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622 records · Page 35Linked to original sources
USGS1992

Bedrock geology and mineral resources of the Knoxville 1° x 2° quadrangle, Tennessee, North Carolina, and South Carolina

The Knoxville 1° x 2° quadrangle spans the Southern Blue Ridge physiographic province at its widest point from eastern Tennessee across western North Carolina to the northwest corner of South Carolina. The quadrangle also contains small parts of the Valley and Ridge province in Tennessee and the Piedmont province in North and South Carolina. Bedrock in the Valley and Ridge consists of unmetamorphosed, folded and thrust-faulted Paleozoic miogeoclinal sedimentary rocks ranging in age from Cambrian to Mississippian. The Blue Ridge is a complex of stacked thrust sheets divided into three parts: (1) a west flank underlain by rocks of the Late Proterozoic and Early Cambrian Chilhowee Group and slightly metamorphosed Late Proterozoic Ocoee Supergroup west of the Greenbrier fault; (2) a central part containing crystalline basement of Middle Proterozoic age (Grenville), Ocoee Supergroup rocks east of the Greenbrier fault, and rocks of the Murphy belt; and (3) an east flank containing the Helen, Tallulah Falls, and Richard Russell thrust sheets and the amphibolitic basement complex. All of the east flank thrust sheets contain polydeformed and metamorphosed sedimentary and igneous rocks of mostly Proterozoic age. The Blue Ridge is separated by the Brevard fault zone from a large area of rocks of the Inner Piedmont to the east, which contains the Six Mile thrust sheet and the ChaugaWalhalla thrust complex. All of these rocks are also polydeformed and metamorphosed sedimentary and igneous rocks. The Inner Piedmont rocks in this area occupy both the Piedmont and part of the Blue Ridge physiographic provinces. The intensity of deformation and metamorphism increases from west to east in the Blue Ridge. The west flank is mostly chlorite grade or relatively unmetamorphosed, and the central part of the Blue Ridge is mostly staurolite, garnet, or biotite grade, although sillimanite grade rocks occur along the eastern part of the central Blue Ridge in the vicinity of the leading edge of the Hayesville fault. The east flank of the Blue Ridge and much of the Inner Piedmont are at kyanite or sillimanite grade of regional metamorphism except for a zone of retrograde rocks in the Brevard fault zone and a small area of biotite-grade rocks in the extreme southwest part of the Grandfather Mountain window in the northeast corner of the quadrangle. The major mineral resources in the Knoxville 1° x 2° quadrangle are construction materials and a variety of industrial minerals mostly related to either granite and pegmatite or ultramafic rocks. Past production in the quadrangle of metals, which are of secondary importance relative to construction materials and industrial minerals, include copper in massive sulfides of the Besshi type, gold-bearing quartz veins, and residual iron and manganese deposits. Resources are discussed in relation to the Valley and Ridge, Blue Ridge, and Piedmont provinces. The following resources are the most important: A. Construction materials: Dimension stone of the Tennessee marble district in the Valley and Ridge. Limestone and dolomite of the Valley and Ridge. Sand and gravel and crushed stone, widespread throughout the quadrangle. B. Industrial minerals: Feldspar, flake mica, and quartz produced by flotation methods from the Spruce Pine Alaskite (muscovite granodiorite) in the east flank of the Blue Ridge. The district produces about half of the U.S. feldspar and significant amounts of the U.S. flake mica. Olivine produced from alpine-type dunite bodies in the east flank of the Blue Ridge. Talc and marble from the Murphy belt in the central part of the Blue Ridge. Vermiculite produced from a large deposit near Tigerville, S.C., in the Inner Piedmont. Deposit worked out and mine backfilled. Smaller deposits associated with ultramafic rocks in the east flank of the Blue Ridge are now uneconomic and have not been worked in the past 20 years. C. Metals: Copper in three deposits, the Fontana and Hazel Creek mines in the Great Smoky Mountains National Park in the Central Blue Ridge, and the Cullowhee mine in the east flank of the Blue Ridge. D. Organic fuels: The rocks of the quadrangle contain no coal and probably lie outside the maximum range in thermal maturity permitting the survival of oil. The rocks in the Valley and Ridge and for a short distance eastward below the west flank of the Blue Ridge probably lie within a zone of thermal maturity permitting the survival of natural gas. Consequently the western part of the quadrangle is an area of high risk for hydrocarbon exploration. No exploration drilling has been done in this belt.

North Carolina, South Carolina, Tennessee↗
USGS2004

Bedrock geology and mineral resources of the Knoxville 1° x 2° quadrangle, Tennessee, North Carolina, and South Carolina

The Knoxville 1°x 2° quadrangle spans the Southern Blue Ridge physiographic province at its widest point from eastern Tennessee across western North Carolina to the northwest corner of South Carolina. The quadrangle also contains small parts of the Valley and Ridge province in Tennessee and the Piedmont province in North and South Carolina. Bedrock in the Valley and Ridge consists of unmetamorphosed, folded and thrust-faulted Paleozoic miogeoclinal sedimentary rocks ranging in age from Cambrian to Mississippian. The Blue Ridge is a complex of stacked thrust sheets divided into three parts: (1) a west flank underlain by rocks of the Late Proterozoic and Early Cambrian Chilhowee Group and slightly metamorphosed Late Proterozoic Ocoee Supergroup west of the Greenbrier fault; (2) a central part containing crystalline basement of Middle Proterozoic age (Grenville), Ocoee Supergroup rocks east of the Greenbrier fault, and rocks of the Murphy belt; and (3) an east flank containing the Helen, Tallulah Falls, and Richard Russell thrust sheets and the amphibolitic basement complex. All of the east flank thrust sheets contain polydeformed and metamorphosed sedimentary and igneous rocks of mostly Proterozoic age. The Blue Ridge is separated by the Brevard fault zone from a large area of rocks of the Inner Piedmont to the east, which contains the Six Mile thrust sheet and the ChaugaWalhalla thrust complex. All of these rocks are also polydeformed and metamorphosed sedimentary and igneous rocks. The Inner Piedmont rocks in this area occupy both the Piedmont and part of the Blue Ridge physiographic provinces. The intensity of deformation and metamorphism increases from west to east in the Blue Ridge. The west flank is mostly chlorite grade or relatively unmetamorphosed, and the central part of the Blue Ridge is mostly staurolite, garnet, or biotite grade, although sillimanite grade rocks occur along the eastern part of the central Blue Ridge in the vicinity of the leading edge of the Hayesvil Ie fault. The east flank of the Blue Ridge and much of the Inner Piedmont are at kyanite or silli manite grade of Manuscript approved for publication February 22, 1991. regional metamorphism except for a zone of retrograde rocks in the Brevard fault zone and a small area of biotite-grade rocks in the extreme southwest part of the Grandfather Mountain window in the northeast corner of the quadrangle. The major mineral resources in the Knoxville 1°x2° quadrangle are construction materials and a variety of industrial minerals mostly related to either granite and pegmatite or ultramafic rocks. Past production in the quadrangle of metals, which are of secondary importance relative to construction materials and industrial minerals, include copper in massive sulfides of the Besshi type, gold-bearing quartz veins, and residual iron and manganese deposits. Resources are discussed in relation to the Valley and Ridge, Blue Ridge, and Piedmont provinces. The following resources are the most important: A. Construction materials: Dimension stone of the Tennessee marble district in the Valley and Ridge. Limestone and dolomite of the Valley and Ridge. Sand and gravel and crushed stone, widespread throughout the quadrangle. B. Industrial minerals: Feldspar, flake mica, and quartz produced by flotation methods from the Spruce Pine Alaskite (muscovite granodiorite) in the east flank of the Blue Ridge. The district produces about half of the U.S. feldspar and significant amounts of the U.S. flake mica. Olivine produced from alpine-type dunite bodies in the east flank of the Blue Ridge. Talc and marble from the Murphy belt in the central part of the Blue Ridge, Vermiculite produced from a large deposit near Tigerville, S.C-, in the Inner Piedmont. Deposit worked out and mine backfilled. Smaller deposits associated with ultramafic rocks in the east flank of the Blue Ridge are now uneconomic and have not been worked in the past 20 years. C. Metals: Copper in three deposits, the Fontana and Hazel Creek mines in the Great Smoky Mountains Abstract Figure 1. Location of the Knoxville 1ºx2º quadrangle, with state and county boundaries National Park in the Central Blue Ridge, and the Cullowhee mine in the east flank of the Blue Ridge. D. Organic fuels: The rocks of the quadrangle contain no coal and probably lie outside the maximum range in thermal maturity permitting the survival of oil. The rocks in the Valley and Ridge and for a short distance eastward below the west flank of the Blue Ridge probably lie within a zone of thermal maturity permitting the survival of natural gas. Consequently the western part of the quadrangle is an area of high risk for hydrocarbon exploration. No exploration drilling has been done in this belt.

