Regional Watershed Modeling and Trends Implementation Plan

San Francisco Estuary Institute (SFEI) | July 1st, 2019

Regional Watershed Spreadsheet Model (RWSM) Year 5 Progress Report

San Francisco Estuary Institute (SFEI) | March 1st, 2016

The Regional Watershed Spreadsheet Model (RWSM) is a regional-scale planning tool developed primarily to estimate long-term average annual loads from the small tributari

The Regional Watershed Spreadsheet Model (RWSM) is a regional-scale planning tool developed primarily to estimate long-term average annual loads from the small tributaries surrounding San Francisco Bay, and secondarily to provide supporting information for prioritizing watersheds or areas within watersheds for management actions. The RWSM has been in development since 2010. In previous years, obstacles to calibrating the PCB and Hg models included issues associated with GIS data underlying the Model, a simplistic model structure and parameterization, lack of available empirical data for calibrating concentrations associated with specific land uses and source areas, and the high uncertainty with the empirical calibration dataset. The modeling effort in Years 2014 and 2015 (Year 4 and 5 of the model development) focused on improving the model calibration to attempt to resolve these issues. The major changes included switching from a sediment-based model to a water-based model, elimination of double counting of source areas on top of general land uses, changes in the model calibration approach, and changes to the land use grouping.

Regulatory steps needed to protect and conserve wetlands not subject to the Clean Water Act

California State Water Resources Control Board (SWRCB) | November 17th, 2003

This report responds to legislative direction to describe the steps and resources needed to protect California wetlands and other waters that are not covered by the feder

This report responds to legislative direction to describe the steps and resources needed to protect California wetlands and other waters that are not covered by the federal Clean Water Act (CWA). It gives special attention to "isolated" waters removed from CWA jurisdiction by the U.S. Supreme Court's 2001 decision in Solid Waste Agency of Northern Cook County v. U.S. Army Corps of Engineers (SWANCC). Wetlands and riparian areas support extraordinary biodiversity and are uniquely important in sustaining the hydrologic, chemical, and ecological integrity of broader aquatic systems. However, for physical and legal reasons, they present special management challenges. Neither CWA nor the state Porter-Cologne Water Quality Control Act (Porter-Cologne) were designed to conserve wetlands, and their regulatory protection is therefore often problematic and incomplete.

Reimagining Water Infrastructure in a Changing California

American Water Resources Association (AWRA) | April 15th, 2023

For much of the 20th century, California’s water supply strategy has relied on building large reservoirs and conveyance systems to store and divert surface water and dr

For much of the 20th century, California’s water supply strategy has relied on building large reservoirs and conveyance systems to store and divert surface water and drilling ever deeper wells to tap declining aquifers. This approach has brought many benefits but has also come at great social, economic, and environmental costs. Moreover, these traditional water supplies are tapped out. Even in wet years, the state’s major rivers are overallocated and major aquifers severely overdrafted. Dry years intensify these issues. Persistent water challenges, the severe drought, and the intensifying effects of climate change highlight the vulnerability of California’s water systems and the need for new approaches.

Reinitiation of Consultation on the Coordinated Long-Term Modified Operations of the Central Valley Project and State Water Project

U.S. Bureau of Reclamation (USBR) | February 18th, 2020

U.S. Bureau of Reclamation ROD index page

U.S. Bureau of Reclamation ROD index page

Relationship between wetland condition, stress, and buffer

San Francisco Estuary Institute (SFEI) | April 25th, 2016

Relationship between wetland size and CRAM condition scores for depressional wetlands

San Francisco Estuary Institute (SFEI) | March 28th, 2016

Relationship of Delta Cross Channel Gate Operations to Loss of Juvenile Winter-run Chinook Salmon at the CVP/SWP Delta Facilities

California Department of Fish and Wildlife (CDFW) | July 1st, 2003

Winter-run Chinook salmon are distinguishable from the three other Chinook runs in the Sacramento River system by the timing of their upstream migration and spawning. Due

Winter-run Chinook salmon are distinguishable from the three other Chinook runs in the Sacramento River system by the timing of their upstream migration and spawning. Due to precipitous decline in the population from the late 1960’s through the late 1980’s, NOAA Fisheries listed the run as “threatened” in August 1989, and subsequently reclassified the run as “endangered” in 1992. The state of California listed the run as endangered in 1989.  Many factors contributed to the decline in the winter-run Chinook population. Among these factors, operation of the federal Central Valley Project and State Water Project has had continuing impacts on winter-run Chinook. Of particular concern have been the direct entrainment losses of juvenile winter-run Chinook at the project export facilities in the Delta. 

