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At least 1,765 records · Page 98Linked to original sources
USGS1982

Water resources of southeastern Oahu, Hawaii

Southeastern Oahu comprises the eastern end of the Koolau Range and is divided into two roughly equal parts by the crest of the range. The northside of the crest is commonly called the windward side and the southside, the leeward. Precipitous cliffs aproned by a gently sloping landscape are the main topographic features on the windward side. The leeward side is a gentle lava-flow slope incised by steep narrow valleys. The main Koolau fissure zone, including the caldera, lies on the windward side. The leeward side includes minor rift zones that are perpendicular to and intersect the main fissure zone. Dikes in the main fissure zone strike from nearly east-west in the eastern end to about N. 55? W. in the western part. Dikes in the minor rift zones strike from north-south to slightly northeasterly. Water use is about 18 Mgal/d (million gallons per day) of which only 4 Mgal/d is obtained locally from ground-water sources. About a third of the 14 Mgal/d deficit is imported from sources northwest of the study area on the windward side and the remainder from sources in the Honolulu and Pearl Harbor areas on the leeward side. The 4 Mgal/d being developed represents only about 3 percent of the area's rainfall compared to a development-rainfall ratio of 20 percent for the rest of the island. Streams are short and flashy. Perennial streamflow to the sea occurs only in Maunawili Valley and in the Waimanalo area. Mean annual discharge is estimated at 20 Mgal/d in the windward side and at 15 Mgal/d on the leeward side. Low flow, expressed as the flow that is equaled or exceeded 90 percent of the time, is 5 Mgal/d windward of the crest and zero leeward of it. Most fresh ground water occurs in lava flows of the Koolau Volcanics. It is impounded by dikes in the rift zones and floats on saline ground water as lenses outside the rift zones. Small but important bodies of freshwater are perched in volcanic rocks of the Honolulu Group in Maunawili Valley. Fresh ground water occurs in near-shore calcareous sands that overlie a clay horizon in the Waimanalo area. Deeply buried talus and alluvium also carry fresh ground water in the Waimanalo area. Wells tapping saline ground water in fresh lava flows of the Honolulu Group provide water for a sea-life park in the Makapuu area. The same aquifer is tapped by wells for disposal of the saline waste water. The current development scheme in the windward side that utilizes only the free-flow equilibrium discharge of dike-impounded water is inefficient and does not cope with the annual weather cycle. The flow available for development under this scheme is greatest in the rainy winter months when demand is the lowest and least in the summer months when demand is the highest. A more optimal scheme would be to change this natural flow pattern by depleting storage by pumping to increase flow in the high-demand summer months and allowing the depleted storage to recover naturally in the low-demand winter months. Depleting storage would lower water levels which would provide more room for infiltration and provide less opportunity for evapotranspiration. The basal-water reservoir in the leeward side is isolated hydrologically from abutting reservoirs outside the area and can and should be fully exploited. The existing development of the basal-water reservoir is small compared to the natural ground-water flow and that part not being developed is wasting to the sea. Because the area is hydrologically isolated, development will not be detrimental to or reduce the ground-water supply outside the area.

Open-File Report↗
USGS1984

Water-quality data for the Potomac-Raritan-Magothy aquifer system in southwestern New Jersey, 1923-83

Water-quality data for wells in and near the outcrop area of the Potomac-Raritan-Magothy aquifer system in Mercer, Burlington, Camden, Gloucester, and Salem Counties, New Jersey, have been compiled for the period 1923-83. The data were collected during various U.S. Geological Survey projects, including county-wide ground-water studies, the New Jersey saltwater-intrusion monitoring network, and regional ground-water assessments.