North Carolina, South Carolina, Tennessee↗
USGS1996

Geohydrology of the Weldon Spring ordnance works, St. Charles County, Missouri

Bedrock units at the Weldon Spring ordnance works in St. Charles County, Missouri, dip to the northeast at about 60 feet per mile, as measured by the top of the Chouteau Group. The top of the bedrock forms a generally east-west trending ridge through the Weldon Spring training area and the Weldon Spring chemical plant. This surface contains a large, broad bedrock low centered about the unnamed tributary to Dardenne Creek that contains Burgermeister spring. The low has been interpreted to be a paleodrainage that existed before deposition of glacial drift. This feature consists of smaller, more elongate paleovalleys at and west of the chemical plant where more dense drillhole data provide better definition. The uppermost bedrock unit throughout most of the ordnance works is the BurlingtonKeokuk Limestone of Mississippian age. It is subdivided based on weathering characteristics into a lower, unweathered unit; an upper, weathered unit; and a strongly weathered subunit of the weathered unit. The unweathered unit is a light to medium gray, coarse to less commonly fine crystalline, thin to massive bedded, fossiliferous, cherty limestone. The unweathered unit can be silty or argillaceous, or can locally be dolostone or siltstone. The weathered unit is characterized by an increase in mostly horizontal fractures and partings, increased porosity, vugs, voids, breccia, and discoloration by iron oxides. A strongly weathered subunit of the weathered unit is identified in some monitoring wells where these features are particularly abundant or intense. The overburden units are, in ascending order: residuum, basal till, glacial till, including a glacial outwash subunit, the Ferrelview Formation, loess, alluvium, and fill. Some of the thickest overburden occurs in the northern part of the training area and north of the training area and may be caused by a larger thickness of glacial drift. The paleodrainage centered about the unnamed tributary to Dardenne Creek that contains Burgermeister spring appears to have been partially filled by glacial drift, and a surface-water divide now exists southeast of the tributary. The upper, more permeable part of the shallow aquifer consists of the residuum, basal till, glacial outwash (where there is no glacial till below it), and the weathered unit of the Burlington-Keokuk Limestone. The lower, less permeable part of the shallow aquifer consists of the unweathered unit of the Burlington-Keokuk Limestone and the Fern Glen Formation. Generally, the upper part of the shallow aquifer thins to the north, reflecting the thin to absent weathered unit north of the training area and chemical plant. A glacial drift confining unit consists of parts of the glacial till and the Ferrelview Formation. Ground water as recharge and discharge probably moves in fractures through this unit. It confines ground water where the potentiometric surface of the shallow aquifer is above its base. There are stream reaches where the streams have cut through the glacial drift confining unit to expose the underlying shallow aquifer. A potentiometric surface map of the shallow aquifer shows a large ground-water mound in the south-central part of the training area. This mound is part of a generally east-west trending ground-water ridge through the training area and the chemical plant that defines a ground-water divide. Precipitation that percolates downward through fractures in the glacial drift confining unit recharges the shallow aquifer. Where the glacial drift confining unit is not present, precipitation can be expected to recharge the shallow aquifer more readily. There is the potential for groundwater flow in permeable overburden units where the potentiometric surface is above the top of bedrock. Generally, the residuum and locally other overburden units of the shallow aquifer potentially become more important as mediums of ground-water flow north and downgradient of the ground-water ridge. This is probably limited where clay-rich zones in the residuum confine ground water below in the bedrock. Because the thickness of the weathered unit generally decreases to the north, it generally becomes a less important medium of ground-water flow downgradient to the north. Also to the north, the potentiometric surface of the shallow aquifer is above the base of the glacial drift confining unit over a large area, indicating that the aquifer is confined. Upward ground-water gradients measured in monitoring well pairs, Burgermeister and other springs, the gaining unnamed tributary to Dardenne Creek upstream of Burgermeister spring, and Dardenne Creek indicate ground-water discharge in the northern part of the ordnance works.

