Journal of Applied Hydrology

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1 Journal of Applied Hydrology (1)(1) (2014) Journal of Applied Hydrology Licensed by; MSRT of I.R.of Iran; No. 3/18/ January 29, 2014 Investigation of infiltration in center pivot irrigation system Amin Rostami a *, Ali Ashraf Sadraddini b, Amir Hossein Nazemi c, Reza Delir Hasannia d a Former student of Water Engineering, Agriculture Faculty, Tabriz University, Tabriz, Iran b Associate professor, University of Tabriz, Iran c Professor, University of Tabriz, Iran d Assistant professor, University of Tabriz, Iran Corresponding author: Amin_rostami1@yahoo.com Article history: Received: 26 Feb Revised: 15 Mar Accepted: 16 June 2014 Abstract Use of the double ring infiltrometer to measure soil water infiltration in center pivot irrigation systems isn t an accurate approach; because the real conditions of infiltration under center pivot sprinklers is different from what happens in the double ring. In this study the infiltration parameters were evaluated in real conditions of a center pivot system. For this purpose a single ring with drainage equipment was used which could measure both infiltration and runoff rates during experiments. Field tests were carried out at agricultural research station of Tabriz University that soil texture of field was sandy loam. Treatments of experiments were two types of sprinkler (Ldn, I-wob), three operation pressures (15, 20 and 25 psi) and two sprinkler heights (1.6 and 2 meter) with three replications. The results showed that the average amounts of infiltration rate and cumulative infiltration in the double ring method were double of the mentioned amounts in the single ring method. Therefore the consideration of double ring method amounts in design phase causes a significant runoff in operation. The maximum amounts of infiltration rate and cumulative infiltration were obtained in irrigation with operation pressure of 25 psi and sprinkler height of 1.6 meter. The model of Kostiakov had the maximum amount of determination coefficient (R 2 ) and the model of Green- Ampt had the minimum amount of standard error (SE) in fitting with the measured infiltration data in real condition of a center pivot system in the field. Keywords: Center pivot, Double ring, Infiltration, Runoff, Single ring with drainage. 1. Introduction One of the main purposes in utilization of a sprinkler irrigation system is achieving to a desirable uniformity of water distribution with minimum runoff. Runoff problem increases in systems with high water application rate, due to mismatch of high application rate with soil infiltrability. Centre pivot is one of the irrigation systems that apply water with highapplication rates, especially when operating with low-pressure sprinklers. Use of such systems in soils with low infiltrability usually results large amounts of runoff and soil erosion. Sprinklers on the end part of lateral have a higher potential runoff than sprinklers around pivot. Potential runoff is the difference between water application rate and soil infiltration rate over time. Many researchers by assuming that water infiltration in center pivot system is a one dimensional vertical process use a double ring infiltrometer data. However, water infiltration conditions in these tests (with a water head ponding over the soil surface) are different from those occurring in sprinkler systems that have variable application rates. This issue has been investigated by some researchers. Chowdary et al. (2006) conducted experiments showed that different ponding heads and ring diameters of infiltrometer influence the infiltration process and thus affect the obtained data. Mohamoud (1991) and Keller and Bliesner (1990) used rainfall simulators or sprinkler infiltrometers to determine infiltration equation parameters.

