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At least 577 records · Page 32Linked to original sources
USGS2006

U.S. Geological Survey activities related to American Indians and Alaska Natives: Fiscal year 2004

The USGS works in cooperation with American Indian and Alaska Native governments to conduct research on (1) water, energy, and mineral resources, (2) animals and plants that are important for traditional lifeways or have environmental or economic significance, and (3) natural hazards. This report describes most of the activities that the USGS conducted with American Indian and Alaska Native governments, educational institutions, and individuals during Federal fiscal year (FY) 2004. Most of these USGS activities were collaborations with Tribes, Tribal organizations, or professional societies. Other activities were conducted cooperatively with the U.S. Bureau of Indian Affairs (BIA) or other Federal entities.

Circular↗
USGS2024

Development of a hydrogeologic visualization model for western Sarpy County, Nebraska

Population in western Sarpy County, Nebraska, has steadily increased over the last several decades and has led to increased groundwater use for domestic purposes. To meet the increase in demand, the Papio-Missouri River Natural Resources District is seeking to use all available sources of groundwater in western Sarpy County. Additionally, elevated groundwater nitrate plus nitrite as nitrogen concentrations were detected, indicating the need to better understand the groundwater quality of the area. Although the general geology of the area is understood, the area does not have detailed information on the extent of the various aquifers, particularly the Dakota aquifer. To characterize these aquifers, the Papio-Missouri River Natural Resources District invested in airborne electromagnetic surveys of the area to better understand the subsurface geology. Although these surveys improved understanding of the groundwater systems in the area, the Papio-Missouri River Natural Resources District wanted to integrate the subsurface information with available water-quality and groundwater-level data. In response, the U.S. Geological Survey, in cooperation with the Papio-Missouri River Natural Resources District, the Nebraska Natural Resources Commission, and the Nebraska Department of Natural Resources, assembled geologic, hydrogeologic and nitrate plus nitrite as nitrogen information for the selected area into a three-dimensional visualization computer software package called GeoScene3D. The completed GeoScene3D project was assembled to provide a visualization of the groundwater systems and associated water-quality results in Sarpy County and to provide the Papio-Missouri River Natural Resources District managers with information that can be used to make more informed groundwater resource-planning decisions in the future. This report details the development of a three-dimensional model created within GeoScene3D to visualize the subsurface, particularly the Dakota Sandstone in western Sarpy County.

Nebraska↗
USGS2014

Two approaches for incorporating climate change into natural resource management planning at Wind Cave National Park

Wind Cave National Park (WICA) protects one of the world’s longest caves, has large amounts of high quality, native vegetation, and hosts a genetically important bison herd. The park’s relatively small size and unique purpose within its landscape requires hands-on management of these and other natural resources, all of which are interconnected. Anthropogenic climate change presents an added challenge to WICA natural resource management because it is characterized by large uncertainties, many of which are beyond the control of park and National Park Service (NPS) staff. When uncertainty is high and control of this uncertainty low, scenario planning is an appropriate tool for determining future actions. In 2009, members of the NPS obtained formal training in the use of scenario planning in order to evaluate it as a tool for incorporating climate change into NPS natural resource management planning. WICA served as one of two case studies used in this training exercise. Although participants in the training exercise agreed that the scenario planning process showed promise for its intended purpose, they were concerned that the process lacked the scientific rigor necessary to defend the management implications derived from it in the face of public scrutiny. This report addresses this concern and others by (1) providing a thorough description of the process of the 2009 scenario planning exercise, as well as its results and management implications for WICA; (2) presenting the results of a follow-up, scientific study that quantitatively simulated responses of WICA’s hydrological and ecological systems to specific climate projections; (3) placing these climate projections and the general climate scenarios used in the scenario planning exercise in the broader context of available climate projections; and (4) comparing the natural resource management implications derived from the two approaches. Wind Cave National Park (WICA) protects one of the world’s longest caves, has large amounts of high quality, native vegetation, and hosts a genetically important bison herd. The park’s relatively small size and unique purpose within its landscape requires hands-on management of these and other natural resources, all of which are interconnected. Anthropogenic climate change presents an added challenge to WICA natural resource management because it is characterized by large uncertainties, many of which are beyond the control of park and National Park Service (NPS) staff. When uncertainty is high and control of this uncertainty low, scenario planning is an appropriate tool for determining future actions. In 2009, members of the NPS obtained formal training in the use of scenario planning in order to evaluate it as a tool for incorporating climate change into NPS natural resource management planning. WICA served as one of two case studies used in this training exercise. Although participants in the training exercise agreed that the scenario planning process showed promise for its intended purpose, they were concerned that the process lacked the scientific rigor necessary to defend the management implications derived from it in the face of public scrutiny. This report addresses this concern and others by (1) providing a thorough description of the process of the 2009 scenario planning exercise, as well as its results and management implications for WICA; (2) presenting the results of a follow-up, scientific study that quantitatively simulated responses of WICA’s hydrological and ecological systems to specific climate projections; (3) placing these climate projections and the general climate scenarios used in the scenario planning exercise in the broader context of available climate projections; and (4) comparing the natural resource management implications derived from the two approaches.

