fremont Weir is two miles long and marks the beginning of the Yolo Bypass.  The Fremont Weir is passive, meaning that no management is needed to allow flood water to overflow into the Bypass.  Overflow waters of the Sacramento River, Sutter Bypass, and the Feather River run into the Yolo Bypass with a design capacity of 343,000 cfs.

Unlike the Fremont Weir, the Sacramento Weir is manually opened during high flow events. It consists of 48 gates that must be opened with a long hooked pole. The weir was designed primarily to protect the City of Sacramento from excessive flood stages in the Sacramento River channel downstream of the American River.  The Sacramento Weir can divert a maximum flow of 112,000 cfs. This year the Sacramento Weir opened for the first time since 2006.

How the Sacramento Weir works. Picture originally published by the Sacramento Bee on Jan 9, 2017.

How the Sacramento Weir works. Picture originally published by the Sacramento Bee on Jan 9, 2017.

Although flood control is the major function of the Yolo Bypass, the Bypass is a multi-benefit landscape.  During the non-flood season, agriculture and wildlife management are the main activities in the Bypass.  Agriculture in the Yolo Bypass is predominantly rice farming. The largest contiguous area of non-agricultural floodplain habitat is the Vic Fazio Yolo Bypass Wildlife Area, managed by California Department of Fish and Wildlife. At 16,600 acres, this area is a haven for waterfowl, shorebirds and wading birds, neotropical migratory birds, raptors, invertebrates, snakes, turtles, toads, and bats. Vegetation community types include managed seasonal and permanent wetland, natural seasonal wetland, natural perennial wetland, and riparian woodland.

An often unnoticed benefit of the flooded landscape is the benefit for juvenile salmon.  During winter floods, juvenile salmon are washed down from upstream rivers into the productive habitats of the Yolo Bypass.  Juvenile salmon grow much faster on the Bypass compared to the river channel the runs through Sacramento River.  Even though it is hard to observe while stuck in traffic, the thriving aquatic ecosystem in the flooded Bypass is much richer than the river not far away.

A flooded Yolo Bypass is a sign that the Sacramento River Flood Control System is working to protect the greater Sacramento area from flooding. Although less tangible, the Sacramento Flood Control System also serves a valuable ecosystem benefit by mimicking some of the historic flooding within a more controlled, human friendly environment. With more wet months to come in 2017, the Bypass will continue to remain an inland sea.   So the next time that you are stuck in traffic on the causeway take to moment to appreciate the amazing multi-benefit environment below you.

Megan Nguyen is a GIS researcher at the Center for Watershed Sciences. Her work and interests revolve around a variety of topics such as drought impacts, flood mitigation, environmental policy, and education outreach.

Further Reading

Kelley, Robert (1989), Battling the Inland Sea: Floods, Public Policy, and the Sacramento Valley, University of California Press, Berkley, CA.

Suddeth, R. Dec. 2, 2014. Reconciling fish and fowl with floods and farming. California WaterBlog.

Fleenor, W. Suddeth, R. Oct. 18, 2013. Innovations in floodplain modeling: A test drive on the Yolo Bypass. California WaterBlog

Sacramento River Flood Control Project Weirs and Flood Relief Structures, by California Department of Water Resources, 2010.

Lund, J.R., “Flood Management in California,” Water, Vol. 4, pp. 157-169; doi:10.3390/w4010157, 2012.

Suddeth, R. and J. Lund “Multi-Purpose Optimization of Reconciliation Ecology for an Engineered Floodplain – Yolo Bypass, California,” San Francisco Estuary and Watershed Science, Volume 14, Issue 1, 2016.

Department of Water Resources. Yolo Bypass Flood Protection Presentation.

Center for Watershed Sciences. Nigiri Project.

Center for Watershed Sciences. Sacramento River Flood Control Project.


Posted in flood, Floodplains, Planning and Management | Tagged | 5 Comments

Reconciling conservation and human use in the Delta

This view of a duck hunting club in Suisun Marsh shows both a highly modified environment and reflects its potential for being managed as a reconciled ecosystem. Photo by P Moyle.

This view of a duck hunting club in Suisun Marsh shows both a highly modified environment and reflects its potential for being managed as a reconciled ecosystem. Photo by P Moyle.

By John Durand, Peter Moyle, and Amber Manfree 

In a previous blog, we presented a Grand Scheme for habitat conservation in the North Delta Arc (the Arc). This follows up on our earlier broad vision for recreating a Delta more friendly to its native species.  In this essay, we give philosophical and historical reasons to approach habitat conservation on the regional scale of the Arc, using reconciliation ecology as our guide.

The Sacramento-San Joaquin Delta has been extensively altered over the past 150 years. Major changes include manipulation of river flows, alien species invasions, conversion of wetlands to agriculture and, most recently, climate change. Changes have been incremental and slow enough that successive generations of Delta residents, fishermen, scientists, and managers have not seen the full extent of transformation. Each generation assumes the conditions they encounter are not much different from those of the recent past. This problem of slowly shifting baselines means that our understanding of historical conditions shifts with changing conditions, because the change is difficult to accept and because we cannot directly observe what conditions were like in the more distant past (Pauly 1995; Papworth et al. 2009).

