Geology Reports⌕ Search

Geology topics

Tracy Nishikawa

Publications and source records attributed to Tracy Nishikawa.

33 records · Page 2Linked to original sources
USGS2006

Water Resources Investigations at Edwards Air Force Base since 1988

Edwards Air Force Base (EAFB) in southern California (fig. 1) has relied on ground water to meet its water-supply needs. The extraction of ground water has led to two major problems that can directly affect the mission of EAFB: declining water levels (more than 120 ft since the 1920s) and land subsidence, a gradual downward movement of the land surface (more than 4 ft since the late 1920s). As water levels decline, this valuable resource becomes depleted, thus requiring mitigating measures. Land subsidence has caused cracked (fissured) runways and accelerated erosion on Rogers lakebed. In 1988, the U.S. Geological Survey (USGS), in cooperation with the U.S. Air Force, began investigations of the effects of declining water levels and land subsidence at EAFB and possible mitigation measures, such as the injection of imported surface water into the ground-water system. The cooperative investigations included data collection and analyses, numerical simulations of ground-water flow and land subsidence, and development of a preliminary simulation-optimization model. The results of these investigations indicate that the injection of imported water may help to control land subsidence; however, the potential ground-water-quality impacts are unknown.

Fact Sheet↗
USGS2006

Geology, ground-water hydrology, geochemistry, and ground-water simulation of the Beaumont and Banning Storage Units, San Gorgonio Pass area, Riverside County, California

Ground water has been the only source of potable water supply for residential, industrial, and agricultural users in the Beaumont and Banning storage units of the San Gorgonio Pass area, Riverside County, California. Ground-water levels in the Beaumont area have declined as much as 100 feet between the early 1920s and early 2000s, and numerous natural springs have stopped flowing. In 1961, the San Gorgonio Pass Water Agency (SGPWA) entered into a contract with the California State Department of Water Resources to receive 17,300 acre-feet per year of water to be delivered by the California State Water Project (SWP) to supplement natural recharge. Currently (2005), a pipeline is delivering SWP water into the area, and the SGPWA is artificially recharging the ground-water system using recharge ponds located along Little San Gorgonio Creek in Cherry Valley with the SWP water. In addition to artificial recharge, SGPWA is considering the direct delivery of SWP water for the irrigation of local golf courses and for agricultural supply in lieu of ground-water pumpage. To better understand the potential hydrologic effects of different water-management alternatives on ground-water levels and movement in the Beaumont and Banning storage units, existing geohydrologic and geochemical data were compiled, new data from a basin-wide ground-water level and water-quality monitoring network were collected, monitoring wells were installed near the Little San Gorgonio Creek recharge ponds, geohydrologic and geochemical analyses were completed, and a ground-water flow simulation model was developed. The San Gorgonio Pass area was divided into several storage units on the basis of mapped or inferred faults. This study addresses primarily the Beaumont and Banning storage units. The geologic units in the study area were generalized into crystalline basement rocks and sedimentary deposits. The younger sedimentary deposits and the surficial deposits are the main water-bearing deposits in the San Gorgonio Pass area. The water-bearing deposits were divided into three aquifers: (1) the perched aquifer, (2) the upper aquifer, and (3) the lower aquifer based on lithologic and downhole geophysical logs. Natural recharge in the San Gorgonio Pass area was estimated using INFILv3, a deterministic distributed- parameter precipitation-runoff model. The INFILv3 model simulated that the potential recharge of precipitation and runoff in the Beaumont and Banning storage units was about 3,710 acre-feet per year and that the potential recharge in 28 sub-drainage basins upstream of the storage units was about 6,180 acre-feet per year. The water supply for the Beaumont and Banning storage units is supplied by pumping ground water from wells in the Canyon (Edgar and Banning Canyons), Banning Bench, Beaumont, and Banning storage units. Total annual pumpage from the Beaumont and Banning storage units ranged from about 1,630 acre-feet in 1936 to about 20,000 acre-feet in 2003. Ground-water levels declined by as much as 100 feet in the Beaumont storage unit from 1926-2003 in response to ground-water pumping of about 450,160 acre-feet during this period. Since ground-water development began in the San Gorgonio Pass area, there have been several sources of artificial recharge to the basin including return flow from applied water on crops, golf courses, and landscape; septic-tank seepage; and infiltration of storm runoff diversions and imported water into recharge ponds. Return flow from applied water and septic-tank seepage was estimated to reach a maximum of about 8,100 acre-feet per year in 2003. Owing to the great depth of water in much of study area (in excess of 150 feet), the return flow and septic-tank seepage takes years to decades to reach the water table. Stable-isotope data indicate that the source of ground-water recharge was precipitation from storms passing through the San Gorgonio Pass as opposed to runoff from the higher altitudes of the San Bernar

