Uncertainties in Digital-Computer Modeling of Ground-Water Basins
AffiliationU.S. Geological Survey, Tucson, Arizona
Hydrology and Water Resources, University of Arizona
KeywordsWater resources development -- Arizona.
Hydrology -- Arizona.
Hydrology -- Southwestern states.
Water resources development -- Southwestern states.
MetadataShow full item record
RightsCopyright ©, where appropriate, is held by the author.
Collection InformationThis article is part of the Hydrology and Water Resources in Arizona and the Southwest collections. Digital access to this material is made possible by the Arizona-Nevada Academy of Science and the University of Arizona Libraries. For more information about items in this collection, contact email@example.com.
PublisherArizona-Nevada Academy of Science
AbstractMuch future computer modeling of the responses of groundwater to water development stresses may be poorly done if the errors and limitations of digital models are not fully appreciated by groundwater hydrologists. Two digital models were constructed of the Tucson basin, one with 1,890 nodes of 1/4 square mile area each and one with 509 nodes of 1 square mile each. The starting point for the digital model was the 2-dimensional, linear, parabolic, time-and space-invariant differential equation of incompressible flow through porous media. An explicit finite-difference equivalent was determined, and a set of 1,890 equations were put in implicit form and solved on a computer in less than 20 seconds at a cost of 2.00 dollars. The errors associated with the model are discussed. In deciding what new data collected in the Tucson basin would give the most improvement in the digital model, a statistical decision theory approach was utilized in which expected opportunity loss and expected worth of sample were calculated for 5 variables. The data was computed using about 110 seconds of computer time, costing about 13.00 dollars. This technique has the advantage of including basin dynamics in estimating worth of additional data by means of using the digital model to compute all values of predicted and 'true' water levels included in the loss function.
Showing items related by title, author, creator and subject.
A GEOCHEMICAL APPROACH TO DETERMINE GROUND-WATER FLOW PATTERNS IN THE SIERRA VISTA BASIN, ARIZONA, WITH SPECIAL EMPHASIS ON GROUND-WATER/SURFACE-WATER INTERACTIONMaddock, Thomas, III; Coes, Alissa L. (The University of Arizona., 1997)Water quality in the Sierra Vista Ground-Water Basin is of extreme importance due to the basin's unique ecosystem and predicted future population growth. Portions of the Upper San Pedro River, flowing through the Sierra Vista Basin, contain some of the few remaining perennial streamflows in the southwest. Baseflow in the perennial reaches of the river are maintained almost entirely by the regional and floodplain aquifer systems. A population increase is predicted for the Sierra Vista Basin, and an impact on groundwater quality and availability can be expected. Due to the closely linked hydrologic systems within the basin, contamination or depletion of the regional aquifer could have direct implications for the San Pedro River. Water samples were collected within the study area from the regional and floodplain aquifers, the San Pedro River, and a bedrock spring in the Huachuca Mountains. Samples were analyzed for field parameters, major-ions, and stable isotopes to describe the main chemical characteristics of the hydrologic systems within the basin. Analysis of regional aquifer geochemistry indicates a ground-water system strongly controlled by calcite precipitation. Specific conductance, deuterium and oxygen-18 values indicate a mixing of regional-aquifer ground water and San Pedro River surface water within the floodplain aquifer. Estimates of inflow to perennial reaches of the floodplain aquifer from the regional aquifer vary from 50 to 80%, depending on location. Inflow to the San Pedro River at Charleston from the regional aquifer is estimated to be about 50 to 70% of the stream discharge.
Water Service Organizations in Arizona: A Report to the Arizona Water Commission and the Central Arizona Water Conservation DistrictWater Resources Research Center, University of Arizona; DeCook, K. James; Emel, Jacque L.; Mack, Stephen F.; Bradley, Michael D.; Water Resources Research Center (Water Resources Research Center, University of Arizona (Tucson, AZ), 1978-08)
Quantifying Spatial Variability of Snow Water Equivalent, Snow Chemistry, and Snow Water Isotopes: Application to Snowpack Water BalanceGustafson, Joseph Rhodes; Brooks, Paul D. (The University of Arizona., 2008)This study quantifies spatial and temporal patterns in snow water equivalent (SWE), chemistry, and water isotopes associated with snowpack shading due to aspect and vegetation in the Valles Caldera National Preserve, New Mexico. Depth, density, stratigraphy, temperature, and snow chemistry, isotope, and biogeochemical nutrient samples were collected and analyzed from five snowpit locations on approximate monthly intervals between January-April 2007. SWE showed little variability between sites in January (~10mm) but differences expanded to 84mm (30%) by max accumulation in open sites and 153mm (45%) between all sites. Sulfate varied by 22% (10.6-13.5 microeq/L), Cl- by 35% (17.4-26.9 microeq/L), and d18O by 17% (-16.3 to -13.5), with SWE exhibiting inverse correlations with d18O (r2=0.96), SO42- (r2=0.75), and Cl- (r2=0.60) at max accumulation. Regression relationships suggest variability in SWE and solutes/water isotopes are primarily driven by sublimation. Mass balance techniques estimate sublimation ranges from 1-16% between topographically- and non-shaded open sites.