Agriculture Reference
In-Depth Information
3.4.4.3 Length of Run
Time required for advance increases with furrow length. Irrigation runs which are
too long result in water being lost by deep percolation at the head of the furrow by
the time the lower end is adequately irrigated.
3.4.4.4 Cutoff Ratio
Deep percolation and runoff depends on cutoff ratio.
3.4.4.5 Tailwater Reuse
In most cases, tailwater reuse systems are essential to properly manage furrow irri-
gation systems so that the best distribution uniformity and irrigation efficiency may
be achieved.
3.4.4.6 Wetted Perimeter
Furrow intake increases with average wetted perimeter and decreases with dis-
tance from the water source, because wetted perimeter decreases as the flow depth
declines, assuming homogeneous soil and hydraulic conditions. Likewise, for lower
inflow rates, steeper slopes, and hydraulically smoother surfaces, wetted perimeter
and thus intake will decrease.
3.4.5 Management Controllable Variables and Design Variables
3.4.5.1 Management Controllable Variables
In the furrow system, the water should reach the end of the field in about one-half
of the total irrigation time, and the irrigator can manipulate that time by controlling
the outflow volume, slope, number and shape of furrows, and field length.
Factors the farmer can readily vary or manage are as follows:
•
furrow shape
•
roughness
•
length of furrow
•
irrigation set time
•
flow rate (stream size for furrow)
•
cutoff time
3.4.5.2 Design Variables
A furrow irrigation system has several design variables. These are as follows:
•
the inflow rate
•
the length of the run in the direction of the flow
•
the time of irrigation cutoff
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