Scientific Investigations Report↗
USGS2006

Geohydrological characterization, water-chemistry, and ground-water flow simulation model of the Sonoma Valley area, Sonoma County, California

The Sonoma Valley, located about 30 miles north of San Francisco, is one of several basins in Sonoma County that use a combination of ground water and water delivered from the Russian River for supply. Over the past 30 years, Sonoma Valley has experienced rapid population growth and land-use changes. In particular, there has been a significant increase in irrigated agriculture, predominantly vineyards. To provide a better understanding of the ground-water/surface-water system in Sonoma Valley, the U.S. Geological Survey compiled and evaluated existing data, collected and analyzed new data, and developed a ground-water flow model to better understand and manage the ground-water system. The new data collected include subsurface lithology, gravity measurements, groundwater levels, streamflow gains and losses, temperature, water chemistry, and stable isotopes. Sonoma Valley is drained by Sonoma Creek, which discharges into San Pablo Bay. The long-term average annual volume of precipitation in the watershed is estimated to be 269,000 acre-feet. Recharge to the ground-water system is primarily from direct precipitation and Sonoma Creek. Discharge from the ground-water system is predominantly outflow to Sonoma Creek, pumpage, and outflow to marshlands and to San Pablo Bay. Geologic units of most importance for groundwater supply are the Quaternary alluvial deposits, the Glen Ellen Formation, the Huichica Formation, and the Sonoma Volcanics. In this report, the ground-water system is divided into three depth-based geohydrologic units: upper (less than 200 feet below land surface), middle (between 200 and 500 feet), and lower (greater than 500 feet). Synoptic streamflow measurements were made along Sonoma Creek and indicate those reaches with statistically significant gains or losses. Changes in ground-water levels in wells were analyzed by comparing historical contour maps with the contour map for 2003. In addition, individual hydrographs were evaluated to assess temporal changes by region. In recent years, pumping depressions have developed southeast of Sonoma and southwest of El Verano. Water-chemistry data for samples collected from 75 wells during 2002-04 indicate that the ground-water quality in the study area generally is acceptable for potable use. The water from some wells, however, contains one or more constituents in excess of the recommended standards for drinking water. The chemical composition of water from creeks, springs, and wells sampled for major ions plot within three groups on a trilinear diagram: mixed-bicarbonate, sodium-mixed anion, and sodium-bicarbonate. An area of saline ground water in the southern part of the Sonoma Valley appears to have shifted since the late 1940s and early 1950s, expanding in one area, but receding in another. Sparse temperature data from wells southwest of the known occurrence of thermal water suggest that thermal water may be present beneath a larger part of the valley than previously thought. Thermal water contains higher concentrations of dissolved minerals than nonthermal waters because mineral solubilities generally increase with temperature. Geohydrologic Characterization, Water-Chemistry, and Ground-Water Flow Simulation Model of the Sonoma Valley Area, Sonoma County, California Oxygen-18 (d18 O) and deuterium (dD) values for water from most wells plot along the global meteoric water line, indicating that recharge primarily is derived from the direct infiltration of precipitation or the infiltration of seepage from creeks. Samples from shallow- and intermediate-depth wells located near Sonoma Creek and (or) in the vicinity of Shellville plot to the right of the global meteoric water line, indicating that these waters are partly evaporated. The d18 O and dD composition of water from sampled wells indicates that water from wells deeper than 200 feet is isotopically lighter (more negative) than water from wells less than 200 feet deep, possibly indicating that older ground wate

California↗
USGS2005

Combined use of flowmeter and time-drawdown data to estimate hydraulic conductivities in layered aquifer systems

The vertical distribution of hydraulic conductivity in layered aquifer systems commonly is needed for model simulations of ground-water flow and transport. In previous studies, time-drawdown data or flowmeter data were used individually, but not in combination, to estimate hydraulic conductivity. In this study, flowmeter data and time-drawdown data collected from a long-screened production well and nearby monitoring wells are combined to estimate the vertical distribution of hydraulic conductivity in a complex multilayer coastal aquifer system. Flowmeter measurements recorded as a function of depth delineate nonuniform inflow to the wellbore, and this information is used to better discretize the vertical distribution of hydraulic conductivity using analytical and numerical methods. The time-drawdown data complement the flowmeter data by giving insight into the hydraulic response of aquitards when flow rates within the wellbore are below the detection limit of the flowmeter. The combination of these field data allows for the testing of alternative conceptual models of radial flow to the wellbore.

