Tuesday, April 9, 2013

SARE conference workshops: water cisterns

Tuesday morning: Water cisterns and rainwater collection
with guest speaker Billy Kniffen, Texas A&M University

Billy Kniffen, retired Texas AgriLife Extension Service agent, got a good laugh out of his audience early on, when he said: "I acknowledge that Alaska is bigger than Texas. That's hard to do." That admission out of the way, he went on to give a thorough review of rainwater collection and why it's important, not only in the Lone Star State but worldwide.
"When the well runs dry we will know the worth of water." —Ben Franklin
Billy Kniffen at the 2013 SARE conference during the afternoon session of a two-part all-day workshop on water conservation, rainwater catchment, and cistern installation. CES photo by Taylor Maida.
A major driver to current interest in rainwater catchment and water conservation is climate change and desertification. Kniffen showed how the continent over the Ogallala Aquifer is in drought—but so is Alaska, even though it may not feel like it. Alaska has wildly different climatic regions (Interior, Southeast, Arctic Coast, Aleutians, Southcentral) but looking at the overall temperature and precipitation over time, the state is showing a trend toward a drier, hotter climate.

Although the part of Texas where Kniffen is from can experience torrential rainfall in the space of an hour, on an annual basis it is drier than the Interior, which is itself just above desert-level precipitation (9-10 inches/year). Despite that, he and his family are able to live year-round off of collected rainwater.

Kniffen showed his audience a map of Alaska with the incredible variety of rainfall and precipitation in the state. Using the example of Fairbanks, he provided a chart of precipitation levels: April through September in rain, October through March in snowfall, which builds up to melt that can be captured.

Kniffen showed a photo of a petroglyph, a cloud dancer with stalk of corn. Over the tens of thousands of years of humans living in North America, he said, there have been many peoples and nations, but we don't know much about them—their civilizations have gone extinct.

Asked Kniffen, "Are we going to be extinct if we do not take care of our resources?"
"Water is the oil of the 21st century."—Andrew Liveris, chief executive, Dow, August 2008
Watersheds, the water cycle, and water supply

Institutions using collected rainwater are garnering good publicity as well as good use from the sustainability of it. Rainwater collection for fire departments!

Kniffen went on to talk about the difference in land before typical development and after:
  • In predevelopment, the evapotranspiration cycle from plants, where the plants take up water from the soil and breathe it out from their leaves, is uninterrupted. The soil has roots, compost, and humus to hold water and filter it. Leaves may catch rain before it hits the ground and it evaporates from there. Water slowly penetrates the ground, recharging the soil and aquifer.
  • In post development, the soil has been stripped away, there are no plants, nothing to prevent rain from striking the ground (leaves), nothing to slow the stormwater to allow deep infiltration to the soils below and recharge the local aquifer. Runoff then has to be managed and is typically mixed in with sewage systems and treated as waste.
Low-impact development mimics the predevelopment environment, relying on design that treats water as a valuable resource. Design principles that are crucial for moving from a stormwater paradigm to a rainwater paradigm include conservation and restoration, among others. 

What is a watershed? Simply put, water flows from the top of an area and moves down, shed through the landscape.

There are two methods to sustain water supply: increase supply, or reduce demand. The climate is not generally increasing the supply of fresh water, although eliminating use of fossil fuels, planting trees, and changing landscaping and city design could alleviate this. Conservation reduces demand, but restoration of the watershed to a more natural environment also conserves water. All rainfall is valuable. Vegetation plays an important part in filtering water on the landscape, trickling eventually into streams, to rivers.

Passive collection of water includes not just cisterns: spreader dams, stock tanks, ripping, berms, and basins also hold or delay water. There is also the effect of low impact development: bioretention, or groundwater recharge through landscaping, such as constructed wetlands or rain gardens, shallow depressions that capture water when it rains, hold it there for a time and release it back into the ground. The plants in these gardens help filter the water, hold it, beautify the area, and provide vegetables or flowers.

Constructing a system: considerations

The basic rule: You will collect: .6 gallons per square foot per 1 inch rainfall. Alaska's rain intensity is highest in Fairbanks: 1 inch per hour (higher than Juneau): .01 gallons per minute per square foot.
  • there are 90,400 drops in a gallon of water
  • there are 86,400 seconds in a day
Each gallon has more drops in it than a day has seconds. Consider how many gallons your roof could collect in a good downpour, and then how many days that represents.

There are roughly 3 inches of water in 18 inches of snow (dry Interior snow). The winter snow load is your first catchment of the season.

The two most import things in collecting rainwater (or snow melt): have good filtration and keep sunlight out.

Filtration is a must: pollen, mosquitoes, etc. can turn the water septic. Products to pre-filter are fairly cheap, such as basic screens. Some are very thorough and expensive, and come from countries like Australia and Germany, so one is paying for long-distance shipping. However, a new US company in Texas is coming on line. To ensure that rainwater is safe for human consumption, the most common method of sterilization and disinfection of microorganisms is ultraviolet light using a 5 micron filter; other methods are reverse osmosis, chlorination, or ozone.

Some systems use water diverters: the first rainfall washes the roof off before starting to fill the collection tank. First flush down the pipe cleans out pollens, bird debris, leaves, etc. 
  • dry line vs. wet line. Dry line: does not go to the ground, enclosed, enters rain barrel at top. Wet line: underground or on the ground, goes into the barrel at top.
  • collection tanks: polyethylene, galvanized metal. Bigger ones use a liner, food grade material. MAKE SURE rain barrel is a food grade quality plastic.
  • cisterns: durable and watertight material; size where it goes and how much you will collect and need; cost ranges from $.50 to $2.25 per gallon collected (cost in shipping). Cisterns come in various shapes and sizes, including crates, pillows, barrels, concrete. Some cisterns are enormous.
  • catchment surface and pump stations. Kniffen described legal situations in other states where water landing on the ground or rooftops became property of the state, and elaborate catchment traps had to be set up by landowners. Pumps and auxiliary catchment surfaces may be useful for long distance distribution and dual-purpose shelter/catchment arrangements.
Other items and uses:
  • pump and pressure tank, water gauge, or gravity feed
  • for distribution: drip irrigation, water garden and bird baths, wildife and livestock water, sprayer tanks, sprinklers with pressure, house use
  • overflow pipe: filtration
  • 75-watt solar panel 12-volt battery to charge pump
In Alaska, protection from freezing is vital. Kniffen had a few suggestions on the cistern and the collection tank: locate indoors, bury below frost line, insulate tanks (1 inch of blue foam = 1 foot of soil in terms of insulating quality), circulate/aerate, winterize, heat with elements or resistant tape, put water barrels in greenhouse to keep warm, etc.

Kniffen was an enthusiastic speaker, seeing many possibilities for rainwater catchment in Alaska. Interestingly, while his talk drew mostly on his work in Texas, he borrowed from an Alaska CES publication on household water cisterns translated from Norwegian by Nils Johansen and Richard Seifert. Interest in these systems in the North has been around for a long time!

More resources and publications:

Kniffen's full workshop PowerPoint presentation is available here, 292 pp. (pdf), plus his conference presentation, Rainwater Harvesting for Farmers, 117 pp. (pdf).

Drip irrigation movie with Billy Kniffen.

Kniffen is the vice president of the American Rainwater Catchment Association and helped organize the Texas Rainwater Catchment Association. He recommended several resources during his talk, including:

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