Pedotransfer functions for estimating saturated hydraulic conductivity: implications for modeling storm flow generation

We evaluated the performance of nine published pedotransfer functions (PTFs ) for estimating saturated hydraulic conductivity (K-s) in modeling the sto rmflow generated in a rainforest catchment. Using available input data cons isting of particle size distribution. bulk density, and saturated moisture content information, these empirically-based PTFs were found to be inadequa te in estimating K-s for this catchment. At shallow depths (0-0.1 m). PTFs commonly underestimated K-s by variable amounts with the exception of the J abro PTF, which either overestimated K-s or was not significantly different from measured values. At subsequent depths (0.1-0.4 m), PTFs typically ove restimated K-s by variable amounts, the exception being the Campbell and Sh iozawa PTF, which typically underestimated K-s. We used TOPOG_SBM to model storm flow generation by replacing measured K-s values from the 0 to 0.1 m depth interval with PTF-estimated K-s values. The simulation set using Rose tta SSC (PTF with input of % sand. silt, clay) K-s values overestimated run off for all events, and overland flow occurred across the entire catchment for all events. Simulations using Rosetta SSC-BD (PTF with input of % sand, silt, clay, and bulk density) K-s values predicted hydrograph attributes a s well as the simulations using measured K-s values, but the Rosetta SSC-BD simulation set predicted a much larger spatial frequency of overland flow across the catchment than the measured K-s simulation set. Model simulation s using the Jabro PTF, which generated large estimates of K-s, produced hyd rographs that overestimated total runoff and time of rise but underestimate d peak runoff. This model predicted much less overland flow than other mode ls. Currently published PTFs used in this study are inadequate in estimatin g K-s for the La Cuenca catchment, which in turn make them inadequate for m odeling storm flow generation. Enhanced model performance could likely be a chieved by utilizing PTFs that better account for the influence of macropor osity. (C) 2001 Elsevier Science BN. All rights reserved.