Fig. 4. The number of fingers created at a depth of 14 cm with different flow rates. The left picture was taken after the rainfall rate of 0.3 cm/h during the third set of experiments (three fingers were delineated with a marker for convenience). The picture on the right is for the 1.8 cm/h of rainfall intensity in the second set of experiments. Under the higher rate of rain, fingers merged in the center of the column (dark area), but the outer edge of the column was still dry (bright area).