Making a difference: using multiple event based LiDAR datasets to guide river management decisions following extreme floods

The response to managing the effects of a flood event can be reactive. Landholders often want immediate compensation for soil loss and river encroachment into productive floodplains, and methods to set priorities for river stabilisation are often not available. Without a clear understanding of catchment scale impacts decisions can be made in a vacuum, usually based on rapid assessments at discrete sample locations. As a result of the Lockyer Creek LiDAR and aerial datasets, pre and post the 2011 and 2013 flooding, recommendations can be made about how to undertake remotely sensed monitoring for management. An initial low flow LiDAR run enables a baseline dataset to be established. Hydraulic models can be created to delineate the bankfull, bed, and in-stream geomorphic features. Evidence of sediment accumulation and relict erosional features can aid process determination and, in concert with existing data, the construction of a model of how the channel is functioning and its likely geomorphic trajectory. Collection of a subsequent LiDAR dataset means a DEM of Difference can be built. Firstly this allows an evaluation of catchment scale patterns of erosion and deposition, identifying hotspots. Subsequently the key drivers of processes can be determined, such as those responsible for riverbank erosion, and the channel trajectory model revisited. In the Lockyer, wet flow mass failures contributed ⅓ of the eroded sediment and in subsequent events were unlikely to erode further, more often becoming depositional features. This alters the traditional management response of remediating existing failures to a programme of rehabilitation of sites without failures. As LiDAR collection will not be instantaneous after the flood, initial management that involves infrastructure/asset protection must occur in the absence of these information. Other channel works should wait until the data is available to avoid undertaking inappropriate management actions