Cure for waterlogged areas
by G. S. Dhillon
THE skimming tubewell is of recent origin and forms the latest addition to the engineering lexicon. The device is based on the belief that there exists a fresh or sweet water layer over the native saline water encountered at greater depths.

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Science Quiz by J.P. Garg

SKIMMING TUBEWELLS
Cure for waterlogged areas
by G. S. Dhillon

THE skimming tubewell is of recent origin and forms the latest addition to the engineering lexicon. The device is based on the belief that there exists a fresh or sweet water layer over the native saline water encountered at greater depths. The tubewell is designed to “skim” or remove the fresh water without disturbing the lower saline layer.

The problem involved is to minimise upconing or keeping the fresh-saline water interface at a stable position. This requires optimising the depth of the well to obtain safe maximum yield without salt water intrusion. Based on the theoretical and analogue studies relationship are available to fix the various parameters of the skimming tubewells, considering the field data. The skimming tubewells are best suited for use by the small farmers because their discharge is small.

When a partially penetrating well in an aquifer containing fresh water overlying saline water is pumped, the reduced head near the well causes the underlying salt water to rise in the form of a cone in response to pumping and the phenomenon is called upconing. The maximum discharge that can be obtained from a well before the cone becomes unstable, is called the critical discharge. There exists an optimum penetration depth of the well into the fresh water layer, which permits maximum discharge without salt water intrusion. In the case of anisotropic aquifers with vertical permeability being much smaller compared to the horizontal permeability, the optimum penetration depth is larger compared to isotropic media. The available obtained data fixes the above limit to be around 66 per cent to 70 per cent. This is based on the consideration of a factor of safety so that the salt water interface should not rise to about onehalf the distance between the original interface and the bottom of the skimming well.

Extensive pumping of water from ground water resources in certain areas of scarps (Salinity Control and Reclamation Projects) resulted in upconing of saline water in Pakistan’s Punjab. As a result many public deep-tubewells were required to be closed on the request of farmers as their lands were getting salinised when saline water or brackish water was used even after dilution with canal water.

As a result, experimental studies were initiated at the Mona Reclamation Project and also at the Niazbeg Experimental Station (near Lahore) of the Irrigation Research Institute Punjab (Pakistan), to investigate the phenomenon of freshsaline water interface and the feasibility of using multiple strainer wells for skimming good quality water over-riding the saline water.

Investigations were carried out on a small well constructed in 1974 in the Phulawan research farm, which was 105 feet deep and on operation it started pumping saline water (TDS value of 2300 ppm and SAR of 14) which was considered unfit for irrigation. This well was taken for detailed study.

Investigations revealed the depth of interface around 90 feet. It was decided to reduce the depth of the well to 60 feet by plugging lower 45 feet depth and also to reduce the discharge to one-third by fixing an orifice in the discharge pipe of the well, which reduced the discharge to 0.3 cusecs from original pumping yield of 0.9 cusecs. The altered design had 30 feet of strainer, as the upper 30 feet pipe was blank. The distance of 30 feet was available between bottom of the converted well and the interface.

Pumping tests carried out revealed that even with four hours continuous pumping, the water pumped had TDS value of 830 ppm against 2300 ppm in the original design. To restore the original yield, two new skimming wells were installed nearby (50 ft away) to be operated by a common pump. These wells had the blank length of 20 ft and depth of 60 ft. The set of three skimming tubewells gave 0.9 cusecs of fresh water safe for irrigation against one 105 ft tubewell which pumped saline water unfit for irrigation.

At the field experimental station, Niazbeg (near Lahore), the working of the multiple-strainer wells equipped with different types of strainers: such as brass, porous concrete (Ghaffor type) and double-wound coir strainers, was evaluated. It was found that the double-wound coir strainer, though most economical yielded 8.2% less water and involved about 8% greater head loss compared to the brass strainer. The skimming well complex yielded 1.86 cusecs of fresh water and consumed 10.2 horse power. The setup involved three strainer wells, laid in a circle of 75 ft diameter and the depth of each well was 60 ft with 30 ft of blank pipe. The pipes of 8 inches diameter were installed in 15 inches diameter pipes installed by repercussion technique. It was found that a single deep well of the same capacity (though pumping saline water) required 36% less power compared to the multi-strainer complex of skimming well. The extra power consumption was on account of larger length of pipes and greater number of bends. Provision of reflex values in each bore located near the water table required less priming effort while starting each pump. More than five strainers were found to introduce air in the system and the position of the leak was difficult to locate if the pipes were connected to the pump in series. Hence “Star” pattern of connection was preferred.

As a result of the above studies carried out in Punjab (Pakistan), the following recommendations came to be evolved:

* Shalow multiple wells are successful in skimming fresh water where the interface between the fresh-saline water is around 80 to 100 ft.

* Three to five shallow wells can be operated by a common centrifugal pump and these wells should be connected to the pump in “Star” pattern and not in series. The distance between the wells be kept around 50 ft and length of blank pipe to around 20 ft.

