Fog on the brine - Fog-catching systemsfor arid landsby Cristobal Pinche and Loren Ruiz

Along Peru's coastline, rain is a rarity, but fog isnever far away. For ten years, a team ofengineers developed a system to capture thisfree water supply. Did they succeed - and whostood to benefit?

Figure I. The Peruvian coastline northand south of Lima where lomas formsbetween rivers.

not being met; those in low-incomesettlements, for example, have to relyon poor-quality water sold from trucks.

10LS

Lomas in Lima-Peru(after aka y Ogawa, (:31984)

12LS

10LS

Inappropriate water-resource manage-ment has caused rapid deteriorationof the lomas vegetation and pollutionof the rivers; severe droughts everyfew years compound the problem.Traditional water supplies are inade-quate for a population which growsby 3 per cent every year. Currently,only 15.3 per cent of the total waterresources are used.

Tackling water scarcityLarge-scale projects The Governmentof Peru has poured money into largeprojects for the people of Lima, itherural poor. These are long-termschemes, taking around 30 years tocomplete. The people's daily needs are

PERU'S COASTLINE IS almost totaldesert, with only lOmm of rainfall peryear. A thick belt of fog covers the areafrom April to November. It arises fromthe cold, northerly, flowing current,and south-westerly winds continuallyblow the fog masses over the land.These rise over the coastal hills andmaintain a band of fog measuringbetween 600 and 800m, enablinglomas (coastal hill) areas to form,where plants and animal have evolvedto absorb the fog. This article looksspecifically at the area of coastline tothe north and south of Lima, wherelomas vegetation forms frequentlybetween the rivers (see Figure 1).

Seven million people live inLima, and most of them are poor.

People collect water - probably of poor quality -from a battered truck in one of Lima's many crowded slum areas.

4 WATERLINES VOL. 14 NO.4 APRIL 1996

5 metres-----j

altitude. The planners then assess thepotential amount of water that can be'caught' each day, and how manycatchers are needed. FinaIly, the qualityof the water must be tested, both at theinitial catching stage, and in storage.The materials must be cheap, andavailable 10caIly.

Initially, one 'trial-run' fog catcher,measuring 1m2 is put into position. If itworks, stage 2 goes into action, with upto 20 m2 catchers. By the final projectstage, as many as 300 may be incorpo-rated.• Maintenance To prevent mossclogging up the holes in the mesh, thecatchers must be cleaned at least once ayear. The storage tank should be keptclean and, where possible, covered, toprevent birds fouling the water.

Evaluating fog waterThe success or failure of the systemcan only be assessed if careful recordsare kept for at least a year. To measurefog water, the daily volume of water inthe container must be recorded as litresof water per m2 of mesh per day(I/m2/d).

Evaporation from the storage tank isnegligible during fog periods. Thepurity of the water should be testedevery month especially if it is to beused for drinking.

per year, and when it occurs, must betaken into account, together with thearea's geographical position, slope, and

Fogwater being collected in a mining area 250km south of Lima. Pollution hasaffected the natural colour of the lomas, and the fogwater shows a highconcentration of iron. It can be purified by filtration.

Figure 2. A typical fog-catcher system.

The fog-catching system• First principles The fog dropletscoIl ide with a mesh, build up intolarger drops, and coIlect in a PVC gut-ter where they run down a pipe into astorage tank or container .• Design The simplest fog catcheris a m2 of green polypropylenemosquitero (mosquito) mesh with10mm-diameter holes - any largerand the droplets wiIl faIl through. Thecatcher is fixed to a treated tree trunk,and faces the prevailing winds. Thetree trunk is supported by wire guysfixed into the rocky ground. The wateris coIlected in a PVC gutter whichleads to a 4m3 reservoir, iIlustrated inFigure 2. This method will average5.57 litres of water per day; a collec-tion of fog catchers can provide suffi-cient water for a community. The sizeof the catcher varies from 1 to 4mhigh, and between 5 and 30m long.• Installation Weather conditions, suchas wind direction, the amount of fog

An appropriate initiative Over the last Idecade, the idea of catching fog hasbeen explored as a short-term, water- I

supply solution. Sufficient, good-qual-ity water can be coIlected, usingappropriate, smaIl-scale technology.To pursue this further, in 1990 Grupode Trabajo Nieblas (GTN), or 'FogWorking Group', was set up by theauthors and four other six professionalengineers and planners.

WATERLINES VOL. 14 NO.4 APRIL 1996 5

Llanavilla Farmers' Communityto supply water to small rural set-tlements. The 'experimental' fogcatcher produced 5.57 litres perday - a good result - so twobigger fog catchers wereinstalled, giving a total area of80m2. The women were able toirrigate their land and grow veg-etables. Atocongo has becomeapilot project of fog-water man-agement for small coastal com-munities (see Figure 3 below).

350 m.a.s.!· and 105km north ofLima, was the site of the second fog-catching project, in 1992 . The mainobjective was to regenerate a deterio-rating lomas oasis. ECCO (Ecologyand Conservation) provided funding-for GTN to carry out the work.Five fog catchers were installed,producing 10 000 lid. The betterresult, proportionately, was a resultof more fog.

