OREGON WATER SCIENCE CENTER

Deschutes Basin Ground-Water Study

Abstracts from the study

Groundwater Hydrology of the Upper Deschutes Basin and its Influence on Streamflow

Marshall W. Gannett, U.S. Geological Survey, Portland, Oregon

Michael Manga, Department of Earth and Planetary Science, University of California, Berkeley, California

Kenneth E. Lite Jr., Oregon Water Resources Department, Salem, Oregon

Abstract

The remarkable stability of flow in the Deschutes River, relative to other rivers with comparable mean discharges, can be attributed to the substantial fraction of flow that originates as groundwater discharge in the upper Deschutes River basin, the region upstream of the Pelton Dam. Indeed, groundwater discharge from the upper Basin provides more than three quarters of the total streamflow for the entire Deschutes River basin. In order to understand the factors that result in such a large component of groundwater discharge and the stability of the flow, we develop a conceptual model for the hydrology of the upper basin. The model is based on the regional geology, the distribution and rate of groundwater recharge and discharge, and measurements of hydraulic head, water temperature and isotopic tracers. We show that three hydrogeologic aspects of the upper basin contribute to the stability of flow in the Deschutes River. First, the large vertical and lateral scale of the groundwater system damp out seasonal and longer period variations of discharge. Second, the high permeability of near-surface rocks, combined with the lack of an integrated surface drainage system, permits high recharge rates and thus high groundwater discharge rates, and reduces surface and shallow subsurface runoff. Third, the high storage capacity of the groundwater system filters out large and abrupt changes in recharge, resulting in greatly subdued changes in groundwater discharge. All three factors are responsible for the absence of serious floods in the upper basin, even during rain on snow events that cause significant flooding elsewhere in Oregon.

Hydrogeology of the Upper Deschutes Basin, Central Oregon: A Young Basin Adjacent to the Cascade Range Volcanic Arc

David R. Sherrod, U.S. Geological Survey, P.O. Box 51, Hawaii National Park, Hawaii  96718, dsherrod@usgs.gov

Marshall W. Gannett, U.S. Geological Survey, 10615 S.E. Cherry Blossom Drive, Portland, Oregon  97216, mgannett@usgs.gov

and Kenneth E. Lite, Jr., Oregon Water Resources Department, 158 12th Street N.E., Salem, Oregon  97310, kenneth.e.lite@wrd.state.or.us

Introduction

The upper Deschutes Basin encompasses about 11,700 km² of the Deschutes River drainage basin in central Oregon.  Draining the east flank of the Cascade Range, the upper Deschutes Basin extends northward from a drainage divide near Chemult that separates it from the Klamath Basin to the south.  The eastern margin of the basin lies along the crest of Newberry volcano and the west end of the Ochoco Mountains.  The northern boundary is near Warm Springs, northwest of Madras.

The upper Deschutes Basin is underlain by Quaternary and Tertiary volcanic and sedimentary rocks.  The occurrence and movement of ground water and the interaction of ground water and streams are controlled by the distribution of permeability within the depositional sequence.  The permeability distribution reflects the age, lithology, and depositional environment of the strata and the geologic structure imposed subsequently.

The Cascade Range crest, including a broad upland area east of the Three Sisters, is the principal source of recharge for the ground-water system.  The average annual rate of recharge from precipitation in the upper Deschutes Basin is estimated to be roughly 108 m³/s (3,800 ft³/s) (Gannett and others, 2001).

Ground water moves eastward from the Cascade Range and then generally northward through permeable Quaternary and upper Tertiary deposits.  North of Madras, the permeable deposits thin out against relatively impermeable lower Tertiary deposits of the John Day and Clarno Formations, forcing nearly all of the northward-flowing ground water to discharge to the Deschutes River and its tributaries.  This massive amount of ground-water discharge, exceeding 60 m³/s (2,000 ft³/s) near the confluence of the Deschutes and Crooked Rivers, is the principal reason for the remarkably stable flow of the Deschutes River.

Participants on this trip will explore the visible and conceptual aspects of the regional ground-water hydrology of the upper Deschutes Basin, including the interaction of ground water and streams.  The trip follows the general direction of ground-water flow northward from the headwaters of spring-fed streams near the margin of the Cascade Range to the principal regional discharge area near Lake Billy Chinook.  This guidebook describes a two-day trip.  Day 1 begins in the La Pine subbasin (uppermost Deschutes Basin) and proceeds through Bend, concentrating chiefly on the hydrologic controls created by Quaternary stratigraphy and structure.  Day 2 examines strata of the Deschutes Formation from Bend to Madras and the geologic factors influencing regional ground-water discharge.

