Fig. 3. (A), (C): Measured matric potential gradient during steady state flow. For each imposed matric potential, the difference in water tension within microporous membranes on either side of the porous medium sample was 1 cm. (B), (D): Matric potentials measured at the same vertical depth, 7 cm apart, during approach to steady horizontal flow in a 3-cm depth of porous medium. Imposed suction within porous membranes on either side of the sample: –19 to –20 or –7.5 to –8.5 cm H₂O suctions for 0.25- to 1- or 1- to 2-mm porous medium.