Ground Water↗
USGS2005

Application of flowmeter and depth-dependent water quality data for improved production well construction

Ground water production wells commonly are designed to maximize well yield and, therefore, may be screened over several water-bearing zones. These water-bearing zones usually are identified, and their hydrogeologic characteristics and water quality are inferred, on the basis of indirect data such as geologic and geophysical logs. Production well designs based on these data may result in wells that are drilled deeper than necessary and are screened through zones having low permeability or poor-quality ground water. In this study, we examined the application of flowmeter logging and depth-dependent water quality samples for the improved design of production wells in a complex hydrogeologic setting. As a demonstration of these techniques, a flowmeter log and depth-dependent water quality data were collected from a long-screened production well within a multilayered coastal aquifer system in the Santa Clara-Calleguas Basin, Ventura County, California. Results showed that the well yields most of its water from four zones that constitute 58% of the screened interval. The importance of these zones to well yield was not readily discernible from indirect geologic or geophysical data. The flowmeter logs and downhole water quality data also show that small quantities of poor-quality water could degrade the overall quality of water from the well. The data obtained from one well can be applied to other proposed wells in the same hydrologic basin. The application of flowmeter and depth-dependent water quality data to well design can reduce installation costs and improve the quantity and quality of water produced from wells in complex multiple-aquifer systems.

Ground Water↗
USGS2005

Evaluation of geohydrologic framework, recharge estimates and ground-water flow of the Joshua Tree area, San Bernardino County, California

Ground water historically has been the sole source of water supply for the community of Joshua Tree in the Joshua Tree ground-water subbasin of the Morongo ground-water basin in the southern Mojave Desert. The Joshua Basin Water District (JBWD) supplies water to the community from the underlying Joshua Tree ground-water subbasin. The JBWD is concerned with the long-term sustainability of the underlying aquifer. To help meet future demands, the JBWD plans to construct production wells in the adjacent Copper Mountain ground-water subbasin. As growth continues in the desert, there may be a need to import water to supplement the available ground-water resources. In order to manage the ground-water resources and to identify future mitigating measures, a thorough understanding of the ground-water system is needed. The purpose of this study was threefold: (1) improve the understanding of the geohydrologic framework of the Joshua Tree and Copper Mountain ground-water subbasins, (2) determine the distribution and quantity of recharge using field and numerical techniques, and (3) develop a ground-water flow model that can be used to help manage the water resources of the region. The geohydrologic framework was refined by collecting and interpreting water-level and water-quality data, geologic and electric logs, and gravity data. The water-bearing deposits in the Joshua Tree and Copper Mountain ground-water subbasins are Quarternary alluvial deposits and Tertiary sedimentary and volcanic deposits. The Quarternary alluvial deposits were divided into two aquifers (referred to as the 'upper' and the 'middle' alluvial aquifers), which are about 600 feet (ft) thick, and the Tertiary sedimentary and volcanic deposits were assigned to a single aquifer (referred to as the 'lower' aquifer), which is as thick as 1,500 ft. The ground-water quality of the Joshua Tree and Copper Mountain ground-water subbasins was defined by collecting 53 ground-water samples from 15 wells (10 in the Joshua Tree ground-water subbasin and 5 in the Copper Mountain ground-water subbasin) between 1980 and 2002 and analyzing the samples for major ions, nutrients, and selected trace elements. Selected samples also were analyzed for oxygen-18, deuterium, tritium, and carbon-14. The water-quality data indicated that dissolved solids and nitrate concentrations were below regulatory limits for potable water; however, fluoride concentrations in the lower aquifer exceeded regulatory limits. Arsenic concentrations and chromium concentrations were generally below regulatory limits; however, arsenic concentrations measured in water from wells perforated in the lower aquifer exceeded regulatory limits. The carbon-14 activities ranged from 2 to 72 percent modern carbon and are consistent with uncorrected ground-water ages (time since recharge) of about 32,300 to 2,700 years before present. The oxygen-18 and deuterium composition of water sampled from the upper aquifer is similar to the volume-weighted composition of present-day winter precipitation indicating that winter precipitation was the predominant source of ground-water recharge. Field studies, conducted during water years 2001 through 2003 to determine the distribution and quantity of recharge, included installation of instrumented boreholes in selected washes and at a nearby control site. Core material and cuttings from the boreholes were analyzed for physical, chemical, and hydraulic properties. Instruments installed in the boreholes were monitored to measure changes in matric potential and temperature. Borehole data were supplemented with temperature data collected from access tubes installed at additional sites along study washes. Streambed hydraulic properties and the response of instruments to infiltration were measured using infiltrometers. Physical and geochemical data collected away from the stream channels show that direct infiltration of precipitation to depths below the root zone and subsequent gro

