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• 1. [Article] A seismic refraction study of a portion of the northeastern margin of the Tualatin Valley, Oregon

  The Tualatin Valley is a well defined elliptical basin centered at Hillsboro, with a major axis trending roughly N65°W. The valley is bordered on the northeast by the Tualatin Mountains (Portland Hills) ...

  Citation × Citation Citation Abstract Copy Title: A seismic refraction study of a portion of the northeastern margin of the Tualatin Valley, Oregon Author: Nazy, David John Year: 1987 The Tualatin Valley is a well defined elliptical basin centered at Hillsboro, with a major axis trending roughly N65°W. The valley is bordered on the northeast by the Tualatin Mountains (Portland Hills) which are a faulted, northwest-trending asymmetrical anticline. Topographic and geophysical evidence have defined the Portland Hills fault, which occurs along the northeast side of the Tualatin Mountains. The possibility that a fault or fault zone occurs along the southwest side of the Tualatin Mountains was investigated in this study. Title: A seismic refraction study of a portion of the northeastern margin of the Tualatin Valley, Oregon Author: Nazy, David John Year: 1987 The Tualatin Valley is a well defined elliptical basin centered at Hillsboro, with a major axis trending roughly N65°W. The valley is bordered on the northeast by the Tualatin Mountains (Portland Hills) which are a faulted, northwest-trending asymmetrical anticline. Topographic and geophysical evidence have defined the Portland Hills fault, which occurs along the northeast side of the Tualatin Mountains. The possibility that a fault or fault zone occurs along the southwest side of the Tualatin Mountains was investigated in this study. Close

• 2. [Article] Biostratigraphy of the Cowlitz Formation in the upper Nehalem River Basin, northwest Oregon

  Examination of stream and roadcut exposures of the Cowlitz Formation allows the selection of measured representative sections, and collection of fossils, from an area roughly defined by the intersection ...

  Citation × Citation Citation Abstract Copy Title: Biostratigraphy of the Cowlitz Formation in the upper Nehalem River Basin, northwest Oregon Author: Shaw, Neil B. Year: 1986 Examination of stream and roadcut exposures of the Cowlitz Formation allows the selection of measured representative sections, and collection of fossils, from an area roughly defined by the intersection of the boundaries of Clatsop, Columbia, Tillamook and Washington counties in Oregon. The study defines the features of the local environment of deposition, correlates sections to derive a composite columnar section, and develops a checklist of species for both microfossils and megafossils of the Cowlitz Formation. Title: Biostratigraphy of the Cowlitz Formation in the upper Nehalem River Basin, northwest Oregon Author: Shaw, Neil B. Year: 1986 Examination of stream and roadcut exposures of the Cowlitz Formation allows the selection of measured representative sections, and collection of fossils, from an area roughly defined by the intersection of the boundaries of Clatsop, Columbia, Tillamook and Washington counties in Oregon. The study defines the features of the local environment of deposition, correlates sections to derive a composite columnar section, and develops a checklist of species for both microfossils and megafossils of the Cowlitz Formation. Close

• 3. [Article] Landforms along the Lower Columbia River and the Influence of Humans

  River systems, such as the Columbia River in the Pacific Northwest, USA have been influenced by human activities, resulting in changes to the physical processes that drive landform evolution. This work ...

