PART 7 Aquifers and aquitards
Definitions
Aquifer - geological formation which contains and yields water.
- saturated, permeable geologic unit which can transmit significant quantities of water.
Aquitard - saturated, permeable geologic unit which cannot transmit significant quantities of water (but can transmit small quantities). Also called a semi-pervious formation or leaky formation.
Aquiclude- geologic formation which may contain water, but is incapable of transmitting water.
Aquifuge - geologic formation which neither contains nor transmits any water.
In reality, there are no aquicludes and aquifuges and these terms are no longer used.
Types of aquifers
(1) Unconfined aquifer is one whose upper boundary is the water table, i.e., where pressure is zero (p=0).
Look ate the total head h: h = z + p/γ
γ At the top of the aquifer, htop = ztop + ptop/ but because ptop = 0, we have:
htop = ztop which means that if the head (h) increases, groundwater table rises.
Hydrogeology, 431/531 - University of Arizona - Fall 2002 Dr. Marek Zreda Aquifers and aquitards 46
There are four types of unconfined aquifers:
(a) valley aquifer
VALLEY AQUIFER
water table
vadose zone
phreatic aquifer
bedrock divide