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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.
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The Edwards aquifer is the principal source of water supply for the San Antonio area. Increasing urban development on or adjacent to the recharge area of the aquifer is causing great concern because of possible pollution of the ground water. A detailed map of the surface geology has been prepared for areas where the greatest threat of pollution exists. Water-quality data are being collected throughout the San Antonio area to provide background reference information and to detect any current pollution of the ground water in the Edwards and associated limestones. Mapping of the surface geology will continue in areas where waste waters may be recharging the aquifer. Water-quality data will be collected at additional sites, and some sites will be resampled where pollution may be occurring or where more background data are needed.
Digital computer processing of 12 wavelength bands of visible and reflective infrared scanner data has resulted in successful automatic computer mapping of eight terrain units in a Yellowstone National Park test site. Target areas in the scene were selected for training the computer. Statistical parameters of radiance such as mean, standard deviation, divergence, and covariance were computed for each category of material. These data were used in the computer program to determine which channels are most useful for recognition of all object categories studied, and to actually classify all the unknown data points into the known categories. The following terrain types have been mapped with greater than 80 percent accuracy in a 12-square-mile area with 1,800 feet of relief: bedrock exposures, talus, vegetated rock rubble, glacial kame terrace, glacial till, forest, bog, and water, and shadows. In addition, shadows of clouds and cliffs are depicted. In addition, studies were made of the effectiveness of the proposed Earth Resources Technology Satellite (ERTS) data channels as compared to the computer-selected best four channels in the automatic recognition and mapping of the same terrain types based on simulations, using the same set of data. These simulations resulted in maps whose accuracies were only a few percent less than that using the best set of four channels; they indicate that the ERTS data channels are likely to be successful for terrain analysis of a wide variety of categories encompassing a broad range of spectral reflectance. These studies also indicate that, for a broad range of terrain categories, many' combinations of 3 or 11 channels of data would be satisfactory. We need worry about careful selection of specific wavelength bands only if there is a specific category being sought.
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The magnitude and frequency of floods is defined regionally for streams in New Mexico. An analysis was made, using multiple- regression techniques, relating flood peaks of 2, 5, 10, 25, and 50-year recurrence intervals to selected physical and climatic basin characteristics. The state was divided into three flood regions, and the resulting equations and associated standard error of prediction are presented for each of these regions. In addition the maximum observed discharges at regular and crest-stage gaging stations, and all peak discharges by indirect measurements at miscellaneous sites are presented in tabular and graphical form. The equations developed in the study can be used to compute peak discharges of floods of given recurrence intervals for use in the design of drainage structures.