Roof-to-Garden: How to Irrigate with Rainwater
By Brian Barth
The average American household uses about 320 gallons of water per day, a third for irrigation and other outdoor uses. Collecting the water flowing down your downspouts in rainstorms so you can use it to irrigate in dry periods is often touted as a simple way to cut back. But setting up a functional rainwater irrigation system—beyond the ubiquitous 55-gallon barrels under the downspout, which won't irrigate much more than a flower bed or two—is a fairly complicated DIY project.
If you live in a townhouse or apartment with a tiny yard, one of those store-bought barrels will probably do the trick. In that case, there's not much to know—most come with instructions and all the hardware you need. But if you're planning a more ambitious project consider the following pointers before getting started. Before you begin, make sure that rain harvesting is legal in your area.
Calculating Your Water Budget
To give you an idea of how much water you have at your disposal for irrigation, here is a simple equation for figuring out how many gallons your roof sheds when it rains:
roof size (in square feet) X annual rainfall (in inches) X .6
There are rain tank calculators online so you don't have to do the math, but here is an example. If you lived in a modest 20' by 30' house (measure roof size as the length times the width of the house) in a modestly wet region with 40 inches of annual rainfall, that's (20 X 30) X 40 X .6 = 14,400 gallons. Here's a handy web tool to find out how much rainfall you get in your area each year.
In a very dry climate where most of the rain falls in winter, as is the case along most of the West Coast, you could easily use that much irrigation water in spring, summer, and fall—and much more, depending on the size of your garden. But if you live an area that typically gets rainfall throughout the warm parts of the year (plants rarely need irrigation in the winter), how much water you can catch in a year is not as relevant as how much you'll need during a summer dry spell.
Irrigation needs vary considerably depending on climate, shade, soil type, and vegetation type, but this equation will give you a rough idea of your garden's water demand:
area to be irrigated (in square feet) X maximum number of weeks between major summer rainstorms X .5
If you have a modest 30' by 30' yard and want to have enough water to irrigate for a month-long dry spell (light rain doesn't count—at least one inch of precipitation is needed to saturate the soil in dry conditions), which is not uncommon in most of the country (except in the Southwest and on the West Coast, where dry spells last many months), that's (30 X 30) X 4 X .5 = 1800 gallons.
In arid regions like Los Angeles or Phoenix, where eight months can pass between major rainstorms, the equation looks like this (30 X 30) X 32 X .5 = 14,400 gallons. So you can see why it makes sense to focus on how much you can actually collect from your roof in such climates, rather than how much you can use.
Sizing the System
The size of your rainwater catchment system may ultimately depend on your budget and how much space you are willing to dedicate to it. Rainwater is typically stored in polyethylene (plastic) tanks, which can be purchased at farm supply stores or shipped from online suppliers like The Tank Depot and Plastic-Mart. Most tanks cost roughly 50 cents per gallon of storage, though the larger sizes are often much pricier.
Larger tanks are also very unwieldy to install and are an eyesore in the landscape. A 15,000-gallon tank, for example, is roughly 12 feet in diameter by 18 feet tall and weighs more than 3000 pounds. Most people who want to store that much water opt for three 5000-gallon tanks, which are roughly 10 feet in diameter by 10 feet tall and weigh 800 pounds—light enough for a few strong people to push around and maneuver into place. Most folks in urban areas prefer to stick with 1000-gallon size tanks (6 feet in diameter by 6 feet tall and around 200 pounds), or smaller.
Finding a Location
Tanks are typically positioned at or near a downspout so the water can be funneled in directly. Rain tanks aren't pretty, so you'll probably want to situate them out of sight, or conceal them with a trellis, shrubbery, or other enclosure.
One option to prevent an eyesore next to your house is to collect water in small barrels at the downspouts, and then pump the water into a large central tank located away from the house. Another option is to bury rain tanks near the house—in this case, they'd be considered cisterns—and let the water flow from the downspouts through buried drain pipes and into the tanks. Typical polyethylene tanks may not be used underground, though specially designed underground tanks are available (they cost two to three times as much as aboveground tanks, however).
Of course, you can also collect water from the roofs of barns, sheds, and other outbuildings, which may offer better opportunities to conceal the tank than positioning it next to your house. Keep in mind that each downspout only drains a portion of the roof, so match tank size to roof area accordingly. Where you have several downspouts along one side of a house or outbuilding, it's possible to combine the flows into a single tank.
