Managing Semi-Arid Watersheds: Watershed Basics - Water Harvesting

Water harvesting is a method of storing water from rainfall for later use - for 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 tank.