CHANNEL EVOLUTION OF THE LOWER SAN JUAN RIVER, SE UTAH

The San Juan River is one of the major tributaries to the Colorado River system. It serves as a popular recreation corridor, and a portion of it lies within the boundaries of Glen Canyon National Recreation Area. The area boasts a rich environmental history that includes numerous conflicting uses of the river basin over several hundred years. The lower San Juan River in southeastern Utah exposes outcrops of the Paradox Formation, which is a major oil producer in the nearby Aneth field. Also, Laramide deformation is beautifully exposed at the Comb Ridge and Raplee Ridge anticlines. After the completion of the Navajo Dam in northwestern New Mexico in 1962, stream morphology has been controlled on the lower San Juan River. This study addresses channel evolution through spatially opulent photography by cross referencing current and archival spatial photography to show how stream flow has affected the channel width.

Similar to other rivers in the Colorado River drainage basin, the San Juan River experienced Tamarisk establishment during the 20^th century. Scientific studies concerning other rivers have made strong correlations between the influences of dams on channel width and Tamarisk establishment. Precipitation and discharge data as well as spatial, aerial, and archival photograph data, have been documented for the lower San Juan River. These four data sources have been integrated to describe their effect on channel evolution.

Using Esri ArcMap 10.2.2, USGS databases, and Google Earth, channel widths have been analyzed quantitatively and qualitatively to show that channel narrowing has resulted from manmade factors. The study area consists of one location along the Comb Ridge Anticline directly below Comb Wash. Temporal data for this study begins from the pre-dam era in 1952 and ends with the most recent data from 2015. It has been possible to show changes in channel width by using spatial photographs from 1952, 1998, and 2015, along with aerial and satellite photographs from 1952, 1993, and 2015. Photogrammetry, along with hydrological data, were temporally correlated to substantiate that the dam has affected channel evolution. This in turn has affected the density of vegetation that has also aided in channel narrowing.