  Citation × Citation Citation Abstract Copy Title: Landforms along the Lower Columbia River and the Influence of Humans Author: Cannon, Charles Matthew Year: 2015 River systems, such as the Columbia River in the Pacific Northwest, USA have been influenced by human activities, resulting in changes to the physical processes that drive landform evolution. This work describes an inventory of landforms along the Columbia River estuary between the Pacific Ocean and Bonneville Dam in Oregon and Washington. Groupings of landforms are assigned to formative process regimes that are used to assess historical changes to floodplain features. The estuary was historically a complex system of channels with a floodplain dominated by extensive tidal wetlands in the lower reaches and backswamp lakes and wetlands in upper reaches. Natural levees flank most channels in the upper reaches, locally including areas of ridge and swale topography and crevasse splays that intrude into backswamps. Other Holocene process regimes affecting floodplain morphology have included volcanogenic deltas, tributary fans, dunes, and landslides. Pre-Holocene landforms are locally prominent and include ancient fluvial deposits and bedrock. Historical changes to streamflow regimes, floodplain isolation by flood-control systems, and direct anthropogenic disturbance have resulted in channel narrowing and limited the amount of floodplain that can be shaped by flowing water. Floodplain isolation has caused relative subsidence of tidal floodplains along much of the lower estuary. Most extant landforms are on trajectories controlled by humans and new landforms are mostly created by humans. Title: Landforms along the Lower Columbia River and the Influence of Humans Author: Cannon, Charles Matthew Year: 2015 River systems, such as the Columbia River in the Pacific Northwest, USA have been influenced by human activities, resulting in changes to the physical processes that drive landform evolution. This work describes an inventory of landforms along the Columbia River estuary between the Pacific Ocean and Bonneville Dam in Oregon and Washington. Groupings of landforms are assigned to formative process regimes that are used to assess historical changes to floodplain features. The estuary was historically a complex system of channels with a floodplain dominated by extensive tidal wetlands in the lower reaches and backswamp lakes and wetlands in upper reaches. Natural levees flank most channels in the upper reaches, locally including areas of ridge and swale topography and crevasse splays that intrude into backswamps. Other Holocene process regimes affecting floodplain morphology have included volcanogenic deltas, tributary fans, dunes, and landslides. Pre-Holocene landforms are locally prominent and include ancient fluvial deposits and bedrock. Historical changes to streamflow regimes, floodplain isolation by flood-control systems, and direct anthropogenic disturbance have resulted in channel narrowing and limited the amount of floodplain that can be shaped by flowing water. Floodplain isolation has caused relative subsidence of tidal floodplains along much of the lower estuary. Most extant landforms are on trajectories controlled by humans and new landforms are mostly created by humans. Close

• 4. [Article] A geophysical study of the North Scappoose Creek, Alder Creek, Clatskanie River lineament, along the trend of the Portland Hills fault, Columbia County, Oregon

  The Portland Hills fault forms a strong northwest trending lineament along the east side of the Tualatin Mountains. An en echelon lineament follows North Scappoose Creek, Alder Creek, and the Clatskanie ...

  Citation × Citation Citation Abstract Copy Title: A geophysical study of the North Scappoose Creek, Alder Creek, Clatskanie River lineament, along the trend of the Portland Hills fault, Columbia County, Oregon Author: Haas, Nina Year: 1982 The Portland Hills fault forms a strong northwest trending lineament along the east side of the Tualatin Mountains. An en echelon lineament follows North Scappoose Creek, Alder Creek, and the Clatskanie River along the same trend, through Columbia County, Oregon. The possibility that this lineament follows a fault or fault zone was investigated in this study. Geophysical methods were used, with seismic refraction, magnetic and gravity lines run perpendicular to the lineament. The seismic refraction models indicate the near surface basalt is broken in many places, with 15 - 30 meters (50 - 100 feet) vertical displacement, down to the west, at Bunker Hill along the Alder Creek fault. Gravity models required a faulted zone approximately two kilometers wide across the lineament. The proposed fault zone is more clearly defined in the south, becoming more diffuse and branching in the northern part of the study area. The Bouguer gravity values from this study distort the -40 milligal contour farther to the northwest than is shown on the Complete Bouguer Gravity Anomaly Map of Oregon {Berg and Thiruvathukal, 1967b). The existence of sharp topographic features and the geophysical evidence indicate fault activity along the zone. Title: A geophysical study of the North Scappoose Creek, Alder Creek, Clatskanie River lineament, along the trend of the Portland Hills fault, Columbia County, Oregon Author: Haas, Nina Year: 1982 The Portland Hills fault forms a strong northwest trending lineament along the east side of the Tualatin Mountains. An en echelon lineament follows North Scappoose Creek, Alder Creek, and the Clatskanie River along the same trend, through Columbia County, Oregon. The possibility that this lineament follows a fault or fault zone was investigated in this study. Geophysical methods were used, with seismic refraction, magnetic and gravity lines run perpendicular to the lineament. The seismic refraction models indicate the near surface basalt is broken in many places, with 15 - 30 meters (50 - 100 feet) vertical displacement, down to the west, at Bunker Hill along the Alder Creek fault. Gravity models required a faulted zone approximately two kilometers wide across the lineament. The proposed fault zone is more clearly defined in the south, becoming more diffuse and branching in the northern part of the study area. The Bouguer gravity values from this study distort the -40 milligal contour farther to the northwest than is shown on the Complete Bouguer Gravity Anomaly Map of Oregon {Berg and Thiruvathukal, 1967b). The existence of sharp topographic features and the geophysical evidence indicate fault activity along the zone. Close

