Published in Soil Sci. Soc. Am. J. 68:1833-1837 (2004).
© 2004 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
Division S-1—Notes
A LOW-INTENSITY, HIGH-UNIFORMITY WATER APPLICATION SYSTEM
M. Hankeb,
D. Perrya,
K.-J. S. Kunga,* and
G. Bubenzerb
a Dep. of Soil Science, Univ. of Wisconsin-Madison, Madison, WI 53706-1299
b Dep. of Biological System Engineering, Univ. of Wisconsin-Madison, Madison, WI 53706-1299
* Corresponding author (kung{at}calshp.cals.wisc.edu)
 |
ABSTRACT
|
|---|
Rainfall simulators with high uniformity and low intensities are required in many research areas related to environmental quality. To examine the characteristics of field-scale macropore-type preferential flow, we designed a portable water application system suitable to apply water with intensity < 5 mm h–1 for long-term steady-state infiltration experiments under different climatic conditions. Our results showed that, when water was applied at 345 kPa pressure, the system could deliver 4.36 mm h–1 of water to 19.2 by 2.7 m with 80 to 85% uniformity, while uniformity of the inner 16.2 by 2.1 m reached 94 to 97%. The performance of this system was not influenced by the ambient wind speed. Lower intensities of water application can be achieved by applying water intermittently.
|
INTRODUCTION
|
|---|
IN MANY RESEARCH AREAS related to environmental quality, rain simulators with high uniformity are required. For example, to examine the effect of precipitation on runoff or soil erosion, many types of rain simulators were designed (Amerman et al., 1970; Bubenzer et al., 1985; Williams et al., 1998; Battany and Grismer, 2000). The irrigated areas, intensity, duration, and Christiansen uniformity of these rain simulators generally ranged from 1 to 10 m2, 50 to 150 mm h–1, 0.5 to 2 h, and 80 to 90%, respectively. On the other hand, more delicate water application systems have also been designed to apply agrichemicals with very high uniformity (Ghodrati et al., 1990; Sumner et al., 1996). The intensity, duration, and Christiansen uniformity of these systems generally ranged from 10 to 100 mm h–1, 0.5 to 10 h, and 90 to 99%, respectively. All the uniformities of the above systems were measured under the calm conditions. Under windy conditions, the Christiansen uniformity decreased significantly (Tarjuelo et al., 1999).
To conduct field experiments to measure chemical breakthrough patterns under steady-state infiltration conditions, it is essential to use a water application system that has high uniformity under field climatic conditions for a long period of time (e.g., 1 mo) (Gish et al., 2004). Under a long-term steady-state infiltration condition, the saturated hydraulic conductivity of most agricultural soils with fine textures is low (e.g., 1–5 mm h–1), and the rain simulators mentioned above had a high intensity and would cause surface runoff. None of the above systems were designed to continuously and uniformly deliver water with low intensity to a large area for a long period of time. The objective of this study is to design and test a portable water application system that could offer low-intensity rain with high uniformity under different climatic conditions for a long period of time.
|
Materials and Methods
|
|---|
In preliminary experiments, many nozzles from different manufacturers were first tested to measure their water application rates. Water pressure for each nozzle was set at the level recommended by its manufacturer. The results showed that, when water was applied under low intensity, most nozzles sprayed water mist. This made them unsuitable because mist is too sensitive to air movement to provide a uniform water application. The mini compact micro sprinkler (model 52863-05 made by the DIG Corp., Vista, CA) offered a low-intensity irrigation rate around 4 to 5 mm h–1. This nozzle applied small water droplets with a bowl-shaped pattern. Preliminary tests were conducted to determine the water distribution patterns of 150 nozzles under indoor no-wind conditions. The nozzles were mounted on a frame where the lower tip of each nozzle was 0.7 m above the floor surface. The water distribution pattern of each nozzle was collected on a 2.7- by 2.7-m area with 30- by 30-cm grid. Results showed that most nozzles had nonsymmetric water distribution with either lopsided patterns or with a peak at the center (Fig. 1)
, while only about one fourth had the desired bowl-shaped pattern. The 38 nozzles that passed the preliminary screening were ranked according to their averaged flow rates and their bowl-shaped patterns, and two sets of 10 nozzles were chosen.