Missouri↗
USGS2013

Tectonic map of the Circum-Pacific region, Pacific basin sheet

Circum-Pacific Map Project : The Circum-Pacific Map Project was a cooperative international effort designed to show the relationship of known energy and mineral resources to the major geologic features of the Pacific basin and surrounding continental areas. Available geologic, mineral, and energy-resource data are being complemented by new, project-developed data sets such as magnetic lineations, seafloor mineral deposits, and seafloor sediment. Earth scientists representing some 180 organizations from more than 40 Pacific-region countries are involved in this work. Six overlapping equal-area regional maps at a scale of 1:10,000,000 form the cartographic base for the project: the four Circum-Pacific Quadrants (Northwest, Southwest, Southeast, and Northeast), and the Antarctic and Arctic Sheets. There is also a Pacific Basin Sheet at a scale of 1:17,000,000. The Base Map Series and the Geographic Series (published from 1977 to 1990), the Plate-Tectonic Series (published in 1981 and 1982), the Geodynamic Series (published in 1984 and 1985), and the Geologic Series (published from 1984 to 1989) all include six map sheets. Other thematic map series in preparation include Mineral-Resources, Energy-Resources and Tectonic Maps. Altogether, more than 50 map sheets are planned. The maps were prepared cooperatively by the Circum-Pacific Council for Energy and Mineral Resources and the U.S. Geological Survey and are available from the Branch of Distribution, U. S. Geological Survey, Box 25286, Federal Center, Denver, Colorado 80225, U.S.A. The Circum-Pacific Map Project is organized under six panels of geoscientists representing national earth-science organizations, universities, and natural-resource companies. The six panels correspond to the basic map areas. Current panel chairmen are Tomoyuki Moritani (Northwest Quadrant), R. Wally Johnson (Southwest Quadrant), Ian W.D. Dalziel (Antarctic Region), vacant. (Southeast Quadrant), Kenneth J. Drummond (Northeast Quadrant), and George W. Moore (Arctic Region). Project coordination and final cartography was being carried out through the cooperation of the Office of the Chief Geologist of the U.S. Geological Survey, under the direction of General Chairman, George Gryc of Menlo Park, California. Project headquarters were located at 345 Middlefield Road, MS 952, Menlo Park, California 94025, U.S.A. The framework for the Circum-Pacific Map Project was developed in 1973 by a specially convened group of 12 North American geoscientists meeting in California. The project was officially launched at the First Circum-Pacific Conference on Energy and Mineral Resources, which met in Honolulu, Hawaii, in August 1974. Sponsors of the conference were the AAPG, Pacific Science Association (PSA), and the Coordinating Committee for Offshore Prospecting for Mineral Resources in Offshore Asian Areas (CCOP). The Circum-Pacific Map Project operates as an activity of the Circum-Pacific Council for Energy and Mineral Resources, a nonprofit organization that promotes cooperation among Circum-Pacific countries in the study of energy and mineral resources of the Pacific basin. Founded by Michel T. Halbouty in 1972, the Council also sponsors conferences, topical symposia, workshops and the Earth Science Series books. Tectonic Map Series : The tectonic maps distinguish areas of oceanic and continental crust. Symbols in red mark active plate boundaries, and colored patterns show tectonic units (volcanic or magmatic arcs, arc-trench gaps, and interarc basins) associated with active plate margins. Well-documented inactive plate boundaries are shown by symbols in black. The tectonic development of oceanic crust is shown by episodes of seafloor spreading. These correlate with the rift and drift sequences at passive continental margins and episodes of tectonic activity at active plate margins. The recognized episodes of seafloor spreading seem to reflect major changes in plate kinematics. Oceanic plateaus and other prominences of greater than normal oceanic crustal thickness such as hotspot traces are also shown. Colored areas on the continents show the ages of deformation and metamorphism of basement rocks and the emplacement of igneous rocks. Transitional tectonic (molassic) and reactivation basins are shown by a colored boundary, and if they are deformed, a colored horizontal line pattern indicates the age of deformation. Colored bands along basin boundaries indicate age of inception, and isopachs indicate thickness of platform strata on continental crust and cover on oceanic crust. Colored patterns at separated continental margins show the age of inception of rift and drift (breakup) sequences. Symbols mark folds and faults, and special symbols show volcanoes and other structural features. Affiliations are as of compilation of the data. This map was created in quadrants and then compiled together. They are the Northwest land, Northwest Marine (different compilers), Northeast, Southwest and Southeast, and parts in plate-boundary sections.

Circum-Pacific Map↗
USGS2023

First investigations on lamprey responses to elevated total dissolved gas exposure and risk of gas bubble trauma

A flexible spill program in the federal Columbia River power system increased the total dissolved gas (TDG) water quality standards (i.e., the gas cap) from 120% to 125%. Spill is used to pass juvenile salmon (Oncorhynchus spp.) over dams, but it can generate elevated TDG, and exposed fish can develop gas bubble trauma (GBT) or experience mortality. Juvenile salmon are monitored for GBT through the Fish Passage Center’s (FPC), and under the flexible spill program, native non-salmonid fishes are also monitored. Pacific Lamprey (Entosphenus tridentatus) are exposed to elevated TDG, but nothing is known about their risk for GBT. This project is the first to evaluate GBT in lamprey, beginning with larval and juvenile lamprey in a controlled laboratory setting. These early life stages were chosen for this initial work because they have been shown to be more sensitive to GBT in other fish species. We modified the FPC protocol for GBT exams to be specific to lamprey and ranked bubbles in the mouth, eyes (juveniles only), gill pores, first and second dorsal fins, caudal fin, anal fin, vent, and body. We followed the FPC ranking criteria and assigned rank based on the proportion of the area occluded with bubbles, as 0=no bubbles, 1=1-5%, 2=6-25%, 3=26-50%, and 4=>50%. Four experiments were completed with larval lamprey from January to September 2022 using small (70 mm total length or less) and large (86 mm total length or greater) larvae in approximately equal proportions. Experiments included: (1) 130% TDG for 31 d, (2) 125% TDG for 91 d, (3) 130% TDG for 20 d with assessments of burrowing performance, and (4) 128-138% TDG for 3-4 d with assessments of predator avoidance ability and the corresponding untreated control groups. The first and second experiments had similar study designs and findings. First, we tested an acute exposure at 130% TDG and then we tested a chronic exposure at 125%, to represent a full spill season. None of the controls (exposed to normally saturated water) experienced mortality or showed GBT signs. Few lamprey in the treatment groups (5% in Experiment 1; 0% in Experiment 2) showed GBT signs, and there were no mortalities (n=200 fish experiment 1; n=100 fish Experiment 2). Lamprey with GBT signs had bubbles on the body, with low severity ranks. During external exams for Experiment 2, we observed bubbles in the gut of several lamprey. The light coloration and transparency of the body made these observations possible, and we confirmed the finding with internal exams. From day 9 to day 91, 70.8% of the lamprey examined had bubbles in the gut. We observed five lamprey that were positively buoyant in the test tanks, and we likely underestimated the prevalence of floating as our procedures were not initially designed to document this sign. In our third experiment, burrowing performance was not significantly different between lamprey exposed to 130% TDG and controls. Mortality was 4.2% in the treatment group, but no GBT signs were observed. The proportion of lamprey with positive buoyancy increased through time, with 87.5% of fish floating on day 20 (end of the test). Bubbles in the gut were observed for some lamprey on each of five sampling dates (day 2 to 20), with prevalence ranging from 50-100%. Median burrow times ranged from 28 to 154 sec for treatment fish and from 40 to 100 sec for controls. We noted some atypical behaviors during burrow performance tests, including lamprey that were positively buoyant and unable to descend through 0.5 m of water to reach the sediment as well as lamprey that were unable to complete burrowing (within 10 min test period). These lamprey were so buoyant that they repeatedly floated to the surface of the water when they stopped or slowed their burrowing movements. Predator avoidance ability was assessed in our fourth experiment by exposing lamprey with GBT signs (floating) and controls to sculpin (Cottus spp.) until about 50% of the fish had been consumed or 2 h had passed. We completed five predation trials, testing the hypothesis that an equal proportion of treatment and control lamprey would be consumed. Treatment groups were generated by exposing 15 lamprey to 128-138% TDG for 3-4 d, until at least 10 lamprey were floating. Overall, 41 treatment and 46 control fish were eaten and there was no evidence that sculpin preferentially preyed upon lamprey with GBT signs. Additional tests with another predator are recommended. Two experiments were completed with juvenile lamprey from March to November 2022: Experiment 5 exposed fish to 125% TDG for 10 d and Experiment 6 exposed fish to 125% for 16 d. Mortality rates for the treatment groups were 21.7% and 20.0% for these experiments, respectively, and few lamprey (4 per experiment) showed GBT signs. With the results from experiments pooled, bubbles were observed in all body areas with low severity ranks (means 0-1). We observed some exophthalmia and bubbles behind the gill pores, in addition to bubbles in the gut and fish floating. The presence of bubbles in or near the gill pores was the likely cause of death as exam findings included enlarged gill pore areas and restricted openings. This project provided the first insights into lamprey responses to elevated TDG, but substantial learning opportunities remain. Our findings highlight that lamprey are vulnerable to GBT, but the effects are generally sublethal and would not be detected using FPC exam procedures. For example, we observed larval and juvenile lamprey that had bubbles in the gut and/or were floating, although these conditions were not consistently linked. More data are needed, but we surmise that it takes some time for bubbles to form in sufficient quantity to create the floatation required to overcome the mass of the lamprey. Positive buoyancy in natural settings could have substantial impacts to the risk of mortality for lamprey. Future studies could test GBT risk for larval lamprey in burrows, investigate the influence of lamprey size, measure performance (e.g., burrowing, swimming, predator avoidance ability) after elevated TDG exposure, and describe the rate that GBT signs dissipate when lamprey are returned to normally saturated water.

