Browsing Hydrology and Water Resources in Arizona and the Southwest, Volume 11 (1981) by Issue Date
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Hydrology and Water Resources in Arizona and the Southwest, Volume 11 (1981)Arizona-Nevada Academy of Science, 1981-05-02
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Aspects of Aquifer Test Error AnalysisErrors in the estimation of the aquifer parameters T and S derived from aquifer test data are examined as to their cause and effects. The analysis is based on the Theis equation. The basic causes of error are in the measurements of drawdown and pumping rate, in fitting the model to the data and in violations of model assumptions. Measurement errors were studied experimentally. Curve fittings by hydrologists were compared to "automatic" curve fittings obtained by nonlinear regression. The covariance matrix of T and S obtained in this manner was used, in conjunction with sensitivity analysis, to estimate the error in prediction of future drawdown. While automatic fitting is not a perfect substitute for graphical fitting, there is a definite relation between the two methods which allows the use of the statistics developed by nonlinear regression theory to be used to study the cause, effects and risks inherent in aquifer analysis.
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Estimations of Aquifer Characteristics Using Drillers' LogsIn an effort to utilize the lithologic information contained within the thousands of drillers' logs on file with the Arizona Department of Water Resources (DWR), a computer program was developed to analyze the logs for basic aquifer characteristics. These characteristics, estimations of specific yield, hydraulic conductivity and transmissivity, are calculated for each well log by comparing drillers' descriptions of alluvial sediments to standardized drillers' terms for which predetermined specific yield values have been assigned. These values approximate conditions in alluvial basins in Arizona. This information and identified hydrostratigraphic units are then coded for computer input. The computer program then calculates estimated aquifer characteristics for the total depth of the saturated sediments and hydrostratigraphic units. When a sufficient density of acceptable drillers' logs exist in the area being studied, the logs are used to approximate the extent and depth of the hydrostratigraphic units present. Thus the gross morphology of features, such as large clay bodies, which can have a significant effect on a hydrologic system, can be evaluated. This program has proven to be valuable by providing a preliminary overview of the geohydrologic systems of alluvial basins and for calculating initial estimates of aquifer characteristics for use in DWR computer modeling studies.
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A Study of Salinity in Effluent Lakes, Puerto Penasco, Sonora, MexicoAn investigation of salt build -up in two saline discharge lakes was conducted during 1979 in Puerto Peñasco, Mexico. Salt water was discharged to the smaller, deeper Lake I from a shrimp aquaculture prototype at an average rate of 70 liters per second. Water flowed to Lake II through a short channel, and exited the system through either evaporation or infiltration into the underlying sandy soil. In an attempt to differentiate between the evaporation and infiltration terms in the water budget, salt-budget equations have been derived for the two-lake system. These equations have been approximated in a series of monthly time steps, using averages of weekly salinity and water level measurements. Due to imprecision in the data, meaningful results have been obtained only for Lake II. The average calculated infiltration rate is 0.015 meters per day, and calculated evaporation rates show good correspondence with pan evaporation records for a station 2 kilometers away from the lakes. Examination of the salt budget equations shows that, under steady-state conditions, the ultimate salinity is finite. Thus, the maximum expected salinity of a lake may be calculated from worst-case (summertime) values of lake volume, inflow, evaporation, and salinity of incoming water.
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Correcting Tidal Responses in Observed Water Well Levels During Coastal Aquifer TestsA modified tidal efficiency algorithm, ESTA, was developed to correct observed water well levels in tidally responsive coastal areas to get best estimates of aquifer properties and well production characteristics. The algorithm was developed during groundwater studies in Puerto Peñasco, northeastern Gulf of California, Sonora, Mexico. ESTA predicts standing water well levels in response to tides. ESTA requires initial sea and well calibration data, from which sea-well relationships are calculated. It needs tidal data for the time period when projected standing water well levels are desired. The method uses a single cosine or sine function for rising or falling tides, respectively. ESTA tended to overpredict water levels, especially on rising tides, on the average of about 0.05 ft, as shown in analyses at five coastal well sites completed in low to moderately permeable sand and coquina. ESTA can be improved by application of error analysis, but this will not be necessary in most cases, as errors are generally very small for most aquifers and tidal ranges. When ESTA was applied to an aquifer test in highly permeable coral near Kahuku, northehore Oahu, Hawaii, rising -tide water well levels were overpredicted and falling -tide water well levels were underpredicted by 0.10 and 0.33 ft, respectively. Error analysis reduced these errors to 0.06 and 0.16 ft.
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The Alternatives and Impacts Associated with a Future Water Source Transition for Tucson WaterAnticipating a surge in the future growth of the Tucson urban area accompanied by a need for the preservation of the local groundwater resource, Tucson Water is planning for a major transition in its source of supply during the next fifty years. The completion of the Central Arizona Project to the Tucson area represents the primary ingredient to the formulation of a future water supply plan for the community. Tucson, which presently relies totally upon groundwater for its potable water supply, is diligently preparing to accept its first surface water source. The task of planning for this event is extremely complex and is further hampered by the fact that many critical factors relating to the Tucson Division of the Central Arizona Project are yet undefined. Tucson Water engineers utilize contemporary computerized hydraulic models as tools to define an array of technical solutions to the problem of accomplishing a major conversion from a multi-point system source to a predominantly single source of supply. Elements such as construction, operation, and maintenance costs associated with water treatment and delivery systems are addressed.
