Managing Semi-Arid Watersheds: Watershed Basics - Water Harvesting
Water harvesting is a method of storing
water from rainfall for later usefor watering livestock, wildlife,
small-scale farming, and domestic purposes. Extensive rainwater harvesting
apparatus existed 4,000 years ago in the Negev Desert. In ancient Rome,
residences were built with individual cisterns and paved courtyards to capture
rainwater to augment water from the city's aqueducts. And as recently as
early in this century, rainwater was the primary water source on many ranches,
with stone and steel cisterns still standing today on homesteads.
One of the beauties of rainwater harvesting systems is their flexibility.
A simple system is a 55 gallon drum placed under a rain gutter downspout.
Most systems include five basic components: (1) a catchment area, such
as the roof of a house, (2) gutters and down spouts to channel water from
catchment to storage, (3) cisterns and storage tanks, (4) a conveyance
system, either gravity-fed or pumped, and (5) water treatment. Rainwater
offers advantages in water quality for both irrigation and domestic use.
Rainwater is naturally soft, contains almost no dissolved mineral or salts,
and is free of chemical treatment.
The shape of a water harvesting system depends upon the topography of
the site, the type of catchment treatment, the intended use, and the personal
preference of the designer. Microcatchments, strip harvesting, roaded
catchments, and harvesting aprons are some the more common types used.
Microcatchments and strip harvesting can be successful in years of normal
or above normal rainfall and are best suited for situations in which drought-resistant
trees or other drought-hardy perennial species are grown. The microcatchment
procedure can be used in complex terrain or on steep slopes, where other
water harvesting techniques may be difficult to install. The collection
area can range from 30 to 3000 square feet, depending upon the precipitation
in the areas and plant requirements; usually from one to several plants
are grown on the low side of the catchment.
The village of Shungopovi on the Hopi Reservation in northeastern Arizona
is a good example of the use of water harvesting in dry regions. Shungopovi
was built on the top of a sandstone rock mesa and had no source of water.
From the time of first establishment, the villagers carried water up from
the valley, initially on foot and later on the backs of burros. In the
early 1930s, a small water harvesting system was installed to partially
relieve the water shortage. An area of about one acre was cleared and
the loose rock was removed to expose the sandstone bedrock. Below the
area, a deep cistern was hewed into the rock and a concrete roof was constructed
over it. This system was a functional part of the village water supply
for about 30 years, at which time, a community well and pump was installed
on the valley floor to supply water to the community on top of the mesa.
One simple and common type of water harvesting is the stock
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