• Atocongo. In Atocongo, 25km southof Lima, and 252 m.a.s.!, a mothers'association was working with the

Trials

Costs and fundingAn effective fog-catcher system,incorporating 1000m2 of mesh,costs US$14 000. For this, com-munities can expect to collect 20000 lid over a ten-year period,

A fog catcher installed in La Molina in 1991. It is one of a group of 19 which provides with maintenance carried outwater for the stafJand pupils of the high school below, near an urban area. once a year.

Up to now, fog-catcher systemshave been funded mainly by out-side agencies. If the initial system

is judged successful, private organiza-tions, such as schools, may be preparedto pay for the full system. Otherwise,other agencies should be approached.

In areas like Atocongo, the watersupplied by the government costsUS$2 per 1000 litres, while the sameamount of trucked-in water costs $1.5.Fog-catcher systems can produce 1000litres for $1 are is, therefore, very com-petitive .

The system should last for 10 to 15years. With a small-scale system, it is

• UI Molina. The first project was car-ried out in 1991, in a rocky area atLa Molina, 790 m.a.s.1 (metres abovesea level), 15km south of Lima. Thiswas specifically to provide sufficientwater for a high-school garden. Ini-tially, two catchers were installedand, once they had proved success-ful, the school decided to invest in ascheme incorporating 19 fog catch-ers. The result was 12 000 litres ofwater per day.

• Lachay. Lachay National Reserve,

\

Crops:maize and sweet

potato

------.-- -"- -..•..

ill

'-'\.Fog

Livestock

~ -.. ....•Fog catcher system

Domestic animals

~r-#~o1:~

......---'- ..--,-.....•....... __ ._~--,

Fif<ure3. Grupo de Trabajo Nieblas' proposal for sustainable fogwater management in Peru.

6 WATERLINES VOL. 14 NO.4 APRIL 1996

Rearing pigs with fog water from the Atocongoproject. The fog catchers can just be seen onthe hilltop (above). The mothers' associationhelped the Llanavilla farmers to establishsmall horticultural plots with crops such aspotatoes and maize (right).

essential that the users, such as theL1anavilla farmers, can take over themaintenance.

be placed around the crops atleast and, ideally, around the wholeproject.

the coastal areas of Chile's AtacamaDesert, lower California, Mexico, N.W.Australia, Western Sahara, Morocco,Namibia, Somalia, Oman, and Yemen.

ProblemsFog-catching systems are not inde-structible. They are sometimes vandal-ized and the materials sold off. Thiscan only be prevented by strengtheningthe construction, and applying securitymeasures; security fencing would bevery expensive.

Goats pose another challenge: theydevour both the natural vegetation andthe crops being irrigated by the fog-catcher system. Initially, fences should

The future is foggyThe fog-catcher system has proveditself to be an appropriate, small-scalemethod of obtaining water in the poorrural areas along the coast of Peru.Experience shows that the water isgood quality and, therefore, can beused for drinking, horticulture, andlivestock. With external funding andadequate community management thefog-catching will benefit not only thepeople living near Lima, but could beeffectively replicated in such areas as

Cristobal Pillelll? \\'orks ill water supply .IiJrcoastal rural com/llullities. III 1<;<;4he ren'iI·,'d amedal for the h,'st lIatiollal research ill

technological illllol'ation /991-3. Lort'n Rlli~ i.l· ageographical engineer \,'ho \\'Ork"d forSENAMHI for ji\'e years. COllttlct the/ll 110th at:Grupo de Trahajo Niehlas (GTN), AparttldoPostal 055 - SM P - Lima 31, Peru.

WATER

wellsupply

Table 1. Locations and yields of fog water along the Peruviancoastline

Fog as a water resourceA small fog catcher was designed: a plastic mesh held up towards the prevail-ing winds by a post, a PVC gutter to collect the water, and a hose connected toa reservoir.

The experiments shown in Table I proved that, under specific geographicaland meteorological conditions, fog could provide between 1.7 and 32 litres ofwater per m2 mesh exposure per day (I/m2/d).

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Yield(l/m2/d)

7.8312.901.728.467.573.604.403.305.57

Period

Apr-Oct. '84Jun-Oct.'84May-Aug.'88Jan. '88 - Jan. '89Jul-Dec. '90Nov. '90Nov. '91Nov-Dec.'92Nov.'92 - May '93

Altitude data(m.a.s.l)

450350650530435790920765535

Place

L* PasamayoL* LachayL* AtiquipaC* CampanaC* OraraC* La MolinaL* MarconaL* TacnaL* Atocongo

Key - L *: Lomas G*: HillThe results were technically successful, although most of the experiments

lasted only a few months. No significant differences in fog-water yieldresulted from using the Chilean plastic mesh racshell instead of Peru'smosquitero mesh.

WATERLINES VOL. 14 NO.4 APRIL 1996 7