Rain tanks are extremely heavy when full of water (water weighs about 8 pounds per gallon), so you need to create a firm base for them to rest on; otherwise, the earth below may settle under the weight and cause the tank to shift.
First, remove the topsoil and then spread a 6-inch layer of gravel or granite fines to create a pad for the tank, grading the surface flat and smooth and tamping it (with a manual tamper for small areas, or a power tamper for large installations) to prevent the material from settling. Building codes typically require a 6-inch concrete slab to be poured as a base for tanks 5000 gallons in size and larger.
Next, you'll need to route the downspouts to the openings on top of their respective tanks. Simply cut into existing downspouts above the height of the tank and use a combination of "A" and "B" style elbows and lengths of downspout (a selection of gutter supplies is available at any building supply center) to reroute the downspout to the tank. Use a carpenter's level to ensure that horizontal sections of downspout are sloped "downstream" at a minimum ratio of ¼-inch per linear foot.
Here are a few recommended accessories to place between the top of the downspout and the opening of the tank:
- A self-cleaning filter to divert sticks, leaves, and other debris from the downspout.
- A tank screen to prevent smaller gutter debris from washing into the tank, and to keep mosquitoes and rodents out of the tank.
- A first flush diverter to divert the first bit of water from each rainfall, which may contain bacteria from dead insects, lizards, rodents, snakes and other critters that sometimes end up in gutters, as well as bird and animal droppings, chemical residues and fine particles from roofing materials, and anything else that might wash of your roof that an irrigation system is better off without.
All rain tanks have an overflow outlet near the top of the tank that should be connected by drain pipe to the drainage system that the downspout previously flowed into.
Connecting to the Irrigation System
Your irrigation system may be as simple as a hose connected to the valve at the bottom of the rain tank. Of course, this gravity-powered approach only works if the area you're irrigating is lower in elevation than the water level inside the tank.
Sprinklers and drip irrigation systems are likely to require a pump to provide sufficient water pressure unless the tank is significantly higher in elevation than the area to be irrigated. Each foot of elevation results in .43 pounds per square inch (psi) of water pressure. Drip systems generally require at least 15 psi (35 feet of elevation), while most sprinkler systems require at least 30 psi (70 feet of elevation).
There are a variety of pumps and pump accessories available to pressurize your irrigation system with water from a rain tank, but unless you have serious plumbing and electrical expertise, you're better off hiring an expert for this part. Setting up an effective pumping system depends on the specific context of your water storage and irrigation system; there are many technical details to be aware of to make sure you get the pressure you need, minimize electricity consumption, and avoid wearing out your (expensive) pumping equipment prematurely.
For automated irrigation systems, it's possible to tie the pump to the irrigation control box, so when each irrigation valve opens according to its schedule, the pump kicks on and provides water from the tank.
Reposted with permission from our media associate Modern Farmer.
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EcoWatch Daily Newsletter
By Mark Hertsgaard
What follows are not candidate endorsements. Rather, this nonpartisan guide aims to inform voters' choices, help journalists decide what races to follow, and explore what the 2020 elections could portend for climate action in the United States in 2021 and beyond.
Will the White House Turn Green?<p>Whether the White House changes hands is the most important climate question of the 2020 elections. President Donald Trump rejects climate science, is withdrawing the United States from the Paris Agreement, and has accelerated fossil fuel development. His climate policy seems to be, as he tweeted in January when rejecting a U.S. Army Corps of Engineers proposal to protect New York City from storm surges, "Get your mops and buckets ready."</p><p>Joe Biden, who started the 2020 campaign with a climate position so weak that activists gave it an "F," called Trump a "climate arsonist" during California's recent wildfires. Biden backs a $2 trillion plan to create millions of jobs while slashing emissions—a Green New Deal in all but name. Equally striking, his running mate, California Senator Kamala Harris, has endorsed phasing out fossil fuel production—a politically explosive scientific imperative.</p><p>The race will be decided in a handful of battleground states, five of which already face grave climate dangers: Florida (hurricanes and sea-level rise), North Carolina (ditto), Texas (storms and drought), Michigan (floods), and Arizona (heat waves and drought). <a href="https://climatecommunication.yale.edu/visualizations-data/ycom-us/" target="_blank">Public concern is rising</a> in these states, but will that concern translate into votes?</p>