• 5. [Article] The stratigraphy and structure of the Columbia River basalt group in the Bull Run watershed, Multnomah and Clackamas Counties, Oregon

  Approximately 150 meters (500 feet) of Grande Ronde Basalt and 140 meters (450 feet) of Wanapum Basalt of the Columbia River Basalt Group are exposed in the Bull Run Watershed. In Bull Run, the Grande ...

  Citation × Citation Citation Abstract Copy Title: The stratigraphy and structure of the Columbia River basalt group in the Bull Run watershed, Multnomah and Clackamas Counties, Oregon Author: Vogt, Beverly Frobenius Year: 1981 Approximately 150 meters (500 feet) of Grande Ronde Basalt and 140 meters (450 feet) of Wanapum Basalt of the Columbia River Basalt Group are exposed in the Bull Run Watershed. In Bull Run, the Grande Ronde Basalt is divided into three mappable units: "low Mg" R2 (at least one flow), "low Mg" N2 (approximately four flows), and "high Mg" N2 (two to three flows}. The Wanapum Basalt is represented by two members: Frenchman Springs Member (six flows) and Priest Rapids Member (one flow). These units are identified by instrumental neutron activation analysis, paleomagnetism based on measurements with a fluxgate magnetometer, petrography, lithology, jointing, and stratigraphic position. Title: The stratigraphy and structure of the Columbia River basalt group in the Bull Run watershed, Multnomah and Clackamas Counties, Oregon Author: Vogt, Beverly Frobenius Year: 1981 Approximately 150 meters (500 feet) of Grande Ronde Basalt and 140 meters (450 feet) of Wanapum Basalt of the Columbia River Basalt Group are exposed in the Bull Run Watershed. In Bull Run, the Grande Ronde Basalt is divided into three mappable units: "low Mg" R2 (at least one flow), "low Mg" N2 (approximately four flows), and "high Mg" N2 (two to three flows}. The Wanapum Basalt is represented by two members: Frenchman Springs Member (six flows) and Priest Rapids Member (one flow). These units are identified by instrumental neutron activation analysis, paleomagnetism based on measurements with a fluxgate magnetometer, petrography, lithology, jointing, and stratigraphic position. Close

• 6. [Article] Groundwater-Surface Water Interactions near Mosier, Oregon

  The town of Mosier, Oregon, is located near the east, dry end of the Columbia River Gorge, and the local area is known for cherry orchards that rely heavily on groundwater for irrigation. The CRBG groundwater ...