Malwa region

The Cis-Sutlej Tract, called Malwa Region, is known to have native ground water of highly saline nature. The studies carried out by the CGWB (Central Ground Water Board) reveal that in the phreatic zone of Southern Punjab, the EC (electrical conductivity) value ranges between 5,000 and 15,000 us/cm and the chemical character varying from HCO3-Na, HCO3-Ca-Na to HCO3-C1-Na, C1-SO4-Na (bicarbonates of sodium, calcium to bicarbonates and chlorides and sulphates of sodium). Even the presence of boron has been detected in the ground water which makes its use still more harmful.

According to guidelines issued by the U.S. Salinity Lab. (1954) waters having EC value between 2250 and 5000 us/cm are classed highly saline (not fit for use in irrigation). Waters having EC value above 5000 us/cm should be used where provision for leaching of salts through underground drainage system exists. Otherwise the salt-balance of the area will soon get upset, which will be difficult to cure.

The native ground water of the above characteristics existed in the Malwa region at great depth (100 to 150 ft) in the pre-irrigation period. Due to the introduction of irrigation on a very intensive scale through a network of canal system, the water table began to rise gradually. Seepage from twin canal systems of Gang Canal-Eastern Canal and Sirhind Feeder-Rajasthan Feeder, contributed greatly to this rise in water table. More than 2.5 lakh acres of land has already got affected by the waterlogging and other areas have become endangered or prone to waterlogging.

It is expected that the seepage water, which is of fresh origin may be over-riding the deep native saline water. The lenses of sticky clay, whose presence has been well established to south of Faridkot city, are expected to retain the fresh water (perched up pockets) which can be skimmed. However, no authentic data is yet available about the depth of interface between the saline and fresh water.

As per a scheme for combating the waterlogging, the farmers of the Old Faridkot district and Mansa district would be given tubewell connections on a top priority basis in spite of blanket ban having been imposed in Punjab for grant of new tubewell connections in the post free-power for tubewells era. The process has already set in since May 1, 1998. Through this step the cotton belt is proposed to be converted into paddy growing area. The proposal covers 78 villages; 37 of Muktsar segment, 27 of Malout segment, 13 located in the Gidderbaha Segment and one in Abohar subdivision of Ferozepore district. The villagers of many other villages, like Hunsar, Lakkarwala, Tarkhanwala, Ram Nagar and Bhalrian also clamour for grant of such tubewells as their land had already been affected by waterlogging.

The tubewells of conventional design (150 ft deep with 30 ft blank pipe) may cut across the interface of the fresh or sweet water and the native saline water. Hence pump water may be unfit for irrigation even after dilution, due to the absence of horizontal drainage system and the low vertical drainability of the area. Some the wells of the above design installed in the Mansa area have been found to pumping highly saline water (pH above 18).

So, it is suggested that the farmers be provided technical guidance to go in for skimming shallow multi-bore wells, to avoid any disappointments.

(The writer is a water resources consultant.)

1. Name the world’s fastest supercomputer developed by the USA recently. How many calculations can it perform per second?

2. Name the Indian space vehicle that will put into orbit German and Korean satellites during the first quarter of 1999.

3. Telephones installed with a new technology called WILL function like a sophisticated wireless system and require use of antennas instead of cables. What does WILL stand for?

4. A South Korean company has invented a device which is able to transform water into an electrically charged liquid that cleans clothes with the same power as a conventional washing powder. Machines using such a system will completely eliminate the use of detergents and thus revolutionise the whole concept of washing. What has such a system been named?

5. A unique satellite-based and land-based communication network would place India in the forefront of network education. It will combine all the planned intranets of the University Grants Commission, Council of Scientific and Industrial Research, Human Resources Development Ministry and state-level networks. Name this network the first phase of which would become operational by August 15, 1999.

6. PTFE is used these days for coating on non-sticking pans and for other such purposes. What is the full form of PTFE?

7. A few decades ago, Asiatic lions were found in many forests of India. Now, due to poaching and other reasons, they are confined to only one forest. Which is this forest? Where is a biological park aimed at developing a breeding centre for these rare lions being set up?

8. Name the three dolphins that died in a marine amusement park near Chennai recently, due to which import of mammals like dolphins and sea-lions has been stopped in our country.

9. Which particles are produced in a cathode-ray-tube. In which home appliance is such a tube used?

(Answers)

1. “Blue pacific” 3.9 trillion 2. PSLV - C2 3. Wireless In Local Loop 4. Midas system 5. Vidya Vahini Network 6. Poly - tetra - fluoro - ethylene 7. Gir forest of Gujarat; near Taj Mahal at Agra 8. Anthony, Pippi and Daisy 9. Electrons ; television.

In the service of humanity

Although quite a few people have started putting Internet to good use, in the common man’s perception, it is still a fancy, expensive toy. He seems to think that its practical uses are few, considering that there are not very many Indian sites. That is true to some extent but not entirely. An occasion to make the sceptics change their mind came in unexpectedly. The train accident near Khanna shook the whole nation. In such calamities, getting to know the fate of the passengers can be an almost impossible task. The Railways do try to set up information centres but the information is not only sketchy but also dated. But this time, the Punjab Government quickly put the information on the Internet at punjabgovt.nic.in and www.nic.in/punjab. Various details like the names of those killed, those injured and lying at various places such as Civil Hospital, Ludhiana; Dayanand Medical College and Hospital, Ludhiana; CMC, Ludhiana, and Civil Hospital, Khanna was thus available to everyone in the world. What is even more laudable is that it was promptly updated.

