-
p. 1
Name:__________________________ EPS 50 - Lab 10: Groundwater
Flow and Glaciers Part 1: Groundwater Flow -Chapter 17, p. 478-492:
Hydrology of Groundwater Part 2: Darcy’s Law -Chapter 17, p.
485-486: Darcy’s Law Part 3: Glacial Deposits and Flow -Chapter 21,
p. 587-606: Glacial Flow and Landforms Introduction: Water is an
important resource that is essential to life. The oceans and seas
contain most of Earth’s water (96%), but this water contains salt
or high concentrations of other dissolved materials. So where can
humans populations get their water? Glaciers and polar ice
represent the highest percentage of freshwater, but they are not
easily accessible. The most common source of freshwater is located
beneath the surface as groundwater. Some of the rain and snow that
falls on the land runs off into streams (runoff), some evaporates
into air, and some is absorbed by plants. The rest of it sinks into
the ground through infiltration (a process by which water enters
rock or soil through cracks or small pores between particles), and
is called groundwater. Groundwater is a vital resource that must be
carefully managed. In this lab, we will look at some of the basic
principles that govern the flow of groundwater. Objective: First,
you will encounter an everyday groundwater flow scenario in which
you are tasked with locating the source of groundwater pollution by
inferring subsurface water flow. We then “dig deeper” to understand
how water flows through porous media via Darcy’s Law, with a
hands-on exercise. Finally, the third part of this lab familiarizes
you with ice flow in glaciers and the types of landforms that
glaciers can create. Answers: All answers should be your own, but
we encourage you to discuss and check your answers with 2-3 other
students. This lab will be graded out of 100 points.
--------------------------------------------------------------------------------------------------------------
Part 1: Groundwater Flow (29 pts) Groundwater pollution is becoming
a critical issue as populations increase and the demand for water
goes up. Scenario: The Smiths just bought a home in a nice suburban
town. A few months ago, they started noticing a strange smell when
they took showers, and that the drinking water had a foul taste to
it. A week before, the local TV station ran a report on leakage
from storage tanks at gas stations, and the Smiths suspected that
this might be the cause of their problem. They hired a local
environmental consulting firm, which has put you, as an all-star
EPS 50 student, in charge. The following figure is a map of the
Smith’s neighborhood, showing the location of their home and two
local gas stations the Smiths suspect to be the cause of their
problem. You have surveyed the
-
p. 2
neighborhood, and measured the amount of semi-volatile compounds
in the soil around the Smith’s home (marked by the dots on the
map). These chemicals are released into the ground when corroded
gas tanks leak and are indicators of soil and groundwater
contamination. Concentrations greater than 50 parts per million
(ppm) are considered dangerous. Useful information: 1 mL = 1 cm3 nd
= no detection
Figure 1.
1.) Make a contour map of the soil contamination using 20 ppm
intervals in Figure 1. Use red for values above the danger
threshold, a second color for probable future threat (between 30-50
ppm), and a third color for possible future threat (10-30 ppm).
(Optional: use the semi-transparent version of this figure on the
last page of the lab, if you think it will improve readability.)
(14 pts)
-
p. 3
2.) Does either gas station have a leakage problem? Explain. (5
pts)
3.) In which direction does the local groundwater flow? How do
you know? (5 pts)
4.) Which homes will be the next to feel the effects of the
gasoline leakage? (color in those areas on the map and be sure to
add a key to the map)(5 pts)
Part 2: Darcy’s Law (37 pts) Darcy’s law is an empirical
equation that describes the flow of a fluid through a porous
medium. It was formulated by Henry Darcy in the 19th century based
on observations of the flow of water through sand beds. Darcy’s law
is widely used in the earth sciences, especially by hydrologists,
who study the movement, distribution, and quality of water on Earth
and other planets. In this section, we are going to conduct a
simple experiment to verify Darcy’s law, and to estimate the
permeability of a geological material. Darcy’s law can be written
as:
-
p. 4
, Where Q is the total discharge (units in m3/s); A is the
cross-sectional area of flow (m2); µ is the viscosity of the fluid
(Pa*s); Pa-Pb is the fluid pressure change from a to b (Pa); L is
the distance the fluid travels (m).
Figure 2.
6.) Solve for the units of permeability, k, which is not
described above. Show your work. (Hint: compare the units on the
left and right hand sides of Darcy’s law) (4 pts)
Next, we are going to test Darcy’s law and use it to measure the
permeability of different materials. The device we are going to use
is similar to Figure 2, but we are only going to test fine and
coarse grain sand sizes. You are going to measure the discharge(Q)
and the pressure change (Pb-Pa) from one end to the other. The
pressure can be converted from the height difference using
ΔP = ρ g (h2 – h1) Again, you need to be careful to keep all of
the units in MKS (meters, kilograms, seconds). ρ= density;
g=acceleration due to gravity.