A road log for each day is at the end of the field-trip guide.  The metric system is used for all scientific aspects of the guidebook except altitudes and water discharge rates, which are given in both meters and feet (altitude) or cubic meters per second and cubic feet per second (rates) owing to the widespread familiarity with U.S. traditional units in these matters.  The road log is reported in miles to match most car odometers.

Regional-scale geologic maps may aid travelers wishing a more thorough understanding of the geology along the trip route.  Day 1 stops are within the area of the west half of the Crescent 1° by 2° quadrangle (MacLeod and Sherrod, 1992) and the Bend 30-minute by 60-minute quadrangle (Sherrod and others, 2004).  Maps of the Mount Bachelor volcanic chain (Scott and Gardner, 1992) and Newberry volcano (MacLeod and others, 1995) provide more detail around the margins of Day 1 travel.  A road map of the Deschutes National Forest is helpful for navigating the maze of Forest Service and county roadways during Day 1.

Most Day 2 stops are within the Bend quadrangle (Sherrod and others, 2004).  The most northerly stops, however, are in an area that lacks regional-scale geologic mapping.  Several 1:24,000-scale maps cover the northern part of the trip, including those by Smith (1987a, b), Smith and Hayman (1987), and Ferns and others (1996).  The “Geologic Map of Oregon” (scale 1,500:000; Walker and MacLeod, 1992) would also be helpful in the northern area.

Download the full paper (PDF 3.8MB)

References Cited

Ferns, M.L., Stensland, D.E., and Smith, G.A., 1996, Geologic map of the Steelhead Falls Quadrangle, Deschutes and Jefferson Counties, Oregon: Oregon Department and Geology and Mineral Industries Geological Map Series GMS-101, scale 1:24,000.

Temporal and Spatial Variations in Ground-Water Discharge to Streams in the Cascade Range in Oregon and Implications for Water Management in the Klamath Basin

GANNETT, Marshall W., U.S. Geological Survey, 10615 SE Cherry Blossom Drive, Portland, Oregon 97216, mgannett@usgs.gov, LITE, Kenneth E. Jr, Oregon Water Resources Department, 158 12th Street NE, Salem, Oregon 97310, and LA MARCHE, Jonathan L., Oregon Water Resources Department, 1340 NW Wall Street, Suite 100, Bend, Oregon 97701

The Cascade Range volcanic arc represents what is arguably the single most important ground-water resource in Oregon. Yet, the unique hydrogeology of the Cascade Rangepresents challenges to resource managers. Much of the unique hydrologic character of the Cascade volcanic arc in Oregon can be attributed to two factors: (1) substantial orographic precipitation and resulting ground-water recharge, and (2) ground-water storage in extensive, highly permeable strata. These factors result in the major streams draining the eastern slopes of the southern and central Oregon Cascade Range being dominated by ground-water discharge. These streams have flows that are relatively constant compared to similar-size streams elsewhere in the region, but not without important temporal variations. The temporal variations in the Cascade streams, unlike many other streams, are not driven solely by current-year precipitation and snow pack, but strongly reflect antecedent conditions from previous years. Data from the upper Deschutes and upper Klamath Basins show that the temporal signals in ground-water discharge to springs and streams vary depending on scale of the flow system and the nature of the underlying geology. Discharge to small streams tends to be controlled by recent climate conditions, but discharge to volumetrically important larger-scale streams tends to integrate climate signals over longer periods. The hydrologic response of streams is also affected by geologic heterogeneity. Permeability and storage properties of the volcanic arc vary laterally, primarily as a function of the age of the rock. Hydraulic properties vary vertically as a function of the age of the rock and the degree of hydrothermal alteration. As a result, similar-scale flow systems may exhibit different hydrologic behavior in different areas. The unique aspects of the hydrology of the Cascade Range volcanic arc have confounded accurate streamflow forecasting and water management. Forecast uncertainty has been a particular problem in the Klamath Basin, where severe water shortages exist and year-to-year water management strategies are highly dependent on accurate forecasts. An important next step is to apply the increasing knowledge of the hydrogeology of the Cascade Range volcanic arc to water management using statistical or numerical models.