  Citation × Citation Citation Abstract Copy Title: Groundwater-Surface Water Interactions near Mosier, Oregon Author: Jones, Cullen Brandon Year: 2016 The town of Mosier, Oregon, is located near the east, dry end of the Columbia River Gorge, and the local area is known for cherry orchards that rely heavily on groundwater for irrigation. The CRBG groundwater system in Mosier has experienced groundwater declines of up to 60 meters due to over-pumping and or commingling. Declining groundwater levels have led to concerns over the sustainability of the resource, as it is the principle water source for irrigation and domestic use. Despite numerous previous studies of groundwater flow in CRBG aquifers here and elsewhere in the Columbia River basin, an aspect that has received relatively little attention is the interaction between groundwater and surface waters at locations where interflow zones are intersected by the surface waters. The objective of my research is to investigate how CRBG interflow zone exposures in Mosier Creek may be controlling groundwater elevations in the area. The methods used include: (1) geochemical analysis of well cuttings and detailed geologic mapping along area streams to identify interflow zones of individual CRBG flows, (2) analysis of stream discharge data and groundwater elevation data to confirm exchange of groundwater and surface waters, and (3) collection and analyses of 31 water samples from area wells, streams, and springs, to determine if waters from individual CRBG aquifers can be hydrochemically identified and to further constrain understanding of surface and groundwater interactions. My study confirms that the general elevation of the Pomona Member and Basalt of Lolo interflow zone creek exposure is coincident with the elevation where a change in slope of the decline trend in 2004 is seen in Mosier area well hydrographs. Furthermore, the results of stream discharge data indicated a close connection between drawdown from groundwater pumping during irrigation season and groundwater- surface water interaction. At the time of drawdown in the upper-most CRBG aquifer (Pomona), the stream transitions from gaining to losing water into the groundwater system. Elemental chemistry data indicates the Frenchman Springs Sentinel Gap aquifer waters are the most evolved waters in this study. Stable isotopic data reinforced this determination as the Sentinel Gap waters are the lightest, or most negative, with regard to δD and δ18O. Sentinel Gap samples were more depleted than other aquifer samples by 4.38 to 6.89 0/100 for δD and 0.39 to 0.59 0/100 for δ18O. The results of the general chemistry and isotope data reveal a more evolved chemical signature in lower watershed groundwater versus a less evolved signature for waters from wells located higher up on the Columbia Hills anticline. This was interpreted to be the result of the major structural features in the area providing for a more regional pathway of recharge in lower watershed groundwaters, versus a more local source of recharge for upper watershed groundwaters. There was also a pronounced commingled signature in the elemental ratios of lower watershed aquifer waters. The suspected mechanism of recharge to lower watershed wells is through younger Cascadian deposits upslope from the local watershed. The findings of this study reveal the importance of a detailed understanding of CRBG stratigraphy and its relation to surface waters, especially for other areas within the Yakima Fold Belt or Oregon and Washington. Studies that do not consider the influence that individual CRBG flows can have on groundwater-surface water interactions, and the groundwater system as a whole, run the risk of improperly assessing the groundwater resource for a region. Title: Groundwater-Surface Water Interactions near Mosier, Oregon Author: Jones, Cullen Brandon Year: 2016 The town of Mosier, Oregon, is located near the east, dry end of the Columbia River Gorge, and the local area is known for cherry orchards that rely heavily on groundwater for irrigation. The CRBG groundwater system in Mosier has experienced groundwater declines of up to 60 meters due to over-pumping and or commingling. Declining groundwater levels have led to concerns over the sustainability of the resource, as it is the principle water source for irrigation and domestic use. Despite numerous previous studies of groundwater flow in CRBG aquifers here and elsewhere in the Columbia River basin, an aspect that has received relatively little attention is the interaction between groundwater and surface waters at locations where interflow zones are intersected by the surface waters. The objective of my research is to investigate how CRBG interflow zone exposures in Mosier Creek may be controlling groundwater elevations in the area. The methods used include: (1) geochemical analysis of well cuttings and detailed geologic mapping along area streams to identify interflow zones of individual CRBG flows, (2) analysis of stream discharge data and groundwater elevation data to confirm exchange of groundwater and surface waters, and (3) collection and analyses of 31 water samples from area wells, streams, and springs, to determine if waters from individual CRBG aquifers can be hydrochemically identified and to further constrain understanding of surface and groundwater interactions. My study confirms that the general elevation of the Pomona Member and Basalt of Lolo interflow zone creek exposure is coincident with the elevation where a change in slope of the decline trend in 2004 is seen in Mosier area well hydrographs. Furthermore, the results of stream discharge data indicated a close connection between drawdown from groundwater pumping during irrigation season and groundwater- surface water interaction. At the time of drawdown in the upper-most CRBG aquifer (Pomona), the stream transitions from gaining to losing water into the groundwater system. Elemental chemistry data indicates the Frenchman Springs Sentinel Gap aquifer waters are the most evolved waters in this study. Stable isotopic data reinforced this determination as the Sentinel Gap waters are the lightest, or most negative, with regard to δD and δ18O. Sentinel Gap samples were more depleted than other aquifer samples by 4.38 to 6.89 0/100 for δD and 0.39 to 0.59 0/100 for δ18O. The results of the general chemistry and isotope data reveal a more evolved chemical signature in lower watershed groundwater versus a less evolved signature for waters from wells located higher up on the Columbia Hills anticline. This was interpreted to be the result of the major structural features in the area providing for a more regional pathway of recharge in lower watershed groundwaters, versus a more local source of recharge for upper watershed groundwaters. There was also a pronounced commingled signature in the elemental ratios of lower watershed aquifer waters. The suspected mechanism of recharge to lower watershed wells is through younger Cascadian deposits upslope from the local watershed. The findings of this study reveal the importance of a detailed understanding of CRBG stratigraphy and its relation to surface waters, especially for other areas within the Yakima Fold Belt or Oregon and Washington. Studies that do not consider the influence that individual CRBG flows can have on groundwater-surface water interactions, and the groundwater system as a whole, run the risk of improperly assessing the groundwater resource for a region. Close

