No description available.

The Tucson Basin is a semi-arid alluvial basin in southeastern Arizona in which the Santa Cruz River, an ephemeral stream, flows south to north with its flows resulting directly from rainfall. The City of Tucson discharges treated sewage effluent into the bed of the Santa Cruz and to some irrigated farms. Previous investigations indicate that sewage effluent is recharging the Tucson Basin Aquifer with the water spreading horizontally in the Fort Lowell Formation. The ¹⁸0/¹⁶0 ratios determined in water samples by the author support the findings of these previous investigations. Sewage effluent had an average δc0-18 value of -7.9 per mil and water samples from the north Santa Cruz wells had an average δc0-18 value of -9.3 per mil. Up hydraulic gradient, the ¹⁸0/¹⁶0 ratios are lighter indicating that sewage recharge water has mixed with ground water. In the case of one well in the mixed zone, it is calculated that approximately 70 percent of the water comes from sewage recharge and 30 percent from normal ground water. Recharge water spreads horizontally in the Fort Lowell Formation up to two miles on each side of the river. The δc0-18 values of water samples from the south Santa Cruz wells averaged -8.9 per mil and compared closely to the average δc0-18 values for summer flows in the Santa Cruz River of -8.2 per mil.

No description available.

Expansive soils contain clay minerals that undergo a change in bulk volume in response to variances in environmental conditions. The ability to predict the occurrence and geotechnical behavior of swelling soils with a known degree of certitude would allow engineers to take measures to limit the damage resulting from these metastable soils. Research was conducted to investigate the regional distribution, mineralogy, and engineering properties of expansive soils in the Tucson Basin. Mineralogic studies employed X-ray diffraction procedures for the identification of clay mineralogy. The compilation of expansion-related soil parameters, from the geotechnical job-files of a local engineering consulting firm, allowed the development of an engineering database. The application of geostatistical analysis for the cartographical representation of mineralogic and geotechnical data permitted a regional characterization of expansive clay soils. Clay mineralogy was found to be directly related to the volumetric stability displayed by native soils, as well as the geology of the Tucson Basin.

The concept of hydrochemical facies is used to study the distribution and, indirectly, to identify the origin of the chemical character of ground water in the basin-fill aquifer of the Tucson Basin in relationship to the hydrogeologic framework. Hydrochemical fades of ground water is defined operationally in terms of the lateral (horizontal) variation of chemical quality. The following chemical constituents are included in this study: total dissolved solids, calcium, magnesium, sodium, potassium, chloride, sulfate, bicarbonate, pH, nitrate, fluoride, strontium and zinc. A conceptual process-response model relates the regional distribution of dissolved constituents to the following hydrogeologic controls: (a) the chemical composition of the rock and soil in the drainage area before recharge to the ground-water basin and conditions at the recharge sites, (b) the lithology of the basin-fill aquifer, and (c) the direction of groundwater flow within the aquifer itself. Trend surface analysis suggests that the regional distribution patterns of total dissolved solids, calcium, sodium, sulfate and strontium show a tendency to parallel the direction of ground-water flow. The distribution pattern of chloride ions based on old analyses shows a trend opposite to the distribution pattern of chloride ions based on new analyses from the same area. Nitrate content of ground water and specific capacity of wells seem to be related. Q-factor analysis of data from the basin-fill aquifer demonstrates that the overall chemical character of the ground water does not change substantially as it moves through the basin. It is concluded that the chemical character of ground water in the basin-fill aquifer of the Tucson Basin was acquired mainly during contact with various rock types in the drainage basin before recharge. The lithology of the aquifer, presumably, only plays a secondary role in determining the overall chemical composition of the ground water. After recharge to the basin-fill aquifer the distribution of dissolved constituents is controlled primarily by the flow pattern. A chemical equilibrium model of calcite and water is used to approach the problem of determining whether precipitation or dissolution of calcite takes place in the aquifer. Measured calcium ion concentrations and pH values are compared to calcium ion concentrations and pH values computed for the equilibrium model. Assuming that the equilibrium model represents actual conditions in the aquifer, departures from the equilibrium model may be used to predict the chemical behaviour of calcite In the basin-fill aquifer.

Tucson, Arizona is often said to have a water problem. The water table is falling, giving rise to concern on the part of the public and conflicts between water users in the Basin. Many see the problem as a shortage of water to be solved by bringing more water to Tucson by means of the Central Arizona Project. This dissertation examines the occurrence and use of water in the region in order to determine the real nature of Tucson's water problem. First, the institutions governing the use of water in the Basin are described and the disputes between the local water users are discussed. Next, an account is given of the use of water by businesses and residences in Tucson, by the copper mines to the south of Tucson, and by the farms in the Basin. The effect of changes in the cost and availability of water on each of these classes of water user is investigated and the effect that changes in water use could have on the region's economy is discussed. Next, an account is given of the water available for use in the Basin. The occurrence of groundwater in the region is described and the merits of the proposed Central Arizona Project are investigated. The information on the use of water in the Basin and the information on the sources of water available for use in the Basin are then combined to forecast the depletions of groundwater that will take place under various circumstances. Various ways of balancing the region's water budget are described and an assessment is made of the effect that curtailing the use of water in the region would have upon the local water users and the region's economy. The principal conclusions of this study are as follows. First, there is no danger of the supply of water in the Basin becoming exhausted in the near future. The economic and physical effects of the continuing fall in the level of the water table are unlikely to be serious. The second main conclusion is that the region's water budget could be balanced very economically by retiring all agriculture in the region and making modest reductions in the amount of water consumed by urban water users and the copper mines. Given suitable institutional arrangements, curtailing the use of water in the Basin would be a much more economical way of balancing the region's water budget than building the Central Arizona Project. The final conclusion is that the real water problem is an institutional problem. The threat of the Indians' claims to the groundwater of the Tucson Basin, together with the difficulty of resolving the continual disputes between the mines, the farms, and the City of Tucson over water puts all of the local water-using interests in a position where they see the provision of more supplies of water as the only cure to their woes. The remedy to the region's water problem is not the provision of more supplies of water, but a settlement of the Indians' claims and a reform of Arizona's groundwater law to enable a resolution of the conflicts between the water users in the Tucson Basin.