7.) There are four materials in Figure 3. The grain size
decreases from left to right (labeled a-d in the figure). Which
materials do you think will transmit water best? Rank the four
-
p. 5
materials in decreasing order of permeability and explain your
prediction. (4 pts)
(a) (b) (c) (d)
Figure 3.
8.) Record your measurements below: (13 pts)
Observation Container A (Coarse) Container B (Fine) Grain size
(m)
A (m2)
ΔH (m)
ΔP (Pa)
-
p. 6
Volume (m3) of Water (20 s)
Volume (m3) of Water (40 s)
Volume (m3) of Water (60 s)
Volume (m3) of Water (80 s)
Q1 (m3/s)
Q2 (m3/s)
Q3 (m3/s)
Q4 (m3/s)
Qavg
9.) In this experiment we try to keep the water level at the
same height, so ΔH is a constant. What will happen if we don’t keep
the water level at the same height? Explain what quantities will
change and what will not. Can you still obtain a reasonable
permeability with this new condition? (6 pts)
10.) The viscosity of water at room temperature (~20°C) is
8.9*10-4 Pa*s. Use this number to estimate the permeability of the
two materials (show work). (6 pts)
Coarse Sand
-
p. 7
Fine Sand
11.) Below is a table for the permeability of unconsolidated
gravel, sand, and clay. Do your measured values fall within the
range of the expected values? Why or why not? (4 pts)
Permeability Pervious Semi-Pervious Impervious
Unconsolidated sand & gravel
Well Sorted Gravel
Well Sorted Sand or Sand & Gravel
Very Fine Sand, Silt, Loess, Loam
k (m2) 10-7 10-8 10-9 10-10 10-11 10-12 10-13 10-14 10-15
10-
16 10-17
10-18
10-19
Part 3: Glacial Deposits and Glacial Flow (34 pts) The last
major glaciation occurred during the end of the Pleistocene epoch,
and in North America this glacial advance is called the Wisconsin
Glaciation. The Wisconsin Glaciation reached its maximum between
21,000 and 18,000 years ago. Since then, the massive ice sheets
that covered all of Canada and much of the northeastern United
States in over 2 km of ice have receded and disappeared. During
this period, glaciation was not just limited to North America. In
fact, geologists have found evidence of extensive continental ice
sheets covering Northern Europe and Asia, and the
-
p. 8
Antarctic ice sheet expanded to the southern tips of South
America and Africa. Glaciers have the power to dramatically alter
the land, by leveling peaks, carving out valleys, and transporting
materials hundreds of miles. These features are still evident today
and allow the astute observer to reconstruct where these massive
ice sheets existed. The following exercises will investigate a few
prominent glacial features associated with the erosion,
transportation, and deposition of material.
12.) Figure 4 below (page 9) is a topographic map of a glaciated
section of New York. The scale bar indicates 1 mile. 10 foot
contours, heavy lines every 50 feet. Use the map to produce three
topographic profiles along the long axes of the drumlins. Label
your three profiles with the notation A-A’, B-B’, and C-C’
respectively. Illustrate your selected profile traces on the
topographic map. Be sure to identify the Scale you are using and
what units it is in. (15 pts)
-
p. 9
-
p. 10
Figure 4.
13.) Given your understanding of how drumlins form, what
direction was the ice sheet flowing when these were formed? Explain
your logic. Be sure to answer with compass coordinates (Azimuthal
or Quadrant), left/right up/down is not a sufficient answer. (3
pts) *hint-pages 598-606 of your textbook discuss glacial
landforms.
14.) How does the formative process and morphology of drumlins
differ from the formative process and morphology of roches
moutonnées? To answer this question, either describe in words or
sketch how these two glacial features are similar and how they
differ. If the profiles you constructed for the drumlins in this
exercise were roches moutonnées, what direction would ice flow have
been? (8 pts)
-
p. 11
15.) The image below (Figure 5) has a prominent feature
associated with glaciation. What is this feature? (2 pts)
Figure 5.
16.) Explain how this feature is formed, and what materials it
is typically composed of. Are these materials most likely sorted or
unsorted? Provide your reasoning. (6 pts)
-
p. 12
Optional semi-transparent version for making color contour map
for Question 1:
Figure 6.