2 34 Rostami,A., et.al / Journal of Applied Hydrology. 1 (1) (2014) Although such methods simulate water application by sprinkler irrigation systems but it s difficult to simulate the high application rates of center pivot systems. Chu et al. (1987) indicated when water application rate increase from 25 to 125 mm per hour, water infiltration rate doubles. DeBoer and Chu (1994) found that soil infiltration parameters derived from low application rate tests overestimated runoff values for sprinklers with higher application rates. DeBoer and Chu (2001) in research on continuous moving sprinkler irrigation system concluded that in addition to soil type, plow operations, initial moisture content of soil and irrigation method also impact on infiltration parameters. Shatanawi and Awwad (1994) concluded that the measured infiltration rate by double ring test is much more than average rainfall rate, and excessive runoff is created even in lower rainfall rates. Luz et al. (1998) suggested a simple statistic approach for potential runoff estimation in Center Pivot systems, based on theoretical results of Richards equation numerical solution. This model was presented for soil surface without crust, and Luz and Heermann (2005) generalized it for soil surface with crust, too. Evaluations showed that this model give accurate results and is agreement with Richards s equation. Silva (2007) experiments showed that infiltration rate is decreased, not only with increasing of soil moisture content, but also with soil surface compression. This author also demonstrated the soil infiltrability, particularly in time ranges lower than 25 to 30 minutes of test is increased with increasing of water application rate. Among different infiltration equations, Kostiakov equation due to its simplicity and good accuracy used more frequently in studies and design of irrigation systems. Esfandiyari (2001) in his research on various operation conditions of moving gun sprinklers concluded that the empirical Kostiakov model had the best matching with observation data, as compared to other infiltration models. Also by increasing of sprinkler pressure from 7 to 9 bar the thickness of crust was decreased and soil infiltration was increased. Sun et al. (2008) implemented a research to evaluate the sprinkler irrigation effects on surface soil porosity characteristics. They concluded that increase of water application rate, droplet diameter, and water application depth reduces total porosity, vacuity porosity, and micro porosity. Liu et al. (2011) studied effects of rainfall rate and initial moisture content on soil infiltration. Results showed that surface crust formation, due to contact energy of rainfall droplets, causes significant decrease in soil infiltration. Carlesso et al. (2011) implemented a research on runoff in various soils and different rainfall rates in southern Brazil, and concluded that with increase of rainfall rate, the runoff rate is increased. In this research an apparatus was used for precise measuring of infiltration and runoff under a center pivot sprinkler. On the basis of field experiments some infiltration models have been evaluated and the impacts of different operational condition of sprinkler on infiltration phenomenon have been discussed. 2. Materials and Methods 2.1. Experiments This study was performed on agriculture research station of Tabriz University. After initial survey, a plot with dimensions of 30m 30 m (900 sq. meters) near pump station was chosen as an experiment site. The station's well water characteristics has been showed in table 1, that indicates this water is in class C2S1, based on Wilcox Chart (means medium salinity and alkalinity). Soil type was sandy loam with sand, silt and clay percentage equal to 63.3%, 24.2% and 12.2% respectively. In experiments, two types of sprinklers with trade mark of Senninger Co. were used. The first one was a spray fixed pad sprinkler Ldn type with two blue and one black plate and with nozzle diameter of inch. The second one was an oscillating-pad spray sprinkler I-wob type with 9-grooves standardangle plate and with nozzle diameter of 5.16 inch. The plot was initially plowed and soil surface prepared for experiments. The all steps of experiment, including distance of cans lattice, catch cans shape and size, catch

3 Rostami,A., et.al / Journal of Applied Hydrology. 1 (1) (2014) cans arrange on ground, test time and recording of wind speed and direction was performed in according to the international standards ISO-8026 and ASAE S Based on these standards 625 cans were set on ground in a square lattice of nodes. The sprinkler was set in the lattice center. Sprinklers were fixed face-to-down by a steel frame; in a condition similar to their position on Center Pivot system (fig. 1). Pressure regulators were used to fix operational pressure of sprinklers. Table 1: Chemical characteristics of experiment water (Soluble ions density, meq/lit) EC PH Total Anions Measurements of wind speed and direction, relative humidity percentage and air temperature were done by a mobile digital aerologic station type TFA MATRIX II. In each experiment, Initial soil moisture content and time variations of infiltration rate were determined by sampling and use of the double ring test, respectively. Then water was supplied to sprinklers in predetermined height and pressure. After water discharge on cans lattice for one hour, the experiment was stopped and immediately water level values in the cans were red. Soil infiltration was measured with the presented infiltrometery method (single ring with drainage). The tests was performed in three operation pressures 15, 20, and 25 psi and in two sprinkler height 1.6 and 2 meter for each sprinkler type in 3 replications to identify the effects of different operation conditions on soil infiltrability. These effects are not recognizable in double ring test Infiltration measurements with single ring with drainage In this method, a cylinder with approximately 60 cm diameter and 20 cm height, which at near the bed and heel edge had a drain pipe for SO 4 CL HCO 3 Total Cations Fig. 1: disposition of spray nozzle at the lattice center Na + K CA + MG (µmhos/cm) SAR runoff directing to out was used for infiltration measurements. In operational domain of the sprinkler three cylinders were set with different distances relative to the sprinkler point, to identify a location which was receiving the maximum water application rate and hence maximum runoff value. The cylinders were inserted in the soil to the depth of the drainage pipes are tangent to the soil surface. A container was put in the dog hole near each cylinder for gathering the runoff water; and this container was connected with a hose to the cylinder's drain pipe. After starting of sprinklers action, total volume of distributed water in the can adjacent cylinder, runoff volume collected in can posited in holes were measured at 5 minute intervals. Regarding to the ratio of cylinder cross section area to can cross section area, the total volume of distributed water in cylinder was determined. By subtracting runoff volume from total volume of distributed water, infiltrated water volume in sequential times was calculated and thereby accumulative infiltration and average infiltration rate for each sprinkler in certain operation pressures and sprinkler height were calculated.

