This paper proposes a commutative flow technology of drip irrigation in a looped pipe network. Switching the flow direction of the drip irrigation pipe can improve the flow velocity in the lateral, consequently washing up the sediment deposited in the lateral and flow channel of the emitter. Thus, this technology can reduce sediment deposition and prevent blockage of the drip irrigation pipe. To verify the effectiveness of the commutative flow technology, the drip irrigation experiment was conducted, and the unidirectional flow technology experiment was the control. At the end of the tests, the emitter average relative discharge (Dra) of the commutative and unidirectional flow drip irrigation pipes decreased to 92.8 and 62.9%, the emitter blocking rate was 7.7 and 35.9%, respectively; the total amount of sediment deposited in the commutative flow lateral was 37.5% of that in the unidirectional flow lateral. Compared with the unidirectional flow technology, the commutative flow technology could significantly mitigate the decline rate of flow discharge, and effectively reduce the emitter blockage rate and the lateral sediment amount. Thus, the application of the commutative flow technology in the drip irrigation field pipe network can improve irrigation quality and promote the development of muddy water drip irrigation.

  • Commutative flow technology changes the flow direction and velocity of drip irrigation pipes.

  • Large sediment particles settle at the front of the drip irrigation pipe causing emitter blockage.

  • Small sediment particles settle at the second half of the drip irrigation pipe causing lateral deposition.

  • Commutative flow technology can promote the applying and development of muddy water drip irrigation.

Graphical Abstract

Graphical Abstract
Graphical Abstract

The Yellow River Basin of China is facing a severe water shortage (Xie et al. 2020) and agricultural water consumption accounts for approximately 80% of the total water consumption (Ren et al. 2016). Vigorously developing and popularizing the Yellow River water drip irrigation project (Liu et al. 2017) can effectively solve the supply–demand imbalance of water resources in this region (Xu et al. 2010; Feng et al. 2020). However, the high sediment concentration in the main stream of the Yellow River aggravates the blocking and deposition problems of the drip irrigation system (Miao et al. 2015), which limits the development of the drip irrigation project in Yellow River Basin (Ma & Huang 2016; Han et al. 2018). Therefore, it is necessary to explore anticlogging performance in the drip irrigation system and to reduce the deposition of the muddy water used in this system.

The use of muddy water for drip irrigation in the field pipe network leads to two major problems: lateral siltation and emitter clogging, which are mutual feeding processes (Puig-Bargues et al. 2010). To improve the anticlogging performance of emitters, some researchers have altered the flow channel structure to improve the sediment discharge of emitters (Wei et al. 2006; Zhang et al. 2011; Zhou et al. 2014; Yu et al. 2019; Yang et al. 2020). Some scholars have investigated the external operating environmental factors of emitters, such as the sediment particle concentration and sediment particle size in muddy water. The muddy water with a sediment particle concentration lower than 1 g·L−1 does not significantly affect the relative flow discharge of the emitter, and for sediment particle concentration higher than 1 g·L−1, the Dra of the emitter decreases as the sediment particle concentration increases (Oliveira et al. 2017). The sediment particle concentration significantly affects the clogging process of the emitter, and the clogging degree of the emitter is aggravated with the increase in the sediment particle concentration (Niu et al. 2013). Compared with the sediment particle concentration, the sediment particle size has a greater impact on clogging in the emitter (Adin & Sacks 1991). Although the filter can prevent sediment particles from entering the drip irrigation system to a certain extent (Capra & Scicolone 2007), sediment particles still accumulate and cause siltation and clogging in the drip irrigation pipe (Bounoua et al. 2016; Yu et al. 2018a, 2018b). Based on many years of sediment particle research, Migniot (1968) found the flocculation effect for sediment particle sizes of less than 0.03 mm, especially for a particle size of less than 0.01 mm (Chien & Wan 1999). Small sediment particles have higher followability than large sediment particles; sediment particle sizes between 0.03 and 0.05 mm have the highest passing rate in the flow channel of the emitter (Zhang et al. 2007). Large suspended sediment particles with a size of more than 0.1 mm are likely to cause rapid blockage of the emitter (Adin & Sacks 1991), and sediment particles with a size of 0.15 mm or more are mainly affected by inertial force; they can easily enter the vortex area of the emitter flow channel and cause severe blockage (Yu et al. 2018a, 2018b). The aforementioned studies have only focused on the problem of clogging of drip irrigation emitters but have not investigated the problem of lateral deposition.

Critical nondeposit velocity is an important parameter in the design of pipeline irrigation with muddy water, and it is the key factor affecting lateral deposition in muddy water drip irrigation. Durand (1953) regarded the flow velocity at the beginning of sedimentation at the bottom of the pipeline as the critical nondeposit velocity. The main factors affecting the critical nondeposit velocity of the muddy water pipeline include the pipe diameter, sediment particle concentration, and sediment particle size and density (Zong et al. 2012; He et al. 2013). When the flow velocity of muddy water in the drip irrigation pipe is lower than the critical nondeposit velocity, the turbulent energy provided by the water flow is insufficient to support the suspended movement of sediment particles. Deposition occurs in the flow channel of the lateral and emitter, which reduces the cross-sectional area of the lateral and emitter, resulting in a flow capacity decrease in the lateral and emitter and further reducing the flow discharge and flow velocity of the lateral and emitter. Finally, sediment deposition is increased in the lateral, clogging the emitter.

