Fig. 1. Diagram of hanging water column system. One or both water columns were used to control inflow/outflow from the porous medium. Horizontal steady flow was induced by maintaining a 1-cm height difference between h₁ and h₂. Transient flow was induced by changing the h of one water column from 0 to –15 or –25 for 1- to 2- or 0.25- to 1-cm porous medium. Continuous pumping from the supply reservoirs to water columns and overflow from the water columns back to supply reservoirs maintained a constant head. P = pressure transducer.