Climate-Driven Fluctuations in Hydraulic Head and Groundwater Discharge to Streams in the Upper Deschutes Basin, Oregon.

Marshall W. Gannett, U.S. Geological Survey, 10615 SE Cherry Blossom Dr., Portland, Oregon 97216, 503-251-3233 (mgannett@usgs.gov), and Kenneth E. Lite Jr., Oregon Water Resources Department, 158 12th St. NE, Salem, Oregon 97310, 503-378-8455 (liteke@wrd.state.or.us)

Fluctuations in hydraulic head and groundwater discharge to streams have been measured in the upper Deschutes Basin in central Oregon. The flow of the upper Deschutes River is dominated by groundwater discharge from the highly permeable volcanic terrane. Head fluctuations were evaluated using long-term observation well data (up to 50 years of record) and continuous water-level recorder data. Groundwater discharge fluctuations were evaluated using streamgage data. Both natural and anthropogenic fluctuations occur at a variety of temporal and spatial scales. Daily fluctuations in head are attributable to barometric and earth-tide effects. Annual fluctuations in head and discharge are related to variations in both natural recharge and artificial recharge from leaking irrigation canals. The largest and most geographically widespread fluctuations in head and groundwater discharge are driven by decadal-scale climate cycles.

Wet and dry climate cycles are reflected in the snowpack in the Cascade Range, the locus of groundwater recharge in the basin. Decadal-scale head fluctuations exceeding 20 feet have been observed in and near the Cascades over the past 50 years and are common in some populated parts of the basin. A major increase in recharge caused by the onset of a wet climate cycle starting in 1996 was reflected almost immediately in groundwater levels in the Cascade Range. The effects of this change were attenuated and delayed with increasing distance from the Cascade Range. Wells in the central part of the basin show climate-driven fluctuations of less than 10 feet, and their response to climate shifts lags wells in the Cascades by 1 to 2 years.

Groundwater discharge also fluctuates in response to climate cycles. The annual mean groundwater discharge to individual major streams (with mean annual flow greater than 100 ft3/s) varies in response to climate by factors ranging from approximately 0.2 to 2.0. Groundwater discharge in the entire upper Deschutes basin varies over 1,000 ft3/s in response to climate cycles. This variation represents approximately 25 percent of the baseflow (as represented by late-season streamflow) and about 20 percent of the mean annual streamflow.

Analyzing natural fluctuations in the hydraulic head and groundwater discharge has provided an understanding of the dynamics of the regional groundwater flow system and enabled calibration of a transient flow model. This model can be used, in turn, to gain insights into the distribution, magnitude, and timing of the effects of both natural and anthropogenic stresses to the groundwater system.

Mitigating the Effects of Groundwater Development on Streamflow in the Upper Deschutes Basin, Oregon.

Kenneth E. Lite, Jr., Oregon Water Resources Department, 158 12th St. NE, Salem, Oregon 97310, 503-378-8455 (liteke@wrd.state.or.us), Marshall W. Gannett, U.S. Geological Survey, 10615 SE Cherry Blossom Dr., Portland, Oregon 97216, 503-251-3233 (mgannett@usgs.gov), and Lara E. Burgel, Oregon Water Resources Department, 158 12th St. NE, Salem, Oregon 97310, 503-378-8455

A hydrologic investigation of the upper Deschutes Basin recently completed by the U.S. Geological Survey (USGS) and Oregon Water Resources Department (OWRD) quantified the groundwater / surface water connection in the basin and developed a numerical flow model that incorporates this connection.  The study concluded, among other things, that groundwater discharge contributes about 75 percent of the 4,660 cfs mean annual flow in the Deschutes River, with much of it occurring near the confluence with the Metolius and Crooked Rivers.  About 400-500 cfs of the groundwater that discharges to the lower Crooked River originates as artificial recharge from leaky irrigation canals, which lose about 50 percent of the total water diverted.

Concerns have been raised that groundwater pumping resulting from the rapid development and growth in the upper Deschutes Basin is impacting already stressed stream reaches within the basin and is interfering with a state-designated scenic waterway and instream water rights for fish and wildlife protection. Measures to mitigate the effects of some existing and all new groundwater use are being considered as part of a water-management strategy for the upper Deschutes River system.  

