Objectives 14

Department of Earth Science |Northeastern Illinois University

PRINCIPLES OF HYDROGEOLOGY
ESCI 337
Fall, 2005

Daily Objectives #14 (October 19, 2005)                                        Dr. Sanders

By the end of today's class, you should be able to do the following:

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

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. There are three different types of boundaries to this flow system! Show where they are, and pay particular attention to how your flow lines relate to each specific type of boundary.

v From memory, state Darcy's Law.

v Use the results from your Darcy tube experiment to estimate the hydraulic conductivity of the sediment in the tube, and tell whether or not the value is reasonable.

v Demonstrate your understanding of each of the following:

        hydraulic head: 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: 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: 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, butwith 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 Determine how you would find flow paths, find hydraulic gradients, and estimate travel times if you had only data from the piezometers to work with.

v Next up: Using data from piezometers, draw a ground water flow map, showing where the water table is.