Effects of entrapped air in a closed soil pipe on the soil pipe flow during a rainfall
Abstract
Soil pipes, continuous macropores parallel to the slope, are considered to have an important role in hillslope hydrological processes. However, knowledge of water flow in the closed soil pipe is still limited due to the lack of the nondestructive observations. The objective of this study is to clarify water flow dynamics in the closed soil pipe directly by the laboratory experiment using a soil box with an artificial soil pipe. An acrylic plastic pipe, 7 mm inner diameter, 10 mm outer diameter, and 40 cm long, was used as an artificial soil pipe. Drain holes were evenly opened on the pipe wall and covered by nylon mesh. Soil pipe was connected to a pressure transducer to measure air pressure in the pipe. Two-needle electrodes were set inside the pipe to detect a pipe flow. Acrylic rectangular box, 60 cm long, 4 cm wide and 35 cm high, was filled with Toyoura sand with 3 % mass water content to a thickness of 30 cm. Drainage holes were opened at the downward outlet of the box. Artificial soil pipe was buried at center of soil box and 2.5 cm high from the base of the box. After packing the sand, soil box was inclined, and then artificial rainfall, 40-250 mm h-1, was applied. During the experiments, outflow rate and soil water pressure were measured. In the slope of 10°, soil pipe flow was not observed under either rainfall intensities, though groundwater table rose above the soil pipe. Increase in air pressure in the soil pipe started prior to the water saturation of soil around the soil pipe. This suggested that entrapped air in the soil pipe prevented water intrusion into the soil pipe. In the slope of 20°, soil pipe flow started when soil around the lower end of the soil pipe was saturated, but steady-state groundwater table was similar to that under no pipe condition. Release of the air in the soil pipe greatly decreased the groundwater level, indicating that even after the soil pipe flow started, entrapped air restricted the drainage through the soil pipe.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.H13E1420Y
- Keywords:
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- 1804 Catchment;
- HYDROLOGYDE: 1847 Modeling;
- HYDROLOGYDE: 1865 Soils;
- HYDROLOGYDE: 1875 Vadose zone;
- HYDROLOGY