Scientific Investigations Report↗
USGS2004

Comparison of ground-water flow model particle-tracking results and isotopic data in the Mojave River ground-water basin, southern California, USA

Flow-path and time-of-travel results for the Mojave River ground-water basin, southern California, calculated using the ground-water flow model MODFLOW and particle-tracking model MODPATH were similar to flow path and time-of-travel interpretations derived from delta-deuterium and carbon-14 data. Model and isotopic data both show short flow paths and young ground-water ages throughout the floodplain aquifer along most the Mojave River. Longer flow paths and older ground-water ages as great as 10,000 years before present were measured and simulated in the floodplain aquifer near the Mojave Valley. Model and isotopic data also show movement of water between the floodplain and regional aquifer and subsequent discharge of water from the river to dry lakes in some areas. It was not possible to simulate the isotopic composition of ground-water in the regional aquifer away from the front of the San Gabriel and San Bernardino Mountains - because recharge in these areas does not occur under the present-day climatic conditions used for calibration of the model.

Journal of Hydrology↗
USGS2003

Geohydrology, geochemistry, and ground-water simulation-optimization of the Central and West Coast Basins, Los Angeles County, California

Historical ground-water development of the Central and West Coast Basins in Los Angeles County, California through the first half of the 20th century caused large water-level declines and induced seawater intrusion. Because of this, the basins were adjudicated and numerous ground-water management activities were implemented, including increased water spreading, construction of injection barriers, increased delivery of imported water, and increased use of reclaimed water. In order to improve the scientific basis for these water management activities, an extensive data collection program was undertaken, geohydrological and geochemical analyses were conducted, and ground-water flow simulation and optimization models were developed. In this project, extensive hydraulic, geologic, and chemical data were collected from new multiple-well monitoring sites. On the basis of these data and data compiled and collected from existing wells, the regional geohydrologic framework was characterized. For the purposes of modeling, the three-dimensional aquifer system was divided into four aquifer systems?the Recent, Lakewood, Upper San Pedro, and Lower San Pedro aquifer systems. Most pumpage in the two basins is from the Upper San Pedro aquifer system. Assessment of the three-dimensional geochemical data provides insight into the sources of recharge and the movement and age of ground water in the study area. Major-ion data indicate the chemical character of water containing less than 500 mg/L dissolved solids generally grades from calcium-bicarbonate/sulfate to sodium bicarbonate. Sodium-chloride water, high in dissolved solids, is present in wells near the coast. Stable isotopes of oxygen and hydrogen provide information on sources of recharge to the basin, including imported water and water originating in the San Fernando Valley, San Gabriel Valley, and the coastal plain and surrounding hills. Tritium and carbon-14 data provide information on relative ground-water ages. Water with abundant tritium (greater than 8 tritium units) is found in and downgradient from the Montebello Forebay and near the seawater barrier projects, indicating recent recharge. Water with less than measurable tritium is present in, and downgradient from, the Los Angeles Forebay and in most wells in the West Coast Basin. Water from several deep wells was analyzed for carbon-14. Uncorrected estimates of age for these samples range from 600 to more than 20,000 years before present. Chemical and isotopic data are combined to evaluate changes in chemical character along flow paths emanating from the Montebello and Los Angeles Forebays. A four-layer ground-water flow model was developed to simulate steady-state ground-water conditions representative of those in 1971 and transient conditions for the period 1971?2000. Model results indicate increases in ground-water storage in all parts of the study area over the simulated thirty-year period. The model was used to develop a three-dimensional ground-water budget and to assess impacts of two alternative future (2001?25) ground-water development scenarios?one that assumes continued pumping at average current rates and a second that assumes increasing pumping from most wells in the Central Basin. The model simulates stable or slightly increasing water levels for the first scenario and declining water levels (25 to 50 ft in the Central Basin) in the second scenario. Model sensitivity to parameter values and to the assumed Orange County boundary condition was evaluated. Particle tracking was applied to simulate advective transport of water from the spreading ponds, the coastline, and the seawater injection barriers. Particle tracking results indicate that most flow within the Upper San Pedro aquifer system occurs within about 20 percent of the total aquifer system thickness and that virtually all water injected into the seawater barrier projects has flowed inland. The simulation model was linked with optimizatio

California↗
USGS2001

Water Supply in the Mojave River Ground-Water Basin, 1931-99, and the Benefits of Artificial Recharge

The Mojave River and the associated aquifer system are important water supplies in the Mojave Desert of southern California. The river and aquifer system are in hydraulic connection in many areas, and when flow conditions change in one, the other usually is affected. The river is an unpredictable source of water; therefore, residents of the basin rely almost entirely on ground water for their water supply. This reliance on ground water has resulted in overdraft conditions that have caused water-level declines, changes in the quantity and spatial distribution of recharge from the Mojave River, and loss of riparian habitat. The U.S. Geological Survey (USGS), in cooperation with the Mojave Water Agency (MWA), has completed several studies to determine the likely effects of overdraft on the ground-water and surface-water relations along the Mojave River. This report summarizes those studies, highlighting some of the simulation results from a ground-water flow model, and describes the ground-water and surface-water conditions of the Mojave River Basin.