Based on the above discussion, we propose a commutative flow technology to reduce sediment deposition and improve anticlogging performance for muddy water drip irrigation. Experimental research was conducted to verify the effectiveness of this commutative flow technology.

Commutative flow technology

To solve the problems of lateral deposition and emitter clogging in the drip irrigation system utilizing muddy water, we proposed a commutative flow technology. It is based on the fact that the flow velocity plays a decisive role in the deposition sediment particles in muddy water (Puig-Bargues & Lamm 2013). The schematic diagram of this technology under the drip irrigation looped pipe network is shown in Figure 1. The layout comprises two adjacent branch pipes connected to the main pipe and two adjacent branch pipes connected with both ends of drip irrigation pipes, which can supply water to the drip irrigation pipes. The running time of every irrigation process is called one irrigation duration (Omer et al. 2020), and one irrigation duration is divided into two phases: irrigation working conditions 1 and 2. In irrigation working condition 1, the water flow direction in the drip irrigation pipe is from left to right, the water flow rate and velocity are reduced step-by-step from left to right, which is termed forward water flow. In the irrigation working condition 2, the water flow direction in the drip irrigation pipe is from right to left, the water flow rate and velocity are reduced step-by-step from right to left, which is termed reverse water flow. By controlling the opening and closing of the inlet valve on the branch pipe, the water flow direction, rate and velocity in the drip irrigation pipe can be switched alternately, this is called the commutative flow technology. The flow velocity in the low-velocity pipe segment increases rapidly after the water flow direction is switched, thereby increasing the turbulent energy of the water flow in the pipe segment; thus, the water flow has sufficient energy to wash up the deposited sediment particles previously. Sediment particles and water are fully mixed into a suspended load state and discharged from the emitter, which increases the discharged sediment concentration of the emitter, thereby reducing the amount of lateral sediment. During the irrigation process, the water flow in the drip irrigation pipe varies, which can not only reduce the amount of lateral sediment but also mitigate the clogging degree of the emitter, reducing siltation, improving blocking of the drip irrigation field pipe network, and improving the quality of irrigation.
Figure 1

Schematic diagram of irrigation commutative flow technology.

Figure 1

Schematic diagram of irrigation commutative flow technology.

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Experiment equipment

To verify the effectiveness and feasibility of the commutative flow technology, we conducted tests with unidirectional flow technology and commutative flow technology drip irrigation pipe test device. The unidirectional flow technology drip irrigation pipe test device diagram is shown in Figure 2(a). It was used to simulate unidirectional flow technology drip irrigation conditions. The commutative flow technology drip irrigation pipe test device diagram is shown in Figure 2(b). It was used to simulate commutative flow technology drip irrigation conditions. By adjusting the opening degree of the water valve on the test device, the inlet pressure and the end flow rate of the drip irrigation pipe is controlled under the conditions of forward and reverse water flow respectively.
Figure 2

(a) Unidirectional flow technology and (b) Commutative flow technology drip irrigation pipe test device diagram. a. Water bucket; b. Stirrer; c. Water valve 1; d. Inlet pipe; e. Water pump; f. Filter; g. Water valve 2; h. Water valve 3; i. Flowmeter 1; j. Pressure gage 1; k. Drip irrigation pipe; l. Water valve 4; m. Holder; n. Pressure gage 2; o. Flowmeter 2.

Figure 2

(a) Unidirectional flow technology and (b) Commutative flow technology drip irrigation pipe test device diagram. a. Water bucket; b. Stirrer; c. Water valve 1; d. Inlet pipe; e. Water pump; f. Filter; g. Water valve 2; h. Water valve 3; i. Flowmeter 1; j. Pressure gage 1; k. Drip irrigation pipe; l. Water valve 4; m. Holder; n. Pressure gage 2; o. Flowmeter 2.

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Experiment material

The experiment was performed from March to June 2021. The experiment site was located at the State Key Laboratory Base of Eco-hydraulic Engineering in Area, Xi'an University of Technology, Xi'an, Shaanxi Province, China (108°59′51″N, 34°15′32″E).

The drip irrigation pipe used in this experiment was manufactured by Israel Netafim Company; the inner flow channel of the emitter was the flat labyrinth type, and the distance between emitters was 30 cm, with the outer diameter of the drip irrigation pipe of 16 mm and a wall thickness of 0.38 mm. Throughout the test, the flow coefficient of the emitter was 0.1512, the flow index was 0.4745. The length of the drip irrigation pipes used in the experiment were 12 m, and 40 emitters were evenly distributed on the drip irrigation pipe. Each emitter was numbered along the drip irrigation pipe according to the forward water flow direction, from emitter No. 1 to No. 40. The pipe segment number corresponding to emitter No. (n) was pipe segment No. (n). The number of the emitter and the pipe segment on the drip irrigation pipe are shown in schematic diagram Figure 3.
Figure 3

Schematic diagram of the emitter and the pipe segment number on the drip irrigation pipe.

