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Articles 121 - 128 of 128
Full-Text Articles in Water Resource Management
Sadc Challenges Country Water Partnerships To Make Impact, Stanley Mubako
Sadc Challenges Country Water Partnerships To Make Impact, Stanley Mubako
Stanley Mubako
No abstract provided.
New Isotopic Evidence For Chronic Lead Contamination In The San Francisco Bay Estuary System: Implications For The Persistence Of Past Industrial Lead Emissions In The Biosphere, Douglas J. Steding, Charles E. Dunlap, A. Russell Flegal
New Isotopic Evidence For Chronic Lead Contamination In The San Francisco Bay Estuary System: Implications For The Persistence Of Past Industrial Lead Emissions In The Biosphere, Douglas J. Steding, Charles E. Dunlap, A. Russell Flegal
Charles Dunlap
Measurements of lead isotope compositions in unfiltered San Francisco Bay waters from 1989 to 1998 have brought new insights into the cycling of anthropogenic lead in estuaries. Isotopic com- positions of lead in the shallow (<2 m) southern reach were essentially invariant (~90% derived from 1960s–1970s leaded gasoline) during the study period because of limited hydraulic flushing and the remobilization of lead from bottom sediments. In contrast, in the northern reach freshwater flushing from the San Joaquin and Sacramento rivers produced seasonal and decadal variations in lead isotope compositions. The seasonal shifts are attributed to advection of soils containing late 1980s gasoline lead into the bay during winter rains. Mass balance calculations indicate that only a small fraction (1–10%) of this leaded gasoline fallout from the late 1980s has been washed out of the San Joaquin and Sacramento rivers’ drainage basin by 1995. Superimposed on this seasonal cycling was a long-term systematic shift in the component of gasoline lead expressed in the river systems, with a small (~5–10%) decrease in the amount of 1960s–1970s gasoline lead in river and North Bay waters. The retention of gasoline lead in the river systems draining into the bay as well as San Francisco Bay sediments indicates that historic gasoline deposits may remain in the combined riparian/estuarine system for decades. Such a persistence is in contraindication to recent reports of rapid (annual) decreases in lead contamination in other environments, and the link between climate and contaminant transport suggests local or global climate change will have an impact on contaminant distribution and fate.
Past Leaded Gasoline Emissions As A Nonpoint Source Tracer In Riparian Systems: A Study Of River Inputs To San Francisco Bay, Charles E. Dunlap, Robin Bouse, A. Russell Flegal
Past Leaded Gasoline Emissions As A Nonpoint Source Tracer In Riparian Systems: A Study Of River Inputs To San Francisco Bay, Charles E. Dunlap, Robin Bouse, A. Russell Flegal
Charles Dunlap
Variations in the isotopic composition of lead in 1995- 1998 river waters flowing into San Francisco Bay trace the washout of lead deposited in the drainage basin from leaded gasoline combustion. At the confluence of the Sacramento and San Joaquin rivers where they enter the Bay, the isotopic compositions of lead in the waters define a linear trend away from the measured historical compositions of leaded gas in California. The river waters are shifted away from leaded gasoline values and toward an isotopic composition similar to Sierra Nevadan inputs which became the predominant source of sedimentation in San Francisco Bay …
Regional Hydrology Of The Dixie Valley Geothermal Field, Nevada: Preliminary Interpretations Of Chemical And Isotopic Data, Gregory Nimz, Cathy Janik, Fraser Goff, Charles Dunlap, Mark Huebner, Dale Counce, Stuart Johnson
Regional Hydrology Of The Dixie Valley Geothermal Field, Nevada: Preliminary Interpretations Of Chemical And Isotopic Data, Gregory Nimz, Cathy Janik, Fraser Goff, Charles Dunlap, Mark Huebner, Dale Counce, Stuart Johnson
Charles Dunlap
Chemical and isotopic analyses of Dixie Valley regional waters indicate several distinct groups ranging in recharge age from Pleistocene (<20 ka) to recent (<50a). Valley groundwater is older than water from perennial springs and artesian wells in adjacent ranges, with Clan Alpine range (east) much younger (most <50a) than Stillwater range (west; most > 1OOOa).Geothermal field fluids (-12-14 ka) appear derived from water similar in composition to non-thermal groundwater observed today in valley artesian wells (also -14 ka). Geothermal fluid interaction with mafic rocks (Humboldt Lopolith) appears to be common, and significant reaction with granodiorite may also occur. Despite widespread occurrence of carbonate rocks, largescale chemical interaction appears minor. Age asymmetry of the ranges, more extensive interaction with deep- seated waters in the west, and distribution of springs and artesian wells suggest the existence …
Green And Ampt Infiltration With Redistribution, Fred L. Ogden
Green And Ampt Infiltration With Redistribution, Fred L. Ogden
Fred L. Ogden
Distributed, physically based watershed and irrigation advance models require robust infiltration estimation capabilities. The empirical Green and Ampt (GA) equation of infiltration is a popular method for estimating infiltration. The GA parameters have physical basis and considerable prior research has focused on relating these parameters to soil textural classification. However, the original GA method is limited in that it is applicable only for a single ponding period. An explicit Green and Ampt redistribution (GAR) technique is developed herein to estimate interstorm redistribution of soil water and allow multiple ponding simulations using the GA methodology. Soil water redistribution during interponding periods …
Strength Of Bentonite Water-Well Annulus Seals In Confined Aquifers, Fred Ogden
Strength Of Bentonite Water-Well Annulus Seals In Confined Aquifers, Fred Ogden
Fred L. Ogden
The advantages of bentonite clay for sealing applications are well known. Bentonites have extremely low permeability, do not affect formation water chemistry, and have the ability to swell and deform in response to subsurface changes. The major limitation on the applicability of bentonite for water well annulus sealing is strength. Strength tests conducted in a physical model of a water well identified the expected magnitude of shear strength for several commercially available bentonite well-sealing products. The dependence of bentonite strength in the annulus of a water well on both setting time and borehole geometry is discussed. Force balance calculations for …
Setting Time Effects On Bentonite Water-Well Annulus Seals, Fred L. Ogden
Setting Time Effects On Bentonite Water-Well Annulus Seals, Fred L. Ogden
Fred L. Ogden
Shear strength tests are conducted in a model of a water well on four, commercially available, granular bentonite well sealing products. The time dependency of annulus seal shear strength and resistance to piping is examined. Dry bentonite samples are placed through water in the annular space between the casing and borehole and allowed to set for a specified time. Pressure is applied at a constant rate to one end of the clay seal until shear or piping failure occurs. Pressure and seal displacement data are recorded on a digital data acquisition system. Annulus seal strength and resistance to piping increase …
Removal Of Phosphorus From Static Sewage Effluent By Waterhyacinth, W Harold Ornes
Removal Of Phosphorus From Static Sewage Effluent By Waterhyacinth, W Harold Ornes
W. Harold Ornes
Waterhyacinth [Eichhornia crassipes (Mart.) Solms] was grown in static sewage effluent during May to July 1974 in outdoor concrete containers with a capacity of 760 liters and a surface area of 1.66 m². The plants were removed weekly from one-half of the surface area of the containers during 5-wk growth periods. Tissue phosphorus (P) and nitrogen (N), plant productivity, and some parameters of water quality were measured. A maximum uptake of 5,500 µg of P/g dry weight of plant material occurred when the level of orthophosphate phosphorus (available P) in the effluent was 1.1 µg/ml. Phosphorus in the effluent was …