Fact Sheet↗
USGS2001

Simulation of ground-water flow in the Mojave River basin, California

The proximity of the Mojave River ground-water basin to the highly urbanized Los Angeles region has led to rapid growth in population and, consequently, to an increase in the demand for water. The Mojave River, the primary source of surface water for the region, normally is dry-except for a small stretch of perennial flow and periods of flow after intense storms. Thus, the region relies almost entirely on ground water to meet its agricultural and municipal needs. Ground-water withdrawal since the late 1800's has resulted in discharge, primarily from pumping wells, that exceeds natural recharge. To better understand the relation between the regional and the floodplain aquifer systems and to develop a management tool that could be used to estimate the effects that future stresses may have on the ground-water system, a numerical ground-water flow model of the Mojave River ground-water basin was developed, in part, on the basis of a previously developed analog model. The ground-water flow model has two horizontal layers; the top layer (layer 1) corresponds to the floodplain aquifer and the bottom layer (layer 2) corresponds to the regional aquifer. There are 161 rows and 200 columns with a horizontal grid spacing of 2,000 by 2,000 feet. Two stress periods (wet and dry) per year are used where the duration of each stress period is a function of the occurrence, quantity of discharge, and length of stormflow from the headwaters each year. A steady-state model provided initial conditions for the transient-state simulation. The model was calibrated to transient-state conditions (1931-94) using a trial-and-error approach. The transient-state simulation results are in good agreement with measured data. Under transient-state conditions, the simulated floodplain aquifer and regional aquifer hydrographs matched the general trends observed for the measured water levels. The simulated streamflow hydrographs matched wet stress period average flow rates and times of no flow at the Barstow and Afton Canyon gages. Steady-state particle-tracking was used to estimate travel times for mountain-front and streamflow recharge. The simulated travel times for mountain-front recharge to reach the area west of Victorville were about 5,000 to 6,000 years; this result is in reasonable agreement with published results. Steady-state particle-tracking results for streamflow recharge indicate that in most subareas along the river, the particles quickly leave and reenter the river. The complaint that resulted in the adjudication of the Mojave River ground-water basin alleged that the cumulative water production upstream of the city of Barstow had overdrafted the ground-water basin. In order to ascertain the effect of pumping on ground-water and surface-water relations along the Mojave River, two pumping simulations were compared with the 1931-90 transient-state simulation (base case). The first simulation assumed 1931-90 pumping in the upper region (Este, Oeste, Alto, and Transition zone model subareas) but with no pumping in the remainder of the basin, and the second assumed 1931-90 pumping in the lower region (Centro, Harper Lake, Baja, Coyote Lake, and Afton Canyon model subareas) but with no pumping in remainder of the basin. In the upper region, assuming pumping only in the upper region, there was no change in storage, recharge from the Mojave River, ground-water discharge to the Mojave River, or evapotranspiration when compared with the base case. In the lower region, assuming pumping only in the upper region, there was storage accretion, decreased recharge from the Mojave River, increased ground-water discharge to the Mojave River, and increased evapotranspiration when compared with the base case. In the upper region, assuming pumping only in the lower region, there was storage accretion, decreased recharge from the Mojave River, increased ground-water discharge to the Mojave River, and increased evapotranspiration when compared with the base case. In the lower region, assuming pumping only in the lower region, there was less storage depletion, increased recharge from the Mojave River, increased ground-water discharge to the Mojave River, and increased evapotranspiration when compared with the base case. Overall, pumping in the lower region does not negatively affect the upper region; however, pumping in the upper region negatively affects the lower region by decreasing recharge from the Mojave River. Streamflow, pumpage, and water-level data from calendar years 1995-99 were used to validate the calibrated ground-water flow model, that is, to test that the ground-water flow model will duplicate measured data for a noncalibration period without modification of the model parameters. In general, the simulated results are in good agreement with the measured data, and the simulated hydrographs for wells in the floodplain and regional aquifers follow the measured water-level trends. Simulated streamflow data for the 1995-99 wet and dry stress periods at the Lower Narrows, Barstow, and Afton Canyon were compared with the measured data for average streamflow for the same periods; in general, the model reflects 1995-99 streamflow conditions. The simulation results also indicate that the streambed conductance values calibrated to the 1931-94 conditions reasonably simulate the 1995-99 conditions and therefore can be used for predictive purposes. To visualize the magnitude, spatial distribution, and timing of water-level changes in the basin through time, simulated hydraulic heads for 1932-99 were compared with simulated hydraulic heads for 1931. Greater than average annual inflows to the Mojave River from the headwaters during the late 1930's and throughout much of the 1940's resulted in simulated hydraulic heads that were higher than the 1931 hydraulic heads along the Mojave River in most model subareas. Parts of the Baja and Harper Lake model subareas had declines in the simulated hydraulic head because of the increase in agricultural pumpage. By 1960, the simulated hydraulic heads were lower than the simulated hydraulic heads for 1931 in all model subareas of the floodplain and the regional aquifers because of pumpage. After 1960, the size and the magnitude of the areas of the regional aquifer for which simulated hydraulic heads were lower than those for 1931 continued to increase until the end of the simulation (1999). Along the Mojave River, hydraulic heads fluctuated in the floodplain aquifer in response to recharge during years with large inflows with little apparent effect on the simulated hydraulic heads in the regional aquifer. Three water-management alternatives were evaluated to determine their effect on ground-water resources using the calibrated ground-water flow model. The water-management alternatives consider the artificial recharge of imported water allocated to the Mojave Water Agency (MWA): the first assumes that zero percent of the MWA allocation is available (alternative 1), the second assumes that 50 percent of the MWA allocation is available (alternative 2), and the third assumes that 100 percent of the MWA allocation is available (alternative 3). Each of the three water-management alternatives were evaluated for a 20-year drought. Streamflow conditions were simulated using the 20-year drought of 1945-64 with associated calibrated stream parameters. Management alternative 1 results in a reduction in ground-water recharge from the Mojave River compared with average recharge for 1995-99; this reduction is reflected in simulated hydraulic-head declines between 1999 and 2019 of as much as 45 feet. Management alternatives 2 and 3 result in no change in recharge from the Mojave River for management alternative 2 and a small increase for management alternative 3 when compared with recharge for management alternative 1. The artificial recharge of imported water causes increases in simulated hydraulic head for both management alternatives at each of the artificial-recharge sites. Some of the increases are related to water that recharges into areas of low transmissivity which implies that the recharge operations may benefit from being distributed over a larger area.

