A lidar-based approach to measure channel incision in headwater streams in an urbanizing landscape

Abstract

Stream channel incision can occur following landscape disturbances commonly related to urbanization. A method was developed to map reach-scale incision from lidar-derived digital elevation models using topographic openness, a landscape metric measuring the enclosure of an area (i.e. channel bottoms) relative to the surrounding landscape (i.e. stream banks). The method was validated with field surveys and local photogrammetric models of stream banks. The method was then applied to watersheds undergoing urban development with lidar coverage for six time steps spanning an 11 year period. Channel incision was detected near the outlet of newly developed stormwater management facilities, but temporal analysis also identified areas already severely incised prior to urbanization, highlighting influence from previous agricultural land use, as well as areas that have resisted incision following urbanization. Although incision patterns varied across each watershed, there appeared to be no direct connection to the placement of SWM facilities beyond outlets.