SCIENCE TRIBUNE Thursday, April 27, 2000, Chandigarh, India
 

Artificial recharge of wells
by G.S. Dhillon
WATER decline is being experienced in more than 75% of Punjab and 62 blocks out of 116 have been ranked as “over-exploited” where the groundwater draft exceeds annual recharge. Eight others have the ranking of “dark” blocks where the withdrawals have exceeded the 85% limit and are approaching the 100% level. The situation is a cause for concern. The decline of over 15 ft has been observed on an average, it being much larger in or near the large urban centres where draft is much large as it has to meet the entire requirements of the municipal and industrial units.

Science Quiz
by J. P. Garg

New products & discoveries — IT Digest

 




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Artificial recharge of wells
by G.S. Dhillon

WATER decline is being experienced in more than 75% of Punjab and 62 blocks out of 116 have been ranked as “over-exploited” where the groundwater draft exceeds annual recharge. Eight others have the ranking of “dark” blocks where the withdrawals have exceeded the 85% limit and are approaching the 100% level. The situation is a cause for concern. The decline of over 15 ft has been observed on an average, it being much larger in or near the large urban centres where draft is much large as it has to meet the entire requirements of the municipal and industrial units.

Recharge measures can be broadly classified into:- i) Water spreading or ponding through flooding, basins, furrows etc. needing large space due to small depth of recharge, and ii) Soaking wells and wells where recharge is done through gravity or reverse pumping. The latter category requires small space and so is best suited for locations near urban centres. In this writeup this category will be reviewed.

Recharge wells are also known as “injection wells” or “inverted wells” or “diffuser wells”. The mechanism involved is shown in Figure 1. There are two distinct situations involved depending upon the nature of the aquifer to be charged: a) confined aquifer and b) un-confined aquifer. Recharge rate depends upon the head causing recharge, size of the well and the permeability of the aquifer.

A recharge well is defined as a well which admits water from the surface to the underground formation or aquifer. In it, flow is “reverse” of pumping but the mode of its construction is not much different. Rather, some wells have been utilised to perform both these functions, pumping water at one time and recharging water at another time, with a little change in the equipment.

During recharging the fine particles, if present in the recharging water, tend to flow into pore space of the aquifer present around the well and this results in gradual decrease of recharge rate. In addition, the dissolved air present in the recharge water gets released and it tends to reduce the hydraulic permeability of the aquifer and the phenomenon is called “air binding”. If the recharge water contains bacteria, it tends to promote formation of growth which leads to the reduction of the flow area.

The chemical constituents of the recharge water may also differ from the normal ground water and this may result in an undesirable chemical reaction, such as base exchange in the aquifer containing sizeable fraction of silt and clay and the resultant effect being the reduction in the recharge rate. So before undertaking recharge operations, local conditions and quality of water to be used need to be studied.

American experience

California State has carried out comprehensive recharging operations, using treated river water. In order to avoid clogging or formation or slime in and around the well by bacteria, the recharge water was chlorinated (5 to 10 ppm dose). The recharge head of40 to 50 ft was used and wells of one foot diameter adopted. From the above several lessons came to be learnt: i) provide gravel packing around the recharge wells. This will not only reduce caving around the wells but reduce the entrance velocity of the recharge water entering the aquifer and thus lessen the chances of clogging. The gravel packing can be replenished at the surface if the situation demands. ii) Sealing of the well by grouting at the clay layers above the aquifer in the case of the confined aquifer will prevent upward movement of water around the casing during recharging operations.

In Long Island (New York) more than 1100 recharge wells have been installed and a recharge rate of 0.2 to 0.5 cu-ft/sec has been obtained. The recharge is carried out in compliance with the provision that the amount of water pumped must be compensated by recharging an equal volume. Here two types of recharge wells have been deployed: i) dry type which discharge water well above the watertable, and ii) wet type which deliver recharge below the watertable. Of the two, the latter type have been found more successful as in the case of the former frequent air binding occurs due to the release of air carried by the recharge water. Experience here has shown that 36-inch outer casing, gravel filler and an inner well screen, gives most satisfactory performance. It is essential to ensure that the recharge water is free from sediment and other agents, which may contaminate the aquifer.

