Τρίτη, 10 Μαΐου 2011

Fog Harvesting

Fog Tower
Above: a fog harvester design that took 4th place in Evolo's 2008 Skyscraper Design Competition
Inhabitants of the coastal desert communities of Peru and Chile are hoping for a bumper crop of fog this year, made possible by a clean and renewable source of alternative freshwater production.  Known as fog harvesting, this innovative technique is being used in some of the planet’s most arid regions as an inexpensive, low-tech solution to freshwater shortages. Freshwater augmentation technologies are an ever-increasing global priority as the demand for clean water is sharply on the rise.  Cognizant of an imminent international crisis, the United Nations called for a movement in 1993 to recognize the universal importance of freshwater and to advocate the sustainable management of freshwater resources.  Since then, the international community has observed World Water Day every year on March 22.

The Chungungo Expirement

Fog harvesting has already proved to be a viable means of freshwater collection in a number of countries where conventional freshwater sources such as wells, lakes, rivers, and pipelines are unavailable.  Robert Schemenauer and Pilar Cereceda have conducted extensive research throughout South America and other parts of the world with fog collection technologies.
Schemenauer is an Emeritus Research Scientist with the Department of Environment in Canada and  Cerceceda is a professor of geography at the Pontifical Catholic University in Santiago, Chile.  Both played an instrumental role in one of the world’s first successful fog harvesting experiments in the remote Chilean fishing village of Chungungo.
Chungungo is located in one of the planet’s driest regions—the Atacama Desert—and receives an average of less than 5cm of rainfall annually.  Before the arrival and implementation of fog collection technologies in 1992, the village’s inhabitants relied on water delivered from distant wells, a process that proved to be both expensive and unhealthy as the water was often contaminated.
Six years later, with the help of 80 fog collectors, village residents were enjoying an average of 10,000 liters of fresh drinking water each day—an estimated 35 liters per individual.1 Consequently, the quality of life in Chungungo improved dramatically as the freshwater boom lead the village to flourish.
"This project was always designed to supplement the existing water supply, which was trucked-in water,” opined Cereceda on the success of the project.  “But during the first year of the project the truck did not have to come to the village. Even during exceptionally dry years, the truck has only had to come from time to time. So now we believe that the main source of water for this area is the fog collectors.”2
"We are always going to need some way to solve water problems for rural villages, isolated villages, and clusters of remote homes in the uplands of developing countries,” commented Schemenauer.  “That's how the fog collector projects got started, by trying to solve water problems that couldn't be solved any other way."3

Desert volleyball?

Fog CatcherAt a glance, a typical fog collection site resembles an oversized beach volleyball court: two poles standing perpendicular to the ground with a rectangular, mesh net in between.  The net is designed to trap tiny water droplets as prevailing coastal winds blow fog inland.  Gravity then takes over, causing the accumulated droplets to pass through gutters that lead to a reservoir.
An average fog collecting net covers a surface area of 48m2 and is may result in anywhere from 150 to 750 liters of freshwater production a day.  At about $400 USD per net, which is usually subsidized by international aid organizations, the cost of fog harvesting makes it accessible to virtually any community that meets the proper meteorological, geographic, and societal conditions.
Schemenauer and Cereceda note these conditions must be met if the technology is to be a success.  Prerequisites include an in-depth study of regional wind patterns and the presence of a nearby mountain range to intercept fog cover carried by the prevailing winds.  The candidate community must also be one that is unable to meet its water needs with existing freshwater supplies.4
Other international projects

In observance of the Republic of South Africa’s National Water Week and the U.N.’s World Water Day, a new fog harvesting project was recently launched in the South African Cabezane Village, located in the Mount Ayliff region of the Eastern Cape Province.  The project was lead by University of South Africa (UNISA) climatologist Jana Olivier, along with Johan van Heerden, Hannes Rautenbach, and Tinus Truter of Pretoria University.
Olivier and her colleagues received funding for the project from the South African Water Research Commission.  UNISA has spearheaded similar projects in other arid regions of the country, but claims enormous success in Cabezane Village, thanks to heavy amounts of fog that roll in over Mount Ayliff.  Olivier reported the water quality as “very high”, meeting the World Health Organization’s standards for drinkable water.
The South African water conservation group Water Rhapsody responded enthusiastically to Olivier’s work: “We are so thrilled with the new fog collection technique being developed and deployed around rural South Africa. At least all South Africans can have a chance of having fresh clean water without having to walk miles to get it. Rainwater cannot be harvested off a thatch roof which is often the case for houses in rural SA [South Africa]. What a great revelation to arrive just in time for World Water Day.”5


