The Valley Bottom Extraction Tool (V-BET): A GIS tool for delineating valley bottoms across entire drainage networks

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The shape, size and extent of a valley bottom dictates the form and function of the associated river or stream. Consequently, accurate, watershed-wide delineation of valley bottoms is increasingly recognized as a necessary component of watershed management. While many valley bottom delineation approaches exist, methods that can be effectively applied across entire drainage networks to produce reasonably accurate results are lacking. Most existing tools are designed to work using high resolution topography data (i.e. > 2m resolution Digital Elevation Model (DEM)) and can only be applied over relatively short reach lengths due to computational or data availability limitations. When these precise mapping approaches are applied throughout drainage networks (i.e. 102–104km), the computational techniques often either do not scale, or the algorithms perform inconsistently. Other tools that produce outputs at broader scale extents generally utilize coarser input topographic data to produce more poorly resolved valley bottom approximations. To fill this methodology gap and produce relatively accurate valley bottoms over large areas, we developed an algorithm that accepts terrain data from one to 10m with slope and valley width parameters that scale based on drainage area, allowing for watershed-scale valley bottom delineation. We packaged this algorithm in the Valley Bottom Extraction Tool (V-BET) as an open-source ArcGIS toolbox for ease of use. To illustrate V-BET's scalability and test the tool's robustness across different physiographic settings, we delineated valley bottoms for the entire perennial drainage network of Utah as well as twelve watersheds across the interior Columbia River Basin (totaling 55,400km) using 10m DEMs. We found that even when driven with relatively coarse data (10m DEMs), V-BET produced a relatively accurate approximation of valley bottoms across the entire watersheds of these diverse physiographic regions.