If you cross the plain north of Erfoud you will see something that does not fit the landscape: very long lines of earth mounds, each with a hole in the middle, aligned towards the horizon. They look like the work of some enormous animal.
They are the visible part of a hydraulic infrastructure that explains why there are towns in a place that gets sixty millimetres of rain a year.
01 What exactly a khettara is
A khettara is an almost horizontal tunnel dug by hand underground. It starts at a mother well opened in the upper part of the valley, where groundwater sits at shallow depth, and runs for kilometres until it emerges at the surface much further down.
It is not a well and it is not a canal. It is both at once: it collects water like a well and carries it like a canal, with the particularity that the transport happens underground, where neither sun nor wind can reach it.
That is the first reason for its existence. An open canal in this region loses an enormous share of its flow to evaporation before it gets anywhere. A tunnel several metres down loses practically nothing.
No pump, no motor, no electricity: five hundred galleries running on nothing but a gradient of millimetres.
02 Everything depends on a minimal gradient
The entire system rests on one calculation. The gallery has to descend, because the water moves by gravity, but it has to descend less steeply than the ground above it: if it descended at the same rate, it would never reach the surface.
Nor can it descend much. Too steep a gradient makes the water run fast and erode the floor and walls of the tunnel, which are not lined. The working gradient is a few millimetres per metre.
Holding that gradient over kilometres, digging from inside, in the dark and without modern measuring instruments, is the part of the craft you do not see. Each vertical shaft also served as a level reference: the level was passed from one to the next with rope and plumb line.
03 Why the desert is full of anthills
The aligned mounds are a direct consequence of the digging method. Since you cannot dig kilometres of tunnel from a single end — there would be no way to get the earth out or the air in — vertical shafts are opened every few dozen metres.
Each shaft lets you attack the tunnel in two directions at once, hoist the spoil out and ventilate. The spoil is piled around the mouth, and that ring of earth is what forms the mound, with the added advantage of stopping sand and rainwater from falling in.
The shafts keep a function after construction: they are the maintenance accesses. An uncleaned gallery silts up, so someone has to go down periodically to clear falls and sediment. Whether it keeps delivering water depends on that.
04 Water is measured in time, not volume
Once outside, the water enters a distribution system that solves a difficult problem: how to divide a continuous, modest flow among dozens of owners without being able to measure it.
The traditional solution is elegant. You do not divide the flow, you divide the time: each plot has the right to receive all the water for a set number of hours within a cycle that repeats. The turn is inherited, sold and rented just like land.
To time those turns before clocks existed, simple instruments were used, among them the perforated bowl that sinks in a vessel of water in a fixed time. The unit of property here is an interval.
05 Why they are drying up
The system has worked for six centuries and has been failing over recent decades. There are hundreds of abandoned khettaras in the Tafilalet and Drâa valleys, and most of those remaining deliver less water than before.
The reasons add up. The first is physical: a khettara only works if the water table sits above the gallery's roof. Pumped wells, which can extract at any depth and in any quantity, lower that level, and when it falls below the gallery, the gallery runs dry.
The second is labour. Maintenance requires people willing to go down a narrow tunnel to remove spoil, hard and dangerous work that has become difficult to organise. And the third is drought, which recharges less of the aquifer the whole system depends on.
06 Where to see them
The easiest thing to spot is the lines of mounds, and for that you do not need to search: they appear beside the road on the Tafilalet plain, between Errachidia and Erfoud, and around Ouarzazate and Skoura.
There is also an ecomuseum dedicated to khettaras in the region, where the workings of the system are explained and a restored gallery can be seen. It is the sensible way to understand the whole before going out to look for it in the field.
One serious warning: do not approach the edge of a shaft. They are holes several metres deep, in many cases with no parapet, with loose ground around them and no signage at all. Looking at the line from a distance tells the same story and carries no risk.
