Fig. 2. Visualized preferential flow in the field using (NH4)2CO3 and a pH indicator. Pictures (a), (b), (c) show a section of the three-dimensional preferential flow plumes in the Hanford sandy loam 48 h after the end of infiltration. Pictures (d), (e), and (f) show a plume section in the Delhi sand 64 h after the end of infiltration. Preferential flow was not visible in (a) and (d). However, after application of the pH indicator, fingered flow patterns emerged as shown in pictures (b) and (e). Pictures (c) and (f) are computer enhanced pictures of (b) and (e), respectively.
