Modelling flash flood using LiDAR and high resolution satellite imagery: a case study of West Creek, Toowoomba

Australia is one of the most heavily exposed countries in the world to different natural hazards, such as floods. In December 2010 and January 2011, large areas of the south and central Queensland were affected by flooding. On Monday 10th January 2011 heavy rains continued from 12:30 pm to 2:00 pm in the City of Toowoomba catchment area. Flash flooding occurred suddenly and unexpectedly making it difficult to prevent or predict before it occurred. This led to a rise in water levels in streets and roads, disrupting traffic and causing loss of life and properties. To reduce the effect of flood disasters and minimize the damages, flood inundation maps can be used to determine the locations of threat. This research used an integration of the HEC-Hydrologic Modelling System (HEC-HMS), HEC-River Analysis System (HEC-RAS) with Geographic Information Systems (GIS) to develop an improved model of the West Creek flood extent and flood event in the city of Toowoomba. The flood extent and depth in the different flow conditions of the West Creek channel was described in this study. The Hydrologic model (HEC-HMS) was used for 15 minutes time series data to create the flow rate at West Creek catchment from 12:00 pm to 4:00 pm. HEC-RAS with HEC-GeoRAS extension in ArcGIS was applied to simulate the flash flood in West Creek from Spring Street to Long Street. Digital Elevation Model (DEM) derived from high density LiDAR data and land cover data extracted from high resolution remote sensing imagery were used to model the flood inundation in the study area. The HEC-GeoRAS extension was used to prepare data sets for the stream centreline, banks, flow paths and cross-sections for import to the HEC-RAS hydraulic model. The downstream boundary conditions were defined in HEC-RAS. The hydrological results from HEC-HMS showed the maximum discharge value of West Creek Catchment at different periods of time. These results were comparable with Toowoomba Regional Council Report (TRCR). The flood inundation maps showed the maximum flood width and depth of West Creek Channel (starting from Spring Street and ending at Long Street) at 1:00 pm to 3:00 pm, which was greater than any previous floods in Toowoomba. The validation between the modelled flood extent at peak time and flood extent in the Nearmap aerial photo showed a high degree of correlation. Therefore, the model can provide a sound basis on which to analyse similar scenarios.