San Joaquin River

High Resolution Measurement of Levee Subsidence Related to Energy Infrastructure in the Sacramento-San Joaquin Delta

California Energy Commission (CEC) | August 31st, 2018

We assess flood overtopping potential (when flood water elevation exceeds levee elevation) to the levees surrounding the islands in the interior of California's S

We assess flood overtopping potential (when flood water elevation exceeds levee elevation) to the levees surrounding the islands in the interior of California's Sacramento-San Joaquin Delta. Because critical natural gas infrastructure is susceptible to overtopping-related disruption, we focus our analysis on regions that are crossed by the network of the state's natural gas pipelines. We use laser scanning data collected during 2015-2016 to estimate subsidence rates since 2007 when an earlier, Delta-wide, airborne laser-scanning topographic dataset was collected. For each levee studied, we combine: (1) the estimated subsidence rate, (2) a conservative range of sea-level rise projections and, (3) an estimate of the 100-year freshwater flood stage to project the time until exceedance of the federal levee height standard (PL84-99). We find that subsidence rates vary from 0-5 centimeters per year (cm/yr) with mean values of ~1-2 cm/year. Local gradients in subsidence can be on the order of cms/yr over a distance of 10s of meters parallel to the levee crests, and these types of gradients are present near some pipeline crossings. The Sherman Island region has subsidence rates close to a factor of 2 greater than other areas considered. Our projections indicate general ranges of exceedance date from about 2060 (fast sea-level rise scenario) to 2080 (slow sea-level rise scenario) with some places projected to exceed threshold by about 2050.

Highlights Central Valley Flood Protection Plan 2022 Update

California Department of Water Resources (DWR) | January 23rd, 2023

The 2022 Central Valley Flood Protection Plan Update was adopted by the Central Valley Flood Protection Board on December 16th, 2022. Just days later, beginning on Decemb

The 2022 Central Valley Flood Protection Plan Update was adopted by the Central Valley Flood Protection Board on December 16th, 2022. Just days later, beginning on December 27th, 2022, a series of atmospheric rivers began to impact California. This succession of atmospheric rivers resulted in 34 trillion gallons of water falling across California in 24 days, and 21 forecast points in the Central Valley reaching flood or monitor stage. Governor Gavin Newsom declared a state of emergency on January 4th, 2023; federal emergency and disaster declarations followed soon thereafter. These events underscore the importance of the CVFPP as the State’s strategic blueprint for investment in flood risk reduction in the Central Valley, especially in an era of whiplash weather—from drought to flooding— driven by the impacts of climate change.

History of Legislation and Policy Formation of the Central Valley Project

U.S. Department of Agriculture (USDA) | March 15th, 1946

History of the Delta Division, Central Valley Project

U.S. Bureau of Reclamation (USBR) | October 1st, 1994

The Delta Division of the Central Valley Project (CVP) acts as the hub around which the CVP revolves. The Delta Division contains the facilities that transfer water from

The Delta Division of the Central Valley Project (CVP) acts as the hub around which the CVP revolves. The Delta Division contains the facilities that transfer water from the Sacramento River, to bolster irrigation supplies to thirsty lands formerly dependent on water from the San Joaquin River. In time, the Delta Division became the hub for controversy revolving around the Central Valley Project. This document recounts the history of the Delta Division.  It was produced by the Bureau of Reclamation.

Holocene paleoclimate records from a large California estuarine system and its watershed region: linking watershed climate and bay conditions

Quaternary Science Reviews (Elsevier) | July 10th, 2006

The San Francisco Bay-Delta system includes a watershed that covers a large area of California and provides water to two-thirds of the State's population. Climate

