Ancient system could carry water to dry regions

Certain arid regions in Africa grapple with severe water scarcity attributed to scant rainfall. The “qanat system,” an age-old method of extracting water from aquifers, may offer a solution. Environmental scientist Gaathier Mahed, who specializes in groundwater management, has explored the viability of implementing these systems.

How does the qanat system work?

The qanat system accesses underground water sources called aquifers, which are located in valleys or near mountains. Water flows over long distances through gravity in underground tunnels, ultimately emerging at a lower elevation.

After emerging from the tunnel, the water becomes available for crop irrigation, benefiting farmers. Individuals can also access the water through wells along the tunnel’s path.

The system is collectively managed, with shared benefits and active participation from everyone, fostering a sense of shared interest and roles for all and strengthening community bonds— a notable contrast to the tensions often observed in contemporary water resource disputes.

The communal system is intricately managed, with laws dating back to the 9th century. These regulations pertain to the construction and spacing of qanat tunnels and their exits. Landowners at the exits have the privilege of using the water first. They are obligated to contribute to the system’s management.

Where is it used and where did it originate?

Qanats, which have been used for centuries in dry and semi-arid regions of North Africa, the Middle East, and Asia, where water is limited, are known by many different names. In North Africa, it’s referred to as “foggara,” in Oman as “falaj,” and in particular Asian areas as “qarez.”

Qanats are thought to have originated in Persia during the first millennium BC, but their knowledge and use proliferated as the Islamic Empire extended across the Arabian Peninsula, the Levant, North Africa, and parts of Europe between 661 and 750 CE.

Some qanat systems in the region, such as those in Iran, hold heritage status protection. Despite declining numbers, some of these qanats are still in use, primarily safeguarded for their historical and cultural significance.

Why is it less widely used?

Various factors contribute to the limited adoption of tunnel systems in Africa.

The construction of qanats requires specific geological conditions, typically found in fractured sandstones. The groundwater level is critical to ensuring flow within the qanat because rainfall in mountainous places impacts the aquifer’s water volume.

Qanats necessitate a sloped terrain, such as a mountain or valley, with a specific angle. If the slope is excessively steep, erosion and collapse of the qanat can result. Conversely, if the slope is too gentle, water flow may be insufficient, and potential chemical alterations may occur due to mineral interaction in the ground.

Tunnel excavation and the extensive development of the qanat system across vast areas are labor-intensive processes spanning several years. Maintaining qanats, covering substantial distances, requires annual efforts to clear accumulated silt.

The knowledge of constructing and preserving qanats is diminishing, partly due to rural-to-urban migration. People have opted for boreholes as an alternative water source in some areas.

Certain qanats are facing depletion as a result of excessive exploitation of their water resources.

Why should the system be used more widely?

In arid regions, people commonly drill wells to tap into groundwater. However, these boreholes have a limited lifespan, requiring periodic drilling of new wells. Factors such as the deterioration of pumps and materials and potential clogging from microbial organisms and fine subsurface materials contribute to this necessity.

First, qanats are sustainable because they operate on gravity, eliminating the need for electricity. Additionally, they can be harnessed for clean energy applications—such as in Iran, where cold air from qanat tunnels is utilized to cool the interiors of sizable buildings.

Second, the amount of water lost to evaporation is significantly less than that of surface water sources.

Third, qanats can have a broad-reaching impact, spanning multiple kilometers. When the water reaches a floodplain, it can irrigate extensive areas, covering various hectares of land.

Fourth, it promotes social unity as diverse individuals with various skills collaborate to sustain the system.

Fifth, the system’s longevity surpasses that of a deep water well, typically lasting around 20 years. Tunnels also experience less frequent clogging compared to wells.

Lastly, the water originating from the mountains in the qanat system tends to be of higher quality, featuring lower salinity, making it more beneficial for both crops and people.

Read the original article on: Phys.Org

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