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| SCIENCE & TECHNOLOGY | Thursday, July 17, 2003, Chandigarh, India |
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Harvesting rainwater UNDERSTANDING THE UNIVERSE |
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Harvesting
rainwater
THE concept of water harvesting is very old but it came into prominence only in the drought year of 1987. Water harvesting essentially means storing/conserving rainwater runoff either through a storage reservoir or by injection in substrata formations through boreholes. Three considerations should be taken into account before launching water harvesting projects. a) Where run-off goes to sea: The discharge from hills into sea is of little utility. Hence it should be harvested to prevent floods and get additional benefits of consumptive use. Of course, prevention of river flow into sea by storage dams causes some ecological changes to the marine life in coastal areas. It also accelerates the ingress of sea water towards land and also prevents delta formation. b) Where run-off does not go to sea: In case of the Ghaggar river the entire runoff is absorbed into the sand dunes of Thar desert. The lush green agriculture fields in the districts of Hanumangarh and Ganganagar are the benediction of Ghaggar-Markanda river flows. So, water harvesting in the catchment areas of these rivers will make the Thar desert advance towards Punjab and Haryana States (desertification) with disastrous effects and hence should be avoided in preference to local benefits. c) Water harvesting in areas where underground water is brackish: Water harvesting is not very useful where underground water is brackish and water table is only a few feet below the ground. In such situations, water harvesting will accentuate waterlogging conditions and the remedy will prove worse than the disease. However, heavy pumping of brackish water during offseason will lower water table and infiltration of rain water will improve the quality of sub surface water successively over the next few years. This will be possible if pumped ground water is carried to sea through drains and the river tributaries. d) Water harvesting in areas where underground water is potable: In the rice belt underground water is potable and is extensively used for irrigation. In southern districts, underground water is potable but water table has gone very deep (220-250 ft) due to continuous pumping. If the rainfall is heavy and continuous the fields get submerged and excess water is drained off through artificial drains e.g. diversion Drain No. 8. But in normal rainfall precipitation is immediately absorbed and water table is stabilised. But normal rainfall generates lot of flow in towns and cities because of low absorption on builtup surfaces. For example builtup area in Gurgaon town is 50 sq km and it may be 400 sq km in Delhi. Rainfall of one inch per hour over an area of 12 acres will create a flow of one cuses. Rainfall of one inch per hour over an of 1 sq km (after taking into account a run-off coefficient of 0.6) will generate a volume of 150 cubic metres or 12.5 acre ft. Hence if you store the entire rainfall water of Gurgaon township with a rainfall of one inch in one hour, you save 625 acre ft of water. This is no small amount and it can maintain the water supply of Udyog Vihar Complex for 40 days. Methods of water harvesting: Method of water harvesting for plain areas are essentially two: (i) In case of towns (builtup areas) where each house has a yard (as per building bye-laws or otherwise), a small pit should be constructed together with an injection well. The flow from the rooftop should be directed towards the pit. The pit helps in decanting the water. The decanted water should be directed to flow down into the injection well. The injection well is nothing but a bore hole of 8" dia consisting of perforated PVC pipe. The water passing through the bore hole will be immediately absorbed into the ground. The Central Ground Water Board has prepared the drawings of this arrangement and made this mode of water harvesting compulsory through a gazette notification. Haryana Urban Development Authority (HUDA) has also passed such guidelines. The details are given in Figure I and the cost of the system is only Rs 15,000 for an industrial plot of 500 sq mtr . (ii) All the houses in builtup areas, particularly old townships, do not have such facility. The runoff from such houses and roads will go out of the town and join some stream to finally go to some river (Najafgarh drain in Gurgaon township). In such situation, the only solution of storing rainfall water is by constructing water bodies at different locations depending upon configuration of land (contours). Construction of water bodies is no doubt costly but ultimately very useful in sustaining the groundwater table. The bodies should be accompanied by bore holes. An 8" dia bore hole up to a depth of 150 ft may take one cusec discharge. Such water bodies can be developed as bird sanctuaries (Sultanpur lake) with a lot of afforestation. The size of the water body has to be worked out in light of normal rainfall pattern during the past 10 years to justify the cost of the project. Recently there has been
spate of speeches on water conservation ("Future wars would be
fought on water issues and hence every drop of rainwater be
conserved"). The situation of water scarcity will never arrive in
India provided we build dams across all the rivers whose water in
mammoth quantity is wastefully into the sea every year. There was a
freak rainfall in the Yamuna basin in February-March, 2002, and 90000
cusecs of water just passed over the Tajewala headworks to flow to the
sea ultimately. This is the real loss. Conservation of rainwater for
cities outflow and hillocks is not even 0.001% of the loss of water
through undammed rivers. It is, however, heartening to note that the
Ministry of Power and Irrigation, Government of India, has made a
blueprint for developing hydropower of 50000 MW by the year 2017. If
this dream comes true, then dams constructed for the purpose will also
achieve water harvesting. |
