Department of Earth Science |Northeastern Illinois University
Daily Objectives #11 (October 2, 2007)                                        Dr. Sanders

 By the end of today's class, you should be able to do the following: v Properties of Porous Materials Define the following terms, using appropriate units of measurement: hydraulic conductivity and permeability, and explain the difference between them. Characterize rocks and sediments in terms of their hydraulic conductivity and permeability, giving typical ranges of values of these properties for each type of rock and sediment. Define the terms aquifer and aquitard, giving examples of rocks/sediments that might compose each. Explain what makes water flow. Define the term hydraulic gradient. Find total hydraulic head at any point in a system of tubes and buckets (e.g. a siphon) and correctly predict which way flow will proceed (if at all). Use Darcy's Law by applying it to a permeameter system.

Today's Agenda:

v Reminders:
v Properties of Porous Materials:
• Define these properties of porous materials: hydraulic conductivity and permeability.   Explain the difference between them.  Write formulas to express each quantity.  Give a typical range of values for each property in various rocks and sediments.
• Define the terms aquifer and aquitard.
v Hydraulic Head, Hydraulic Gradient, and Flow:
• Determine the hydraulic head within a bucket of water.  (Hint: you will need to start by setting an arbitrary datum.)
• If two buckets are connected by a tube (see a simple worksheet here), find the total hydraulic head at each end of the tube.  What does this tell you about direction of flow?  What if the end of the tube is higher than water level in the lower bucket?  What happens if the tube is made longer?  Looped?  Made shorter?  Packed with sand?
• Given a system of two water buckets with a tube between them (see the worksheet here), say whether water will flow from one bucket to the other (and if so, which way).  Come up with a general rule that tells whether water will flow or not and if so, which way.
• Return to the system of two buckets connected by a long tube, the tube packed with sand.  Find the hydraulic head at a point exactly halfway between the two ends of the tube, and at points exactly one-fourth of the way from each end.   Then, consider a shorter tube packed with sand, but starting and ending at the same places as the longer one.  Find the hydraulic head at the 1/4, 1/2, and 3/4 points.  How is this system like/unlike the system with the longer tube?  Explain the term hydraulic gradient.
• Formulate a way to combine hydraulic conductivity, cross sectional area, and hydraulic gradient to give the discharge of water flowing through a tube packed with sand.  Check to be sure the units of measurement work out!  Find a statement of Darcy's Law in your textbook, and tell how it compares with what you just formulated.
• Draw a sketch of your experimental set-up from last time (the permeameter).  Determine the hydraulic head at these two points: as water entered the sediment sample, and as it exited the sediment sample.  Find the hydraulic gradient within the sample.  How could you have increased discharge (Q) through the sample by altering your experimental set-up?

© 2007 Laura L. Sanders.  Last updated October 2, 2007.