The provided text originates from Australian Rainfall and Runoff (ARR), a comprehensive technical guide published by Engineers Australia to standardise flood estimation and water engineering practices. It primarily focuses on the conceptualisation and application of catchment modelling systems, bridging the traditional gap between hydrologic and hydraulic models to better replicate real-world water movement. The document outlines essential steps for practitioners, including model calibration, validation, and the use of regional relationships to estimate parameters for ungauged catchments. Significant emphasis is placed on accounting for uncertainty ...