Figure 3

Schematic diagram of the emitter and the pipe segment number on the drip irrigation pipe.

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The muddy water used in this experiment was artificially prepared. The sediment was naturally air-dried and ground, passed through a 120-mesh screen (aperture of 0.125 mm), and then mixed with water to prepare muddy water with particular sediment concentration. To speed up the test process, the sediment concentration of muddy water was configured to 10 g·L−1. The Malvern Laser Particle Sizer 2000 was used to analyze the gradation composition of sediment particles. The specific results are shown in Table 1.

Table 1

Sediment grain gradation

Particle size (μm) <2 2–5 5–10 10–20 20–50 50–100 100–200 
Proportion (%) 10.84 29.46 22.44 16.92 12.11 5.68 2.55 
Particle size (μm) <2 2–5 5–10 10–20 20–50 50–100 100–200 
Proportion (%) 10.84 29.46 22.44 16.92 12.11 5.68 2.55 

Note: Sediment physical properties sample date: 2021/3/8.

Experiment designs

In this experiment, a clean water test was conducted first, and the initial flow discharge of each emitter on the drip irrigation pipe was measured. The clean water trial protocol is shown in Table 2. Next, 21 times muddy water tests were conducted and verified the effectiveness and feasibility of the commutative flow technology. The muddy water trial protocol is presented in Table 3.

Table 2

Clean water trial protocol

Test groupWater flow directionInlet water pressure (kPa)Irrigation duration (h)Sediment concentration (g·L−1)
Commutative flow technology test Forward water flow 100 
Reverse water flow 100 
Unidirectional flow technology test Forward water flow 100 
Test groupWater flow directionInlet water pressure (kPa)Irrigation duration (h)Sediment concentration (g·L−1)
Commutative flow technology test Forward water flow 100 
Reverse water flow 100 
Unidirectional flow technology test Forward water flow 100 
Table 3

Muddy water trial protocol

Test groupWater flow directionInlet water pressure (kPa)Irrigation duration (h)Sediment concentration (g·L−1)
Commutative flow technology test Forward water flow 100 10 
Reverse water flow 100 
Unidirectional flow technology test Forward water flow 100 10 
Test groupWater flow directionInlet water pressure (kPa)Irrigation duration (h)Sediment concentration (g·L−1)
Commutative flow technology test Forward water flow 100 10 
Reverse water flow 100 
Unidirectional flow technology test Forward water flow 100 10 

Over the course of the clean water and muddy water test, a commutative flow technology experiment group and a unidirectional flow technology control group were set up. The commutative flow technology test consisted of forward water flow and reverse water flow test. The unidirectional flow technology test consisted of only forward water flow test. Under the condition of the forward water flow test, the pressure at the left end (water inlet) of the drip irrigation pipe was set to 100 kPa, and the flow rate at the right end (water outlet) of the drip irrigation pipe was set to 0 L·h−1, the direction of water flow in the drip irrigation pipe was from left to right. Switching the water flow direction in the drip irrigation pipe to the reverse water flow test, the pressure of the right end of the drip irrigation pipe (water inlet) was set to 100 kPa, as well as that at the left end of the water outlet, and the flow rate was 0 L·h−1, the water flow direction in the drip irrigation pipe was from right to left. The commutative flow technology and unidirectional flow technology test were conducted simultaneously, and daily test time was 8 hours. In each time commutative flow technology test, the forward water flow test lasted for 4 hours, and the reverse water flow test lasted for 4 hours. The unidirectional flow technology control test consisted of only the forward water flow test and lasted 8 hours each time. The interval between two tests was 16 hours. The experiment was repeated three times. After all experiments were completed, the test device was flushed with clean water.

Measurement index

Emitters flow discharge

During the irrigation test, the weighing method (Li et al. 2019) was adopted to measure the flow discharge of emitters. The specific operation used 80 measuring cylinders with a capacity of 250 mL to collect water from each emitter for 5 minutes, and the flow discharge of a single emitter was then calculated. Emitter flow discharge measurement was conducted every 2 hours. In each test, flow discharge measurements were performed four times for each emitter, and the average value of the measurements was taken as the flow discharge of an emitter.

Emitter discharge sediment concentration

The emitters No. 1, No. 10, No. 20, No. 30, and No. 40 were selected as the five sampling points of the emitter. During each muddy water irrigation test, the drying and weighing method was used to measure the discharge sediment concentration of the emitter every 2 hours. The discharge sediment concentration of the emitter was measured a total of four times at the sampling points, and the average value of the discharge sediment concentration of the emitter in this test was calculated.

Sediment amount of pipe segments

At the end of the irrigation test, the drip irrigation pipe was cut to pipe segments: a 30-cm length lateral with one emitter constituted one pipe segment. After drying naturally, the weight of each pipe segment was measured; the sediment in each pipe segment was then washed, and the weight was taken again. The difference between the two weights was the sediment amount of each pipe segment, as shown in Equation (1). Then the distribution of the sediment amount of entire drip irrigation pipe was obtained:
formula
(1)
where denotes weight of sediment deposited in the drip irrigation pipe segment (n); is weight of sediment deposited in the drip irrigation pipe segment (n); represents net weight of the drip irrigation pipe segment (n).

