Download - Preserving Water

7/28/2019 Preserving Water

1/7

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.


2/7

Our Water Resources


3/7

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.


4/7

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.


5/7

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 Water Exports; Mekong River Dam; Baikal Wood Pulp Pollution; James Bay Project; Aral Sea Loss and Cotton; The Los Angeles Aqueduct and the Owens and Mono Lakes; Israel and Lebanons Conict over the Litani; Nile River and Conict; Danube Pollution; Assyrian Water Warfare; Dead Sea Canal.All o these controversies relating to the use o precious

water are either ongoing or have been only partly resolved.How can engineers contribute to solving some o these wa-

ter-related problems? Apart rom doing whatever they can toalleviate the current global warming problem, which, as men-tioned earlier, is partly responsible or the stress on our waterresources, there are clearly areas o investigation that are worthpursuing. The most promising are as ollows:

Cisterns; Reservoir covers; Water canals and piping; Desalinization;

Filtration; Windmill pumps.This issue can be rephrased: how does the water crisis in-

tersect with shell and spatial structures? Reservoir covers o-er the best opportunities or innovation, as every town or cityin the world has to minimize evaporation o its water supplyand prevent the introduction o contaminants into its waterstorage acilities. Birds treat reservoirs as their natural habi-tat and pollute the water with ecal matter and even disease-causing germs. New York City aced this issue a number oyears ago when it was given the option by health authoritiesof either subjecting the principal water reservoir for the cityto fltration or providing a cover or it. As the cost o fltra-tion was extremely high, the option o a reservoir cover ap-peared attractive.

Many reservoirs in the past have relied on concrete cov-ers, essentially placing the reservoir underground. This typeo solution is very costly and introduces a orest o columnsinto the reservoir. An aluminum dome supported by a re-ticulated structure is another possible design solution, butit can be used only to cover reservoirs that are circular or atleast oval in plan.

As most reservoirs are not regularly shaped, anoth-er option is to use a oating cover, or exible membrane,made o polypropylene, polyethylene, or a combination o

[66] 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

weidlinger

associates,inc.

CoveR types


6/7

materials. The membrane must be resistant to ultraviolet ra-diation and suitable or the environment in which it is to beinstalled. In cold weather, when ice can orm, the cover may

be subject to bending and twisting caused by ice movementand uctuations in water level. Reinforced membranes havebeen designed to solve some o these problems, and the ma-terials have included Hypalon (a product o E.I. du Pont deNemours and Company, o Wilmington, Delaware), high-density polyethylene, and a number o composites withDacron fbers (also rom DuPont) and complex fller com-pounds. Removing debris and standing water rom suchcovers is another problem. The introduction o troughs orwater collection and wash down, as shown on page 65, isone possibility.

In a study or a cover or New Yorks Hillview Reservoir, a

number o alternative confgurations were consid-ered. The reservoir covers 365,000 m and isdivided with a concrete wall into two sec-tions so that one section can be cleanedwhile the other remains in opera-tion. The irregularly shaped planresults in maximum spans oneach side o the dividing wallof 290 and 114 m. The objec-tives o the study were to de-sign a cover that would oer

the ollowing: Present minimum

maintenance requirements; Be self-cleaning, durable,

easily repairable, and resistantto vermin;

Be aesthetically pleas-ing and in keeping with its urbanenvironment;

Have minimal effect on air and waterquality and on fsh and wildlie;

Be economical and provide the least im-pact rom construction.

Several alternatives were considered: A tower-supported Tenstar cover (a cable

dome system pioneered and patented by Weidlinger Associ-ates, Inc., of New York City; see Floating Fabric over Geor-gia Dome, Civil Engineering, November 1991);

A cable net cover; A posted Tenstar cover; An air-supported cover (see illustrations opposite).The results o the study indicated that an air-supported

fabric cover would best meet the objectives. This scheme re-

quired the development o anchorages on the east and westsides o the ring beam circling the reservoir and the construc-tion o a series o posts on top o the dividing wall Also in

pressure under the roo under normal conditions as well asduring high winds and heavy snows. Normal seam and jointleaks were assumed, as well as leakage caused by accidental

damage or loss of a fabric panel. For efcient construction, theuse o barges on the reservoir to assemble the cable net wascontemplated. The city ultimately decided to use chemicaldisinection rather than a cover.

In the distant past, Greek, Indian, and Chinese philoso-phers independently recognized the existence o our plan-ets our classical elements: earth, air, water, and fre. Today,mankind is well on its way to destroying three o these. Weabuse the earth with litter and indiscriminate mining, pollutethe water with chemicals and waste, and poison the air withgreenhouse gases. The ourth, fre, escapes our wrath, but eventhough it provides us with light and heat, it is itsel a destroy-

er, burning orests and homes and using preciousoxygen in the process. Clearly, our planet is

out o balance, and the frst problems thatwe must address are political and psy-

chologicalapathy, obsolete gov-ernment policies, and ingrained

habits and attitudesbeore wecan redirect mankind and orgea new environmental con-sciousness. Some o these is-sues have penetrated our con-

sciousness and made us awareo problems and solutions. Inthe past ew years, we have o-

cused our attention on the is-sue o global warming. And we

are aware o the destruction o theearth and have initiated recycling

to reuse materials torn rom the earthand have undertaken rehabilitation e-

orts to repair the damage caused by miningand deorestation.

Moreover, there is now general consensusthat a problem exists and that we must take ac-tion to change the way we use and dispose o car-bon products so that we can return the planets

atmosphere to the balance that existed a century and a hal ago.The issue o water conservation is only now coming into ocus,and this article is meant to sound the alarm or water conserva-tion and to get out the message that there is much work to bedone by motivated scientists beyond orecasting our doom. CE

Matthys Levy,p.e., f.asce, is the chairman emeritus o Weid-linger Associates, o New York City. This article is based on a pa-

per that appeared in the proceedings o the iass (International As-sociation or Shell and Spatial Structures) Symposium 2009, whichwas held last October in Spain at the Universidad Politcnica de

Seventy percent o the earths

surace is covered with water,

and water is the key to our de-

velopment and our survival.

Scientists have recognized or a long time that billions o peopledo not have access to reshwater or drinking and sanitation.


7/7

Copyright of Civil Engineering (08857024) is the property of American Society of Civil Engineers and its

content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's

express written permission. However, users may print, download, or email articles for individual use.