In the past, if the children of Tshanowa junior primary school in Venda, South Africa, wanted a sip of water at school, they had to bring it from home in containers. At the school itself there wasn’t a drop to drink, let alone to wash hands or grow plants.
But now the school and much of the adjacent community has enough water to drink, wash, clean, cook and even grow vegetables–thanks to a system of collecting water from low-hanging clouds.
“The life-giving liquid is the purest you could hope to taste–and it’s also free and environmentally friendly,” said Doreen Gough, media affairs manager for the University of South Africa (UNISA).
Photo courtesy of University of South Africa
UNISA is launching another of its fog-harvesting systems in South Africa today, this one in the country’s Eastern Cape Province.
The university “has been engaged with a largescale research and development project on fog harvesting as an alternative source of potable water for many isolated rural communities struggling to access pure and clean water. Many of the communities where the research projects have been conducted experience scarce water supply and the villagers travel long distances to fetch it,” Gough said in an e-mail to Nat Geo News Watch.
With South Africa already classified as a water-stressed country, Unisa Climatologist Jana Olivier, an associate professor in the UNISA School of Agriculture and Environmental Sciences, launched the fog harvesting research project in half a dozen places in South Africa.
Hundreds of liters a day
The Eastern Cape project launched today is the latest and most efficient as it produces hundreds of liters of water a day, Gough said.
The system was designed to be used in rural areas and to be as cost effective as possible, using materials readily available and suitable in places with no electricity.
“The water quality of fog is very high and conforms to the World Health Organization and South African water quality standards for potable water,” Gough said.
Perched on a peak in the Soutpansberg mountains, the Tshanowa junior primary school’s nearest water sources are several hours’ walk away. “The closest, 2 kilometers [1.25 miles] from the school, is a non-perennial spring that runs dry in the hot months. The other option, 5 kilometers [3.1 miles] away, is a dam with poor-quality water,” Gough said.
“However, the area is often cloaked in mist, making it an ideal site for Professor Jana Olivier’s fog water-collection project.”
“Within four days, the [students] were drinking water–which was found to be of exceptionally high quality.”
In 1999 Olivier’s team erected the school’s first fog screen, consisting simply of a few poles, cables and pieces of shade cloth. “Within four days, the [students] were drinking water–which was found to be of exceptionally high quality–collected by the fog screen,” Olivier said. “It was the first time they had ever had water on site.”
Encouraged by the initial results, Olivier’s team expanded and refined the school’s fog-collection system. Today it includes three 10,000-liter (2,600-gallon) tanks, each fitted with a faucet, and yields an average of 300 liters (80 gallons) of water a day. “The actual amount of water collected varies with weather conditions,” Olivier said. “On sunny days, nothing is collected, but on wet and foggy days, yields of 3,800 liters [1,000 gallons] have been recorded.”
The water collected is more than enough to meet the needs of the local community as well as the school, all year round, according to UNISA. The school’s 130 students have even started a garden in which they grow spinach, cabbages and tomatoes.
Similar water yields and quality have been recorded at the collection system in Lepelfontein, a mission station of about 200 people on South Africa’s arid West Coast. Residents count themselves lucky if they have 100 millimeters (4 inches) of annual rainfall, UNISA said. “Moreover, the groundwater is so bitter that it is unsuitable for human consumption, so water had to be trucked to the mission station from a village 70 kilometers (43 miles) away,” Olivier said.
Photo courtesy of University of South Africa
Fog-collection systems have since also been erected at a number of schools in the Lusikisiki area of the Eastern Cape. These systems are the only source of water for the schools and surrounding villages.
Many more water-thirsty communities in South Africa could benefit from similar systems, although fog-harvesting cannot be used everywhere, Doreen Gough said.
“It is only viable where fog occurs frequently, preferably for at least 40 days a year, and persists for a few hours at a time,” Olivier explained. “It is the West Coast and the mountainous areas–stretching from the Soutpansberg in the north, along the Drakensberg in the east to the Cape Mountains in the south–that have the highest fog harvesting potential.”
Since these two types of areas cover an extensive part of South Africa, fog-harvesting could be applied effectively in many more communities, especially in rural areas, Gough said.
Specifications for fog-collection system
Olivier’s fog collector was specially designed to be used in rural areas, to be as cost effective as possible, to use material that is readily available in the area, and to be suitable for use in areas with no electricity.
“Each collection system consists of three six-meter-high (twenty feet) wooden poles, mounted nine meters (thirty feet) apart. Steel cables stretch horizontally between the poles and anchor the structure. A double layer of 30 percent shade cloth is then draped over the cables and fixed to the poles on each side. This forms a fog collection screen of about 70 square meters (750 square feet), with a gutter attached to its lower end.
“The technology behind fog collection is extremely simple,” Olivier continued. “During foggy conditions, the tiny fog particles are blown against the screen and deposited on it. As the drops become larger, they trickle downwards and drop into the gutter. From there, the water is channeled through a filter to a pipe that leads to a water collection tank.”
The system works best when the wind is blowing, although Olivier has designed a collector that is effective during calm conditions. “A prototype has been constructed and tested, and found to work well,” she said. Refinements to the new collector are being made prior to getting it patented.
Professor Olivier’s project is a collaboration with three researchers from the University of Pretoria: Professor Johan van Heerden, Professor Hannes Rautenbach and Tinus Truter.
Update from Doreen Gough: At the launch [today] the local municipality asked for more of these structures to be put up in the area which is one of the poorest in the country, fairly inacessible and with poor infrastructure, so this project is really taking off. 
Related National Geographic News story:
Fog Catchers Bring Water to Parched Villages
When dense fog sweeps in from the Pacific Ocean, special nets on a hillside catch the moisture and provide precious water to the village of Bellavista, about 10 miles (16 kilometers) outside of Lima, Peru.
National Geographic Freshwater Initiative

By 2050, a third of the people on Earth may lack a clean, secure source of water. Join National Geographic in exploring the local stories and global trends that define the world’s water crisis. Learn about freshwater resources and how they are used to feed, power, and sustain all life. See how the forces of technology, climate, human nature, and policy create challenges and drive solutions for a sustainable planet. Visit our Freshwater home page.

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