Lecture 3

Question 1

*What does a piezometer measure?

Answer 1

Hydrostatic pressure at various depths in an aquifer

Question 2

*What are the hydrostatic pressure head, pressure head, and hydraulic head?

Answer 2

Hydrostatic Pressure Head, Ph: the potential within a well in Pa, measured at the base of the water column inside a well

Pressure Head, hp: the height of water in the well in m

Hydraulic Head, h: the height of the water surface in the well from sea level in m

Question 3

Why does groundwater move?

Answer 3

Gradients (differences in potential energy) in:
- elevation (hydraulic pressure gradient)
- temperature
- salinity

Question 4

Does groundwater flow in the direction of decreasing or increasing hydraulic head?

Answer 4

Decreasing hydraulic head (high to low hydrostatic pressure)

Question 5

What does hydraulic head increase/decrease with depth indicate about groundwater flow?

Answer 5

• Hydraulic head decreases with depth, groundwater flows downward (recharge)
• Hydraulic head increases with depth, groundwater flows upward (discharge)
• Constant hydraulic head with depth, no vertical flow (but can still flow horizontally)

Question 6

What is required for data collection with wells and piezometers?

Answer 6

• Precise location (coordinates using UTM)
• Precise depth, elevation must be with respect to a common datum (eg. 0 m asl must be the same for all elevations)
• If being used to determine direction of hydraulic gradient between wells, measurements must be taken within the same day or shorter because flow is highly variable with time

Question 7

What does isotropic/anisotropic mean with respect to an aquifer?

Answer 7

In an isotropic aquifer, the material and properties are homogenous, so the hydraulic properties are independent of direction, and flow lines cross equipotential lines at right angles

In an anisotropic aquifer, aquifer properties (eg. porosity, conductivity) vary spatially and with direction, and therefore affect the angles at which flow lines cross equipotential lines

Question 8

What are the three important boundary conditions in flownets?

Answer 8

• No-flow boundary: equipotential lines intersect at right angle, boundary is impermeable (eg. bedrock or concrete wall)
• Constant-head boundary: an equipotential line where recharge or discharge may occur (eg. a shoreline)
• Water table: not a flow or equipotential line, but a line of known head. If there is recharge/discharge across the water table, flow lines are oblique (an angle that isn’t 90 degrees) to it, if there is no recharge/discharge, flow lines are parallel to it like with a no-flow boundary

Question 9

*Components of Hydraulic Head Diagram:

Answer 9

See diagram 2