• 7. [Article] Beyond the Angle of Repose: A Review and Synthesis of Landslide Processes in Response to Rapid Uplift, Eel River, Northern Eel River, Northern California

  In mountainous settings, increases in rock uplift are often followed by a commensurate uptick in denudation as rivers incise and steepen hillslopes, making them increasingly prone to landsliding as slope ...

  Citation × Citation Citation Abstract Copy Title: Beyond the Angle of Repose: A Review and Synthesis of Landslide Processes in Response to Rapid Uplift, Eel River, Northern Eel River, Northern California Author: Roering, Joshua J., Mackey, Benjamin H., Handwerger, Alexander L., Booth, Adam M., Schmidt, David A., Bennett, Georgina L., Cerovski-Darriau, Corina Year: 2015 In mountainous settings, increases in rock uplift are often followed by a commensurate uptick in denudation as rivers incise and steepen hillslopes, making them increasingly prone to landsliding as slope angles approach a limiting value. For decades, the threshold slope model has been invoked to account for landslide-driven increases in sediment flux that limit topographic relief, but the manner by which slope failures organize themselves spatially and temporally in order for erosion to keep pace with rock uplift has not been well documented. Here, we review past work and present new findings from remote sensing, cosmogenic adionuclides, suspended sediment records, and airborne lidar data, to decipher patterns of landslide activity and geomorphic processes related to rapid uplift along the northward-migrating Mendocino Triple Junction in Northern California. From historical air photos and airborne lidar, we estimated the velocity and sediment flux associated with active, slow-moving landslides (or earthflows) in the mélange- and argillite-dominated Eel River watershed using the downslope displacement of surface markers such as trees and shrubs. Although active landslides that directly convey sediment into the channel network account for only 7% of the landscape surface, their sediment flux amounts to more than 50% of the suspended load recorded at downstream sediment gauging stations. These active slides tend to exhibit seasonal variations in velocity as satellite-based interferometry has demonstrated that rapid acceleration commences within 1 to 2 months of the onset of autumn rainfall events before slower deceleration ensues in the spring and summer months. Curiously, this seasonal velocity pattern does not appear to vary with landslide size, suggesting that complex hydrologic-mechanical feedbacks (rather than 1-D pore pressure diffusion) may govern slide dynamics. A new analysis of 14 years of discharge and sediment concentration data for the Eel River indicates that the characteristic mid-winter timing of earthflow acceleration corresponds with increased suspended concentration values, suggesting that the seasonal onset of landslide motion each year may be reflected in the export of sediments to the continental margin. The vast majority of active slides exhibit gullied surfaces and the gully networks, which are also seasonally active, may facilitate sediment export although the proportion of material produced by this pathway is poorly known. Along Kekawaka Creek, a prominent tributary to the Eel River, new analyses of catchment-averaged erosion rates derived from cosmogenic radionuclides reveal rapid erosion (0.76 mm/yr) below a prominent knickpoint and slower erosion (0.29 mm/yr) upstream. Such knickpoints are frequently observed in Eel tributaries and are usually comprised of massive (>10m) interlocking resistant boulders that likely persist in the landscape for long time periods (>105yr). Upstream of these knickpoints, active landslides tend to be less frequent and average slope angles are slightly gentler than in downstream areas, which indicates that landslide density and average slope angle appear to increase with erosion rate. Lastly, we synthesize evidence for the role of large, catastrophic landslides in regulating sediment flux and landscape form. The emergence of resistant blocks within the mélange bedrock has promoted large catastrophic slides that have dammed the Eel River and perhaps generated outburst events in the past. The frequency and impact of these landslide dams likely depend on the spatial and size distributions of resistant blocks relative to the width and drainage area of adjacent valley networks. Overall, our findings demonstrate that landslides within the Eel River catchment do not occur randomly, but instead exhibit spatial and temporal patterns related to baselevel lowering, climate forcing, and lithologic variations. Combined with recent landscape evolution models that incorporate landslides, these results provide predictive capability for estimating erosion rates and