Effect of irrigation commutative flow technology on reducing deposition and improving anticlogging performance of a flat labyrinth drip pipe

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.

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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.