Report↗
USGS2018

Deep aquifer recharge in the Columbia River Basalt Group, upper Umatilla River Basin, northeastern Oregon

Groundwater is an important component of the water resources of the upper Umatilla River Basin of northeastern Oregon. As such, understanding the capacity of the resource is vital. Past studies have estimated recharge in the study area. One recent study of the upper Umatilla River Basin indicated that about 80 percent of recharge entering the groundwater system is discharged to streams in the study area through shallow groundwater-flow paths, leaving about 20 percent of recharge to infiltrate deeper parts of the aquifer system. The purpose of this work is to quantify the spatial distribution and variability of deep aquifer recharge in the study area and to understand the reasons for a relatively low percentage of total recharge reaching the deeper parts of the groundwater-flow system. The study area is divided into two distinct physiographic regions—the highly dissected Blue Mountains and the lowland plains. Underlying both regions of the study area are basalts of the Columbia River Basalt Group (CRBG), which is the principal aquifer in the study area. Deep incision by streams in the Blue Mountains disrupts the lateral continuity of the CRBG aquifer units, and infiltrating water is more readily diverted laterally and discharged to streams and springs. In the lowland plains, incision is less pronounced. The shallow CRBG units might be disrupted, but deeper aquifer units retain their lateral continuity and enable groundwater to infiltrate deeper and flow laterally farther downgradient before discharging. Recharge to the deep basalt aquifers is estimated as the difference between total recharge and base flow. Total recharge is the portion of precipitation and applied irrigation water that infiltrates past the root zone to become groundwater recharge. Of this total recharge, a proportion discharges to springs and streams in the study area, and the remaining water infiltrates below the base level of streams and recharges the deep basalt aquifers and contributes to the regional groundwater flow system. The portion of total recharge that recharges the regional flow system is referred to as deep aquifer recharge. Total recharge is the portion of precipitation and applied irrigation water that infiltrates past the root zone to become groundwater recharge. It is the sum of recharge from precipitation and recharge from infiltration of irrigation water. Recharge from precipitation was calculated using a regression method developed for the Columbia Plateau. Recharge from infiltrating irrigation water was obtained from a water balance model developed for the Columbia Plateau. Base flow, the component of streamflow that represents groundwater discharge as opposed to runoff from the land surface, was estimated using the Base Flow Index Modified (BFI-Modified) method, an empirical hydrograph separation technique. Base flow was estimated in eight subbasins with streamgages within the study area. Five of the eight subbasins in which base flow was estimated had permitted water rights for irrigation that specified surface water as the primary source of water. Maximum surface-water withdrawal for irrigation was estimated for all subbasins in which water rights for irrigation occur. The base-flow estimate from BFI-Modified is assumed to be the minimum amount of base flow. The sum of the BFIModified base-flow estimate and the maximum permitted surface-water withdrawal estimate for each subbasin is assumed to be the maximum amount of base flow at the streamgage. These minimum and maximum estimates of base flow were used to calculate minimum and maximum values of deep aquifer recharge in each subbasin analyzed within the study area. Subbasin estimates were scaled up to the Blue Mountains and lowland plains regions, and to the entire study area. Mean annual total recharge for 1981–2010 in the subbasins, analyzed as part of this work, ranged from 6 inches (in.) in the Patawa and Wildhorse Creek subbasins in the lowland plains to as much as 20 in. in the Umatilla River above Meacham Creek subbasin. Mean annual total recharge totaled 4 in. in the lowland plains region and 14 in. in the Blue Mountains. Mean annual total recharge for the entire study area was 11 in. Mean annual base flow ranged from 1 in. in the Patawa and Wildhorse Creek subbasins in the lowland plains to as much as 14 in. in the Umatilla River above Meacham Creek subbasin in the Blue Mountains. Mean annual deep aquifer recharge ranged from 4 in. in the Patawa and Wildhorse Creek subbasins in the lowland plains to as much as 8 in. in the Isqu’ulktpe Creek subbasin in the Blue Mountains. Deep aquifer recharge was 3–4 in. in the lowland plains region and 6 in. in the Blue Mountains. Over the entire study area, mean annual deep aquifer recharge was 5 in. Most groundwater recharge (both total and deep aquifer) in the study area occurred in the Blue Mountains, which highlights the importance of the Blue Mountains as the principal source of groundwater for the study area and for aquifers farther downgradient. Total recharge in the Blue Mountains region represents 86 percent of the mean annual total recharge in the study area in an area that encompasses 65 percent of the study area. However, only 43–44 percent of the mean annual total recharge remains in the system to recharge the deeper, regional aquifer system because the rest is discharged as base flow within the Blue Mountains region. Within the lowland plains region of the study area, an estimated 67–84 percent of the mean annual total recharge remains in the system to recharge the deep, regional aquifer system. Although total recharge in the study area represents only 14 percent of the total recharge across the study area, it contributes 20–24 percent of the water to the deep aquifer. The difference in the percentage of deep groundwater recharge in the Blue Mountains and the lowland plains is attributed to differences in the degree of stream incision. Stream channels are more incised in the Blue Mountains region than they are in the lowland plains. The dissection of the landscape in the Blue Mountains disrupts the lateral continuity of the CRBG aquifer units and allows groundwater to discharge to springs and streams rather than infiltrate more deeply. In the lowland plains region, incision is much less pronounced and deeper CRBG units likely retain their lateral continuity, enabling groundwater to infiltrate more deeply than in the Blue Mountains.