Evaluation index for clogging and siltation

In the drip irrigation system, the average relative discharge (Dra) is generally used to determine the flow discharge change of the emitter, and the uniformity coefficients (CU) is used to characterize the irrigation uniformity of the drip irrigation pipe; the clogging rate of the emitter is used to indicate how many emitters are blocked. The combination of the three indicators can characterize the blockage of the emitter on the entire drip irrigation pipe (Pei et al. 2014). In this paper, the sediments amount of pipe segments is used to characterize the siltation degree of drip irrigation pipes.

The average relative discharge (Dra)

The Dra of the emitter is calculated using Equation (2). When the Dra of the emitter decreases by 25% (Dra <75%), the emitter is believed to be blocked (Zhou et al. 2017):
formula
(2)
where denotes Dra of the emitter; is real-time measured discharge of the emitter; represents initial discharge of the emitter.

The irrigation uniformity coefficients (CU)

In this paper, the CU is used to characterize the irrigation uniformity of the drip irrigation pipe. CU is calculated using the Christiansen formula (Christiansen 1942), which is listed as Equation (3) below:
formula
(3)
where CU represents Christiansen uniformity coefficients; n denotes total number of the emitter on the drip irrigation pipe; represents discharge of the emitter No.(i); is Dra of the emitter.

Emitter discharge distribution along the drip irrigation pipe

Figure 4 shows the emitter discharge distribution along the drip irrigation pipe in the commutative and unidirectional flow technology tests. Figure 4(a) shows the emitter discharge distribution during the clean water test. Figure 4(b)–4(d) presents the emitter discharge distribution during the 1st, 11th, and 21st muddy water tests respectively.
Figure 4

(a) Clean water irrigation test, (b) First muddy water irrigation test, (c) 11th muddy water irrigation test and (d) 21st muddy water irrigation test emitters discharge distribution along the drip irrigation pipe.

Figure 4

(a) Clean water irrigation test, (b) First muddy water irrigation test, (c) 11th muddy water irrigation test and (d) 21st muddy water irrigation test emitters discharge distribution along the drip irrigation pipe.

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From Figure 4(a), it can be seen that in the clear water test, the emitter discharge under the commutative and unidirectional flow technology test were similar along the drip irrigation pipe. The calculation results showed that the average discharge of the commutative and unidirectional flow technology drip irrigation pipes were both 1.35 L·h−1; this average discharge value was used as the initial discharge of the emitters. From Figure 4(c), it can be seen that in the 11th time muddy water test, the discharge of nine emitters on the unidirectional flow technology drip irrigation pipe was significantly reduced, and the discharge of three emitters decreased to 0 L·h−1, indicating that they were completely blocked; but in the commutative flow technology test, the discharge of only one emitter on the drip irrigation pipe decreased to 0 L·h−1, and the discharge of the remaining emitters did not decrease significantly. From Figure 4(d), it can be seen that in the 21st time muddy water test, the discharge of 18 emitters on the unidirectional flow technology drip irrigation pipe was significantly reduced, and the discharge of 13 emitters decreased to 0 L·h−1; but in the commutative flow technology test, the discharge of three emitters on the drip irrigation pipe decreased to 0 L·h−1, and the discharge of the remaining emitters was not significantly reduced. By comparing Figure 4(b)–4(d), it can be seen that with the increase of the muddy water test number, the emitter discharge of the commutative and unidirectional flow technology drip irrigation pipes continued to decrease. The discharge of the unidirectional flow technology drip irrigation pipe was significantly reduced, whereas the discharge decrease of the commutative flow technology drip irrigation pipe was not obvious. The emitter clogging position of the unidirectional flow technology test was mainly distributed in the front one-quarter of the lateral and three-quarters of the drip irrigation pipe, and the clogging position of the commutative flow technology test was mainly distributed at both ends of the drip irrigation pipe.

Emitter average discharge variation with the test number

In each muddy water test, the emitter discharge of the commutative and unidirectional flow technology drip irrigation pipes was measured. The average discharge of 40 emitters on the commutative and unidirectional flow technology drip irrigation pipes was calculated respectively and taken as the drip irrigation pipes average discharge of this time test.

Figure 5 shows the average discharge variation of emitters with the test number increased in the unidirectional and commutative flow technology tests. Figure 5 shows that with the increase of the test number, the emitters average discharge showed a downward trend overall, which is consistent with the research results of Zhang et al. (2020). In the first three tests, (the emitter average discharge of the unidirectional flow technology drip irrigation pipe) and (the emitter average discharge of the commutative flow technology drip irrigation pipe) did not decrease significantly. With the increase of the test number, and gradually decreased, and decreased significantly to 1.33 L·h−1 (Dra = 98.5%) from the fourth test, and decreased significantly to 1.34 L·h−1 (Dra = 99.3%) from the sixth test. When the test progressed to the intermediate stage (i.e., 11th test), decreased to 1.24 L·h−1 (Dra = 91.8%), and decreased to 1.32 L·h−1 (Dra = 97.7%). In the last test (i.e., 21st test), decreased to 0.85 L·h−1 (Dra = 62.9%), which was already below the 75% discharge baseline, indicating that the emitter discharge of the unidirectional flow technology drip irrigation pipe decreased by a large margin. Thus, a major blockage problem occurred, and the irrigation demand could no longer be met. However, only decreased to 1.24 L·h−1 (Dra = 91.8%) in the last test, which was still higher than the 75% discharge baseline, indicating that the decline of emitter discharge of the commutative flow technology drip irrigation pipe was small. Although blockage occurred in the commutative flow technology drip irrigation pipe, no major blockage problem occurred, and the irrigation demand was still met. Based on the aforementioned analysis, the average discharge of the drip irrigation pipes continued to decrease with the increase of irrigation duration. Compared with the unidirectional flow technology, the commutative flow technology can significantly mitigate the average discharge of the emitter on the drip irrigation pipe, improve irrigation quality, and extend the service life of the drip irrigation system.
Figure 5