A recent review of anthropological studies, early travelogues, and scientific surveys of the Delta gives a better sense of the transformation. The Delta originally was a place where the sky darkened with migratory waterfowl in fall, where salmon runs crowded tributary rivers, tule elk browsed on oak-topped natural levees, and delta smelt were a common prey for fishes and birds. Flows in the Sacramento and San Joaquin Rivers were highly variable, but predictable in pattern, with winter floods and summer droughts. Such aspects of the historic landscape were gradually lost with marsh reclamation, damming, levee construction, water diversions and pollution from mining, agriculture, waste water and urban runoff. It is impossible to restore natural conditions—little quality habitat remains, connectivity among habitats has been lost, and many historically abundant species are extinct or their populations are greatly reduced in number.  Native species have been largely replaced by alien plant and animal species such as largemouth bass, Mississippi silversides and Brazilian waterweed. These new arrivals are abundant because they are adapted to conditions created by the expanding human-altered landscape.

Governor Brown’s EcoRestore initiative aims to provide habitat restoration projects to reverse the decline of native species and create habitat that functions to support native species . We agree that it is imperative that some of our pre-19th century historic natural legacy be maintained. Given the depth of transformation, restoration to perceived “baseline conditions” is impracticable. That historic Delta is lost.

As a workable alternative, we promote the idea of reconciling current land uses with desirable ecological outcomes. A reconciliation approach to Delta conservation offers opportunities to recapture lost ecological functions that support threatened species. It involves creative management of the current landscape to balance benefits for fish, waterfowl, food webs, and human uses. This idea can help to manage the emergence of novel ecosystems globally, landscapes with new conditions and  combinations of organisms with no historical analogue, but which provide valuable and viable species conservation opportunities, as well as human benefits (Rosenzweig 2003; Hobbs et al. 2006).



This map of North and Central Sacramento-San Joaquin Delta shows reserve networks across the North Delta Arc of Habitat, and the Yolo Bypass Floodplain. Click link or image for detailed information on the reserves. View the full map here.

This approach may involve some dramatic and expensive actions that involve earth moving to recreate marshes and meandering channels. But more often, it involves working with farmers, duck club owners, anglers, and other stakeholders to adjust breaching of levees and the operation of tidal gates to facilitate the movement of water across the landscape.

The Nigiri project on the Yolo Bypass illustrates this concept.  Here, young salmon are raised in rice fields before being released to the Delta and before farmers need to plant, with involvement of local farmers, state agencies, county government, CalTrout, and UC Davis. But Nigiri is not the only reconciliation project in the Delta. In Suisun Marsh, the Potrero Duck Club, historically operated as a private hunting club, is being managed to promote not only water fowl, but as an incubator to create food for the larger aquatic ecosystem. Although these sites differ from historical conditions, they effectively capture the ecological functions of an earlier Delta that are largely lost: they grow and disperse food, act as nursery habitat for young fish and provide food for nearby wildlife. While opportunities to re-create the Delta’s original habitats have faded, opportunities have arisen to create new habitats that serve human needs, provide ecosystem services, and support native fish and wildlife. We see wild lands being integrated with managed lands as the most productive way to create a reconciled Delta.

In future essays, we will explore the use of reconciliation ecology to several important sites in the Delta. These include: Meins Landing, Montezuma Wetlands, Potrero Club, Lindsey Slough, Denverton Slough, Blacklock Pond, Liberty Island, North Liberty Mitigation Bank and Beaver Ponds, Prospect Island and Roaring River.

John Durand is a researcher specializing in estuarine ecology and restoration at the UC Davis Center for Watershed Sciences. He oversees projects in the north Delta Arc of habitat including the Cache Lindsey complex and Suisun Marsh.  Peter Moyle is a UC Davis Professor Emeritus of fish biology and an associate director of the Center for Watershed Sciences. Amber Manfree is a postdoctoral researcher with the UC Davis Center for Watershed Sciences.

Further reading

Hobbs RJ, Arico S, Aronson J, Baron JS, Bridgewater P, Cramer VA, Epstein PR, Ewel JJ, Klink CA, Lugo AE, et al. 2006. Novel ecosystems: theoretical and management aspects of the new ecological world order. Glob. Ecol. Biogeogr. 15:1–7.

Mount J, Bennett W, Durand J, Fleenor W, Hanak E, Lund J, Moyle P. 2012. Aquatic ecosystem stressors in the Sacramento–San Joaquin Delta. Public Policy Inst. Calif.

Moyle PB, Light T. 1996. Fish invasions in California: do abiotic factors determine success? Ecology 77:1666–16670.

Nichols FH, Cloern JE, Luoma SN, Peterson DH. 1986. The modification of an estuary. Science 231:567–567.

Papworth S k., Rist J, Coad L, Milner-Gulland E j. 2009. Evidence for shifting baseline syndrome in conservation. Conserv. Lett. 2:93–100.

Pauly D. 1995. Anecdotes and the shifting baseline syndrome of fisheries. Trends Ecol. Evol. 10:430.

Rosenzweig ML. 2003. Reconciliation ecology and the future of species diversity. Oryx 37:194–205.

Sommer TR, Nobriga ML, Harrell WC, Batham W, Kimmerer WJ. 2001. Floodplain rearing of juvenile Chinook salmon: evidence of enhanced growth and survival. Can. J. Fish. Aquat. Sci. 58:325–333.

Whipple A, Grossinger RM, Rankin D, Stanford B, Askevold R. 2012. Sacramento-San Joaquin Delta historical ecology investigation: Exploring pattern and process. Richmond, CA: San Francisco Estuary Institute-Aquatic Science Center Historical Ecology Program Report No.: 672.

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