VEGETATION CHARACTERISTICS AND FLOODPLAIN TOPOGRAPHY FROM TERRESTRIAL LASER SCANNING FOR HYDRAULIC ANALYSES

This study investigates the applicability of terrestrial laser scanning (TLS) in determining floodplain topography and vegetation characteristics for hydraulic analyses. Field investigations were conducted in a compound channel with five differently vegetated sub-reaches from bare soil to grasses and willow saplings. Comparison of TLS to manual surveys brought new insight in to the reliability of TLS to determine the ground level and vegetation characteristics of vegetated floodplains. The mean absolute error (MAE) of the TLS-based ground level was 2-14 cm in the grassy sub-reaches with 50 cm window size. Even though scanning the reach after snowmelt decreased the MAE, for high resolution erosion and deposition monitoring TLS needs to be supplemented with other surveying methods. A digital surface model of 1 cm in resolution appeared suitable for estimating grass heights and its distribution. Different methods were needed for grassy type of vegetation in comparison to woody vegetation; for grasses mean heights were applied, whereas for woody vegetation a voxel-based method was derived.