Rainwater Harvesting for Drylands, Volume I
by Doug Pushard
Rainwater Harvesting for Drylands, Volume 1, is a recently published book by Brad Lancaster. It is a practical guide to holistic rainwater management; featuring not just information on rainwater harvesting, but also covers site planning, water conservation strategies and much, much more. The 181 page manual is jammed packed with examples, stories, data and illustrations.
I highly recommend this guidebook for anyone serious about living a more sustainable lifestyle or just to get to know someone that is.
REAL LIFE EXAMPLE - AN INTEGRATED URBAN RAINWATER HARVESTING RETROFIT
Right after Rodd, my brother, and I bought our east-west-ori¬ented, fixer-upper of a house, the summer rains poured from the sky. We saw where the roof leaked, where runoff pooled against the house, and how the bulk of the rain ran off our site into the street. We mapped these observations, and others (noise, head¬lights, and pollution coming from street; where we wanted privacy; where we needed shade; and where we needed to enhance solar exposure to south-facing windows, etc.) on a plan we made of the property. More observations were added as we spent more time on the site, and we continue to do so today. Many hours were also spent imagining how we could improve the site with earthworks, cisterns, plantings, solar technologies, passive heating and cooling strate¬gies, and more. We brainstormed how such improve¬ments could be integrated with existing on-site needs and resources for maximum beneficial effect.
Expanding on this practice of long and thoughtful observation we calculated the rainwater resources we could harvest within our site's watershed. In an aver¬age year of 12 inches (304 mm) of rain, about 6,000 gallons (22,800 liters) runs off our 990 square foot (91 square meter) roof, while an additional 38,000 gallons (143,600:liters) falls on our 132 X 46-foot yard. Just outside our fence 29,000 gallons (109,600 liters) of rain falls on the 20-foot (6-meter) wide public right-of-way on the south and east sides of our corner lot, while another 3,000 gallons (113,400 liters) per year can be harvested off the adjoining resi¬¬dential streets. In addition, a 270 square-foot section of our neighbor's roof 1,600 gallons of runoff into our yard. This totaled about 104,600 gallons (397,000 liters) of rain!
We started harvesting roof runoff at the top of our watershed - the roof. We removed a leaky asphalt roof and hauled the toxic pile of old asphalt to the dump - we didn't know then that asphalt could be recycled. We expanded the roof area by calculating and installing an extension of our roof overhang just long enough for more summer shade, while still short enough to allow the free heat and light of the winter sun to enter our south-facing windows. However, we forgot to include the width of the gutter (we'd later install) when determining the ideal length of roof overhang so now (with the gutter installed) a bit more of the winter sun is shaded than would be ideal. Then we installed 26-gauge galvanized steel metal roofing that should last for the rest of our lives. Metal was selected for its durability, ease of installation, strength, and, above all else, its non-toxic nature, allowing for more uses of its higher quality runoff water.
We focused the earthworks and the water where we wanted to stack functions with multi-use vegetation, forming a solar arc of cooling shade trees on the east, north, and west sides of our home; along the property line to create a living fence of native plants, beauty, and wildlife habitat; and around an existing citrus tree that would form part of a sun trap shading a future organic garden from the afternoon sun. The 200-square-foot (18-m2) garden of sunken, mulched basins was placed just south of the home since the low-growing veggies would not block winter sun from the south-facing windows. But first we had to remove a palm tree that was blocking the winter sun. With the palm removed we had ideal winter solar exposure for winter gardening (the most productive and least water consumptive season in Tucson); passive solar heating of our home and water, and the potential to put solar panels on our roof to produce our own electricity. Between the garden and home we built a sparse trellis on which we grow winter deciduous vines for summer shade. In winter we cut back the vines to let the sun shine in. More summer shade is created with a ramada and trees south of the home and garden, yet all are far enough to the south to maintain the winter's beneficial solar gain where we want it. The sun is now our home's main source of heat, powers our solar oven, helps grow an abundance of winter greens, and with the installation of solar panels and a solar hot water heater, is our sole source of electricity and heat for water. Our home's east-west orientation, extended overhang, solar arc of shading vegetation, and other passive strategies such as nighttime ventilation are our main source of cooling. Electric bills no longer exist, and our gas and water bills are for little more than the service charge, since consumption is negligible to nonexistent.
Along with sun and water, we also harvest the power of gravity. We guttered the section of the neighbor's roof draining onto our property to redirect the runoff to the high point of our yard where the citrus tree is located. Water used to drain away from the tree, now it passively drains to it. Gutters and the pitch of our roof direct just under half of the roof’s runoff to earthworks and fruit trees north of the house, and the rest is directed to an above-ground cistern installed west of the garden along our property boundary on top of a 2-foot (60 cm) high earthen platform. The cistern, coupled with the citrus tree, provides multiple functions by enhancing the beneficial microclimate of a sun trap for the garden, acting as part of the property fence, and provided a privacy screen from a peering neighbor. By elevating the cistern we can use gravity to move water from the roofs gutter to the tank, and from the tank to the garden. Gravity pressure is low, so having the garden right next to the cistern keeps our hose length to just 25 feet (7.6 m), reducing pressure-reducing friction inside the hose and making cistern water convenient to use.
