Estimating Macroporosity in a Forest Watershed by use of a Tension Infiltrometer

Abstract

The ability to obtain sufficient field hydrologic data at reasonable cost can be an important limiting factor in applying transport models. A procedure is described for using ponded‐flow‐ and tension‐infiltration measurements to calculate transport parameters in a forest watershed. Thirty infiltration measurements were taken under ponded‐flow conditions and at 3, 6, and 15 cm (H₂O) tension. It was assumed from capillarity theory that pores >0.1‐, 0.05‐, and 0.02‐cm diam, respectively, were excluded from the transport process during the tension infiltration measurements. Under ponded flow, 73% of the flux was conducted through macropores (i.e., pores >0.1‐cm diam.). An estimated 96% of the water flux was transmitted through only 0.32% of the soil volume. In general the larger the total water flux the larger the macropore contribution to total water flux. The Shapiro‐Wilk normality test indicated that water flux through both matrix pore space and macropores was log‐normally distributed in space.