View larger version (35K):
[in this window]
[in a new window]
|
Fig. 1. Water application rate (mm h–1): (A) a normal bowl-shaped pattern; (B) an abnormal pattern with a peak at center; (C) an abnormal lopsided pattern.
|
|
To apply water uniformly under different climatic conditions in agricultural fields, a portable shed is necessary to minimize the impact of winds and to divert natural precipitation. A 3.5-m-wide by 24-m-long shed made of aluminum channels was constructed (Fig. 2)
. Height of the shed was 1.5 m at center and 0.6 m on the sides. The roof and sidewall were made of corrugated clear PVC panels with 90% light transparency. Gutters were installed on two sides to divert natural precipitation away from the shed. The only opening was the corrugated gap between the roof panels and the side panels. Preliminary experiments were conducted to monitor the difference in the wind speed. Four hot-wire anemometers were installed to measure wind speed inside the shed and a pulse anemometer was installed 3 m away from the center of the shed to measure outside ambient wind speed at 1.8 m. The results showed that the relationship between the inside and outside wind speeds was random. The wind speed inside the shed fluctuated around 0.5 to 2% of the outside wind speed, which ranged from 1.5 to 12 m s–1. When the outside ambient wind speed was below 1.5 m s–1, wind speed inside the shed was below the 0.05 m s–1 detection limit of our hot-wire anemometers.
View larger version (96K):
[in this window]
[in a new window]
|
Fig. 2. (A) Cross-section view of the irrigation shed; (B) Mechanical design inside the shed to oscillate the water application system.
|
|
To transform the bowl-shaped water application patterns of individual nozzles into a uniform pattern across a large area, eight selected nozzles spaced 2.4 m apart were mounted on a trolley inside the shed. The two extra nozzles from the same set were used as spares for replacement. The trolley oscillated these nozzles with a stroke of 2.4 m along the length of the shed. As shown in Fig. 2B, a motor with a 6.35-cm sprocket was used to drive a chain. The other side of the chain was mounted on another 6.35-cm sprocket. The chain drove a push rod connected to the trolley. Instead of stopping at the end of each stroke, the push rod simply moved quickly and smoothly around a sprocket. As a result, the trolley reversed direction almost instantaneously. This design avoided over-application of water at the end of each stroke.
The water pressure for these nozzles recommended by the manufacturer was 207 kPa. However, results from our preliminary test showed that, at this pressure, the uniformity of water application inside the shed was very poor (
50%). The effect of water pressure at 276, 310, and 345 kPa on the water application pattern was examined under the full-flow rate. The shed was placed on a flat asphalt surface, and the water application pattern inside the shed was measured on a 0.3- by 0.3-m grid in a 2.7- by 19.2-m area. These grids had nine columns of measuring cups labeled from A to I. Column E was aligned with the trolley track directly under the nozzles along the center of the shed. There were 64 measuring cups (20.3-cm2 opening and 30 cm apart) along each column.
Because we could not find nozzles that could apply water uniformly at lower intensity, we tested the performance of our water applicator by applying water intermittently. To achieve half of the water application rate, water was applied under 345 kPa for 39 s and shut off for 39 s. This interval was used to make the turn-on and shut-off locations random within the range of trolley oscillation. This minimized the effect of the dripping problem. We also tested the water application pattern under quarter-flow rate, when water was applied for 39 s and off for 117 s.
During the intermittent water application, a solenoid valve controlled by a digital timer was installed to control water supply inside the shed. However, after the solenoid valve was instantaneously shut off, water that remained in the pipe would drip from 8 nozzles for about 10 s. Similarly, the nozzles would first drip when the solenoid valve was suddenly turned on. This greatly reduced the uniformity of our water application system. To alleviate the problem, an antileak valve (model 52-530-10 from Dig Corp.) was connected to each nozzle. This antileak devices prevented water application when the pressure dropped to 83 kPa and would not initiate water movement until the pressure increased to 138 kPa. With the antileak valve, the dripping problem was reduced to 1 s.
At the full-flow rate when water was continuously applied under 345 kPa, the water application patterns in the shed were measured 15 times. At the half-flow rate, the water application patterns in the shed were measured 10 times. At the quarter-flow rate, the water application patterns in the shed were measured five times. At different times, there were different outside ambient wind conditions. The differences among the replications were used to examine the performance of our water application system under different climatic conditions.
|
Results and Discussion
|
|---|
Water pressure had a significant effect on the overall water application rate and uniformity. At 276 kPa, the Christiansen uniformity of the entire area (2.7 by 19.2 m) was only 61%. The averaged water application rate of the entire area was 3.62 mm h–1. At this pressure, the outer two columns (i.e., A and I) had significantly less water, while the next two columns (i.e., B and H) had slightly more water (Fig. 3A)
. Furthermore, the water application rate tapered off in the first four rows and the last four rows within each column. These were because of the nature of the bowl-shaped water application pattern of these nozzles and the nature of the oscillating trolley. Other water application systems designed to achieve high uniformity also had similar problems along the edges (Ghodrati et al., 1990). If the two outside columns and the three end rows on each side were excluded, water application rate increased to 4.42 mm h–1 and the uniformity improved to 90%.