4 36 Rostami,A., et.al / Journal of Applied Hydrology. 1 (1) (2014) Models of water infiltration in soil In this study, four water infiltration models were evaluated for both infiltrometery methods which each model name, its equation and its coefficients was given in Table 2. In this table, I(t) represents accumulative infiltration and i(t) is infiltration rate. For investigation on models accuracy comparing to farm observations data two parameters R 2 (determination Coefficient) and SE (standard error) were used. The model with maximum R 2 and minimum SE was chosen as preferable model for water infiltration in soil in the location. Table 2: Water infiltration models in soil and their coefficients Model name Equation for infiltration rate or accumulative infiltration coefficients Philip 2 I t st A t Green-Ampt I t Kostiakov b Modified kostiakov I t at b ct Levels 1 p s, A p i t k b b, k I t at a, b Table 3: Experimental factors and their level Factors a, b, c A (operation pressure) B (sprinkler height) C (sprinkler type) 1 15 psi 2m LDN 2 20 psi 1.6 m I-wob 3 25 psi - - Table 4: Levels of experimental factor in each treatment Treatment No. Sprinkler type Operation pressure Sprinkler height 1 Ldn Ldn Ldn Ldn Ldn Ldn I-wob I-wob I-wob I-wob I-wob I-wob Experimental design As was mentioned, test data in this study included: accumulative infiltration and infiltration rate. Experimental factors were operation pressure, sprinkler height, and sprinkler type. For evaluation of effect of these factors on the data, the Factorial experiment with Completely Randomized design was chosen. Table 3 shows experimental factors and their levels. Totally, the experiment included 12 treatments for each irrigation test in 3 replications, and results were analyzed with SPSS software. In Table 4, levels of experimental factors in every 12 treatment were given.

