Water is one of our most important natural resources, yet it is almost invisible to the general public. Unless a person runs out of water they almost never think about its value. Public utilities effectively give it away for free, in principle only charging the cost of energy to pump it to your house. However under a changing climate, water will likely become one of the major resources of trade and unfortunately conflict. This is the motivation for training the next generation of scientists, managers, and general public on the basic principles that govern water resources. In particular, there is a strong interest in water that his held underground. This water that is held underground is termed groundwater and represents a volume of water much large than all the worlds fresh water held in lakes and rivers combined. The volume of groundwater is second only to the amount of water held in ice and glaciers. As a result of groundwater being held below the surface of the earth it is protected and typically represent a high quality resource.
In training the next generation of groundwater keepers there are a
handful of basic principles that guide us in the movement and storage of groundwater resources. These principles are not
complicated and can be described on the most basic level in the statements listed below:
Groundwater flows from high energy to low energy (high to low hydraulic head)
Storage groundwater is governed by conservation of mass (in – out = change in storage)
While the statements listed above may seem simple, the complexity in the
study of groundwater increases as we deal with space and time.
Groundwater is held in the void space between rocks or grains of
sediment. These rocks and sediment come in all sorts of shapes and
sizes, which results in three dimensional problems. In addition, water
can be added or removed from the ground through natural and human
interactions that occur at a range of time scales. As a result,
scientists, managers, and general public need to be able to visualize
these process in three dimensions through time.
The goal of this project is to develop a set of resources that allow
those interested in groundwater science to better visualize the three
dimensional aspects of groundwater flow. This visualization will be
achieved through a series of foldable three dimensional paper models.
Each paper model will come with a series of problems to be solved to
help reinforce the basic governing principles of groundwater flow.
While this is not meant to be an exhaustive study of groundwater
science, it is a goal to try to cover as many useful examples as
Please enjoy the journey into the Foldable Aquifer Project.
This following is an updated model that is a bit of an easier problem for students. The original model made students estimate thickness of the aquifer and you had to change units from cm/sec to m/day. It also had such high conductivity aquifer units that the water table was basically flat. If you want to really challenge students try the other version. However, if you want to easy students into the concepts of Darcy’s law and how to rearrange the equation try this version.
Objectives: Determine the hydraulic head across an aquifer system with two distinct hydraulic conductivities.
1. As water flow from one aquifer to another aquifer with differing hydraulic conductivities there must be a change in hydraulic head or a change in discharge. In the problem below, we are going to assume that water flow from Well A to Well C, through a two-aquifer system. Both aquifers are confined by an upper shale unit and the discharge (Q) through the aquifers is 0.02 m3/day. Using the foldable aquifer model address the following problems.
A. Determine the hydraulic head in Well B.
B. Determine the hydraulic head in Well C.
C. Identify if the aquifer at Well C is confined or unconfined based on the water level in the well.
Objectives: Quantify the impact of groundwater pumping on
drawdown near a wetland.
1. There are scenarios where water managers must balance the
need for water supply against those of ecosystem services. An example is the problem shown below where you
are asked to install a pumping well to provide water for a community but at the
same time there is a legal framework that prevents you from lowering the water
table in a nearby wetland.
Using the foldable aquifer models given below answer the
A. Without changing the level of the water table at the
wetland determine the maximum pumping rate at the water supply well.
B. If the lake were to be removed from this problem would your
maximum pumping rate increase or decrease?
By how much?
Objectives: Determine the maximum pumping rate on a well
possible without drawing water from a lake or wetland.
1. There are times that you need to determine the maximum
pumping rate in a well that can be used without extracting water from a nearby
lake or wetland. This is a classic image
well problem. The foldable aquifer model
that is provided in the problem below asks you to solve this exact style of problem. Before pumping there is a gradient across the
confined aquifer that shows water is flowing toward the lake. Use the foldable aquifer model provided to answer
the following question
A. Determine the maximum pumping rate at the well that is
possible without drawing water from the lake.
Objectives: Determine the impact of a now flow boundary on
groundwater pumping in a confined aquifer.
1. Groundwater drawdowns in wells can be impacted in
aquifers that are adjacent to no flow boundaries, such as impermeable faults or
even building foundations. These no flow
boundaries cause an asymmetry in the cone of depression. In order to solve this style of problem, we
can use image wells, which are imaginary wells that are added to the system to
represent drawdown at the no flow boundary.
The foldable aquifer model that is provided in the problem below asks
you to solve one of these drawdown problems, where the pumping well is adjacent a no
flow boundary. Before pumping there is no
gradient across the confined aquifer as shown by the dashed line. Use the foldable aquifer model provided to
answer the following question
A. Determine the pumping rate at the well needed to cause
the confined limestone aquifer to become unconfined adjacent to the fault.
B. Once the confined limestone aquifer becomes unconfined adjacent
to the fault what is the direction of groundwater flow. If you were to then turn the pumping well off
how would this direction of groundwater flow change.
C. If the fault was replaced by a lake of infinite volume
what would the pumping rate would be needed to cause the limestone aquifer to
Objectives: Quantify the drawdown in the potentiometric surface
due to groundwater pumping near a constant head boundary.
