Replenishing Groundwater in the San Joaquin Valley: 2024 Update

Public Policy Institute of California (PPIC) | June 6th, 2024

Strategies to replenish groundwater basins—long used in some areas of the San Joaquin Valley—have increasingly come into focus as the region seeks to bring its overd

Strategies to replenish groundwater basins—long used in some areas of the San Joaquin Valley—have increasingly come into focus as the region seeks to bring its overdrafted groundwater basins into balance under the Sustainable Groundwater Management Act (SGMA). In late 2023, following a very wet winter and spring, we conducted a repeat survey of local water agencies about their recharge activities and perspectives, building on a similar survey at the end of 2017, a year with similar levels of precipitation. We found signs of progress on recharge since 2017, as well as areas where more work is needed to take full advantage of this important water management tool.

Sacramento County | Making Room for Recharge: Cosumnes River Levee Removal and Floodplain Restoration

Nature Conservancy | June 12th, 2014

Reconnecting rivers to floodplains can facilitate groundwater recharge. A recent project along the Cosumnes River is one of the first to intentionally demonstra

Reconnecting rivers to floodplains can facilitate groundwater recharge. A recent project along the Cosumnes River is one of the first to intentionally demonstrate this recharge benefit. While this project was expensive and more complex than many forms of recharge, public funding paid for the project and a partnership with UC Davis is improving the understanding of groundwater-surface water interactions and basin groundwater conditions. In 2014, The Nature Conservancy piloted this concept by selectively removing portions of a private levee system along the Cosumnes River to enhance floodplain processes and restore approximately 500 acres of riparian habitat. The levee removal project offers multiple environmental benefits, including increased groundwater recharge in the floodplain.

Santa Cruz Mid-County Groundwater Basin Groundwater Sustainability Plan

Santa Cruz Mid-County Groundwater Basin Groundwater Sustainability Agency | November 21st, 2019

Due to size, this file has been divided Part 1, Part 2, Part 3, Part 4, Part 5

Due to size, this file has been divided Part 1, Part 2, Part 3, Part 4, Part 5

Seasonal and Long-Term Clarity Trend Assessment of Lake Tahoe, California–Nevada

U.S. Geological Survey (USGS) | July 20th, 2022

The clarity of Lake Tahoe, observed using a Secchi disk on a regular basis since the late 1960s, continues to be a sentinel metric of lake health. Water clarity is influe

The clarity of Lake Tahoe, observed using a Secchi disk on a regular basis since the late 1960s, continues to be a sentinel metric of lake health. Water clarity is influenced by physical and biological processes and has declined in the five decades of monitoring, revealing differences between summer (June–September) and winter (December–March). This document summarizes key findings of a study of Lake Tahoe water clarity, including long-term variability and the relative importance of several influencing variables and processes. This study, prepared in cooperation with the Nevada Division of Environmental Protection, focused on (1) an apparent divergence in clarity trends between summer and winter periods, (2) observed changes in in-lake physical and ecological variables that may influence or control seasonal and annual clarity trends, and (3) five research hypotheses regarding lake clarity that were developed by Lake Tahoe management agencies. Previously collected data were used to complete this study. Trend analysis confirmed that winter clarity stabilized (that is, there is no longer a statistically significant trend up or down) during the last 20 years. Evaluation of clarity for selected months in the 50-year Secchi disk clarity dataset showed that only two summer months, July and August, had statistically significant decreases in clarity from 2000–19. Different subsets of available data were analyzed to reveal the presence or absences of trends for each season, decade, and month. Five hypotheses related to lake clarity were part of the study described by this report. Hypothesis 1 stated that clarity is controlled predominantly by the distribution and volumetric density of fine particles in suspension. This hypothesis was studied using available data describing in-lake fine (0–20 micrometers) particles from 2008–19. Water clarity was negatively correlated with in-lake particle abundance, with particles in the 1.0-4.6 μm range having the greatest effect, consistent with light-scattering theory. Estimated abundances of diatoms of the genus Cyclotella also were found to be negatively correlated with clarity. Data limitations precluded a complete investigation of hypothesis 2, which stated that the observed improvements in winter water clarity are a response to decreasing fine suspended-sediment concentrations in the lake resulting from load reductions from upland sources in and near urbanized areas. Data describing fine-sediment loading from urban areas to the lake were only available since 2014, and only once or twice per month. A slight, statistically significant, negative correlation was identified between urban fine-particle loading and monthly lake clarity with a 4-month lag. Particle abundance in monitored streams is highly correlated with simultaneous particle abundance in the lake.