Oregon↗
USGS2015

Groundwater quality in Geauga County, Ohio: status, including detection frequency of methane in water wells, 2009, and changes during 1978-2009

Domestic wells that are not safeguarded by regular water-quality testing provide drinking water for 79 percent of the residents of Geauga County, in northeastern Ohio. Since 1978, the U.S. Geological Survey (USGS) has worked cooperatively with the Board of Commissioners and Geauga County Planning Commission to monitor the quality of groundwater in four commonly used aquifers in county—the glacial deposits, the Pottsville Formation, the Cuyahoga Group, and the Berea Sandstone. A 33-percent growth in population from 1980 to 2009 increased the potential for humans to influence groundwater resources by withdrawing more groundwater, disposing of more human waste near the land surface, treating an expanded network of township roads with deicing salt, and likely using more solvents, pesticides, and other chemicals on the land surface than were used in preceding decades. To describe the status of groundwater quality in 2009 and its suitability for drinking, USGS personnel collected samples of water prior to treatment from 16 wells (mostly domestic) during June 9–19. The samples were analyzed for 92 properties and constituents, 41 of which had human-health benchmarks to which analytical results could be compared to evaluate suitability for drinking. Four of these benchmarks were exceeded at the following frequencies: arsenic (2 of 16 wells, 12.5 percent), total coliform bacteria (2 of 16 wells, 12.5 percent), fecal coliform bacteria (1 of 14 wells, 7 percent), and sodium (6 of 16 wells, 38 percent). No domestic wells sampled in 2009 exceeded the health-based benchmark of 300 micrograms per liter (µg/L) for manganese, although 5 of 65 wells (8 percent) sampled since 1978 have. Analyses from domestic wells were augmented with water-quality data from seven public-supply well fields that were obtained from the Ohio Environmental Protection Agency. These public-supply data were typically collected between 2000 and 2010 and represent water samples that were collected prior to treatment or that were treated by a method that does not effectively remove the constituents of interest. Similar to the domestic-well data, these data indicated that some samples from public-supply wells have also exceeded health-based benchmarks for arsenic and sodium, along with occasional exceedances of health-based benchmarks for cadmium and lead. Concentrations of nitrate, pesticides, and volatile organic compounds in ground-water samples from domestic and (or) public-supply wells were either considerably less than the human-health benchmarks for these constituents or were not detected. Water-quality data collected in 2009 were also compared to aesthetically based benchmarks developed by the U.S. Environmental Protection Agency, called Secondary Maximum Contaminant Levels (SMCLs). Iron and manganese most frequently exceeded SMCLs (in samples from 10 of 16 domestic wells and in untreated water from 3 of 4 public-supply well fields). To evaluate the frequency of methane detection in water wells in the county, the USGS sampled 16 wells across the county and screened the samples for combustible gas within the headspace (the air above the water in a closed container). Water from three (19 percent) of the wells contained detectable combustible gas (0.10 to 0.40 percent by volume). All three detections were from wells tapping the Cuyahoga Group or the Berea Sandstone, and all detections were less than the lower explosive limit of 5 percent by volume—the concentration at which methane in air can be flammable if an ignition source is present. Analyses of dissolved gas composition in water from these three wells showed methane concentrations ranging from 0.007 to 1.8 milligrams per liter (mg/L). The primary effect of human activities on groundwater quality found during this study is the input of salinity, or chloride, near land surface. On the basis of ratios of chloride to bromide, the main sources of chloride are road salt and septic leachate rather than oil-field brines (either spilled at land surface or sprayed on roads for dust control). The correlation of chloride concentration to distance of well from road for 31 wells in the county sampled by the U.S. Geological Survey in 1999 suggests that road salt is the dominant source of chloride. The majority of constituents exceeding health-based and aesthetically based benchmarks in groundwater were those that are naturally present in aquifer rocks and sediments rather than constituents introduced by human activities. Concentrations of such natural contaminants are controlled by geochemical processes in the subsurface, particularly by oxidation-reduction (redox) reactions. The categorization of redox conditions based on the water quality of 116 samples collected from 65 wells in Geauga County during 1978 through 2009 indicates that most groundwater samples were strongly reducing (60 percent) or oxic (18 percent). Oxic waters were found only in the Pottsville Formation and Berea Sandstone and were generally associated with nitrate at concentrations of 0.38 to 6.0 mg/L. Strongly reducing waters occurred in all four commonly used aquifers and were associated with the following naturally occurring contaminants: (1) arsenic and manganese at concentrations exceeding the health-based benchmarks (10 µg/L and 300 µg/L, respectively) in some samples, (2) iron and manganese at concentrations exceeding the aesthetically based standards (300 µg/L and 50 µg/L, respectively) in most samples, and (3) total sulfides (consisting of hydrogen sulfide gas with its characteristic rotten-egg odor and [or] iron sulfide minerals that appear as finely disseminated particulates in water). Because of the association of redox conditions with specific contaminants, attempts were made to further document spatially where oxic and strongly reducing conditions occur so that contaminant occurrence can be better anticipated by planners and well owners. Within the Pottsville Formation, wells tapping strongly reducing groundwater tended to have a greater thickness of overlying low-permeability (recharge-inhibiting) material such as clay and shale than other wells tapping oxic or nitrate-reducing groundwater. In the Berea Sandstone, oxic conditions were found at well locations where either depth to groundwater was shallow (less than 45 feet [ft] below land surface) or the measured water level was within the open interval (uncased portion) of the well, whereas strongly reducing groundwater was found at well locations where depths to water were greater than 60 ft below land surface and measured water levels were 15 ft or more above the open interval of the well. To evaluate whether constituent concentrations consistently increased or decreased over time, the strength of the association between sampling year (time) and constituent concentration was statistically evaluated for 116 water-quality samples collected by the USGS in 1978, 1980, 1986, 1999, and 2009 from a total of 65 wells across the county (generally domestic wells or wells serving small businesses or churches). Results indicate that many of the constituents that have been analyzed for decades exhibited no consistent temporal trends at a statistically significant level (p-value less than 0.05); fluctuations in concentrations of these constituents represent natural variation in groundwater quality. Dissolved oxygen, calcium, and sulfate concentrations and chloride:bromide ratios increased over time in one or more aquifers, while pH and concentrations of bromide and dissolved organic carbon decreased over time. Detections of total coliform bacteria and nitrate did not become more frequent from 1986 to 2009, even though potential sources of these constituents, such as number of septic systems (linked to population) and percent developed land in the county, increased during this period.

Geauga County↗
USGS2008

Occurrence of organic compounds and trace elements in the upper Passaic and Elizabeth Rivers and their tributaries in New Jersey, July 2003 to February 2004: Phase II of the New Jersey toxics reduction workplan for New York-New Jersey Harbor