The city of Fresno (Calif.) has developed a most successful system which takes care of city’s storm water disposal problem and leads to recharge. In this case several hundred wells have been installed at the gutter inlets which take care of the storm water run off. Thirysix inch dia wells were bored and backfilled with gravel around 8 inches dia casings. The bottom of the wells are kept about 10 ft above the watertable. This was to prevent contamination of the ground water as the recharge water gets filtered through 10 ft thick soil before joining the water table. To minimise clogging and for providing easy maintenance, a special filter system has been installed at the top of each well, which includes a perforated metal basket at the entrance of each well and can be cleaned readily of leaves and debris after each storm. The average recharge well capacity obtained is about 0.2 cfs for 24 hours period. (Ref. Hellsten, J. Wells for drains. Highway Magazine: vol 46 pp 212-213, 1995).

Ghaggar basin

The experimental site of Dabkheri adopted for extensive investigations carried out under the UNDP Programme during 1977-78, is located about 3 km upstream of the Jyotisar Canal Rest House of the Narwana Branch Canal. At the site confined aquifer was obtained which had been tapped earlier through 120 augmentation tubewells located along 48 km length of the canal bank.

The purpose of the investigation was to establish the feasibility of artificial recharge of a confined aquifer and also to determine how long water injection could be sustained without causing clogging of the recharge system.

After several trials, the well considered most appropriate was the one which had a screen 130 ft below the ground level with gravel packing properly sealed with cement. Here 414 hours injection gave a recharge rate of 1.4 cfs (40 litres/s). The canal water used for recharge had suspended sediment load of around 18 ppm and temperature around 20o C.

From the above investigation it came to be concluded that artificial recharge of confined aquifer is possible by means of injecting canal water and rate obtained being nearly 10 times that possible under gravity recharge. The maximum pressure build up after 90 days of recharge is of 6 atm (atmosphere). If at any time pressure rises above 6 atm is experienced, it indicates that the system has got clogged and needs cleaning.
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Science Quiz
by J. P. Garg

1. While being a professor of physics at Calcutta, he turned to statistics, winning recognition the world over for his pioneering work in this field. Name this Indian statistician who founded the Indian Statistical Institute, Calcutta, in 1931 and played a major role in formulating Five Year Plans.

2. This mother spacecraft, to be launched by the European Space Agency in 2003 to find if there is life on Mars, will send a probe on to the Martian surface to dig out soil samples and analyse their mineral make-up, age and water content. Name the mother ship and the probe.

3. A new disease, which normally affects children below five years of age, causes high fever that is not cured by normal medicines. It has symptoms similar to those of many other diseases, making it very difficult to be diagnosed. If the disease is not treated properly, the child can suffer from serious heart problems throughout his life. Which disease are we talking about?

4. Some sugarcane juice mixed with yeast was kept in an airtight jar. After a few days, on opening the jar this juice started to give a strong smell. Name the process involved and the main product formed.

5. One ore of a metal is found in nature as its sulphide. Besides being put to other uses, the wires and cables made from this metal have been used to transmit and distribute electricity. Identify the metal.

6. To ensure the security of a transaction over the Internet, the relevant document/information can be transformed into a coded information. Then it can be decoded and read only by the person who has full knowledge of how it was encoded, thus eliminating the chances of misuse of the transaction. What it this latest technology called?

7. Diamonds shine with beautiful colours. Which two main optical phenomena are involved in the brilliance of diamonds?

8. The female reproductive part of a flower is called CARPEL. What is a group of carpels called and what does it represent?

9. Red wine, generally formed from grapes, is considered to be useful for reducing the risk of heart attack. Scientists have recently found a chemical in grapes which is responsible for this property. (Incidentally, this chemical is found only in women who are less prone to heart attack than men.) Can you name this chemical?

10 SASE is an organisation mainly engaged in studies and research about snow avalanches. What is the complete name of this institute and where are its headquarters?