Report↗
USGS2010

Estimating aboveground biomass for broadleaf woody plants and young conifers in Sierra Nevada, California forests

Quantification of biomass is fundamental to a wide range of research and natural resource management goals. An accurate estimation of plant biomass is essential to predict potential fire behavior, calculate carbon sequestration for global climate change research, assess critical wildlife habitat, and so forth. Reliable allometric equations from simple field measurements are necessary for efficient evaluation of plant biomass. However, allometric equations are not available for many common woody plant taxa in the Sierra Nevada. In this report, we present more than 200 regression equations for the Sierra Nevada western slope that relate crown diameter, plant height, crown volume, stem diameter, and both crown diameter and height to the dry weight of foliage, branches, and entire aboveground biomass. Destructive sampling methods resulted in regression equations that accurately predict biomass from one or two simple, nondestructive field measurements. The tables presented here will allow researchers and natural resource managers to easily choose the best equations to fit their biomass assessment needs.

California↗
USGS2011

Geologic map of Big Bend National Park, Texas

The purpose of this map is to provide the National Park Service and the public with an updated digital geologic map of Big Bend National Park (BBNP). The geologic map report of Maxwell and others (1967) provides a fully comprehensive account of the important volcanic, structural, geomorphological, and paleontological features that define BBNP. However, the map is on a geographically distorted planimetric base and lacks topography, which has caused difficulty in conducting GIS-based data analyses and georeferencing the many geologic features investigated and depicted on the map. In addition, the map is outdated, excluding significant data from numerous studies that have been carried out since its publication more than 40 years ago. This report includes a modern digital geologic map that can be utilized with standard GIS applications to aid BBNP researchers in geologic data analysis, natural resource and ecosystem management, monitoring, assessment, inventory activities, and educational and recreational uses. The digital map incorporates new data, many revisions, and greater detail than the original map. Although some geologic issues remain unresolved for BBNP, the updated map serves as a foundation for addressing those issues. Funding for the Big Bend National Park geologic map was provided by the United States Geological Survey (USGS) National Cooperative Geologic Mapping Program and the National Park Service. The Big Bend mapping project was administered by staff in the USGS Geology and Environmental Change Science Center, Denver, Colo. Members of the USGS Mineral and Environmental Resources Science Center completed investigations in parallel with the geologic mapping project. Results of these investigations addressed some significant current issues in BBNP and the U.S.-Mexico border region, including contaminants and human health, ecosystems, and water resources. Funding for the high-resolution aeromagnetic survey in BBNP, and associated data analyses and interpretation, was from the USGS Crustal Geophysics and Geochemistry Science Center. Mapping contributed from university professors and students was mostly funded by independent sources, including academic institutions, private industry, and other agencies.