California↗
USGS1999

Evaluation of surface-water/ground-water interactions in the Santa Clara River Valley, Ventura County, California

The interactions of surface water and ground water along the Santa Clara River in Ventura County, California, were evaluated by analyzing river-discharge and water-quality data and geohydrologic information collected by the U.S. Geological Survey between 1993 and 1995 for the Piru, Fillmore, and Santa Paula subbasins. Measurements of discharge and water quality were made at multiple locations along the Santa Clara River and its tributaries at eight different time periods during different releases from Lake Piru. Geologic, hydraulic, and water-quality data were collected from three new multiple-completion ground-water monitoring wells. These data, together with data collected as part of the U.S. Geological Survey Southern California Regional Aquifer-System Analysis (RASA) study, were analyzed in order to quantify rates and locations of ground-water recharge and discharge within the river, characterize the correlation of recharge and discharge rates with ground-water conditions and reservoir releases, and better characterize the three-dimensional ground-water flow system. Analysis of the data indicates that the largest amount of ground-water recharge from the river consistently occurs in the Piru subbasin. Some ground-water recharge from the river may occur in the upper part of the Fillmore subbasin. Increases in sulfate concentrations indicate that increases in flow at the lower ends of the Piru and Fillmore subbasins result from high-sulfate ground-water discharge. Increases in flow in the lower part of the Santa Paula subbasin are not accompanied by significant sulfate increases. Several sets of regressions indicate possible correlation between net flow changes in the river and depths to ground water and release rates from Lake Piru. These statistical relations may be of use for evaluating alternative Lake Piru release strategies. Data on the stable isotopes of hydrogen and oxygen from the ground-water monitoring wells that were installed as part of this investigation were used to distinguish between zones affected by recharge from the Santa Clara River and zones affected by recharge from local precipitation. Tritium data from a new multiple-completion monitoring site indicate that near the river in the upper Santa Paula subbasin, recent (post-1950) recharge water is not present at depths greater than about 350 feet below land surface. Water-level and lithologic data from the monitoring site indicate that the river and the Shallow aquifer have only limited hydraulic connection to the underlying aquifers at this location. Water-level data from the Shallow aquifer and from an in-stream drive point were used in an analytic model to estimate hydraulic properties governing stream?aquifer interactions in the upper Santa Paula subbasin. Hydraulic conductivities in all the USGS monitoring wells were estimated on the basis of slug tests.