New Jersey↗
USGS2004

Documentation of the Santa Clara Valley regional ground-water/surface-water flow model, Santa Clara Valley, California

The Santa Clara Valley is a long, narrow trough extending about 35 miles southeast from the southern end of San Francisco Bay where the regional alluvial-aquifer system has been a major source of water. Intensive agricultural and urban development throughout the 20th century and related ground-water development resulted in ground-water-level declines of more than 200 feet and land subsidence of as much as 12.7 feet between the early 1900s and the mid-1960s. Since the 1960s, Santa Clara Valley Water District has imported surface water to meet growing demands and reduce dependence on ground-water supplies. This importation of water has resulted in a sustained recovery of the ground-water flow system. To help support effective management of the ground-water resources, a regional ground-water/surface-water flow model was developed. This model simulates the flow of ground water and surface water, changes in ground-water storage, and related effects such as land subsidence. A numerical ground-water/surface-water flow model of the Santa Clara Valley subbasin of the Santa Clara Valley was developed as part of a cooperative investigation with the Santa Clara Valley Water District. The model better defines the geohydrologic framework of the regional flow system and better delineates the supply and demand components that affect the inflows to and outflows from the regional ground-water flow system. Development of the model includes revisions to the previous ground-water flow model that upgraded the temporal and spatial discretization, added source-specific inflows and outflows, simulated additional flow features such as land subsidence and multi-aquifer wellbore flow, and extended the period of simulation through September 1999. The transient-state model was calibrated to historical surface-water and ground-water data for the period 1970–99 and to historical subsidence for the period 1983–99. The regional ground-water flow system consists of multiple aquifers that are grouped into upper- and lower-aquifer systems. Ground-water inflow occurs as natural recharge in the form of streamflow infiltration and areal infiltration of precipitation along stream channels, artificial recharge from infiltration of imported water at recharge ponds and along selected stream channels, and leakage along selected transmission pipelines. Ground-water outflow occurs as evapotranspiration, stream base flow, discharge through pumpage from wells, and subsurface flow to the San Francisco Bay. The geohydrologic framework of the regional ground-water flow system was represented as six model layers. The hydraulic properties were redefined on the basis of cell-based lithologic properties that were delineated in terms of aggregate thicknesses of coarse-grained, fine-grained, and mixed textural categories. The regional aquifer systems also are dissected by several laterally extensive faults that may form at least partial barriers to the lateral flow of ground water. The spatial extent of the ground-water flow model was extended and refined to cover the entire Santa Clara Valley, including the Evergreen subregion. The temporal discretization was refined and the period of simulation was extended to 1970–99. The model was upgraded to MODFLOW-2000 (MF2K) and was calibrated to fit historical ground-water levels, streamflow, and land subsidence for the period 1970–99. The revised model slightly overestimates measured water levels with an root-mean-square error of -7.34 feet. The streamflow generally shows a good match on gaged creeks and rivers for flows greater than 1.2 cubic feet per second. The revised model also fits the measured deformation at the borehole extensometer site located near San Jose within 16 to 27 percent and the extensometer site near Sunnyvale within 3 percent of the maximum measured seasonal deformation for the deepest extensometers. The total ground-water inflow and outflow of about 225,500 acre-feet per year (acre-ft/yr) for the period 1970–89 and of about 205,300 acre-feet per year for the period for the period 1970–99 is comparable with that of the previous model, 207,200 acre-ft/yr for the period 1970–89. Overall the simulated net change in storage increased by about 189,500 acre-ft/yr for the entire period of simulation, which represents about one and a half years of the 1970–99 average pumping. The changes in ground-water flow and storage generally reflect the major climate cycles and the additional importation of water by Santa Clara Valley Water District, with the basin in recovery since the drought of the late 1980s and early 1990s. The average total recharge rate, from natural and artificial recharge and from streamflow infiltration for the revised model for the entire simulation period 1970–99, was about 157,100 acre-ft/yr, which represents about 59 percent of the inflow to the ground-water flow system. The average rate of artificial recharge of about 77,600 acre-ft/yr represents about 30 percent of the inflow to the ground-water flow system. The average pumpage for the entire 29.75-year simulation period is about 133,400 acre-ft/yr and represents about 69 percent of the outflow from the ground-water flow system. Most of the simulated recharge infiltrates and flows through the uppermost layers (i.e. model layers 1 and 3) of the aquifer system. Most of the water that flows to the deeper model layers is occurring through wellbores, with wellbore flow representing 19 percent of the total ground-water inflow between model layers.

