Introduction The development and application of ground-water models has been an important component of USGS hydrologic investigations since the early 1970s. During the past 35 years, the USGS has developed a wide range of computer models to simulate saturated and unsaturated subsurface flow, solute transport, and chemical reactions. The most widely used of these programs is the MODFLOW model, w...

background and purpose: fluoride is one of the drinking water contaminants regulated by epa. this ion, in low doses in the mouth reduces tooth decay without health risk and at much higher doses causes health complications and can be toxic. the major sources of exposure to fluoride are drinking water, food, dental products, and pesticides. the biggest contributor to exposure for most people in i...

A long-term study of four degraded streams in the upper Owens River watershed documented the recovery of riparian habitats and significant improvement in channel morphology in response to grazing strategies, recreation management, and pre-irrigation peak flows. Increased control of livestock distribution, timing of forage use and degree of forage utilization on and near stream banks was designe...

A baseflow survey of 41 tributary creeks investigated the tiansport of alrazine, nilrate-nitrom chloride and sulfate in two 5,000 ha Jasper County, Iowa watersbeds. The waterskds comprise a long-tam paired shldy to evaluate the effects of largesale conversion of row nop to prairie in Walnut creek watershed compared to highly agricultural Squaw creek watershed. Discharge and chemical concentrati...

Stable water isotopologues, mainly H 2 O, HHO (HDO), and H2 18O, are useful tracers for processes in the global hydrological cycle.The incorporation of water isotopes into Atmospheric General CirculationModels (AGCMs) since 1984 has helped scientists gain substantial new insights into our present and past climate. In recent years, there have been several significant advances in water isotopes m...

Soil erosion is a widespread problem causing the deterioration of both land and water resources. The water quality and quantity “Q and Q” connection is vital for sustainable water resources development and management. The prime objective of the research work is to quantify suspended sediment concentrations in surface waters by means of ALOS and ASTER satellite data. In this research work multis...

■ Abstract We review selected geological processes to which numerical modeling has been applied, with the aim of describing some of the general approaches and applications of the modeling. All of these examples involve multiphase fluid flow, in some cases coupled with heat transport and phase changes. First, we describe modeling approaches to a human-made geological system—a potential undergrou...