INFILTRATION, MACROPOROSITY, AND MESOPOROSITY DISTRIBUTIONS ON 2 FORESTED WATERSHEDS

Macro- and mesopore processes substantially control the subsurface flow in forested watersheds. Limited field scale information is available on spatial variability of macropore infiltration and associated porosity of the hydrologically active macro- and mesopores. The double-ring and tension infiltrometer methods were employed at 37 and 39 locations, respectively, on two contrasting forested watersheds. The spatial variability of infiltration under ponded-flow (macropore-flow) and under 2-, 50, and 14-cm water tension (mesopore-flow) conditions was determined. The infiltration rates were found to be lognormally distributed, with the mesopore infiltration rates as variable (coefficients of variation of 102-184%) as the macropore infiltration rates (coefficient of variation of 107%). Macropore flow constituted 85% of the ponded flux; however, the mesopore fluxes were large ( approximately equals 2 multiplied by 10** minus **5 m s** minus **1) and were considered sufficient to infiltrate rainfall without macropores filling and contributing to the flow.