| District Distribution
System
Unlike many agricultural water
delivery agencies, water in Westlands is metered. All of the water delivered,
whether it is for agricultural or non-agricultural purposes, is recorded
by more than 3,300 on-farm meters and meters on the San Luis Canal. The
water is distributed to each farmer in a highly efficient, closed-pipeline
distribution system.
On Farm
Irrigation Systems
Westlands farmers employ various
types of irrigation systems during the crop year. This is a fairly recent
phenomenon , as less than 20 years ago a majority of the District was
irrigated exclusively by surface irrigation (furrow or border strip).
Today, most District lands are now irrigated by a combination of sprinkler
and furrow or by drip/trickle techniques. The use of on-farm tailwater
reuse systems has also dramatically increased in the District.
Various factors may account for these trends. The District has experienced
a decrease in its water supply during the drought that began in 1987 .
In 1990, the District received only 50 percent of its contract allocation.
To cope with these reductions and to continue farming their land, farmers
had to fallow land and pump additional groundwater. The pumped groundwater
is more expensive than the surface water, and in most cases is of poorer
quality.
Data indicate that sprinkler pre-irrigations followed by regular season
furrow irrigations produce the highest irrigation efficiencies. Also,
tailwater reuse systems, when used with furrow irrigation, increased distribution
uniformity, thus facilitating better irrigation efficiencies.
Shallow-rooted vegetable crops are difficult to irrigate efficiently with
surface systems and are best irrigated by sprinklers during the early
portion of the growing season when small applications of water are desirable.
Well-managed furrow irrigation will suffice during the remainder of the
season, especially on those crops that are susceptible to mildew caused
by mid-to-late season sprinkler irrigations.
High-value, shallow rooted crops such as tomato, garlic, and onion are
most likely irrigated by a combination of sprinklers and furrow during
the season. Lower-valued, deeper-rooted crops such as alfalfa and wheat
are more likely surface irrigated. Moderate valued crops such as cotton
have about one-half the fields irrigated by sprinklers for at least a
portion of the season. Trees and vines such as almonds and grapes tend
to be irrigated by pressurized systems and new plantings are almost exclusively
drip/trickle irrigated .
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