Electrical Resistivity Investigation of Fluvial Geomorphology to Evaluate Potential Seepage Conduits to Agricultural Lands along the San Joaquin River, Merced County, California, 2012–13

U.S. Geological Survey (USGS) | ?

Increased flows in the San Joaquin River, part of the San Joaquin River Restoration Program, are designed to help restore fish populations. However, increased seepage los

Increased flows in the San Joaquin River, part of the San Joaquin River Restoration Program, are designed to help restore fish populations. However, increased seepage losses could result from these higher restoration flows, which could exacerbate existing drainage problems in neighboring agricultural lands and potentially damage crops. Channel deposits of abandoned river meanders that are hydraulically connected to the river could act as seepage conduits, allowing rapid and widespread water-table rise during restoration flows. There is a need to identify the geometry and properties of these channel deposits to assess their role in potential increased seepage effects and to evaluate management alternatives for reducing seepage. Electrical and electromagnetic surface geophysical methods have provided a reliable proxy for lithology in studies of fluvial and hyporheic systems where a sufficient electrical contrast exists between deposits of differing grain size. In this study, direct-current (DC) resistivity was used to measure subsurface resistivity to identify channel deposits and to map their subsurface geometry. The efficacy of this method was assessed by using DC resistivity surveys collected along a short reach of the San Joaquin River in Merced County, California, during the summers of 2012 and 2013, in conjunction with borings and associated measurements from a hydraulic profiling tool. Modeled DC resistivity data corresponded with data from analyses of core samples, hand-auger samples, a hydraulic profiling tool, and aerial photographs, confirming that DC resistivity was effective for differentiating between silty and sandy deposits in this setting. Modeled DC resistivity data provided detailed two-dimensional cross-sectional resistivity profiles to a depth of about 20 meters. The distribution of high-resistivity units in these profiles was used as a proxy for identifying areas of high hydraulic conductivity. Estimates of the cross-sectional area of channel deposits from DC resistivity pseudosections can provide critical input for groundwater-flow models designed to simulate river seepage and evaluate seepage-management alternatives.

Empirical Models of Shallow Groundwater and Multi-Hazard Flood Forecasts as Sea-Levels Rise

American Geophysical Union (AGU) | February 8th, 2025

Knowledge of coastal hydrogeology and hazards as groundwater responds to sea-level rise (SLR) can be improved through installation of shallow groundwater monitoring piezo

Knowledge of coastal hydrogeology and hazards as groundwater responds to sea-level rise (SLR) can be improved through installation of shallow groundwater monitoring piezometers and continuous observations. Interpolation of site data enables mapping of the present-day state of groundwater elevation, depth to groundwater (DTW), their temporal statistical variation, and differing spatial responses to tides and rainfall. Future DTW and its variability can be projected under increments of SLR, with assumptions and caveats, to show where and when episodic and/or permanent inundation can be expected. This methodology is outlined in a case study of Dunedin, New Zealand, which enabled comparison of rising groundwater's contribution to pluvial flooding and groundwater emergence with coastal inundation. Changes in relative land exposure with SLR shows evolution in flood hazard from current pluvial-dominated events, into “flooding from below” and groundwater emergence, in advance of any overland coastal inundation. Dunedin exemplifies how groundwater transfers effects of SLR surprisingly far inland, but the lowest-lying or shoreline-proximal suburbs are not necessarily the most vulnerable. Unlike coastal inundation, rising groundwater is unconstrained by protective topography and presents as a creeping hazard, or contributor to hazards such as pluvial flooding, which can be widespread, occurring already and difficult to defend against. The empirical models contain assumptions and uncertainties important to the veracity of results and application. While conservative (“risk averse”) and a compromise from computationally expensive numerical solutions, their value is in providing the spatial and temporal precision needed for multi-source hazard assessment and holistic adaptive planning.

Enhancements to EcoAtlas’ CRAM analysis tools: Habitat Development Curves and Ecoregional Cumulative Distribution Function plots (CDFs)

San Francisco Estuary Institute (SFEI) | April 5th, 2016

Erosion and Sediment Manual

U.S. Bureau of Reclamation (USBR) | June 4th, 2017

Engineers in the Bureau of Reclamation's Sedimentation and River Hydraulics Group provide technical assistance and conduct studies to meet the needs of other Reclamation

