Model development and calibration
The flood model comprises a hydrological model and a hydraulic model. The hydrologic model determines the runoff that occurs following a particular rainfall event. The primary output from the hydrologic model is hydrographs at varying locations along the waterways to describe the quantity, rate and timing of stream flow that results from rainfall events. These hydrographs then become a key input into the hydraulic model. The hydraulic model simulates the movement of flood waters through waterway reaches, storage elements, and hydraulic structures. The hydraulic model calculates flood levels and flow patterns and also models the complex effects of backwater, overtopping of embankments, waterway confluences, bridge constrictions and other hydraulic structure behaviour.
The Bureau of Meteorology (BoM) has established and calibrated an URBS hydrologic model of the Johnstone River catchment. This model was reviewed and adopted for the study. Some minor modifications to the model sub-catchments were done by WBM to match the locations of the hydraulic model boundaries.
The complicated nature of the floodplain flow patterns and importance of obtaining community confidence in the process required that state-of-the-art modeling techniques be adopted. For these reasons, TUFLOW, a fully 2D dynamic hydraulic modeling system was adopted. In total, the hydraulic model covers approximately 125 km2 of the rivers and floodplain.
Comparing the model with the actual rainfall at Innisfail
Click the charts to enlarge