The San Francisco Bay-Delta system includes a watershed that covers a large area of California and provides water to two-thirds of the State's population. Climate over the estuary and its watershed in the dry summer months is controlled by the subtropical high which dominates and deflects storms from California. The subtropical high weakens and migrates south as the Aleutian Low strengthens, bringing wet winter storms to the region. Paleoclimatic records from the Bay and its greater watershed, spanning the Holocene, are reviewed here in order to better understand natural variations of precipitation and runoff and the linkages between those variations and the salinity and ecosystems of the estuary. To better understand regional-scale climate patterns, paleoclimate records from coastal California and the Great Basin are also considered. Large fluctuations in climate have occurred during the period of interest, and there is generally good agreement between the paleoclimate records from different regions. Early Holocene climate throughout California was marked by rising temperatures and reduced moisture as seen in fire records from the watershed. This warmth and aridity peaked about 5000–7000 years ago and was followed by a cooling trend, with variable moisture conditions. The Estuary formed relatively rapidly in response to a high rate of sea level rise that dominated the Holocene until about 6000 years ago, and the subsequent reduced rate of inundation allowed vast tidal marshes to form along the edges of the estuary, which have since been recording changes in environmental conditions. The impacts of changing regional climate patterns are experienced in the San Francisco Bay-Delta system, as altered fresh water flows result in altered estuary salinity. For example, approximately 3800 cal yr B.P., records from throughout the state indicate a cool, moist period, and Bay salinity was reduced; this period was followed by a general drying trend throughout California over the last two millennia, punctuated by decades to centuries-long droughts and brief, extremely wet events. In particular, during the period ca. 1000–800 cal yr B.P. (A.D. 950–1150) conditions seem to have been unusually dry in many parts of the watershed, reducing the fresh water flows to the estuary, and shifting tidal marsh plant assemblages toward less diverse, but more salt-tolerant plants. In contrast, the Little Ice Age (ca. 550–200 cal yr B.P.) brought unusually cool and wet conditions to much of the watershed, and lowered salinity in the Bay. Many reconstructions suggest that notably stable conditions have prevailed over the instrumental period, i.e., after ca. A.D. 1850, even including the severe, short-term anomalies experienced during this period. Interdecadal variability is common in many of the records, with timescales of ca. 55, 70, 90, 100, 150, and 200 years.

Hourly storm characteristics along the U.S. West Coast: Role of atmospheric rivers in extreme precipitation

American Geophysical Union (AGU) | June 21st, 2017

Gridded hourly precipitation observations over the conterminous U.S., from 1948 to 2002, are analyzed to determine climatological characteristics of storm precipitation t

Gridded hourly precipitation observations over the conterminous U.S., from 1948 to 2002, are analyzed to determine climatological characteristics of storm precipitation totals. Despite generally lower hourly intensities, precipitation totals along the U.S. West Coast (USWC) are comparable to those in southeast U.S. (SEUS). Storm durations, more so than hourly intensities, strongly modulate precipitation-total variability over the USWC, where the correlation coefficients between storm durations and storm totals range from 0.7 to 0.9. Atmospheric rivers (ARs) contribute 30–50% of annual precipitation on the USWC and make such large contributions to extreme storms that 60–100% of the most extreme storms, i.e., storms with precipitation-total return intervals longer than 2 years, are associated with ARs. These extreme storm totals are more strongly tied to storm durations than to storm hourly or average intensities, emphasizing the importance of AR persistence to extreme storms on the USWC.

How freeing rivers can help California ease flood risks and revive ecosystems

Los Angeles Times | February 20th, 2024

Natural floodplains — the lush green lands along rivers that historically flooded, retained water, and nourished life in the heart of the valley — were mostly drained

Natural floodplains — the lush green lands along rivers that historically flooded, retained water, and nourished life in the heart of the valley — were mostly drained and converted to farmland generations ago as the state’s waters were dammed and diverted. Today, an effort to bring back some of those floodplains is flourishing at the 2,100-acre Dos Rios Ranch Preserve near Modesto, where workers years ago planted native trees on retired farm fields and removed berms to create space for water to spread out again.

How Much Snow?