Samples of surface water and suspended sediment were collected from the Passaic and Elizabeth Rivers and their tributaries in New Jersey from July 2003 to February 2004 to determine the concentrations of selected chlorinated organic and inorganic constituents. This sampling and analysis was conducted as Phase II of the New York-New Jersey Harbor Estuary Workplan—Contaminant Assessment and Reduction Program (CARP), which is overseen by the New Jersey Department of Environmental Protection. Phase II of the New Jersey Workplan was conducted to define upstream tributary and point sources of contaminants in those rivers sampled during Phase I work, with special emphasis on the Passaic and Elizabeth Rivers. Samples were collected from three groups of tributaries: (1) the Second, Third, and Saddle Rivers; (2) the Pompton and upper Passaic Rivers; and (3) the West Branch and main stem of the Elizabeth River. The Second, Third, and Saddle Rivers were sampled near their confluence with the tidal Passaic River, but at locations not affected by tidal flooding. The Pompton and upper Passaic Rivers were sampled immediately upstream from their confluence at Two Bridges, N.J. The West Branch and the main stem of the Elizabeth River were sampled just upstream from their confluence at Hillside, N.J. All tributaries were sampled during low-flow discharge conditions using the protocols and analytical methods for organic constituents used in low-flow sampling in Phase I. Grab samples of streamflow also were collected at each site and were analyzed for trace elements (mercury, methylmercury, cadmium, and lead) and for suspended sediment, particulate organic carbon, and dissolved organic carbon. The measured concentrations and available historical suspended-sediment and stream-discharge data (where available) were used to estimate average annual loads of suspended sediment and organic compounds in these rivers. Total suspended-sediment loads for 1975–2000 were estimated using rating curves developed from historical U.S. Geological Survey (USGS) suspended-sediment and discharge data, where available. Average annual loads of suspended sediment, in millions of kilograms per year (Mkg/yr), were estimated to be 0.190 for the Second River, 0.23 for the Third River, 1.00 for the Saddle River, 1.76 for the Pompton River, and 7.40 for the upper Passaic River. On the basis of the available discharge records, the upper Passaic River was estimated to provide approximately 60 percent of the water and 80 percent of the total suspended-sediment load at the Passaic River head-of-tide, whereas the Pompton River provided roughly 20 percent of the total suspended-sediment load estimated at the head-of-tide. The combined suspended-sediment loads of the upper Passaic and Pompton Rivers (9.2 Mkg/yr), however, represent only 40 percent of the average annual suspended-sediment load estimated for the head-of-tide (23 Mkg/yr) at Little Falls, N.J. The difference between the combined suspended-sediment loads of the tributaries and the estimated load at Little Falls represents either sediment trapped upriver from the dam at Little Falls, additional inputs of suspended sediment downstream from the tributary confluence, or uncertainty in the suspended-sediment and discharge data that were used. The concentrations of total suspended sediment-bound polychlorinated biphenyls (PCBs) in the tributaries to the Passaic River were 194 ng/g (nanograms per gram) in the Second River, 575 ng/g in the Third River, 2,320 ng/g in the Saddle River, 200 ng/g in the Pompton River, and 87 ng/g in the upper Passic River. The dissolved PCB concentrations in the tributaries were 563 pg/L (picograms per liter) in the Second River, 2,510 pg/L in the Third River, 2,270 pg/L in the Saddle River, 887 pg/L in the Pompton River, and 1,000 pg/L in the upper Passaic River. Combined with the sediment loads and discharge, these concentrations resulted in annual loads of suspended sediment-bound PCBs, in grams per year (g/yr), of 37 in the Second River; 132 in the Third River; 2,320 in the Saddle River; 352 in the Pompton River; and 644 in the upper Passaic River. Annual loads of dissolved PCBs, in grams per year, are 9.2 in the Second River; 47 in the Third River; 212 in the Saddle River; 349 in the Pompton River; and 549 in the upper Passaic River. Concentrations of total suspended sediment-bound polychlorinated dibenzo-p-dioxins and polychlorinated dibenzo-p-difurans (PCDD/PCDFs) were 6,000 pg/g (picograms per gram) in the Second River; 11,300 pg/g in the Third River; 37,700 pg/g in the Saddle River; 7,140 pg/g in the Pompton River; and 9,640 pg/g in the upper Passaic River. Total toxic equivalence quotients (TEQs), which included PCDD/PCDFs and coplanar PCBs, ranged from 2.7 pg/g in the Second River to 132 pg/g (as 2,3,7,8-TCDD) in the Saddle River. Average annual loads of PCDD/PCDFs were from 1.1 g/yr in the Second River to 71 g/yr in the upper Passaic River. The load of TEQs (as 2,3,7,8-TCDD) from PCDD/PCDFs and coplanar PCBs in the tributaries were 0.5 mg/yr (milligrams per year) in the Second River, 5.8 mg/yr in the Third River, 130 mg/yr in the Saddle River, 46 mg/yr in the Pompton River, and 100 mg/yr in the upper Passaic River. These loads represent an addition to the TEQ load estimated to cross the head-of-tide of 0.1 percent by the Second River, 0.7 percent by the Third River, and 15 percent by the Saddle River. Loads of sediment-bound trace elements mercury, methylmercury, lead, and cadmium were calculated using concentrations obtained from grab samples, which were assumed to represent average annual concentrations in these rivers. Loads of sediment-bound mercury were estimated to be 1,200 g/yr in the Second River; 130 g/yr in the Third River; 4,200 g/yr in the Saddle River; 3,400 g/yr in the Pompton River; and 6,500 g/yr in the upper Passaic River. Loads of sediment-bound lead were estimated to be 56 kg/yr (kilograms per year) in the Second River; 89 kg/yr in the Third River; 1,140 kg/yr in the Saddle River; 310 kg/yr in the Pompton River; and 1,040 kg/yr in the upper Passaic River. Loads of sediment-bound cadmium were estimated to be 1 kg/yr in the Second River; 0.59 kg/yr in the Third River; 60 kg/yr in the Saddle River; 16 kg/yr in the Pompton River; and 11 kg/yr in the upper Passaic River. These loads indicate the importance of the sediment-bound contributions of organic compounds and trace elements to the upper Passaic and Saddle Rivers. Concentrations of suspended sediment-bound PCBs in the main stem and the West Branch of the Elizabeth River were 806 ng/g and 3,100 ng/g, respectively, representing loads of 40 g/yr and 1,150 g/yr, respectively. These loads were estimated using assumed discharge conditions. Concentrations of suspended sediment-bound PCDD/PCDFs were 7,270 pg/g and 9,980 pg/g in the main stem and West Branch, respectively, representing average annual loads of 0.36 g/yr and 3.7 g/yr, respectively. Total TEQ loads (sum of PCDD/PCDFs and PCBs) were 2.1 mg/yr (as 2,3,7,8-TCDD) in the main stem and 34 mg/yr in the West Branch, respectively. These load estimates, however, were directly related to the assumed annual discharge for the two branches. Long-term measurement of stream discharge and suspended-sediment concentrations would be needed to verify these loads. On the basis of the concentrations measured in this work, it appears that the West Branch is the principal source of PCBs, PCDD/PCDFs, total TEQs, and metals to the main stem of the Elizabeth River. Additional sources of these constituents may exist between the confluence and the head-of-tide.

