Showing papers by "Marios Sophocleous published in 1987"

Seismic Reflection Study of a Shallow Aquifer During a Pumping Test

Abstract: Seismic reflection surveys were used to follow the drawdown in a shallow aquifer during a pumping test. Using severe analog low-cut filters and 1/4-m geophone spacings, 335 Hz reflections were obtained from the top of the saturated zone 2.7 m deep. The reflections moved down in time as the saturated zone dropped in response to pumping. The dominant frequency and bandwidth both dropped during pumping indicating a more diffuse reflecting boundary. Slight pullups of reflectors at specific locations on the CDP sections may indicate a higher elevation of the capillary fringe and therefore finer sediments in those locations. Other potential applications of this technique include mapping cones of depression and detecting and delineating perched-water tables.

Basinwide water-balance modeling with emphasis on spatial distribution of ground water recharge

Abstract: A detailed but simple hydrologic budget for the entire Rattlesnake Creek basin (3,768 km2) in south-central Kansas was developed. With this budget, using minimal daily-weather input data and the soil-plant-water system-analysis methodology, we were able to characterize the spatial distribution of the hydrologic components of the water balance within the basin. A combination of classification and meteorological methods resulted in a basinwide integration methodology. Using this methodology, we found that, in addition to obvious climatic controls, soil, vegetation, and land-use factors also exert considerable influence on the water balance of the area. The available-water capacity (AWC) of soil profiles plays a dominant role in soil-water-deficit development and deep drainage. Vegetation and dryland or irrigated farming particularly affect the evapotranspiration (ET) components, with ET from irrigated corn and alfalfa being two to three times that from wheat. Deep drainage from irrigated wheat fields was found to be significantly higher than that from grassland and dryland wheat; deep drainage from alfalfa is practically nonexistent. We demonstrated how vegetation changes may affect components of the hydrologic cycle. We also showed that different portions of the watershed have different water-balance components and that use of single average values of hydrologic variables in management practices may not be realistic.

Measuring and computing natural ground-water recharge at sites in south-central Kansas

Abstract: To measure the natural ground-water-recharge process, two sites in south-central Kansas were instrumented with sensors and data microloggers. The atmospheric-boundary layer and the unsaturated and saturated soil zones were monitored as a single regime. Data from the various sensors were collected using microloggers in combination with magnetic cassette tapes, graphical and digital recorders, and analog paper-tape recorders in order to automate data collection and processing. Direct observations also were used to evaluate the measurements. Atmospheric sensors included an anemometer, a tipping-bucket rain gage, an air-temperature thermistor, a relative-humidity probe, a net radiometer, and a barometric-pressure transducer. Sensors in the unsaturated zone consisted of soil-temperature thermocouples, tensiometers coupled with pressure transducers and dial gages, gypsum blocks, and a neutron-moisture probe. The saturated-zone sensors consisted of a water-level pressure transducer, a conventional float gage connected to a variable potentiometer, soil thermocouples, and a number of multiple-depth piezometers. Evaluation of the operation of these sensors and recorders indicates that certain types of equipment, such as pressure transducers, are very sensitive to environmental conditions. Extraordinary steps had to be taken to protect some of the equipment, whereas other equipment seemed to be reliable under all conditions. Based on such experiences, a number of suggestions aimed at improving instrumentation of recharge investigations are outlined. The amounts and timing of ground-water recharge from precipitation over an approximately 19-month period were investigated at two instrumented sites in south-central Kansas. Precipitation and evapotranspiration data, taken together with soil-moisture profiles and storage changes, water fluxes in the unsaturated zone and hydraulic gradients in the saturated zone at various depths, soil temperature water-level changes in nearby wells, d Antecedent moisture conditions and unsaturated zone were found to be the Although the two instrumented sites are 1 cated in sand-dune environments table and n subhumid continental rved in the estimated total rethan 2.5 millimeters at the eters at the Burrton site from sons that the Burrton site had more precipitation, less evapothe water table. Effective winter and spring. No summer or during the observation period