Utah Statewide Valley Bottom Waterbodies

These combined projects consisted of delineating the valley bottoms of all perennial streams within the state of Utah. Specifically, the perennial 1:24,000 National Hydrography Dataset (NHD) stream network and 10m Digital Elevation Model (DEM) were used within the Valley Bottom Extraction Tool (V-BET), an ArcGIS Tool Box, was used to delineate valley bottoms. Valley bottoms, as we define them, consist of the active channel and the modern alluvial floodplains (deposition zones of alluvium since Holocene). The idea behind the Valley-Bottom Extraction Tool (V-BET) is that valley bottom is determined by slope, upstream drainage area, and location within a basin, which can be used as parameters to derive a valley bottom. The tool uses two inputs, a DEM and stream network, along with some specified parameter values to generate a valley bottom based on a slope analysis with different, empirically derived parameters for the different locations within the watershed. By identifying areas along river corridors with relatively low slope, V-BET generates a shapefile that represents valley bottom margins of the input streams. These various valley bottoms were then subject to a manual editing process to ensure they were as accurate as possible. Valley bottom editing was conducted in ArcMap at a scale of 1:10,000, however in confined valley settings and on small streams 1:8,000 or 1:6,000 scale was required to capture the required detail. We used multiple lines of evidence including: aerial photography, hillshade, DEM, slope, and Google Earth, to most accurately edit and validate the valley bottom output. In most cases the physical features that confine valleys were fairly obvious using these layers. In difficult areas Google Earth was a helpful resource and allowed zooming into an area of interest using the 3D view with vertical exaggeration added to visualize breaks in slope and other features that were not obvious in other data sets. Additionally, valley bottom shapefiles were converted to KML files which could be opened and observed in Google Earth, where any obvious flaws could be spotted and corrected. In confined valley settings the original valley delineations from V-BET were fairly accurate, and required only minor editing. In partly confined and unconfined valley settings, the raw data was less accurate, and required more editing. In addition, the valley bottoms of small headwater streams tended to be slightly over exaggerated because at the scale that we were performing the edits it was virtually impossible to clip these areas down anymore.