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| DOI：10.13522/j.cnki.ggps.2020017 |
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| Simulating Water Flow and Salt Transport in Soil under the Impact of Subsurface Drains Using the SWAP Model |
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ZHUANG Xudong, FENG Shaoyuan*, YU Hao, YUAN Chengfu, QIAN Zheng
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College of Hydraulic Science and Engineering, Yangzhou University, Yangzhou 225009, China
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| Abstract: |
| 【Background】Hetao Irrigation District takes water from the Yellow River for irrigation and is the largest gravity-driven irrigation district in Asia. It is also one of the most important grain production bases in China. Water used in irrigation accounts for about 90% of the total water consumed in the district with its agricultural production relying entirely on irrigation. Due to the double whammy of increased demand for water and dwindling water resources, however, its quota of the Yellow River water has been continuously reduced. This, along with the implementation of water-saving irrigation projects and new subsurface drainage systems, has substantially alerted regional water flow and salt transport in the district. Understanding how subsurface drains affect water flow and salt transport is important to optimize burying depth and spacing of the drains to ensure agricultural production without compromising ecological environment and sustainable economic development of the region.【Objective】The objective of this paper is to numerically elucidate the impact of burying depth and spacing of subsurface drains on soil water and slat dynamics in the district.【Method】We used the SWAP (soil-water-atmosphere-plant) model and calibrated and validated it against data measured from 2018 and 2019, including soil water content, soil salinity, crop leaf area index, plant height and soil texture. The calibrated model was used to simulate water and salt fluxes in 0~ 40 cm soil with the subsurface drains buried at depths of 1.5 m and 2.0 m, spaced from each other at 30 m and 45 m, respectively.【Result】①The calibrated SWAP model was able to reproduce the measured change in soil water and salt. Following irrigation or rainfall, both simulation and measurement showed that water in the 0~40 cm of soil flowed downward. Taking burying depth and spacing at 1.5 m and 45 m respectively as the control during the 2019 growth season, reducing drain spacing by 15 m increased downward water flux by 5.2%, while increasing the burying depth by 0.5 m increased downward water flow by 83.9%. In the absence of irrigation and rainfall, water in the 0~40 cm soil flowed upward, and a change in burying depth or spacing had little effect on soil water movement, with the simulated water flux varying from 0 to 0.14 cm/d. ②The change in salt flux was consistent with water movement. During the 2019 growth season, reducing drain spacing by 15m increased downward salt flux by 5.1% while increasing the burying depth by 0.5 m increased downward salt flux by 82.6%, compared to the control. Without irrigation and rainfall, salt in the 0~40 cm of soil moved upward, and a change in burying depth or spacing did not result in a noticeable effect on salt movement.【Conclusion】The SWAP model is capable of simulating water flow and salt transport induced by subsurface drains. Changing burying depth and spacing of the drains can improve soil desalinization and safeguard crop yield. Comparison revealed that the optimal burying depth and spacing of the drains were 2.0 m and 45 m respectively. |
| Key words: SWAP model; Subsurface pipe drainage; Helianthus; Soil water-salt dynamics |
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