Debris-Restraining Barriers of the Yuba River

Scientific American | November 19th, 1904

In the years following the discovery of gold in California, the processes of mining for this precious metal caused the removal of vast quantities of detritus from the w

In the years following the discovery of gold in California, the processes of mining for this precious metal caused the removal of vast quantities of detritus from the western slopes of the Sierra Mountains into the streams and rivers of the valleys below. Gold was found in the beginning in gravel beds, where it had probably been deposited by rivers flowing in prehistoric times. These gravel beds exist in great numbers in a comparatively small area along the western slopes of the Sierra Mountains near the headwaters of streams draining into the Sacramento and San Joaquin valleys. In securing gold from these mountains the sorting action of water was necessary, and in order to facilitate mining operations. ditches of great length and size were built, frequently at great expense, to carry water to the localities where gold had been discovered. Streams of water under great pressures were directed at these gravel banks through nozzles sometimes as large as nine inches in diameter, to break down the gravel banks and wash the detritus through sluice ways where the gold could be caught. Streams carry ing as much as 3,500 miner's inches were not uncommon. It is thus easily seen that such powerful agencies would rapidly wash down whole hillsides, which would naturally be carried into the canyons and small streams in the vicinity of the mines, to be washed farther and farther down stream with each succeeding rainy season. These mining operations were carried on for a number of years without interruption until the valley country below became more thickly populated, when the injuries caused to the rivers and the neighboring farm lands became important enough to cause those damaged to seek legal redress.

Decadal Shifts in Groundwater Age Detected by Environmental Tracers Across California

American Geophysical Union (AGU) | March 23rd, 2026

Groundwater age tells us how long water has been underground since it last infiltrated the land surface. Monitoring changes in groundwater age helps identify aquifer stre

Groundwater age tells us how long water has been underground since it last infiltrated the land surface. Monitoring changes in groundwater age helps identify aquifer stress from pumping or shifts toward new hydrologic conditions—key factors for sustainable water management. In this study, changes in groundwater age were tested by comparing chemical tracer data collected about 10 years apart from hundreds of wells across California. Chemical tracers are dissolved substances with known historical records and decay rates that can be used to infer groundwater age. Using models that estimate expected tracer concentrations under steady-age conditions, this study found that nearly one-third of the wells showed significant changes in groundwater age over time. These changes were most common in areas with heavy agricultural use, where pumping and irrigation have altered how water moves underground. These shifts in age can also affect water quality, especially when younger water carries contaminants like nitrate. By using a statistical modeling approach, this study shows how changes in groundwater age can help identify aquifers under stress and support efforts to manage groundwater sustainably.

Decadal trends in the quality of groundwater used for public drinking-water supply in California, 2004–2023, California groundwater ambient monitoring and assessment program, priority basin project

U.S. Geological Survey (USGS) | February 25th, 2026

This study provides a comprehensive assessment of decadal changes in the quality of groundwater used for public drinking-water supply at 444 monitoring site

This study provides a comprehensive assessment of decadal changes in the quality of groundwater used for public drinking-water supply at 444 monitoring sites across California during 2004–2023. We assessed decadal step trends in groundwater quality for 145 water-quality constituents and geochemical indicators statewide and across geographic and land-use based network groups. We evaluated the statistical significance of directional changes (predominant increase or decrease of constituent concentrations) and the magnitude of those changes across all network groups. Uranium showed the most widespread directional and high-magnitude increases of all constituents with regulatory benchmarks statewide, particularly in the agriculture-dominated Central Valley as well as urban- and desert-dominated regions of Southern California. Fluoride and perchlorate showed the most widespread directional and high-magnitude decreases of all constituents with regulatory benchmarks statewide, which were also most pronounced in Southern California. Although arsenic and nitrate did not often register significant directional changes across network groups, they showed widespread, high-magnitude changes in both directions (increase and decrease) at levels often exceeding 10 percent of respective regulatory benchmarks statewide. Triazine herbicides (atrazine and simazine) and the gasoline oxygenate methyl tert-butyl ether (MTBE) showed significant directional decreases statewide, but not at levels considered to be of high magnitude compared to respective regulatory benchmarks. We observed significant directional and high-magnitude increases of total dissolved solids (TDS) statewide, which were most pronounced in agricultural areas. Analysis of explanatory geochemical indicators indicated that prevalent statewide increases of alkalinity and calcium were the predominant components of the observed statewide increases in TDS by mass. Widespread increases in groundwater alkalinity and calcium across agricultural and urban areas may be related, in part, to warm-season irrigation and other anthropogenic factors that have shifted soil weathering dynamics over the long term. Increasing alkalinity concentrations were related to increasing uranium concentrations, particularly in areas with aquifer materials derived from granitic rocks. Conversely, increasing calcium concentrations were related to decreasing fluoride concentrations, particularly in areas where fluoride occurred naturally at elevated concentrations. Decrease of perchlorate, triazine herbicides, and MTBE are likely related to decreased anthropogenic source inputs over time and natural attenuation in aquifers.

