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Ground water in the Great Lakes Basin: the case of southeastern Wisconsin

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Graphic Link - Concept, Effect of pumping on ground-water dividesEFFECT OF PUMPING ON GROUND-WATER FLOW LINES IN SOUTHEASTERN WISCONSIN

Schematic maps of deep flow directions in 1920 and 2000 (62kb) Schematic maps of deep flow directions in 1920 and 2000
(source: K.R. Bradbury, Wisconsin Geological and Natural History Survey)
  • Brown line corresponds to western extent of Maquoketa shale.
  • Blue line corresponds to subcontinental divide.
  • Blue arrows indicate flow originating as recharge to the water table.
  • Red arrows indicate flow from below Lake Michigan toward pumping centers.

Ground water typically travels short distances over relatively short time spans when it discharges to local streams. It generally travels long distances over long time spans when it discharges to deep wells open to the sandstone aquifer. The three-dimensional flow lines followed by ground water from the water table to its destination can be visualized through a modeling technique called "particle tracking". Particle tracking simulates the movement of imaginary mathematical particles through the ground-water system in response to the geometry, aquifer, properties, and stresses input to the model. It is possible to use the mathematical particles to estimate not only the configuration of ground-water flow lines, but also the relative times of travel between the water table where the ground water is recharged and its discharge point at a stream or well.

Selected three-dimensional paths followed from the water table to deep wells are illustrated in a VIDEO CLIP (2436 kb) based on the ground-water flow model results. Another view of the same flow lines, viewed from south to north, is shown in a second VIDEO CLIP (3052 kb). In both video clips the vertical lines correspond to well locations and the colors along the flow lines correspond to relative times of travel. The color-coded values indicate the minimum estimated travel time in years.

The model provides snapshots of ground-water flow lines that originate as recharge to the water table. The following plots show flow lines corresponding to 2000 conditions (assuming that these conditions hold constant over time) for water entering the ground-water system along four east-west lines that span southeastern Wisconsin:

Map of starting locations of flow lines (110 kb) Thumbnail map of starting locations of flow lines
(source: D.T. Feinstein, U.S. Geological Survey)

In the following 2D plots selected flow lines are projected against geologic sections to show the relation of ground-water circulation to aquifers and aquitards. Although most flow lines from the water table circulate relatively short distances to local water bodies, these plots highlight flow lines from areas where recharge to the water table circulates long distances to deep wells:

A

Model output: 2D flow lines originating at water table and projected against east-west geologic sections in A) So. Dodge / Washington Counties (59 kb)
Thumbnail model output: 2D flow lines originating at water table and projected against east-west geologic sections in
A) southern Dodge / Washington
Counties

B

Model output: 2D flow lines originating at water table and projected against east-west geologic sections in B) northern Jefferson / Waukesha Counties (63 kb)
Thumbnail model output: 2D flow lines originating at water table and projected against east-west geologic sections in
B) northern Jefferson / Waukesha Counties

C

Model output: 2D flow lines originating at water table and projected against east-west geologic sections in C) south-central Jefferson / Waukesha Counties (73 kb)
Thumbnail model output: 2D flow lines originating at water table and projected against east-west geologic sections in
C) south-central Jefferson / Waukesha Counties

D

Model output: 2D flow lines originating at water table and projected against east-west geologic sections in D) northern Rock / Walworth Counties (80 kb)
Thumbnail model output: 2D flow lines originating at water table and projected against east-west geologic sections in
D) northern Rock / Walworth Counties

(source: Wisconsin Geological and Natural History Survey Open-File Report 2004-01)

In the following 3D plots selected flow lines are shown in relation to the Maquoketa shale with an indication of the time of travel along each path:

B
Model output: 3D flow lines originating at water table in B) northern Jefferson/Waukesha Counties (33 kb)
Thumbnail model output: 3D flow lines originating at water table in
B) northern Jefferson/Waukesha Counties

(source: D.T. Feinstein, U.S. Geological Survey)

Before pumping ground-water flow lines were directed everywhere toward Lake Michigan. Today deep flow is reversed and moves from the Lake toward pumping centers:

Model output: Flow lines originating from Lake Michigan under 2000 pumping conditions (35 kb)


Model output: Flow lines originating from Lake Michigan under 2000 pumping conditions
(source: D.T. Feinstein, U.S. Geological Survey)

 

NOTE: These simulated flow lines represent the flow field that would exist if 2000 pumping were to continue for hundreds of years.

However, this figure does not tell the whole story. Most of the flow that moves toward wells from beyond the Lake shore does not originate as Lake water, but rather is derived from water already stored in deep rocks below the shale. In this sense, the wells are withdrawing ground water that originated hundreds if not thousands of years ago as precipitation over land, entered the flow system as recharge, and migrated eastward over long flow paths to be stored below the Lake.

So much for the relation of deep ground water to Lake Michigan. Shallow ground water has its own story.

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Page Last Modified: March 26, 2007