3.3 Rainfall Simulators with Spouts or Sprayers
39
The sprayer rainfall simulator is one of the most widely used devices in soilerosion experiments. On the basis of nozzle direction, the spray-type rainfall simulator consists of nozzles pointing upwards, nozzles pointing downwards, and nozzles
pointing sideward. There is a rotatable sprinkler in each nozzle pointing upwards or
downwards, which may produce an arc of water, spread the water current in a large
area, and break the current into pieces. In comparison, an oblique board is installed
in the nozzle pointing sideward. Water rushes to the oblique board, and then changes
the direction and horizontally run out of the sprayer to form scattered raindrops in
a large area. According to the scattering mechanism, spray-type rainfall simulators
may be classified as one of the rotation type simulators, where a rotating helical
blade is used to spread the rainfalls, and as one of the aeration type, in which water is
atomized to improve the uniformity coefficients. In addition, the spray-type rainfall
simulators may also include movable and stationary type based on the movement
style of the nozzle.
As mentioned before, most simulators currently used in infiltration experiments
are in the sprayer forms. Meyer and McCune (1958) invented a rainfall simulator
with a downward sprayer alternately moving to and fro on a slide bar. The simulator
achieved good uniformity of rainfall intensity. The rainfall simulator designed by
Esteves et al. (2000) included spraying nozzles mounted on the top of the pipe at
a height of 6.5 m. Water was jetted to a height of approximately 7.5–8 m. Under
the water pressure of 41.4 kPa, the mean drop diameter was 2.4 mm, the calculated
kinetic energy was 23.5 J/(m
2 mm), and the rainfall intensity was 1.1 mm/min.
Ye et al. (2001) carried out a field experiment to analyze erosion due to railway
construction on representative slopes. Wu et al. (2003) designed a sprayer rainfall
simulator to investigate the benefits and characteristics of grass-shrub vegetation for
reducing soil erosion in the Loess Hill Ravine Region. The sprayer rainfall simulators
are also applied to test the soil loss of compressed loess roadbed (Shen et al. 2003)
and the infiltration under the conditions of conservation tillage (Wang et al. 2000).
The simulator introduced by Sharpley and Kleinman (2003) was trailer-mounted,
with 10 rotating booms (each 7.6 m long) radiating from a central stem, which
rotated at about 4 r/min. The nozzles sprayed downward from an average height of
2.4 m, applied the rainfall intensity of 70 mm/h and produced drop-size distributions
similar to natural rainfall. In recent years, no major revision has been made on the
raindrop generators, even though the sprayer rainfall simulators have been used in
experiments under various operating conditions. Many of them are designed for field
studies, which are easy to handle and suitable for the areas difficult to access (e.g.,
Al et al. 2017; Lora et al. 2016; Wildhaber et al. 2012). Some of the field simulators
are at very large scales. The simulator designed by Adams and Elliott (2006) has
13 rainfall stands at 9 m spacing, and the total application area under the sprinkler
stands was greater than the catchment area of the plot (approximately 1050 m
2 ).
39
The sprayer rainfall simulator is one of the most widely used devices in soilerosion experiments. On the basis of nozzle direction, the spray-type rainfall simulator consists of nozzles pointing upwards, nozzles pointing downwards, and nozzles
pointing sideward. There is a rotatable sprinkler in each nozzle pointing upwards or
downwards, which may produce an arc of water, spread the water current in a large
area, and break the current into pieces. In comparison, an oblique board is installed
in the nozzle pointing sideward. Water rushes to the oblique board, and then changes
the direction and horizontally run out of the sprayer to form scattered raindrops in
a large area. According to the scattering mechanism, spray-type rainfall simulators
may be classified as one of the rotation type simulators, where a rotating helical
blade is used to spread the rainfalls, and as one of the aeration type, in which water is
atomized to improve the uniformity coefficients. In addition, the spray-type rainfall
simulators may also include movable and stationary type based on the movement
style of the nozzle.
As mentioned before, most simulators currently used in infiltration experiments
are in the sprayer forms. Meyer and McCune (1958) invented a rainfall simulator
with a downward sprayer alternately moving to and fro on a slide bar. The simulator
achieved good uniformity of rainfall intensity. The rainfall simulator designed by
Esteves et al. (2000) included spraying nozzles mounted on the top of the pipe at
a height of 6.5 m. Water was jetted to a height of approximately 7.5–8 m. Under
the water pressure of 41.4 kPa, the mean drop diameter was 2.4 mm, the calculated
kinetic energy was 23.5 J/(m
2 mm), and the rainfall intensity was 1.1 mm/min.
Ye et al. (2001) carried out a field experiment to analyze erosion due to railway
construction on representative slopes. Wu et al. (2003) designed a sprayer rainfall
simulator to investigate the benefits and characteristics of grass-shrub vegetation for
reducing soil erosion in the Loess Hill Ravine Region. The sprayer rainfall simulators
are also applied to test the soil loss of compressed loess roadbed (Shen et al. 2003)
and the infiltration under the conditions of conservation tillage (Wang et al. 2000).
The simulator introduced by Sharpley and Kleinman (2003) was trailer-mounted,
with 10 rotating booms (each 7.6 m long) radiating from a central stem, which
rotated at about 4 r/min. The nozzles sprayed downward from an average height of
2.4 m, applied the rainfall intensity of 70 mm/h and produced drop-size distributions
similar to natural rainfall. In recent years, no major revision has been made on the
raindrop generators, even though the sprayer rainfall simulators have been used in
experiments under various operating conditions. Many of them are designed for field
studies, which are easy to handle and suitable for the areas difficult to access (e.g.,
Al et al. 2017; Lora et al. 2016; Wildhaber et al. 2012). Some of the field simulators
are at very large scales. The simulator designed by Adams and Elliott (2006) has
13 rainfall stands at 9 m spacing, and the total application area under the sprinkler
stands was greater than the catchment area of the plot (approximately 1050 m
2 ).