Texas↗
USGS2005

Visitor and community survey results for Kilauea Point National Wildlife Refuge and Lighthouse: Completion report

The U.S. Fish and Wildlife Service (USFWS) and the Central Federal Lands Highway Division of the Federal Highway Administration, U.S. Department of Transportation are currently pursuing the planning and potential design of an alternative transportation system (ATS) for Kilauea Point National Wildlife Refuge (Refuge or Kilauea Point NWR). The USFWS and CFLHD seek an alternative transportation solution that provides the highest quality visitor experience and is sensitive to biological and cultural resources and the needs of the local community. In planning the alternative transportation system, managers need to consider how an ATS would change factors such as visitor access, visitor experience, visitor willingness to pay, and visitor net economic benefits. The Policy Analysis and Science Assistance branch (PASA) at the U.S. Geological Survey Fort Collins Science Center is dedicated to studying relations between humans and the environment. The objective of PASA is to conduct studies to understand how humans are affected by environmental management decisions and how human activities impact use and conservation of natural resources.

Hawaii↗
USGS2005

Drought-sensitive aquifer settings in southeastern Pennsylvania

This report describes the results of a study conducted by the U.S. Geological Survey, in cooperation with the Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey, to determine drought-sensitive aquifer settings in southeastern Pennsylvania. Because all or parts of southeastern Pennsylvania have been in drought-warning or drought-emergency status during 6 of the past 10 years from 1994 through 2004, this information should aid well owners, drillers, and water-resource managers in guiding appropriate well construction and sustainable use of Pennsylvania's water resources. 'Drought-sensitive' aquifer settings are defined for this study as areas unable to supply adequate quantities of water to wells during drought. Using information from previous investigations and a knowledge of the hydrogeology and topography of the study area, drought-sensitive aquifer settings in southeastern Pennsylvania were hypothesized as being associated with two factors - a water-table decline (WTD) index and topographic setting. The WTD index is an estimate of the theoretical water-table decline at the ground-water divide for a hypothetical aquifer with idealized geometry. The index shows the magnitude of ground-water decline after cessation of recharge is a function of (1) distance from stream to divide, (2) ground-water recharge rate, (3) transmissivity, (4) specific yield, and (5) duration of the drought. WTD indices were developed for 39 aquifers that were subsequently grouped into categories of high, moderate, and low WTD index. Drought-sensitive settings determined from the hypothesized factors were compared to locations of wells known to have been affected (gone dry, replaced, or deepened) during recent droughts. Information collected from well owners, drillers, and public agencies identified 2,016 wells affected by drought during 1998-2002. Most of the available data on the location of drought-affected wells in the study area were from Chester and Montgomery Counties because those counties have well-construction regulations that identify wells that failed during drought. The locations of drought-affected wells in Chester and Montgomery Counties indicated the most highly sensitive settings are uplands and slopes in aquifers with high WTD index and uplands in aquifers with moderate WTD index. The least sensitive settings are in aquifers with low WTD index, in valleys, or on slopes. A map was developed showing the relative drought sensitivity (low, moderate, and high) of aquifers in southeastern Pennsylvania. Study results were limited by the inability to obtain much information about the location of drought-affected wells, with the exception of Montgomery and Chester Counties. Also, the construction characteristics (particularly depth) of drought-affected wells generally were not available. Well depth could be used to distinguish between problems caused by shallow well depth (generally less than 100 ft) and those caused by deficiency of the aquifer to supply water. With the exception of owner-derived information from a public survey on drought-affected wells (35 wells), depth data were not obtained. Data from the 35 drought-affected wells indicated most were drilled (not dug) and were completed to depths greater than 100 feet. This finding indicates that the affects of recent droughts in southeastern Pennsylvania were not restricted to shallow dug wells, but also affected deeper drilled wells.