Answers
1. Prasanta Chandra Mahalanobis 2. Mars Express; Little Lander Beagle 2 3. Kawasaki disease, named after the Japanese doctor who discovered it 4. Fermentation; ethanol (ethyl alcohol) 5. Copper 6. Cryptography 7. Dispersion and total internal reflection 8. GYNOECIUM; complete female reproductive structure within a flower 9. Oestrogen (a hormone) 10. Snow and Avalanche Studies Establishment, Manali (Himachal Pradesh).
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New products & discoveries — IT Digest

Personal assistant
A NEW device is threatening to make the stenographers and typists extinct. Though much talked about in the last few years, the PDA has only now made its entry into offices. The world’s first PDA (Personal Digital Assistant) has been produced by Amstrad and has just been introduced in the European markets.

Retailing for $ 500, this “Pen Pad PDA600” instantly recognises any handwriting and turns it into text for storage, transfer, fax transmission or printout.

The project, which is expected to revolutionise office efficiency, is directed at the traditional loose-leaf and the electronic organiser markets. Among the many features of a “Pen Pad” are a full function calculator, a calendar, a search facility for any word or number, alarm call and a world time clock.

HCL introduces Toshiba notebooks
HCL Infosystems has bagged orders worth Rs 3.5 crore within days of introducing the latest generation of Toshiba Intel Pentium III microprocessor-based notebooks,

Toshiba Pentium III notebooks are available in two models. They are Tecra 8000 Y in the Tecra 8000 series, the highest end range of Toshiba notebooks and the Satellite Pro 4220, a new entrant to its popular Satellite Pro family.

E-business centre launched
Information technology powerhouses, Intel Compaq, I2 and Pricewaterhouse Coopers (PwC) have launched a dedicated Centres of Excellence for Intelligent e-Business.

A first of its kind in India, this centre has been set up to enable clients to evaluate how intelligent eBusiness solutions can add value by transforming their organisations into high velocity enterprises.

The Centre is located at PwC Technology Centre in Calcutta. The solutions show-cased at the centre may be accessed by clients at any PwC office in India over the PwC Wide Area Network.

Virtual Reality Centre
SGI and Regional Engineering College, Trichy, have set up a Virtual Reality Centre offering advanced level training in the manufacturing design. The centre will focus to begin with on areas like digital prototyping, large assembly visualisation, design reviews and finite element analysis.

The Centre will be equipped with Silicon Graphics Onyx2, the world’s only graphics supercomputer. Apart from this, the centre will also be equipped with Silicon Graphics 320 and 540 workstations, both of which are part of the new Intel processor and Microsoft Windows NT based family of visual workstations launched by SGI.

Sun Microsystem, Tech Pacific tie-up
Sun Microsystems and Tech Pacific have tied up to offer Makess ERP from Eastern Software systems to small and medium enterprises (SMEs).

Under this scheme, a complete solution, including a Sun Enterprise Ultra 10s Server, Oracle RDBMS. Makess ERP and implementation services will be offered as a low cost bundle for the first time ERP users.

Sun server bundle along with Makess non-manufacturing suite is priced at Rs 7.5 lakh and with manufacturing functionality the price is Rs 9.9 lakh.

Business intelligence solutions
The four industry leaders — Informix International Inc.. Pricewaterhouse Cooper. Sun Microsystems and Wipro infotech have announced strategic business intelligence partnership to provide leading edge business solutions to the customers in India. This partnership will provide the users with a complete end-to-end data warehousing solutions based on Red Brick.

In this venture Informix International, the technology leader in database powered solutions, will provide its RedBrick Data Warehouse Solutions with advanced analytic engine capabilities. Sun Microsystems will provide the scalable hardware and Pricewaterhouse Coppers, the world leader in developing and executing solutions to build value manage risk and improve global performance will provide consultancy and implementation services.

RedBrick is the only relational database that has focused exclusively on delivering technology specific to decision support or data warehouse application. It is a specialised server technology designed for complex queries, fast load performance, high-capacity/high performance processing and for efficient management of very large databases.

IEC alliance with Chemtech Asia
IEC Software has entered into a strategic alliance with Chemtech Asia, an Australia based IT major, to provide e-commerce solutions to financial institutions, telecom sector and ISPs. The global IT market is expected to be 1.5 trillion dollars by 2002.

— R. Suryamurthy and Gaurav Chaudhury

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