managing hazards in mountainous regions. Title: Beyond the Angle of Repose: A Review and Synthesis of Landslide Processes in Response to Rapid Uplift, Eel River, Northern Eel River, Northern California Author: Roering, Joshua J., Mackey, Benjamin H., Handwerger, Alexander L., Booth, Adam M., Schmidt, David A., Bennett, Georgina L., Cerovski-Darriau, Corina Year: 2015 In mountainous settings, increases in rock uplift are often followed by a commensurate uptick in denudation as rivers incise and steepen hillslopes, making them increasingly prone to landsliding as slope angles approach a limiting value. For decades, the threshold slope model has been invoked to account for landslide-driven increases in sediment flux that limit topographic relief, but the manner by which slope failures organize themselves spatially and temporally in order for erosion to keep pace with rock uplift has not been well documented. Here, we review past work and present new findings from remote sensing, cosmogenic adionuclides, suspended sediment records, and airborne lidar data, to decipher patterns of landslide activity and geomorphic processes related to rapid uplift along the northward-migrating Mendocino Triple Junction in Northern California. From historical air photos and airborne lidar, we estimated the velocity and sediment flux associated with active, slow-moving landslides (or earthflows) in the mélange- and argillite-dominated Eel River watershed using the downslope displacement of surface markers such as trees and shrubs. Although active landslides that directly convey sediment into the channel network account for only 7% of the landscape surface, their sediment flux amounts to more than 50% of the suspended load recorded at downstream sediment gauging stations. These active slides tend to exhibit seasonal variations in velocity as satellite-based interferometry has demonstrated that rapid acceleration commences within 1 to 2 months of the onset of autumn rainfall events before slower deceleration ensues in the spring and summer months. Curiously, this seasonal velocity pattern does not appear to vary with landslide size, suggesting that complex hydrologic-mechanical feedbacks (rather than 1-D pore pressure diffusion) may govern slide dynamics. A new analysis of 14 years of discharge and sediment concentration data for the Eel River indicates that the characteristic mid-winter timing of earthflow acceleration corresponds with increased suspended concentration values, suggesting that the seasonal onset of landslide motion each year may be reflected in the export of sediments to the continental margin. The vast majority of active slides exhibit gullied surfaces and the gully networks, which are also seasonally active, may facilitate sediment export although the proportion of material produced by this pathway is poorly known. Along Kekawaka Creek, a prominent tributary to the Eel River, new analyses of catchment-averaged erosion rates derived from cosmogenic radionuclides reveal rapid erosion (0.76 mm/yr) below a prominent knickpoint and slower erosion (0.29 mm/yr) upstream. Such knickpoints are frequently observed in Eel tributaries and are usually comprised of massive (>10m) interlocking resistant boulders that likely persist in the landscape for long time periods (>105yr). Upstream of these knickpoints, active landslides tend to be less frequent and average slope angles are slightly gentler than in downstream areas, which indicates that landslide density and average slope angle appear to increase with erosion rate. Lastly, we synthesize evidence for the role of large, catastrophic landslides in regulating sediment flux and landscape form. The emergence of resistant blocks within the mélange bedrock has promoted large catastrophic slides that have dammed the Eel River and perhaps generated outburst events in the past. The frequency and impact of these landslide dams likely depend on the spatial and size distributions of resistant blocks relative to the width and drainage area of adjacent valley networks. Overall, our findings demonstrate that landslides within the Eel River catchment do not occur randomly, but instead exhibit spatial and temporal patterns related to baselevel lowering, climate forcing, and lithologic variations. Combined with recent landscape evolution models that incorporate landslides, these results provide predictive capability for estimating erosion rates and managing hazards in mountainous regions. Close

• 8. [Article] Investigating the Link Between Surface Water and Groundwater in the Tule Lake Subbasin, Oregon and California

  Water allocation in the upper Klamath Basin of Oregon and California has been challenging. Irrigators have increasingly turned to groundwater to make up for surface water shortages because of shifts in ...