The OWRD is developing administrative rules to define mitigation, establish timetables for its implementation, and outline specific mitigation options for the upper Deschutes Basin.  Most of the options involve surface water and groundwater permit transfers and water right leases.  However, two popular options have been identified that utilize the leaky canal system in two opposing ways.  One identifies the canal system as a mechanism for groundwater recharge and would promote off-season operation of the canals to increase annual leakage.  The other identifies the leaky canals as an opportunity for water conservation and would reduce leakage through canal lining and piping, which would allow more water to remain in the streams.

Some of the mitigation options are controversial and raise technical questions regarding the timing of impacts versus the timing of mitigation measures and where those impacts and remedies are likely to occur.  Hydrologic knowledge of the flow system gained through the study and judicious use of the flow model will be used to guide the evaluation of potential mitigation projects.     

Simulation of Regional Ground-Water Flow in a Young Volcanic Terrane Using Inverse Methods

GANNETT, Marshall W., U.S. Geological Survey, Water Resources Division, 10615 S.E. Cherry Blossom Drive, Portland, Oregon, 97216, mgannett@usgs.gov; and LITE, Kenneth E., Jr., Oregon Water Resources Dept., 158 12th St. N.E., Salem, Oregon, 97310, Kenneth.E.LITE@wrd.state.or.us.

A regional-scale ground-water flow model was developed for the 4,500 square-mile upper Deschutes Basin in central Oregon to provide a scientific basis for ground-water management decisions. The modeled area is composed mostly of Pliocene and younger volcanic rocks, extends from the crest of the Plio-Pleistocene Cascade Range eastward to the contact with low-permeability early Tertiary volcanic rocks, and has several thousand feet of relief. Model calibration was complicated by the complexity of the topography and geology of the Cascade volcanic arc and the limits of available hydrologic data; inverse methods were used to address these complications. The main complicating factors were (1) precipitation varies across the modeled area from greater than 160 in/yr in the Cascade Range to less than 10 in/yr in the desert, and recharge varies from more than 135 in/yr to near zero; (2) the transient behavior of the system is driven by both annual and decadal variations in natural recharge, and by artificial recharge from leaking irrigation canals; (3) the young volcanic deposits are very heterogeneous at a great range of scales, with individual hydrogeologic units rarely extending more than a few miles and hydraulic conductivity contrasts commonly exceeding three orders of magnitude; (4) hydraulic head data were clustered both spatially and temporally; and (5) stream-flux data, although abundant for steady-state calibration, were geographically limited for transient calibration. Inverse methods (using nonlinear regression) were used in model calibration to test a variety of parameterization schemes efficiently and objectively. Parameterization schemes inconsistent with or not supported by hydrologic data were quickly identified. Surprisingly, when properly constrained by geologic information, simpler parameterization schemes gave better results.

The Use of Numerical Models in Conjunctive Use Management in the Upper Deschutes Basin, Oregon

M.W. Gannett (U.S. Geological Survey, 10615 SE Cherry Blossom Dr., Portland, Oregon, 97216), and K.E. Lite, Jr. (Oregon Water Resources Dept., 158 12th St. NE, Salem, Oregon, 97310)

Effective conjunctive management of ground-water and surface-water resources requires a quantitative understanding of the relation between the ground-water and surface-water systems. Numerical models are a practical method of quantifying this relation, particularly in complex systems where analytical methods are unsuitable. For a numerical model to be useful for predictive purposes, however, appropriate data on ground-water elevations (heads) and ground-water fluxes to and from streams must be available for proper model calibration. A numerical model has been developed to simulate the regional ground-water flow system and its interaction with streams in the upper Deschutes Basin in Central Oregon. The reliability of model predictions is related to the type, distribution, and uncertainty of data used for calibration.

The Deschutes Basin encompasses approximately 4,500 square miles in Central Oregon, extending from the crest of the Cascade Range east to the high desert. Ground-water recharge occurs primarily in the Cascade Range, and much of the ground water discharges to streams along the margins of the range. The remaining regional ground water discharges to streams in the northern part of the upper basin near the confluence of the Deschutes, Crooked, and Metolius Rivers, where the aquifers pinch out against older, less permeable strata.

