River channel migration and characteristics from 1988 to 2019 at 74 bridges in the Philippines

Bridge characteristics were derived from a geospatial database of Philippine bridges retrieved in April 2020 from the Detailed Bridge Inventory Application (DPWH, 2020). The database was filtered to include only permanent bridges where the bridge deck length was equal to or greater than 200 m (n = 256). A visual inspection was performed to ensure that bridges were located at contemporary river crossings (n = 182) and only those bridges where the active river channel width exceeded 150 m (equivalent to five Landsat pixels) were retained for analysis (n = 74).

Stream network and geomorphology characteristics were derived from a nationwide digital elevation model (DEM) acquired in 2013 and generated through airborne Interferometric Synthetic Aperture Radar, with a 5 m spatial resolution and 1 m root-mean-square error vertical accuracy (Grafil and Castro, 2014) was used for topographic analysis and extraction of the stream network.

Google Earth Engine (GEE) was used to extract active river channel masks from Landsat 5, 7 and 8 satellite imagery. The workflow contained three main processing steps: (i) cloud masking and temporal compositing; (ii) active river channel classification; and, (iii) cleaning and image export.