  Citation × Citation Citation Abstract Copy Title: Investigating the Link Between Surface Water and Groundwater in the Tule Lake Subbasin, Oregon and California Author: Pischel, Esther Maria Year: 2014 Water allocation in the upper Klamath Basin of Oregon and California has been challenging. Irrigators have increasingly turned to groundwater to make up for surface water shortages because of shifts in allocation toward in-stream flows for Endangered Species Act listed fishes. The largest increase in groundwater pumping has been in and around the Bureau of Reclamation's Klamath Irrigation Project, which includes the Tule Lake subbasin in the southern part of the upper Klamath Basin. Previous groundwater flow model simulations indicate that water level declines from pumping may result in decreased flow to agricultural drains in the Tule Lake subbasin. Agricultural drains on the Klamath Project are an important source of water for downstream irrigators and for the Tule Lake and Lower Klamath Lake National Wildlife Refuges. To better assess the impact of increased pumping on drain flow and on the water balance of the groundwater system, flow data from agricultural drains were evaluated to investigate the changes that have taken place in groundwater discharge to drains since pumping volumes increased. Additionally, a fine-grid groundwater model of the Tule Lake subbasin was developed based on the existing regional flow model. The fine-grid model has sufficient vertical and horizontal resolution to simulate vertical head gradients, takes advantage of time-series data from 38 observation wells for model calibration, and allows agricultural drains to be more explicitly represented. Results of the drain flow analysis show that the groundwater discharge to agricultural drains has decreased by approximately 4000 hectare-meters from the 1997-2000 average discharge. Most of this decrease takes place in the northern and southeastern portions of the subbasin. Results of the groundwater model show that the initial source of water to wells is groundwater storage. By 2006, approximately 56% of the water from wells is sourced from agricultural drains. Title: Investigating the Link Between Surface Water and Groundwater in the Tule Lake Subbasin, Oregon and California Author: Pischel, Esther Maria Year: 2014 Water allocation in the upper Klamath Basin of Oregon and California has been challenging. Irrigators have increasingly turned to groundwater to make up for surface water shortages because of shifts in allocation toward in-stream flows for Endangered Species Act listed fishes. The largest increase in groundwater pumping has been in and around the Bureau of Reclamation's Klamath Irrigation Project, which includes the Tule Lake subbasin in the southern part of the upper Klamath Basin. Previous groundwater flow model simulations indicate that water level declines from pumping may result in decreased flow to agricultural drains in the Tule Lake subbasin. Agricultural drains on the Klamath Project are an important source of water for downstream irrigators and for the Tule Lake and Lower Klamath Lake National Wildlife Refuges. To better assess the impact of increased pumping on drain flow and on the water balance of the groundwater system, flow data from agricultural drains were evaluated to investigate the changes that have taken place in groundwater discharge to drains since pumping volumes increased. Additionally, a fine-grid groundwater model of the Tule Lake subbasin was developed based on the existing regional flow model. The fine-grid model has sufficient vertical and horizontal resolution to simulate vertical head gradients, takes advantage of time-series data from 38 observation wells for model calibration, and allows agricultural drains to be more explicitly represented. Results of the drain flow analysis show that the groundwater discharge to agricultural drains has decreased by approximately 4000 hectare-meters from the 1997-2000 average discharge. Most of this decrease takes place in the northern and southeastern portions of the subbasin. Results of the groundwater model show that the initial source of water to wells is groundwater storage. By 2006, approximately 56% of the water from wells is sourced from agricultural drains. Close

• 9. [Article] Hydrogeologic Investigation of a Pumice Aquifer, Fremont/Winema National Forest, Oregon

  The middle Holocene cataclysmic eruption of Mount Mazama blanketed Walker Rim, in south central Oregon, with 270 cm to 300 cm of pumice, causing capture of surface water systems by groundwater, stream ...

