40
3 A Conventional Experimental Technique …
Compared with the sprayer-styled rainfall simulator, the coverage area and uniform coefficient of spout-type rainfall simulator are less influenced by water supply
pressure, and the adjustable range of the rainfall intensity is relatively large. However, similar to the needle droppers, the spouts also have to overcome the unsteady
effects of pre-rainfall in the beginning and residual water at the end in an experiment. Besides, a spray-type or sprout-type rainfall simulator may be composed of
several independent rainfall units. The flexible combination of the units can overcome the difficulties of the great difference in the elevation of the underlying surface
and the large scale of coverage area of simulated rainfall. In practice, better than the
spout-type rainfall simulator, a spray-type simulator may be employed with moveable nozzles to make rainfall distribution more uniform, or expand the area covered
by the rainfall in the case of fewer sprinklers.
3.4 Automated Rainfall-Simulation Hall
With the development of soil erosion research, many rainfall-simulation halls
equipped with comprehensive advanced facilities have recently emerged. The world’s
largest rainfall simulation hall was built in 1974 by the National Research Institute
for Earth Science and Disaster Prevention, Japan, and it still undertakes the experimental study of soil and water conservation until present (NIED 2015). The hall
has an effective rainfall simulation area of 3168 m
2 , which measures 44 m × 72 m,
and a rainfall intensity in the range between 0.25 and 3.30 mm/min. Drops sprayed
out of the combined nozzle rainfall simulator with automatic control have an initial
fall velocity, and the height of the nozzles is 16 m above the ground which is far
enough for raindrops to reach their terminal velocity. Several academic institutes
in China, e.g., Institute of Soil and Water Conservation—Chinese Academy of Sciences & Ministry of Water Resources (ISWC), Institute of Geographic Sciences and
Natural Resources Research—Chinese Academy of Sciences, Heilongjiang Institute
of Soil and Water Conservation, and Xi’an University of Technology, have constructed highly automated rainfall-simulation halls. The hall built by the ISWC is
the second largest but the most advanced in the world. It has an effective application
area of 1296 m
2 , which is equipped with a series of experimental devices including
the downward-spraying or sideward-spraying rainfall simulators, and stationary or
moveable hydraulic lifting and descending soil-bins. Other advanced technologies
also have been employed, consisting of the computer system automatically controlling the rainfall characteristics and the observation device dynamically monitoring
erosion processes on the slope.
Large-scale model experiments for soil and water conservation could be conducted
in the rainfall simulation hall because in the hall, the rainfall area is so large, and the
distribution of the simulated rainfall energy closely approximates natural rainfall.
The result of soil erosion research will be more reliable and efficient in virtue of the
3 A Conventional Experimental Technique …
Compared with the sprayer-styled rainfall simulator, the coverage area and uniform coefficient of spout-type rainfall simulator are less influenced by water supply
pressure, and the adjustable range of the rainfall intensity is relatively large. However, similar to the needle droppers, the spouts also have to overcome the unsteady
effects of pre-rainfall in the beginning and residual water at the end in an experiment. Besides, a spray-type or sprout-type rainfall simulator may be composed of
several independent rainfall units. The flexible combination of the units can overcome the difficulties of the great difference in the elevation of the underlying surface
and the large scale of coverage area of simulated rainfall. In practice, better than the
spout-type rainfall simulator, a spray-type simulator may be employed with moveable nozzles to make rainfall distribution more uniform, or expand the area covered
by the rainfall in the case of fewer sprinklers.
3.4 Automated Rainfall-Simulation Hall
With the development of soil erosion research, many rainfall-simulation halls
equipped with comprehensive advanced facilities have recently emerged. The world’s
largest rainfall simulation hall was built in 1974 by the National Research Institute
for Earth Science and Disaster Prevention, Japan, and it still undertakes the experimental study of soil and water conservation until present (NIED 2015). The hall
has an effective rainfall simulation area of 3168 m
2 , which measures 44 m × 72 m,
and a rainfall intensity in the range between 0.25 and 3.30 mm/min. Drops sprayed
out of the combined nozzle rainfall simulator with automatic control have an initial
fall velocity, and the height of the nozzles is 16 m above the ground which is far
enough for raindrops to reach their terminal velocity. Several academic institutes
in China, e.g., Institute of Soil and Water Conservation—Chinese Academy of Sciences & Ministry of Water Resources (ISWC), Institute of Geographic Sciences and
Natural Resources Research—Chinese Academy of Sciences, Heilongjiang Institute
of Soil and Water Conservation, and Xi’an University of Technology, have constructed highly automated rainfall-simulation halls. The hall built by the ISWC is
the second largest but the most advanced in the world. It has an effective application
area of 1296 m
2 , which is equipped with a series of experimental devices including
the downward-spraying or sideward-spraying rainfall simulators, and stationary or
moveable hydraulic lifting and descending soil-bins. Other advanced technologies
also have been employed, consisting of the computer system automatically controlling the rainfall characteristics and the observation device dynamically monitoring
erosion processes on the slope.
Large-scale model experiments for soil and water conservation could be conducted
in the rainfall simulation hall because in the hall, the rainfall area is so large, and the
distribution of the simulated rainfall energy closely approximates natural rainfall.
The result of soil erosion research will be more reliable and efficient in virtue of the