IMPACT OF FORESTED RIPARIAN AREAS ON STREAM MORPHOLOGY USING AERIAL LIDAR

The influence of riparian land use on stream morphology and dynamics is still disputed despite many decades of research. Prior research on the relationship between stream morphology and riparian vegetation often have taken place within a single watershed on a reach-scale, limiting the statistical power of morphological datasets. With the growing availability of high-resolution, classified LiDAR (including freely-available statewide coverage within Iowa), it has become possible to address these issues within a GIS environment. For this study, a statistical relationship between riparian vegetation height and along-channel deviations in channel width was obtained using the Iowa LiDAR product for each. Using the Iowa Department of Natural Resource’s digitized top of bank data, stream width was extracted on regularly-spaced transects along the channel in eight Iowa watersheds. At the end-points of each transect using first-return LiDAR, canopy heights were obtained. Using these variables, width residuals were calculated as a function of upstream contributing area in order to seek correlations between the width residuals and riparian land cover. The expected result was a partial correlation between land cover and channel width residuals that suggests that forested channels are indeed wider than unforested. A similar analysis conducted on the Iowa Wadeable Streams dataset suggested that this relationship could be at least partly explained by the greater abundance of large woody debris (LWD, pieces of wood exceeding 10cm in diameter and 1m in length) in forested reaches. We hypothesize that changes in flow resistance require corresponding changes in channel width, which could give rise to a scale-dependent effect.