THE EFFECT OF RIP-RAP NEAR THE CONFLUENCE OF SODA BUTTE CREEK AND THE LAMAR RIVER, YELLOWSTONE NATIONAL PARK

Aerial photographs since 1954 and derived maps show the significant effect of rip-rap on Soda Butte Creek and the Lamar River- Soda Butte Creek confluence. Systematic stream adjustments include changes in channel form, the formation of a channelized stream, truncated meanders, and sediment deposition. In 2009, the channelized stream along the Northeast Entrance Road captured the headwaters of Soda Butte Creek. The Lamar River-Soda Butte confluence forms a right-angle junction today. These significant changes in Soda Butte Creek and its confluence with the Lamar River are the result of rip-rap along the Northeast Entrance Road and not unusual discharge.

An automatic feature extraction routine in ENVI’s image processing software enabled the efficient analysis of the georectified aerial photography and provided quantification of stream adjustments. Consistent selection of all stream channels in black-and-white, natural color or color infrared aerial photographs involved the entry of optimum image parameters (spectral signature, texture, brightness, etc.). The result of this automatic feature extraction routine is a map of polygons. Using the ArcGIS software, interactive selection, editing, and grouping the polygons corresponding with water in the aerial photographs assisted in generating a time-series of stream adjustments for quantitative analysis or for visualizing channel change over time. When displayed as a time-series sequence, resource specialists and managers easily can see the channel changes and clearly communicate about the responses of the fluvial system.

Similar and continued placement of rip-rap along the Northeast Entrance Road either at the Lamar River-Soda Butte confluence or Soda Butte Creek at Round Prairie will yield significant changes to Soda Butte Creek and the riparian ecosystem. Alternatives exist to maintain access along the Northeast Entrance Road and allow Soda Butte Creek to self-adjust and self-maintain its drainage.