Dear wwh:

Here's some parts I copied that may be of interest, especially since the spellings slightly differ from what you've gathered. I think karez and ghanat must be synonymous:

"Safe yield of groundwater: The definition varies between countries and is explained in the country profiles. It may or may not include fossil water. For example, in Malta, the safe yield of groundwater is considered less than the renewable groundwater potential in order not to deplete the storage capacity of the main aquifer without causing salt water intrusion. In Qatar, it includes fossil water from the aquifers underlying a large part of the Arabian Peninsula.
Kareze or Qanat: Unlined tunnel in the hillside, bringing water by free flow from underground aquifers to the surface.
Shat or Chott: Salty depression.
Sabkhas: Evaporative areas."

Kareze or Qanat (both from the above) are your karez, ghanat, and quanat..am tempted to make a smart-A comment about gnats, but won't. These spelling variants remind me of Tchaikovsky, Tchaikoffsky, Chaikovesky, Chaikoffsky...and heaven only knows what else!

Now about the guide shafts: "Several guide shafts, with relatively large intervals, are dug in the established direction..." Is this done to insure that one will hit pay dirt...or pay water?

Aluvially your Fan,
WordWell