10.8: Surge Flow Irrigation
- Page ID
- 44624
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The Surge Flow Process
Surge irrigation or surge flow is the process of intermittently applying water in surface irrigation (Yonts et al., 1996) as compared to continuous flow where water is applied for the entire irrigation set time. Surge irrigation was first studied as a method of reducing the amount of runoff that occurred during irrigation (Stringham and Keller, 1979). It was discovered that the time required for water to move to the end of the field was reduced by applying water intermittently rather than continuously.
Water can be applied intermittently by cycling irrigation water between two irrigation sets. In years past, irrigation water was cycled when it was not getting to the end of a field. The irrigator would move on to subsequent sets and return in 1 or 2 days to finish irrigating the partially watered sets. The second time, the irrigation water could be moved all the way to the end of the field because the soil surface had sealed where previously wetted by irrigation and thus more water was available at the point where flow had stopped. This same process is used with surge irrigation, except 3 to 6 cycles are used and the cycling is done automatically for short durations of 20 minutes to 2 hours.
When water first contacts the soil in an irrigation furrow, the infiltration rate is high. As the water continues to run, the infiltration rate at that point in the furrow is reduced to a near constant rate. If water is shut off and the furrow is briefly allowed to dry, the surface soil particles consolidate and form a surface seal in the furrow. When water is reintroduced to the furrow, the infiltration rate is low due to this sealing action. The result is more water moving down the furrow rather than infiltrating into the soil in the initial reach of the furrow. Surge flow can increase irrigation performance by providing a more uniform application.
Rather than turning the water on and off to achieve an on-off cycle, an irrigation surge valve (Figure 10.19) is used to alternate flow between two irrigation sets. Figure 10.20 shows one method of using a surge valve. Cycle times used with surge irrigation vary with soil texture and slope. Fine-textured soils respond less to surge irrigation than do coarse- textured soils that have higher initial infiltration rates. If field slope is so steep that it causes a rapid rate of advance, the effects of surge irrigation will be reduced. If the infiltration rate of a soil is low due to soil texture or compacted layers, surge irrigation is likely to be ineffective in reducing the irrigation advance times below those for continuous flow.
Surge flow has been used to reduce irrigation runoff in some cases by using short duration cycles after the water has reached the end of a field. This helps maintain high uniformity of water application and improve overall irrigation performance. Another application of a surge valve is to use it for semi-automatic operation. The surge controller provides a 2-set semi-automated furrow irrigation system. For example, if an irrigator is limited to returning to the field to every 12 hours, two 6-hour sets can be accomplished in that time frame.
Surge flow may not always reduce the advance time of water down the furrow. If it does not, there may still be benefits of labor savings and runoff reduction.
Figure 10.19. Tee-type surge irrigation valve.
Figure 10.20. Field installation of a surge valve (Yonts et al., 1991).
Management of Surge Flow Irrigation
Normally intermittent application is accomplished by using surge valves to alternate the water between a left and right irrigation set (Figure 10.20). The irrigation on times, during which water is applied to one side of the surge valve, are normally between 20 minutes and 2 hours. For each irrigation, an equal amount of off time occurs during each cycle. This will not be the case when different cycles times are used to compensate for an irregular shaped field. A cycle time—the time it takes to complete a full on time and off time cycle—is based on furrow length, soil texture, and field slope. The number of surge cycles used should be based on field length and field condition. Long fields and fields with high intake soils will require more cycles (5 to 6); shorter fields with low intake soil will need fewer cycles (3 to 4).
It is common to advance water during each surge cycle a distance that is equal to that fraction of the number of surge cycles used. For example, if using 4 surge cycles during advance, divide the field into 4 parts and advance the water one-fourth of the field distance during the first surge cycle. The time required to move the water that distance is the Cycle 1 on time. For the second and subsequent on times, multiply the factors given in Table 10.7 by the Cycle 1 on time. Table 10.7 provides the on-time factors for four and six cycles during advance.
Following the final advance cycle, set the valve for the cutback or post-advance phase. During cutback, the valve cycles the water at a shorter frequency between the two irrigation sets until irrigation is complete. Table 10.7 gives the on time factors for the post advance or cutback cycles.
If water does not reach the end of the field by the last surge cycle, adjustments are necessary. Options include increasing the number of surge cycles or decreasing the number of furrows in the set to increase furrow flow rate. If water reaches the end of the field sooner than desired, increase the number of furrows or decrease the number of surge cycles.
Cycle times and the number of cycles can be adjusted for each set of conditions. Many commercially sold valves will have preprogrammed cycle times based on furrow length or expected advance time. In addition, cycle times can be developed based on individual conditions. The valve will automatically change at those times selected.
|
Cycle No. |
Four Cycles Fraction of Field |
Four Cycles On Time Factor |
Six Cycles Fraction of Field |
Six Cycles On Time Factor |
|---|---|---|---|---|
| 1 | 0.25 | 1.0 | 0.17 | 1.0 |
| 2 | 0.50 | 1.9 | 0.34 | 1.9 |
| 3 | 0.75 | 2.4 | 0.51 | 2.4 |
| 4 | 1.00 | 2.9 | 0.68 | 2.9 |
| 5 | - | - | 0.85 | 3.3 |
| 6 | - | - | 1.00 | 3.7 |
| Post advance or cutback | - | 0.8–1.6 | - | 1.5–3.0 |
Determine the number of cycles and the on time for each cycle for a 1,200-ft long field. Assume that 4 cycles are desired during advance. Water reaches 300 ft (1/4 the length) in 30 min. The irrigator plans to return to the field every 12 hr to change sets.
Given: On time for Cycle 1 = 30 min
4 cycles during advance are desired
360 min total on time for each side of valve (based on 720 min return interval to field)
Solution
| Cycle Advance | Surge on Time (min) | Left Set | Right Set | Total Time 1 Cycle (min) | Cumulative Time (min) |
|---|---|---|---|---|---|
| 1 | 30 | 7:00 am | 7:30 | 60 | 60 |
| 2 | 57 | 8:00 | 8:57 | 114 | 174 |
| 3 | 72 | 9:54 | 11:06 | 144 | 318 |
| 4 | 87 | 12:18 | 1:45 | 174 | 492 |
| Cutback | - | - | - | - | - |
| 5 | 38 | 3:12 | 3:50 | 76 | 568 |
| 6 | 38 | 4:28 | 5:06 | 76 | 644 |
| 7 | 38 | 5:44 | 6:22 | 76 | 720 |
| New Set | 7:00 pm |