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.