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UNDERSTANDING THE UNIVERSE I want to know why the earth revolves on its axis and how? Celestial bodies are formed through accretion of dust and gas in large wandering clouds. Clouds interact with other clouds. In this movement affected by the gravitational interaction with many other bodies it is natural that they would also acquire rotational motion. This might be slow motion in a large cloud, but when the cloud contracts to form a star and its accompanying planets, conservation of angular momentum requires that these smaller bodies begin to rotate faster. You must have seen movies or TV programmes where a spinning skater pulls in her arms and starts going around like a top. You can yourself do an experiment. Sit in a revolving chair with good bearings. Hold your arms out and take a heavy book in each hand. Then ask some one to spin you. If you pull in your arms while spinning you will start going around much faster. This is also due to conservation of angular momentum. Therefore, the reason that the earth and other celestial bodies like the sun, the moon and the planets we know are all spinning can all be ascribed to the manner of their birth. Theoretically you could have a probability of a body ending up with a zero spin, but the probability of that is very small. Your next question is "what keeps them moving". Once they are moving they keep moving unless some other forces act on them. This does occur. There is evidence that some billions of years ago the earth was spinning faster, so much so that a day was only 18 hours long. At that time the moon was much closer to the earth, having been formed in a collision of a large body with the earth. The tidal force between the moon and the earth was much higher. This caused a loss of energy and momentum. Another consequence of this was that the moon started moving away from the earth. It is still moving away - at a rate of a few centimetres every year. How do electromagnetic waves propagate without the help of a medium? You have raised a question that occupied the minds of physicists towards the later part of the 19th century. Indeed a hypothetical medium called the ether was postulated to exist in all space to allow the propagation of light and other electromagnetic waves. Famous experiments were done to detect the effect of the drag of this medium depending on the direction of propagation of light — a difference in velocity would be expected between the rays moving with the medium and those moving against the medium. No such difference was found. Simultaneously a theory was developed that could explain electromagnetic propagation without requiring a medium. This theory summarised by Maxwell’s equations describes all electromagnetic phenomena, including radiation. It does not need a medium as an intermediary for propagation unless you call vacuum also an intermediary. To feel comfortable with this
assertion remember that a magnet does keep attracting iron filings even through
a paper. Its field exists. The same is true of an electric charge or the
magnetic field around a current loop. The change in these fields is what
produces radiation. |
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Viruses that eat bacteria
Smaller than bacteria, some of them look like microscopic spacecraft. You can find them almost anywhere: under a rosebush or miles out to sea. These strange entities are bacteriophages, viruses that prey upon bacteria, and there’s a staggering number of them. A pinch of soil or drop of seawater, for example, contains many millions of bacteriophages. "They’re nature’s most successful experiment," says Marisa Pedulla of the University of Pittsburgh. "They outnumber all the bacteria, all the humans, whales, trees, et cetera, put together." Bacteriophages, also known simply as phages, came to light around 90 years ago, when two European scientists independently discovered that there are viruses that kill bacteria. Like an Apollo spacecraft landing on the moon, these viruses settle onto the surface of a bacterium. Next, they inject their genes. They reproduce inside the microbe, and eventually their multitudinous descendants explode out of the host. One of the discoverers of these odd viruses was Felix d’Herelle of the Pasteur Institute in Paris. He coined the word bacteriophage, which translates to "eater of bacteria," and began to promote the viruses as treatments for infectious diseases, such as cholera and bubonic plague, caused by bacteria. Because of inconsistent results, phage therapy never took root in the United States, especially after powerful antibiotics such as penicillin emerged. Yet many physicians in the former Soviet Union continue to use bacteriophages. And with the rise of antibiotic-resistant bacteria, some investigators and biotech firms in the United States are trying to resurrect d’Herelle’s dream. Miniature biolab on silicon chip Researchers from Cornell University have developed a miniaturised DNA-based biological testing system that fits on a silicon chip and can be customised to detect a wide variety of microorganisms. They have presented their research at the American Society for Microbiology’s (ASM) Conference on Bio- Micro- Nano-systems. The chip consists of two areas. The first area captures the DNA from the sample and purifies it. The second is a reaction chamber where a process called polymerase chain reaction is performed to rapidly replicate the selected segment of DNA, which can then be tested. "Other people have developed real-time PCR on silicon chips, but nobody has really done the purification of the DNA sample on the same chip," says Nathan Cady, one of the researchers on the study. "As near as we can tell, we are one of the first groups to incorporate the purification step into the chip." Cady and his colleagues are currently working on incorporating a third step to the process that uses fluorescence technology where an added dye would glow green to indicate a positive sample. The chip itself is 2 cm x
4 cm in size. Because PCR requires a precise series of specific
temperatures at specific times, it fits into a tiny device (5 cm x 5 cm
x 3 cm) that handles the cycling of the temperature. Once they have
finally incorporated the fluorescence, Cady expects they will have a
device roughly the size of a shoebox that will be capable of real-time
automated detection of biological agents. |
Celestial
bodies are formed through accretion of dust and gas in large wandering clouds.
Clouds interact with other clouds. In this movement affected by the
gravitational interaction with many other bodies it is natural that they would
also acquire rotational motion. This might be slow motion in a large cloud, but
when the cloud contracts to form a star and its accompanying planets,
conservation of angular momentum requires that these smaller bodies begin to
rotate faster.