New Jersey, New York↗
USGS2015

Southern Salish Sea Habitat Map Series: Admiralty Inlet

In 2010 the Environmental Protection Agency, Region 10 initiated the Puget Sound Scientific Studies and Technical Investigations Assistance Program, designed to support research in support of implementing the Puget Sound Action Agenda. The Action Agenda was created in response to Puget Sound having been designated as one of 28 estuaries of national significance under section 320 of the U.S. Clean Water Act, and its overall goal is to restore the Puget Sound Estuary's environment by 2020. The Southern Salish Sea Mapping Project was funded by the Assistance Program request for proposals process, which also supports a large number of coastal-zone- and ocean-management issues. The issues include the recommendations of the Marine Protected Areas Work Group to the Washington State Legislature (Van Cleve and others, 2009), which endorses a Puget Sound and coast-wide marine conservation needs assessment, gap analysis of existing Marine Protected Areas (MPA) and recommendations for action. This publication is the first of four U.S. Geological Survey Scientific Investigation Maps that make up the Southern Salish Sea Mapping Project. The remaining three map blocks to be published in the future, located south of Admiralty Inlet, are shown in figure 1. Puget Sound is a deep, fjord-type estuary covering an area of 2,330 km 2 in the Pacific Northwest region of the United States (fig. 1). It is connected to the ocean by the Strait of Juan de Fuca, a turbulent passage approximately 160 km in length and 22 km wide at its west end, expanding to over 40 km wide at its east end (Thomson, 1994). During the Pleistocene, the area was occupied several times by lobes of continental ice, resulting in a complex basin-fill of glacial and interglacial deposits that are locally as thick as 1100 m (Johnson and others, 2001). The last glaciation, called the Fraser glaciation, began after 28,800±740 14 C yr B.P. when ice started a slow expansion (Clague, 1981). At peak advance the westward Juan de Fuca lobe reached the edge of the continental shelf through the Juan de Fuca Strait shortly before 14,460±200 14 C yr B.P. (Herzer and Bornhold, 1982). The southward Puget lobe advanced to its terminal position in Puget Sound by around 14,150 14 C yr B.P. (Porter and Swanson, 1998). Ice retreated from its maximum to northern Whidbey Island by 13,650±350 14 C yr B.P. (Dethier and others, 1995). Retreating glaciers resulted in a thick sequence of ice-contact, glacial-marine sediment, and early post-glacial sediments (Linden and Schurrer, 1988). These deposits have experienced the effects of a marine transgression followed by regression, resulting in a sea-level several tens of meters lower than the present day (Linden and Schurrer, 1988). A second transgression brought sea level to about the present level by around 5,470±120 14 C yr B.P. (Clague and others, 1982) establishing the present oceanographic and geologic environment Puget Sound is separated into four interconnected basins; Whidbey, Central (Main), Hood Canal, and South (Thomson, 1994). The Whidbey, Central, and Hood Canal basins are the three main branches of the Puget Sound estuary and are separated from the Strait of Juan de Fuca by a double sill at Admiralty Inlet. The Admiralty Inlet map area includes the Inlet and a portion of the Whidbey Basin (fig. 1). The shallower South Basin is separated by a sill at Tacoma Narrows and is highly branched with numerous finger inlets. Flow within Puget Sound is dominated by tidal currents of as much as 1 m/s at Admiralty Inlet, reducing to approximately 0.5 m/s in the Central Basin (Lavelle and others, 1988). The lack of silt and clay-sized sediments in the Admiralty Inlet map area is likely a result of the strong currents (see Ground-Truth Studies for the Admiralty Inlet Map Area, sheet 3). The subtidal component of flow reaches approximately 0.1 m/s and is driven by density gradients arising from the contrast in salty ocean water at the entrance and freshwater inputs from stream flow (Lavelle and others, 1988). The total freshwater input to Puget Sound is approximately 3.4 x 10 6 m 3 /day, primarily from the Skagit River (Cannon, 1983). The subtidal circulation mostly consists of a two-layered flow in the basins with fresher water exiting at the surface and saltier water entering at depth (Ebbesmeyer and Cannon, 2001). In general, surface waters flow north and deeper waters flow south; variations arise from wind effects that can drive a surface current in the same direction as the wind, and a baroclinic response in the lower layer to about 100-m depth (Matsuura and Cannon, 1997). Oceanographic properties are influenced by temporal forcing parameters such as reduced stream flow during the 2000-01 drought that increased surface salinity and decreased differences between surface and bottom waters (Newton and others, 2003). On offshore seismic-reflection profiles, Pleistocene strata (excluding latest Pleistocene glacial and post-glacial deposits) form a distinct seismic unit, bounded below by pre-Tertiary or Tertiary basement and above by typically flat-lying latest Pleistocene to Holocene deposits that fill in erosional or depositional relief (Johnson and others, 2001). Cores from central Puget Sound have accumulation rates that range from 85 to 1200 mg/cm 2 /yr, or 0.12 to 2.4 cm/yr; the highest accumulation rates are near the southern end of central Puget Sound (Carpenter and others, 1985). Carpenter and others (1985) un-weighted arithmetic mean of accumulation rates for central Puget Sound deeper stations is 480±340 (± one standard deviation) mg/cm 2 /yr. Lavelle and others (1985) also found rates as high as 1200 mg/cm 2 /yr over the past approximately 70 years in cores in the Central Basin off of and north and south of Elliott Bay. Puget Sound basin rates are comparable to rates in midshelf silt deposits on the Washington coast north of the Columbia River (Nittrouer and others, 1979). The deep subtidal (in other words, below SCUBA depths) habitats of Puget Sound are relatively poorly known. A few subtidal surveys exist for several habitat types from the 1960s and 1970s (reviewed in Dethier, 1990), using grab and box core data. The Dethier (1990) review divides habitat up into Coast and Marine Ecological Classification Standard (CMECS) substrate, water column energy, and depth zones but does not attempt to map these habitats, rather it is an inventory of habitats found in the area and the flora and fauna associated with each habitat. The approach of the Southern Salish Sea Mapping project is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data (the undersea equivalent of satellite remote-sensing data in terrestrial mapping), acoustic backscatter, seafloor video, seafloor photography, and bottom-sediment sampling data. This approach is based in part on methods presented and data collection and product needs identified at the Washington State Seafloor Mapping Workshop (Washington State Seafloor Mapping Workshop Steering Committee, 2008), attended by coastal and marine managers and scientists. The map products display seafloor geomorphology and substrate, and identify potential marine benthic habitats. It is emphasized that the more interpretive habitat and geology maps rely on the integration of multiple, new high-resolution datasets and that mapping at small scales would not be possible without such data. Oceanographic current and wave data is not included in this analysis, however, the accompanying geographic information system (GIS) data set is designed and intended to be combined with oceanographic and biologic data sets assembled by others in the future and some of the GIS data has already been incorporated in the unpublished Nature Conservancy Benthic Habitats of Puget Sound database. This publication includes four map sheets, explanatory text, and a descriptive pamphlet. Each map sheet is published as a portable document format (PDF) file. ESRI ArcGIS compatible geotiffs (for example, bathymetry) and shapefiles (for example video observation points) will be available for download in the data catalog associated with this publication (Cochrane, 2015). An ArcGIS Project File with the symbology used to generate the map sheets is also provided. For those who do not own the full suite of ESRI GIS and mapping software, the data can be read using ESRI ArcReader, a free viewer that is available at http://www.esri.com/software/arcgis/arcreader/index.html .