Pennsylvania↗
USGS2021

Simulation of water-table and freshwater/saltwater interface response to climate-change-driven sea-level rise and changes in recharge at Fire Island National Seashore, New York

The fresh groundwater system at Fire Island National Seashore in New York is one of the natural resources that is most vulnerable to climate change; the various federally listed threatened or endangered species that live on Fire Island, including the piping plover, roseate tern shorebird, and seabeach amaranth may be affected by changes in the groundwater system. The U.S. Geological Survey, in cooperation with the National Park Service, developed a three-dimensional groundwater-flow model to simulate climate-change-related changes in depth to the water table and depth to freshwater/saltwater interfaces on Fire Island. An existing SEAWAT three-dimensional variable-density groundwater flow and transport model was converted to a MODFLOW–NWT three-dimensional finite-difference groundwater model with the Seawater Intrusion (SWI2) package and recalibrated using the UCODE_2005 automatic calibration software. The simulated groundwater divide was found to be skewed strongly toward the ocean shore in response to the modeled wave setup and tidal pumping overheight. Effects of climate change include sea-level rise and changes in groundwater recharge rates. Sea-level rise scenarios included specified uniform steady states at 0.2-, 0.4-, and 0.6-meter increases above the 2015 level, applied to the existing topography. A high-recharge scenario was created by increasing 2015 recharge rates by 10 percent. Under all scenarios except the low-recharge scenario, the depth to the water table and the thickness of the unsaturated zone decreased. The thickness of the freshwater lens decreased under every scenario. Resulting maps were generated on a 25-meter grid and indicate changes in areas where natural resources may be vulnerable because of projected climate changes.

New York↗
USGS1971

Geology and water resources of the Spanish Valley area, Grand and San Juan Counties, Utah

This water-resources investigation was initiated in order to provide an estimate of the average annual water yield of the Mill Creek-Pack Creek drainage basin, the parts of that total yield available as surface water and ground water, the amount of ground water that might be recovered for beneficial use, and the effect of this use on the usable ground-water storage within the valley fill in Spanish and Moab Valleys. Detailed information has been sought which is basic to the establishment of sound policies for the development and management of water resources. The investigation was carried out as part of water-resources investigations in Utah with the Utah Division of Water Rights, Department of Natural Resources. Fieldwork was done during the period July 1967-November 1969.

Utah↗
USGS2013

U.S. Geological Survey water-resource monitoring activities in support of the Wyoming Landscape Conservation Initiative

The quality of the Nation’s water resources are vital to the health and well-being of both our communities and the natural landscapes we value. The U.S. Geological Survey investigates the occurrence, quantity, quality, distribution, and movement of surface water and groundwater and provides this information to engineers, scientists, managers, educators, and the general public. This information also supplements current (2013) and historical water data provided by the National Water Information System. The U.S. Geological Survey collects and shares data nationwide, but how those data are used is often site specific; this variety of data assists natural-resource managers in addressing unique, local, and regional challenges.

Wyoming↗
USGS2001

Abstracts from "Coastal Marsh Dieback in the Northern Gulf of Mexico: Extent, Causes, Consequences, and Remedies

In the spring of 2000, scientists discovered a new and unprecedented loss of salt marsh vegetation in coastal Louisiana and other areas along the northern coast of the Gulf of Mexico. This dieback of salt marsh vegetation, sometimes called the brown marsh phenomenon', primarily involved the rapid browning and dieback of smooth cordgrass (Spanina alterniflora). Coastal Louisiana has already undergone huge, historical losses of coastal marsh due to both human-induced and natural factors, and the current overall rate of wetland loss (25-35 sq mi 65-91 SQ KM each year) stands to threaten Louisiana's coastal ecosystem, infrastructure, and economy. On January 11-12, 2001, individuals from Federal and State agencies, universities, and the private sector met at the conference 'Coastal Marsh Dieback in the Northern Gulf of Mexico: Extent, Causes, Consequences, and Remedies' to discuss and share information shout the marsh dieback. Presentations discussed trends in the progress of dieback during the summer of 2000 and in environmental conditions occurring at field study sites, possible causes including drought and Mississippi low flow' conditions, changes in soil conditions (salinity, the bioavailability of metals, pathogens, etc.), the potential for wetland loss that could occur if above and below normality occurs and is sustained over an extended period, advanced techniques for tracking the dieback via aerial photography and remote sensing, linkages of marsh hydrology to the dieback, and mechanisms of modeling dieback and recovery. In addition, presentations were made regarding development of a web site to facilitate information sharing and progress in preparation for requests for proposals based on an emergency appropriation by the U.S. Congress. All findings tended to support the idea that the dieback constituted a continuing environmental emergency and research and natural resource management efforts should be expended accordingly.

