Eight Principles of Rainwater Harvesting

8/13/2019 Eight Principles of Rainwater Harvesting

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ight Principles for Successfulainwater HarvestingLancaster

INTEREST IN WATER HARVESTING AROSEfrom a desire both to reduce my cost of living and tobe part of the solution rather than the problem in myrt city of Tucson, Arizona. One of Tucson's biggestlems is mismanagement of water resources, pulling moreyear from the water table than nature can replace. This is a

tice that has dried out the Santa Cruz river, killed countlesss and wens, and severely depleted available groundwaterurces. '

iving in the desert-and as the planet heats up, deserts arending-has put a special emphasis on water harvesting forbut it's a valuable strategy for non-desert environments, too.

ater harvesting is effective for reducing or preventingon and downstream flooding while improving stormwater'ity. Thus, Portland and Seattle have embraced water-csting to protect salmon populations, and Maryland is doingame to protect the Chesapeake Bay. And anywhere in thed, water harvesting is a smart strategy for helping to rechargendwater tables. springs, wells, and rivers.

Back in 1994, my brother Rodd was also interested in waterharvesting, but as long as we were both renting, all we could dowas read up on the subject. At the time, we were both selfemployed, making what the government considers povertywages. No bank would touch us. On our own, neither of us could'afford to purchase a home, but together, it was feasible. (It helpedthat the house we wound up purchasing was about to becondemned.) We did 95% of the renovation work ourselves andused mainly salvaged materials.

Twelve years later, our property value has shot through theroof. The integrated water-harvesting techniques Rodd and Ilearned and implemented on this once-barren urban lot havetransformed it into an oasis in the desert, with temperaturesranging an average ten degrees lower than our neighbors'. Ourland produces 15-25% of our food, which includes organic,homegrown fruits, nuts, vegetables, eggs, honey, and mes


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In the course of creating a sustainable oasis here in Tucson,Rodd and I arrived at eight basic principles that anyone can use toimplement successful rainwater harvesting of their own.Principle : Begin with long and thoughtfulobservation

Right after we bought the house, monsoon rains poured fromthe sky. Rodd and I got to lear.n 'Yhere.runoff pooled against thehouse and how the bulk of the rain ran off our site into the street.We mapped these observations and others, including noise,headlights, and pollution from the street: where we wantedplivacy; where we needed shade; and where we needed toenhance winter solar exposure. Wherever you direct rainwater,you will be nurturing plant life, so take the time to ensure thatthis vegetation is part of your overall plan.

Next, calculate the rainwater resources available within yoursite's watershed. For us, that area included not only the 12inches of annual rainfall on our roof and 1 8th acre property. butthe 20-foot wide public right-of-way adjoining our propelty, thesection of street draining past the right-of-way, and the runofffrom our neighbor's roof. (See Table) This totaled about 104,600gallons (397,000 liters) of rainwater in an average yearPrinciple 2: Start harvesting rain at the top ofyour watershed then work your way down

In most cases, the top of your watershed means the roof ofyour house. Our leaky asphalt roof was a mess, so we removed itand installed 26-gauge galvanized steel metal roofing instead,which harvests rainwater in a potable form. However, as long as

you're only harvesting rainwater for use ih landscape irrigation,this isn't a necessary step. (Rainwater harvested off aconventional asphalt roof can also be made safe for consumptionwith appropriate filtration.)

Take a look at your roof. Where do the gutters drain? Whereis rainfall currently being directed? This is where you shouldbegin with mulched water-harvesting basins and plantings (atleast ten feet from the building's foundation.) On our property,just under half of the roof runoff is directed to earthworks andfruit trees north of the house. The rest is directed to an aboveground cistern west of the garden along our property boundarytop of a two-foot (60 em) high earthen platform.

Living in the desert-and as the planetheats up deserts areexpanding has puta special emphasison water harvestingfor me...

Our cistern is a custom-modified new ferrocement septic tanbut a number of good alternatives exist. (See, Choosing a Tank.)We selected the location of our cistern to provide multiple

Brad s design captures rainwater from all surfaces tofeed a lush landscape abundant with food and micro climate enhancingvegetation and soil.