Washington↗
USGS2025

Fluvial sediment dynamics in the Shoshone River and tributaries around Willwood Dam, Park County, Wyoming

Sedimentation affects many of the aging reservoirs in the United States. Dams and water diversions from rivers have been central elements of infrastructure supporting agricultural irrigation in the arid and semiarid regions of the Western United States for more than a century. The Willwood Irrigation District diversion dam (hereafter referred to as “Willwood Dam”) in Park County, Wyoming, is approximately 12 miles northeast of Cody, Wyo.; has a structural height of 70 feet; and impounds the Shoshone River for diversion into the Willwood Canal. Willwood Dam is part of a larger irrigation scheme supported by water storage in the much larger Buffalo Bill Dam, which is approximately 20 miles upstream. In October 2016, renovation construction activities at Willwood Dam and the Willwood Canal caused an unplanned evacuation of nearly 96,000 cubic yards of fine sediment. The fine sediment release in 2016 raised concerns that ongoing sediment management at Willwood Dam could impose limits on the long-term health of the aquatic ecosystem and fish populations. The U.S. Geological Survey, in cooperation with Wyoming Department of Environmental Quality and Willwood Work Groups 2 and 3, initiated an investigation of the dynamics of sediment transport in the Shoshone River and selected tributaries between Buffalo Bill Dam and Willwood Dam. The goal of the study was to quantify sediment transport into and out of Willwood Dam on an annual, seasonal, and event basis to better understand the relative quantities of sediment coming from natural sources and human activities on the landscape. The study ran from March 2019 through October 2021 and used observations of streamflow, turbidity, and acoustic backscatter collected at streamgages upstream and downstream from Willwood Dam to quantify suspended-sediment loads into and out of the dam during irrigation and fallow seasons, precipitation-runoff events, and deliberate sediment releases. Each tributary’s relative contribution to the sediment load upstream from Willwood Dam was examined using discrete measurements of suspended-sediment concentration and bedload during irrigation and fallow seasons, precipitation events, and stable conditions. Analysis of daily precipitation and temperature data indicated that conditions in the study area during the 2019 agricultural year were wetter and colder than period of record normal, and drier and near normal temperatures for the 2020 and 2021 agricultural years. Not all sediment load records between 2019 and 2021 are complete because of rejected observations (outliers), instrument failures or fouling, and instrument removal for calibrations. Statistical modeling of suspended-sediment concentration using paired values of turbidity and acoustic backscatter produced four models that, after refinement, had coefficients of determination indicating that more than 84 percent of the variance was explained by either turbidity or acoustic backscatter. A system of rules was developed to select the model predictions based on the seasonal operations of Willwood Dam, assumptions about the grain sizes mobilized during these operations, and assumed accuracy of the models at the downstream streamgage (Shoshone River below Willwood Dam, near Ralston, Wyo. [streamgage 06284010]) under different operational conditions. The sediment budget between upstream and downstream estimates of loads was interpreted using the mean predicted values bound by their respective model prediction intervals. When mean predicted loads of one streamgage were contained in the prediction intervals of the other streamgage, and vice-versa, difference in the sediment budget were interpreted as “indeterminate.” Modeled sediment load balances demonstrated the depositional and erosional behaviors expected from the conceptual model of dam operations whereby sediment tends to accumulate during irrigation seasons when the dam is spilling over the top, and sediment tends to evacuate during the fallow seasons when it is flowing through the sluice gates at the base of the dam. The sediment load calculations using the rules-based model criteria indicated that between 14,200 and 380,000 tons of suspended sediment moved through the Shoshone River around Willwood Dam during the irrigation seasons of 2019, 2020, and 2021; 380,000 tons of suspended sediment were transported during the cool, wet year of 2019, and 14,200 tons of suspended sediment were transported in 2020, which was relatively dry. During fallow seasons 2019, 2020, and 2021, which had fewer complete records, between 1,140 and 106,000 tons of suspended sediment was estimated to have moved through the river. For all seasons except fallow season 2022, the models estimated that more sediment was released from the dam than entered the dam, but the modeled mean loads at each streamgage were nearly always within the prediction intervals of each other, making the sediment balance indeterminant. Examination of suspended-sediment loads during irrigation seasons indicated that between 65 and 85 percent of fine sediment was transported during annual high flows and storm events, with the remainder transported during steady, lower streamflows. Examination of suspended loads during fallow seasons indicated that deliberate sediment releases through Willwood Dam accounted for between 39 and 67 percent of the total sediment moved during the fallow seasons. Deliberate sediment releases from Willwood Dam had estimated net exports of between 1,360 and 22,400 tons. Between August 2017 and July 2023, suspended-sediment concentration and bedload sediment samples were collected from 9 tributaries to the Shoshone River during 137 sampling events, including stable and precipitation-runoff conditions. During irrigation season precipitation events, the mean total sediment yields ranged from 0.33 to 9.51 tons per day per square mile; during fallow season precipitation events, the mean total yields ranged from 0.04 to 0.95 ton per day per square mile. The mean total sediment yield per unit area across all samples at each tributary site ranged from 0.26 to 3.08 tons per day per square mile. Bedload was a minor fraction of the total load, constituting a mean of 4 percent across all samples; 3 and 6 percent for events and nonevents, respectively, during irrigation season; and 3 and 1 percent for events and nonevents, respectively, during the fallow season. With the exception of one tributary, Dry Creek, these mean yield values were within the range of watershed-scale background sediment yield values estimated from reservoir surveys and previous suspended-sediment studies. Imagery from irrigation seasons 2012, 2015, 2017, 2019, and 2022 was used to determine the planimetric backwater extent of the pool area in the Shoshone River behind Willwood Dam to identify any changes in sediment storage. Active river channel widths in the Shoshone River upstream from Willwood Dam were all similar between years except 2015, which was determined to be statistically different from all other years. Bathymetric data taken in the pool behind Willwood Dam during three different surveys between November 2017 and April 2022 indicated no statistically significant differences in bed elevations between the years. Results from the planimetric and bathymetric survey data provide multiple lines of evidence indicating that sediment did not accumulate behind the dam within the error of the methods used. Examination of how precipitation affects sediment transport in the Shoshone River upstream from Willwood Dam indicated that accumulated rainfall from the natural runoff events captured during the study period varied from a trace to as much as 4.26 inches, with associated predicted suspended-sediment loads varying from 112 to 232,000 tons of suspended sediment. The behavior of the sediment loads relative to accumulated precipitation did not appear to change depending on irrigation or fallow season. A model of suspended-sediment concentrations relative to the 2-day accumulated precipitation indicated that suspended-sediment concentrations in the Shoshone River upstream from Willwood Dam increased exponentially for accumulations of 0.3 inch or more; such storms accounted for 10 percent or less of precipitation events observed during the 1981 to 2018 period of record. The gaps in records, precision of the instrumentation, and large variation in grain sizes in suspended-sediment mixtures downstream from the dam made closing the sediment budgets for most seasons unattainable. The biggest recent change in sediment storage measured using the planimetric area of deposits behind Willwood Dam took place between 2015 and 2017. The main event between these two measurements was the installation of new Willwood Canal gates in October 2016, which resulted in the large unplanned sediment release. Because the sediment budgets were nearly always indeterminate and the planimetric and bathymetric data indicated little change in the bed and bank material, it is likely that the change in sediment storage behind the dam during the study period was small relative to the precision of the statistical models and other uncertainties. This body of evidence suggests that, averaged during the 3-year study period, no major changes in storage took place, and that the current operations may be keeping storage at near-equilibrium. This condition could have been initiated because the middle sluice gate has now been operational since 2014, and the sediment release in October 2016 evacuated a large amount of legacy sediment from storage. Although the uncertainties are large, sluicing events allow for controlled releases of sediment that contributed to the near equilibrium conditions observed over an annual basis during this study.

Wyoming↗