Department of Earth Science |Northeastern Illinois University

PRINCIPLES OF HYDROGEOLOGY
ESCI 337
Fall, 2005

Daily Objectives #23 (November 23, 2005)                                        Dr. Sanders

In today's class, do the following:

v  Take a cube of "aquifer" and label it Top, Bottom, Left, Right, Front, Back.  Imagine water is flowing from left to right through the cube.  Write a formula that quantifies the discharge through the cube.  What would you have to know to calculate the discharge?

Imagine water is flowing from front to back through the cube.  Write a formula to quantify discharge through the cube.  What is different this time?  What is the same?  What would you have to know to calculate the discharge?

Imagine water is flowing from top to bottom through the cube.  Write a formulat to quantify discharge through the cube.  What is different?  What is the same? What would you have to know to calculate the discharge?

Imagine water is flowing diagonally from the top left front corner to the back right bottom corner.  Write a formula to quantify discharge through the cube.  What is different?  What is the same?  What would you have to know to calculate the discharge?

v  Cooperating with another person, line up three cubes in a row.  Imagine water is flowing from left to right through the line of three cubes.  If you are given the hydraulic head values at the points in the exact center of each of the three cubes, how would you calculate discharge through the center cube?  (Note: This is the basis of a "block-centered grid"--as opposed to a "mesh-centered grid", where you would be given the hydraulic head value at the left and right faces of the cubes.) 

v  Now line up nine cubes in a three-by-three layer.  Imagine water is flowing through the nine cubes at some angle going roughly from left to right but not perfectly parallel with the cube faces.  If you are given the hydraulic head values at the points in the exact center of the eight cubes surrounding the center one (but not the center one itself), how could you figure out the hydraulic head value within the center cube?

v  What if you knew the hydraulic head in only three of the cubes--how could you calculate the value in the center one?

v  Look at the example of 27 cubes stacked together.  If we know the hydraulic head within every single cube except the center one, how can we calculate head in the center one? 

v  Slice the stack of 27 cubes vertically into left, center, and right.  Imagine we know the hydraulic head in the left vertical slice of cubes and the right slice, and we know it is constant with time.  How does this help us with calculating the hydraulic head in the center slice?

v  Imagine there is a change or stress to the system (for example, a well starts pumping, it rains and recharges the aquifer, there's a flood, evaporation takes water out, recharge comes into the aquifer from a far-away outcrop exposure, an injection well is used to pump water into the aquifer).  How does this affect your calculations?

v  What if we know the hydraulic head in only a few of the cubes?  Can we still calculate the value in the center one?

v  Explain how the concept of anisotropy applies to your calculations.

v  Explain how the concept of inhomogeneity applies to your calculations.

v  Explain how the concept of boundaries applies to your calculations.

v  Explain the concept of using a grid in a numerical model.

v  With your group members, identify the hydrostratigraphic units in your study area (aquifers and aquitards). 

v  With your group members, identify the boundaries to the aquifer(s) in your system.  They may be constant head  or no-flow boundaries.  They may be due to hydrogeologic conditions (for example, the aquifer ends, or there's a stream in contact with the aquifer) or they may be due to hydraulic conditions (for example, flow doesn't cross a "ground water divide"--see Figure 13.4 on p. 523 for an example).

v  Before you leave this evening, bring me a map of the study area and show me where the boundaries are and what type they are (constant head or no-flow).

v  Cross sections are due on Monday!  One cross section per person (three per group).  Each group also must hand in a map with the lines of cross section shown on it. 

Department of Earth Science | Northeastern Illinois University

© 2005 Laura L. Sanders.  Last updated November 23, 2005.