Unsaturated‐zone wedge beneath a large, natural lake

Abstract

At the shoreline the water table is as much as 6.7 rn below the lake surface. Modeling results of a similar hypothetical setting indicate that the horizontal extent of an unsaturated zone beneath a lake depends on (1) the permeability contrast between the outwash and the lake bed, (2) anisotropy, (3) lake bed slope, and (4) thickness of the lower-permeability lake bed sediments. Although rarely documented, unsaturated sediments beneath a lake may not be extremely uncommon. Similar, much smaller unsaturated-zone areas also have been observed beneath two other lakes in Minnesota.

Role of a groundwater–lake interface in controlling seepage of water and nitrate

“…Increasing anisotropy could result in an increase in K h of the lake bed. A similar conclusion was also reached by Rosenberry (2000). Finally, the effects of changing the anisotropy of the plant cover was not investigated; it could be lower or higher than 50.…”

“…We tried to use the same method, but came up with an unrealistic value (<1), which supports our suspicion that it is the plant zone that controls discharge in the littoral zone. Schafran and Driscoll (1993) report a value of 3, Lee et al (1980) and Smerdon et al (2007) a value of 10, Rosenberry (2000) a value of 100, while modeling studies by Winter (1978) and Genereux and Bandopadhyay (2001) have used ratios up to 1000. An anisotropy ratio of 50 is therefore not unrealistic although we note that the RMS increased very slightly with increasing anisotropy.…”

“…Genereux and Bandopadhyay (2001) numerically explored such effects (here a 2 m uniform thick lake bed) and found that decreasing the hydraulic conductivity caused the distribution of discharge to flatten out from the exponential trend forcing more groundwater to discharge off-shore. Rosenberry (2000) used the observations of an unsaturated-zone wedge beneath a lake to calibrate a variable-saturated flow model by changing the hydraulic properties of the aquifer and lake bed. He found that the contrast in hydraulic conductivity between the aquifer and lake bed (or barrier effect) and the anisotropy were correlated and the simulated extension of the unsaturated-zone wedge sensitive to changes in these parameters.…”

Comparison of Instream Methods for Measuring Hydraulic Conductivity in Sandy Streambeds

“…Consequently, a comparative study of instream methods was performed as a pilot investigation to guide subsequent efforts to generate streambed K data for input into regional groundwater-flow models of the Platte River in Nebraska (COHYST 2000) being developed to quantify river gains and losses from interaction with ground water (Figure 1). Tnstream methods of determining K include slug tests (Lee and Cherry 1978;Duwelius 1996;Cey et al 1998;Springer et al 1999), in situ permeameter tests (McMahon et al 1995;Duwelius 1996;Lindgren and Landon 2000;Rosenberry 2000), and seepage flux measurements with seepage meters coupled with measurement of hydraulic gradient through the streambed (Lee and Cherry 1978;Wolf et al 1991b). In addition, streambed samples can be collected for grain-size analysis and K can be estimated from grainsize distribution (Vukovic and Soro 1992).…”

Hydrologic response of the Crow Wing Watershed, Minnesota, to mid-Holocene climate change

“…In the case of Belle Taine, and several other lakes in the Crow Wing Watershed in a similar geologic setting, lake-stage fl uctuation is enhanced because the lake receives surfacewater fl ow but has no surface-water outlet. During wet periods the additional gain from surfacewater infl ow is only partially offset by a slower loss of lake water to groundwater, which causes the lake stage to rise more than most other area lakes (Rosenberry, 2000). In addition, the model also predicts large head declines (~20 m) in the southeastern part of the watershed (Fig.…”