I was doing some light reading on hydrogeology the other day and came upon something that interested me, and hopefully will be of some interest and/or use to you. I’m always fascinated by history and the way ancient civilizations came up with ingenious ways to survive in harsh conditions, and what I found in my book was exactly that.
The technology I’m talking about is called a qanat. Well, that’s what it was called in what is present-day Iran, which is where the first one was constructed. Since then it has spread to a number of other countries throughout the world where it is known by a number of names; kanat, khanat, kunut, kona, konait, ghanat, and ghundat.
A qanat is a fairly simple way to bring groundwater from one place to another. Well, simple on paper; construction took a lot of knowledge, time, and manpower. Let me start with a picture so you can see what I’m talking about and then I’ll describe it in more detail.
Qanats are used to move water from underground aquifers deep inside a hillside to lower elevations. The system is simple and basically consists of a gently sloping horizontal shaft (called qanat channel in picture) and vertical access shafts. Not surprisingly, the first step in constructing a qanat is finding the water. The location for a qanat is usually a hillside or somewhere where sediment has been (at some point in time) washed out and has formed an alluvial fan.
The process starts with a surveyor, or someone who is knowledgeable about the geology of the area, going out and finding a site that they believe has water. From there 2-4 people start digging the first vertical shaft up on the hillside to see if they’re on the water. As they get dipper a windlass is set up to collect the spoils and haul them to the top. The shaft can be anywhere from 50 feet deep to hundreds of feet deep depending on the depth of the groundwater. One simple, but ingenious step in the process is to dump the spoils around the opening of the vertical shaft. This creates a buffer around the opening and keeps rain water that is running down the hill from pouring into the shaft and adding sediment or contaminants to the groundwater. If this first shaft does not hit water then additional shafts will need to be dug in different locations until the water is found.
Once water is found the next step is deciding on a path for the qanat to follow in order to carry water down to a place where it will be useful (a town, village, field, etc.). Then, more vertical shafts are added along the path. These additional vertical shafts serve as a way to ventilate the qanat as well as to guide the people digging the qanat along the decided on path. Also, the spoils accumulated along the way are hauled up through these vertical shafts. Once all the vertical shafts are complete the diggers can begin digging the qanat. Once the qanat is complete the water should start flowing, and can continue to do so for years to come.
Well, there’s actually a decent amount of other work that needs to be done before that. Someone needs to figure out the slope of the qanat. This seems like a simple task, but the slope is very important and must be given a lot of thought. If you dig the slope too steep the water will move too quickly through the qanat and wash away or damage the tunnel. If you dig the slope too gentle then the water will not flow down the tunnel.
Once the slope is worked out then the depth of all of the vertical shafts need to be calculated to match the slope. If the shafts don’t go deep enough then they will never intersect the qanat and will serve no purpose, and if they go too deep they will disrupt the flow of water.
All of this work is not easy. Actually it is very hard, back-breaking, work. On average a typical qanat is 6-10 miles long. One very old qanat is Iran is 30 km long! To give you an idea of how much work goes in, they say that it takes one year to dig one km. Wow!
This work is not only hard, it’s dangerous. Cave-ins are one of the dangers faced. If a tunnel is being dug in hard rock or compacted clay it is fairly safe, and should not cave in. However, if the qanat is being dug through less desirable ground then reinforcing of some kind will be needed. Suffocation is another danger faced. Lack of oxygen or the presence of gas can kill the workers. To stay safe the workers watch their oil lamps for signs of depleting oxygen. Lastly, and maybe most dangerous, is the point when the workers reach the first shaft. It could be years before the initial shaft is reached, and over that time it could have partially filled with water. As the diggers break through into the shaft a wall of water can come through and drowned them, or wash them away (hitting them on rocks and injuring them). To avoid this the first vertical shaft should be drained of water before it is penetrated if there is a means of doing this. Otherwise, the diggers need to use caution to tap the shaft very gently and let the water drain into the qanat before continuing.
Finally, it must be decided what will happen at the mouth of the qanat. In most cases there is one, or several, canals that branch off from the mouth and distribute the water to different places.
For a technology to still be in use thousands of years after it was introduced to the world it must be beneficial to the population it’s serving. In the case of the qanat there are several benefits. Considering qanats are generally used in arid/semi-arid environments where it can get very hot, one of the benefits of keeping the water underground as long as you can is that it is not lost to evaporation. This may seem like a small thing, but over the years keeping the water underground can save millions of gallons. A second benefit is that no electricity is needed for pumps since the system uses gravity to keep the water flowing. Thirdly, a qanat is sustainable because its source is groundwater. The qanat will never significantly deplete an aquifer because it only takes as much as the aquifer can give. If the level of the aquifer drops too much then the water will stop flowing into the qanat, and the aquifer can recharge itself. Further, once the water gets into a town or village the water can be used as a power source to turn mills. And finally, needless to say, a qanat brings much needed water to an area so that it can flourish, grow crops, and establish itself.
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While qanats were first developed centuries ago, they are still very much in use today. For instance, in Iran there are still 37,000 qanats in use that are providing water to millions of people (and that is just in Iran). It astounds me that an idea someone had thousands of years ago is still providing an essential need to so many people around the world. It’s nice to know that in our day and age, where you can’t turn a corner without hearing about some new technology, there are still some traditional, simple, technologies being put to use. Below you’ll find a great video where you can get a closer look at the inside of a qanat and how they were/are built. Finally, this is just a brief overview; there are a lot more details of the qanat system that I did not include in this article. If you’d like to read some more please take a look at the sources listed below.
As always, thank you for reading, and please leave a comment and let me know what you thought.
Introduction to Hydrogeology by Johannes C. Nonner