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Aferrocement cistern partially concealed by stone and vegetation stores rain watfrom the roof cools the landscape and provides privacy from neighbors.

functions. By placing it on the western boundary of our yard toshade out the hot afternoon sun, it creates a beneficialmicroclimate for our garden. By acting as part of the propertyline, it provides a privacy screen from a peering neighbor. Andby placing the cistern on an elevated platform, water can flow bygravity from the tank to the garden.

Whatever type of cistern you choose, locating your gardennearby will keep hose length to a minimum (25 ft. ideal) Thiswill reduce water-pr~ssure loss to surface-friction inside the hoseand make watering with rainwater aconvenience. (Your plants will love it too )Principle : :4lways plan anoverflow route and manageoverflow s resource

Eventually, all water-harvesting systemswill meet a storm that exceeds their capacity,so don't get taken by surprise. All rainwaterharvesting structures should be managed sothey can overflow in a beneficial. rather thandestructive way.

In that spirit, overflow from our backyardcistern is directed via a four-inch diameterpipe to a series of adjoining mulch basins thatpassively irrigate a citrus tree and our garden.In addition, all of our sunken earthworks haveoverflow spillways. Typically, one earthwork.overflows to another and another, until all arefull and then, if needed, the lowest basin can'spil to a natural drainage-or, in a typical citycontext, the street.

Your goal should be to harvest the rain.but never get flooded by it. This is key.4 Start with small simple strategies: harvestthe rain s close s possible to where it falls

When people think of rainwater harvesting, cisterns and tanksusually spring to mind. But the water collected from the roof istypically much less than what's falling on your whole property.Simple earthworks, such as basins, terraces, contour berms, andcheck dams will harvest the rain where it falls on the land.

The earthworks Rodd and I created collect most of our rain.We dug flat-bottomed basins throughout our watershed, andmulched them deeply (about four inches)-starting at the highestpoints of the yard and working down. Overflow was directedfrom the upper to the lower basins.5 Spread slow and infiltrate flowing waterinto the soil

Cisterns, along with mulched vegetation and overflow routes,will effectively transform erosive runoff from heavy rainfall intoa calm, productive resource, while reducing losses to evaporationand downstream flooding.

Raised pathways and gathering areas are also a great strategfor spreading water through the landscape. This pattern of higand dry regions that drain to adjoining basins kept sunken amoist will help to define those areas through vegetation whilespreading and sinking the flow of water. (This also helps keepoff walkways and driveways in colder regions.) At our place, wuse earthworks to redirect the runoff that used to pool againsthouse to planting areas ten feet or more away from the buildingfoundation.

6 Maximize living and organic groundcoverAll your basins and other earthworks should be well mulche

and planted. This creates a living sponge effect that will useharvested water to create food and beauty in your surroundinglandscape while steadily improving the soil's ability to inftltratand hold water due to the vast network of growing roots andbeneficial microorganisms.

Groundcover is equally important in helping to ensure that,your enthusiasm for harvesting rainwater, you don't wind upcreating a haven for mosquitoes. Mosquitoes need three days ostanding water to transform from eggs to adults. Basins typicalallow water to infiltrate below the soil surface within one hour.

Take a hike in the unmanaged natural areas near your hornedetermine what native vegetation would be best to plant withinbeside your earthworks. In the wild, you'll notice which plantsgrow naturally in low spots-they can be planted in your basinWild plants preferring better drainage can be planted beside, bnot within earthworks.

Blue paloverdes, velvet mesquite, chuparosa, oreganHlo, andesert lavender are natives found along the ephemeral washesour area of Tucson that we plant within our earthworks.

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Produce from the rain fed landscape provides additional incometo the household and makes good neighbors7 Maximize beneficial relationships andefficiency by stacking functions. 11

As mentioned previously, water-harvesting strategies offermaximum benefits when they're integrated into a comprehensiveoverall site plan. We focused on locating the earthworks wherewe wanted to stack functions with multi-use vegetation.

