PREDICTING GEOMORPHIC FLOOD HAZARDS AND SENSITIVE ECOLOGIC AREAS USING A UNIFORM, REPEATABLE, PROCESS-BASED DELINEATION OF RIVER CORRIDORS

To understand flood hazards, as well as natural and human disturbances near rivers, one must delineate the extent of river corridors. The challenge is to efficiently predict areas—at high resolution and over large regions—that are critical for 1) geomorphic and hydrologic hazards, 2) ecological conservation, 3) water quality protection, 4) and geomorphic and hydrologic sensitivity to climate and land use change. Currently-applied river corridor delineation methods rely on input data such as: field surveys, historic map analysis, hand digitization of river features, and calibrated empirical equations. Here we present a novel method that utilizes widely available geospatial data to delineate areas susceptible to flooding and geomorphic change, and locations important for riparian ecology and water quality. The approach generates a total river corridor as the sum of five process units: (i) flood unit, derived from hydraulic modeling to determine areas prone to overbank deposition and erosion, in-channel deposition and erosion, bank erosion, and channel avulsions; (ii) landslide and steep terrain unit, based on terrain slope to show locations of accelerated material delivery to the flood unit; (iii) wetland unit, based on the U.S. National Wetlands Inventory; (iv) channel migration unit, based on channel location and adjacent areas susceptible to lateral channel movement; and (v) riparian ecologic unit. The result is a consistent and reproducible river corridor delineation, suitable for analysis from local scales (10’s to 100’s of m) to regional scales (state-wide and beyond). Our river corridors show general agreement with more time-intensive and less reproducible delineation approaches. Compared with existing regional-scale delineation approaches, our corridors show higher-resolution delineation, with easily accessible physical justification for why areas are included in the corridor. In tests of the predicted area of the river corridor versus known locations of channel avulsions, floodplain sedimentation, and near-channel landslides, our corridor encompasses 87% to 100% of areas showing geomorphic change during floods. This work exhibits the potential for rapid, uniform, and objective river corridor delineation across large areas with transparent communication of the data inputs.