The River Process Corridor: A Modular River Assessment Method Based on Process Units and Widely Available Data in the Northeast US.

We define the river process corridor (RPC) as the area adjacent to a river that is likely to affect and be affected by river and floodplain processes. Here we present a novel approach for delineating the RPC that utilizes widely available geospatial data, can be applied uniformly across broad and multi-scalar spatial extents, requires relatively low levels of expertise and cost, and allows for modular additions and adaptations using additional data that is available in particular areas. Land managers are increasingly using a variety of delineated river and floodplain areas for applied purposes such as hazard avoidance, ecological conservation, and water quality protection. Currently, the most-used delineation methods rely on historic maps, field surveys, and/or calibrated empirical models. These approaches are examples of what is possible, but they may be time-intensive, may rely on jurisdiction or organization-specific data or data information systems, or may require specific local-user input or hand-drawing. Our approach, the River Process Corridor Modular Assessment Method, offers a rapid, uniform and objective river and floodplain process area delineation method that uses transparent, easily accessible data, and may be used across large areas. it is derived from the sum of five functional process units that together capture the RPC: (i) the Flood Processes Unit, derived from hydraulic modeling to determine areas subject to overbank deposition and erosion, in-channel deposition and erosion, bank erosion, and channel avulsions; (ii) the Landslide and Steep Terrain Processes Unit, based on terrain slope to show locations subject to sediment delivery, bank failures, and other mass wasting proximal to the flood-prone area; (iii) Wetland Processes Unit, based on the U.S. National Wetlands Inventory to show areas where wetland processes occur; (iv) Channel Migration Processes Unit, based on channel location and migration rates to show areas susceptible to lateral channel movement; and (v) Riparian Ecologic Processes Unit. This paper details the assessment approach for each of these units, and provides a summary outline and table for users. To illustrate and evaluate its potential, we apply the approach in three river reaches in mountainous and low-relief watersheds in the northeastern U.S. and compare results with recent geomorphic change, observed in the field and in historic imagery. The River Process Corridor Modular Assessment Method performs very well, capturing 92% of observed landslide areas, 87% of observed floodplain deposition areas, and 100% of channel migration areas. We also provide an example of how additional data available from the State of Vermont could be added in a modular approach. These results indicate the RPC method is successful at providing both an accurate assessment of potential active hazard areas and sensitive environmental areas, and that it also includes a margin of safety that many managers desire. Its modular nature allows for flexible weighting of different metrics to suit specific applications, and piecewise updating as new data or approaches become available. We conclude that maps of the RPC can be useful as an advisory layer to natural resource managers, property owners, planners and regulators to identify areas that may be valuable for ecological conservation or at risk of future damage during floods, or where they might consider allowing natural river processes occur, in order to enhance ecological processes and help attenuate future flood damage elsewhere