Engineers in the Bureau of Reclamation's Sedimentation and River Hydraulics Group provide technical assistance and conduct studies to meet the needs of other Reclamation offices and of domestic and international water resources agencies. In addition to using the latest state-of-the art technology, engineers in the Sedimentation and River Hydraulics Group often have to develop new technology, methods, and computer programs for solving erosion, sedimentation, and river hydraulic problems. All the authors of the Erosion and Sedimentation Manual are members of the Sedimentation and River Hydraulics Group. Information, computer programs, and materials included in the manual are based on proven technology existing in the literature and some of them were developed by the authors for solving practical engineering problems. The objectives of writing this manual are twofold: to summarize the authors' experience and knowledge and to share with the public what they have learned and used in solving erosion and sedimentation problems. The Erosion and Sedimentation Manual is intended for engineers with basic background and knowledge in open channel hydraulics, sediment transport, and river morphology. The manual can also be used as a reference book for university professors, graduate students, and researchers for solving practical engineering problems. This manual contains nine chapters and three appendices. Each chapter is self-contained, with an introduction, summary, and a list of references. Cross references are made to avoid duplications of materials in different chapters. Basic theories, concepts, and approaches in erosion, sediment transport, river morphology, computer modeling, and field survey are reviewed and summarized in the manual. Examples are used to illustrate how to use the methods and programs contained in the manual.

Estimated Ground-Water Withdrawals from the Death Valley Regional Flow System

U.S. Geological Survey (USGS) | July 1st, 2003

Estimating Historical California Precipitation Phase Trends Using Gridded Precipitation, Precipitation Phase, and Elevation Data

California Department of Water Resources (DWR) | July 18th, 2014

Climate change projections for California indicate reduction in the percentage of precipitation that falls as snow, and increase in the percentage that falls as rain, due

Climate change projections for California indicate reduction in the percentage of precipitation that falls as snow, and increase in the percentage that falls as rain, due to warmer temperatures in the future. Previous work has shown overall decreases in rainfall / snowfall ratios for the western US over the last 60 years. Of interest in this study is the quantification of snow/rain ratios for smaller regions, specifically in California. Estimating cumulative precipitation phase ratios for specific regions is difficult due to large differences in local precipitation. In California, the high relief of the surface topography makes such estimates particularly difficult. The low spatial resolution of suitable precipitation/snow water equivalent monitoring stations contributes to the difficulty in quantifying the trends for sub-state sized regions of interest in this study. The present exploratory study develops and describes a methodology that uses readily available research data sets to produce gridded estimates of historical rainfall as a fraction of total precipitation for areas comprising the major water-supply watersheds of California. Using this methodology, statistically significant increases in the ratio of annual liquid to total precipitation are seen for large areas in the northern part of the State and northern Sierra over the water year. No significant annual trends are seen for regions in the central and southern portions of the Sierra. Future work extending the analysis to distinct elevation ranges and seasonality would provide more refined conclusions.

Estimating the potential economic impacts of climate change on Southern California beaches

Climatic Change (Springer) | November 24th, 2011

Climate change could substantially alter the width of beaches in Southern California. Climate-driven sea level rise will have at least two important impacts on beaches: (

Climate change could substantially alter the width of beaches in Southern California. Climate-driven sea level rise will have at least two important impacts on beaches: (1) higher sea level will cause all beaches to become more narrow, all things being held constant, and (2) sea level rise may affect patterns of beach erosion and accretion when severe storms combine with higher high tides. To understand the potential economic impacts of these two outcomes, this study examined the physical and economic effects of permanent beach loss caused by inundation due to sea level rise of one meter and of erosion and accretion caused by a single, extremely stormy year (using a model of beach change based on the wave climate conditions of the El Niño year of 1982/1983.) We use a random utility model of beach attendance in Southern California that estimates the impacts of changes on beach width for different types of beach user visiting public beaches in Los Angeles and Orange Counties. The model allows beachgoers to have different preferences for beach width change depending on beach size. We find that the effect of climate-driven beach change differs for users that participate in bike path activities, sand-based activities, and water-based activities. We simulate the effects of climate-related beach loss on attendance patterns at 51 public beaches, beach-related expenditures at those beaches, and the non-market (consumer surplus) value of beach going to those beaches. We estimate that increasing sea level will cause an overall reduction of economic value in beach going, with some beaches experiencing increasing attendance and beach-related earnings while attendance and earnings at other beaches would be lower. We also estimate that the potential annual economic impacts from a single stormy year may be as large as those caused by permanent inundation that would result from a rise in sea level of one meter. The economic impacts of both permanent inundation and storm-related erosion are distributed unevenly across the region. To put the economic impacts of these changes in beach width in perspective, the paper provides simple estimates of the cost of mitigating beach loss by nourishing beaches with sand.

