Using a terrestrial laser scanner to detect wood characteristics in gravel-bed rivers

The possibility of analysing the characteristics and volume of inchannel large wood (LW) is of importance for river management but the traditional manual field activities are usually time-consuming and not easy to apply at a larger spatial scale. This paper presents an alternative and faster method to detect the characteristics and measurements of large wood in rivers by using the terrestrial laser scanner (TLS) technology. Field-measurements data and TLS scans were collected in August 2013 along 14 ha of the Piave River (Italy) analysing 230 and 208 woody elements for the manual method and the TLS one, respectively. TLS data were processed using the Cyclone 7 software and the LW measurements were extracted adopting two specific tools. The resulting low margin of error in the comparison between field data and those derived from TLS surveys confirmed the ability of TLS in the detection of large wood and wood jams characteristics. The greatest deviations were found for wood jams height which the TLS showed a tendency to overestimate (+24.37%) and LW length with a slight underestimation (–19.76%). Considering the wood volume, the relative difference between the TLS and manual method was within a negligible margin of error of ±7%. Characteristics and measurements of LW in rivers can be obtained from TLS surveys, but some progress in this technique is still needed to allow a better management of the 3D point cloud and a faster extraction of the wood measurements. The proposed method represents an alternative tool for faster and repeated surveys of wood characteristics in a complex river environment, ensuring a reliable quantification of spatial and temporal variation of wood volume.