View larger version (37K):
[in this window]
[in a new window]
|
Fig. 3. Impact of pressure on water application rate and uniformity. (A) Pressure = 276 kPa; (B) Water pressure = 345 kPa.
|
|
The performance improved significantly when the water pressure was increased. Results from full-flow rate under 345 kPa (shown in Fig. 3B) demonstrated that the two edge columns, A and I, received more water. However, the three edge rows still received much less water. Among the 15 replicated measurements, the uniformity of the entire area was always around 80 to 85%, and the averaged water application rate of the entire area was 4.36 mm h–1. In the inner 16.2- by 2.1-m area where the two outer columns and three edge rows were excluded, the uniformity was around 94 to 97% and the averaged water application rate was 4.78 mm h–1.
The two gaps without measurements (between Rows 19–21 and 49–51) in Fig. 3 are because of the two installed hot-wire anemometers to measure the wind speed inside the shed. Among the measured results, there was no relationship between the outside ambient wind speed and the wind speed inside the shed and no relationship between the wind speed inside the shed and the uniformity. These results demonstrated that this water applicator can achieve high uniformity under a wide range of climatic conditions.
Among the replicated measurements under the half-flow rate, the water application patterns were very similar to that shown in Fig. 3B. The uniformity of the entire area was around 80% and the averaged water application rate of the entire area was 2.1 mm h–1. In the inner 16.2- by 2.1-m area, the uniformity was around 94 to 96%, and the averaged water application rate was 2.4 mm h–1. Among the replicated measurements under the quarter-flow rate, the water application patterns were again very similar to that shown in Fig. 3B. The uniformity of the entire area was around 80%, and the averaged water application rate of the entire area was 1.03 mm h–1. In the inner area, the uniformity was around 93 to 95%, and the averaged water application rate was 1.16 mm h–1.
The reason that the uniformity of the entire area decreased under half- and quarter-flow rates was because the two outer columns (A and I) received less water during intermittent water supply. When water supply was suddenly shut off, the nozzles still sprayed as the pressure dropped from 345 to 83 kPa. The outer-edge Columns A and I received much less water during this period. On the other hand, when water supply was suddenly turned on, it took about 3 s for water pressure to increase to 345 kPa. During this period, the outer-edge Column A and I again received much less water.
|
Summary
|
|---|
We designed a portable water application system suitable for long-term steady-state infiltration experiments under a wide range of climatic conditions. The performance of the system was not influenced by the ambient wind speed. At 345 kPa pressure, the system could deliver water at an intensity of 4.36 mm h–1 to 19.2 by 2.7 m with around 80 to 85% uniformity, while the inner 16.2- by 2.1-m area has around 94 to 97% uniformity. This system has a linear response when water was applied intermittently to achieve lower irrigation intensities. Because the water application pattern of these nozzles was sensitive to water pressure, the uniformity decreased slightly when water was applied intermittently.
Received for publication January 31, 2004.
|
REFERENCES
|
|---|
- Amerman, C.R., D.I. Hillel, and A.E. Peterson. 1970. A variable-intensity sprinkling infiltrometer. Soil Sci. Soc. Am. Proc. 34:830–832.
- Battany, M.C., and M.E. Grismer. 2000. Development of a portable field rainfall simulator for use in hillside vineyard runoff and erosion studies. Hydrol. Proc. 14:1119–1129.
- Bubenzer, G. D., M. Molnau, and D.K. McCool. 1985. Low intensity rainfall with a rotating disk simulator. Trans. ASAE. 28(4):1230–1232.
- Ghodrati, M., F.F. Ernst, and W.A. Jury. 1990. Automated spray system for application of solutes to small field plots. Soil Sci. Soc. Am. J. 54:287–290.[Abstract/Free Full Text]
- Gish, T.J., K.-J.S. Kung, D.C. Perry, J. Posner, G. Bubenzer, C.S. Helling, E.J. Kladivko, and T.S. Steenhuis. 2004. Impact of preferential flow at varying irrigation rates by quantifying mass fluxes. J. Environ. Qual. 33:1033–1040.[Abstract/Free Full Text]
- Sumner, H.R., R.D. Wauchope, C.C. Truman, C.C. Dowler, and J.E. Hook. 1996. Rainfall simulators and plot design for mesoplot runoff studies. Trans. ASAE 39(1):125–130.
- Tarjuelo, J.M., J. Montero, P.A. Carrion, F.T. Honrubia, and M.A. Calvo. 1999. Irrigation uniformity with medium size sprinklers part II: Influence of wind and other factors on water distribution. Trans. ASAE 42(3):677–689.
- Williams, J.D., D.E. Wilkins, D.K. McCool, L.L. Baarstad, B.L. Klepper, and R.I. Papendick. 1998. A new rainfall simulator for use in low-energy rainfall areas. Appl. Eng. Agric. 14(3):243–247.
This article has been cited by other articles:
|
|
|
|
 
K.-J. S. Kung, M. Hanke, C. S. Helling, E. J. Kladivko, T. J. Gish, T. S. Steenhuis, and D. B. Jaynes
Quantifying Pore-Size Spectrum of Macropore-Type Preferential Pathways
Soil Sci. Soc. Am. J.,
June 28, 2005;
69(4):
1196 - 1208.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
