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University of Melbourne (2020)

Overland flow scaling behaviour in a burned dry hillslope

Kasraie, Leila

Titre : Overland flow scaling behaviour in a burned dry hillslope

Auteur : Kasraie, Leila

Université de soutenance : University of Melbourne

Grade : Doctor of Philosophy (PhD) 2020

Résumé partiel
Wildfire may introduce higher spatio-temporal variability to the factors controlling soil infiltration by vast alteration in soil and vegetation, and as a result of that scaling effects on hydrological processes may be altered in burned landscapes (Moody et al., 2013). However, the impact of fire on scaling behaviours is poorly investigated and only few practical studies have measured runoffs scaling on burned hillslopes (Sheridan et al., 2014). There are significant knowledge gaps in understanding overland flow scaling effects in relation to post-fire soil, surface factors and rainfall properties (Moody et al., 2013).

This study aimed to investigate overland flow scaling behaviours in relation to soil and rainfall properties on a burnt hillslope by observations, measurements, and simulations. This was obtained by i) collecting rainfall-runoff data from different plot lengths at a eucalyptus hillslope, Southeast Australia burned by wildfire in 2013, ii) quantifying the degree of runoff scale-dependency from empirical rainfall-runoff data, iii) conducting stepwise regression analysis to investigate scaling behaviours of the observed runoffs in relation to the rainfall characteristics, iv) simulating overland flow and scaling effects by coupling traditional infiltration theory, run-on process and rainfall temporal variations, v) investigating macropore flow contribution to runoff scaling behaviour by measuring vertical pathways of activated macropores with a blue dye experiment at the site, modelling macropore flow in relation to runoff depth, and accounting macropore flow into rainfall-runoff simulations.

This is the first study to investigate isolated impact of spatial variability of soil hydraulic conductivity, rainfall parameters, and macropore flow on overland flow scaling behaviour in a burned hillslope. The outcome of this study was partly obtained from field and laboratory measurements and rainfall-runoff monitoring at the field. These measurements and monitoring data were used for rainfall-runoff models parametrisation and verifications.

The empirical rainfall-runoff data were collected from multi-scale runoff plots under natural rainfall conditions. The instruments were installed on a severely burned hillslope of eucalyptus forest in southeast Australia. Forty-one rainfall-runoff events were extracted from data collected during the second year following the fire. Strong scaling behaviour was observed for all observed events, seasonally and the whole study period where the rate of runoff declined with increasing plot length.


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