5 Rostami,A., et.al / Journal of Applied Hydrology. 1 (1) (2014) Results and Discussion 2.2. Comparison of measured infiltration parameters with two infiltrometery methods For comparison of measured infiltration parameters of single ring with drainage method in the Center Pivot sprinkler with parameters of double ring method, paired t- Test approach was used. Comparison results showed that measured accumulative infiltration and infiltration rate in two methods had a notable difference with each other. Average accumulative infiltration value and average infiltration rate in the double ring method nearly is twice of single ring with drainage method amounts. Existence of this difference has agreement with Shatanawi and Abu-Awwad (1994) results. Figure 2 shows accumulative infiltration and infiltration rate curves of two infiltrometery methods for two treatments, 5 and 11. As it is seen, measured infiltration rate of double ring method initially is much more than single ring with drainage method; this difference continues until the 30 th minute and then gradually decreases. The existence of this initial great difference is due to large variations of soil infiltration in double ring method in initial times of the test. Because in the beginning of the test, moisture content is low and soil matrix potential difference in upper layers is high, on the other hand in this method there is a ponding head on soil surface and there is no limitation in water source. Actually in the double ring method the determining or limiting factor of infiltration is the soil infiltrability and with increasing of moisture content and decreasing of soil matrix potential difference, soil infiltrability decreases. But, in the single ring with drainage method, these large variations aren't observed in test performing time, because in this method distributed water from the sprinkler acts as feeding source in soil surface. Therefore, before the ponding time, feeding source is propounded as infiltration limiting factor and water infiltration rate in soil is equal to water application rate that is nearly a constant value. Though, due to increase of soil moisture and decreasing of soil matrix potential difference, a descending treatment is seen in soil infiltration in next stages of test. Table 5 shows the variance analyses results of measured infiltration rate in single ring with drainage method in the experimental design. From this table is deduced that effects of A factor (operation pressure), B factor (sprinkler height), and C factor (sprinkler type) on infiltration rate (at 1% probability level) are significant, but interactive effects are not significant. In figure 3, the interactive effects diagrams of operation pressure and sprinkler height on infiltration rate have been displayed for each constant level of sprinkler type. As diagram shows, with increasing of operation pressure from 15 psi to 25 psi, infiltration rate was increased, too; but, with increasing sprinkler height from 1.6 to 2 meter infiltration rate was decreased. The cause of infiltration rate increasing with increasing of operation pressure is the small size of exiting water droplets and then decreasing of droplet contact energy and finally, lowering of crust diameter on the soil surface. But, the cause of infiltration rate decreasing with sprinkler height increasing is the increase of potential energy of exiting droplets and then increasing of droplets speed at the moment of contact with soil; so in this condition, a thicker crust is formed on the soil surface and soil infiltration decreases (crust diameter values is given in table 6). These results conform to Esfandiyari (1380), Chu et al. (1987), and Silva (2000) findings. In figure 4, the interactive effects diagrams of operation pressure and sprinkler type on infiltration rate have been displayed for each constant level of sprinkler height. As diagram shows, resulted infiltration rate for Ldn sprinkler is higher than infiltration rate of sprinkler type I-wob. Sprinkler type effect on soil infiltration is dependent on two factors: nozzle size (sprinkler discharge) and water distribution pattern. As noted earlier, sprinkler nozzle of Ldn is bigger than sprinkler nozzle of I-wob, hence in operation of Ldn sprinkler water is distributed in higher rates on the ring with drainage, and because of high soil infiltrability in early stages of test, infiltrated water amount was increased. Figure 5 shows water application patterns for both sprinklers,

6 36 Rostami,A., et.al / Journal of Applied Hydrology. 1 (1) (2014) in the same operation pressure and sprinkler height. Comparison of water application patterns demonstrates that uniformity coefficient of I-wob sprinkler is greater than Ldn sprinkler, but distributed water depth for Ldn was higher than I-wob, particularly in locations with maximum receiving depth (in two experiments, wind speed was nearly equal and about 3 m/s). Table 5: variance analyses results of Experimental factor impacts on infiltration rate Variance source Freedom degree Sum of squares Average squares F replication ns A ** B ** C * A B ns A C ns B C ns A B C ns Experimental Error Total value

7 Rostami,A., et.al / Journal of Applied Hydrology. 1 (1) (2014) Fig. 3: Interactive impacts diagrams of operation pressure and sprinkler height in sprinkler type A- I-wob, and B- Ldn Fig. 4: Interactive impacts diagrams of operation pressure and sprinkler type in sprinkler height A- 2 meter, and B- 1.6 meter Fig. 5: Water distribution patterns, in the same operation pressure and sprinkler height for two sprinklers: A- Ldn, and B-I-wob It is clear that the effect of water distribution depth (or in better words, sprinkler discharge effect) on the infiltrated water only exists as long as when water application rate would be lower than soil infiltration. From table 6 it is seen that although net infiltrated water volume in the Ldn sprinkler is more than this volume for I- wob, infiltrated water percentage relative to distributed water for I-wob is more than Ldn. Runoff percentage for I-wob lower than Ldn that shows better performance in I-wob sprinkler. Variance analyses results of accumulative infiltration is showed in table 7. As table shows, the effect of A factor (operation

