Geology topics

G.J. Folmar

Publications and source records attributed to G.J. Folmar.

3 recordsLinked to original sources

USGS2008

Comparison of recharge estimates at a small watershed in east-central Pennsylvania, USA

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. ?? US Government 2008.

Hydrogeology Journal↗

USGS2007

Watershed scaling effect on base flow nitrate, valley and ridge physiographic province

A study of stream base flow and NO 3 -N concentration was conducted simultaneously in 51 subwatersheds within the 116-square-kilometer watershed of East Mahantango Creek near Klingerstown, Pennsylvania. The study was designed to test whether measurable results of processes and observations within the smaller watersheds were similar to or transferable to a larger scale. Ancillary data on land use were available for the small and large watersheds. Although the source of land-use data was different for the small and large watersheds, comparisons showed that the differences in the two land-use data sources were minimal. A land use-based water-quality model developed for the small-scale 7.3-square-kilometer watershed for a previous study accurately predicted NO 3 -N concentrations from sampling in the same watershed. The water-quality model was modified and, using the imagery-based land use, was found to accurately predict NO 3 -N concentrations in the subwatersheds of the large-scale 116-square-kilometer watershed as well. Because the model accurately predicts NO 3 -N concentrations at small and large scales, it is likely that in second-order streams and higher, discharge of water and NO 3 -N is dominated by flow from smaller first-order streams, and the contribution of ground-water discharge to higher order streams is minimal at the large scale.

Pennsylvania↗

USGS2007

Multiple-methods investigation of recharge at a humid-region fractured rock site, Pennsylvania, USA

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.

Pennsylvania↗