California↗
USGS2005

Simulated water-level responses, ground-water fluxes, and storage changes for recharge scenarios along Rillito Creek, Tucson, Arizona

A local ground-water flow model is used to simulate four recharge scenarios along Rillito Creek in northern Tucson to evaluate mitigating effects on ground-water deficits and water-level declines in Tucson's Central Well Field. The local model, which derives boundary conditions from a basin-scale model, spans the 12-mile reach of Rillito Creek and extends 9 miles south into the Central Well Field. Recharge scenarios along Rillito Creek range from 5,000 to 60,000 acre-feet per year and are simulated to begin in 2005 and extend through 2225 to estimate long-term changes in ground-water level, ground-water storage, ground-water flux, and evapotranspiration. The base case for comparison of simulated water levels and flows, referred to as scenario A, uses a long-term recharge rate of 5,000 acre-feet per year to 2225. Scenario B, which increases the recharge along Rillito Creek by 9,500 acre-feet per year, has simulated water-level rises beneath Rillito Creek that range from about 53 feet to 86 feet. Water-level rises within the Central Well Field range from about 60 feet to 80 feet. More than half of these rises occur by 2050, and more than 95 percent occur by 2188. Scenario C, which increases the recharge along Rillito Creek by 16,700 acre-feet per year relative to scenario A, has simulated water-level rises beneath Rillito Creek that range from about 71 feet to 102 feet. Water-level rises within the Central Well Field range from about 80 feet to 95 feet. More than half of the rises occur by 2036, and more than 95 percent occur by 2100. Scenario D, which initially increases the recharge rate by about 55,000 acre-feet per year relative to scenario A, resulted in simulated water levels that rise to land surface along Rillito Creek. This rise in water level resulted in rejected recharge. As the water table continued to rise, the area of stream-channel surface intersected by the water table increased causing continual decline in the recharge rate until a long-term recharge rate of about 34,000 acre-feet per year was sustained. The long-term recharge rate for scenario D is about 29,000 acre-feet per year greater than the long-term recharge rate for scenario A. Simulated long-term water-level rises beneath Rillito Creek range from about 97 feet to 131 feet, resulting in water levels near or at the land surface. Shallow depths to water associated with this scenario have implications for contamination owing to the presence of landfills within or adjacent to Rillito Creek. Water-level rises for cells within the Central Well Field range from about 96 feet to 109 feet. More than half of the water-level rises occur by 2018 and more than 95 percent occur by 2041. Almost all the increased water added to the ground-water system in the recharge scenarios can be accounted for by a combination of increased storage near Rillito Creek, ground-water flux to the south, ground-water flux to the northwest, and increased discharge as evapotranspiration along Rillito Creek. The percentage of newly added water accounted for by storage changes is large relative to the percentage accounted for by changes in flux and evapotranspiration at the onset of each scenario; however, the changes in storage become smaller throughout the simulation, and the long-term component accounted for by storage is minimal. Long-term ground-water fluxes to the south increase by about 3,300, 4,840, and 7,500 acre-feet per year for scenarios B, C, and D, respectively. The percentage of increased recharge that flows south toward the Central Well Field, therefore, is 35, 29, and 26 percent for scenarios B, C, and D, respectively. Long-term ground-water fluxes to the northwest increase by about 3,100, 3,900, and 6,980 acre-feet per year for scenarios B, C, and D, respectively. The long-term percentage of increased recharge flowing northwestward is about 31, 25, and 21 percent for scenarios B, C, and D, respectively. Shallow ground-water evapotranspiration along Rillito Creek incr

Scientific Investigations Report↗
USGS2010

Interpretation of Flow Logs from Nevada Test Site Boreholes to Estimate Hydraulic Conductivity Using Numerical Simulations Constrained by Single-Well Aquifer Tests

