Dense fog engulfs Amritsar, unlocks a door to fog harvesting

By Bharati Kumari

Car passengers of Punjab have been facing problems due to reduced visibility. The fog has forced to drive the vehicle at the speed of 20-25 km per hour. As per the weather report, Cold Wave conditions are likely at isolated pockets over Uttar Pradesh. Very Dense fog is on the cards at isolated places of Punjab. Dense fog in the morning hours is likely at isolated pockets over Assam, Meghalaya and Manipur.

According to the Indian Metrological Department, “Dense to very dense fog is likely over Punjab, Haryana, Chandigarh & Delhi in morning hours on 28th to 30th December and Dense fog also likely over Uttar Pradesh in morning hours on 29th & 30th December 2020.”

Fogs have the capability to render an auxiliary source of fresh water in dry regions and can be harvested through the use of simple and low-cost collection systems. Captured water can be used for agricultural irrigation and domestic purposes. Research suggests that fog collectors work best in locations with frequent fog periods, such as coastal areas where water can be harvested as the fog moves inland driven by the wind. Fog harvesting systems are best installed in open locations with a fairly high elevation that is exposed to wind flow.

photo credits- regeneration international

Through a technique used to capture water from wind-driven fog, fog harvesting provides an alternative source of fresh water.

Fog harvesting systems are predominantly installed in areas where the presence of fog is naturally high, typically coastal and mountainous regions.

Fog harvesting technology consists of a single or double-layer mesh net supported by two posts rising from the ground.  A mesh net is, stabilized between two posts that are spread out at an angle perpendicular to the prevailing wind carrying the fog. As the wind passes through the mesh, drops of freshwater form and drip into an underlying gutter, from which pipes lead the water into a storage tank. The material used for the mesh is usually nylon, polyethene or polypropylene netting.

The collectors are positioned on ridgelines perpendicular to prevailing wind and capture and collect water when fog sweeps through. The number and size of meshes chosen will depend on the local topography, demand for water, and availability of financial resources and materials.

The collector and conveyance system functions due to gravity. Water droplets that collect on the mesh run downwards and drip into a gutter at the bottom of the net from where they are channelled via pipes to a storage tank or cistern. According to fog quest Typical water production rates from a fog collector range from 200 to 1,000 litres per day, with variability occurring on a daily and seasonal basis. The efficiency of collection improves with larger fog droplets, higher wind speeds, and narrower collection fibres/mesh width.

For agricultural purposes, water is collected in a regulating tank, transferred to a reservoir and then finally into an irrigation system that farmers can use to water their crops.

Operation and maintenance are relatively simple processes once the system has been properly installed. Nevertheless, an important factor in the sustainability of this technology is the establishment of a routine quality control programme which should include, Inspection of mesh nets and cable tensions to prevent loss in water harvesting efficiency and avoid structural damage. Maintenance of nets drains and pipelines to include removal of dust, debris and algae. Maintenance of the storage tank or cistern to prevent the accumulation of fungi and bacteria. Where spare parts are not available locally, it is recommended that a stock of mesh and other components be kept in reserve as local supply might be restricted, especially in remote mountainous regions.

On October 9, 2018, The Indian Institute of Technology Mandi Researchers has developed a nature-inspired material that can harvest water from fog. The Researchers have designed water harvesting surfaces based on the surface structure of the leaves of an ornamental plant called the Dragon’s lily head (Gladiolus dale ii).

Fog harvesting provides a way of capturing vital water supplies to support farming. Furthermore, when used for irrigation to increase forested areas or vegetation coverage, water supplies from fog harvesting can help to balance out the desertification process. If the higher hills in the area are planted with trees, they too will collect fog water and contribute to the aquifers. The forests can then sustain themselves and contribute water to the ecosystem helping to build pliability against drier conditions. As the occurrence of fogs is uncertain, fog harvesting technologies depend on a water source that is not always reliable.

Fog water collection has emanated as a futuristic technology for mountainous communities without access to traditional sources of water. Still, largely in a state of development, there is an opportunity for research and development into fog harvesting technology and its potential to support agricultural production.  This technology also provides a vacancy to restore natural vegetation and support agricultural practices through the sourcing of clear water for crops and livestock.

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