Detecting and quantifying morphological change in tropical rivers using Google Earth Engine and image analysis techniques

Various tools have been demonstrated that are capable of delineating and characterizing river channels, but efforts to scale these analyses up to multi-temporal, catchment-scale applications are in their infancy.  Here, we use Google Earth Engine (GEE) to extract the active channel (including the wetted channel and unvegetated, alluvial deposits) from the Bislak and Cagayan Rivers in the Philippines.  Using temporal composites of Landsat 5, 7 and 8 satellite imagery over ~30 years, the active channel is resolved at annual intervals.  The active channel occurrence frequency is mapped using image analysis techniques to detect large-scale planimetric change.  Quantification of active channel centerline change is achieved using the RivMAP toolbox.  Over a 135 km reach of the Cagayan River, the average migration rate was 17.5 m.a^-1 ranging from 7.7 m.a^-1 in 1988 to 37.0 m.a^-1 in 2005.  The findings quantify patterns of dynamism in tropical river systems and demonstrate the utility of GEE in fluvial geomorphology applications.