There is a new word appearing in war stories from Afghanistan. The tribal authorities in the region of Tora Bora are worried that bombing bin Laden's hideout there will damage the "karez" which are small tunnels that start from the low valley areas and penetrate deep into the hills above to find water to irrigate the valley agriculture. Afghanistan has had a three year drought, and any injury to these irrigation structures would be very harmful.
These irrigation structures have been built in many places in the Middle East. There was an article about them in Scientific American quite a few years ago, but I can't remember the name for the structures used in the article. Do any of you remember it?

Ghanat: this is the word I could not remember, a tunnel dug into hillside to get irrigation water

Underground Tunnels (Ghanat)
A ghanat is an underground tunnel dug into alluvial deposits on the mountain skirt, which
taps the aquifer and brings the water to the surface by gravity flow (Fig. 1). The
construction of a ghanat system is time demanding, costly and risky for builders
(Safinegad, 1979; Ghobadian, 1982; Kardawani,1990). An experienced senior ghanat
builder (moghanni) surveys the area where a ghanat is planned to be excavated. A long
rope, a water level, a large triangle with a plumb are the only tools that a surveyor uses.
Local criteria, such as type, slope and setting of the alluvial fan in relation to groundwater
recharge, are decisive. Other factors including precipitation, vegetation cover, number and
distribution of existing ghanats and wells, which might influence the recharge of the ghanat,
are also taken into account in such a survey. Usually, several trial wells are dug to examine
the thickness and capacity of the aquifer. If the evaluation of the aquifer is satisfactory, the
course, gradient, and outlet point of the underground tunnel are determined. Several guide
shafts, with relatively large intervals, are dug in the established direction.

I found still another word for this, as used in Iran: quanat

Summary: The 3,000-year-old Zarch quanat, situated in Iran's southern Province of Yazd, the water volume of which is
reduced to 150 liters per second during last 100 years, is on the verge of drying up. The above aqueduct, 85 meters deep and
80 kilometers long, is the longest quanat in Yazd which still has potable water at its origin. Sweet (desalinated) water of Zarch
aqueduct, in addition to supplying potable water for inhabitants of the region, irrigates 300 hectares of the farmland too. This
aqueduct is the second-longest and the most ancient aqueduct in the world.

NB - In this instance it is not clear that a tunnel is involved. I doubt very much existence of a tunnel 80 km long!

Here is another paragraph about "karezes"

Background- Arable Land and Irrigation:
The UN reports that approximately 85 percent of the country's population is directly dependent on agriculture. Agriculture and
animal husbandry have historically been the most important items of Afghanistan’s Gross National Product. According to the
Cooperative Institute for Applied Meteorology at University of Missouri-Columbia, only about 12 percent of Afghanistan's
total area is arable. Most of the land is semi-area to arid with very rugged terrain. The irrigated areas are known as ‘Abi’ and
the dry farmed areas are called ‘Lalmi’. Nearly 50 percent of the arable land is irrigated and three-quarters of it is located
north of the Hindu Kush Mountains. The short growing season at elevations above 2000 meters permits only one crop to be
grown. Two crops a year can be grown at lower elevations, if enough water is available. Canal systems convey some 80-85
percent of the irrigation water, while the traditional karezes, springs, and wells feed the remaining 15-20 percent. According to
FAO’s Land Cover Atlas of Afghanistan and FAO AQUASTAT data, the equipped annual irrigated land amounts to some 2.5
million hectares. However, an estimated 30 percent of all irrigation systems are believed to have been damaged or destroyed
by the war. Adding in the effects of abandonment, neglect and lack of maintenance, another 15 to 20 percent of the irrigation
infrastructure is probably unusable for agricultural purposes. Hence, the actual irrigated land amounts to 1.2–1.3 million
hectares, decreasing every year. The decline in irrigation availability and efficiency has exacerbated the already-failing crop
production.

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

Dear WW: If I remember correctly, they used to drill vertical shafts every hundred yards or so to connect with the horizontal tunnel below. I don't remember it being said why they did this, but it might be for ventillation need by the miner, and it might be easier to pull excavated material up the shaft instead of having to crawl all the way out with each bucketful.

The Arabic term for the canal is qanat. The extra U in quanat is just a blunder.

In Persian q borrowed from Arabic is usually pronounced gh, whence ghanat is specifically the Persian form.