Sediment Lithology and Borehole Erosion Testing, American and Sacramento Rivers, California

U.S. Geological Survey (USGS) | July 9th, 2020

A field investigation intended to measure the potential for erosion of sediments beside the American and Sacramento Rivers near Sacramento, California, is described. The

A field investigation intended to measure the potential for erosion of sediments beside the American and Sacramento Rivers near Sacramento, California, is described. The study featured two primary components: (1) drilling and soil sampling to reveal lithology, down to depths matching the local river thalweg, where possible, and (2) borehole erosion tests (BETs) as described by Briaud and others (2017) at many of the same locations. The latter test involved drilling a vertical hole, measuring its diameter profile, inserting a hollow drilling rod to almost the bottom of the hole, and pumping fluid through the drilling rod at a known discharge for a chosen time interval. The hole was then resurveyed to establish an erosion rate (change in borehole radius divided by duration of flow event) as a function of depth, and the test was repeated. This test was performed with water as the erosive fluid at 12 locations, with 1 test repeated with drilling mud. Lithology holes were drilled at these same locations and an additional five locations. Drilling operations took place on river left and river right on the American River and river left (left bank, when looking downstream) on the Sacramento River.

Soil and Groundwater Contamination: Nonaqueous Phase Liquids–Principles and Observations

American Geophysical Union (AGU) | January 1st, 2005

Published by the American Geophysical Union as part of the Water Resources Monograph Series, Volume 17. Nonaqueous phase liquids (NAPLs) are frequently found as soil a

Published by the American Geophysical Union as part of the Water Resources Monograph Series, Volume 17. Nonaqueous phase liquids (NAPLs) are frequently found as soil and groundwater contaminants. Highly toxic even in small volumes, NAPLs can pose a threat to human health and damage surface and subsurface ecosystems. In this book, we clarify the complex phenomena of NAPL migration and offer insight into the behavior of NAPLs at sites undergoing monitoring and remediation. Contents include discussion on: * Principles of NAPL behavior in the subsurface, including flow, transfer of components to water and gas phases, and transport * Migration and distribution * Site characterization and monitoring * Remediation methods, including hydraulic removal, pump and treat, and soil vapor extraction * Further discussion on gaps in our understanding of NAPLs at the field scale along with a thorough tutorial approach and supplemental CD, make this book an important guide and resource for practicing engineers and scientists, risk assessment professionals, teachers, and students.

Statement of Findings regarding the Approval of the Coastal Plain of Orange County Alternative Groundwater Sustainability Plan

California Department of Water Resources (DWR) | June 17th, 2019

Statement of Findings regarding the Approval of the Sacramento Valley - Solano Subbasin Groundwater Sustainability Plan

California Department of Water Resources (DWR) | January 18th, 2024

The Department of Water Resources (Department) has evaluated the groundwater sustainability plan (GSP or Plan) submitted for the Sacramento Valley – Solano Subbasin and

The Department of Water Resources (Department) has evaluated the groundwater sustainability plan (GSP or Plan) submitted for the Sacramento Valley – Solano Subbasin and has determined the GSP is approved. The approval is based on recommendations from the Staff Report, included as an exhibit to the attached Statement of Findings, which describes that the Solano Subbasin GSP satisfies the objectives of the Sustainable Groundwater Management Act (SGMA) and substantially complies with the GSP Regulations. The Staff Report also proposes recommended corrective actions that the Department believes will enhance the GSP and facilitate future evaluation by the Department. The Department strongly encourages the recommended corrective actions be given due consideration and suggests incorporating all resulting changes to the GSP in future updates.

Statement of Findings regarding the Periodic Review and Approval of the Coastal Plain of Orange County Basin Alternative Groundwater Sustainability Plan

California Department of Water Resources (DWR) | June 27th, 2024

Sustainable Groundwater Management Act 2019 Basin Prioritization Process and Results

California Department of Water Resources (DWR) | April 1st, 2019