Grahams stuff

Question 1

Dupuit approximation for radial flow to a well assumptions

Answer 1

1. All geological formations are horizontal and of infinite extent
2. The piezometric surface is horizontal prior to pumping
3. All changes to piezometric surface are due to pumping alone
4. Aquifer is HOMOGENEOUS and ISOTROPIC
5. flow towards the well is radial
6. Groundwater flow is only horizontal
7. Pumping well and observation wells FULLY PENETRATE the aquifer

Question 2

What is a confined aquifer

Answer 2

• Bounded above and below by impervious formations
• A well just penetrating such an aquifer will show a water level that is above the upper confining layer
• The subsequent water level indicates the piezometric head

Question 3

What is an artesian aquifer?

Answer 3

A confined aquifer with the piezometric surface is above the ground surface
Water therefore flows from well freely, without pumping

Question 4

Phreatic aquifer

Answer 4

• Unconfined aquifer
• Water table is the upper boundary
• Directly recharged from the ground surface

Question 5

What is a leaky aquifer?

Answer 5

Membrane either above or below part of the aquifer through which water can flow

Question 6

What is a perched aquifer?

Answer 6

Underground lake
Sits on a impervious or semi-impervious bed

Question 7

In most cases aquifers are ____

Answer 7

Anisotropic

Question 8

Aquifers can have different layers, each having its own ____

Answer 8

Hydraulic conductivity, therefore different Q value. Q for the whole aquifer of depth B is the sum of Q for each layer

Question 9

What is the specific storage Ss

Answer 9

The volume of water (Vw) released from storage per unit volume of the porous media (Va) per unit decline in piezometric head (dphi)

Question 10

Dupuit approximation

Answer 10

equipotential lines are vertical and all flow streamlines are horizontal
Both are curved in reality

Question 11

What is specific retention (Sr)

Answer 11

The volume of water retained in an aquifer per unit horizontal area and unit drop in the water table

Volume of water left in the aquifer after being drained by gravity

Question 12

What is the specific yield (effective porosity) (Sy)?

Answer 12

The drainable porosity defined as the volume of water (Vwd) that will drain under the influence of gravity

The volume of water drained by gravity