Information and Technology Report↗
USGS2004

Colorado Canyons National Conservation Area 2003 visitor use survey: Completion report

This report represents the analysis of research conducted by the U.S. Geological Survey (USGS) for the Bureau of Land Management (BLM). The purpose is to provide socio-economic and recreational use information that can be used in the development of a Resource Management Plan (RMP) for the Colorado Canyons National Conservation Area (CCNCA). The results reported here deal primarily with recreation-based activities in four areas: Kokopelli Loops, Rabbit Valley, Loma Boat Launch, and Devil’s Canyon. In the fall of 2002, researchers from the Policy Analysis and Science Assistance Program (PASA) of the Fort Collins Science Center (FORT) in the USGS met with the staff of the CCNCA to discuss the issues related to social, economic, and human dimensions of natural resource management related to the RMP. As a result, a research study was designed to investigate the recreational experiences of visitors and their attitudes toward the management of the conservation area. In the spring of 2003, PASA conducted an intercept survey of recreational users at the CCNCA and a mail survey of local residents who were actively involved in decision-making regarding recreation on public lands in Mesa County, Colorado. Two hundred and three (203) mail surveys (66%) were returned and all of them were completed in full and considered usable. The intercept survey had a response rate with a range from 56%–64% among the four sites that were surveyed. We developed a questionnaire (OMB Control Number: 1040-0001) to answer the following questions: What are the important differences in citizens’ attitudes regarding recreation at the CCNCA? What are the factors that explain the differences in attitudes and preferences regarding recreation management of the NCA? What are citizens’ attitudes and preferences regarding their attitudes about paying a fee to visit the CCNCA? In general, respondents at all sites reported having an excellent or good recreation experience and almost all indicated that they intended to return. The results from the intercept survey indicated that across four sites 1(Kokopelli Loops, Devil’s Canyon, Loma Boat Launch, and Rabbit Valley) respondents reported support for undeveloped use and recreation restrictions to limit resource impacts. Respondents indicated that managing sites for undeveloped use was a good idea. The respondents from the mail survey generally had a positive orientation toward current management practices of the CCNCA. According to our surveys, non-motorized trail related activities were among the three most popular activities people engaged in both close to home and while away. These trail-based recreational activities included walking, running, mountain bike riding, and horseback riding. Research has shown that people participate in these activities for many reasons including learning about nature, exercising, to learning about paleontology, escaping for awhile, and socializing with family and friends (Taylor, 2000). National data indicate that larger percentages of the general American population engage in trail activities than in many other traditional outdoor activities (Cordell, 1999). Over 65% of people in the U.S. engage in walking as a recreational activity (Figure 1). We found that people wanted to experience the outdoors and the CCNCA provided a good place to do it. Trail activities are often those that people participate in on a regular basis as a way to exercise. This can make trail related activities more attractive from a management standpoint because people who participate in an activity may be more likely to be repeat visitors.

