Dupuit approximation for radial flow to a well assumptions
- All geological formations are horizontal and of infinite extent
- The piezometric surface is horizontal prior to pumping
- All changes to piezometric surface are due to pumping alone
- Aquifer is HOMOGENEOUS and ISOTROPIC
- flow towards the well is radial
- Groundwater flow is only horizontal
- Pumping well and observation wells FULLY PENETRATE the aquifer
What is a confined aquifer
- 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
What is an artesian aquifer?
A confined aquifer with the piezometric surface is above the ground surface
Water therefore flows from well freely, without pumping
Phreatic aquifer
- Unconfined aquifer
- Water table is the upper boundary
- Directly recharged from the ground surface
What is a leaky aquifer?
Membrane either above or below part of the aquifer through which water can flow
What is a perched aquifer?
Underground lake
Sits on a impervious or semi-impervious bed
In most cases aquifers are ____
Anisotropic
Aquifers can have different layers, each having its own ____
Hydraulic conductivity, therefore different Q value. Q for the whole aquifer of depth B is the sum of Q for each layer
What is the specific storage Ss
The volume of water (Vw) released from storage per unit volume of the porous media (Va) per unit decline in piezometric head (dphi)
Dupuit approximation
equipotential lines are vertical and all flow streamlines are horizontal
Both are curved in reality
What is specific retention (Sr)
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
What is the specific yield (effective porosity) (Sy)?
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
