Impact of saturated hydraulic conductivity on the prediction of tile flow

Preferential flow through macropores and other structural voids in field so ils most often occurs at or near saturation. Our earlier research revealed significant differences in the value of the saturated hydraulic conductivit y (K-s) of a glacial till soil in central Iowa when obtained with five diff erent measurement techniques. The five techniques included one laboratory c onstant-head permeameter method and four in situ methods: disc permeameter, Guelph permeameter, velocity permeameter, and double-tube permeameter. Dif ferences in measured K-s values were attributed to differences in sample si ze, the existence or absence of open-ended macropores, and measurement prin ciples. In this study, we used the different K-s estimates in a two-dimensi onal numerical model, CHAIN_2D, to predict water now into a subsurface tile drain in the same field. Comparisons between predicted and observed tile f lows were made during four crop growing seasons. Preferential flow observed in the tile drain during large storm events was predicted best by the mode l when using K-s values measured with the disc permeameter method, which le ast disturbed the boundary conditions of the now field and better accounted for the macropore structures of the field soil. Quantitative and qualitati ve findings suggest that the disc permeameter was best suited for the field site.