Calibration of the root water uptake spatial distribution of a young Melaleuca styphelioides, an Australian-native plant, by means of a large-scale apparatus experiment

The stability of slopes is greatly influenced by seasonal variations in pore water pressures (pwp) induced by rainfall infiltration and evapotranspiration processes. Despite that, the prediction of the hydrological effects of long-stem planting is often simplified or neglected because it is challenging to address. Its computation requires a proper definition of the plant root water uptake spatial distribution, which depends, in turn, on geometry and spatial root density. A well-suited case study in this field of application has been provided by a soil-filled embankment, close to an important traffic artery in Newcastle (Australia), which experienced shallow instability. The implementation of long-stem planting has been suggested as a remediation intervention. Based on this, an experimental study focusing on the effects of plant roots on the distribution of pwp in the site soil has been performed by means of a large-scale laboratory experiment on a 2-year-old native plant. Suction measurements were recorded within the vegetated soil mass under controlled boundary conditions and used to calibrate two different root spatial distributions in a seepage simulation. One is based on a flexible RWU spatial distribution function, and the other, specific for the plant RWU pattern, is simpler in its formulation and requires the definition of a lower number of parameters. A comparison between their performances in reproducing pwp distribution suggests that the second one is a better alternative. The methodological approach adopted has proven to be suitable for representing the hydraulic behaviour of a vegetated hillslope, to be eventually implemented in a proper stability assessment problem.