Preserving Water

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    Water covers 70 percent

    o our planets surace

    but is becoming an

    increasingly scarce resource.

    As the earths population

    continues to expand, the

    amount o potable water isbecoming severely limited.

    Exacerbated by global

    warming, the evaporation

    o reshwater into the

    atmosphere is progressing

    at aster rates, and water

    is cycling back to earth

    where it is not necessarily

    needed. And a smallamount that dissipates

    into the atmosphere is

    lost orever. Engineers

    are equipped to create

    structures that contain

    water efciently and help

    prevent its evaporation.

    Spatial structures and

    tensioned membrane

    structures are ideally suited

    to the task o protecting

    this most vital o resources.

    By Matthys Levy,

    p.e., f.asce

    Billionso years ago, icy comets passedthrough the inner solar systemand lew near the planet wenow call earth. The heat romthe young sun caused water toboil o these comets and be-come trapped by the earthsgravity. This unique event is

    Preserving

    weidlinger

    associates,inc.

    [62] C i v i l E n g i n e e r i n g j a n u a r y 2 0 1 0

    A number

    o alternative con-

    fgurations were consid-

    ered in a study or a cover

    or New Yorks Hillview Res-

    ervoir. The reservoir covers

    365,000 m and is divided with

    a concrete wall into two sec-

    tions so that one section may

    be cleaned while the otherremains in operation.

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    Our Water Resources

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    widely believed to be the reason that 70 per-cent o our planets surace is covered with wa-ter and the earth is known as the Blue Planet.When lie frst appeared on earth, it did so be-cause o the presence o water. No other plan-

    et in our solar system was as luckyas ar aswe know. In examinations o other planets,we have ound only barren wastes or poison-ous atmospheres. Water, then, is the key toour development and our survival. In the dis-tant uture, 6 billion years rom now, our sunwill become a giant star with a power output5,000 times greater than today. Our oceans will boil o, andearth will become a hot rocky planet no longer ft or humanhabitation. At present we have more immediate concerns.

    O all the water on the planet, only 3 percent is reshwa-ter; the balance is saline ocean water. And two-thirds o thisreshwater is trapped in ice caps and glaciers, leaving onlyone-third available or our use. But even that is not the endo the story, because this small remainder is available both asgroundwater and as surace water in lakes and rivers. The bot-tom line is that very little water is available or human use,and o the reshwater that is available 70 percent is used or

    agriculture, the cultivation o rice, cotton,and sugar being the most water intensive.There are more than 6 billion people in theworld today. O this total, 1 billion lack ac-cess to reshwater, and almost 3 billion lack

    adequate sanitation acilities. Consideringthat each o us needs approximately 30 L owater per day to survive, where will we con-tinue to obtain this required water, especiallyin light o the act that by the end o the cen-tury our population is expected to grow to10 billion?

    Looking at the world rom space, those areas with thegreatest population growthArica, Southeast Asia, and thesouthwestern part o the United Statesare in the greatestdanger o suering rom water scarcity. Water will be thedefning issue o the century, says Natasha Iskander, Ph.D.,an assistant proessor o public policy at New York Univer-sity. As she puts it, While we have enough land to eed theworlds growing population, we may not have enough waterunless we discover new ways o using it much more efcient-ly. There is no question that the water crisis is partly the re-sult o the current global warming trend, but that is too easy

    [64] C i v i l E n g i n e e r i n g j a n u a r y 2 0 1 0 0885-7024-/1-0010-0062/$25.00 per article

    The results o the cover study

    or New Yorks Hillview Reser-

    voir showed that an air-sup-

    ported abric cover best satis-

    fed the objectives. That scheme

    required the development o

    anchorages on the east and

    west sides o the ring beam cir-

    cling the reservoir and the con-

    struction o a series o posts

    on top o the dividing wall.

    While we have enough land to eed the worlds growingpopulation, we may not have enough water unless wediscover new ways o using it much more efciently.

    weidlinger

    associates,inc.

