In the past, using traditional surveying methods (measurements of cross sections), height data was collected manually, which was very expensive and time consuming. As a result, flow models simulated flow in one dimension through these cross sections. Nowadays, with height data collected by LiDAR that is data for large areas, entire floodplain, flow can be simulated everywhere. This two-dimensional simulation, gives us a much more detailed picture of where water will go during a flood. Out of LiDAR data it is possible to make maps of forecast floods.
Flood risk maps gives a critical information in flood forecasting: information on when and where floodwater will arrive. The maps also show how deep the water is expected to be all across the floodplain. There are softwares to simulate flood flows all across the floodplain and GIS softwares that turns the model results into maps and overlay them on other maps. Still, it is essential to have high quality height data and that is where LiDAR shows all advantages as a leading technology in hydrological analysis.