Variation of the average discharge of emitters with the test time increased.

Figure 5

Variation of the average discharge of emitters with the test time increased.

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Distribution of emitter sediment discharge

The average sediment discharge of the emitter at five sampling points along the commutative and unidirectional flow technology test drip irrigation pipes is shown in Table 4. The average sediment discharge of the emitter along the water flow direction in the drip irrigation pipe showed a trend of continuous decrease. The sediment discharge of the emitter on the commutative flow technology drip irrigation pipe changed while the water flow direction was switched, and the low sediment discharge of emitters improved. The sediment discharge of the emitter on the unidirectional flow technology drip irrigation pipe remained the same. In the commutative flow technology test, the sediment discharge of emitters at five sampling points in the forward water flow and reverse water flow were 9.66 and 9.64 g·L−1 respectively; the sediment discharge of emitters at five sampling points in the unidirectional flow technology test was 8.71 g·L−1. The average sediment discharge of the emitter on the commutative flow technology drip irrigation pipe was higher than that of the emitter on the unidirectional flow technology drip irrigation pipe, indicating that the commutative flow technology can improve the sediment discharge capacity of emitters.

Table 4

Sediment discharge of the emitter

Test groupWater flow directionSediment discharge of emitter No.(n) (g·L−1)
No. 1No. 10No. 20No. 30No. 40
Commutative flow technology test Forward water flow 10.32 ± 0.16a 10.12 ± 0.18ab 9.68 ± 0.27bc 9.31 ± 0.40cd 8.86 ± 0.31d 
Reverse water flow 8.98 ± 0.22c 9.23 ± 0.14c 9.63 ± 0.32b 10.06 ± 0.17a 10.28 ± 0.26a 
Unidirectional flow technology test Forward water flow 10.02 ± 0.34a 9.38 ± 0.39b 8.78 ± 0.23c 7.83 ± 0.32d 7.56 ± 0.25d 
Test groupWater flow directionSediment discharge of emitter No.(n) (g·L−1)
No. 1No. 10No. 20No. 30No. 40
Commutative flow technology test Forward water flow 10.32 ± 0.16a 10.12 ± 0.18ab 9.68 ± 0.27bc 9.31 ± 0.40cd 8.86 ± 0.31d 
Reverse water flow 8.98 ± 0.22c 9.23 ± 0.14c 9.63 ± 0.32b 10.06 ± 0.17a 10.28 ± 0.26a 
Unidirectional flow technology test Forward water flow 10.02 ± 0.34a 9.38 ± 0.39b 8.78 ± 0.23c 7.83 ± 0.32d 7.56 ± 0.25d 

Note: The data are the means ± SD of three replicate samples. Different letters indicate values significantly different emitters (P<0.05).

Distribution of sediment deposit in the different pipe segments

Figure 6 presents the distribution of sediment deposits in each pipe segment along the drip irrigation pipe. The sediment deposit amount in the unidirectional flow technology drip irrigation pipe increased slowly in the pipe segments No. 1–10 and increased rapidly in the pipe segments No. 11–31, then, slightly decreased in the pipe segments No. 31–40. Flow velocity decrease constantly led to more and more sediment deposit in the drip irrigation pipe along the direction of water flow. At the end of the drip irrigation pipe, although the flow velocity was still decreasing, the sediment concentration of the muddy water was reduced due to the increased sediment deposit in the front of lateral; thus, the sediment amount in the end of lateral was slightly decreased. However, the sediment amount in the end of lateral was still high, which is consistent with the conclusion of Duran-Ros et al. (2009) that the amount of sediment deposition in the back segment of the lateral is higher.
Figure 6

Distribution of sediment amount in each pipe segment along the drip irrigation.

Figure 6

Distribution of sediment amount in each pipe segment along the drip irrigation.

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During the commutative flow technology test in the first half of the lateral (pipe segments No. 1–20), the sediment amount gradually increased with the increase of the pipe segment number and reached a peak in the middle of lateral, and the sediment amount in the second half of the lateral (pipe segments No. 21–40) gradually decreased; the distribution of sediment amount was generally symmetrically in the lateral. While the direction of the water flow was switched, the flow velocity improved rapidly, and then, the previously deposited sediment particles washed up and fully mixed with the water flow to become a suspended load that was discharged from the emitter. Thus, the sediment discharge concentration of the emitter improved, and the sediment amount in the lateral reduced.

