Mapping stream and floodplain geomorphic characteristics with the Floodplain and Channel Evaluation Tool (FACET) in the Mid-Atlantic Region, United States

Quantifying channel and floodplain geomorphic characteristics is essential for understanding and modeling sediment and nutrient dynamics in fluvial systems. The increased availability of high-resolution elevation data from light detection and ranging (lidar) has helped improve methods for extracting these metrics at a greater accuracy across regional scales. The Floodplain and Channel Evaluation Tool (FACET) was developed as an open source tool to calculate a suite of geomorphic metrics describing channel and floodplain geometry from high-resolution digital elevation models (DEMs), providing estimates of channel width, bank height, cross-sectional area, and floodplain extent. Field data from sites in the Chesapeake Bay and Delaware River watersheds were used to calibrate and validate FACET within five physiographic provinces in the Mid-Atlantic region of the United States. Stream banks were identified using either a slope-threshold method at cross sections which are automatically generated at a user-defined interval along the delineated stream network, or by applying a curvature-threshold method for grid cells within a buffered distance from the stream network. The floodplain extent was mapped using a height above nearest drainage (HAND) grid and empirical regression models built for each physiographic province relating the HAND threshold to drainage area. Other user-defined input parameters within FACET control the sensitivity of calculations to DEM resolution, relief, and stream order, allowing for the ability to optimize FACET at multiple scales and/or regions if field survey data are available for calibration. Geomorphic metrics derived from FACET are currently being used to develop predictive models to estimate bank erosion and floodplain deposition to enhance our understanding of watershed sediment and nutrient budgets.