Environmental Engineering Reference
In-Depth Information
the cation exchange sites, displacing calcium or magnesium. Sands, on
the other hand, do not owe their properties to aggregation of fine soil
particles, so presence of sodium ions in sand is not as damaging. If SAR
values exceed desired limits, addition of gypsum may relieve the prob-
lem. Water-testing laboratories often provide a value called
residual so-
dium carbonate
(RSC), which indicates how much gypsum should be
added to the water to offset the sodium hazard. In some countries, this
value is calculated in kilograms of gypsum per hectare of a pond at a
standard depth of 1 or 2 m. In others, the calculations are in kilograms of
gypsum per 1000 m
3
of water.
Irrigation Methods
Turf is irrigated by three main methods: (i) overhead; (ii) surface; and
(iii) subsurface. Overhead irrigation is used on the overwhelming major-
ity of turfs. Water is distributed through some type of irrigation system,
either pipes or garden hoses, and sprayed by a sprinkler head. The
purpose of a sprinkler head is to disperse water into fine droplets that
fall uniformly on the turf surface, as would a light rain. A great variety of
sprinkler heads is available on the market. Some are designed for use with
high-pressure water lines for irrigating large areas, some for intermediate
areas such as parks, some for small areas such as home lawns, some for
athletic fields, and so on. They vary greatly in size, design, efficiency,
methods of spraying water and material used for their assembly. Except
for a few unique types, most can be classified as either rotary or fixed.
Overhead irrigation
Rotary sprinkler heads
Rotary sprinkler heads shoot water as one or more streams of spray.
Water flowing through the sprinkler head makes it rotate to cover a
circular area or a set portion of a circle (Fig. 7.5).
During sprinkler head rotation, the area of the circle of turf near the
sprinkler ismuch smaller than that of the outer band far from it. Astreamof
spray from which the same amount of water falls at every distance there-
fore delivers much more water per unit area to the inner area than to areas
farther away. The result is a wedge-shaped irrigation pattern, a direct
result of the changing ratio of volume of water to amount of area covered
by this water (Fig. 7.6). When two adjacent heads are properly spaced, their
overlapping pattern can provide relatively uniform coverage along a line
drawn between them. Unfortunately, sprinkler heads are frequently
placed in the centres of golf course fairways and sport fields. This type of
