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Christopher S. Heppner John R. Nimmo Gordon J. Folmar William J. Gburek Dennis W. Risser 《Hydrogeology Journal》2007,15(5):915-927
Lysimeter-percolate and well-hydrograph analyses were combined to evaluate recharge for the Masser Recharge Site (central Pennsylvania, USA). In humid regions, aquifer recharge through an unconfined low-porosity fractured-rock aquifer can cause large magnitude water-table fluctuations over short time scales. The unsaturated hydraulic characteristics of the subsurface porous media control the magnitude and timing of these fluctuations. Data from multiple sets of lysimeters at the site show a highly seasonal pattern of percolate and exhibit variability due to both installation factors and hydraulic property heterogeneity. Individual event analysis of well hydrograph data reveals the primary influences on water-table response, namely rainfall depth, rainfall intensity, and initial water-table depth. Spatial and seasonal variability in well response is also evident. A new approach for calculating recharge from continuous water-table elevation records using a master recession curve (MRC) is demonstrated. The recharge estimated by the MRC approach when assuming a constant specific yield is seasonal to a lesser degree than the recharge estimate resulting from the lysimeter analysis. Partial reconciliation of the two recharge estimates is achieved by considering a conceptual model of flow processes in the highly-heterogeneous underlying fractured porous medium. 相似文献
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A field study site was installed in east‐central Pennsylvania to examine processes controlling groundwater recharge. It was instrumented to monitor climatic inputs, soil water dynamics and groundwater response. Characterization of the layered fractured bedrock underlying the site by rock coring, seismic surveys and interval packer testing showed consistencies between layer depths, fracture frequencies, seismic velocities and hydraulic conductivities. Monthly summaries of rainfall and percolate over two years showed that percolate rates were generally high and closely related to precipitation during the dormant season. During the growing season, however, the relationship became erratic with large variabilities occurring between individual lysimeter measurements. Eight dormant season rainfall events were examined in detail. Smaller events produced similar responses from 1 m deep percolate lysimeters. Approximately 10–15 mm of rain was required to initiate percolate, with the time delay in response dependent on how long it took this depth to accumulate; 5 to 6 mm of the rain was retained in storage, with the remainder becoming percolate. Larger rains, from 30–110 mm, caused correspondingly larger depths of percolate and larger water table responses, but generally similar patterns of site response. Groundwater at the site was typically about 6 m below the land surface during the dormant season. It responded 1–2 hours after the onset of percolate, and reached its maximum elevation anywhere from 4 to 16 hours after that, even though percolate was still occurring. Based on causative depth of recharge and amount of water level rise in wells, the specific yield of the aquifer was found to be of the order of 0·01. This value is characteristic of fracture geometry rather than matrix properties of the bedrock. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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The common recommendation that recharge should be estimated from multiple methods is sound, but the inherent differences of the methods make it difficult to assess the accuracy of differing results. In this study, four methods for estimating groundwater recharge and two methods for estimating base flow (as a proxy for recharge) are compared at two hydrologic research sites in east-central Pennsylvania, USA. Results from the multiple methods all provided reasonable estimates of groundwater recharge that differed considerably. The estimates of mean annual recharge for the period 1994-2001 ranged from 22.9 to 35.7 cm—about 45% of the mean of all estimates. For individual years, recharge estimates from the multiple methods ranged from 30 to 42% of the mean value during the dry years and 64 to 76% of the mean value during wet years. Comparison of multiple methods was found to be useful for determining the range of plausible recharge rates and highlighting the uncertainty of the estimates. 相似文献
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A 40 m × 20 m mowed, grass hillslope adjacent to a headwater stream within a 26‐ha watershed in east‐central Pennsylvania, USA, was instrumented to identify and map the extent and dynamics of surface saturation (areas with the water table at the surface) and surface runoff source areas. Rainfall, stream flow and surface runoff from the hillslope were recorded at 5‐min intervals from 11 August to 22 November 1998, and 13 April to 12 November 1999. The dynamics of the water table (0 to 45 cm depth from the soil surface) and the occurrence of surface runoff source areas across the hillslope were recorded using specially designed subsurface saturation and surface runoff sensors, respectively. Detailed data analyses for two rainfall events that occurred in August (57·7 mm in 150 min) and September (83·6 mm in 1265 min) 1999, illustrated the spatial and temporal dynamics of surface saturation and surface runoff source areas. Temporal data analyses showed the necessity to measure the hillslope dynamics at time intervals comparable to that of rainfall measurements. Both infiltration excess surface runoff (runoff caused when rainfall intensity exceeds soil infiltration capacity) and saturation excess surface runoff (runoff caused when soil moisture storage capacity is exceeded) source areas were recorded during these rainfall events. The August rainfall event was primarily an infiltration excess surface runoff event, whereas the September rainfall event produced both infiltration excess and saturation excess surface runoff. Occurrence and disappearance of infiltration excess surface runoff source areas during the rainfall events appeared scattered across the hillslope. Analysis of surface saturation and surface runoff data showed that not all surface saturation areas produced surface runoff that reached the stream. Emergence of subsurface flow to the surface during the post‐rainfall periods appeared to be a major flow process dominating the hillslope after the August rainfall event. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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S. Gburek J. Sylwester M. Kowalinski J. Bakala Z. Kordylewski P. Podgorski S. Plocieniak M. Siarkowski B. Sylwester W. Trzebinski S. V. Kuzin A. A. Pertsov Yu. D. Kotov F. Farnik F. Reale K. J. H. Phillips 《Solar System Research》2011,45(3):189-199
The goals and construction details of a new design Polish-led X-ray spectrophotometer are described. The instrument is aimed to observe emission from entire solar corona and is placed as a separate block within the Russian TESIS X- and EUV complex aboard the CORONAS-PHOTON solar orbiting observatory. SphinX uses silicon PIN diode detectors for high time resolution measurements of the solar spectra in the range 0.8–15 keV. Its spectral resolution allows for discerning more than hundred separate energy bands in this range. The instrument dynamic range extends two orders of magnitude below and above these representative for GOES. The relative and absolute accuracy of spectral measurements is expected to be better than few percent, as follows from extensive ground laboratory calibrations. 相似文献