According to the measurement data, the total amount of sediment in the unidirectional flow technology drip irrigation pipe was 850.91 g, and the total amount of sediment in the commutative flow technology drip irrigation pipe was 309.07 g. The total amount of sediment in the unidirectional flow technology lateral was significantly higher than that in the commutative flow technology lateral. As can be seen from Figure 6, the distribution of the sediment amount in the first half of the unidirectional and commutative flow technology laterals was similar. The sediment amount in the second half of the unidirectional flow lateral was 704.52 g, and the amount in the second half of the commutative flow technology lateral was only 144.39 g, which was much less than that in the unidirectional flow technology lateral. A portion of sediment was deposited in the first half of the commutative flow technology lateral due to the flow velocity decrease after the water flow was switched. However, after the water flow was switched again, the sediment discharge of the emitter increased, and the sediment in the lateral was discharged. Therefore, the distribution of the sediment amount in the first half of the lateral was similar. The flow velocity in the second half of the unidirectional flow technology lateral gradually decreased. As the flow velocity decreased, sediment deposition was easier, and the sediment discharge of the emitter was lower; thus, much sediment was deposited in the second half of the unidirectional flow. The flow velocity and water flow direction of the commutative flow technology lateral were switched alternately. When the lateral flow velocity increased, the sediment deposited in the lateral under the low flow velocity was washed up and discharged from the emitter, thereby improving the sediment discharge of the emitter and reducing the sediment amount in the lateral.

Influence of commutative flow technology on flow velocity in different pipe segments

The flow velocity of muddy water significantly affected the sediment amount in the drip irrigation pipe. For drip irrigation pipe with a constant pipe diameter, the flow velocity was proportional to the flow discharge. As the flow discharge decreased along the direction of water flow, the flow velocity continued to decrease as well. In each test, the flow velocity in the commutative flow technology test was divided into two stages: the forward water flow velocity and the reverse water flow velocity, whereas the flow velocity in the unidirectional flow technology drip irrigation pipe had only one stage: the forward water flow velocity. Table 5 lists the flow velocities of the pipe segments No. 1, No. 10, No. 20, No. 30, and No. 40 in the 1st, 11th, and 21st tests respectively. The forward water flow velocity of the commutative flow technology drip irrigation pipe from the water inlet (pipe segment No. 1) to the water outlet (pipe segment No. 40) decreased from 0.0831 to 0.0021 m·s−1, 0.0806 to 0.0021 m·s−1, and 0.0751 to 0.0021 m·s−1 in the 1st, 11th, and 21st tests respectively. After 4 hours of the forward water flow test, the reverse water flow test was conducted, and the water inlet and outlet of lateral was switched. The reverse water flow velocity of the commutative flow technology drip irrigation pipe from the water inlet (pipe segment No. 40) to the water outlet (pipe segment No. 1) decreased from 0.0830 to 0.0021 m·s−1, 0.0804 to 0.0021 m·s−1, and 0.0748 to 0.0021 m·s−1 in the 1st, 11th, and 21st tests, respectively. The forward water flow velocity in the unidirectional flow technology drip irrigation pipe from the water inlet (pipe segment No. 1) to the water outlet (pipe segment No. 40) decreased from 0.0831 to 0.0021 m·s−1, 0.0744 to 0.0021 m·s−1, and 0.0521 to 0.0020 m·s−1 in the 1st, 11th, and 21st tests, respectively.

Table 5

Flow velocity of pipe segment varies with test times

Test timesIrrigation water flow technologyDirection of water flowFlow velocity (m·s−1)
Pipe segment number
No. 1No. 10No. 20No. 30No. 40
1st Commutative flow Forward flow 0.0831 0.0645 0.0435 0.0227 0.0021 
Reverse flow 0.0021 0.0207 0.0417 0.0625 0.0830 
Unidirectional flow Forward flow 0.0831 0.0645 0.0436 0.0229 0.0021 
11st Commutative flow Forward flow 0.0806 0.0640 0.0432 0.0224 0.0021 
Reverse flow 0.0021 0.0188 0.0395 0.0603 0.0804 
Unidirectional flow Forward flow 0.0744 0.0620 0.0413 0.0214 0.0021 
21st Commutative flow Forward flow 0.0751 0.0608 0.0405 0.0203 0.0021 
Reverse flow 0.0021 0.0164 0.0366 0.0569 0.0748 
Unidirectional flow Forward flow 0.0521 0.0459 0.0258 0.0138 0.0020 
Test timesIrrigation water flow technologyDirection of water flowFlow velocity (m·s−1)
Pipe segment number
No. 1No. 10No. 20No. 30No. 40
1st Commutative flow Forward flow 0.0831 0.0645 0.0435 0.0227 0.0021 
Reverse flow 0.0021 0.0207 0.0417 0.0625 0.0830 
Unidirectional flow Forward flow 0.0831 0.0645 0.0436 0.0229 0.0021 
11st Commutative flow Forward flow 0.0806 0.0640 0.0432 0.0224 0.0021 
Reverse flow 0.0021 0.0188 0.0395 0.0603 0.0804 
Unidirectional flow Forward flow 0.0744 0.0620 0.0413 0.0214 0.0021 
21st Commutative flow Forward flow 0.0751 0.0608 0.0405 0.0203 0.0021 
Reverse flow 0.0021 0.0164 0.0366 0.0569 0.0748 
Unidirectional flow Forward flow 0.0521 0.0459 0.0258 0.0138 0.0020 