Decadal trends in the quality of groundwater used for public drinking-water supply in California, 2004–23

U.S. Geological Survey (USGS) | July 30th, 2026

This study provides a comprehensive assessment of decadal changes in the quality of groundwater used for public drinking- water supply at 444 monitoring sites across Cali

This study provides a comprehensive assessment of decadal changes in the quality of groundwater used for public drinking- water supply at 444 monitoring sites across California during 2004–23. We assessed decadal step trends in groundwater quality for 145 water- quality constituents and geochemical indicators statewide and across geographic and land- use based network groups. We evaluated the statistical significance of directional changes (predominant increase or decrease of constituent concentrations) and the magnitude of those changes across all network groups.

Decision on Petition for Rulemaking to Set Permanent Minimum Flows on the Shasta River

California State Water Resources Control Board (SWRCB) | February 16th, 2024

Decision Scaling Evaluation of Climate Risks to the State Water Project

California Department of Water Resources (DWR) | May 29th, 2019

This Final Decision Scaling Vulnerability Assessment Report updates and describes a joint endeavor of the California Department of Water Resources (DWR) and the Universit

This Final Decision Scaling Vulnerability Assessment Report updates and describes a joint endeavor of the California Department of Water Resources (DWR) and the University of Massachusetts, Amherst (UMass) to improve planning for the uncertain effects of climate change on the California Central Valley Water System (CVS)1 by integrating vulnerability-based analysis with traditional risk-based assessment methods. This report summarizes the research goals, analytical approach, workflow of modeling tools, evaluation of alternative experimental designs, refined strategy for data visualization, and assessment of the vulnerability of the CVS to climate change.  This report begins with a review of historical and projected climate change in California, which includes descriptions of several DWR-UMass team investigations of historical records, observed climate trends, and many climate projections for the CVS, specifically. The next section of this report summarizes the work previously accomplished by the academic community, the government, and the community of water resources practitioners evaluating climate change-related risks to the CVS.  With that background in place, this report explains the methodology developed for this study (illustrated in Figure ES1) and provides details on each sub-step of the process. Whereas previous studies have tested the response of some aspect of the California water system to ahistorical climate traces, the decision scaling approach adopted for this study allows systematic assessment of the vulnerability of the entire (interconnected and complex) CVS to a wide range of potential future climate conditions, and quantification of the significance of climate shift relative to natural (and climate-change-amplified) variability. The climate response function that results from the decision scaling approach depicts expected water system performance relative to historical performance across a range of climate changes. An important benefit of this approach is the ability to use a variety of climate information sources to assess the level of concern to assign to the vulnerabilities that are identified. Consequently, climate information, including climate change projections and formal probability estimates, can be used as a sensitivity factor when assessing risk, rather than the driver of the analysis. This allows discussion of risk and opportunity (each a function of impact and likelihood) in water system investment.  This assessment of long-term and persistent hydrologic impacts of climate change focuses on the effects to the operation of the State Water Project (SWP), including ecological conditions that dictate operating rules. DWR owns and operates the SWP for flood control, maintenance of environmental and water quality conditions, water supply, hydropower, and recreation. Consequently, analysis of SWP performance under climate-changed conditions yields an array of impact metrics across these areas of concern. The analysis focuses on persistent medium- and long-term conditions evaluated at a monthly time-step. Short-duration extreme precipitation events that cause flooding may also stress water resource management but are beyond the scope of this study.  This study has adopted CalLite 3.0 to simulate the coordinated operations of the Central Valley Project (CVP) and SWP under a wide range of climate possibilities. Climate traces are developed through coupling historical daily temperature and precipitation (1950–2013) (Livneh et al. 2013) to the paleo-dendrochronological reconstructed streamflow record of the Sacramento-4-river annual streamflow (900–2013) (Meko et al. 2014). An advanced hydrologic model, the Sacramento Soil Moisture Accounting distributed hydrologic model (SAC-SMA-DS), translates the hydroclimatic traces into streamflow, which are the key inputs to the water system model.

