To sustain settlement in the desert, North African oasis communities built foggaras (also called khettara), gently sloping underground galleries that tap groundwater from the high desert and carry it by gravity, without pumping, to the palm gardens and towns below. At the oasis the flow is divided among households and plots by finely calibrated comb-shaped weirs (the kasria), an exacting communal system of water rights. Whole towns such as those of the Touat and the Mzab valley depend on these tunnels, which require constant collective maintenance. The technique is kin to the Iranian qanat but locally elaborated.
The foggara made permanent towns and intensive gardens possible in the hyper-arid Sahara and embedded a sophisticated communal law of water division at the heart of oasis urban life.