1. There are many cases in coastal aquifer where you must
calculate groundwater drawdown near an infinite source of water (i.e. the ocean
or large lake). As a result of this configuration
it is necessary to account for this boundary condition. To do this we use a method of images where a ‘fake’
or image well is placed in the lake or ocean an equal distance between the pumping
well and the boundary. In the problem below,
it is your job to determine the water level in well B due to pumping in the pumping
well at a pumping rate of 200 m3/day (36.7 gal/min). Note that before pumping there is a gradient
across the confined aquifer that shows water is flowing toward the lake. Use the foldable aquifer model provided to
answer the following question
A. Draw in map view a diagram showing the position of the
pumping well, observation well (well A) and image well.
B. Determine the water level in well A after pumping has
reached steady state.
C. Explain how the results would change if there was no
initial gradient in the potentiometric surface prior to pumping. In your description please state where you
would expect to see the water level in well A.
Objectives: Determine drawdown around a pumping well under
steady state conditions.
1. The following confined aquifer has four wells that fully
penetrating the confined aquifer. The
center pumping well has been pumping at a constant rate of 400 m3/day
for the last four years resulting in a steady state potentiometric
surface. The water level in MW-1 was
measured at 350 meters above sea level.
Using the foldable aquifer answer the following questions:
A. Before making any sort of quantitative analysis explain
the general trend in water levels between MW-1, MW-2 and MW-3.
B. Determine the
water level in MW-2, MW-3.
C. Describe how the
cone of depression would change if the hydraulic conductivity changed to 102
cm/sec (Coarse Gravel) from 10-5 cm/sec (Sandstone).
Objectives: Quantify hydraulic conductivity in an unconfined
aquifer based on slug test data of changes in water levels over time.
1. The biggest
unknown in groundwater problems is knowing the hydraulic conductivity of an
aquifer. While there are multiple
methods available for quantifying hydraulic conductivity one of the most
popular methods is the slug test. This
method artificially changes the water level in a well and monitors the response
back to the static level. Using the data
provided below and foldable aquifer model address the following problems.
Table1. Time vs drawdown data.
A. Quantify the hydraulic conductivity using the Hevorslev
B. Based on the value of hydraulic conductivity above determine
if this geologic unit makes a better aquifer or confining unit. Please explain your answer.
The following problem is a classic homework assignment that I first saw when taking classes at Iowa State University. While it has been adapted here into a three dimensional foldable aquifer model the basic problem is still the same. The purpose of this problem is to investigate how hydraulic conductivity and aquifer thickness are related. After folding the aquifer the equipotential lines on the top of the model are meant to represent the the total head in the aquifer for both the Sand/Gravel aquifer of uniform thickness and the gravel aquifer of variable thickness on the paper model. The horizontal scale, which needs to be used to determine they hydraulic gradient is given in the lower right hand corner of the model on the Sand/Gravel aquifer side. Please remember the goal here is to have something that is useful but at the end of the day this is still a model (See Box quote)
The problem is given below:
1. Your boss gives
you a potentiometric surface map of an aquifer (Figure A) and tells you that
some tests have shown that the total discharge (Q) through the aquifer is
1,400,000 GPD. She also tells you that
the effective porosity of the aquifer is 0.25.
You are also given two conceptual models of what may be going on in the
aquifer (Figure B, and C). Based on this
information your boss wants you to answer the following questions.
is the transmissivity of the gravel of the Sand/Gravel aquifer?
is the transmissivity of the sand of the Sand/Gravel aquifer?
is the transmissivity of the thick portion of the Gravel only aquifer?
is the transmissivity of the thin portion of the Gravel only aquifer?
is the specific discharge for the thick portion of the Gravel only aquifer?
is the specific discharge for the thin portion of the Gravel only aquifer ?
is the average linear velocity for the thick portion of the Gravel only aquifer?
is the average linear velocity for the thin portion of the Gravel only aquifer?
Objectives: Determine the effective hydraulic conductivity
of a heterogeneous aquifer in the horizonal and vertical directions.
1. When aquifers are heterogenous there is a simplification
that can sometimes be made in order to calculate a bulk or effective hydraulic
conductivity across the whole aquifer.
This assumption only works if water is flowing parallel or perpendicular
to the bedding planes (see figure below).
When these conditions are met, it is possible to then calculate an
effective hydraulic conductivity where the hydraulic conductivity of an
individual layer is weighted based on the layer thickness. Then each of the products of layers and
thickness are summed. The equations used to calculate this effective hydraulic
conductivity are given below. Using the
foldable aquifer model address the following problems.
For groundwater flow parallel to
the bedding plane.
is the hydraulic conductivity of a layer i in the x direction
is the thickness of layer i
For groundwater flow perpendicular
to the bedding plane.
is the hydraulic conductivity of a layer i in the z direction
is the thickness of layer i
A. Determine effective hydraulic conductivity for horizontal
flow in aquifers A, B, and C.
effective hydraulic conductivity for vertical flow in aquifers A, B, and C.
C. Explain why the
effective hydraulic conductivity is different when flow is in the horizontal
directions as compared to when flow is in the vertical direction.
Objectives: Determine the effective hydraulic conductivity of a heterogeneous aquifer to quantify groundwater discharge. 1. The world of geology is complex and aquifer are typically not made up of homogeneous materials. As a result, we must find ways to approximate aquifer heterogeneity in order to quantify groundwater discharge. In this problem there are two wells drilled into two different aquifer materials. For illustrative purposes there is a sharp vertical interface between the two materials. Using the foldable aquifer model address the following problems.
A. Determine effective hydraulic conductivity of the total aquifer in the direction of groundwater flow.
B. Calculate the groundwater discharge (Q) across the aquifer.
C. Draw the equipotential lines between the wells with an increment of 5 m.