WSP00669

• File Number: 8276.855
• Description: Grand Valley Demonstration Project - Colorado Salinity River Control Program
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1975
• Title: Uniform Irrigation With A Closed-Conduit/ Gravity Distribution System
• Water Supply Pro - Doc Type: Report/Study

its horizontal side arm at the desired outflow elevation. The delivery
hose is then connected to the bottom arm and an additional length of hose
is attached to the side arm to conduct water away from the tree trunk.
The upper arm of the tee draws air, breaking the siphon, which maintains
the effective outflow elevation at the side arm of the tee, regardless
of the actual elevation of outflow from the hose attached to it. A
length of hose attached to the upper arm of the tee allows a small head
to build up momentarily when the system is turned on to flush any air
blockages from the hose attached to the horizontal side arm.

Because the system operates at low pressure, the existing elevation
of ditches or pipes used for furrow or flood irrigation should often be
sufficient to provide it. There is, of course, a minimum elevation
required, either to keep the lateral pipe size within economic limits,
or, in some cases to maintain flow velocities high enough either to
prevent siltation or to allow for periodic flushing. The kinds of
questions that need to be considered can be illustrated by a specific
example.

Assume water is available at 1 meter (3.30 ft) elevation above
one end of the field 200 m (660 ft) long. The slope down the rows is
1%, and each row has 40 trees. Assume that each tree is to be supplied
"ith 0.063 ~/sec (1 gpm). If one lateral serves two rows, the inlet
flow rate is 5.0 ~/sec (80 gpm). If this flow rate ran the full length
of the lateral, the head loss would be 13 m (43 ft) for 76-~" (3-in) ID
pipe, or 2.6 m (8.5 ft) for 102-mm (4-in) ID pipe. Multiplying each by
a reduction coefficient of 0.364 to account for flow from the 40 outlets
(Table 1), the actual head loss would be 4.7 m (16 ft) for 76 nun (3 in)
ID pipe, or 0.95 m (3.1 ft) for 102 mm (4 in) ID pipe. As a conse-
quence of the 1% slope, the elevation change along the row (2 m or 6.6
ft) would more than compensate (by a factor of 2) for the head loss
for 102 rom (4 in) ID pipe, but would be only half enough to compensate
for the head loss along a 76 rom (3 in) ID lateral. A tapered lateral,
half 102 rom (4 in) ID and half 76 mm (3 in) ID would have a total head
loss of 1.1 m (3.6 ft), which would still be more than compensated for
by the slope of the field. If a 5 m (16 f~) length of 9.5-rom (3/8-in)
ID hose were used to deliver water to each tree, the head required to
supply a flow rate of 0.063 ~/sec (1 gpm) to each tree would be (from
Fig. 6) about 0.59 m (1.9 ft).

Figure 8 shows elevation for the ground, the hydraulic head in the
lateral, and the required elevations for the delivery hose outlets,
relative to the reference level, for the tapered lateral described
above. The reference level is arbitrarily chosen to be 0.3 m above the
ground level at the water source. The hydraulic head level in the
lateral was found by calculating the head loss for each section using
Fig. 5. The break in the hydraulic head curve at 100 m (330 ft) is the
result of decreasing the lateral pipe diameter from 102 to 76 rom. (4 to
3 in). The delivery hose outlet level is shown a constant distance of
0.59 m (1.9 ft) below the hydraulic head level. This provides the
required constant head across each delivery tube. The minimum eleva-
tion of a delivery hose outlet above the ground occurs at tree 6,
0.38 m (1.2 ft). The maximum occurs at tree 40, 1 m (3.3 ft)a ~~
~4~69

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