Decline of the world's saline lakes

Nature Portfolio (Springer Nature) | October 23rd, 2017

Many of the world's saline lakes are shrinking at alarming rates, reducing waterbird habitat and economic benefits while threatening human health. Saline lakes are long-t

Many of the world's saline lakes are shrinking at alarming rates, reducing waterbird habitat and economic benefits while threatening human health. Saline lakes are long-term basin-wide integrators of climatic conditions that shrink and grow with natural climatic variation. In contrast, water withdrawals for human use exert a sustained reduction in lake inflows and levels. Quantifying the relative contributions of natural variability and human impacts to lake inflows is needed to preserve these lakes. With a credible water balance, causes of lake decline from water diversions or climate variability can be identified and the inflow needed to maintain lake health can be defined. Without a water balance, natural variability can be an excuse for inaction. Here we describe the decline of several of the world's large saline lakes and use a water balance for Great Salt Lake (USA) to demonstrate that consumptive water use rather than long-term climate change has greatly reduced its size. The inflow needed to maintain bird habitat, support lake-related industries and prevent dust storms that threaten human health and agriculture can be identified and provides the information to evaluate the difficult tradeoffs between direct benefits of consumptive water use and ecosystem services provided by saline lakes.

Declines in Peak Snow Water Equivalent and Elevated Snowmelt Rates Following the 2020 Cameron Peak Wildfire in Northern Colorado

American Geophysical Union (AGU) | March 28th, 2023

The loss of tree canopy greatly increases the amount of solar energy that reaches the snow surface. Soot and debris from burned trees make the snow surface darker, result

The loss of tree canopy greatly increases the amount of solar energy that reaches the snow surface. Soot and debris from burned trees make the snow surface darker, resulting in more of this energy being absorbed. Late-season snow storms were able to temporarily counteract some of these effects by burying the darker snow surface. As more and more of the western United States is fire-impacted, it is essential to better understand and account for these impacts on this critical water reservoir for this region.

Declining Freshwater Availability in the Colorado River Basin Threatens Sustainability of Its Critical Groundwater Supplies

American Geophysical Union (AGU) | May 27th, 2025

Climate change is causing more frequent and intense droughts around the world, including in the Colorado River Basin, which supplies water to seven U.S. states and Mexico

Climate change is causing more frequent and intense droughts around the world, including in the Colorado River Basin, which supplies water to seven U.S. states and Mexico, and is facing severe water shortages. This study investigates how changes in water storage components (e.g., snow, surface water, soil moisture and groundwater) and water use are contributing to these shortages, and impacting agriculture and municipal water supplies, using data from the NASA GRACE and GRACE Follow-On (GRACE-FO) satellite missions, land surface models, and in situ data over the past two decades. Results show significant losses of groundwater: 7.8.0 ± 5.3 km3 in the Upper CRB (UCRB) and 25.5 ± 7.4 km3 in the Lower CRB (LCRB). Progress toward sustainable groundwater could be achieved by reducing groundwater extraction, in line with current rates of depletion (0.35 km3 in the UCRB and 1.15 km3 in the LCRB). This research highlights the importance of understanding the factors affecting groundwater levels to create sustainable water management strategies that can help secure water resources for the region's future.

Declining Groundwater Level Effects on Supply Well Operations

University of California, Davis (UC Davis) | December 1st, 2017

Pumping more from groundwater basins than they can sustainably supply decreases groundwater levels, often by undesirable amounts. Economic impacts from overdraft

Pumping more from groundwater basins than they can sustainably supply decreases groundwater levels, often by undesirable amounts. Economic impacts from overdraft and drought include increased costs for supplying water and lost revenue from inability to meet water demands. The combination of decreased groundwater level with existing well depth may limit well production as pumping costs increase and wells run dry. Declining groundwater elevations may also incur costs to move pumps deeper in the wells. Further falling groundwater elevation increases costs for production and maintenance, and decreases production capacity, as pumping levels drop into the screened intervals of wells and cause screen clogging and corrosion. In more extreme cases, well replacement costs may be incurred if groundwater drops so low that adequate submergence of pumps cannot be maintained, and wells become unusable. The potential impacts of decreasing groundwater elevation on supply well operations were evaluated for a study area in California’s Central Valley (greater vicinity of Tulare, CA). Well construction data from logs provided by the California Department of Water Resources (DWR) were characterized through statistical analysis of the elevations for the tops and bottoms of screened intervals. Groundwater elevation time series were obtained from the DWR Water Data Library. Estimated trends in well capacity loss were developed from estimates of the fraction of wells over time that had standing water levels (minus an estimated pumping drawdown) below 1) the top of the screened interval and 2) the bottom of the screened interval. The end result is a method for estimating the costs of water level declines over time from drought or groundwater overdraft due to effects on proper operation and pumping of wells. The conceptual approach, data, methods, and conclusions of this thesis draw from a research report funded by the California Department of Food and Agriculture (CDFA).