Posted on January 6th, 2015

Back to School – River Impact on Endangered Species Habitat

The establishment of critical habitat under the Endangered Species Act (ESA) is intended to provide significant enough and appropriate living, roaming and breeding grounds for species deemed seriously at risk. Frequently a confrontational topic due to the government’s ability to restrict private landowner’s use of their own resources, its intention is to preserve and protect critical components of an area that are necessary to a species’ ability to thrive, and hopefully grow.

lower_colorado_mapMap of the Lower Colorado River study area.
backwatersMap of the backwaters selected for this study.

A study done in the West through Colorado State University (CSU) and the U.S. Bureau of Reclamation (USBR) set out to investigate river systems with natural and manmade backwater systems. Frequently, these backwater systems are vital to the life of numerous aquatic and bird species, in some cases, listed as endangered under the ESA. The researchers used GIS tools to create models which quantified changes in surface area, perimeter and depth of backwater areas to improve the evaluation of water resources frequently used by endangered species. The creation of these tools allows resource managers to better estimate how to control water flow, and what ramifications might occur if reservoirs are left at insufficient levels.

The area of focus for this study was the Lower Colorado River, where it diverged from the Upper Colorado River at Lee’s Ferry, Arizona and heads south to the Pacific Ocean in Baja California. The specific area of investigation started at the Parker Dam and extended south to the Imperial Dam in Arizona. Prior to the creation of reservoirs, there was little known about backwaters due to their high evaporation rates. However, after the creation of the Hoover Dam in 1935, backwaters were much easier to estimate and investigate due to increased stability.

The CSU/USBR study utilized infrared images to precisely map and measure water edges. Surface elevations could not be measured with this technique, so the research team relied on raster data to fill in the holes. This secondary data set was instrumental in understanding the definition of the bank areas. The analysis also relied on the assumptions of consistent points on the water’s surface. The prediction of these points allowed for the creation of grids that represented high-resolution surfaces for more accurate examination. This conglomeration of methodologies enabled researchers to predict best management practices for endangered species who frequented the backwaters of interest. Of note was the importance for future study in the same area to look at consistency in habitat as the potential for change within seasons and from year to year is great.

Two specific areas of focus within the study region were the effects of flow reduction from those controlling the water consistency (i.e. the dam operators) and the release patterns associated with it. Each of the 21 backwaters were greatly affected in terms of their total surface area, perimeter, critical surface area and average depth by these water releases. One caveat was that the change of flow for backwaters decreased as one moved away from the headway and thus their specifications were more stable. Future research suggested by the team included the potential effects of reducing non-native species encroachment to increase the habitat of endangered species. This would include further investigation into water flow impacts on surrounding areas and species, and into the impacts of non-native species reduction on those that are threatened or endangered.

Justin Harmon
Staff Writer

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