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The Modeled_PAHD_Flowpath geometries are the result of a conflation study that incorporated elevation data and preexisting hydrography. These geometries were produced using QL2 lidar deliverables (published in 2020) and preexisting elevation-derived hydrography that had also been generated from QL2 lidar deliverables (published in 2015). The workflow involved four main steps: (1) use the most recently available QL2 lidar to create a geomorphon derivative delineating channelized structures identified from the elevation surface, (2) compare the monotonicity of these channelized features with equivalent geometries in the 2015 Allegheny County Hydrography Dataset to evaluate which feature better conformed to the elevation surface, (3) use a TPI product to better winnow out "false channels" picked up in heavily urbanized areas, and (4) ultimately use monotonicity values to evaluate the legitimacy of all geometries.This workflow has a number of weaknesses; for instance, it is nearly impossible to winnow out channelizations adjacent to road features based on elevation characteristics of these lines. The Pennsylvania Bureau of Geological Survey (PaGS) therefore does not recommend using these geometries as a cartographic product without a manual review of the geometries. Please reach out to PaGS if you would like to provide critique of techniques used or this product, or you would like to learn more about the developing PAHD workflow. |