The Bear River Migratory Bird Refuge, located west of Brigham City, Utah, where the Bear River terminates into the Great Salt Lake, is a critically important feeding, resting, and breeding area for many species of migratory water birds. Established by Congress in 1928 to help conserve and protect the once vast, productive marshes on the Bear River delta, the refuge today faces many challenges including excess nutrients and sedimentation, invasive plants, and altered hydrology. Refuge staff is currently drafting a habitat management plan that will provide management direction into the future.
To support ongoing planning efforts, understanding past hydrologic characteristics and patterns (i.e., when water is present on the landscape and how it is managed) is important, especially on a deltaic system such as Bear River. To better understand past water management, FWS scientists used the long-term Landsat archive to search for appropriate images that document the extent of water in spring (early to mid-May) and fall (early August) for the 26-year time period 1990 through 2016. While usable Landsat 5 data exist back to 1984, the refuge was completely submerged from 1984–1988 when the Great Salt Lake reached record levels before receding to more normal elevations. (Note: 2012 was not included due to lack of suitable Landsat 7 images during the time periods of interest.)
Images were located using the U.S. Geological Survey (USGS) LandsatLook Viewer web application. Upon review, suitable images were downloaded and areas of open water were extracted using band-specific criteria within ArcMap software. Individual raster grids by year showing areas of open water were combined into one composite image for spring and summer showing water availability. Various map products and summary statistics were compiled to help refuge staff better visualize which areas within the refuge (and surrounding landscape) are consistently wet (or dry) over this time period. Water frequency is one component of hydrology being correlated with measures of wetland productivity and use by water birds. In addition, water frequency data are also being used to understand ecological drivers directly related to the extent and spread of invasive plants (principally Phragmites australis) on the refuge. Understanding these relationships enables refuge staff to become better positioned to make informed decisions now and into the future.
Spring (May) water availability at Bear River Migratory Bird Refuge over a 26-year time period (Landsat 5/8 from 1990–2016; 2012 excluded).
Summer (August) water availability at Bear River Migratory Bird Refuge over a 26-year time period (Landsat 5/8 from 1990–2016; 2012 excluded).