The analysis of the flow velocity data of each pipe segment revealed that the flow velocity in the pipe segments showed a decreasing trend segment by segment along the water flow direction, and the flow velocity in the pipe segment showed a decreasing trend with the increase of test number. The flow velocity of the pipe segment in the commutative flow technology test decreased slower than that in the unidirectional flow technology test. This is because with the increase of test number, the flow discharge of the emitter in the commutative flow technology test and unidirectional flow technology test showed different levels of decline and even indicated blockage, which caused the flow velocity in the pipe segments to decrease to varying degrees. From Figure 5 and Table 5, it can be seen that in the first muddy water test, the flow discharge and flow velocity were no different between the commutative and unidirectional flow technology drip irrigation pipes. In the 11th and 21st tests, the descent speed of the flow discharge and the number of blocked emitter in the unidirectional flow technology test were much more than those in the commutative flow technology test; thus, the flow velocity in the commutative flow technology pipe segments was lower than that in the unidirectional flow technology pipe segments. The analysis results indicate that the commutative flow technology can significantly slow down the decrease of flow velocity in the drip irrigation pipe.

Influence of commutative flow technology on quantity of clogged emitter

Figure 7 presents the variation of the quantity of clogged emitters on the commutative and unidirectional flow technology drip irrigation pipe with the test times. The clogged rate of emitter was defined as the percentage of the quantity of clogged emitters divided by the total quantity of emitters on the drip irrigation pipe. As shown in Figure 7, emitter clogging occurred on the unidirectional flow technology drip irrigation pipe and was earlier than that on the commutative flow technology drip irrigation pipe. The increasing rate of quantity of clogged emitters on the unidirectional flow technology drip irrigation pipes was faster than that on the commutative flow technology drip irrigation pipe with the increase of the test times. When the test was conducted to the terminal stage (21st test), the quantity of clogged emitters on the unidirectional flow technology drip irrigation pipe was 14, and the emitter clogged rate reached up to 35.0%; whereas the quantity of clogged emitters on the commutative flow technology drip irrigation pipe was not more than 3, and the emitter clogged rate was only 7.5%. This is owing to the flow velocity in the unidirectional flow technology drip irrigation pipe continuously decreasing along the water flow direction, and the water flow direction was not switched during the whole irrigation process. The critical nondeposit velocity varies by the particle size of sediment. A part of large particles of sediment settled in the front part of the drip irrigation pipe and entered the flow channel of the emitter, causing emitter clogging rapidly. A mass of small particles of sediment settled in the posterior part of the drip irrigation pipe with a low flow velocity, and these particles entered the flow channel of the emitter with a high concentration. The deposit of small particles of sediment blocked the flow channel of the emitter, which caused a flow discharge decrease of the emitter (Liu et al. 2018). With the increase of test times, the blockage degree of the emitter increased, resulting in a continuous increase of the clogged emitter quantity. The flow velocity in the commutative flow technology drip irrigation pipe continuously decreased along the direction of water flow, and sediment was deposited in the low-velocity pipe segment, but when the direction of water flow was switched, the flow velocity of the low-velocity pipe segment increased rapidly, so that the sediment in the lateral was washed up and the sediment in the flow channel of the emitter was disrupted. Avoiding the deposit of a large amount of sediment in the lateral; this reduced the quantity of clogged emitters. Based on the above analysis, the commutative flow technology can significantly reduce the quantity of clogged emitters and the blockage rate of emitters on the drip irrigation pipe.
Figure 7

Variation of the quantity of clogged emitters with test times.

Figure 7

Variation of the quantity of clogged emitters with test times.

Close modal

Influence of commutative flow technology on drip irrigation CU

The CU is an important index of the quality of drip irrigation. Based on the flow discharge of the emitters, the CU of the commutative and unidirectional flow technology drip irrigation pipe was calculated, and the variation of the CU with the test times is shown in Figure 8. During the whole experiment, the CU of the commutative and unidirectional flow technology drip irrigation pipes showed a decreasing trend with increasing of the test times. Compared with the unidirectional flow technology test, the decreasing rate of CU in the commutative flow technology test was slower. In the first three experiments, the CU of the commutative and unidirectional flow technology tests were higher than 98%. CU began to decrease from the fourth and sixth unidirectional and commutative flow technology tests, respectively. When the test was conducted to the terminal stage (21st test), the CU of the unidirectional flow technology test was decreased to 28.2%, which was much lower than the minimum standard of 80% (Wang et al. 2017); this coefficient did not meet the requirements of drip irrigation uniformity. The CU of the commutative flow technology test was reduced to 84.6%, which was still higher than 80%, meeting the requirements of drip irrigation uniformity. This is because the commutative flow technology can improve the sediment discharge of the emitter and reduce the sediment amount in the lateral after the water flow is switched, thereby mitigating the decrease rate of the flow discharge and drip irrigation uniformity, and reducing the quantity of clogged emitters. The commutative flow technology test can still meet the irrigation uniformity requirements after multiple times of the muddy water drip irrigation test. Compared with the unidirectional flow technology, the commutative flow technology can significantly mitigate the decline rate of drip irrigation uniformity and improve irrigation quality.
Figure 8

Variation of irrigation uniformity coefficients with the test times.