  Citation × Citation Citation Abstract Copy Title: Hydrogeologic Investigation of a Pumice Aquifer, Fremont/Winema National Forest, Oregon Author: Weatherford, Jonathan Michael Year: 2015 The middle Holocene cataclysmic eruption of Mount Mazama blanketed Walker Rim, in south central Oregon, with 270 cm to 300 cm of pumice, causing capture of surface water systems by groundwater, stream relocation, and the formation of biologically diverse fens and seasonal wetlands. The pumice aquifer at Round Meadow, an 8.6 km2 basin, hosts both a fen and seasonally ponded wetlands. The Round Meadow watershed lies within a closed basin between the upper Klamath and Deschutes river basins. As the highest meadow at Walker Rim, it is a relatively well-constrained system to study the effects of hydrological disruption. A water budget was calculated for the basin, hydraulic conductivity was evaluated for the three main sediment layers in the meadow, recharge sources and evaporative trends were studied using stable isotope analysis, and aquifer residence times were estimated using CFC tracer water age dating. Water year 2014 was a drought year and observation of the system under stressed conditions allowed discrimination of four independently functioning components of the hydrogeologic system. These were the meadow, which is by far the largest component in terms of water storage, the fen where iron cementation and up to 1 m of peat holds water in a berm above the meadow, three springs which are sourced from deeper groundwater hosted in the bedrock which underlies the pumice deposit, and the outflow area. In all cases, the aquifer material is pumice, but the influence of the pre-eruption landscape and post-eruption modifications of the aquifer material have resulted in partial isolation of the components. The water budget analysis indicated that the basin lost 44 cm of water storage during WY 2014. Hydraulic conductivity values of 1x10-6, 2x10-2, and 4x10-5 cm/s, were determined for the diatomaceous silt underlying the pumice, the Plinian pumice fall aquifer, and for the diatomaceous silt overlying the pumice, respectively. The pumice is characterized as a perched, weakly confined aquifer and residence times in the pumice are much longer (decades) than for water near the surface of the meadow. Water discharging at the springs is isotopically different (lighter) than either the surface water or groundwater in the pumice aquifer. The fen at Round Meadow appears dependent on seasonal precipitation to recharge water, and responds to fluctuations in annual precipitation. The wetland meadows are volumetrically the main water-storing features at Round Meadow, and these are not homogenous features, but a combination of discrete components. Title: Hydrogeologic Investigation of a Pumice Aquifer, Fremont/Winema National Forest, Oregon Author: Weatherford, Jonathan Michael Year: 2015 The middle Holocene cataclysmic eruption of Mount Mazama blanketed Walker Rim, in south central Oregon, with 270 cm to 300 cm of pumice, causing capture of surface water systems by groundwater, stream relocation, and the formation of biologically diverse fens and seasonal wetlands. The pumice aquifer at Round Meadow, an 8.6 km2 basin, hosts both a fen and seasonally ponded wetlands. The Round Meadow watershed lies within a closed basin between the upper Klamath and Deschutes river basins. As the highest meadow at Walker Rim, it is a relatively well-constrained system to study the effects of hydrological disruption. A water budget was calculated for the basin, hydraulic conductivity was evaluated for the three main sediment layers in the meadow, recharge sources and evaporative trends were studied using stable isotope analysis, and aquifer residence times were estimated using CFC tracer water age dating. Water year 2014 was a drought year and observation of the system under stressed conditions allowed discrimination of four independently functioning components of the hydrogeologic system. These were the meadow, which is by far the largest component in terms of water storage, the fen where iron cementation and up to 1 m of peat holds water in a berm above the meadow, three springs which are sourced from deeper groundwater hosted in the bedrock which underlies the pumice deposit, and the outflow area. In all cases, the aquifer material is pumice, but the influence of the pre-eruption landscape and post-eruption modifications of the aquifer material have resulted in partial isolation of the components. The water budget analysis indicated that the basin lost 44 cm of water storage during WY 2014. Hydraulic conductivity values of 1x10-6, 2x10-2, and 4x10-5 cm/s, were determined for the diatomaceous silt underlying the pumice, the Plinian pumice fall aquifer, and for the diatomaceous silt overlying the pumice, respectively. The pumice is characterized as a perched, weakly confined aquifer and residence times in the pumice are much longer (decades) than for water near the surface of the meadow. Water discharging at the springs is isotopically different (lighter) than either the surface water or groundwater in the pumice aquifer. The fen at Round Meadow appears dependent on seasonal precipitation to recharge water, and responds to fluctuations in annual precipitation. The wetland meadows are volumetrically the main water-storing features at Round Meadow, and these are not homogenous features, but a combination of discrete components. Close