EghtesadOnline: A whopping 3 billion cubic meters of water evaporates annually from dams nationwide, head of water technology development workgroup at the Presidential Office for Science and Technology said.
“As the water crisis worsens, developing efficient water management techniques to preserve finite resources (like aquifers) should become a priority,” Jahangir Porhemmat was quoted as saying by ISNA.
Amir Kabir Dam, one of the biggest in Tehran, can hold maximum 200 million cubic meters of water, and the amount of water wasted in dams (3 bcm/year) due to exposure to direct sunlight is 15 times the size of this structure, Financial Tribune quoted him as saying.
Referring to global data, he added that about 170 cubic kilometers of water evaporates from the world's reservoirs every year -- more than 7% of the total amount of freshwater consumed by all human activities.
Despite the fact that dams offer a variety of services including water storage, flow regulation, hydropower and flood protection, the artificial lakes cause more water to evaporate than the natural surface water flow before the dam was built because dams increase surface area of the body of water exposed to direct sunlight.
Lost water is referred to as “consumed” because it is removed from resources. “In some cases in Iran, this amount of water consumption (waste) is quite substantial” as there are 172 dams in the country and 120 are under construction.
Despite the fact that in the past several years huge amounts have been invested in dam construction to collect surface and rain water, the measures have hardly produced the desired results, nor have they helped the government in controlling the disturbing water crisis.
Reducing evaporation from where water is stored would allow additional crop production, water trade or water for the environment.
One proposed solution for curbing water loss is construction of underground (subsurface) dams, a system to store groundwater by a “cut-off wall” (dam body) built across a groundwater channel.
This approach is most common in arid areas of Brazil while also being used in southwest United States, Mexico, India, Germany, Italy, Greece and France.
Such dams have merits that surface dams lack. For instance, the surface area can be used in the same way before and after construction of the subsurface dam. Building subsurface dams does not require heavy funds and expertise since they are simple structures that can be set up without the need for skilled and costly human resources.
Secondly, the evaporation rate is marginal due to the near constant temperature in the reservoir. Furthermore, they are more eco-friendly as they do not degrade species and their habitats.
Last but not least, unlike surface dams whose collapse spell human and economic disaster on a large scale, underground dams do not cause much damage when things go wrong.
The new method of dam construction was put on the national agenda a few years ago. Although the structures are common in other parts of the world, in Iran these are still new. The method is especially beneficial in desert regions and arid provinces where the rate of water evaporation is high.
With increasing environmental concern and concentration on water efficiency in farming, there is now considerable pressure on the people and government to optimize the use of the most precious and limited resource - water.