8 40 Rostami,A., et.al / Journal of Applied Hydrology. 1 (1) (2014) pressure) and C factor (sprinkler type) at 1% probability level and the effect of B factor (sprinkler height) at 5% probability level on accumulative infiltration is significant, but interactive impacts on accumulative infiltration are not significant. The affecting manner of experimental factors on accumulative infiltration is similar to infiltration rate, and as we expected, with operation pressure increasing and sprinkler Test Num. height decreasing, accumulative infiltration increases. Also, accumulative infiltration for sprinkler Ldn is higher than I-wob. Therefore, maximum infiltration in both sprinklers is correlated to operation pressure 25 psi and sprinkler height 1.6 m (treatments 2, 7). Minimum infiltration is also correlated to operation pressure 15 psi and sprinkler height 2 m, in both sprinklers (treatments 3, 10). Table 6: Distribution depth, infiltrated water percentage, runoff percentage, and crust diameter in all treatments Depth of Distributed water (cm) Depth of Infiltrated water (cm) Infiltarated water % Runoff % Crust Thickness (mm) Table 7: Variance analyses results of Experimental factors impacts on accumulative infiltration Variance source Freedom degree Sum of squares Average squares F Replication ns A ** B * C ** A B ns A C ns B C ns A B C ns Experiment Error Total value Evaluation of infiltration models and determining of coefficients With the fitting obtained data of two infiltrometery methods, coefficients of infiltration equations determined. Table 8 shows the average values of equation's coefficients for two infiltrometery methods. In Green-Ampt model, K factor that represents soil hydraulic conductivity, has a little difference in two infiltrometery methods, and was a little greater in double ring method. b

9 Rostami,A., et.al / Journal of Applied Hydrology. 1 (1) (2014) factor value in single ring with drainage method is much lower than double ring method, which is the result of lower infiltration rate in single ring with drainage method. In Phillip model, S factor is soil attractive factor and in double ring method is much greater than single ring with drainage method that caused by transcending soil infiltration amount in double ring method. Also, it is seen that c factor in modified Kostiakov model that represents final soil infiltration rate, has a greater value in single ring with drainage method, because the test time in this method in respect of irrigation time and minimum machine movement speed, was 1 hour, whereas, double ring method was continued as long as when final soil infiltration achieved; about 3 hours. It is clear that in the single ring with drainage method the infiltration rate doesn t reach its final level. Standard Error (SE) and determination coefficient(r 2 ) of infiltration models for both infiltrometery methods is given in table 9. In the single ring with drainage method, the Green-Ampt model has the lowest standard error, and the Kostiakov model has the maximum determination coefficient. This indicates that due to short time of infiltration in this method the Kostiakov model limitation in long periods is removed (i=0 in t ). The high estimating accuracy of Kostiakov model has been also reported in many studies such as Clemmens (1983), Clausnitzer et al. (1998), Silva (2007), and Neyshabouri et al. (1388). In the double ring method also, Green- Ampt model has the minimum standard error (SE), but the maximum determination coefficientis of the modified Kostiakov model that is originated from long infiltration period (3 hours) in this method. As many of researchers such as smith (1976) and Haverkamp et al. (1988) have suggested modified Kostiakov model in long periods that original Kostiakov model is limited. Table 8: The average infiltration models coefficients in both infiltrometery methods Infiltrometery methods Single ring with outlet Double rings Green Ampt K b Infiltration models S Philip A P a Kostiakov b Modified kostiakov a b c Table 9: The average determination coefficient(r 2 ) and standard error (SE) in both infiltrometery methods Infiltration models Infiltrometery methods Green Ampt Philip Kostiakov Modified kostiakov Single ring with drainage Double rings R 2 Se R 2 Se R 2 Se R 2 Se Conclusion In this study, the new single ring with drainage method was used for a detailed examination of water infiltration characteristics in Center Pivot irrigation systems, and its results were compared with results of using double ring infiltrometery. Comparison showed that infiltration rate and accumulative infiltration values of double ring method in farm experiments was nearly twice of single ring with drainage values. The effects of operation pressure, sprinkler height, and sprinkler type on soil infiltration indicated that with operation pressure increasing, infiltration rate and accumulative

