Kinematic cell model of macropore flow from intermittent irrigation pulses

Abstract

Significant fluctuations in soil water flux were observed in the drainage hydrographs from lysimeters (1220 mm diam., 900 mm deep) of undisturbed field soil, recorded at 5-min intervals, in response to intermittent 1-min pulses of irrigation water (3.4 or 6.8 mm) at irregular time intervals (4–17 min). The hypothetical process for this phenomenon was flow through soil macropores, in association with non-linear sorption into soil micropores. The kinematic wave approach to analysing macropore flow was modelled as a series of bi-continuum cells, which can be expressed as a set of non-linear ordinary differential equations. This non-linear state-space description enables the use of MATLAB software for convenient coding of the model and numerical integration of the model response to transient water flux input. Model simulation of drainage response to the irrigation pulse sequences showed good prediction of the wetting and draining fronts of the hydrograph but gave only indicative prediction of the magnitudes and wavelengths of the flow fluctuations. The model demonstrates the sensitivity of macropore flow to variations in the intervals between irrigation pulses, and supports previous evidence of fluctuations in macropore flow even for single water flux input pulses under laboratory conditions.