Relative impacts of mitigation, temperature, and precipitation on 21st-century megadrought risk in the American Southwest

American Association for the Advancement of Science (AAAS) | October 5th, 2016

Megadroughts are comparable in severity to the worst droughts of the 20th century but are of much longer duration. A megadrought in the American Southwest would

Megadroughts are comparable in severity to the worst droughts of the 20th century but are of much longer duration. A megadrought in the American Southwest would impose unprecedented stress on the limited water resources of the area, making it critical to evaluate future risks not only under different climate change mitigation scenarios but also for different aspects of regional hydroclimate. We find that changes in the mean hydroclimate state, rather than its variability, determine megadrought risk in the American Southwest. Estimates of megadrought probabilities based on precipitation alone tend to underestimate risk. Furthermore, business-as-usual emissions of greenhouse gases will drive regional warming and drying, regardless of large precipitation uncertainties. We find that regional temperature increases alone push megadrought risk above 70, 90, or 99% by the end of the century, even if precipitation increases moderately, does not change, or decreases, respectively. Although each possibility is supported by some climate model simulations, the latter is the most common outcome for the American Southwest in Coupled Model Intercomparison 5 generation models. An aggressive reduction in global greenhouse gas emissions cuts megadrought risks nearly in half.

Relative risk of groundwater-quality degradation near California (USA) oil fields estimated from 3H, 14C, and 4He

Applied Geochemistry (Elsevier) | June 5th, 2021

 Relative risks of groundwater-quality degradation near selected California oil fields are estimated by examining spatial and temporal patterns in chemical and isotopic

 Relative risks of groundwater-quality degradation near selected California oil fields are estimated by examining spatial and temporal patterns in chemical and isotopic data in the context of groundwater-age categories defined by tritium and carbon-14. In the Coastal basins, western San Joaquin Valley (SJV), and eastern SJV; 82, 76, and 0% of samples are premodern (pre-1953 recharge), respectively; and 3, 0, and 31% are modern (recharged during or after 1953), respectively. Carbon-14 and helium-4 data indicate most premodern samples are 1000 to 10,000 (33%) or >10,000 (50%) years old. Organic chemicals that could be associated with deeper hydrocarbon reservoirs (e.g. thermogenic gases and benzene) occur most frequently in premodern groundwater, suggesting premodern groundwater has a higher risk of degradation from upward migration of hydrocarbons than modern and mixed-age groundwater. Low sulfate concentrations in some premodern groundwater containing high thermogenic-methane concentrations (>28 mg/L) indicate methane attenuation associated with sulfate reduction can be limited in premodern groundwater. The more common occurrence of manufactured compounds, like tetrachloroethene, in modern and mixed-age groundwater than in premodern groundwater indicates modern and mixed-age groundwater has a higher risk of degradation from land-surface sources than premodern groundwater. Time-series data for chloride in groundwater affected by disposal of oil-field water in unlined ponds indicate some modern and mixed-age groundwater are susceptible to chemical migration within 2–3 km of surface sources. Timescales for diluting chloride concentrations in groundwater with fresh recharge once disposal ponds are decommissioned are shorter in mixed-age groundwater with large fractions of modern water (9–14 years in one example) than in mixed-age groundwater with large fractions of premodern water (no evidence of dilution after 12 years of monitoring in one example). The presence of predominantly premodern groundwater in the Coastal basins and western SJV indicates these areas have relatively high risk from upward migration of hydrocarbons, reduced methane attenuation capacity, and long dilution times, whereas predominantly modern-and mixed-age groundwater in the eastern SJV indicates this area has relatively high risk from chemical migration from land-surface sources and subsequent extensive spreading. Age-based characterizations of relative risk could inform the design of groundwater-monitoring programs near oil fields in terms of the spatial distribution of monitoring points relative to source areas and monitoring frequency and duration.