Hydraulic conductivities of volcanic and carbonate lithologic units at the Nevada Test Site were estimated from flow logs and aquifer-test data. Borehole flow and drawdown were integrated and interpreted using a radial, axisymmetric flow model, AnalyzeHOLE. This integrated approach is used because complex well completions and heterogeneous aquifers and confining units produce vertical flow in the annular space and aquifers adjacent to the wellbore. AnalyzeHOLE simulates vertical flow, in addition to horizontal flow, which accounts for converging flow toward screen ends and diverging flow toward transmissive intervals. Simulated aquifers and confining units uniformly are subdivided by depth into intervals in which the hydraulic conductivity is estimated with the Parameter ESTimation (PEST) software. Between 50 and 150 hydraulic-conductivity parameters were estimated by minimizing weighted differences between simulated and measured flow and drawdown. Transmissivity estimates from single-well or multiple-well aquifer tests were used to constrain estimates of hydraulic conductivity. The distribution of hydraulic conductivity within each lithology had a minimum variance because estimates were constrained with Tikhonov regularization. AnalyzeHOLE simulated hydraulic-conductivity estimates for lithologic units across screened and cased intervals are as much as 100 times less than those estimated using proportional flow-log analyses applied across screened intervals only. Smaller estimates of hydraulic conductivity for individual lithologic units are simulated because sections of the unit behind cased intervals of the wellbore are not assumed to be impermeable, and therefore, can contribute flow to the wellbore. Simulated hydraulic-conductivity estimates vary by more than three orders of magnitude across a lithologic unit, indicating a high degree of heterogeneity in volcanic and carbonate-rock units. The higher water transmitting potential of carbonate-rock units relative to volcanic-rock units is exemplified by the large difference in their estimated maximum hydraulic conductivity; 4,000 and 400 feet per day, respectively. Simulated minimum estimates of hydraulic conductivity are inexact and represent the lower detection limit of the method. Minimum thicknesses of lithologic intervals also were defined for comparing AnalyzeHOLE results to hydraulic properties in regional ground-water flow models.

Scientific Investigations Report↗
USGS1951

Geology and ground-water resources of the northern part of the Ranegras Plain area, Yuma County, Arizona

The Ranegras Plain area is part of the Basin and Range province in west-central Arizona. The report discusses rocks of pre-Cambrian, pre-Cambrian (?), Paleozoic (?), Mesozoic (?), Cretaceous (?), Cretaceous and Tertiary, Tertiary (?), Quaternary (?), and Quaternary age. All the Paleozoic (?) and Cretaceous (?) rocks and parts of the Mesozoic (?),Cretaceous and Tertiary, and Tertiary (?) rocks have been mapped as a unit because they are so intensely faulted that detailed mapping was not practical. Rocks older than Quaternary form the mountain ranges bordering the Ranegras Plain. Quaternary alluvium underlies the broad, gently sloping valley floor to depths of generally a few hundred feet, locally more. Well logs indicate that the underlying Tertiary (?) alluvium exceeds 1,100 feet in thickness. The structure of the area is controlled by faulting typical of the Basin and Range province, but the major faults are covered by alluvium and are inferred from topographic features. Ground water occurs in Quaternary and Tertiary (?) alluvium and the best aquifers are in sand and gravel of the Quaternary alluvium. Ground-water movement is, in general, to the northwest. Recharge to the aquifers is predominantly from stream flow resulting from heavy rains. There is also minor or unevaluated recharge from underflow from Butler Valley to the east, andsince 1948seepage from irrigation. Discharge is by pumping and by natural processes of underflow and evapotranspiration. In addition to small domestic and stock wells, only two irrigation wells, in the vicinity of Utting, are in use. No accurate data on pumpage are available. The safe yield from the ground-water reservoir may be less than 5,000 acre-feet and probably does not exceed 10,000 to 15,000 acre-feet per year. The quality of ground water ranges from permissible to unsuitable for irrigation purposes. The fluoride content is generally too high for the water to be considered satisfactory for use by young children.

Open-File Report↗