Em4885 irrigation management practices to protect ground water

47
CHAPTER 4
There are several ways a cutback operation can be implemented. One way is with the use
of specialized surge valves as described in IP 2.02.03. Another way when using siphon
tubes would be to use two or more tubes during the initial wetting phase, then pull one or
more tubes for the rest of the irrigation. Gated pipe openings can be larger during initial
wetting and then closed down.
Note that with siphon tubes or gated pipe as just described, a new set will have to be
started as the cutback is implemented. Or, the excess irrigation water supply will have
to be directed to another field or decreased entirely.
IP 2.02.11 - Install Runoff-Reuse Systems
Objective
Improve overall on-farm application efficiency by gathering and reusing surface runoff
on the farm generating the runoff.
Description
The purpose of this Practice is to collect all the tailwater from a field and recycle it back
to the same field, or another field on the same farm, for reuse. The Practice is normally
associated with furrow/border strip irrigation systems. It may also be useful where
low soil infiltration rates or rolling terrain, or both, produce significant runoff with
sprinkle systems.
Since tailwater that might normally leave the farming unit is collected and re-used, the
overall on-farm application efficiency should be improved with this Practice. Another
factor in its use is that it provides management of the increased runoff that would occur if
faster water advance was desired in a furrow irrigation system. (Faster water advance
usually results in better distribution uniformity, which can lead to higher application
efficiency as long as the increased runoff is managed.) This Practice may be considered
as an alternative to, or in conjunction with, IP 2.02.10 - Use Cutback Flows, and also IP
2.02.03 - Use Surge Flow Techniques.
If an appropriate design is used, the runoff reuse system may also act as a sedimentation
pit, allowing sediments to settle out before the water is reused. Some systems will use two
pits. Trash and sediment that is brought in with the runoff will settle out or float on the
surface in the first pit. Clean water only flows into the second pit and is pumped back
for reuse.
If tailwater is to be used on another field, check for adverse reactions due to transferred
chemicals, fertilizers, or diseases.
SCS National Practice 447 covers design and installation of tailwater recovery systems.
American Society of Agricultural Engineers practice EP408.1 also addresses runoff
return system design and installation.