Water-Resources Investigations Report↗
USGS1998

Geohydrology of Storage Unit III and a combined flow model of the Santa Barbara and foothill ground-water basins, Santa Barbara County, California

The city of Santa Barbara pumps most of its ground water from the Santa Barbara and Foothill ground-water basins. The Santa Barbara basin is subdivided into two storage units: Storage Unit I and Storage Unit III. The Foothill basin and Storage Unit I of the Santa Barbara basin have been studied extensively and ground-water flow models have been developed for them. In this report, the geohydrology of the Santa Barbara ground- water basin is described with a special emphasis on Storage Unit III in the southwestern part of the basin. The purposes of this study were to summarize and evaluate the geohydrology of Storage Unit III and to develop an areawide model of the Santa Barbara and Foothill basins that includes the previously unmodeled Storage Unit III. Storage Unit III is in the southwestern part of the city of Santa Barbara. It is approximately 3.5 miles long and varies in width from about 2,000 feet in the southeast to 4,000 feet in the north-west. Storage Unit III is composed of the Santa Barbara Formation and overlying alluvium. The Santa Barbara Formation (the principal aquifer) consists of Pleistocene and Pliocene(?) unconsolidated marine sand, silt, and clay, and it has a maximum saturated thickness of about 160 feet. The alluvium that overlies the Santa Barbara Formation has a maximum saturated thickness of about 140 feet. The storage unit is bounded areally by faults and low-permeability deposits and is underlain by rocks of Tertiary age. The main sources of recharge to Storage Unit III are seepage from Arroyo Burro and infiltration of precipitation. Most of the recharge occurs in the northwest part of the storage unit, and ground water flows toward the southeast along the unit's long axis. Lesser amounts of recharge may occur as subsurface flow from the Hope Ranch subbasin and as upwelling from the underlying Tertiary rocks. Discharge from Storage Unit III occurs as pumpage, flow to underground drains, underflow through alluvium in the vicinity of Arroyo Burro across the Lavigia Fault, evapotranspiration, and underflow to the Pacific Ocean. The faults that bound Storage Unit III generally are considered to be effective barriers to the flow of ground water. Interbasin ground-water flow occurs where deposits of younger alluvium along stream channels cross faults. Ground-water quality in Storage Unit III deposits varies with location and depth. Upward leakage of poor-quality water from the underlying Tertiary rocks occurs in the storage unit, and such leakage can be influenced by poor well construction or by heavy localized pumping. The highest dissolved-solids concentration (4,710 milligrams per liter) in ground water resulting from this upward leakage is found in the coastal part of the storage unit. The ground-water system was modeled as two horizontal layers. In the Foothill basin and Storage Unit I the layers are separated by a confining bed. The upper layer represents the upper producing zone and the shallow zone near the coast. The lower layer represents the lower producing zone. In general, the faults in the study area were assumed to be no-flow boundaries, except for the offshore fault that forms the southeast boundary; the southeast boundary was simulated as a general-head boundary. The Storage Unit III model was combined with the preexisting Storage Unit I and Foothill basin models, using horizontal flow barriers, to form an areawide model. The areawide model was calibrated by simulating steady-state predevelopment conditions and transient conditions for 1978-92. The nonpumping steady- state simulation was used to verify that the calibrated model yielded physically reasonable results for predevelopment conditions. The calibrated areawide model calculates water levels in Storage Unit III that are within 10 feet of measured water levels at all sites of comparison. In addition, the model adequately simulates water levels in the Storage Unit I and Foothill basin areas. A total of 33,430 acre-feet of water was pumped from the study area during the simulation period. Model results indicate that 2,833 acre-feet came from storage and 5, 332 acre-feet crossed the general-head boundary from the ocean, thus indicating that seawater intrusion could occur. A sensitivity analysis indicates that, in general, the model is most sensitive to changes in transmissivity and total recharge.