Open-File Report↗
USGS2010

The use of scenario analysis to assess water ecosystem services in response to future land use change in the Willamette River Basin, Oregon

Human pressures on the natural resources of the United States have resulted in many unintended changes in our ecosystems, e.g., loss of biodiversity, habitat degradation, increases in the number of endangered species, and increases in contamination and water pollution. Environmental managers are concerned about broad-scale changes in land use and landscape pattern and their cumulative impact on hydrologic and ecological processes that affect stream conditions. The type of land use and land cover has direct consequences for most ecosystem services, including water quantity and water quality, erosion control, and biodiversity. As human pressure continues to increase, ecosystem services worldwide are projected to suffer continued loss and degradation, thus reducing the capacity of ecosystems to provide essential goods and services that contribute to human well-being (MEA 2005). The ability to assess, report, and forecast the life support functions of ecosystems is absolutely critical to our capacity to make informed decisions which will maintain the sustainable nature of our environmental services and secure these resources into the future. This study presents an integrated approach to identify areas with potential water quality problems as a result of land cover change projected by stakeholders within a moderately large river basin in the Pacific Northwest (USA). A process-based hydrologic watershed model was used to examine the contribution of land use/land cover to sediment yield, and nitrate and phosphorous loadings, and identify subwatersheds within the Willamette River basin that would be most affected in the year 2050 relative to three possible future scenarios which include inherent differences related to conservation, existing planning trends, and open development. Thus, the objective of this study was to evaluate the effects of alternative future scenarios that describe varying degrees of urban development and human use on hydrological response related to water quality. Results of this study suggest that the amount of forest along streams and agriculture consistently explained a high percentage of variation in nutrients. The AGWA-SWAT model was used to simulate change in sediment yield, nitrate and phosphorus transported with surface runoff for the three future scenarios. With regard to nitrate, the greatest increase was associated with subwatersheds with agricultural land use and urban areas. Although the model predicted some improvement in basin headwaters for all scenarios, nitrate loadings are expected to decrease under the conservation scenario. The largest decrease was observed in the Coast Range. With regard to phosphorous loadings, the lowest reduction was observed in subwatersheds draining predominantly forest areas. The greatest increase was observed under the open development scenario in subwatersheds with agricultural land use. Urbanization and agriculture are presumed to be the major environmental stressors affecting watershed condition of the Willamette River Basin.

Oregon↗
USGS1986

Natural flow and water consumption in the Milk River basin, Montana and Alberta, Canada

A study was conducted to determine the differences between natural and nonnatural Milk River streamflow, to delineate and quantify the types and effects of water consumption on streamflow, and to refine the current computation procedure into one which computes and apportions natural flow. Water consumption consists principally of irrigated agriculture, municipal use, and evapotranspiration. Mean daily water consumption by irrigation ranged from 10 cu ft/sec to 26 cu ft/sec in the Canada part and from 6 cu ft/sec to 41 cu ft/sec in the US part. Two Canadian municipalities consume about 320 acre-ft and one US municipality consumes about 20 acre-ft yearly. Evaporation from the water surface comprises 80% 0 90% of the flow reduction in the Milk River attributed to total evapotranspiration. The current water-budget approach for computing natural flow of the Milk River where it reenters the US was refined into an interim procedure which includes allowances for man-induced consumption and a method for apportioning computed natural flow between the US and Canada. The refined procedure is considered interim because further study of flow routing, tributary inflow, and man-induced consumption is needed before a more accurate procedure for computing natural flow can be developed. (Author 's abstract)

Water-Resources Investigations Report↗
USGS2019

U.S. Geological Survey energy and wildlife research annual report for 2019

Access to affordable and reliable energy remains a critical need for people and the economy. To satisfy society’s demand for energy, the United States is expanding access to vast natural resources to produce electricity as well as petroleum and natural gas products. Development of our Nation’s energy resources, however, often conflicts directly with the equally vast fish and wildlife resources, which contribute billions of dollars to the economy through harvest, recreation, and services to humans and agriculture. The effects of energy development on living resources include fragmentation of populations, degradation or loss of habitat, and mortality of birds, bats, fish, and other wildlife interacting with energy generation facilities. Thus, an expanding energy infrastructure results in new requirements for land and ocean conversion for project siting and operational decisions to minimize risk to fish and wildlife resources. U.S. Geological Survey (USGS) scientists partner with more than 150 Federal, State, and local government agencies; Tribal nations; academic institutions; and nongovernmental organizations to deliver timely and relevant information on pressing resource management issues. This report summarizes ongoing USGS research projects and publications related to the impacts of energy development on fish and wildlife resources, tools to assess those impacts, and solutions to avoid or minimize risk. This information helps decision makers balance development with stewardship of the Nation’s fish and wildlife heritage.