Through rainwater harvesting earthworks, we've nurtured asolar arc of deciduous trees on the east, north, and west sides ofour home that cool us in the summer, but let in the free light andwarmth of the sun in winter. A living fence of native plants alongthe property line (along with an existing citrus tree) form part of asun trap. This suntrap shades our garden from the afternoon sun,controls stormwater on-site, and enhances habitat for nativesongbirds and butterflies.The Big Picture

Within our generative landscape, rainwater has become ourprimary water source, greywater our secondary water source, andmunicipal groundwater a strictly and infrequently usedsupplemental source (meeting no more than 5% of our outdoorwater needs). Most of our established landscape has even becomeregenerative as it thrives on rainwater alone.Our household consumes less than 20,000 gallons ofmunicipal water annually, with over 90% of that being recycledin the landscape as greywater. Additionally, we harvest andinfiltrate over-lOO,OOOgallons of rain and runoff into the soil ofour site (and, by extension, the community's watershed) over thecourse of a year.

As a household, we're shifting more and more to living withinour rainwater budget: one of the natural limits of our localenvironment. As a result, we're enriching the land, growing up to25~7cof our food on site, creating a beautiful home and

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neighborhood environment-and giving back more than we taThe further we go, the easier and more fun it gets, which

brings us to the eighth and last principle: Continually assess and improve your syste

Three years ago, Rodd and I set up an outdoor shower so tbather could either use pressurized municipal water at the shohead or cistern water disttibuted from a shower bucket on a hWe have also created a solar-powered greywater laundromat our backyard (used by seven neighboting households), andreduced the impermeable surface of our yard by replacing theasphalt driveway with lush plantings and earthworks.

Choosing Rainwater CisternOur cistern has a 1,200-gallon (4,560-liter)capacity. We selected this size after calculating the

average annual roof runoff, assessing our waterneeds, and determining the resources we wanted tocommit to the system. We opted for a precastconcrete septic tank for a number of reasons, butprimarily because it was affordable as well as aworkable size and shape for our space (five feetwide, six feet tall, ten. feet long).Our septic tank was custom-made for use as acistern, and further reinforced for above-groundinstallation. The cost back in 1996 was 600, whichincluded delivery and placement. Itfs been workinggreat ever since.Other options for pre-manufactured cisternsinclude light-proof, dark green or black polyurethaneplastic, corrugated metal, and fiberglass. Seewww.watertanks.com for options and look in theyellow pages under tanks for local suppliers.Calculating Your Rainwater

To calculate the volume of rain falling in anaverage year on a specific surface such as yourroof, yard, or neighborhood, use the followingcalculation:

CATCHMENT AREA (in square feet) multiplied bythe AVERAGE ANNUAL RAINFALL (in feet)multiplied by 7.48 (to convert cubic feet to gallons)equals the TOTAL RAINWATER FALLING ONTHAT CATCHMENT IN AN AVERAGE YEAR

or, alternately:CATCHMENT AREA (ft2) x RAINFALL in/yr x 518

= TOTAL AVAILABLE RAINWATER (gal/year)


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One of our most rewarding recent projects has been workingwith our neighbors and the city to replace 26% of the pavementfrom the street intersection with a water-harvesting traffic circleplanted with native vegetation. We also implemented a systemthat captures street runoff in mulched curbside basins to grow agreenbelt of trees along the street and sidewalk, so the street nowpassively irrigates the trees.

As a result, our neighborhood--once the victim of urbanblight-is now one of the greenest and most livable areas of thecity.

My advice to anyone who wants to get started living moresustainably is to start with rainwater harvesting. Start at the top.Start small. But above all-start ~Brad Lancaster (www.HarvestingRaiinvater.com) is apermaculture consultant based in Tucson. His new bookRainwater Harvesting for Drylands, Volume I: GuidingPrinciples to Welcome Rai.1J.nto your Life and Landscape waspublished in 2006 by Rainsource Press. Volume II will bereleased in thefall of 2007.

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Rainwater collection system: bu.cke puUeylweighted gutter arrangement di~erts initial flush of dirty waler,anowing onlyclean water to be stored in large tank. Shower cut-off on right side initiates water conservation measures when tank dropsbelow h lf fun. IlJM,t.ra.'i< Silvia Panons, adapted/rom p.l06, Pennaculture; A Pradlul Guide for a SusWn.ble Future

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Eight Principles of Rainwater Harvesting

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