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 temperatures, water-table hydrographs, and water-level changes in nearby wells, describe the recharge process.
Antecedent moisture conditions and the thickness and nature of the unsaturated zone were found to be the major factors affecting recharge. Although the two instrumented sites are located in sand-dune environments in areas characterized by a shallow water table and a subhumid continental climate, a significant difference was observed in the estimated total recharge. The estimates ranged from less than 2.5 millimeters at the Zenith site, to approximately 154 millimeters at the Burrton site from February to June 1983. The principal reasons that the Burrton site had more recharge than the Zenith site were more precipitation, less evapotranspiration, and a shallower depth to the water table. Effective recharge took place only during late winter and spring. No summer or fall recharge was observed at either site during the observation period of this study.