Geha Foods Evaluation of Irrigation for Processed Tomatoes

Fig. 7. Very limited discharge available for irrigation furrow,
resulting in excessive water applied and frequent irrigation
stalling. Also note the bench in the middle of the field that will
slow the flow before proceeding to the end of the furrow.
Water Supply: The overall supply of irrigation water in the country seems adequate. The
water source is primarily winter snowmelt with little if any supplemental summer rains (Fig.
8). Normally, this results in a snowmelt hydrograph that peaks in late spring and early
summer, such as May and June in the northern hemisphere, and rapidly declines as summer
advances, until the base stream flow is obtained in fall (Fig. 9). However, it appears even
with the summer decline there is ample water for irrigation, a situation that is relatively rare,
unless the late summer irrigations after the normal decline in the snowmelt hydrograph are
based on return flow from early irrigations in the upper part of the system. In this case the
inefficiency of the system is basically the storage system and improving irrigation efficiency
in the upper reaches could have adverse impact on down stream users. The basic physics is
that matter can not be created or destroyed and the surplus water applied has to go some
place. Using the irrigation system to temporarily store water and buffer the hydrograph is
fairly common. Diverting large volumes of water for rice production in the Sacramento
Valley of California even outs the flow of water that has to be pumped into the Central
Valley Project and prevents the pumps from becoming overwhelmed with the spring runoff.
Similarly, the annual diversions of the Platte River in Colorado are more than twice the
annual flow, with the river totally dried into the irrigation system at least four times between
Denver and the Nebraska state line. The down stream users are dependent upon the 70 l/s/km
return flow. When farmers near the mountains started converting to center pivots and
reducing the return flow it created some major problems for down stream users.
The only storage facility in Tajikistan is a hydroelectric dam. While the releases for the dam
are determined by power needs, the discharge goes into the irrigation system and effectively
buffers the hydrograph of its command area and assures the supply of water throughout the
growing season. Given the overall supply of water and normal snowmelt hydrograph, it
should be possible to develop more storage structures and expand the irrigated area, if there
are suitable gravity accessible arable lands. It would also increase the electrical power supply
for the country or export. This would again be analogous to Colorado where virtually all
snowmelt is stored for use in the irrigation system as well as progressively serving the urban
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