Leaching is widely used in poor-drainage areas as a restoration method for salt-affected fields with subsurface drains. However, since such drains require expensive materials, extensive transportation, and elaborate construction, developing a cost-effective subsurface drain system is crucial. A rice husk subsurface drain system (RHSS) offers potential because it is simple and less expensive since it uses only rice husks as its primary drainage material. Although this method may be suitable for arid regions, optimal structure and management methods must be established. Because the water seepage from the RHSS’s rice husk surface is the only outlet at the subsurface drain’s end, the outlet’s opening and closing greatly impact its performance. In this study, we conducted model and numerical experiments to evaluate the effects of the opening and closing of outlets in RHSS drainage. Our results showed that the condition in which the drainage outlet was opened from the start of the water supply largely increased the cumulative drainage rate. When the outlet was opened 120 minutes after starting the water supply, the soil layer became saturated before drainage started, resulting in a significant reduction of the pressure gradient inside the rice husks. Consequently, the water flow diminished toward the outlet, lowering the cumulative drainage volume.

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