Will Democrats Flip the Senate, and by Enough to Pass a Green New Deal?<p>With Democrats all but certain to maintain their majority in the U.S. House of Representatives, the Senate will determine whether a potential Biden administration can actually deliver climate progress. Democrats need to pick up three seats to flip the Senate if Biden wins, four if he doesn't. But since aggressive climate policy is shunned by some Democrats, notably Joe Manchin of coal-dependent West Virginia, Democrats probably need to gain five or six Senate seats to pass a Green New Deal.</p><p>Environmentalists, including the League of Conservation Voters, are targeting six Republicans who polls suggest are vulnerable.</p><ul><li>Steve Daines of Montana, who denies climate science</li><li>Martha McSally of Arizona</li><li>Thom Tillis of North Carolina</li><li>Susan Collins of Maine</li><li>Joni Ernst of Iowa (bankrolled by Charles Koch)</li><li>John James of Michigan (also a Koch beneficiary)</li></ul><p>Republican Senators are even at risk in conservative Kansas and Alaska. In both states, the Democratic candidates are physicians—not a bad credential amid a pandemic—who support climate action. In Kansas, Barbara Bollier faces an incumbent funded by Charles Koch. In Alaska, Al Gross urges a transition away from oil, though his openness to limited drilling in the Arctic National Wildlife Preserve dims his appeal to green groups. He faces incumbent Republican Dan Sullivan, who receives an 8 percent lifetime voting record from the League of Conservation Voters.</p>
Will Local and State Races Advance Climate Progress?<h4>THE CLIMATE HAWKS</h4><p>Under Democratic and Republican leadership alike, Washington has long been a graveyard for strong climate action. But governors can boost or block renewable energy; the Vermont and New Hampshire races are worth watching. Attorneys general can sue fossil fuel companies for lying about climate change; climate hawks are running for the top law enforcement seats in Montana and North Carolina. State legislatures can accelerate or delay climate progress, as the new Democratic majorities in Virginia have shown. Here, races to watch include Pennsylvania, North Carolina, and Colorado.</p><h4>THE CLIMATE POLICY MAKERS</h4><p>Perhaps the most powerful, and most overlooked, climate policy makers are public utility commissions. They control whether pipelines and other energy infrastructure gets built; they regulate whether electric utilities expand solar and energy efficiency or stick with the carbon-heavy status quo. Regulatory capture and outright corruption are not uncommon.</p><p>A prime example is Arizona, where a former two-term commissioner known as the godfather of solar in the state is seeking a comeback. Bill Mundell argues that since Arizona law permits utilities to contribute to commissioners' electoral campaigns, the companies can buy their own regulators. Which may explain why super-sunny Arizona has so little installed solar capacity.</p><p>In South Dakota, Remi Bald Eagle, a Native American U.S. Army veteran, seeks a seat on the South Dakota Public Utilities Commission, which rules on the Standing Rock oil pipeline. And in what <em>HuffPost</em> called "the most important environmental race in the country," Democrat Chrysta Castaneda, who favors phasing out oil production, is running for the Texas Railroad Commission, which despite its name decides what oil, gas, and electric companies in America's leading petro-state can build.</p>
Will the Influencers Usher in a Green New Era?<h4>THE UNCOUNTED</h4><p>The story that goes largely under-reported in every U.S. election is how few Americans vote. In 2016, some 90 million, <a href="https://www.pewresearch.org/politics/2018/08/09/an-examination-of-the-2016-electorate-based-on-validated-voters/" target="_blank" rel="noopener noreferrer">roughly four out of every 10 eligible voters</a>, did not cast a ballot. Attorney Nathaniel Stinnett claims that 10 million of these nonvoters nevertheless identify as environmentalists: They support green policies, even donate to activist groups; they just don't vote. Stinnett's <a href="https://www.environmentalvoter.org/" target="_blank" rel="noopener noreferrer">Environmental Voter Project</a> works to awaken this sleeping giant.</p><h4>THE SUNRISE MOVEMENT</h4><p>Meanwhile, the young climate activists of the <a href="http://www.sunrisemovement.org/" target="_blank" rel="noopener noreferrer">Sunrise Movement</a> are already winning elections with an unabashedly Green New Deal message. More than any other group, Sunrise pushed the Green New Deal into the national political conversation, helping Representative Alexandria Ocasio-Cortez and Senator Ed Markey draft the eponymous congressional resolution. In 2020, Sunrise has helped Green New Deal champions defeat centrists in Democratic primaries, with Markey dealing Representative Joe Kennedy Jr. the first defeat a Kennedy has ever suffered in a Massachusetts election. But can Sunrise also be successful against Republicans in the general elections this fall?</p><h4>THE STARPOWER</h4><p>And an intriguing wild card: celebrity firepower, grassroots activism, and big-bucks marketing have converged behind a campaign to get Latina mothers to vote climate in 2020. Latinos have long been the U.S. demographic most concerned about climate change. Now, <a href="https://votelikeamadre.com/" target="_blank" rel="noopener noreferrer">Vote Like A Madre</a> aims to get 5 million Latina mothers in Florida, Texas, and Arizona to the polls. Jennifer Lopez, Salma Hayak, and Lin-Manuel Miranda are urging mothers to make a "pinky promise" to vote for their kids' climate future in November. Turning out even a quarter of those 5 million voters, though no easy task, could swing the results in three states Trump must win to remain president, which brings us back to the first category, "Will the White House Turn Green?"</p>
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By Tony Carnie
South Africa is home to around 1,300 of the world's roughly 7,100 remaining cheetahs. It's also the only country in the world with significant cheetah population growth, thanks largely to a nongovernmental conservation project that depends on careful and intensive human management of small, fenced-in cheetah populations. Because most of the reserves are privately funded and properly fenced, the animals benefit from higher levels of security than in the increasingly thinly funded state reserves.