10 36 Rostami,A., et.al / Journal of Applied Hydrology. 1 (1) (2014) infiltration were increased, but with sprinkler height increasing, infiltration rate and accumulative infiltration were decreased. The results also showed that infiltration rate and accumulative infiltration in Ldn sprinkler is greater than I-wob sprinkler. Evaluation of water infiltration models showed that in single ring with drainage method, Kostiakov model, and in double ring method modified Kostiakov model had the maximum determining factor; also, in both infiltrometery methods, Green-Ampt model had the minimum standard error (SE). Acknowledgements This article extracted from the Master's thesis which has carried out with the credits and facilities of Agriculture Faculty, University of Tabriz and hereby is appreciated. References Carlesso, R., Spohr, RB., Eltz, F. L. F., Flores, C. H Runoff estimation in southern Brazil based on Smith s modified model and the Curve Number method. Agricultural Water Management. 98: Chowdary, V. M., Rao, M. D., Jaiswal, C. S Study of infiltration process under different experimental conditions. Agricultural Water Management. 83: Chu, S. T., Onstad, C. A., Rawls, W. J Macropores in the soil infiltration process. ASAE. 87: Clausnitzer, V., Hopmans, J. W., Staw, J. L Parameter uncertainty analysis of common infiltration models. Soil Science Society of America Journal. 62: Clemmens, A. J Infiltration equations for border irrigation models. Proceedings of Conference on Advance in Infiltration, December, Chicago, IL. USA: DeBoer, D. W., Chu, S. T Sprinkler technologies, soil infiltration, and runoff. Journal of Irrigation Drainage Engineering. 127 (4): Esfandiyari, S Investigation of irrigation with moving gun sprinkler impact on crust formation and infiltration in soil. MSc thesis, Dept. of Water Engineering, University of Tabriz, Iran. (In Persian). Haverkamp, R., Kutlick, M., Parlang, J. Y., Rendon, I., Krejca, M Infiltration under ponded conditions: 2. Infiltration equation tested for parameter timedependence and predictive use. Soil Sci. 145(5): Keller, J., Bliesner, R. D Sprinkle and trickle irrigation. Van Nostrand Reinhold Press, New York, USA, 440 pp. Liu, H., Lei, T. W., Zhao, J., Yuan, C. P., Fan, Y. T., Qu, L. Q Effects of rainfall intensity and antecedent soil water content on soil infiltrability under rainfall conditions using the run off-on-out method. Journal of Hydrology. 396: Luz, P.B., Fernandes, M. L., Goncalves, M. C Reliable estimate of runoff in center pivot irrigation: statistical approach. Proceedings of the 16e Congress Mondial de Science du Sol, pp., Montpellier, France. Luz, P.B., Heermann, D A statistical approach to estimating runoff in center pivot irrigation with crust conditions. Agricultural Water Management. 72, Mohamoud, Y. M., Evaluating Green and Ampt infiltration parameter values for filled and crusted soils. Journal of Hydrology. 123 (1): Neyshabouri, M., Fakherifard, A., Farsadizadeh, D., Sadegiyan, N., Kheyri, J Coefficients of Kostiakov, Modified Kostiakov and Philip Infiltration Models on the Basis of Soil Bulk Density and Initial Water Content. Water and soil science. 19(2): (In Persian with English abstract). Shatanawi, M.R., Abu-Awwad, A. M Potential for water harvesting in Jordan:

11 Rostami,A., et.al / Journal of Applied Hydrology. 1 (1) (2014) Present situation and future needs. Proceeding of International Conference on Land and Water Resources Management in the Mediterranean Region, vol. III, Tecnomack Silva, L. L Fitting infiltration equations to center-pivot irrigation data in a Mediterranean soil and Agricultural Water Management. 94: Smith, R. E Approximation for vertical infiltration rate patterns. Trans. ASAE. 211, Sun, Z., Kang, Y., Jiang, S Effects of water application intensity, drop size and water application amount on the characteristics of topsoil pores under sprinkler irrigation. Agricultural Water Management. 95:

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