Evaluating GFS and ECMWF Ensemble Forecasts of Integrated Water Vapor Transport along the U.S. West Coast

American Meteorological Society (AMS) | October 28th, 2022

Atmospheric rivers (ARs) are long and narrow regions in the atmosphere of enhanced integrated water vapor transport (IVT) and can produce extreme precipitation and high s

Atmospheric rivers (ARs) are long and narrow regions in the atmosphere of enhanced integrated water vapor transport (IVT) and can produce extreme precipitation and high societal impacts. Reliable and skillful forecasts of landfalling ARs in the western United States are critical to hazard preparation and aid in decision support activities, such as Forecast-Informed Reservoir Operations (FIRO). The purpose of this study is to compare the cool-season water year skill of the NCEP Global Ensemble Forecast System (GEFS) and ECMWF Ensemble Prediction System (EPS) forecasts of IVT along the U.S. West Coast for 2017–20. The skill is analyzed using probability-over-threshold forecasts of IVT magnitudes ≥ 250 kg m−1 s−1 (P250) using contingency table skill metrics in coastal Northern California and along the west coast of North America. Analysis of P250 with lead time (dProg/dt) found that the EPS provided ∼1 day of additional lead time for situational awareness over the GEFS at lead times of 6–10 days. Forecast skill analysis highlights that the EPS leads over the GEFS with success ratios 0.10–0.15 higher at lead times > 6 days for P250 thresholds of ≥25% and ≥50%, while event-based skill analysis using the probability of detection (POD) found that both models were largely similar with minor latitudinal variations favoring higher POD for each model in different locations along the coast. The relative skill of the EPS over the GEFS is largely attributed to overforecasting by the GEFS at longer lead times and an increase in the false alarm ratio.

Evaluating the Accuracy of Reclamation’s 24-Month Study Lake Powell Projections

Utah State University | February 18th, 2022

The bias for inflow predictions will likely be reduced now that the reference period includes a more recent, and somewhat drier, span of time, but projections of future i

The bias for inflow predictions will likely be reduced now that the reference period includes a more recent, and somewhat drier, span of time, but projections of future inflows are likely to remain biased, because the hydrology of the 1991-2020 reference period was still wetter than the current Millennium Drought.

Evaluation of a Ground-Water Flow and Transport Model of the Upper Coachella Valley, California

U.S. Geological Survey (USGS) | June 25th, 1992

A geohydrologic data base was compiled to evaluate the changes in ground-water conditions in the upper Coachella Valley, California, since 1978, when the results of a pre

A geohydrologic data base was compiled to evaluate the changes in ground-water conditions in the upper Coachella Valley, California, since 1978, when the results of a previous ground-water-model study were published. The compiled data were analyzed to improve understanding of the ground-water flow system and the effects on water quality of an existing artificial-recharge program. Analysis of well logs indicates that several zones of differing permeability can be correlated throughout the valley. Analysis of the water-quality data suggests that the artificial recharge of Colorado River water has caused increases in dissolved solids in some wells. Sparse data indicate that the recharged water moves much more rapidly through the uppermost part of the ground-water system than through deeper parts. An evaluation of the existing ground-water simulation model of the upper Coachella Valley that was developed in the 1978 study yielded several conclusions. First, the 300- to 400-foot rise in water levels in the artificialrecharge area in 1985-86 significantly affected the groundwater flow system. Transmissivities in the model had to be increased to reflect the increase in saturated thickness. Storage-coefficient values in the model had to be increased from 0.02 (used in the previous study) to 0.10-0.15 to simulate the unconfined water-level response during this period. Second, stream-recharge and underflow rates from San Gorgonio Pass during 1979-86 seem to have been higher than the values estimated for previous studies. Conditions generally were wetter in 1979-86 than during the period in which the earlier estimates were made. Third, the flow system could be simulated more accurately if the model were extended to its true southeastern boundary, the Salton Sea. Finally, there are important vertical differences in transport of the artificially recharged water that the two-dimensional areal transport model cannot simulate. The study results indicate several additional data collection and modeling needs. The drilling of several sets of monitor wells perforated at different depths could help better define the three-dimensional flow system and waterquality differences. Additional data also are needed on underflow and stream recharge, evaporation rates and infiltration rates at the artificial-recharge facilities, and net pumpage. Three-dimensional flow and transport models are needed to evaluate the effects of ground-water development on water levels and water quality.