EnvironmentalSciences.in Worlds Best Education website for Nature Lovers

Methods of rainwater harvesting

 

The various methods of rainwater harvesting are classified below under two category, Traditional and Modern methods

Traditional rainwater harvesting, which is still prevalent in rural areas, was done in surface storage bodies like lakes, ponds, irrigation tanks, temple tanks etc. In urban areas, due to shrinking of open spaces, rainwater will have to necessarily be harvested as ground water, Hence harvesting in such places will depend very much on the nature of the soil viz., clayey, sandy etc. The below listed are the various kinds of traditional rainwater harvesting methods.

khadin

A khadin, also called a dhora, is an ingenious construction designed to harvest surface runoff water for agriculture. Its main feature is a very long (100-300 m) earthen embankment built across the lower hill slopes lying below gravelly uplands. Sluices and spillways allow excess water to drain off. The khadin system is based on the principle of harvesting rainwater on farmland and subsequent use of this water-saturated land for crop production.

First designed by the Paliwal Brahmins of Jaisalmer, western Rajasthan in the 15th century, this system has great similarity with the irrigation methods of the people of Ur (present Iraq) around 4500 BC and later of the Nabateans in the Middle East. A similar system is also reported to have been practised 4,000 years ago in the Negev desert, and in southwestern Colorado 500 years ago.

Zings
Zings are water harvesting structures found in Ladakh. They are small tanks, in which collects melted glacier water. Essential to the system is the network of guiding channels that brings the water from the glacier to the tank. As glaciers melt during the day, the channels fill up with a trickle that in the afternoon turns into flowing water. The water collects towards the evening, and is used the next day.

Kunds of Thar Desert

These are covered underground tanks usually constructed, where ever the land slopes, with local materials or cement, and developed primarily for storing of drinking water. Kunds are more prevalent in the western arid regions of Rajasthan, and in areas where the limited ground water available is moderate to highly saline. The first known construction of the kund in western Rajasthan was in 1607 AD by Raja Sursingh in the village Vadi-ka-milan .apart from the benefits of cleanliness and quality of water, the Kunds are ideal devices to collect drinking water and to reduce the occurrence of waterborne diseases.

Kund consists of Saucer shaped catchment area with the gentle slope toward the center where a tank is situated. A wire mesh to prevent the entry of floating debris, birds, and reptiles, usually guard’s openings or inlets for water to go into the tank. The top is usually covered with a lid from where water can be drawn out with a bucket. Kunds are by and large circular in shape, with little variation between the depth and diameter that ranges from 3 to 4.5m .lime plaster or cement in typically used for the construction of the tank.

 Kul Irrigation Method

The Spiti area of Himachal Pradesh is a cold desert but surprisingly, agriculture is its mainstay. Spiti's lunar-like terrain was transformed into an agrarian success story by an ingenious system, devised centuries ago to tap distant glaciers for water. But short-sighted developmental policies, though well-intentioned, now threaten both this unique irrigation system and the social consciousness that spawned it.

Spiti is an important trading post on the route connecting Ladakh and the plains of Himachal Pradesh. Villages in the Spiti subdivision are located between 3,000 m and 4,000 m, which means they are snowbound six months a year. Rainfall is negligible in Spiti because it is a rain shadow area.

The soil is dry and lacks organic matter. But, despite these handicaps, the Spiti valley has been made habitable and productive by human ingenuity. But Spiti's unique contribution to farming is kul irrigation, which utilizes kuls (diversion channels) to carry water from glacier to village. The kuls often span long distances, running down precipitous mountain slopes and across crags and crevices. Some kuls are 10 km long, and have existed for centuries. The crucial portion of a kul is its head at the glacier, which is to be tapped. The head must be kept free of debris, and so the kul is lined with stones to prevent clogging and seepage. In the village, the kul leads to a circular tank from which the flow of water can be regulated. For example, when there is need to irrigate, water is let out of the tank in a trickle.

Water from the kul is collected through the night and released into the exit channel in the morning. By evening, the tank is practically empty, and the exit is closed. This cycle is repeated daily.

Bamboo Method

In Meghalaya (one of the seven northeastern states in India), an ingenious system of tapping of stream and spring water by using bamboo pipes to irrigate plantations is widely prevalent. It is so perfected that about 18-20 liters of water entering the bamboo pipe system per minute gets transported over several hundred meters and finally gets reduced to 20-80 drops per minute at the site of the plant. The tribal farmers of Khasi and Jaintia hills use the 200-year-old system.

The bamboo drip irrigation system is normally used to irrigate the betel leaf or black pepper crops planted in areca nut orchards or in mixed orchards. Bamboo pipes are used to divert perennial springs on the hilltops to the lower reaches by gravity. The channel sections, made of bamboo, divert and convey water to the plot site where it is distributed without leakage into branches, again made and laid out with different forms of bamboo pipes. Manipulating the intake pipe positions also controls the flow of water into the lateral pipes. Reduced channel sections and diversion units are used at the last stage of water application. The last channel section enables the water to be dropped near the roots of the plant.

Bamboos of varying diameters are used for laying the channels. About a third of the outer casing in length and internodes of bamboo pieces have to be removed while fabricating the system. Later, the bamboo channel is smoothened by using a dao, a type of local axe which is a round chisel fitted with a long handle. Other components are small pipes and channels of varying sizes used for diversion and distribution of water from the main channel. About four to five stages of distribution are involved from the point of the water diversion to the application point.

The system is found in the ‘war’ areas of Meghalaya but is more prevalent in the ‘war’ Jaintia hills than in the ‘war’ Khasi hills. This system is also widely prevalent in the Muktapur region bordering Bangladesh. The region has very steep slopes and a rocky terrain. Diverting water through ground channels is not possible. The land used for cultivation is owned by the clan, and is allocated for cultivation by the clan elders on payment of a one-time rent. The clan elders have the prerogative to decide who should get what and how much land. Once the rent has been paid and the land taken on lease for cultivation, the lease period operates as long as the plants last. In case of betel leaf cultivation, the lease can last for a very long time since the plants are not lopped off after one harvest. But once the plants die, for whatever reason, the land reverts back to the clan, and can only be leased out again after paying new rent.

The water for betel leaf plants is diverted from streams by temporary diversions into very intricate bamboo canal systems. Betel leaf is planted in March before the monsoon. It is only during winter that irrigation water is required, and the bamboo pipe system is used. Hence, these bamboo systems are made ready before the onset of the winter, and during the monsoon no water is diverted into them.

Previous Post Next Post