Vincent van der Merwe at a cheetah translocation. Endangered Wildlife Trust
Under Pressure<p>Cheetah populations elsewhere in Southern Africa have not prospered over the past 50 years. In Zimbabwe, cheetah numbers have crashed from 1,500 in 1975, to just 170 today. Botswana's cheetah population has held steady at around 1,500 over the same period, but illegal capture for captive breeding and conflicts with farmers and the growing human population are increasing. In Namibia, there were an estimated 3,000 cheetah in in 1975; roughly 1,400 remain today.</p><p>In contrast, South Africa's cheetah numbers have grown from about 500 in 1975 to nearly 1,300 today. Van der Merwe, who is also a Ph.D. student at the University of Cape Town's Institute for Communities and Wildlife in Africa (iCWild), says he's confident that South Africa will soon overtake Namibia and Botswana, largely because the majority of South African cheetahs are protected and managed behind fences, whereas most of the animals in the neighboring countries remain more vulnerable on mainly unfenced lands.</p><p>Wildlife researchers Florian Weise and colleagues have reported that private stock owners in Namibia still trap cheetahs mainly for translocation, but there are few public or private reserves large enough to contain them. Weise says that conservation efforts need to focus on improving tolerance toward cheetahs in commercial livestock and game farming areas to reduce indiscriminate trapping.</p><p>Van der Merwe says fences can be both a blessing and a curse. While these barriers prevent cheetahs and other wild animals from migrating naturally to breed and feed, they also protect cheetahs from the growing tide of threats from humanity and agriculture.</p><p>To simulate natural dispersion patterns that guard against inbreeding, the trust helps landowners swap their animals with other cheetah reserves elsewhere in the country. The South African metapopulation project has been so successful in boosting numbers that the trust is having to look beyond national boundaries to secure new translocation areas in Malawi, Zambia and Mozambique.</p><p>Cheetah translocations have been going on in South Africa since the mid-1960s, when the first unsuccessful attempts were made to move scores of these animals from Namibia. These relocations were mostly unsuccessful.</p>
Charli de Vos uses a VHF antenna to locate cheetahs in Phinda Game Reserve. Tony Carnie for Mongabay
Swinging for the Fences<p>But other wildlife conservation leaders have a different perspective on cheetah conservation strategy.</p><p>Gus Mills, a senior carnivore researcher retired in 2006 from SANParks, the agency that manages South Africa's national parks, after a career of more than 30 years in Kalahari and Kruger national parks. He says the focus should be on quality of living spaces rather than the quantity of cheetahs.</p><p>Mills, who was the founder of the Endangered Wildlife Trust's Carnivore Conservation Group in 1995, and who also spent six years after retirement studying cheetahs in the Kalahari, says it's more important to properly protect and, where possible, expand the size of existing protected areas.</p><p>He also advocates a triage approach to cheetah conservation, in which scarce funds and resources are focused on protecting cheetahs in formally protected areas, rather than diluting scarce resources in an attempt to try and save every single remaining cheetah population.</p><p>"People have an obsession with numbers. But I believe that it is more important to protect large landscape and habitats properly," Mills said.</p><p>He suggests that cheetahs enclosed within small reserves live in artificial conditions: "It's almost like glorified farming."</p><p>"In the long run we have to focus on consolidating formally protected areas," he added. "Africa's human population will double by 2050, so cheetah populations in unfenced areas will become unsustainable if they are eating people's livestock."</p>
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