Lab 2 Modeling Groundwater Flow with Flownets
Purpose: Using a graphic method to model flow (1) under a dam, (2) through
a deep, confined aquifer, and (3) passing from one media to another with
different hydraulic conductivity.
Reading assignment: (Flownet construction procedures)
Lee and Fetter: p 53.-59.
Fetter: p. 153-161.
Groundwater flow beneath a dam
Read the problem in p. 55 of Lee and Fetter. Using the map shown in Fig.
7.1 (make several copies of them, you may need redraw your flow net), answer
the following questions.
(1). Answer questions 1A, 1B, and 1C. (3 pts).
(2). Construct a flownet on Figure 7.1 showing groundwater flow (use arrows
to show flow directions) under the dam. Use 3 or 4 flowtubes. (3 pts).
(3). How much water is lost (in m3/day) under the dam through discharge
Q under the dam?. 3 pts.
Groundwater flow through a deep, confined aquifer
Read the problem in p. 57 of Lee and Fetter. Subsurface information and
structure contour map of an impermeable bedrock is shown in Fig 7.2. and
Fig. 7.3.
Note that all well data measurement in Figure 7.2 of Lee and Fetter are
presented as depth relative to the ground surface. In order to correlate
between wells, we must express the elevation of water table and formation
boundary relative to a common datum, normally sea level. Correlation of
the lithologic logs of the three wells in Fig. 7.2 are shown in the next
page. The permeability of the aquifer is 100 darcys (one darcy _ 3.17_10-5
ft/s _ 2.74 ft/day). The thickness of the aquifer is about 40 feet. Base
on the correlated cross-section, answer the following questions.
(1). What is the direction of "dip" (incline downward from a horizontal
plane) of the aquifer? (3 pts)
(2). Does the aquifer pinch out against the ridges to the east and west
as it continues to the south through the saddle? Explain. (3 pts)
(3). Identify the no-flow boundaries of the flow field, if any. (3 pts).
(4). Construct the flownet in the aquifer in Fig. 7.3 using eight flowtubes.
Starting your construction in the saddle (at the constriction) and work
north. Set the contour interval of the equipotential lines to three feet.
Thus, the net should define three equipotential contours between wells B
and C, which differ by nine feet of head. Extending the net to the north,
well A should fall very close to a contour line of 265 ft. (3 pts)
(5). Determine the discharge (in ft3/day) through the aquifer (3 pts).
Groundwater refraction
The map below represents an area where geological conditions result in a
series of permeability contrasts. Contaminants will migrate in the direction
of flow, and although the contaminants will disperse laterally with distance,
the center of the contaminant plume can be estimated if the flow paths are
known accurately.
A pollutant is discharge at point X, where it enters the groundwater flow
system and migrate southward. The boundaries (solid lines) between different
formations (A, B, C) are oriented at 20í relative to W-E direction.
1. Draw the flow lines across Formations A, B, and C (3 pts).
2. Determine where the flow line (the center of the plume) will leave the
map area (3 pts)