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    an answer. The reality is that we waste a great deal o waterand do not treat it as the precious commodity it is. Considerthe ollowing:

    In the western United States, water is transported hun-dreds o miles rom the lush north to the desert south to sup-port wasteul water-intensive agriculture (spray or channelirrigation rather than more rugal drip irrigation). This wa-ter is also captured behind dams to eed cities in areas thatwould not otherwise support lie. Lake Powell, behind theGlen Canyon Dam, took 17 years to fll ater it was complet-ed, in 1966, and it is now rapidly drying up as a result o along-term drought. (It is now at 60 percent o capacity.) The

    city o Las Vegas depends or its very existence on the waterso Lake Powell and may soon fnd itsel unable to supply itsgrowing population with reshwater.

    Most of the worlds major waterways have been di-verted or dammed or otherwise manipulated. In the UnitedStates, only two percent o rivers run unimpeded, and peoplenow use hal the worlds readily accessible reshwater runo.This is rom The Sixth Extinction? an article by ElisabethKolbert that appeared in the May 25, 2009, edition of the

    New Yorker. Kolbert suggests that man is responsible or thedie-o that will eliminate hal o the worlds current species

    and alleges that shortsighted water management is partiallyto blame.

    Silting of such dams as Egypts Aswan Dam and Chi-

    nas Three Gorges Dam is expected to reduce their long-termcapacity and eectiveness. Reversing the damage caused bythe indiscriminate construction o thousands o dams world-wide over the past century will itsel require a massive, cost-ly eort. Also, as a result o global warming, the shrinkingglaciers in the Alps, the Andes, the Himalayas, and AricasMount Kilimanjaro will lead to a reduction of water runoffand cause drought in the populated lower plains.

    Unortunately, even when people are convinced that thereis reason or concern, they are not always logical or scienti-ic in coming up with solutions. Impressed by the act thatmuch o the available reshwater is locked up in Antarctic ice,

    an entrepreneur in one o the Persian Gul States suggestedtowing an iceberg to their country and parking it in a man-made basin, where it would provide an ample supply o wa-ter or a year. This olly is reminiscent o Ernest HemingwaysThe Old Man and the Sea, in which the old sailor, Santiago,hooks a marlin and, ater fghting or days to reel it in, ties itto the boat. On the way home, however, the bleeding fsh isdevoured by sharks, and only the skeleton remains when San-tiago fnally arrives in port.

    Scientists have recognized or a long time that billions opeople do not have access to reshwater or drinking and san-

    itation. Dean Kamen, the inventor o the gyroscopic-sensor-controlled Segway personal transporter, is one scientist andinventor who is doing something about the problem. He

    lingeras

    sociates,inc.

    ReseRvoiR CoveR seCtions

    Most o the worlds major waterways have been divertedor dammed or otherwise manipulated. In the United States,only two percent o rivers run unimpeded, and people nowuse hal the worlds readily accessible reshwater runo.

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    realized that there were really twoproblems that needed to be solved:how to turn brackish water intopotable water and, i a device weredevised, how to power that devicewhen no electric power was avail-able. His cleverly named solution,Slingshot, is a generator unit thatcombines a Stirling engine power

    source with a vapor compressionwater distiller. (The name is said tobe a reerence to the story o Davidand Goliath. Kamen believes thatwaterborne disease is a goliatho a problem and that technologyis the slingshot.) Each machine ishoused in its own black box rough-ly the size o a dormitory rerig-erator. The generator has a powerof 200 W at 20 percent efciencyand can run on a variety o uels, in-

    cluding cow dung, which makes itideal or use in Third World villag-es, where the need is greatest. Alsoits waste heat can be used in the flter. The distiller makes100 L per day o clean water rom wastewater in a machinethat doesnt need osmosis membranes or activated charcoal.In act, it requires no consumables whatsoever and is there-ore ideally suited or use in isolated locations. Both compo-nents have been tested and work beautiully. They need onlyvolume demand to make them economically easible.

    Water management has added a new word to our vocabu-lary: hydropolitical. It encompasses, or instance, develop-

    ment o the watershed o the Jordan River, which is vital to bothJordan and Israel and is perhaps one o the ew issues that haveled to cooperation between the countries involved. The water-shed is just one example of the cross-border problems created bywaterways that spill over national or regional boundaries, as il-lustrated by the ollowing list o similar challenges:

    Hungarian Dam Controversy; San Diego Tijuana Water Problems; Ataturk Dam and Environment; Colorado River Dispute; Israel/Jordan Water Dispute; Lesotho W