A groundwater recharge field study: site characterization and initial results

Abstract

Abstract:A ®eld 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 speci®c 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.

Influences of Land Use on Water Quality of a Diverse New England Watershed

“…Anion Characterization of MRW. As has been shown in other studies that characterize water quality with land use (1,3,7), concentrations of strong acid and salt anions (SO4 2-, NO3 -, and Cl -), typically derived from anthropogenic sources, are greatest in more densely populated and nonforested regions of the MRW (zone III; Figure 2A). In contrast, concentrations of these anions are low and uniform in remote catchments (zone I).…”

Comparison of methods for estimating ground-water recharge and base flow at a small watershed underlain by fractured bedrock in the Eastern United States

“…Specific yield was computed by the use of equation 4 for 11 periods of streamflow recession from 1993 to 2001 during the months of October through May when evapotranspiration from ground water was expected to be minimal. The average specific yield for the watershed using this method was 0.013, which is nearly the same as the value of about 0.01 determined by Gburek and Folmar (1999) from water-table rises and lysimeter percolate at the Masser Recharge Site. Recharge determined from equation 2, using a specific yield of 0.013 and the water-level rises for upland (mid-slope and headwaters) wells shown in figure 8 indicate recharge ranged from 3.4 to 57 in.…”

“…For the WE-38 watershed, the average distance "a" from streams to ground-water divides was estimated to be about 1,000 ft as computed from 1/(2 * drainage density). The average storage coefficient (specific yield) of about 0.01 was determined by Gburek and Folmar (1999) and this study. Transmissivity of 470 ft 2 /day was used, which is the sum of transmissivity of all layers except the overburden from the calibrated ground-water flow model of Gburek and others (1998).…”

Interaction between runoff – bedrock groundwater in a steep headwater catchment underlain by sedimentary bedrock fractured by gravitational deformation

“…In general, the BG (Bh40) response is characterized by a rapid rise and fall of groundwater levels. The rapid rise of groundwater levels by several meters has been observed in other rock aquifers (Gburek and Folmar, ; Salve et al ., ). Recently, Salve et al .…”