Just imagine the trouble that it could have saved to those living in far-off areas. We await details about how many people assessed the site. A hampering factor is that not many people in India have access to Internet. Here is hoping that government agencies and good samaritans in others states downloaded this information and tried to pass it on to the people who needed it.

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While one expects a boom in the Internet connections, now that private service providers are coming into the market, the hassle of remembering the addresses of websites will be something one will have to learn to live with. The addresses can be long and tedious and a mistake can prove to be costly. Not many people are aware that one slash (/) or one dot (.) can change the address. For instance, even The Tribune slipped when it published the addresses of the websites where the information about the train accident victims could be obtained. The printer’s devil played the mischief and www.nic.in/punjab turned into 222.nic.in/punjab. Such howlers happen all the time, affecting access. Some browsers have made arrangements so that one can reach a site even with a partly right address but not all of them have it. In such a situation, one can do well to try www.websitez.com. Give the incomplete address and ask it to search. Chances are that you will find the right address. You are given several choices and can go to the right one.

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Long and tedious addresses may be a worldwide phenomenon but the change of address is very very unusual. Our semi-sarkari service provider has managed to do that. The address has been changed from ch1.vsnl.net.in to ch1.dot.net.in following the internal changes. Right now the e-mail is reaching the addressees even if the senders use the old addresses. The real fun will start when that will not be the case. The grouse of some of the users is that they were not informed about the change well in advance. As such, quite a few of them got the old address printed on their visiting cards and letterpads. That money has gone down the drain.

There is another related problem. In common parlance, a full stop is pronounced “dot”. For instance ch1.vsnl.net.in is pronounced ch1 dot vsnl dot net dot in. With vsnl having made way for dot (Department of Telecommunication), there is quite a bit of difficulty in explaining to outsiders that one dot stands for fullstop and another is “d”, “o” and “t”. Our resident wag is of the opinion that the DoT can make life miserable for the consumers even in abbreviation. As if, it does not do enough through its deeds! The Internet remained down for long earlier this month and many users ended up tearing their hair in despair. They could not even lodge protests because there was no response on the departmental telephones. Unless they revive their association and fight for their rights, things are not going to improve.

Illuminating earth from space

Russian cosmonauts plan to illuminate a portion of Russia at night by next year using solar rays and radio-wave reflectors placed in a cargoferry in space.

The project called Znamya-2.5, carried out by the 26th Mir Space expedition, uses more advanced technology than the earlier experiment Znamya-2.0.

With an area of 40 square metres, the reflector is expected to illuminate an area of radius five kms between Orenburg and Kursk. People in Europe, Canada and the U.S.A. can also witness the illumination.

The beam’s intensity will be equal to that of 10 full moons, thereby enabling book worms to read at night without any additional lamps, reports RIA Novosti.

The aim of the space-reflector experiment is to attract the entire planet’s attention to the potential of space science, says project manager Vladimir Syromyatnikov from the Energiya space-booster corporation.

The experiment is a part of bigger plan to establish an orbital system for lighting up terrestrial surfaces by 2015.

In theory, special orbital mirrors can illuminate any area of the terrestrial surface with the help of solar beams. For instance, a reflector having length and breadth of 1000 metres each, could be positioned 4,000 km above this planet to illuminate the surface below with an intensity which is typical of cloudy weather at dusk. The entire mirror would weigh 30 tons.

Russian experts also intend to set up a 300-ton standard mirror system equipped with bigger 3,000-mx3000-m mirrors. If positioned along Moscow’s latitude, the system would light up an area of about 10,000 sq. km, ensuring adequate illumination.

An elliptical-orbit system for lighting up the terrestrial surface may be created by the middle of the next century.

The proposed 2,500-ton system would be fitted with 10,000-mx10,000-m mirrors and would have an apogee of about 40,000 km. This would light up the plant’s entire surface, the report says.

Satellite network sans earth station

A satellite network, devoid of conventional terrestrial relay stations for data transmission to increase the speed of transmission, will invade the sky by 2003.

The network, comprising several hundred low earth orbit (LEO) satellites, will handle data for mobile telephony, multimedia, radio and television services.

The new satellites, capable of communicating with each other up to a distance of 45,000 km by laser beam, are currently being developed by the German aerospace research agency ‘DLR’, according to a report in Fraunhofer Gesellschaft Research News.

Satellites will orbit the earth at a height of about 350 km communicating with each other as well as with geostationary satellites at a height of 36,000 km which will serve as reference points.

Unlike today’s satellite system, the planned network will allow bidirectional communication without earth relay stations that serve as the media between individual users and satellites.

After communicating with each other, satellites will process data and retransmit it in the direction required.

The satellites are also equipped with gadgets to search and target the most suitable communication partner in the sky which is a difficult due to the presence of large number of satellites and space debris that can interfere with intersatellite communication.