Steady-state model calibration was based on head measurements in approximately 1,000 wells and estimates of the average ground-water flux to or from all major streams in the upper basin. Time-series data necessary for transient model calibration, however, was available only for a subset of wells and stream reaches. The nature of the data used for calibration has direct implications in determining the appropriate use of the model. Due to the large calibration data set, the steady-state model can simulate, with reasonable reliability, the average ground-water fluxes to and from most major streams in the upper basin. The transient model has the added capabilities to simulate changes in ground-water fluxes to and from streams with time and to account for changes in ground-water storage. Because it was calibrated with a more limited data set, however, the reliability of transient model predictions is limited in parts of the basin.

The Role of Quantitative Hydrology in Conjunctive Water Management in the Upper Deschutes Basin, Oregon.

K.E. Lite, Jr. (Oregon Water Resources Dept., 158 12th St. NE, Salem, Oregon, 97310); M.W. Gannett (U.S. Geological Survey, 10615 SE Cherry Blossom Dr, Portland, Oregon, 97216)

The upper Deschutes Basin in central Oregon is experiencing rapid urban, rural residential, and commercial development. Future growth will depend on the availability of ground water to supply water needs, because the surface-water resources within the basin are almost entirely appropriated, administratively restricted, or otherwise closed to further development.  However, the ground-water system in the basin is hydraulically connected to surface water, and contributes a large percentage of flow to the streams.  A recent study has shown that the effects of major changes in recharge propagate rapidly through the regional ground-water system and can be measured in wells and at stream-gaging stations.  These hydrologic findings also indicate that the effects of consumptive ground-water use propagate to streams and diminish streamflow fairly rapidly.  In accordance with Oregon law, an application for a ground-water right within the upper Deschutes Basin may be rejected if it is found that it has the potential to cause substantial interference with a senior surface-water right, or the use will measurably reduce the surface-water flow necessary to maintain the free-flowing character of the Scenic Waterway.  Mean annual baseflow in the Deschutes River downstream from the ground-water discharge areas is sufficiently large (about 4000 cfs) that the effects of consumptive ground-water uses, which are currently comparatively small (probably totaling less than 100 cfs), cannot be discriminated from other variations in the streamflow record.  Although the effect of consumptive use cannot be measured, a numerical ground-water flow model has been developed that supports the concept that these consumptive ground-water uses affect streamflow. The upper Deschutes Basin example raises interesting questions regarding the role of quantitative hydrology in the development of water-management strategies.  Should the water-management strategy for the area be proactive (based on calculated impacts) or reactive (based on measured impacts)?  And, if an impact cannot be discerned in the streamflow record, should the flows be considered impaired?

Lithological Controls on Groundwater Discharge to the Deschutes River between Lower Bridge and Lake Billy Chinook, Central Oregon

FERNS, Mark L., Oregon Department of Geology  and Minerals Industries, 1831 First Street, Baker City, Oregon  97814; LITE, Kenneth E., Jr., Oregon Water Resources Dept., 158 12th Street NE, Salem, Oregon  97310; and CLARK, Mark D., Oregon Water Resources Dept., 1340 NW Wall, Bend, Oregon  97701

Regional groundwater flow intercepts the Deschutes River Canyon north of Lower Bridge resulting in stream flow in the Deschutes River increasing by an order of magnitude (from 46 to 467 cfs) over a 14 mile long stretch between Lower Bridge and Lake Billy Chinook.  The dramatic increase in stream flow results from groundwater discharge through highly permeable units within the late Miocene Deschutes Formation.

The Deschutes Formation is a nearly flat lying, conspicuously undeformed sequence of interbedded pyroclastic deposits, fluviatile volcaniclastic deposits and mafic lava flows.  Individual flows and volcaniclastic deposits are laterally discontinuous, and are largely confined to intraformational channels which form the framework for an areally extensive, mostly unconfined aquifer unit.

The amount of groundwater discharging to the Deschutes River is not uniform, with 73% of the discharge probably occurring along less than 20% of the 14 mile reach.  Most of the gain (295 cfs) is thought to be controlled by two highly permeable geologic units.  The greatest streamflow gain (156 cfs) occurs where the river cuts around the east flank of a pre- to early Deschutes Age rhyodacite dome.  Water enters the river from springs that appear to issue from carapace and talus breccias on the dome flank.  The other large discharge (139 cfs) occurs where the river has cut through a Deschutes Formation paleochannel filled with coarse conglomerate and sandstone.  The remainder of the stream flow increase (111 cfs) occurs mostly where silt and sand or mafic lava flows of the Deschutes Formation are exposed at river level.     