Figure 8

Variation of irrigation uniformity coefficients with the test times.

Close modal

Relationship between the distribution of sediment and the position of clogged emitters

Figure 6 shows the distribution of sediment amount increased first and reached a peak value at the pipe segment No. 19, then decreased along the commutative flow technology lateral; the distribution of sediment amount continuously increased and reached a peak at the pipe segment No. 31, then decreased slightly along the unidirectional flow technology lateral. As shown in Figure 4(d), a few clogged emitters were observed at both ends of the commutative flow technology drip irrigation pipe and several clogged emitters were distributed in the front one-quarter and three-quarters of the unidirectional flow technology drip irrigation pipe.

Due to different sizes of sediment particles having different critical nondeposit velocity, flow velocity in the drip irrigation pipe decreases continuously from the water inlet to the water outlet. The large particles of sediment first deposit in the water inlet of drip irrigation pipe and present a bed load sediment, then a portion of the bed load sediment entered the flow channel of emitter. Because the flow channel of emitter is sensitive to the size of particles, the large particles of sediment could not pass through the flow channel of emitter smoothly and finally accumulated in the flow channel, causing the emitter to clog rapidly. For the commutative flow technology test, switching the direction of water flow enables the large particles of sediment to be evenly distributed in the both ends of the lateral, and avoids the large particles of sediment accumulation. Therefore, the quantity of clogged emitters caused by large particles of sediment in the commutative flow technology test was fewer than that on the unidirectional flow technology test. A mass of small particles of sediment settles in the lateral with a low flow velocity (Hao et al. 2018). For the unidirectional flow technology test, a mass of small particles sediment deposited in the second half of the lateral due to the low flow velocity. Due to smaller particles depositing in similar locations, a large amount of sediment was deposited in the flow channel of the emitter. With the increase of test times, the cross-sectional area of the channel was continuously reduced, and the flow discharge of the emitter continuously decreased, which eventually caused emitter blockage. For the commutative flow technology test, some pipe segments had low flow velocity in the forward water flow test, but after the water flow was switched to the reverse water flow, the flow velocity increased rapidly, which could wash up sediment and discharge sediment from the nearby emitters. The emitter sediment discharge was improved, and prevented excessive sediment deposition in the drip irrigation pipe. Meanwhile, the flow velocity in the flow channel of the emitter was redistributed, preventing deposition in the flow channel of the emitter and preventing any reduction of the cross-sectional area of the flow channel.

In summary, for unidirectional flow drip irrigation pipe, some large particles of sediment settle at the front of the drip irrigation pipe, and a mass of small particles sediment were deposited in the second half of the lateral. After multiple irrigations, both large and small sediment particles may cause emitter clogging. For commutative flow drip irrigation pipe, switching the water flow direction repeatedly can reduce large particle sediment accumulating in both ends of the lateral and can reduce the deposition of small sediment particles in the second half of the lateral, thereby reducing the risk of nearby emitter clogging.

Under the condition of muddy water as the irrigation water source, the anticlogging performance of the drip irrigation pipe with commutative flow technology and unidirectional flow technology and whether these technologies can reduce sediment deposition in the drip irrigation field pipe network were studied, and the following conclusions were drawn:

  • (1)

    Commutative flow technology can change the water flow direction in the drip irrigation pipe, causing the flow velocity and flow rate in the lateral to be redistributed. By ensuring a high flow velocity, the sediment deposited in the lateral is washed away, and the sediment is discharged from nearby emitters with the water flow, increasing the sediment discharge of emitter and preventing sediment deposition in the drip irrigation pipe.

  • (2)

    Some large sediment particles in muddy water settle at the water inlet of the drip irrigation pipe, and then enter the flow channel of emitter, causing emitter blockage. A mass of small particles sediment deposit in the second half of the drip irrigation pipe and then enter the flow channel of the emitter, forming a large amount of deposit sediment and causing emitter blockage. The commutative flow technology can reduce the accumulation of large particles sediment in the water intel of the lateral and reduce the deposition of small sediment particles in the second half of the lateral, thereby reducing the risk of nearby emitter blockage caused by sediment deposition in the lateral.

  • (3)

    The application of the commutative flow technology in the field pipe network of the drip irrigation system can reduce sediment deposition and improve the anticlogging performance of the drip irrigation pipe. This technology can improve irrigation quality, improving the operation efficiency and service life of the drip irrigation system.

The authors thank the National Natural Science Foundation of China (Nos. 41571222,51909208) and the Postdoctoral Science Foundation of China (2019M663789) for supporting this research study.

Data cannot be made publicly available; readers should contact the corresponding author for details.

The authors declare there is no conflict.

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