Following several recent devastating flood events in Queensland, KBR was commissioned by Central Highlands Regional Council to undertake a floodplain management study and develop a management plan. This study involved the development of a large-scale hydrological model accounting for approximately 131,000 km² or just over 90% of the entire Fitzroy River basin to accurately represent the flooding conditions for two major flood events. Modelling rainfall events over very large catchments to determine the volume of run-off can present multiple challenges. In particular, accurately determining rainfall depths over vast catchments can be problematic. Occasionally the modeller is limited by the number of rainfall recording stations often scarcely dispersed or non-existent in some catchment areas. To accurately model these events, a rainfall interpolation method may be required to adequately represent rainfall depths and determine run-off volumes. The volume of run-off achieved from a catchment is dependent on a number of catchment or sitespecific factors such as catchment slope and size, soil type, vegetation characteristics and infiltration capacity. This paper will focus on accurately calculating the quantity of rainfall-generated run-off for very large catchments, dependent on measured rainfall characteristics such as the intensity, duration and spatial distribution of the rainfall event. Rainfall interpolation methods are compared which take these factors into consideration to achieve a satisfactory calibration at various stream flow gauges. This paper will also discuss a comparison to the Bureau of Meteorology radar rainfall estimates that was undertaken in an attempt to enhance the spatial distribution of rainfall depths