Hydrogeology of Regional Ground-Water Flow in the Middle Deschutes Basin, Central Oregon

GANNETT, Marshall W, U.S. Geological Survey, 10615 S.E.Cherry Blossom Drive, Portland Oregon 97216, mgannett@usgs.gov, and LITE, Kenneth E., Jr., Oregon Water Resources Dept., 158 12th Street N.E., Salem, Oregon 97310, liteke@wrd.state.or.us

A conceptual model of the regional hydrogeology of the middle Deschutes Basin has been developed as a framework for a numerical ground-water flow model. Geologic information utilized included published and unpublished geologic maps, lithologic logs for approximately 1500 field-located water-supply wells, geophysical and lithologic logs of geothermal exploration wells in the Cascade Range, regional gravity maps, and field reconnaissance. Lithologic descriptions derived from the water well logs were coded and stored in a computer data base to automate the analysis. Water-well drillers’ lithologic logs were verified locally by using borehole geophysical logs and drill cuttings. Hydrologic information utilized for the conceptual model included water levels and specific capacities from the field-located wells, long- and short-term water-level fluctuations in selected observation wells, aquifer tests, surface-water gain/loss measurements, and climatic data.

   Although analysis of this information is not yet complete, some conclusions can be made concerning the hydrogeology of the middle Deschutes Basin. The ground-water system is recharged by precipitation in the Cascade Range and by seepage from streams and irrigation canals. Downward head gradients are common throughout much of the area. The dominant ground-water flow in the basin is from the Cascade Range toward discharge areas near Lake Billy Chinook. Ground-water moves primarily through fractured basalt and coarse-grained fluviatile volcaniclastic deposits derived from the Cascades. Pre to early Deschutes Formation silicic domes within the basin are locally important avenues of ground-water flow. Large horizontal hydraulic conductivities are indicated by aquifer testing and the occurrence of very low horizontal hydraulic gradients over large areas. Locally large vertical conductivities are indicated by the rapid response of deep ground-water levels to snow-melt, canal operation, and changes in stream stage. Deschutes Formation deposits derived from erosion of the John Day and Clarno Formations on the eastern part of the basin have hydraulic conductivities lower than the Cascade-derived deposits. Geologic structures also control ground-water flow as evidenced by the very high horizontal head gradients across the Sisters fault zone, a major structural feature that transects the study area.

Groundwater/Surface-Water Interactions in the Upper Deschutes Basin, Central Oregon

Marshall W. Gannett (US Geological Survey, 10615 SE Cherry Blossom Dr, Portland, Oregon, 97216;503-251-3233; mgannett@usgs.gov)

David S. Morgan (US Geological Survey, 10615 SE Cherry Blossom Dr, Portland, Oregon, 97216;503-251-3263; dsmorgan@usgs.gov)

Kenneth E. Lite, Jr. (Oregon Water Resources Dept, 158 12th St NE, Salem, Oregon, 97310; 503-378-8455; liteke@wrd.state.or.us)

Streamflow gain and loss data were collected to enable calibration of a regional groundwater flow model designed to simulate groundwater/surface-water interactions in the upper Deschutes basin in central Oregon. Groundwater/surface-water interactions reflect geologic, climatic, and anthro­pogenic factors. Streams emanating from the Quaternary volcanic terrane of the High Cascade Range are generally gaining in their upper reaches. In the LaPine basin, a sedimentary basin dom­inated by fine-grained deposits, stream and groundwater elevations are roughly coincident and no regionally significant gains or losses were measured. Downstream from the LaPine Basin to the city of Bend, a distance of less than 10 miles in terrane dominated by Tertiary and Quaternary basalt flows, groundwater elevations drop over 1,000 feet. The Deschutes River loses on average approximately 100 cubic feet per second (cfs) in this reach. At Bend, regional groundwater eleva­tions are approximately 400 to 600 feet below stream elevations. From Bend to Lower Bridge, a distance of about 30 river miles in terrane dominated by permeable lava and volcanic sediment of the Deschutes Formation, measurements indicate that there is on average a net gain in the Des­chutes River of approximately 15 cfs. This gain is probably due to near-stream irrigation and canal leakage. Downstream from Lower Bridge the groundwater elevation is at or above that of the Deschutes River and its tributaries the Crooked and Metolius Rivers. Between Lower Bridge and Pelton Dam, the point at which low permeability rocks underlying the Deschutes Formation crop out in the canyon, combined mean annual groundwater inflow to these streams exceeds 2,000 cfs. Seasonal variations in streamflow in the Deschutes River and its major tributaries in this region are small due to their large component of groundwater. The ratio of the highest mean monthly discharge to the mean annual discharge of the Metolius River (the only major stream with unregulated flow) is only 1.09 for the period from 1913 to 1994. Variations in mean-annual groundwater discharge in some drainages appear to be related to precipitation. Groundwater inflow to the Crooked River has increased approximately 400 cfs since the 1920s primarily as a result of irrigation and canal leakage.

