A RAPID, LIDAR-BASED DELINEATION OF WATERSHED-SCALE LARGE WOODY DEBRIS SOURCES

The presence of large woody debris (LWD) in streams provides diverse and quality habitat to aquatic organisms by creating in-channel hydraulic complexity. However, field surveys of coastal Maine rivers have shown these streams to lack LWD, and the critical habitat it creates. While restoration projects aimed at adding wood to streams are underway, such efforts may be enhanced by a rapid watershed-scale technique for discerning areas where the largest quantity of available LWD is located. To that end, we use high-resolution LiDAR digital elevation models to determine the amount of potential channel-spanning wood along the 78-km Narraguagus River in Downeast Maine. Using ArcGIS, potential LWD analyses are performed in buffer zones equal to the average valley width along individual 1-km river reaches. We ground-truth results through field-based channel and riparian wood surveys to ensure accuracy of LiDAR analyses. Overall, we find the amount of potential channel-spanning LWD is small (< 50% by area in all channel buffer zones), and depends heavily on channel width, which generally increases in the downstream direction. Further, the potential channel-spanning LWD we identify tends to be located in spatially discrete reaches, rather than being distributed regularly in the longitudinal direction, underscoring the need for heightened conservation of valley areas with mature forests. The rapid identification of potential LWD sources may prove valuable in locating stream reaches for future restoration projects aimed at increasing channel complexity through wood addition.