Em4885 irrigation management practices to protect ground water

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CHAPTER 4
Surge flow can improve distribution uniformity by reducing the total on-time needed to wet
a furrow. On-time is the time that water is flowing in the furrow. Reducing the amount of
on-time needed to wet the furrow will decrease the difference in soak times between the
top and bottom of the furrow. This should result in improved application efficiency in
conjunction with proper set timing.
However, the surging effect may lower infiltration rates too much. Surge can make it
difficult to infiltrate enough water during irrigations to satisfy the soil water deficit if
applied incorrectly. Surge is usually most effective on coarse-textured soils with very
high infiltration rates. Surge may also create more erosion due to increased flow rates.
Placing straw mulch in furrows can stabilize erosive soils (IP 5.01.03).
WSU Cooperative Extension published a Drought Advisory, EM4826, Surge Flow Surface
Irrigation (March 1988). It contains a more detailed discussion of surge flow techniques.
The local Cooperative Extension or SCS office will have information on what schedule of
pulses work best in a given area. Local irrigation hardware suppliers who distribute
specialized surge valves may also have information and suggestions on best combinations
of on-flow timing and number of pulses.
IP 2.02.04 - Decrease the Length of Furrow Runs
Objective
To reduce the difference in opportunity time between the top and bottom of the furrow
so as to increase down-row uniformity. Reducing furrow run lengths is done to allow a
sufficiently fast advance without resorting to an erosive stream size.
Description
A suitable speed of water advance during initial wetting may not be achievable without
using an erosive stream size due to some combination of furrow length, furrow condition,
soil type, and land slope. One option is to try surge flow irrigation (IP 2.02.03). Another
option is to decrease the length of the furrow. The time of advance is automatically
reduced in relation to the total set time by decreasing the length of the furrow.
For example, assume that it takes a 24-hour irrigation set to infiltrate the desired amount of
water. Using a furrow length of 1,500 feet requires 16 hours of advance time. Thus, the
advance ratio is 16/24 = .67. This would be considered too high for normal soils. By
cutting the furrow in half, the advance time is reduced to 6 hours. Now the advance ratio
is 6/24 = .25. This is actually a little low. In some cases, the furrow flow may be decreased
slightly as the furrow length is reduced.
The decrease in furrow length may be permanent, or it may be temporary by using gated
pipe or dirt ditches. Temporary reductions may be satisfactory for situations where the
infiltration rates of the soil are very high at the start of a season due to cultivations and
field preparation.