Department of Earth Science |Northeastern Illinois University

PRINCIPLES OF HYDROGEOLOGY
ESCI 337
Fall, 2005

Daily Objectives #15 (October 24, 2005)                                        Dr. Sanders

Exam #2 will be held on Wednesday this week.  For the exam, you should be able to do the following:

v Define each of the following terms:

    porosity                effective porosity          specific yield                      specific retention
    piezometer          hydraulic gradient        hydraulic conductivity        intrinsic permeability
    aquifer                 aquitard                       discharge                            cross-sectional area    
    water table          capillary zone              constant head boundary     impermeable boundary  
    hydraulic head    pressure head              elevation head  

v State the hydrogeologic principles that control or affect flow in each of the lab explorations:

            p  Bucket-to-Bucket Transfer            p  Capillary Action
            p  Darcy Discovery                            p  Draining Work
            p  Holey Water Bottle                        p  Infiltration Observation

v  Describe the relationships between and among the following properties of porous materials:

              p  porosity and effective porosity
              p  specific retention and specific yield
              p  specific yield and effective porosity
              p  specific yield, specific retention, and porosity
              p  hydraulic conductivity and intrinsic permeability

v  Give typical ranges of the values of porosity, specific yield, and hydraulic conductivity of different types of porous materials, using the correct units of measurement.
 
v
  List the kinds of rocks and sediments that are generally considered aquifers, and those that are generally considered aquitards.

v
  Sketch a cross section illustrating the generalized hydrostratigraphy of northeastern Illinois. 

v  Look at the map in the Willman (1971) ISGS circular ("Summary of the Geology of the Chicago Area").  Based on the information in the map/document, decide where in the Chicago area people could find abundant ground water that they could tap with wells that tap the sediment layer.  Then, combining this information with the information on the map of the bedrock geology of Illinois, identify areas that are likely to have abundant ground water that can be tapped with wells that tap the bedrock.   On the NEIU campus, to find abundant ground water, would we need to drill wells that tap the sediment layer, or the bedrock?

v
  Use your knowledge of hydraulic properties to solve practical problems:

 q  Given a certain volume of aquifer material and a description of the sediment type, estimate how much water it would take to saturate it.  Then estimate how much water would drain from it, under the force of gravity.

    q  Figure out how much water was lost from an aquifer during a drought (Chapter 3, Problem #9, on p. 111).

v  Tell what causes ground water to flow in an aquifer.

v
  From memory, state Darcy's Law.

v
  Sketch the Darcy tube apparatus and describe how it works. Use Darcy tube experimental data to find hydraulic conductivity (K) of sediment in the tube.   Given values for some of the variables, calculate the others.  For example, given the K value of the sediment, estimate the discharge (Q) that would flow through the tube under a given gradient; or, given K and Q, estimate the gradient (dh/dl).

v  Explain why it is important in the Darcy tube experiment to keep a constant head in the inflow funnel.

v  In the ground water model, find flow paths and hydraulic gradients data from the piezometers only!

v
  Based on hydraulic head measurements from the piezometers in the ground water flow model, draw a "map" showing flow through the model.   Include the following features:  flow lines showing the direction of flow (put an arrow on the end of each flow line to tell the direction), contour lines that connect points of equal hydraulic head, and boundaries to the ground water flow system. 
 
v  List the three different types of boundaries to a flow system, and tell how flow lines in a "map" of ground water flow directions are related to each type of boundary.

v  Demonstrate your understanding of each of the following:

        hydraulic head (h):  Write a definition of hydraulic head, and tell how it is measured in the lab or field.

        piezometer:  Point to a piezometer on the Darcy tube, point to a piezometer on the ground water flow model, find a water level on a piezometer in the ground water flow model, explain to a classmate what the purpose of a piezometer is, and use a piezometer on the ground water flow model to measure hydraulic head at a given point in the system as you explain to a classmate what you are doing.

        hydraulic gradient (dh/dl):  Use hydraulic head measurements that you took last class period from two piezometers to determine the hydraulic gradient in the Darcy tube, explain how the hydraulic gradient is represented in the Darcy's Law equation, point out an area of relatively high gradient on your flow map from the ground water flow model, and point out an area of relatively low gradient.  Tell how your Darcy tube experimental results would have been different if the hydraulic gradient had been higher, and give two ways that you could set up the Darcy tube in such a way as to increase the gradient.

        hydraulic conductivity (K):  Explain the meaning of hydraulic conductivity.  Tell how your Darcy tube experimental results would have been different if the tube had been packed with sediment having a lower hydraulic conductivity.  

        constant head:  Explain what is meant by the term constant head.  Explain how head in the Darcy tube experiment was kept constant during the test.  Point to a boundary on your map from the ground water flow model along which the hydraulic head is constant.

        discharge (Q):  Explain what is meant by the term discharge, and tell how discharge is represented in the Darcy's Law equation.  Give three ways you could have reduced the discharge in your Darcy tube experiment without altering the construction of the tube itself.  Give two ways you could have reduced the discharge in your Darcy tube experiment by altering the construction of the tube itself.
     
v
  Sketch a cross sectional view of three piezometers that tap an aquifer at different depths, but with their openings in a vertical line.  Sketch the relative positions of water levels in the three piezometers in four situations: Water in the aquifer at that location is  A) flowing downward,  B) flowing upward,  C) flowing laterally (horizontally),  and D) not flowing.

v  Next up: Using data from piezometers, draw a ground water flow map, showing where the water table is.
Department of Earth Science | Northeastern Illinois University

© 2005 Laura L. Sanders.  Last updated October 24, 2005.