Estimation of Aquifer Parameters for Water-Bearing Zones in the Deschutes Formation, Middle Deschutes Basin, Oregon

GATES, Sarah Meyer, Oregon Water Resources Department, 158 12th St. N.E., Salem, Oregon 97310, gatessm@chetco.wrd.state.or.us; and GANNETT, Marshall, U.S. Geological Survey, 10615, S.E. Cherry Blossom Drive, Portland, Oregon, 97216, mgannett@usgs.gov

Estimates of the hydraulic characteristics of geologic materials in the late Miocene to early Pliocene Deschutes Formation were required for development of a regional-scale ground-water model in the middle Deschutes Basin in Oregon. Five aquifer tests were conducted in areas that represent a variety of previously described depositional settings. Public supply wells that produce 250 to 1300 gallons per minute were used for these tests to ensure that sufficient pumping stress was applied to the generally highly transmissive aquifers. These wells included the City of Redmond new well #3, the City of Madras well #2, the City of Bend well Rock Bluff #1, and two Juniper Utility wells in the southern part of the Bend area. All wells were pumped at a constant rate for 1 to 3 days. The Jacob straight line, Theis nonequilibrium, and Neuman delayed gravity response methods were used to analyze each test.

Analysis of the Redmond well test, after removal of pretest trends and barometric effects, indicated transmissivity estimates ranging from 1,000,000 to 2,000,000 gpd/ft (gallons per day per foot) and storativity values of .001 to .002. This well produced water from generally coarse- grained fluviatile volcaniclastic deposits and minor lavas probably representative of the ancestral Deschutes River depositional setting. Analysis of the Madras well test resulted in a transmissivity estimate of 13,000 gpd/ft and a storativity estimate of .0001 for sand and gravel deposits underlying 225 feet of Deschutes Formation lava. These deposits probably represent an inactive basin margin depositional setting but may represent deposits transitional between that setting and the ancestral Deschutes River depositional setting. Analysis of the Bend test resulted in a transmissivity estimate of approximately 3,000,000 gpd/ft and a storativity value of .01 for interbedded basalt flows and vent deposits of probable Deschutes Formation affinity. Analysis of the Juniper Water Company tests yielded transmissivity estimates of 800,000 to 1,000,000 gpd/ft and storativites of .003 to .01 for interbedded basalt flows and vent deposits similar to those the Bend wells.

Developing Models for Quantitative Evaluation of Groundwater/Surface- Water Interactions in the Upper Deschutes Basin, Oregon

Kenneth E. Lite, Jr. (Oregon Water Resources Dept, 158 12th St NE, Salem, Oregon, 97310; 503-378-8455; liteke@wrd.state.or.us)

Marshall W. Gannett (US Geological Survey, 10615 SE Cherry Blossom Dr, Portland, Oregon, 97216;503-251-3233; mgannett@usgs.gov)

The Upper Deschutes Basin in central Oregon is experiencing rapid urban, rural residential, and commercial development. Nearly all the current and future development will depend solely on groundwater to supply water needs. Generally the groundwater resource is abundant; however, the hydraulically connected surface-water resources within the basin are mostly fully appropriated, administratively restricted, or otherwise closed to further development. The amount, location, and timing of streamflow depletion caused by groundwater pumping are important considerations in regulating basin groundwater appropriations or granting groundwater rights. The Upper Deschutes Basin has both gaining and losing stream reaches, as well as reaches with no apparent direct groundwater connection. The Oregon Water Resources Department and the U.S. Geological Survey are developing groundwater flow models for the Upper Deschutes Basin that attempt to incorporate the complexities of the groundwater/surface- water interactions as a way to evaluate various cumulative, temporal, and spatial groundwater pumpage effects on surface-water flows. An eight layer, 127 row by 87 column, variable size grid cell model has been devel­oped for a 4,200 square-mile area using the USGS finite difference model code MODFLOWP. Groundwater/surface-water interactions are modeled using the stream routing package of the USGS modular model. The Regional models are limited in functionality for many specific administra­tive uses, but provide estimates for cumulative impacts from groundwater pumpage and initial parameters for subregional models.