Scientific American | March 1st, 1939

Last winter, at 682 different locations in the Rockies and high Sierras, more than 30,000 exact measurements of snow depth and water content were taken, in order to e

Last winter, at 682 different locations in the Rockies and high Sierras, more than 30,000 exact measurements of snow depth and water content were taken, in order to estimate how much water the mountain snowfields would supply in the run-off during summer months. To make this survey cost more than $100,000. On it was predicated the expenditure, and saving, of millions. While the science of surveying snow is still in its infancy, its extent and importance are increasing rapidly. Ridiculed at first, in the last few years it has taken on world-wide aspects. To grasp its significance in our western states, picture a series of snow-covered mountain ranges that by their streams make life possible in dry intervening valleys. Abundant snow means abundant water. Abundant water means power, and cheap electricity. More important still, it means abundant crops. Dearth of snowfall in the mountains means dry river beds in August, machinery standing idle, thirsty cattle, and dying plants.

Human contributions to evapotranspiration mitigate swings in dry-to-wet year transitions

Nature Portfolio (Springer Nature) | January 9th, 2026

California’s food and economic security depends on water availability, particularly under increasingly extreme climate scenarios. A key component of the water balance i

California’s food and economic security depends on water availability, particularly under increasingly extreme climate scenarios. A key component of the water balance is evapotranspiration, the combination of soil and surface evaporation and plant transpiration. Evapotranspiration is influenced by natural drivers (e.g., climate, vegetation cover) and human intervention (e.g., irrigation, land management). Here, we analyze the transition between one of California’s driest years (2022) to an exceptionally wet year (2023) to assess evapotranspiration responses to climate extremes. Despite increased precipitation, total statewide evapotranspiration changed less than 10%. In 2022, human contributions accounted for 30% of statewide evapotranspiration and 80% in managed lands. In 2023, natural evapotranspiration increased, and human contributions fell by 30%, yet still comprised nearly 50% of evapotranspiration in managed areas. Our findings underscore the enduring role of human activity on California’s hydrology, even during wet years, and demonstrate a framework to separate natural and anthropogenic controls on evapotranspiration.

Human Costs of Nitrate-contaminated Drinking Water in the San Joaquin Valley

Pacific Institute | March 1st, 2011

While most Californians take for granted that safe water is readily available at the turn of a tap, a growing number of communities, primarily in the San Joaquin Valley a

While most Californians take for granted that safe water is readily available at the turn of a tap, a growing number of communities, primarily in the San Joaquin Valley and other agricultural areas of the state, face very real impacts from nitrate contamination of the drinking water sources serving their homes and schools. New research led by the Pacific Institute, The Human Costs of Nitrate-Contaminated Drinking Water in the San Joaquin Valley, finds that nitrate contamination of groundwater has wide-reaching effects on California’s health, economic vitality, and environmental well being, disproportionately affecting low-income households and Spanish-speaking residents. The analysis brings a stark reality check to the fore as the Central Valley Water Board considers a new regulatory program for irrigated lands, the primary source of nitrate contamination in the San Joaquin Valley. There have never been any regulatory requirements on irrigated agriculture to protect groundwater from fertilizers, which are the primary source of nitrate in the valley. Nitrate levels have increased dramatically in drinking water supplies over the last few decades. The new study, The Human Costs of Nitrate-Contaminated Drinking Water in the San Joaquin Valley, a collaboration of the Pacific Institute, Community Water Center, Clean Water Fund, and California Rural Legal Assistance Foundation, focuses on the household costs of avoiding nitrate-contaminated drinking water connected to community water systems and the costs to these systems of removing or avoiding nitrates, and it points to key policies and further research needed to better understand and resolve this entrenched challenge. The eight-county San Joaquin Valley has some of the most contaminated aquifers in the nation: 92 drinking water systems in the San Joaquin Valley had a well with nitrate levels above the legal limit from 2005-2008, potentially affecting the water quality of approximately 1.3 million residents. In addition to public water systems, the State Water Board sampled 181 domestic wells in Tulare County in 2006 and found that 40% of those tested had nitrate levels above the legal limit.