For the past eight years a decent portion of my professional life has been spent working on a large, inter-agency study of the Yellowstone River. Over this time we have mapped changes to the river and adjacent land areas in support of a court-mandated, cumulative effects study of human impacts to the river. This study is in response to the unprecedented installation of rip rap, dikes, levees, and other modifications in the river corridor during and after the 1996 and 1997 floods. The courts found that during this time period, the Army Corps of Engineers did not take into consideration the cumulative impacts of the activities they were permitting.
The core data set for most of this effort is a series of historic aerial photography that was georeferenced and mosaiced for use in our GIS mapping system. We have coverage from the 1950’s, 1976, 1995, 2001, 2005, 2009, and 2011. By assessing the trends captured in these images, we can help tease out impacts to the river corridor resulting from human activity. For example, did a levee keep water out of a side channel that provided important habitat for young fish, riparian development, or floodwater storage? Or did the construction of the Interstate cut off access to the floodplain? Or has there been conversion of riparian habitat to agricultural use? These sorts of questions can only be answered through meticulous mapping of the features as evident in the historic imagery.
Here’s a fun sequence of images from around Big Timber, Montana showing exactly when the Interstate came through the area. Each image shows the exact same area at the same scale. The image years are 1950, 1926, 2001, and 2011. In the second image (1976) you can see the current “end” of the Interstate as it is constructed through the region. You can also see a clear shift from flood irrigation to pivots, along with some minor channel migration. For those of you familiar with the area, you can see the Big Timber Water Park and campground appear in the third image.