Effects of Climate, Stream Stage, and Irrigation Canal Seepage on Groundwater Levels in the Middle Deschutes Basin, Oregon

Marshall W. Gannett (U.S. Geological Survey, 10615 S.E. Cherry Blossom Drive, Portland, Oregon, 97216; 503/251-3233; e-mail: mgannett@usgs.gov)

Kenneth E. Lite (Oregon Water Resources Department, 158 12th Street N.E., Salem, Oregon, 97310-0210; 503/378-8455; liteke@wrd.state.or.us)

Monitoring water levels in wells can provide insight into the dynamics of a groundwater flow system, particularly with regard to recharge mechanisms and the effects of climatic- or pumping- induced stresses. The type of information gained from water-level monitoring depends on the frequency of measurements, the duration of monitoring, and the location of the monitored well. Water levels are monitored in more than 90 wells in the middle Deschutes Basin in central Oregon. The frequency and duration of monitoring data from these wells ranges from quarterly measurements for periods exceeding 30 years, to measurements every 2 hours for periods approaching 2 years.

Quarterly water-level measurements made over decades show that groundwater levels fluctuate more than 20 feet in response to long-term variations in annual precipitation. The magnitude of these long-term water-level fluctuations varies throughout the region.

Water-level measurements obtained every 2 hours using water-level recording instruments show that groundwater levels in the Cascade Range respond very rapidly to snowmelt and that annual recharge may take place over several months. Similar measurements in the high desert east of the Cascades show that groundwater levels respond rapidly to changes in river stage and to irrigation canal seepage, even at depths exceeding 600 feet. Data from recorders also show that the water-level response to pumping varies throughout the region.

In addition to providing information about groundwater hydrology, groundwater-level measurements are commonly used to assess the effects of resource development and are often the basis for resource management decisions. A thorough appreciation and understanding of all factors controlling water levels is necessary to ensure proper resource management.

Factors Controlling Seasonal and Long-Term Ground-Water Level Variations in the Middle Deschutes Basin, Oregon

Kenneth E. Lite (Oregon Water Resources Department, 158 12th Street N.E., Salem, Oregon, 97310-0210; 503/378-8455; e-mail: liteke@wrd.state.or.us)

Marshall W. Gannett (U.S. Geological Survey, 10615 S.E. Cherry Blossom Drive, Portland,
 Oregon, 97216; 503/251-3233; e-mail: mgannett@usgs.gov)

Monitoring of water levels in wells in the middle Deschutes Basin has provided insight into the dynamics of the ground-water flow system, particularly with regard to recharge mechanisms and the effects of climate- or pumping-induced stresses. Water levels have been monitored in more than 90 wells that penetrate water-bearing zones within Pleistocene glacial outwash deposits, Pliocene to Pleistocene lavas, and volcaniclastic sediments and lavas of the Deschutes Formation of late Miocene to early Pliocene age. The frequency and duration of water-level data from these wells ranges from quarterly measurements for periods exceeding 30 years, to measurements every 2 hours for periods approaching 2 years.

Quarterly water-level measurements collected for several decades show that ground-water levels fluctuate more than 20 feet in response to long-term variations in annual precipitation. The magnitude of these long-term water-level fluctuations varies throughout the region.

Water-level measurements obtained every 2 hours by using water-level recording instruments show that ground-water levels in the Cascade Range lavas respond very rapidly to climatic change and that annual recharge may take place over several months. Similar measurements in the high desert east of the Cascades show that ground-water levels respond rapidly to changes in river stage and to irrigation canal seepage, even at well depths exceeding 600 feet or distances from canals or rivers of 1 to 2 miles. Data from recorders also show that the water-level response to pumping varies throughout the region.

In addition to providing information about ground-water hydrology, ground-water level measurements are commonly used to assess the effects of resource development and are commonly the basis for resource management decisions. A thorough appreciation and understanding of all factors controlling water levels is necessary to ensure proper resource management.

U.S. Department of the Interior | U.S. Geological Survey
URL: http://or.water.usgs.gov/proj/deschutes_gw/abstracts.html
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Last modified Thursday, March 10, 2005 at 16:13 EST
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