Geology topics

H.O. Pfannkuch

Publications and source records attributed to H.O. Pfannkuch.

4 recordsLinked to original sources

USGS1984

Effect of anisotropy and groundwater system geometry on seepage through lakebeds. 1. Analog and dimensional analysis

Distribution of seepage through lakebeds is controlled partly by geometric configuration of the lake and of the groundwater system interacting with the lake. To evaluate the effect of these factors, conductive-paper electric-analog models were used to analyze a number of lake and groundwater settings having different geometric configurations. Most settings analyzed are of lakes that do not penetrate the groundwater system. The width ratio, the ratio of half the lake width to thickness of the groundwater system, is the principal geometric characteristic used in this study. Because the distribution of groundwater seepage into a lake is not uniform across the lakebed, the concept of a streamlinecrowding factor is developed, and is used to determine seepage patterns from geometric characteristics of the lake and its contiguous groundwater system. Analysis of fourteen different width ratios of lake and groundwater systems indicates that lakes can be defined by three general groups of seepage patterns, which include flow patterns, volumes and rates: (1) lakes having width ratios less than ∼ 0.6 show relatively uniform distribution of seepage across the lakebed; (2) lakes having width ratios of ∼ 0.6 to ∼ 2.0 change in absolute and relative streamline crowding in the near-shore region; and (3) lakes having width ratios greater than ∼ 2.0 show stable flow patterns near shore; however, with increasing lake width, the relative streamline crowding increases relative to that width. For deep lakes and those in anisotropic media, the crowding effect is decreased, resulting in more uniform seepage across the lakebed.

Journal of Hydrology↗

USGS1984

Effect of anisotropy and groundwater system geometry on seepage through lakebeds. 2. Numerical simulation analysis

The interaction of lakes and groundwater is controlled partly by the geologic framework through which the water flows. Two interrelated geometric factors of the groundwater system that affect flow are overall geometry of the system, and anisotropy of the porous media within the system. Numerical simulation analysis was made for variations in the coefficient of anisotropy for each of several lake and groundwater settings having different geometric configurations. These analyses indicate that, for a given geometric setting, as the anisotropy of geologic materials decreases seepage from a lake decreases and depth of the local groundwater flow system associated with the lake increases. Transformation of scale of groundwater systems that have anisotropic media to isotropic equivalents results in a change in the overall geometry. Because of the different slopes of the water table and lakebed resulting from the scale transformations, a series of numerical experiments were made for various geometric configurations for a given anisotropy. These analyses indicate that as thickness of the groundwater system decreases, relative depth of the local flow system increases and seepage from the lake decreases.

Journal of Hydrology↗

USGS1976

Hydrogeology of a drift-filled bedrock valley near Lino Lakes, Anoka County, Minnesota

The bedrock surface of east-central Minnesota is dissected by an intricate network of valleys. Outside the bedrock valley at site B, 3 mi (4. 8 km) from site A, 100 ft (30 m) of drift overlies the bedrock surface. Observation wells were installed at the two sites to determine the vertical ground-water movement between the various aquifer units and the lateral movement between the two sites. An aquifer test of the lowest valley-fill aquifer at site A showed that the observation well completed in the same aquifer as the pumping well responded immediately; whereas a lag of about 100 min occurred between the lower valley fill and uppermost body of sand and gravel. This indicates that the hydraulic connection between these two layers is poor at the immediate site. Test results show that the lower sand-and-gravel aquifer has a transmissivity between 14,000 and 27,000 ft 2 /d (1,300 and 2,500 m 2 /d). Although the hydraulic gradient is vertically downward in the valley, much of the drift fill is poorly permeable. This suggests that the quantity of downward-percolating water reaching the lowest valley-fill aquifer is relatively small at the test site. Because valley cut through a number of bedrock aquifers in the region, they could potentially be an important avenue of contamination from land-surface waste. In addition, the vast network of bedrock valleys in the Twin Cities area might cause contaminants to disseminate rather rapidly throughout a large area.

Minnesota↗

USGS1975

The distribution of seepage within lakebeds

The mutual exchange of water between lakes and contiguous permeable ground-water bodies, which are thin relative to the diameter of the lakes, was modeled digitally. A significant rate of seepage was found to extend only a relatively short distance from shore, thus forming a narrow band around the lake's perimeter. This near-shore concentration of seepage is an effect only of the geometry of the ground-water flow system, which is governed by the geometry of the body of permeable material, the spatial distribution of permeability within it, and the form of the water table. Near-shore seepage occurs independently of the presence of fine-grained, lowpermeability sedimentary bottom materials in the central part of the lake. Digital modeling indicates that the velocity of seepage generally decreases at an exponential rate as a function of distance from shore. Field measurements of seepage rates through the bottom of Lake Sallie, west-central Minnesota, confirm the model results by demonstrating that both the near-shore seepage band and the exponential decrease in seepage velocity actually exist.

Minnesota, Wisconsin↗