POTENTIAL IMPACTS ON NATIVE AND INVASIVE FISH HABITAT IN BRIGHT ANGEL CREEK (AZ) WITH THE REDESIGN OF GRAND CANYON WATER INTAKE INFRASTRUCTURE

Grand Canyon National Park (GRCA) is in the process of evaluating its aging water infrastructure. Potential redesigns provide opportunities to benefit habitat for endangered native fish species including humpback chub and bluehead sucker. Roaring Springs (RS) is the primary water supply for GRCAs 5.5 million annual visitors via the TransCanyon Pipeline. RS is a tributary of Bright Angel Creek (BAC) which flows directly into the Colorado River. BAC holds populations of endangered native fish species that compete with invasive salmonids. One possibility for updating the water intake infrastructure involves moving the intake point from RS to near the mouth of BAC. This would put an additional 1.5 cfs (~5% total flow of BAC) in stream and available for aquatic habitat. Previous research has shown RS is on average 2 °C warmer than BAC and provides some thermal stabilization to the main stem of BAC on both daily and annual timescales and differences become more pronounced during the winter months. Increased water temperature during cooler periods of the year can potentially provide more benefits to native warm-water species relative to invasive cold-water salmonid species slated for removal. We conducted an assessment of potential changes to habitat for native and invasive species from adding the additional RS water to the main stem of BAC. Here, we use the System for Environmental Flow Analysis (SEFA) software to model how parameters including water temperature, depth, substrate size, dissolved oxygen, and velocity varied seasonally. This informs how habitat in BAC may change with an influx of stable temperature water from RS for fish species of interest within GRCA. Modeling of stream parameters is based on discharge and water chemistry measurements taken at cross sections (13) along the mainstem of BAC and continuous records of stage and temperature at multiple (4) locations throughout BAC and the confluence of RS and BAC. Initial results indicate that potential habitat area will increase for both native and invasive fish species but variations may exists between species for different seasons and life stages. Infrastructure adjustments and continued removal of invasives may therefore be a successful strategy for aquatic habitat improvements. Results will be used to inform management and infrastructure decisions at GRCA.