California↗
USGS1998

A simulation-optimization model for water-resources management, Santa Barbara, California

In times of drought, the local water supplies of the city of Santa Barbara, California, are insufficient to satisfy water demand. In response, the city has built a seawater desalination plant and gained access to imported water in 1997. Of primary concern to the city is delivering water from the various sources at a minimum cost while satisfying water demand and controlling seawater intrusion that might result from the overpumping of ground water. A simulation-optimization model has been developed for the optimal management of Santa Barbara?s water resources. The objective is to minimize the cost of water supply while satisfying various physical and institutional constraints such as meeting water demand, maintaining minimum hydraulic heads at selected sites, and not exceeding water-delivery or pumping capacities. The model is formulated as a linear programming problem with monthly management periods and a total planning horizon of 5 years. The decision variables are water deliveries from surface water (Gibraltar Reservoir, Cachuma Reservoir, Cachuma Reservoir cumulative annual carryover, Mission Tunnel, State Water Project, and desalinated seawater) and ground water (13 production wells). The state variables are hydraulic heads. Basic assumptions for all simulations are that (1) the cost of water varies with source but is fixed over time, and (2) only existing or planned city wells are considered; that is, the construction of new wells is not allowed. The drought of 1947?51 is Santa Barbara?s worst drought on record, and simulated surface-water supplies for this period were used as a basis for testing optimal management of current water resources under drought conditions. Assumptions that were made for this base case include a head constraint equal to sea level at the coastal nodes; Cachuma Reservoir carryover of 3,000 acre-feet per year, with a maximum carryover of 8,277 acre-feet; a maximum annual demand of 15,000 acre-feet; and average monthly capacities for the Cachuma and the Gibraltar Reservoirs. The base-case results indicate that water demands can be met, with little water required from the most expensive water source (desalinated seawater), at a total cost of $5.56 million over the 5-year planning horizon. The simulation model has drains, which operate as nonlinear functions of heads and could affect the model solutions. However, numerical tests show that the drains have little effect on the optimal solution. Sensitivity analyses on the base case yield the following results: If allowable Cachuma Reservoir carryover is decreased by about 50 percent, then costs increase by about 14 percent; if the peak demand is decreased by 7 percent, then costs will decrease by about 14 percent; if the head constraints are loosened to -30 feet, then the costs decrease by about 18 percent; if the heads are constrained such that a zero hydraulic gradient condition occurs at the ocean boundary, then the optimization problem does not have a solution; if the capacity of the desalination plant is constrained to zero acre-feet, then the cost increases by about 2 percent; and if the carryover of State Water Project water is implemented, then the cost decreases by about 0.5 percent. Four additional monthly diversion distribution scenarios for the reservoirs were tested: average monthly Cachuma Reservoir deliveries with the actual (scenario 1) and proposed (scenario 2) monthly distributions of Gibraltar Reservoir water, and variable monthly Cachuma Reservoir deliveries with the actual (scenario 3) and proposed (scenario 4) monthly distributions of Gibraltar Reservoir water. Scenario 1 resulted in a total cost of about $7.55 million, scenario 2 resulted in a total cost of about $5.07 million, and scenarios 3 and 4 resulted in a total cost of about $4.53 million. Sensitivities of the scenarios 1 and 2 to desalination-plant capacity and State Water Project water carryover were tested. The scenario 1 sensitivity analysis indicated that incorpo

Water-Resources Investigations Report↗
USGS1998

Statistical analysis and mathematical modeling of a tracer test on the Santa Clara River, Ventura County, California

To better understand flow processes, solute-transport processes, and ground-water/surface-water interactions on the Santa Clara River in Ventura County, California, a 24-hour fluorescent-dye tracer study was performed under steady-state flow conditions on a 28-mile reach of the river. The study reach includes perennial (uppermost and lowermost) subreaches and ephemeral subreaches of the lower Piru Creek and the middle Santa Clara River. Dye was injected at a site on Piru Creek, and fluorescence of river water was measured continuously at four sites and intermittently at two sites. Discharge measurements were also made at the six sites. The time of travel of the dye, peak dye concentration, and time-variance of time-concentration curves were obtained at each site. The long tails of the time-concentration curves are indicative of sources/sinks within the river, such as riffles and pools, or transient bank storage. A statistical analysis of the data indicates that, in general, the transport characteristics follow Fickian theory. These data and previously collected discharge data were used to calibrate a one-dimensional flow model (DAFLOW) and a solute-transport model (BLTM). DAFLOW solves a simplified form of the diffusion-wave equation and uses empirical relations between flow rate and cross-sectional area, and flow rate and channel width. BLTM uses the velocity data from DAFLOW and solves the advection-dispersion transport equation, including first-order decay. The simulations of dye transport indicated that (1) ground-water recharge explains the loss of dye mass in the middle, ephemeral, subreaches, and (2) ground-water recharge does not explain the loss of dye mass in the uppermost and lowermost, perennial, subreaches. This loss of mass was simulated using a linear decay term. The loss of mass in the perennial subreaches may be caused by a combination of photodecay or adsorption/desorption.

Water-Resources Investigations Report↗