Floodplain Accessibility

One of the lines of evidence used to estimate overall riparian condition in RCAT is floodplain accessibility. The first principle of riverscape health is "streams need space," but infrastructure is often built in floodplains, reducing the space available for channels to adjust through time. RCAT contains an automated algorithm for estimating the proportion of the floodplain that is accessible to channels. 

To assess floodplain accessibility, first the valley bottom polygon is rasterized. Then, the available infrastructure layers (roads, railroads) and the channel network are also rasterized. For each valley bottom raster cell, flow directions are traced downstream. If infrastructure is encountered before a channel, each cell in traced downstream from the initial cell is classified as inaccessible (assigned a value of 0). Conversely, if a stream channel is encountered without running into any infrastructure, each cell traced downstream from the initial cell is classified as accessible (assigned a value of 1). 

This raster is then summarized within sample frames to attribute the output point and line features. Within a sample frame, Discrete Geographic Objects (DGOs; the valley bottom segmented into polygons of varying lengths based on stream size) in RCAT, the average of all cells is calculated resulting in a value that represents the proportion of the polygon that as accessible.