The cistern has a 1,200-gallon (4,560 liter) capacity. We selected this size after calculating the average annual roof runoff, assessing our water needs, and determining the resources we wanted to commit to the system. We knew that we did not have enough runoff to meet both domestic water needs and garden and landscape irrigation needs, so we implemented conservation strategies such as installing a composting toilet, installing a greywater system recycling all the water going down our drains within the landscape, and replacing some water-hungry exotic plants with drought-tolerant natives. This helped a lot, but we still did not have enough roof runoff to meet all our water needs. So we committed to using the roof water as part of an experimental start-up cistern system just for irrigation and supplemental outdoor water use. Wanting to keep the tank affordable and under a 1,500-gallon (5,700-liter) capacity, we decided to store the volume of water from a large 3-inch (75-mm) rainfall event that would drain off the 650-square-foot (58-square-meter) section of roof sloping toward the garden. This meant we needed a 1,200-gallon (4,560-liter) capacity tank. Knowing how large a tank we needed, the next question was: What kind of tank did we want to use? Locally available pre-manufactured tanks included metal, plastic, fiberglass, or precast septic tanks. We also had the option of making our own ferrocement tank, or culvert cistern.
We opted for a precast septic tank for the following reasons:
1. They are easy to install, look great and can be a great addition to a rainwater harvesting system. In terms of locally available, ready-made tanks, it was our cheapest option for the volume we needed.
2. The 5-foot-tall, 10-foot-long, 4-foot-wide septic tank was right for our space. We created an elevated pad to improve gravity-fed distribution of the stored water, but because the base of the house was considerably lower than the planned pad we could not have a tank taller than 6.5 feet or the top of the rank would be higher than the drip edge of our roof, eliminating the possibility of gravity-fed inflow into the tank.
3. We wanted to use the tank as part of our western property line fence, privacy screen, and western sunscreen. The 10-foot length of the tank worked well for these uses.
4. Concrete is relatively fireproof material so the tank could act as a firebreak in the event the neighbor to the west sparked a fire.
5. There was a frost-sensitive citrus tree just south of where we wanted to place the tank, so the mass of the tank could help moderate temperature fluctuations and create a slightly warmer microclimate for the tree on winter nights.
6. We wanted to play with the idea of using a septic tank as a cistern to get to know its faults and favors. We figured it could be a viable ready-made system we might end up installing for clients.
The septic rank was custom made for use as a cistern, and further reinforced for above-ground installation. The cost back then was $600, which included delivery and placement.
All has worked great, with 95% of our garden's irrigation water now provided from harvested rainfall.
I no longer feel that Rodd and I are living entirely out of balance with the water resources of our dryland environment. We no longer get all our water from overdrafted groundwater and water imported from distant watersheds. Instead we are shifting more and more to living within our rainwater budget and the natural limits of our local environment. We are not living entirely off rainfall, but we are reducing our degenerative dependence on our community's diminishing groundwater and imported Colorado River water.
Within our generative landscape, rainwater has become our primary water source, greywater has become our secondary water source, and groundwater is strictly an infrequently used supplemental source. Most of our established landscape has even become regenerative by thriving on rainwater alone. The further we go the easier and more fun it gets. It has become a game where we use our creativity to get more and more out of what we find within the natural limits of our site's watershed, while giving back more than we take. In that spirit, we set up the outdoor shower so the bather could either use pressurized municipal water at the shower head or cistern water distributed from a shower bucket hung from a hook. All shower and household greywater goes directly to the landscape via subsurface bucket drains (see the greywater chapter in Rainwater Harvesting for Drylands, volume 2). Other strategies have included creating a greywater laundromat in our backyard, reducing impermeable hardscape by replacing our asphalt driveway with lush plantings within infiltration basins, working with neighbors and the city to replace 26% of the pavement from the corner intersection with a traffic circle planted with native vegetation, and harvesting street runoff within curbside mulched basins to grow a greenbelt of street trees along the public right-of-ways (see the chapter "Reducing Hardscape and Creating Permeable Paving" in volume 2). As a result the landscape is growing and producing in abundance, and our utilities and cost of living are steadily dropping-not the water table. This was recently recognized when we won "First Place Homeowner Landscape under $10,000," "Best Water Harvesting," and the "J.D. DiMeglio Artistry in Landscaping" awards in the 2005 Arizona Department of Water Resources/Tohono Chul Park Xeriscape Contest.
We are increasing our push to improve the efficiency and convenience of our system to make rainwater the primary water source within our home as well. We continually reassess what we have done, and have expanded or modified basins where needed, replaced or relocated poorly selected or planted vegetation, and made our cistern and greywater systems more accessible and convenient to use. We are also planning an outdoor kitchen area with a new covered porch and cistern so we can experiment with rainwater for drinking, cooking, cleaning, and more.
Other people are developing their systems and experience in much the same way. We help, teach, and encourage each other, and the movement grows as the practice, examples, and knowledge within our backyard microwatersheds begin to overflow and nourish the greater community watershed. Start at the top. Start small. Start.