Circular↗
USGS2003

NOGA Online: a USGS resource for energy GIS data and services

The PowerPoint presentation in this report was given at the BLM Resource Management Tools Conference in Phoenix, Arizona, April, 2003. Some diagrams that appeared in the original presentation have been updated in this report. It informs that the U.S. Geological Survey (USGS) Central Energy Resources Team (CERT) in Denver, Colorado, is providing National Oil and Gas Assessment (NOGA) results online at http://energy.cr.usgs.gov/oilgas/noga/. Available at this site are recently completed assessments of the potential for undiscovered oil and natural gas resources of five priority provinces (Montana Thrust Belt, Powder River Basin, San Juan Basin, Southwestern Wyoming, Uinta-Piceance) to meet the requirements of the Energy Policy and Conservation Act of 2000 (EPCA 2000). High demand for current assessment results and for the entirely digital, 1995 NOGA results for other provinces, prompted CERT to develop an internet map application using ArcIMS to deliver geologic data to the public. CERT continues to work on assessing oil and natural gas resources of priority basins in the United States; assessment results and GIS layers are made available at this site on an ongoing basis.

Open-File Report↗
USGS2001

Hydrodynamic and suspended-solids concentration measurements in Suisun Bay, California, 1995

Sea level, current velocity, water temperature, salinity (computed from conductivity and temperature), and suspended-solids data collected in Suisun Bay, California, from May 30, 1995, through October 27, 1995, by the U.S. Geological Survey are documented in this report. Data were collected concurrently at 21 sites. Various parameters were measured at each site. Velocity-profile data were collected at 6 sites, single-point velocity measurements were made at 9 sites, salinity data were collected at 20 sites, and suspended-solids concentrations were measured at 10 sites. Sea-level and velocity data are presented in three forms; harmonic analysis results; time-series plots (sea level, current speed, and current direction versus time); and time-series plots of low-pass-filtered time series. Temperature, salinity, and suspended-solids data are presented as plots of raw and low-pass-filtered time series.The velocity and salinity data presented in this report document a period when the residual current patterns and salt field were transitioning from a freshwater-inflow-dominated condition towards a quasi steady-state summer condition when density-driven circulation and tidal nonlinearities became relatively more important as long-term transport mechanisms. Sacramento-San Joaquin River Delta outflow was high prior to and during this study, so the tidally averaged salinities were abnormally low for this time of year. For example, the tidally averaged salinities varied from 0-12 at Martinez, the western border of Suisun Bay, to a maximum of 2 at Mallard Island, the eastern border of Suisun Bay. Even though salinities increased overall in Suisun Bay during the study period, the near-bed residual currents primarily were directed seaward. Therefore, salinity intrusion through Suisun Bay towards the Delta primarily was accomplished in the absence of the tidally averaged, two-layer flow known as gravitational circulation where, by definition, the net currents are landward at the bed. The Folsom Dam spillway gate failure on July 17, 1995, was analyzed to determine the effect on the hydrodynamics of Suisun Bay. The peak flow of the American River reached roughly 1,000 cubic meters per second as a result of the failure, which is relatively small. This was roughly 15 percent of the approximate 7,000 cubic meters per second tidal flows that occur daily in Suisun Bay and was likely attenuated greatly. Based on analysis of tidally averaged near-bed salinity and depth-averaged currents after the failure, the effect was essentially nonexistent and is indistinguishable from the natural variability.

Water-Resources Investigations Report↗