Evaluating a topo-bathymetric lidar sensor to map river channels for improved hydrodynamic flood risk mapping

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The impacts of river flooding have been felt by many communities, most recently in Alberta and the prairies, where these events have caused millions of dollars damage. In Nova Scotia, communities were severely impacted by flooding in 2012. CBCL, a Halifax based engineering company, and NSCC's Applied Geomatics Research Group (AGRG) are proposing to adopt innovative lidar technology to better understand river systems and contributing areas that drain into the river to reduce the impacts of flood events in the future through more informed mitigation strategies. The topography or elevation of the watershed and floodplain and the land use have a lot to do with why and where a river floods. This information on the land use and topography of the watershed can be mapped using a variety of well-established techniques (air photos, satellite imagery, and laser altimetry - lidar). However, in order to understand how much water the river can hold before it spills out onto the flood plain, we must know the elevation of the river bottom and banks. Hydraulic models used to predict river flooding require accurate river cross-section geometry and flood plain elevations. Currently, there is a lack of adequate survey data representing these key model inputs. Traditional survey techniques to collect these data, such as wading across the river or performing shallow water boat based echo sounding surveys are expensive and potentially dangerous. NSCC's new mapping system, topo-bathymetric lidar, utilizes lasers mounted in an aircraft to precisely measure the topography surrounding a river and can also see through the water to measure what is below. The sensor will measure the river bottom topography, bottom roughness, and composition including vegetation which can cause friction and slow the flow of water. The sensor is also capable of accurately measuring anthropogenic features such as bridges which bottleneck the flow of water within the system. With the lidar sensor mounted in an aircraft, large areas can be surveyed quickly and provide more information than traditional methods. This new approach has the potential to improve our ability to map river systems accurately at a cheaper cost when compared to previous methods.