The Pacific Northwest Hydrography Framework is sponsoring a working group tasked to evaluate the use of lidar-derived DEMs as a principal data source for updating the National Hydrology Database (NHD). The working group has identified a workflow leading to the acceptance of revisions to the national stream network dataset.
Two, 10-digit hydrographic unit watersheds located in Oregon’s Coast Range and Cascade Range were chosen as study areas. For each watershed a bare-earth DEM at 3 foot resolution was created from a lidar point cloud. The workgroup followed the standard sequence for modeling surface drainage patterns from DEMs: 1) resolving depressions, 2) flow routing, 3) calculating flow accumulation values at every cell, and 4) applying a flow accumulation threshold to derive the stream network. The result can be combined with the flow direction grid to determine stream order, generate a vector representation of the stream network, and delimit watershed boundaries.
Our experiences show the quality of stream features modeled from lidar-derived DEMs exceeds that of the original sources used for the Oregon dataset. The lidar-based delineations represent a significant workload, however, and the effort should not be underestimated. Ultimately, programmatic use of lidar-derived DEMs to update NHD will be determined by the perceived benefits to the resource management programs relative to available budgets.
Positional Accuracy of stream features using lidar data (Blue lines are lidar derived and yellow is the NHD)