The problem of evaluating the parameters of the mathematical model of an unconfined aquifer is examined with a view toward development of automated or computer -aided methods. A formulation is presented in which subjective confidence ranges for each of the model parameters are quantified and entered into an objective function as linear penalty functions. Parameters are then adjusted by a procedure which seeks to reduce the model error to acceptable limits. A digital computer model of the Tucson basin aquifer is adapted and used to illustrate the concepts and demonstrate the method.

A chemical-isotopic equilibrium model was developed for adjustment of radiocarbon ages of groundwater from the arid Tucson basin for dilution of the initial groundwater C-14 activity by the solution of soil calcite having a C-14 of 25 ± 19% modern. Input to the model consisted of the laboratory chemical analyses for Ca⁺⁺, Mg⁺⁺, Na⁺, H₄SiO₄, SO₄⁼, HCO₃⁻, CO₃⁼, NO₃⁻, and pH, and δ C-13 for the total dissolved carbon in the groundwater. Output consisted of the equilibrium chemical composition of the groundwater, the ratio of soil CO₂ derived to total dissolved carbon, Q, and δ C-13 of total dissolved carbon, H₂CO₃, HCO₃⁻, and CO₃⁼, and δ C-13 for the soil CO₂ and calcite that initially dissolved in the surface water as it equilibrated with soil minerals. Radiocarbon age of the groundwater is computed from the equation T = 8270 ln [(Q + (1-Q) A(CaCO₃)/Am] where T is the age in years before A.D. 1950, A(CaCO₃) is the soil calcite activity and Am is the measured activity for the dissolved carbonate in the groundwater, both with respect to modern wood. The validity of the model was tested by comparing the predicted values for δ C-13 (CO₂), δ C-13 (CaCO₃) with measured values for samples from the Tucson basin. δ C-13 (CO 2) calculated = (-12.9 ± 1.9) per mil PDB. δ C-13 (CO2) measured = (-15.1 ± 2.8) per mil PDB. δ C-13 (CaCO3) calculated = (-3.9 ± 1.7) per nil PDB. δ C-13 (CaCO3) measured = (-3.6 ± 1.7) per mil PDB. On the basis of these results, the model adequately describes the natural system and may prove useful in future radiocarbon dating work in desert regions.

Thesis (M.S. - Watershed Management)--University of Arizona. / Includes bibliographical references.

Two digital- computer models of the ground -water reservoir of the Tucson basin, in south - central Arizona, were constructed to study errors in digital models and to evaluate the worth of additional basic data to models. The two models differ primarily in degree of detail -- the large -scale model consists of 1,890 nodes, at a 1/2 -mile spacing; and the small -scale model consists of 509 nodes, at a l -mile spacing. Potential errors in the Tucson basin models were classified as errors associated with computation, errors associated with mathematical assumptions, and errors in basic data: the model parameters of coefficient of storage and transmissivity, initial water levels, and discharge and recharge. The study focused on evaluating the worth of additional basic data to the small -scale model. A basic form of statistical decision theory was used to compute expected error in predicted water levels and expected worth of sample data (expected reduction in error) over the whole model associated with uncertainty in a model variable at one given node. Discrete frequency distributions with largely subjectively- determined parameters were used to characterize tested variables. Ninety -one variables at sixty - one different locations in the model were tested, using six separate error criteria. Of the tested variables, 67 were chosen because their expected errors were likely to be large and, for the purpose of comparison, 24 were chosen because their expected errors were not likely to be particularly large. Of the uncertain variables, discharge /recharge and transmissivity have the largest expected errors (averaging 155 and 115 feet, respectively, per 509 nodes for the criterion of absolute value of error) and expected sample worths (averaging 29 and 14 feet, respectively, per 509 nodes). In contrast, initial water level and storage coefficient have lesser values. Of the more certain variables, transmissivity and initial water level generally have the largest expected errors (a maximum of 73 per feet per 509 nodes) and expected sample worths (a maximum of 12 feet per 509 nodes); whereas storage coefficient and discharge/ recharge have smaller values. These results likely are not typical of those from many ground -water basins, and may apply only to the Tucson basin. The largest expected errors are associated with nodes at which values of discharge /recharge are large or at which prior estimates of transmissivity are very uncertain. Large expected sample worths are associated with variables which have large expected errors or which could be sampled with relatively little uncertainty. Results are similar for all six of the error criteria used. Tests were made of the sensitivity of the method to such simplifications and assumptions as the type of distribution function assumed for a variable, the values of the estimated standard deviations of the distributions, and the number and spacing of the elements of each distribution. The results are sensitive to all of the assumptions and therefore likely are correct only in order of magnitude. However, the ranking of the types of variables in terms of magnitude of expected error and expected sample worth is not sensitive to the assumptions, and thus the general conclusions on relative effects of errors in different variables likely are valid. Limited studies of error propagation indicated that errors in predicted water levels associated with extreme erroneous values of a variable commonly are less than 4 feet per node at a distance of 1 mile from the tested node. This suggests that in many cases, prediction errors associated with errors in basic data are not a major problem in digital modeling.